Co-reporter:Jinghua Sun, Xinmin Cui, Ce Zhang, Cong Zhang, Ruimin Ding and Yao Xu
Journal of Materials Chemistry A 2015 vol. 3(Issue 27) pp:7187-7194
Publication Date(Web):01 Jun 2015
DOI:10.1039/C5TC00986C
A double-layer broadband antireflective (AR) coating with excellent transmittance was successfully fabricated using two kinds of silica coatings. The excellent optical performance in a wide wavelength range came from a reasonable refractive index gradient from air to the substrate produced by the mesopores in the bottom-layer silica coating and the particle-packed pores in the top-layer silica coating. The maximum transmittance of the broadband AR coating was approximated to 100.0% at the peak value and above 99.6% in the visible region from 400 to 800 nm. Meanwhile, the average transmittance of the coating was more than 99.0% over the range of 360 to 920 nm. In addition, the double-layer broadband silica AR coating showed strong mechanical performance and good environmental stability. This work provides an alternative way to prepare a broadband AR coating for some applications in energy harvesting and optical devices.
Co-reporter:Ruimin Ding, Xinmin Cui, Cong Zhang, Ce Zhang and Yao Xu
Journal of Materials Chemistry A 2015 vol. 3(Issue 13) pp:3219-3224
Publication Date(Web):13 Feb 2015
DOI:10.1039/C4TC02542C
Regulation of the refractive index over a wide range is very important in the realization of tri-wavelength antireflective (AR) coating in high power laser systems, but many regulation approaches are too complex or violent to satisfy the practical requirements. Here, a simple, template-free sol–gel route was proposed to regulate the refractive index of MgF2 film by heat treating MgF2 sol and hence to control the self-assembly process of colloidal MgF2 nanocrystals. In this self-assembly process, the originally packed nanocrystals gradually evolved into bigger hollow vesicles, which reduced the refractive index of the MgF2 film from 1.38 to 1.2. When the refractive indices of the bottom and top layers were set as 1.34 and 1.2, the tri-wavelength broadband AR coating was finally realized on a quartz substrate, with the transmittance of 99.54%, 98.65% and 98.58% at 351 nm, 527 nm and 1053 nm, respectively.
Co-reporter:Ce Zhang, Cong Zhang, Xinmin Cui, Jinghua Sun, Ruimin Ding, Qinghua Zhang, and Yao Xu
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 40) pp:22157
Publication Date(Web):September 22, 2015
DOI:10.1021/acsami.5b08084
Organic–inorganic hybrid composites have been well-studied as water vapor barrier materials for their long diffusion length of water vapor in coatings which can be realized by improving the aspect ratio of inorganic components and regularity of nanostructure in coatings. In this paper, dense organic–inorganic hybrid coating based on ladder-like alkylene-bridged polymethylsiloxane (ABPMS) was successfully fabricated through the hydrosilylation reaction between polymethylhydrosiloxane and diene (1,5-hexadiene or 1,7-octadiene) in toluene under Pt/C catalysis. Its ladder-like structure was verified by 29Si magic angle spinning (MAS) NMR, 13C MAS NMR, and in-plane and out-of-plane glance-incident X-ray diffraction (GIXRD) techniques. Its corresponding coating showed excellent water vapor barrier ability for a typical water-soluble crystal, potassium dihydrogen phosphate (KDP). When treated in 50% relative humidity (RH) condition at 25 °C for 8 months, the ABPMS coating with 100 nm thickness displayed a very low transmittance loss of 1.6% compared with the high transmittance loss of 10% for uncoated KDP. Moreover, the ABPMS coating showed good ultraviolet radiation resistance, thermal stability, low mechanical property, and excellent compatibility with hydrophobic antireflective (AR) coatings.Keywords: alkylene-bridged polymethylsiloxane; dense coating; hydrosilylation; ladder-like polymer; water vapor barrier coating
Co-reporter:Guomin Li, Liancheng Wang, Wanxi Li, Yao Xu
Microporous and Mesoporous Materials 2015 Volume 211() pp:97-104
Publication Date(Web):15 July 2015
DOI:10.1016/j.micromeso.2015.02.054
•Mesoporous Fe/C and core–shell Fe–Fe3C@C absorbents were designed and synthesized.•Fe/C and Fe–Fe3C@C absorbents process high surface area of 467.3 and 259.5 m2/g.•The bandwidth reaches 3.36 and 5.04 GHz when the matching thickness is 2 and 1.5 mm.Mesoporous Fe/C and core–shell Fe–Fe3C@C composites were successfully prepared through the in-situ polymerization of Fe3+/phenolic resin coupled with F127 and the subsequent high-temperature carbonization. The experiments involved the preparation of an iron-containing carbon precursor and the heat-treatment process. Two composites with different morphology and structure could be obtained by changing the content of Fe(NO3)3·9H2O in the precursor. The crystalline phase, structure and microwave absorption of the two composites were investigated. Fe particles were uniformly embedded into the mesoporous networks to form mesoporous Fe/C composite with high surface area of 467.3 m2/g and low density of 1.92 g/cm3. The Fe–Fe3C particles encapsulated by graphitized carbon layers formed the core–shell structure with surface area and density of 259.5 m2/g and 2.67 g/cm3. Fe/C and Fe–Fe3C@C composites exhibited excellent electromagnetic absorbing ability, the effective absorption bandwidth reached 3.36 and 5.04 GHz with the matching thicknesses of 2 and 1.5 mm correspondingly. This originated mainly from the effective impedance match and multiple interfacial polarizations. Furthermore, the increase of Fe3+ not only promoted the graphitization degree of carbon shell, but also increased the complex permittivity and permeability of core–shell structure, thus improved the impedance matching. Owing to high surface area, low density and excellent microwave absorbability, the mesoporous Fe/C and core–shell Fe–Fe3C@C composites are promising candidates as lightweight and high-efficiency microwave absorbents.
Co-reporter:Wanxi Li, Liancheng Wang, Guomin Li, Yao Xu
Journal of Alloys and Compounds 2015 Volume 633() pp:11-17
Publication Date(Web):5 June 2015
DOI:10.1016/j.jallcom.2015.02.006
•Novel CoFe2O4/carbon balls composites were prepared by one-step hydrothermal route.•Well-dispersed and single-crystal octahedral CoFe2O4 nanoparticles were synthesized.•The CoFe2O4/carbon balls composites possessed very low density.•The composites exhibited excellent microwave absorption at 1.5 mm thickness.Since electromagnetic pollution is becoming more and more serious, the lightweight and highly efficient microwave absorbents are urgently needed to absorb unwanted electromagnetic microwaves. In this work, single-crystal octahedral CoFe2O4 nanoparticles with the diameter of about 20–25 nm were successfully incorporated into the porous carbon balls (CB) via a one-step hydrothermal method. The incorporation of the CoFe2O4 nanoparticles into CB reduced the dielectric loss and increased the magnetic loss, resulting in better impedance matching. When the CoFe2O4 content in CoFe2O4/CB composites was 10 wt.%, the minimum reflection loss (RL) was as low as −37.2 dB, and the frequency band of RL below −10 dB was 12.9–17.1 GHz obtained with 1.5 mm thickness. This excellent microwave absorption performance was much better than that of the pure octahedral CoFe2O4 nanoparticles, CB, and CoFe2O4/CB composites with CoFe2O4 content of 8.5 wt.%. Owing to the low density of 1.1–1.2 g/cm3 and good microwave absorption, the CoFe2O4/CB composite can meet the multiple requirements of microwave absorbent.
Co-reporter:Cong Zhang, Ce Zhang, Jinghua Sun, Ruimin Ding, Qinghua Zhang and Yao Xu
RSC Advances 2015 vol. 5(Issue 70) pp:56998-57005
Publication Date(Web):19 Jun 2015
DOI:10.1039/C5RA07731A
A double-layer film with both moisture barrier protective and antireflective (AR) abilities was prepared. The upper layer was a porous silica AR film. The bottom layer was a nonporous bridged polysilsesquioxane (BPSQ) moisture barrier protective film based on the sol–gel process of a newly synthesized X-bridged silsesquioxane (EG-BPSQ) monomer. The EG-BPSQ monomer was synthesized via the stoichiometric reaction between 3-glycidoxypropyltrimethoxysilane (GPTMS) and ethylene diamine (EDA) at 60 °C with no catalyst. The high polycondensation of the inorganic matrix and the special X-bridging organic chain in EG-BPSQ resulted in the dense structure of the protective film. Transmittance of a KH2PO4 (KDP) crystal coated with the EG-BPSQ film only decreased 1.11% at a wavelength of 1053 nm and 1.49% at a wavelength of 351 nm when tested after being in a 60% humidity environment for 100 days, indicating that the EG-BPSQ protective film possessed an excellent moisture barrier performance for the KDP crystal. For the double-layer film coated on KDP crystal, good AR performance was obtained: 98.09% at a wavelength of 1053 nm and 99.51% at a wavelength of 351 nm.
Co-reporter:Guomin Li, Liancheng Wang, Wanxi Li and Yao Xu
RSC Advances 2015 vol. 5(Issue 11) pp:8248-8257
Publication Date(Web):23 Dec 2014
DOI:10.1039/C4RA13443E
Porous activated carbon balls (PACB) with high specific surface area of 985.5 m2 g−1 and abundant pore structure were used as a matrix to synthesize a series of magnetic PACB composites through in situ impregnation of Fe3+ and Ni2+ ions as well as subsequent carbothermic reaction. The experiments involved the preparation of Fe3+–Ni2+ loaded PACB and the heat-treatment process in an Ar atmosphere. The morphology, from flakes to microspheres, coupled with the crystalline phase of the magnetic constituents in PACB, from Fe2O3–NiFe2O4 to Fe0.64Ni0.36–FeNi, can be well controlled by adjusting the reaction temperature. It was revealed that the framework structure of PACB was not destroyed during the carbothermic process, and the high surface area (713.2–808.2 m2 g−1) of PACB composites was still preserved, providing sufficient space to form an effective interface between the magnetic constituents and the PACB. The PACB composites exhibited excellent microwave absorption, a minimum reflection loss (RL) of −30 dB and effective bandwidth (RL below −10 dB) of 5.04 GHz were observed for the Fe0.64Ni0.36–FeNi/PACB composite when the coating thickness reached 2 and 1.7 mm respectively. Importantly, the absorption bandwidth covered the whole frequency range (2–18 GHz) with a thickness of 1.4–8 mm. The introduction of more alloy phase benefited the relative complex permittivity and permeability of the PACB composites, which in turn enhanced the microwave absorption. The microwave absorbability could be tuned via changing the coating thickness and composition of the absorbent, showing that the as-synthesized PACB composites were versatile in practical application. By considering the high surface area, low density (1.1–1.3 g cm−3) and remarkable absorption properties, we believe the PACB composites can be promising candidates as lightweight and effective microwave absorbents.
Co-reporter:Wanxi Li, Liancheng Wang, Guomin Li, Yao Xu
Materials Chemistry and Physics 2015 Volume 163() pp:431-438
Publication Date(Web):1 August 2015
DOI:10.1016/j.matchemphys.2015.07.062
•A new synthesis of Co3Fe7/C core–shell microspheres was reported.•The Co3Fe7/C microspheres possessed very low density of below 2 g/cm3.•The prepared composites exhibited excellent microwave absorption at 1.4 mm thickness.•The synthesis method provided a new route to design multiple microwave absorbents.Since electromagnetic pollution is becoming more and more serious, novel composite microwave absorbents are gaining much attention. Here, Co3Fe7/C core–shell microspheres for microwave absorption were synthesized for the first time. At first, hollow CoFe2O4 microspheres were prepared via a solvothermal method at 200 °C for 15 h. Then CoFe2O4-hydrochar microspheres were synthesized by hydrothermal method in an aqueous glucose solution containing hollow CoFe2O4 microspheres. After annealed under Ar atmosphere at 500 °C, the CoFe2O4-hydrochar microspheres were converted into CoFe2O4–Co3Fe7/C microspheres. Co3Fe7/C core–shell microspheres came into being after annealed at 600 °C. Both the CoFe2O4–Co3Fe7 nanoparticles and Co3Fe7 nanoparticles were encapsulated in the carbon shells, and the microsphere morphology could be retained during the carbothermal process. Especially, the core–shell structure caused that the density of the Co3Fe7/C microspheres was below 2 g/cm3. Resulting from the synergistic effect of Co3Fe7 nanoparticles and partially graphitized carbon, the minimum reflection loss (RL) of Co3Fe7/C microspheres was as low as −44.4 dB obtained with 1.6 mm thickness. Owing to the characteristics of low density and good microwave absorption, the Co3Fe7/C core–shell microspheres could be used as a lightweight and highly efficient microwave absorbent.
Co-reporter:Guomin Li;Dr. Liancheng Wang;Wanxi Li; Yao Xu
ChemPhysChem 2015 Volume 16( Issue 16) pp:3458-3467
Publication Date(Web):
DOI:10.1002/cphc.201500608
Abstract
Porous activated carbon ball (PACB) composites impregnated with iron, cobalt, nickel and/or their oxides were synthesized through a wet chemistry method involving PACBs as the carrier to load Fe3+, Co2+, and Ni2+ ions and a subsequent carbothermal reduction at different annealing temperatures. The results show that the pyrolysis products of nitrates and/or the products from the carbothermal reduction are embedded in the pores of the PACBs, with different distributions, resulting in different crystalline phases. The as-prepared PACB composites possessed high specific surface areas of 791.2–901.5 m2 g−1 and low densities of 1.1–1.3 g cm−3. Minimum reflection loss (RL) values of −50.1, −20.6, and −20.4 dB were achieved for Fe–PACB (annealed at 500 °C), Co–PACB (annealed at 800 °C), and Ni–PACB (annealed at 800 °C) composites, respectively. Moreover, the influence of the amount of the magnetic components in the PACB composites on the microwave-absorbing performances was investigated, further confirming that the dielectric loss was the primary contributor to microwave absorption.
Co-reporter:Guomin Li, Liancheng Wang, Wanxi Li, Ruimin Ding and Yao Xu
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 24) pp:12385-12392
Publication Date(Web):26 Mar 2014
DOI:10.1039/C4CP00647J
In order to prepare a lightweight and efficient microwave absorbent, porous activated carbon balls (PACB) were used to load Fe3+ and Co2+ ions, because the PACB carrier has a high specific surface area of 800 m2 g−1 and abundant pores, including micropores and macropores. The loaded Fe3+ and Co2+ ions in the PACB composite were transformed into magnetic CoFe2O4 and/or Co3Fe7 particles during subsequent heat-treatment under an Ar atmosphere. According to the XRD and SEM results, the magnetic particles were embedded in the PACB macropores and showed different crystalline phases and morphologies after heat-treatment. CoFe2O4 flakes with spinel structure were obtained at approximately 450 °C, and were then transformed into loose quasi-spheres between 500 °C and 600 °C, where CoFe2O4 and Co3Fe7 coexisted because of the partial reduction of CoFe2O4. Co3Fe7 microspheres appeared above 700 °C. The density of the magnetic PACB composites was in the range of 2.2–2.3 g cm−3. The as-synthesized PACB composites exhibited excellent microwave absorbability, which was mainly attributed to the magnetism of CoFe2O4 and Co3Fe7, as well as the presence of graphitized carbon. The minimum reflection loss value of the CoFe2O4–Co3Fe7–PACB composite reached −32 dB at 15.6 GHz, and the frequency of microwave absorption obeyed the quarter-wavelength matching model, showing a good match between dielectric loss and magnetic loss. The microwave reflection loss (RL) value could be modulated by adjusting the composition and thickness of the PACB composite absorbent. PACB composites with CoFe2O4–Co3Fe7 are a promising candidate for lightweight microwave absorption materials.
Co-reporter:Jinghua Sun, Qinghua Zhang, Ruimin Ding, Haibing Lv, Hongwei Yan, Xiaodong Yuan and Yao Xu
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 31) pp:16684-16693
Publication Date(Web):27 May 2014
DOI:10.1039/C4CP01032A
Porous silica optical antireflective (AR) coatings prepared by traditional sol–gel method have been extensively used for high power laser systems, but a serious drawback is that contamination existing in the high vacuum is easily absorbed by the disordered open pore structure, resulting in a fast decrease in transmittance. To improve the stability of transmittance in vacuum, a contamination-resistant silica AR coating with ordered mesopores completely closed by hydrophobic–oleophobic groups was successfully developed on a fused quartz substrate. The ordered mesopores in the coating were controlled under the direction of surfactant F127 via an evaporation-induced-self-assembling process and then were closed by post-grafting long chain fluoroalkylsilane. The grazing incidence small angle X-ray scattering (GISAXS) and the X-ray reflectivity (XRR) results indicated that the mesopores in the coating constructed a Fmmm orthorhombic symmetry structure with a (010) plane parallel to the substrate. Cage-like mesopores were confirmed by nitrogen adsorption–desorption analysis. The obtained coatings showed low surface roughness, excellent abrase-resistance and high transmittance of 100% on quartz substrate. Especially, the decrease of transmittance tested with polydimethylsiloxane pollution in vacuum within one-month was as small as 0.02%. The laser induced damage threshold was up to 59.8 J cm−2 at a 12 ns laser pulse of 1053 nm wavelength. This work provides an alternative way to fabricate AR coatings with high stability.
Co-reporter:Jinghua Sun, Ce Zhang, Cong Zhang, Ruimin Ding and Yao Xu
RSC Advances 2014 vol. 4(Issue 92) pp:50873-50881
Publication Date(Web):03 Oct 2014
DOI:10.1039/C4RA06788F
Ordered mesoporous silica coating used as an optical antireflective (AR) coating was successfully prepared using tetraethyl orthosilicate as a precursor in the direction of surfactant F127. After various post-treatments, the effect of optical, surface and structural properties on ordered mesoporous silica AR coating was investigated. Ammonia vapor treated ordered mesoporous AR coating showed high transmittance of 99.99% on a quartz substrate. After hexamethyldisilazane (HMDS) treatment, the contact angle with water increased from 7° to 88°. The in situ grazing incident small angle X-ray scattering (GISAXS) was used to investigated the structure evolution of the ordered mesoporous silica coating during the calcination process. The results indicated that the mesopores in the coating constructed a Fmmm orthorhombic symmetry structure with (010) planes parallel to the substrate. The silica network contracted along the direction vertical to the substrate during calcination to remove the template, while in the direction parallel to the substrate, the shrinkage was hindered by the adhesion of the coating. In addition, the Fmmm orthorhombic symmetry structure was maintained after various post-treatments.
Co-reporter:Wanxi Li, Baoliang Lv, Liancheng Wang, Guomin Li and Yao Xu
RSC Advances 2014 vol. 4(Issue 99) pp:55738-55744
Publication Date(Web):15 Oct 2014
DOI:10.1039/C4RA10172C
With the continuing growth in demand for the reduction of electromagnetic radiation, lightweight and highly efficient microwave absorbents are greatly needed. In this study, Fe3O4@C core–shell nanotubes, with Fe3O4 nanotubes as cores and carbon as shells, of about 10 nm thickness have been successfully synthesized. Coating Fe3O4 nanotubes with carbon shells effectively increased dielectric loss and improved impedance matching of the composites, resulting in enhanced microwave absorption performance. The effective absorption bandwidth, with reflection loss (RL) less than −10 dB, was up to 6 GHz when the thickness of the test sample was as little as 1.7 mm, as determined using a vector network analyzer. Possessing a very low density of 1.4 g cm−3 and good microwave absorption performance, the as-fabricated Fe3O4@C core–shell nanotubes can meet the multiple property requirements of microwave absorbents.
Co-reporter:Baoliang Lv;Hai Zhou;Dong Wu
Journal of Nanoparticle Research 2014 Volume 16( Issue 12) pp:
Publication Date(Web):2014 December
DOI:10.1007/s11051-014-2799-y
Dodecahedral α-Fe2O3 particles enclosed by twelve (101) planes were synthesized under the assistance of F– ions, and the particle size was controlled to about 150 nm by affecting the nucleation process of α-Fe2O3. It is interesting to find that its particle size to some extent depends on the second ligand (L) in [FeFa(L)b(OH)c(H2O)6-a-b-c](3-a-b-c)+ ions, which are the real situation of Fe3+ ions in aqueous solution. The synthesized dodecahedral α-Fe2O3 nanoparticles show enhanced catalytic properties in the thermal decomposition of ammonium perchlorate (AP), and that can be attributed to the exposure of (101) planes and its small particle size.
Co-reporter:Baoliang Lv, Zhong Liu, Ruimin Ding, Dong Wu and Yao Xu
Journal of Materials Chemistry A 2013 vol. 1(Issue 18) pp:5695-5699
Publication Date(Web):06 Mar 2013
DOI:10.1039/C3TA10375G
Based on theoretical analysis of the crystal structure of β-Ni(OH)2, the (001) and (100) planes have the highest and the second highest Ni2+ cation concentration, respectively. Therefore, F− anions were selected to control the growth behavior of β-Ni(OH)2 through the selective adsorption of F− anions because of their small size, simple effect and ability to coordinate with Ni2+ cations. As a result, a series of β-Ni(OH)2 nanostructures with (001) and (100) planes exposed were successfully synthesized within several tens of minutes under the stimulation of microwave irradiation. The surface area ratio of (100) to (001) planes can be changed by altering the reaction time. The exposure of (100) planes was found to be favorable to the electrochemical activity rather than (001) planes.
Co-reporter:Qifeng Chen, Huijuan Shi, Weimei Shi, Yao Xu and Dong Wu
Catalysis Science & Technology 2012 vol. 2(Issue 6) pp:1213-1220
Publication Date(Web):27 Feb 2012
DOI:10.1039/C2CY00545J
To utilize efficiently visible light in photocatalytic reactions, a series of doped TiO2 photocatalysts were synthesized via a facile solvothermal method. The photocatalysts were characterized with various techniques. The results indicated that all the photocatalysts were of an anatase phase, the Ag0.010C2.0–TS0.20 sample possessed the largest surface area (306.0 m2 g−1) and pore volume (2.05 cm3 g−1). The carbon dopant existed in the surface layer of the TiO2–SiO2 composite and narrowed the energy band gap, which induced visible light absorption. Silver existed on the particle surface and in two forms, Ag+ and Ag0, which acted together to inhibit the recombination of photogenerated electrons and holes. The photoactivities were evaluated by decomposition of RhB under visible irradiation. It was found that the Ag–C/TS photocatalyst exhibited the highest visible photoactivity, with the molar ratios of Ag–Ti, and C–Ti of 0.005, and 2.0, respectively, corresponding to the reaction rate constant 2.09 h−1. The reaction rate was 52.3, 11.2 and 2.33 times higher than that of TiO2 (0.04 h−1), Ag0.005–TiO2 (0.186 h−1) and C2.0–TiO2 (0.897 h−1), respectively. The enhanced visible photocatalytic activity can be attributed to the synergetic effects of silver and carbon doping, as well as silicon introduction. The photocatalytic reaction mechanism was verified with ESR technique; furthermore, both the hydroxyl radical and superoxide radical played a critical role on the photocatalytic reaction, in addition, DMPO–˙H was found in the ESR experiments.
Co-reporter:Shuhai Chen, Baoliang Lv, Yao Xu
Materials Letters 2012 Volume 77() pp:32-34
Publication Date(Web):15 June 2012
DOI:10.1016/j.matlet.2012.02.129
Si-doped TiO2 nanoparticles were prepared via a solvothermal method and were sensitized by the Fe-quinoline complexes (HQSI) to improve the visible light photocatalytic activity. The used HQSI had a narrow band gap of 1.54 eV and showed strong visible light absorption. HQSI can transfer photoelectrons to the conduction band of TiO2 and be regenerated by the electron injection from Rhodamine B. After sensitization, the Si-doped TiO2 exhibited stronger absorption in the visible region and showed higher visible-light photocatalytic activity for the degradation of Rhodamine B in an aqueous solution than the simple Si-doped TiO2 and sensitized commercial TiO2.Highlights► Fe-quinoline complexes as the sensitizer for Si-doped TiO2. ► Smooth electrons transfer from RhB substrate to sensitizer, and then to TiO2. ► Easy regeneration of sensitizer and high visible photocatalytic activity of HQSI-ST.
Co-reporter:Baoliang Lv, Yao Xu, Dong Wu and Yuhan Sun
Chemical Communications 2011 vol. 47(Issue 3) pp:967-969
Publication Date(Web):12 Nov 2010
DOI:10.1039/C0CC03632C
Single-crystal α-Fe2O3 hexagonal nanorings with hexagonal inner hole were synthesized under the stepwise influence of different anionic ligands (F− and SCN−). This is a new method to design and modify crystal structures of transition metal oxide nanoparticles.
Co-reporter:Weimei Shi, Qifeng Chen, Yao Xu, Dong Wu, Chunfang Huo
Applied Surface Science 2011 Volume 257(Issue 7) pp:3000-3006
Publication Date(Web):15 January 2011
DOI:10.1016/j.apsusc.2010.10.107
Abstract
To deeply understand the effects of Si/N-codoping on the electronic structures of TiO2 and confirm their photocatalytic performance, a comparison theoretical study of their energetic and electronic properties was carried out involving single N-doping, single Si-doping and three models of Si/N-codoping based on first-principles. As for N-doped TiO2, an isolated N 2p state locates above the top of valence band and mixes with O 2p states, resulting in band gap narrowing. However, the unoccupied N 2p state acts as electrons traps to promote the electron–hole recombination. Using Si-doping, the band gap has a decrease of 0.24 eV and the valence band broadens about 0.30 eV. These two factors cause a better performance of photocatalyst. The special Si/N-codoped TiO2 model with one O atom replaced by a N atom and its adjacent Ti atom replaced by a Si atom, has the smallest defect formation energy in three codoping models, suggesting the model is the most energetic favorable. The calculated energy results also indicate that the Si incorporation increases the N concentration in Si/N-codoped TiO2. This model obtains the most narrowed band gap of 1.63 eV in comparison with the other two models. The dopant states hybridize with O 2p states, leading to the valence band broadening and then improving the mobility of photo-generated hole; the N 2p states are occupied simultaneously. The significantly narrowed band gap and the absence of recombination center can give a reasonable explanation for the high photocatalytic activity under visible light.
Co-reporter:Tao Tang, Yanling Zhao, Yao Xu, Dong Wu, Jun Xu, Feng Deng
Applied Surface Science 2011 Volume 257(Issue 14) pp:6004-6009
Publication Date(Web):1 May 2011
DOI:10.1016/j.apsusc.2011.01.096
Abstract
To investigate the driving force for bilirubin adsorption on mesoporous materials, a comparative study was carried out between pure siliceous SBA-15 and three functionalized SBA-15 mesoporous materials: CH3-SBA-15 (MS), NH2-SBA-15 (AS), and CH3/NH2-SBA-15 (AMS) that were synthesized by one-pot method. The obtained materials exhibited large surface areas (553–810 m2/g) and pore size (6.6–7.1 nm) demonstrated by XRD and N2-ad/desorption analysis. The SEM images showed that the materials had similar fiberlike morphology. The functionalization extent was calculated according to 29Si MAS NMR spectra and it was close to the designed value (10%). The synthesized mesoporous materials were used as bilirubin adsorbents and showed higher bilirubin adsorption capacities than the commercial active carbon. The adsorption capacities of amine functionalized samples AMS and AS were larger than those of pure siliceous SBA-15 and MS, indicating that electrostatic interaction was the dominant driving force for bilirubin adsorption on mesoporous materials. Increasing the ionic strength of bilirubin solution by adding NaCl would decrease the bilirubin adsorption capacity of mesoporous material, which further demonstrated that the electrostatic interaction was the dominant driving force for bilirubin adsorption. In addition, the hydrophobic interaction provided by methyl groups could promote the bilirubin adsorption.
Co-reporter:Weimei Shi, Qifeng Chen, Yao Xu, Dong Wu, Chun-fang Huo
Journal of Solid State Chemistry 2011 Volume 184(Issue 8) pp:1983-1988
Publication Date(Web):August 2011
DOI:10.1016/j.jssc.2011.05.056
A first-principles calculation based on the density functional theory (DFT) was used to investigate the energetic and electronic properties of Si-doped anatase TiO2 with various silicon concentrations. The theoretical calculations showed that with Si-doping the valence band and conduction band of TiO2 became hybrid ones with large dispersion, which could benefit the mobility of the photo-generated carriers. This result is in agreement with the experimental reports. At lower doping levels, the band gap of Si-doped anatase TiO2 decreases about 0.2 eV. With the increase of silicon concentration, the band gap increases gradually and larger formation energies are required during the synthesis of Si-doped TiO2.Graphical abstractThe total density of states (TDOS) of Ti1−xSixO2 with (a) x=0, (b) x=0.03125, (c) x=0.0625, (d) x=0.09375 and (e) x=0.125.Highlights► The effect of Si content on the electronic structure in Si-doped anatase TiO2. ► Large dispersion of DOS in VB and CB benefits the mobility of the carriers. ► Low Si-doping level reduces the band gap of Si-doped anatase TiO2 with 0.2 eV.
Co-reporter:Junhua Li, Dan Zhang, Qiang Gao, Yao Xu, Dong Wu, Yuhan Sun, Jun Xu, Feng Deng
Materials Chemistry and Physics 2011 Volume 125(1–2) pp:286-292
Publication Date(Web):1 January 2011
DOI:10.1016/j.matchemphys.2010.09.036
Hollow mesoporous aluminosilicate spheres (HMAS) with middle strong acidity have been successfully synthesized by simply hydrothermally treating mesoporous silica spheres (MSS) in zeolite precursor solution. Based on a set of time-dependent experiments, it was found that the hollowing process was associated with a progressive mass redistribution and changes of pores structures. The surfactant cetyltrimethylammonium bromide (CTAB) located in the pores of MSS protected the mesoporous silica spheres from dissolving into strongly basic zeolite precursor solution and acted as the template for mesoporous shell. Under the templating function of CTAB, primary zeolite units were introduced into the mesopore walls of HMAS. The acidity of the resultant samples HMAS was measured by NH3-TPD techniques. Catalytic tests showed that the HMAS catalysts exhibited high catalytic activity compared with the MSS and Hβ zeolite for catalytic cracking of 1,3,5-triisopropylbenzene.
Co-reporter:Qifeng Chen, Weimei Shi, Yao Xu, Dong Wu, Yuhan Sun
Materials Chemistry and Physics 2011 Volume 125(Issue 3) pp:825-832
Publication Date(Web):15 February 2011
DOI:10.1016/j.matchemphys.2010.09.049
To utilize visible light more efficiently and enhance the photocatalytic performance of TiO2, Ag–Si/TiO2 photocatalyst was synthesized via a two-step method. The obtained materials were characterized by XRD, Raman, TEM, HRTEM, BET, TG–DTA, XPS, ICP as well as UV–vis DRS. All photocatalyst materials held an anatase phase confirmed by XRD, Raman and HRTEM. The Ag–Si/TiO2 photocatalysts possessed high thermal stability and the phase transformation was retarded to about 900 °C revealed by XRD and TG–DTA. The Ag–Si/TiO2 particles synthesized via the nonaqueous method were highly monodispersed and the particles size became smaller compared to the un-doped TiO2, resulting in the enlargement of surface area. In addition, UV–vis light absorption shifted to visible region after Ag doping. XPS results demonstrated that Si weaved into the matrix of TiO2 and enriched in the surface layer, while Ag dispersed on the surface of TiO2 particles. The Ag dopant suppressed the recombination of photogenerated electrons and holes, Si enlarged the surface of photocatalysts. Silver and silicon co-doping improved the visible photocatalytic activity, which was evaluated by Rhodamine B (RhB) degradation. The photocatalytic activity of the obtained Ag–Si/TiO2 sample was much more higher than those of pure TiO2 and Ag/TiO2, reaching the maximum at the Ag and Si content of 0.5 mol% and 20.0 mol%, respectively. The improved visible photocatalytic activity may be attributed to the synergetic effects of codoping by silver and silicon.
Co-reporter:Yanling Zhao, Qiang Gao, Tao Tang, Yao Xu, Dong Wu
Materials Letters 2011 Volume 65(Issue 6) pp:1045-1047
Publication Date(Web):31 March 2011
DOI:10.1016/j.matlet.2010.12.047
Utilizing the reactions between toluene diisocyanate (TDI), silanol, and ethylenediamine (EDA), NH2 groups were successfully grafted on mesoporous SBA-15 surface without any destroy to the mesostructure. TDI was employed as a ‘bridge’ molecule whose one NCO group was used to link SBA-15 surface silanols and the other one was left to link EDA. Such NH2-grafting is highly effective for a high loading amount of NH2 groups on SBA-15 because the special stepwise grafting can avoid amino/silanol and amino/amino interactions. Subjected to remove toxic heavy metal ions in aqueous solution, the obtained NH2-SBA-15 showed very high adsorption rates 99.4%, 100%, 99.7%, 98.7% and 99.9% for Cu2+, Zn2+, Cr3+, Ni2+ and Cd2+, respectively, which should be attributed to the strong complexation reactions between metal ions and grafted NH2 groups.
Co-reporter:Tao Tang, Xiaoan Li, Yao Xu, Dong Wu, Yuhan Sun, Jun Xu, Feng Deng
Colloids and Surfaces B: Biointerfaces 2011 Volume 84(Issue 2) pp:571-578
Publication Date(Web):1 June 2011
DOI:10.1016/j.colsurfb.2011.02.019
To remove bilirubin from human plasma, amine/methyl bifunctionalized SBA-15 materials were directly synthesized from the co-condensation of 3-aminopropylmethyldiethoxysilane and tetraethoxysilane with an amphiphilic block copolymer P123 as template. XRD, N2 sorption analysis, FTIR and 29Si MAS NMR were used to identify their well-ordered mesostructure and the grafting of amine and methyl groups on the surface of as-synthesized materials. Both SEM and TEM indicated that the bifunctionalized SBA-15 possessed platelet morphology. This might be attributed to the charge repulsion brought by protonated amine groups and the diminution of hydroxyl groups on the end of silicate-micelles, which passivated the end-to-end anchoring of silicate-micelles along the longitudinal axis. Such a material was investigated as the adsorbent for selective bilirubin removal from human plasma, which showed a high bilirubin clearance of 51.4% within 1.5 h with a little amount of albumin adsorption. The results of hemolysis assay suggested that the bifunctionalized SBA-15 caused serious hemolysis of red blood cells. However, in practical application, plasma separation technique could avoid direct contact between the adsorbent and red blood cells. The further hemeolysis assay proved that the plasma after contacting with the bifunctionalized SBA-15 could not lead to the hemolysis of red blood cells. Thus, the bifunctionalized SBA-15 is expected to be a potential candidate as a clinical hemoperfusion material.Graphical abstractResearch highlights► Well-ordered bifunctional SBA-15 with platelet morphology was synthesized. ► The synthesized material showed high bilirubin clearance. ► The synthesized material exhibited high bilirubin adsorption selectivity. ► The synthesized material exhibited negligible hemolytic activity.
Co-reporter:Baoliang Lv, Yao Xu, Dong Wu, Yuhan Sun
Materials Research Bulletin 2011 46(6) pp: 941-945
Publication Date(Web):
DOI:10.1016/j.materresbull.2011.02.013
Co-reporter:Baoliang Lv;Zhenyu Liu;Hong Tian;Dong Wu;Yuhan Sun
Advanced Functional Materials 2010 Volume 20( Issue 22) pp:3987-3996
Publication Date(Web):
DOI:10.1002/adfm.201001021
Abstract
Despite significant advances in iron oxide nanoparticles, it is still a challenge to synthesize regular polyhedral single-crystalline α-Fe2O3 particles because the surface energies of several low-index planes are fairly similar. In the work presented here, well-dispersed and single-crystalline dodecahedral and octodecahedral α-Fe2O3 particles are synthesized by a facile hydrothermal method with the aid of F− anions. The crystalline structure of the polyhedral particles is disclosed by various characterization techniques. The dodecahedral particles are of hexagonal bipyramidal shape and enclosed by twelve equivalent (101) planes. The octodecahedral particles are formed by adding six equivalent (111) planes on the two tips of a dodecahedral particle, that is, they are enclosed by twelve (101) planes and six (111) planes. The existence of F− anions plays a crucial role in the control of polyhedral particle shape. The function of F− anions in the shape formation of the polyhedral particles is proposed as follows: 1) A high concentration of exposed Fe3+ cations induces preferential adsorption of F− anions on the (100) plane and leads to the slowest growth along the [100] direction. When the concentration of F− anions is higher than 24 mM, a stable speed ratio of growth along the [001] and [100] directions results in the exposure of (101) planes. 2) With a lower concentration of F− anions, six symmetrical (111) planes with low concentration of exposed Fe3+ cations are present at the tops of a dodecahedral particle to form an octodecahedron. Furthermore, the dodecahedral and octodecahedral α-Fe2O3 particles show much stronger magnetism than the previously reported α-Fe2O3 nanostructures, having coercivities of 4986 Oe and 6512 Oe, respectively. Such high coercivities are attributed to a large local magnetic anisotropy, which might be induced by the polyhedron with equivalent crystallographic planes and/or the presence of F− anions.
Co-reporter:Baoliang Lv, Yao Xu, Hong Tian, Dong Wu, Yuhan Sun
Journal of Solid State Chemistry 2010 Volume 183(Issue 12) pp:2968-2973
Publication Date(Web):December 2010
DOI:10.1016/j.jssc.2010.10.001
To obtain a recyclable surface-enhanced Raman scattering (SERS) material, we developed a composite of Fe3O4\SiO2\Ag with core\shell\particles structure. The designed particles were synthesized via an ultrasonic route. The Raman scattering signal of Fe3O4 could be shielded by increasing the thickness of the SiO2 layer to 60 nm. Dye rhodamine B (RB) was chosen as probe molecule to test the SERS effect of the synthesized Fe3O4\SiO2\Ag particles. On the synthesized Fe3O4\SiO2\Ag particles, the characteristic Raman bands of RB could be observed when the RB solution was diluted to 5 ppm (1×10−5 M). Furthermore, the synthesized particles could keep their efficiency till four cycles.Graphical AbstractFe3O4/SiO2/Ag particles, a recyclable surface-enhanced Raman scattering (SERS) material, were designed and synthesized via a simple ultrasonic route.
Co-reporter:Qiang Gao, Yao Xu, Dong Wu, Wanling Shen, and Feng Deng
Langmuir 2010 Volume 26(Issue 22) pp:17133-17138
Publication Date(Web):October 12, 2010
DOI:10.1021/la102952n
To accomplish pH-controllable drug release on mesoporous carrier, one of the best ways is to graft stimuli-responsive organic molecules around mesopore outlets. In this work, the pH-responsive propyldiethylenetriamine groups (abbreviative phrase: multiamine chains) were grafted around mesopore outlets of mesoporous silica spheres (MSS) and expected to act as pH-responsive gates. To this end, three multiamine-grafted MSS (i.e., NM1, NM2, and NM3) were synthesized under different reaction temperatures and reaction times. The reaction temperature and time for multiamine grafting were 25 °C and 12 h for NM1, 100 °C and 1 h for NM2, and 100 °C and 12 h for NM3, respectively. Through systematic investigations of TEM, SEM, N2 adsorption/desorption, TG, and 29Si MAS NMR, it was found that NM3 had the highest grafting amount of multiamine chains. It was further confirmed that the multiamine chains around the pore outlets of NM3 played the role of “molecular switch” that could well control the transport of guest drug molecules. In contrast, the multiamine chains around the pore outlets of NM2 and NM3 did not show gate effect. The difference should be decided by the fact whether the grafting amount of multiamine chains around mesopore outlets were sufficient under determined reaction temperature and time. In the tests of in vitro drug release, multiamine-gated MSS (i.e., NM3) showed highly sensitive response to the solution pH. At high pH (pH 7.5), ibuprofen (IBU) in this carrier released rapidly and completely within 2 h; at low pH (pH 4.0 or 5.0), only a small part of the IBU (13 wt %) was slowly released from this carrier and the most of IBU was effectively confined in mesopores.
Co-reporter:Qifeng Chen, Dong Jiang, Weimei Shi, Dong Wu, Yao Xu
Applied Surface Science 2009 Volume 255(Issue 18) pp:7918-7924
Publication Date(Web):30 June 2009
DOI:10.1016/j.apsusc.2009.04.167
Abstract
To enhance the visible photocatalytic activity and thermal stability of TiO2, Ce–Si co-doped TiO2 materials were synthesized through a nonaqueous method of which the purpose was to reduce the aggregation between TiO2 particles. The obtained materials maintained anatase phase and large surface area of 103.3 m2 g−1 even after calcined at 800 °C. The XPS results also indicated that Si was weaved into the lattice of TiO2, and Ce mainly existed as oxides on the surface of TiO2 particles. The doped Si might enhance surface area and suppress transformation from anatase to rutile, while the doped Ce might cause visible absorption and inhibit crystallite growth during heat treatment. Evaluated by decomposing dye Rhodamine B, visible photocatalytic activity of Ce–Si co-doped TiO2 was obviously higher than that of pure TiO2 and reached the maximum at Ce and Si contents of 0.5 mol% and 10 mol%.
Co-reporter:Wujun Xu, Qiang Gao, Yao Xu, Dong Wu, Yuhan Sun, Wanling Shen, Feng Deng
Powder Technology 2009 Volume 191(1–2) pp:13-20
Publication Date(Web):4 April 2009
DOI:10.1016/j.powtec.2008.09.001
Mesoporous silica spheres with controllable particle size were synthesized in mixed ethanol–water solvent. These materials possessed same pore size distribution and pore channel geometry. The amount of ibuprofen (IBU) adsorbed in mesoporous channels increased with the surface area of mesoporous silica spheres. Three kinds of release fluids, simulated intestinal fluid (SIF, pH = 7.4), simulated body fluid (SBF, pH = 7.4), and simulated gastric fluid (SGF, HCl aqueous solution, pH = 1.2) were used to investigate drug release. The effects of particle size and dispersancy of mesoporous spheres on drug release rate were discussed in detail. It was found that larger or agglomerate mesoporous silica spheres could delay the drug release process, which could be attributed to pore-mouth amount and mesopore channel length of mesoporous spheres. Furthermore, to obtain a well controlled drug release system, hydrophobic trimethylsilyl (TMS) groups were functionalized on the surface of mesoporous silica spheres. The release of IBU from TMS-functionalized mesoporous spheres was obviously delayed with the increase of TMS content.Monodisperse mesoporous spheres were synthesized to study the effect of particle size on drug release. The release rate of ibuprofen decreased with the increase of particle size. To obtain a well controlled drug release system, hydrophobic trimethylsilyl groups were functionalized on the surface of mesoporous silica spheres. The release of drug could be obviously delayed with the increase of trimethylsilyl content.
Co-reporter:Shengwei Hu, Dongjiang Yang, Yao Xu, Dong Wu, Yuhan Sun
Materials Chemistry and Physics 2009 Volume 114(2–3) pp:868-873
Publication Date(Web):15 April 2009
DOI:10.1016/j.matchemphys.2008.10.071
A new bridged silsesquioxane (BSQ) was synthesized with isophorone diisocyanate (IPDI) and 3-aminopropyltriethoxysilane (APTES). Highly cross-linked bridged polysilsesquioxane (BPSQ) sol was prepared by the sol–gel polycondensation of the as-synthesized BSQ under basic catalysis. Transparent film was obtained by dip-coating the BPSQ sol on the nickel sulfate hexhydrate (NSH, NiSO4·6H2O) crystal wafer, an important kind of UV light filter used at wavelength 300 nm. The obtained BPSQ film was nonporous (pore volume is 2 × 10−3 cm3 g−1) and exhibited very high condensation degree of siloxane (99.0%). This film showed high optical transmittance and excellent moisture-resistant protection to the NSH filter. Moreover, the thermal stability of the NSH filter was also greatly improved by the as-prepared BPSQ film.
Co-reporter:Shengwei Hu, Yao Xu, Dong Jiang, Dong Wu, Yuhan Sun, Feng Deng
Thin Solid Films 2009 Volume 518(Issue 1) pp:348-354
Publication Date(Web):2 November 2009
DOI:10.1016/j.tsf.2009.06.024
Three bridged silsesquioxanes were synthesized via the reactions between 3-aminopropyltriethoxysilane and three different diisocyanates, i.e., m-xylylene diisocyanate, 1, 6-diisocyanatohexane, and isophorone diiocyanate. The subsequent bridged polysilsesquioxane sols were prepared by the room-temperatured polycondensation of these bridged silsesquioxane using basic catalysis. Transparent films with a thickness of around 330 nm were obtained by dip-coating the bridged polysilsesquioxane sols on the nickel sulfate hexahydrate (NiSO4·6H2O, NSH) crystal wafers that are commercially used as ultraviolet light filter working at a wavelength of 300 nm. The N2 adsorption/desorption experimental results showed that the films were all nonporous with pore volume less than 2 × 10− 3 cm3 g− 1. The obtained three polysilsesquioxanes all exhibited very high condensation degree of siloxane (above 99%). These films showed high optical transmittance at desired wavelengths (280–320 nm) and excellent moisture-resistant protection to the NSH filters.
Co-reporter:Baoliang Lv, Yao Xu, Bo Hou, Dong Wu, Yuhan Sun
Particuology 2009 Volume 7(Issue 3) pp:169-174
Publication Date(Web):June 2009
DOI:10.1016/j.partic.2008.11.011
Zr/ZrH2 particles with irregular morphologies and broad size distribution were uniformly coated with acicular α-FeOOH crystal grains via a facile route without using polymers or surfactants. The as-synthesized material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), UV–vis diffusion reflection (UV–vis) and Raman spectrometry. Based on these characterizations, the synthesis mechanism was explained in terms of combined heterogeneous nucleation and solid state transformation reaction. The presence of α-FeOOH coating greatly changed the combustion behavior of Zr/ZrH2 particles: the combustion lasting time decreased from 32 s for un-coated Zr/ZrH2 particles to 0.2 s for coated particles while the maximum temperature in the combustion process increased from 1510 °C to 2036 °C.
Co-reporter:Baoliang Lv, Yao Xu, Dong Wu, Yuhan Sun
Materials Research Bulletin 2009 44(5) pp: 961-965
Publication Date(Web):
DOI:10.1016/j.materresbull.2008.11.022
Co-reporter:Wujun Xu, Qiang Gao, Yao Xu, Dong Wu, Yuhan Sun
Materials Research Bulletin 2009 44(3) pp: 606-612
Publication Date(Web):
DOI:10.1016/j.materresbull.2008.07.001
Co-reporter:Qiang Gao, Yao Xu, Dong Wu, Yuhan Sun and Xiaoan Li
The Journal of Physical Chemistry C 2009 Volume 113(Issue 29) pp:12753-12758
Publication Date(Web):June 25, 2009
DOI:10.1021/jp9043978
A novel method was proposed to coat poly(methacrylic acid-co-vinyl triethoxylsilane) (PMV) on mesoporous silica spheres (MSSs) to obtain a core−shell pH-responsive drug-carrier (MSS/PMV). PMV was prepared by free radical polymerization of methacrylic acid (MAA) and vinyl triethoxylsilane (VTES), in which MAA acted as the pH-sensitive monomer and VTES acted as the siloxane-containing monomer to provide an anchoring effect with the MSS surface. The micrographs of MSSs before and after coating were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that the PMV shell with a thickness of 20 nm had been coated successfully on MSS particles. To confirm the pH-sensitivity of the PMV shell, we investigated the pH-response difference between MSS/PMV and MSS/PMV-H (acidified MSS/PMV) in NH4NO3/C2H5OH solution. It was found that the PMV shell of MSS/PMV was loose (“open” state) and allowed template molecules to penetrate it easily. By contrast, the PMV shell of MSS/PMV-H was compact (“closed” state) and confined template molecules effectively inside MSS pores. These results indicated that the PMV shell played the role of molecular switch that could control the transport of molecules via a pH-dependent “open−close” mechanism. In a test of in vitro drug release, MSS/PMV showed high response to the pH of a drug solution. At high pH (pH = 7.5), ibuprofen (IBU) that loaded in MSS/PMV released rapidly and completely (within 2 h); at low pH (pH = 4.0 or 5.0), only a small part of the IBU (15 wt %) was slowly released from the MSS/PMV, and most of the IBU was effectively confined in MSS pores.
Co-reporter:Dongjiang Yang, Yao Xu, Wujun Xu, Dong Wu, Yuhan Sun and Huaiyong Zhu
Journal of Materials Chemistry A 2008 vol. 18(Issue 45) pp:5557-5562
Publication Date(Web):22 Oct 2008
DOI:10.1039/B804967J
Macroporous silica films with methyl groups grafted on their surface were prepared from polymethylhydrosiloxane (PMHS) and tetraethylorthosilicate (TEOS) without templates. Compared to the conventional template syntheses, this approach has several advantages. First, it avoids the removal of templates, which is sometimes an environmentally unfriendly procedure. Second, it does not require a post-synthesis grafting to form the hybrid structures with methyl groups on the silica surface. Third, the pore size and hydrophobicity (expressed by the water contact angle) of the film can be tuned readily. By adjusting the amount of PMHS used in the synthesis and introducing hexamethyldisilazane (HMDS) we can tune the pore size in a wide range from 50 nm to 500 nm. The hydrophobicity increases substantially as the pore size decreases. Evidently, the reaction mechanism of this synthesis is different from the conventional template synthesis. A tentative mechanism is proposed: the hydrogen gas released from PMHS results in the formation of the macropores in the films. With excellent hydrophobicity, optical transmittance and thermal stability, the obtained silica films have potential applications in the semiconductor industry.
Co-reporter:Yao Xu, Yanxia Cui, Dong Jiang, Dong Wu, Yu Han Sun
Microporous and Mesoporous Materials 2008 Volume 109(1–3) pp:335-341
Publication Date(Web):1 March 2008
DOI:10.1016/j.micromeso.2007.05.009
Following a three-stepped reaction, a novel nonsurfactant method was established to synthesize mesoporous silica using dye Basic Fuchsin (BF) as template, and using m-xylenediisocyanate (m-XDI) and aminopropyltriethoxysilane (APTES) as bridging molecules. The first step is to form the intermediate product (namely XA) of m-XDI and APTES. The second step is to form the intermediate product (namely XAD) of XA and dye BF. The third step is the hydrolysis and condensation of siloxane to construct mesopores. Due to the plane structure of dye BF, it was linked with hydrolyzed siloxane precursors to form mesopores. As expected, mesoporous structure could be formed only when the XA to dye molar ratio was set to 3:1. The synthesized mesoporous silica had narrow pore size distribution centered at 3.56 nm and high surface area of 716 m2 g−1.
Co-reporter:Dong Jiang;Bo Hou;Dong Wu;Yuhan Sun
European Journal of Inorganic Chemistry 2008 Volume 2008( Issue 8) pp:1236-1240
Publication Date(Web):
DOI:10.1002/ejic.200700650
Abstract
High-yield nanocrystalline TiO2 was successfully synthesised using a simple one-step procedure in a non-aqueous system. The synthesis was carried out in a teflon-lined autoclave at a temperature as low as 100 °C using titanium n-butoxide (TB) and acetic acid (AcOH) as starting materials without any co-solvent/additive. The thus formed TiO2 was highly crystallised anatase TiO2. The possible formation mechanism was also proposed based on the FTIR spectra recorded during the various reaction stages. The synthetic method explored in this study might contribute to the preparation of other metal oxides.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Co-reporter:Juan Zou, Yao Xu, Bo Hou, Dong Wu, Yuhan Sun
Powder Technology 2008 Volume 183(Issue 1) pp:122-126
Publication Date(Web):18 March 2008
DOI:10.1016/j.powtec.2007.11.012
This paper describes a novel self-assembly behavior of Ag2O nanoparticles to Ag2O nanowires. In the alkaline water–alcohol solution, Ag+ ions reacted with OH− ions on silica nanoparticles functionalized by N-(2-aminoethyl)-3-aminopropyl-trimethoxy-silane (AEAPTS) to form Ag2O nanoparticles. The Ag2O nanoparticles further self-assembled into Ag2O nanowires. The morphology of Ag2O nanowires could be controlled by adjusting Ag/Si molar ratios in the systems. With low Ag/Si molar ratio, uniform Ag2O nanowires were obtained with diameter of about 50 nm and length of tens micrometers. With the increase of Ag/Si molar ratio, Ag2O nanowires became thicker, shorter and irregular. It was shown by high-resolution transmission electron microscopy (HRTEM) that all Ag2O nanowires consisted of tiny Ag2O nanoparticles with diameter of 10–20 nm. The self-assembly of Ag2O nanoparticles into Ag2O nanowires was observed by transmission electron microscopy (TEM) and the corresponding growth mechanism was proposed.This research described a novel self-assembly from Ag2O nanoparticles into Ag2O nanowires on the effect of silica nanoparticles surface-functionalized by N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTS). The morphology of Ag2O nanowires can be controlled by adjusting the Ag/Si molar ratios in the reactants. All Ag2O nanowires consisted of tiny Ag2O particles with diameter of 10–20 nm. The corresponding growth mechanism of Ag2O nanowires was proposed.
Co-reporter:Wujun Xu, Qiang Gao, Yao Xu, Dong Wu, Yuhan Sun, Wanling Shen, Feng Deng
Journal of Solid State Chemistry 2008 Volume 181(Issue 10) pp:2837-2844
Publication Date(Web):October 2008
DOI:10.1016/j.jssc.2008.07.011
Serial of trimethylsilyl-carboxyl bifunctionalized SBA-15 (TMS/COOH/SBA-15) have been studied as carriers for controlled release of drug famotidine (Famo). To load Famo with large capacity, SBA-15 with high content of carboxyl groups was successfully synthesized by one-pot synthesis under the assistance of KCl. The mesostructure of carboxyl functionalized SBA-15 (COOH/SBA-15) could still be kept even though the content of carboxyl groups was up to 57.2%. Increasing carboxyl content could effectively enhance the loading capacity of Famo. Compared with pure SBA-15, into which Famo could be hardly adsorbed, the largest drug loading capacity of COOH/SBA-15 could achieve 396.9 mg/g. The release of Famo from mesoporous silica was studied in simulated intestine fluid (SIF, pH=7.4). For COOH/SBA-15, the release rate of Famo decreased with narrowing pore size. After grafting TMS groups on the surface of COOH/SBA-15 with hexamethyldisilazane, the release of Famo was greatly delayed with the increasing content of TMS groups.Trimethylsilyl-carboxyl bifunctionalized SBA-15 has been studied as carrier for controlled release of drug famotidine. To load drug with large capacity, SBA-15 with high content of carboxyl groups was successfully synthesized. After grafting trimethylsilyl groups on the surface of carboxyl functionalized SBA-15, the release of Famo was greatly delayed with the increasing content of TMS groups.
Co-reporter:Dongjiang Yang, Yao Xu, Dong Wu, Yuhan Sun
Journal of Solid State Chemistry 2008 Volume 181(Issue 9) pp:2401-2405
Publication Date(Web):September 2008
DOI:10.1016/j.jssc.2008.05.046
Using tetraethylorthosilicate (TEOS), polymethylhydrosiloxane (PMHS) and aluminium isopropoxide (AIP) as the reactants, through a one-step nonsurfactant route based on PMHS–TEOS–AIP co-polycondensation, hydrothermally stable mesoporous aluminosilicates with different Si/Al molar ratios were successfully prepared. All samples exclusively showed narrow pore size distribution centered at 3.6 nm. To assess the hydrothermal stability, samples were subjected to 100 °C distilled water for 300 h. The boiled mesoporous aluminosilicates have nearly the same N2 adsorption–desorption isotherms and the same pore size distributions as those newly synthesized ones, indicating excellent hydrothermal stability. The 29Si MAS NMR spectra confirmed that PMHS and TEOS have jointly condensed and CH3 groups have been introduced into the materials. The 27Al MAS NMR spectra indicated that Al atoms have been incorporated in the mesopore frameworks. The NH3 temperature-programmed desorption showed strong acidity. Due to the existence of large amount of CH3 groups, the mesoporous aluminosilicates obtained good hydrophobicity. Owing to the relatively large pore and the strong acidity provided by the uniform four-coordinated Al atoms, the excellent catalytic performance for 1,3,5-triisopropylbenzene cracking was acquired easily. The materials may be a profitable complement for the synthesis of solid acid catalysts.Based on the nonsurfactant method, a facile one-step synthesis route has been developed to prepare methyl-modified mesoporous aluminosilicates that possessed hydrothermal stability and strong acidity.
Co-reporter:Yonggang Sheng, Liping Liang, Yao Xu, Dong Wu, Yuhan Sun
Optical Materials 2008 Volume 30(Issue 8) pp:1310-1315
Publication Date(Web):April 2008
DOI:10.1016/j.optmat.2007.06.010
Anatase-titania films with high optical performances have been deposited via a modified sol–gel route. This involved several precisely controlled processes including a sufficient hydrolysis of titanium tetraisopropoxide (TTIP) with excessive water, a peptization at pH value of 1–2, a restrained condensation under the hydrothermal conditions at 373 K, and finally a spin-coating process at 293 K. A full characterization of the sols and films indicated that such a well-controlled hydrolysis and condensation of TTIP enabled the formation of high-quality precursor sols consisting of anatase-titania colloidal particles with the mean hydrodynamic diameter of about 17.2 nm, and then endowed the as-deposited films with nanocrystalline structure and the corresponding high refractive index of 1.92 (at 632.8 nm). Moreover, the prepared films exhibited large optical bandgap of 3.38 eV and high laser-induced damage threshold of 16.3 J/cm2 (at 1064 nm, 3 ns pulse duration and R/1 testing mode), which must be closely related to their homogeneous and nearly defect-free network structures derived from the low-temperature sol–gel deposition route.
Co-reporter:Dong Jiang, Yao Xu, Dong Wu, Yuhan Sun
Journal of Solid State Chemistry 2008 Volume 181(Issue 3) pp:593-602
Publication Date(Web):March 2008
DOI:10.1016/j.jssc.2008.01.004
A series of dye-modified TiO2 photocatalysts were synthesized using dye Chrysoidine G (CG), tolylene-2,4-diisocyanate (TDI), and commercial TiO2 (Degussa P25) as starting materials. TDI was used as a bridging molecule whose two –NCO groups reacted with Ti–OH of TiO2 and –NH2 groups of CG, respectively. As a result, special organic complexes were formed on the TiO2 surface via stable π-conjugated chemical bonds between TiO2 and dye molecules, confirmed by FT-IR, XPS, and UV–vis spectra. Due to the existence of π-conjugated surface organic complexes, the as-synthesized photocatalysts showed a great improvement in visible absorption (400–550 nm). Methylene blue, as a photodegradation target, was used to evaluate the photocatalytic performance, and the dye-modified TiO2 exhibited much better activity under the visible light irradiation than bare TiO2.Dye-modified TiO2 photocatalysts were synthesized via the reaction between Chrysoidine G (CG), Degussa P25 (TiO2), and tolylene-2,4-diisocyanate (TDI) as a bridging molecule. As a result, π-conjugated surface organic complexes were formed on TiO2 surface. Due to the existence of organic complexes, dye-modified TiO2 catalysts showed great visible absorption and high activity under the visible light irradiation.
Co-reporter:Liping Liang;Lei Zhang;Dong Wu
Journal of Sol-Gel Science and Technology 2008 Volume 47( Issue 2) pp:
Publication Date(Web):2008 August
DOI:10.1007/s10971-008-1784-2
Polyvinylpyrrolidone (PVP)/ZrO2-based hybrid thin films, with suitable properties for application in the high power lasers, have been prepared combining the advantages of both the sol–gel route and the organic-inorganic hybrid materials. By virtue of light scattering analysis, the chemical composition of the reaction system was fully optimized, endowing the films with good optical properties and high laser-induced damage threshold (LIDT). Light scattering studies also provided valuable structural information about the hybrid sols, which offered a better understanding of the structure and performance of the hybrid films. Our experiments showed that, in the hybrid sols, the incomplete substitution for the chelating ligands by the hydroxyls might considerably conceal and weaken the effect of PVP on the nucleation and growth of ZrO2 particles. Thus, the incorporation of PVP only resulted in slight decreases in the refractive index and LIDT of the films. By energy relaxation through their flexible polymer chains, however, the addition of PVP could easily enhance the stress compatibility between the high- and low-index layers and then facilitate the deposition of the multi-layer highly reflective mirrors.
Co-reporter:Baoliang Lv, Yao Xu, Dong Wu, Yuhan Sun
Particuology 2008 Volume 6(Issue 5) pp:334-339
Publication Date(Web):October 2008
DOI:10.1016/j.partic.2008.04.006
Magnetite (Fe3O4) nanotubes were prepared by reducing synthesized hematite (α-Fe2O3) nanotubes in 5% H2+95% Ar atmosphere, and then maghemite (γ-Fe2O3) nanotubes were obtained by re-oxidizing the Fe3O4 nanotubes. The nanotube structure was kept from collapsing or sintering throughout the high temperature reducing and re-oxidizing processes. The coercivities of the Fe3O4 and γ-Fe2O3 nanotubes synthesized were found to be 340.22 Oe and 342.23 Oe, respectively, both higher than other nanostructures with the same phase and of similar size. Both adsorbed phosphate and the nanotube structure are considered responsible for this high coercivity.
Co-reporter:Lei Zhang, Yao Xu, Dong Wu, Yuhan Sun, Xiaodong Jiang, Xiaofeng Wei
Optics & Laser Technology 2008 Volume 40(Issue 2) pp:282-288
Publication Date(Web):March 2008
DOI:10.1016/j.optlastec.2007.05.002
The effect of polyvinylpyrrolidone (PVP) on the structure and laser-induced damage threshold (LIDT) of sol–gel silica anti-reflective films is investigated. The results of dynamic light scattering, transmission electron microscopy, and small angle X-ray scattering, show that the PVP molecules surrounded the silica sol particles through the strong hydrogen bonds between Si-OH groups and the PVP. As a result, the growth of silica particles was restricted and thus the interface layer between the silica particles and the solvent become thickened with PVP content. Furthermore, the PVP reduced the porosity of the film, so the anti-reflection properties of the film were weakened. A multi-fractal analysis showed that the appropriate addition of PVP, 1 weight percent (wt%), could improve the surface fractal structure of the film, but that higher PVP content resulted in reduced surface uniformity. The addition of PVP lead to improved LIDT.
Co-reporter:Dong Jiang, Yao Xu, Bo Hou, Dong Wu, Yuhan Sun
Journal of Solid State Chemistry 2007 Volume 180(Issue 5) pp:1787-1791
Publication Date(Web):May 2007
DOI:10.1016/j.jssc.2007.03.010
A visible light-activated TiO2 photocatalyst was successfully synthesized by the surface organic modification to sol–gel–hydrothermal synthesized TiO2. The surface hydroxyls of TiO2 nanoparticles reacted with the active –NCO groups of tolylene diisocyanate (TDI) to form a surface complex that was confirmed by the FT–IR and XPS spectra. Due to the existence of surface complex, the absorption edge of as-prepared TDI-modified TiO2 nanomaterial extended well into visible region. Compared with unmodified TiO2 and Degussa P25, the TDI-modified TiO2 photocatalysts showed higher activity for the photocatalytic degradation of methylene blue under visible light irradiation.A visible light-activated TiO2 photocatalyst was successfully synthesized by the surface organic modification to TiO2. The surface hydroxyls of TiO2 nanoparticles reacted with the active –NCO groups of tolylene diisocyanate (TDI) to form a surface complex. The TDI-modified TiO2 photocatalysts showed higher activity for the photocatalytic degradation of methylene blue under visible light irradiation.
Co-reporter:Peng Feng, Yao Xu, Dong Wu
Chinese Chemical Letters 2007 Volume 18(Issue 10) pp:1182-1186
Publication Date(Web):October 2007
DOI:10.1016/j.cclet.2007.08.015
A novel non-surfactant method was described to synthesize mesoporous silica using dye basic fuchsin as template. Chemical reactions were introduced into the formation of mesopores rather than the weak electrostatic or hydrogen-bonding interactions in the traditional surfactant routes. The reactant composition was found to be crucial to the pore structure of objective product. The formation mechanism of mesopore was also proved.
Co-reporter:Liping Liang, Yonggang Sheng, Yao Xu, Dong Wu, Yuhan Sun
Thin Solid Films 2007 Volume 515(20–21) pp:7765-7771
Publication Date(Web):31 July 2007
DOI:10.1016/j.tsf.2007.03.142
Compositional dependences of the optical properties of sol–gel derived ZrO2–TiO2 composite films (with molar ratio of Ti:Zr ranging from 0:10 to 10:0) have been studied. The refractive index, absorption coefficient, and optical band gap were determined from the corresponding transmission spectra based on Swanepoel's method. It was found that the optical properties of the composite films could be easily tailored in a wide range by a simple control on the system composition. As the molar ratio of Ti:Zr increased from 0:10 to 10:0, a clear increase of the refractive index from 1.912 to 2.263 (at 633 nm) was observed. Simultaneously, the optical band gap decreased monotonically from 5.26 to 3.25 eV. Combined with the X-ray diffraction analysis, the observed variations in both the refractive index and optical band gap have been directly correlated with the structural evolution of the composite films.
Co-reporter:Yao Xu, Dong Wu, Yuhan Sun, Wenxue Chen, Hanzhen Yuan, Feng Deng, Zhonghua Wu
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2007 Volume 305(1–3) pp:97-104
Publication Date(Web):15 September 2007
DOI:10.1016/j.colsurfa.2007.04.047
Ammonia-catalyzed sol–gel process of polyvinylpyrrolidone/tetraethoxysilane (PVP/TEOS) system in methanol was studied by in situ liquid 29Si nuclear magnetic resonance (NMR), dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and rheology. A scientific connection was established between the reaction composition and the microstructures of sol particles. It was found that the concentration of PVP played an important role in the hydrolysis kinetics of TEOS and the SiO2 sol–gel process. The results of in situ 29Si NMR showed that PVP addition reduced both hydrolysis rate and condensation rate of TEOS, and the condensation rate decreased more seriously than the hydrolysis rate. The particle size distributions obtained from DLS and SAXS indicated that PVP held back the growth of SiO2 clusters by hydrogen-bonding the silanol groups on particle surface with the electronegative inner amide of PVP side chain. Thus, gelation was retarded and the rheology of sol was largely modified by PVP. Rheology study showed typical Newtonian fluid behavior before gelation and shear thinning fluid behavior after gelation point, respectively. The changes in fractal dimensions of PVP/SiO2 sols, obtained by SAXS, explained the different microstructures of SiO2 sol particles in the presence of PVP. The changes of microstructure and macroscopic properties should be pre-determined by the very early stages of sol–gel process.
Co-reporter:Yao Xu;Dong Wu;Yuhan Sun;Hongchang Gao
Journal of Sol-Gel Science and Technology 2007 Volume 42( Issue 1) pp:13-20
Publication Date(Web):2007 April
DOI:10.1007/s10971-006-1518-2
Liquid-state 29Si NMR was used to investigate the hydrolysis and condensation kinetics of ammonia-catalyzed tetraethoxysilane (TEOS) in methanol system. The reactive rate constants were calculated by applying first-order reaction approximation and the steady state approximation theory. The reaction orders with respect to TEOS, ammonia and water were derived, as well as the activation energies and the Arrhenius constants. It was found that the formation of intermediate species Si(OH)(OEt)3 was the rate-limiting step and its reaction rate equation was rTEOS=7.41×10−3[TEOS][NH3]0.333[H2O]0.227. Higher reactive temperature benefited the hydrolysis of TEOS. The results presented here indicated quantificationally that the formation of colloidal SiO2 particles was controlled by the initial hydrolysis of TEOS.
Co-reporter:Yao Xu;Xianyong Sun;Dong Wu;Yuhan Sun;Yongxia Yang
Journal of Solution Chemistry 2007 Volume 36( Issue 3) pp:327-344
Publication Date(Web):2007 March
DOI:10.1007/s10953-006-9117-y
In-situ29Si liquid-state nuclear magnetic resonance (NMR) was used to investigate the ammonia catalyzed hydrolysis and condensation of the mixed systems of tetraethoxysilane (TEOS) and dimethyldiethoxysilane (DDS) dissolved in methanol. With ammonia catalysis, the hydrolysis reaction orders for TEOS and DDS in the mixed systems remained first order, which is similar to that observed for their corresponding single silane component precursor systems. The hydrolysis rate constant for TEOS in the mixed systems was larger than that of TEOS in the single silane component precursor systems. Meanwhile, the hydrolysis rate constants of DDS in the mixed precursor systems were smaller than those of DDS in the single silane component precursor systems. The hydrolysis and condensation kinetics showed more compatible hydrolysis-condensation relative rates between TEOS and DDS, which remarkably affected the final microstructure of the resulting silica particles. Small angle X-ray scattering (SAXS) experiments showed a typical double fractal structure in the particulate networks.
Co-reporter:Qunli Tang, Yao Xu, Dong Wu, Yuhan Sun, Jiqing Wang, Jun Xu, Feng Deng
Journal of Controlled Release 2006 Volume 114(Issue 1) pp:41-46
Publication Date(Web):10 August 2006
DOI:10.1016/j.jconrel.2006.05.006
To better control drug delivery rate, a simple and effective approach has been developed for controlled drug delivery carrier system through one-step surface modification of the ibuprofen-impregnated silica MCM-41 with 1, 1, 1, 3, 3, 3-hexamethyldisilazane (HMDS). The 29Si MAS NMR characterization demonstrated that different contents of trimethylsilyl (TMS) groups were successfully grafted onto the samples modified with different silylation times. The results obtained from in vitro tests exhibited that the introduction of TMS groups greatly retarded the ibuprofen release rate. Even after in vitro test for 48 h, only 75% of the impregnated ibuprofen could be released from the modified sample with TMS groups content of 14.5% (related to the total silicon atoms). However, the release of ibuprofen could be completed just after about 1 h from the pure silica MCM-41 under the same release conditions. Furthermore, the release rate of ibuprofen could be well modulated by changing the grafted content of TMS groups, and was found to decrease with increasing grafted amount of TMS groups.
Co-reporter:Dongjiang Yang, Junping Li, Yao Xu, Dong Wu, Yuhan Sun, Huaiyong Zhu, Feng Deng
Microporous and Mesoporous Materials 2006 Volume 95(1–3) pp:180-186
Publication Date(Web):18 October 2006
DOI:10.1016/j.micromeso.2006.05.022
A facile pathway has been developed to prepare silica-based micro/mesoporous bimodal hybrids with super hydrophobicity. It is the special feature of this pathway that though there are no surfactants introduced during the hydrolysis and polycondensation process, the obtained materials exhibit high specific surface areas, high porosity and bimodal structure. Actually, polymethylhydrosiloxane (PMHS), one of the silica sources, assembles itself into a special conformation and plays the role of a structure-directing agent that leads to the formation of the micro/mesophases. Thus, it is thought this novel protocol might be a profitable complement to those methods previously reported for the preparation of porous materials.
Co-reporter:Qunli Tang, Yao Xu, Dong Wu, Yuhan Sun
Journal of Solid State Chemistry 2006 Volume 179(Issue 5) pp:1513-1520
Publication Date(Web):May 2006
DOI:10.1016/j.jssc.2006.02.004
A series of pure silica MSU and carboxylic-modified MSU materials were prepared. The formation of mesoporous silica materials with terminal carboxylic groups on pore surface was performed by the acid-catalyzed hydrolysis of cyano to carboxylic. Then their potential applications in controlled drug delivery carriers were investigated. Drug famotidine was selected as a model molecule out of the consideration of the terminal amino groups in its molecule. The adsorption experiments show significant adsorption of famotidine on the carboxylic-modified MSU materials. And, the functionalization level of carboxylic groups has been found to be the key factor affecting the adsorption capacities of the modified MSU materials for famotidine. Subsequently, three kinds of release fluids, including simulated gastric medium, simulated intestinal medium, and simulated body fluid, were used to test the famotidine release rate from the carboxylic-modified MSU material. Obvious delayed effect has been observed for the famotidine release from the carboxylic-modified mesoporous silica material under the in vitro assays.Carboxylic-modified mesoporous silica MSU material was used as drug carrier, and the in vitro assays reveal the release of famotidine from the carboxylic-modified mesoporous silica material can be controlled to a high degree.
Co-reporter:Xianyong Sun, Yao Xu, Dong Jiang, Dongjiang Yang, Dong Wu, Yuhan Sun, Yongxia Yang, Hanzhen Yuan, Feng Deng
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2006 Volume 289(1–3) pp:149-157
Publication Date(Web):15 October 2006
DOI:10.1016/j.colsurfa.2006.04.024
In situ 29Si liquid-state nuclear magnetic resonance was used to investigate the ammonia-catalyzed hydrolysis and condensation of the single phenyltriethoxysilane (PTES) systems and the mixed tetraethoxysilane (TEOS)/PTES systems dissolved in methanol. By varying the molar ratio of the PTES, water and ammonia in the initial solutions, the hydrolysis rate constants for PTES in single precursor systems were disclosed as well as the corresponding reaction orders by fitting the concentration curves of the intermediate species as functions of time. Due to the cooperation of inductive and steric effect, PTES shows a low reaction activity. Under ammonia catalysis, the hydrolysis reaction orders of TEOS and PTES in the mixed precursor systems all retained the first-order, which is similar to single precursor systems. The hydrolysis rate constants of TEOS and PTES in the mixed systems were larger than the values of TEOS and PTES in their single precursor systems, respectively. Another important result was: the reaction orders of both ammonia and water increased to different extent for TEOS and PTES in mixed systems. Hydrolysis and condensation kinetics showed more compatible hydrolysis–condensation relative rates between TEOS and PTES, which affected remarkably the final microstructure of silica particles.
Co-reporter:Juan Zou, Yao Xu, Bo Hou, Dong Wu, Yuhan Sun
China Particuology (June 2007) Volume 5(Issue 3) pp:206-212
Publication Date(Web):1 June 2007
DOI:10.1016/j.cpart.2007.03.006
A two-step synthesis was used to control the shape of silver nanoparticles. First, a few spherical silver nanoparticles, ∼10 nm in size, were prepared via reduction of Ag+ ions in aqueous Ag(NH3)2NO3 by poly(N-vinyl-2-pyrrolidone) (PVP). Then, in a subsequent hydrothermal treatment, the remaining Ag+ ions were reduced by PVP into polyhedral nanoparticles, or larger spherical nanoparticles formed from the small spherical seed silver nanoparticles in the first step. The morphology and size of the resultant particles depend on the hydrothermal temperature, PVP/Ag molar ratio and concentration of Ag+ ions. By using UV–visible spectroscopy (UV–vis), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD), the possible growth mechanism of the silver nanoparticles was discussed.
Co-reporter:Junhua Li, Yao Xu, Dong Wu, Yuhan Sun
Catalysis Today (30 October 2009) Volume 148(Issues 1–2) pp:148-152
Publication Date(Web):30 October 2009
DOI:10.1016/j.cattod.2009.02.046
High dispersion Co3O4 nano-particles supported on hollow mesoporous silica spheres (HMSS) with bimodal pore distribution were prepared by “two-solvent” technique. As-synthesized catalysts were characterized by XRD, N2 adsorption–desorption, XPS, SEM, TEM, and H2-TPR. The results showed that Co3O4 nano-particles were present inside the pore system of HMSS and the particles sizes increased with the increasing loaded cobalt content. The catalysts show good performance and high selectivity of C5–C18 hydrocarbon in F–T synthesis, which should attribute to the unique bimodal pore distribution facilitating reactants to access the active sites and to transport higher hydrocarbon products.
Co-reporter:Ruimin Ding, Xinmin Cui, Cong Zhang, Ce Zhang and Yao Xu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 13) pp:NaN3224-3224
Publication Date(Web):2015/02/13
DOI:10.1039/C4TC02542C
Regulation of the refractive index over a wide range is very important in the realization of tri-wavelength antireflective (AR) coating in high power laser systems, but many regulation approaches are too complex or violent to satisfy the practical requirements. Here, a simple, template-free sol–gel route was proposed to regulate the refractive index of MgF2 film by heat treating MgF2 sol and hence to control the self-assembly process of colloidal MgF2 nanocrystals. In this self-assembly process, the originally packed nanocrystals gradually evolved into bigger hollow vesicles, which reduced the refractive index of the MgF2 film from 1.38 to 1.2. When the refractive indices of the bottom and top layers were set as 1.34 and 1.2, the tri-wavelength broadband AR coating was finally realized on a quartz substrate, with the transmittance of 99.54%, 98.65% and 98.58% at 351 nm, 527 nm and 1053 nm, respectively.
Co-reporter:Baoliang Lv, Yao Xu, Dong Wu and Yuhan Sun
Chemical Communications 2011 - vol. 47(Issue 3) pp:NaN969-969
Publication Date(Web):2010/11/12
DOI:10.1039/C0CC03632C
Single-crystal α-Fe2O3 hexagonal nanorings with hexagonal inner hole were synthesized under the stepwise influence of different anionic ligands (F− and SCN−). This is a new method to design and modify crystal structures of transition metal oxide nanoparticles.
Co-reporter:Dongjiang Yang, Yao Xu, Wujun Xu, Dong Wu, Yuhan Sun and Huaiyong Zhu
Journal of Materials Chemistry A 2008 - vol. 18(Issue 45) pp:NaN5562-5562
Publication Date(Web):2008/10/22
DOI:10.1039/B804967J
Macroporous silica films with methyl groups grafted on their surface were prepared from polymethylhydrosiloxane (PMHS) and tetraethylorthosilicate (TEOS) without templates. Compared to the conventional template syntheses, this approach has several advantages. First, it avoids the removal of templates, which is sometimes an environmentally unfriendly procedure. Second, it does not require a post-synthesis grafting to form the hybrid structures with methyl groups on the silica surface. Third, the pore size and hydrophobicity (expressed by the water contact angle) of the film can be tuned readily. By adjusting the amount of PMHS used in the synthesis and introducing hexamethyldisilazane (HMDS) we can tune the pore size in a wide range from 50 nm to 500 nm. The hydrophobicity increases substantially as the pore size decreases. Evidently, the reaction mechanism of this synthesis is different from the conventional template synthesis. A tentative mechanism is proposed: the hydrogen gas released from PMHS results in the formation of the macropores in the films. With excellent hydrophobicity, optical transmittance and thermal stability, the obtained silica films have potential applications in the semiconductor industry.
Co-reporter:Baoliang Lv, Zhong Liu, Ruimin Ding, Dong Wu and Yao Xu
Journal of Materials Chemistry A 2013 - vol. 1(Issue 18) pp:NaN5699-5699
Publication Date(Web):2013/03/06
DOI:10.1039/C3TA10375G
Based on theoretical analysis of the crystal structure of β-Ni(OH)2, the (001) and (100) planes have the highest and the second highest Ni2+ cation concentration, respectively. Therefore, F− anions were selected to control the growth behavior of β-Ni(OH)2 through the selective adsorption of F− anions because of their small size, simple effect and ability to coordinate with Ni2+ cations. As a result, a series of β-Ni(OH)2 nanostructures with (001) and (100) planes exposed were successfully synthesized within several tens of minutes under the stimulation of microwave irradiation. The surface area ratio of (100) to (001) planes can be changed by altering the reaction time. The exposure of (100) planes was found to be favorable to the electrochemical activity rather than (001) planes.
Co-reporter:Qifeng Chen, Huijuan Shi, Weimei Shi, Yao Xu and Dong Wu
Catalysis Science & Technology (2011-Present) 2012 - vol. 2(Issue 6) pp:NaN1220-1220
Publication Date(Web):2012/02/27
DOI:10.1039/C2CY00545J
To utilize efficiently visible light in photocatalytic reactions, a series of doped TiO2 photocatalysts were synthesized via a facile solvothermal method. The photocatalysts were characterized with various techniques. The results indicated that all the photocatalysts were of an anatase phase, the Ag0.010C2.0–TS0.20 sample possessed the largest surface area (306.0 m2 g−1) and pore volume (2.05 cm3 g−1). The carbon dopant existed in the surface layer of the TiO2–SiO2 composite and narrowed the energy band gap, which induced visible light absorption. Silver existed on the particle surface and in two forms, Ag+ and Ag0, which acted together to inhibit the recombination of photogenerated electrons and holes. The photoactivities were evaluated by decomposition of RhB under visible irradiation. It was found that the Ag–C/TS photocatalyst exhibited the highest visible photoactivity, with the molar ratios of Ag–Ti, and C–Ti of 0.005, and 2.0, respectively, corresponding to the reaction rate constant 2.09 h−1. The reaction rate was 52.3, 11.2 and 2.33 times higher than that of TiO2 (0.04 h−1), Ag0.005–TiO2 (0.186 h−1) and C2.0–TiO2 (0.897 h−1), respectively. The enhanced visible photocatalytic activity can be attributed to the synergetic effects of silver and carbon doping, as well as silicon introduction. The photocatalytic reaction mechanism was verified with ESR technique; furthermore, both the hydroxyl radical and superoxide radical played a critical role on the photocatalytic reaction, in addition, DMPO–˙H was found in the ESR experiments.
Co-reporter:Guomin Li, Liancheng Wang, Wanxi Li, Ruimin Ding and Yao Xu
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 24) pp:NaN12392-12392
Publication Date(Web):2014/03/26
DOI:10.1039/C4CP00647J
In order to prepare a lightweight and efficient microwave absorbent, porous activated carbon balls (PACB) were used to load Fe3+ and Co2+ ions, because the PACB carrier has a high specific surface area of 800 m2 g−1 and abundant pores, including micropores and macropores. The loaded Fe3+ and Co2+ ions in the PACB composite were transformed into magnetic CoFe2O4 and/or Co3Fe7 particles during subsequent heat-treatment under an Ar atmosphere. According to the XRD and SEM results, the magnetic particles were embedded in the PACB macropores and showed different crystalline phases and morphologies after heat-treatment. CoFe2O4 flakes with spinel structure were obtained at approximately 450 °C, and were then transformed into loose quasi-spheres between 500 °C and 600 °C, where CoFe2O4 and Co3Fe7 coexisted because of the partial reduction of CoFe2O4. Co3Fe7 microspheres appeared above 700 °C. The density of the magnetic PACB composites was in the range of 2.2–2.3 g cm−3. The as-synthesized PACB composites exhibited excellent microwave absorbability, which was mainly attributed to the magnetism of CoFe2O4 and Co3Fe7, as well as the presence of graphitized carbon. The minimum reflection loss value of the CoFe2O4–Co3Fe7–PACB composite reached −32 dB at 15.6 GHz, and the frequency of microwave absorption obeyed the quarter-wavelength matching model, showing a good match between dielectric loss and magnetic loss. The microwave reflection loss (RL) value could be modulated by adjusting the composition and thickness of the PACB composite absorbent. PACB composites with CoFe2O4–Co3Fe7 are a promising candidate for lightweight microwave absorption materials.
Co-reporter:Jinghua Sun, Xinmin Cui, Ce Zhang, Cong Zhang, Ruimin Ding and Yao Xu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 27) pp:NaN7194-7194
Publication Date(Web):2015/06/01
DOI:10.1039/C5TC00986C
A double-layer broadband antireflective (AR) coating with excellent transmittance was successfully fabricated using two kinds of silica coatings. The excellent optical performance in a wide wavelength range came from a reasonable refractive index gradient from air to the substrate produced by the mesopores in the bottom-layer silica coating and the particle-packed pores in the top-layer silica coating. The maximum transmittance of the broadband AR coating was approximated to 100.0% at the peak value and above 99.6% in the visible region from 400 to 800 nm. Meanwhile, the average transmittance of the coating was more than 99.0% over the range of 360 to 920 nm. In addition, the double-layer broadband silica AR coating showed strong mechanical performance and good environmental stability. This work provides an alternative way to prepare a broadband AR coating for some applications in energy harvesting and optical devices.
Co-reporter:Jinghua Sun, Qinghua Zhang, Ruimin Ding, Haibing Lv, Hongwei Yan, Xiaodong Yuan and Yao Xu
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 31) pp:NaN16693-16693
Publication Date(Web):2014/05/27
DOI:10.1039/C4CP01032A
Porous silica optical antireflective (AR) coatings prepared by traditional sol–gel method have been extensively used for high power laser systems, but a serious drawback is that contamination existing in the high vacuum is easily absorbed by the disordered open pore structure, resulting in a fast decrease in transmittance. To improve the stability of transmittance in vacuum, a contamination-resistant silica AR coating with ordered mesopores completely closed by hydrophobic–oleophobic groups was successfully developed on a fused quartz substrate. The ordered mesopores in the coating were controlled under the direction of surfactant F127 via an evaporation-induced-self-assembling process and then were closed by post-grafting long chain fluoroalkylsilane. The grazing incidence small angle X-ray scattering (GISAXS) and the X-ray reflectivity (XRR) results indicated that the mesopores in the coating constructed a Fmmm orthorhombic symmetry structure with a (010) plane parallel to the substrate. Cage-like mesopores were confirmed by nitrogen adsorption–desorption analysis. The obtained coatings showed low surface roughness, excellent abrase-resistance and high transmittance of 100% on quartz substrate. Especially, the decrease of transmittance tested with polydimethylsiloxane pollution in vacuum within one-month was as small as 0.02%. The laser induced damage threshold was up to 59.8 J cm−2 at a 12 ns laser pulse of 1053 nm wavelength. This work provides an alternative way to fabricate AR coatings with high stability.
