Co-reporter:Meilin Lv, Xiaoqin Sun, Shunhang Wei, Cai Shen, Yongli Mi, and Xiaoxiang Xu
ACS Nano November 28, 2017 Volume 11(Issue 11) pp:11441-11441
Publication Date(Web):November 1, 2017
DOI:10.1021/acsnano.7b06131
Ultrathin nitrogen-doped perovskite nanosheets LaTa2O6.77N0.15– have been fabricated by exfoliating Dion–Jacobson-type layered perovskite RbLaTa2O6.77N0.15. These nanosheets demonstrate superior photocatalytic activities for water splitting into hydrogen and oxygen and remain active with photon wavelengths as far as 600 nm. Their apparent quantum efficiency under visible-light illumination (λ ≥ 420 nm) approaches 1.29% and 3.27% for photocatalytic hydrogen and oxygen production, being almost 4-fold and 8-fold higher than bulk RbLaTa2O6.77N0.15. Their outstanding performance likely stems from their tiny thickness (single perovskite slab) that essentially removes bulk charge diffusion steps and extends the lifetime of photogenerated charges. Theoretical calculations reveal a peculiar 2D charge transportation phenomenon in RbLaTa2O6.77N0.15; thus, exfoliating RbLaTa2O6.77N0.15 into LaTa2O6.77N0.15– nanosheets has limited impact on charge transportation properties but significantly enhances the surface areas which contributes to more reaction sites.Keywords: doping; exfoliating; perovskite nanosheets; photocatalysis; visible-light photocatalyst; water splitting;
Co-reporter:Lingwei Lu, Meilin Lv, Gang Liu, Xiaoxiang Xu
Applied Surface Science 2017 Volume 391(Part B) pp:535-541
Publication Date(Web):1 January 2017
DOI:10.1016/j.apsusc.2016.06.160
Highlights
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Band gap values can be tuned by adjusting molar ratios between SrTiO3 and BiFeO3.
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Photocatalytic activity is greatly improved after constituting solid solutions.
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Photocatalytic activity is influenced by surface area and light absorption.
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Fe plays an important role for band gap reduction and catalytic activity.
Co-reporter:Guan Zhang, Yurou Zhou, Xiang Fan, Jing Zou, ... Xiaoxiang Xu
International Journal of Hydrogen Energy 2017 Volume 42, Issue 31(Volume 42, Issue 31) pp:
Publication Date(Web):3 August 2017
DOI:10.1016/j.ijhydene.2017.06.153
•Sensitization efficiency of different types of sensitizers are directly compared.•Sensitization efficiency of CdSe500 QDs is 1-2 order of magnitude higher than others..•The larger size of CdSe QDs, the lower sensitization efficiency.•CdSe QDs as TiO2 sensitizer are more efficient and robust than other organic sensitizers.In this work, cadmium selenide quantum dots (CdSe QDs) with different sizes were synthesized and employed as visible light sensitizers of titania, in comparison with other organic molecules based sensitizers, including the well-known ruthenium complex sensitizer, tris(4,4-dicarboxy-2,2-bipyridyl)ruthenium(II) chloride, phenolic-formaldehyde resin and poly (4-vinylphenol). The different sensitizers are linked to titania via different molecular linkages through self-assemble processes. CdSe QDs adsorbed onto titania via stabilization ligand (mercaptopropionic acid) are more stable and efficient in terms of photocatalytic H2 generation and photocurrent generation. The CdSe QDs with a diameter of 2.5 nm exhibits a strong absorption peak centred at 500 nm (CdSe500) and shows the best photocatalytic performance than other QDs with larger size and organic sensitizers. The turnover number of CdSe500 QDs for H2 generation reaches ca. 9000 after 96 h reaction, with a 0.6% quantum yield under irradiation at 450 nm (light intensity = 35 mW/cm2). During the initial 3.0 h reaction, the turnover numbers of different types of sensitizers are estimated about 4.3, 52.5, 323.2 and 16.5 for phenolic-formaldehyde resin, poly (4-vinylphenol), CdSe500 QDs and ruthenium complex, respectively. These results highlights the advantages of utilizing CdSe QDs as stable visible light sensitizers for solar energy conversion.CdSe QDs are more efficient and robust visible light sensitizer of titania compared to Ru-based metal complex, phenolic-formaldehyde resin (PR) and poly (4-vinylphenol) (PVP).Download high-res image (171KB)Download full-size image
Co-reporter:Lingwei Lu, Shuang Ni, Gang Liu, Xiaoxiang Xu
International Journal of Hydrogen Energy 2017 Volume 42, Issue 37(Volume 42, Issue 37) pp:
Publication Date(Web):14 September 2017
DOI:10.1016/j.ijhydene.2017.01.064
•La/Cr co-doping improves the optical and catalytic properties of perovskites.•A-site cations modify the crystal structure of perovskites.•The TiO bond length and TiOTi bond angle govern photocatalytic activity.The crystal structure of a photocatalyst generally plays a pivotal role in its electronic structure and catalytic properties. In this work, we synthesized a series of La/Cr co-doped perovskite compounds ATiO3 (M = Ca, Sr and Ba) via a hydrothermal method. Their optical properties and photocatalytic activities were systematically explored from the viewpoint of their dependence on structural variations, i.e. impact of bond length and bond angles. Our results show that although La/Cr co-doping helps to improve the visible light absorption and photocatalytic activity of these wide band gap semiconductors, their light absorbance and catalytic performance are strongly governed by the TiO bond length and TiOTi bond angle. A long TiO bond and deviation of TiOTi bond angle away from 180° deteriorate the visible light absorption and photocatalytic activity. The best photocatalytic activity belongs to Sr0.9La0.1Ti0.9Cr0.1O3 with an average hydrogen production rate ∼2.88 μmol/h under visible light illumination (λ ≥ 400 nm), corresponding to apparent quantum efficiency ∼ 0.07%. This study highlights an effective way in tailoring the light absorption and photocatalytic properties of perovskite compounds by modifying cations in the A site.Download high-res image (233KB)Download full-size imageStructural variations by altering A-site cations of perovskites ATiO3 (A = Ca, Sr and Ba) strongly govern the light absorbance and catalytic performance. A long TiO bond and deviation of TiOTi bond angle away from 180° substantially deteriorate the visible light absorption and photocatalytic activity.
Co-reporter:Hongmei Chen, Xiaoqin Sun, Xiaoxiang Xu
Electrochimica Acta 2017 Volume 252(Volume 252) pp:
Publication Date(Web):20 October 2017
DOI:10.1016/j.electacta.2017.08.186
Here we report two Ruddlesden-Popper type ferrite perovskites (SrO)(LaFeO3)n (n = 1 and 2) which demonstrate p-type semiconductivity. Their crystal structure, optical absorption and other physicochemical properties have been systematically explored. Our results show that both ferrites crystallize in tetragonal symmetry with structural lamination along c axis. Efficient photocatalytic hydrogen production has been achieved for both samples under full range and visible light illumination. Better performance is noticed for LaSrFeO4 with apparent quantum efficiency approaches 0.31% and 0.19% under full range and visible light illumination, respectively. The p-type semiconductivity is verified by their cathodic photocurrent as well as negative Mott-Schottky slop during Photoelectrochemical measurement. The relative lower activity for La2SrFe2O7 compared to LaSrFeO4 is likely due to its higher defect concentration which facilitates charge recombination. Both compounds exhibit anisotropic phenomenon for charge migrations according to theoretical calculations. Their p-type semiconductivity, strong visible light absorption, chemical inertness and high abundance of constituent elements signify promising applications in the field of solar energy conversion and optoelectronics.Two layered ferrites LaSrFeO4 and La2SrFe2O7 have been investigated which demonstrate interesting p-type semconductivity and efficient hydrogen production from water.Download high-res image (148KB)Download full-size image
Co-reporter:Fangfang Wu;Xiaoqin Sun;Gang Liu
Catalysis Science & Technology (2011-Present) 2017 vol. 7(Issue 20) pp:4640-4647
Publication Date(Web):2017/10/16
DOI:10.1039/C7CY01580A
Despite a strong visible light absorption at a wavelength as far as 610 nm, SrTaO2N generally exhibits poor photocatalytic activity due to photocatalytic self-decomposition. In this study, we introduce Na into the B site of SrTaO2N and perform an investigation on its crystal structure, optical absorption and photocatalytic water oxidation in response to Na incorporation. Our results suggest that Na incorporation effectively enhances local Ta–O(N) bond strength, which is responsible for strong interband light absorption, low tendency to defect formation and high stability against photocatalytic self-decomposition. Efficient photocatalytic water oxidation was realized in Na-modified SrTaO2N (Sr0.8Na0.2TaO2.8N0.2) with an apparent quantum efficiency as high as 0.2% under visible light illumination (≥400 nm). This simple strategy highlights the benefits of alkaline metal modification and can be extended to other nitrides or oxynitrides where management of local bond strength is needed.
Co-reporter:Lu Jiang, Shuang Ni, Gang Liu, Xiaoxiang Xu
Applied Catalysis B: Environmental 2017 Volume 217(Volume 217) pp:
Publication Date(Web):15 November 2017
DOI:10.1016/j.apcatb.2017.06.012
•Up to 20% Cr/Nb can be doped into Bi3TiNbO9 with a slight unit cell expansion.•Cr/Nb co-doping improves visible light absorption and photocatalytic activity.•A new valence band with Cr 3d character accounts for the visible light absorption.•Bi3TiNbO9 has anisotropic charge transportation phenomenon.In this work, we have applied Cr/Nb co-doping strategy to the wide band gap semiconductor Bi3TiNbO9 and have performed a detailed investigation on the structure, optical and photocatalytic properties of these modified Aurivillius compounds Bi3Ti1-2xCrxNb1+xO9 (x = 0, 0.1, 0.2, 0.3). Our results suggest that Cr/Nb doping slightly expand the unit cell of Bi3TiNbO9 with a doping limit around 20%. The involvement of Cr/Nb dopants in the crystal structure significantly reduces the band gap of Bi3TiNbO9 by nearly 1 eV. Photocatalytic experiments and photoelectrochemical measurements confirms the critical role of Cr/Nb dopants in improving photocatalytic hydrogen production and anodic photocurrent. More than two-fold enhancement in hydrogen production has been noticed for merely 10% Cr/Nb co-doping. The highest photocatalytic activity belongs to Bi3Ti0.8Cr0.1Nb1.1O9 (x = 0.1) for full range illumination and to Bi3Ti0.6Cr0.2Nb1.2O9 (x = 0.2) for visible light illumination, with apparent quantum efficiency (AQE) approaching 0.52% and 0.27%, respectively. DFT calculation discloses the role of Cr in forming a new valence band inside the band gap of Bi3TiNbO9. In addition, strong anisotropic phenomenon in charge transportation of Bi3TiNbO9 is also verified by DFT, as both conduction band minimum (CBM) and valence band maximum (VBM) are buried in the [BiTiNbO7]2− perovskite slabs and charges are only allowed to migrate within the slabs.Aurivillius compound Bi3TiNbO9 exhibit interesting layered architectures that are promising for photocatalytic water splitting. Up to 20% Cr/Nb dopants can be incorporated into the crystal structure of Bi3TiNbO9 with laminated framework maintained. Co-doping Cr/Nb greatly extends visible light absorption of Bi3TiNbO9 and is responsible for the much improved photocatalytic activity. Theoretical calculation confirms the critical role of Cr for such modifications and reveals the anisotropic charge transportation phenomenon in Bi3TiNbO9: CBM and VBM located dominantly in [BiTiNbO7]2− perovskite slabs.Download high-res image (131KB)Download full-size image
Co-reporter:Meilin Lv, Gang Liu, and Xiaoxiang Xu
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 42) pp:28700
Publication Date(Web):October 10, 2016
DOI:10.1021/acsami.6b10951
Strong visible light absorption and high charge mobility are desirable properties for an efficient photocatalyst, yet they are hard to be realized simultaneously in a single semiconductor compound. In this work, we demonstrate that these properties coexist in homologous compounds ZnnIn2O3+n (n = 4, 5, and 7) with a peculiar layered structure that combines optical active segment and electrical conductive segment together. Their enhanced visible light absorption originates from tetrahedrally or trigonal-bipyramidally coordinated In atoms in Zn(In)O4(5) layers which enable p–d hybridization between In 4d and O 2p orbitals so that valence band minimum (VBM) is uplifted with a reduced band gap. Theoretical calculations reveal their anisotropic features in charge transport and functionality of different constituent segments, i.e., Zn(In)O4(5) layers and InO6 layers as being for charge generation and charge collection, respectively. Efficient photocatalytic hydrogen evolution was observed in these compounds under full range (λ ≥ 250 nm) and visible light irradiation (λ ≥ 420 nm). High apparent quantum efficiency ∼2.79% was achieved for Zn4In2O7 under full range irradiation, which is almost 5-fold higher than their parent oxides ZnO and In2O3. Such superior photocatalytic activities of these homologous compounds can be understood as layer-by-layer packing of charge generation/collection functional groups that ensures efficient photocatalytic reactions.Keywords: homologous compounds; layered materials; orbital hybridizations; photocatalyst; water splitting
Co-reporter:Meilin Lv, Yawei Wang, Lingwei Lu, Ruinan Wang, Shuang Ni, Gang Liu and Xiaoxiang Xu
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 31) pp:21491-21499
Publication Date(Web):04 Jul 2016
DOI:10.1039/C6CP03522A
The crystal structure of photocatalysts generally plays a pivotal role in controlling their electronic structure as well as catalytic performance. In this work, a series of double perovskite compounds A2InTaO6 (A = Sr or Ba) and their Ni doped counterparts were investigated with the aim of understanding how doping and structural modification will affect their photocatalytic activity. Our results show that Ni doping is effective in improving the optical absorption of these wide band gap semiconductors and accommodating the Sr cation in the A sites leads to severe structural distortion, i.e. the In(Ni)–O–Ta bond angle deviates largely from 180°. A better photocatalytic performance was observed for samples with Ni doping and Ba in the A sites. The best photocatalytic hydrogen production rate recorded was ∼293.6 μmol h−1 for Ba2In0.9Ni0.1TaO6 under full range irradiation, corresponding to an apparent quantum efficiency of 2.75%. DFT calculations reveal the role of Ni doping by forming additional spin-polarized bands inside the intrinsic band gap of the native perovskite. The better photocatalytic activity of Ba2In0.9Ni0.1TaO6 can then be understood as a result of a reduced band gap as well as a linear In(Ni)–O–Ta bond arrangement that is favorable for the strong metal–oxygen–metal interactions.
Co-reporter:Meilin Lv, Shuang Ni, Zhuo Wang, Tongcheng Cao, Xiaoxiang Xu
International Journal of Hydrogen Energy 2016 Volume 41(Issue 3) pp:1550-1558
Publication Date(Web):21 January 2016
DOI:10.1016/j.ijhydene.2015.11.057
•Dopant ordering/disordering could be the reason for the optimal doping content.•Dopant ordering will cause blue shift of optical absorption by enlarging band gaps.•Dopant ordering is detrimental for photocatalytic activity.Doping has generally been served as one of the most efficient strategies for the improvement of wide band gap semiconductor photocatalysts. However, atomic arrangements of doped elements in the host crystal structure have often been overlooked, particularly during the investigation and evaluation of dopant functionality. It is known that electronic structures of a semiconductor are profoundly controlled by atomic occupancies in different crystallographic positions. Knowledge about dopant accommodations in the crystal structure and their influence towards photocatalytic performance is highly desired. Here, we investigated four compositional and structural relevant compounds CrNbO4, CrTaO4, Sr2CrNbO6 and Sr2CrTaO6 with the aim to study the effects of cation ordering/disordering upon their photocatalytic activity. Our results showed that ordered cations, namely Cr and Nb/Ta, are detrimental to the photocatalytic performance. Theoretical calculations indicate that cation ordering would enlarge the band gap and inhibit charge transfer between Cr and Nb/Ta. Our findings imply that ordered dopants in photocatalytic materials would severely offset the benefits of doping and might be a reason for the decreased activity at high doping levels often encountered.Ordering of the B-site cations in Sr2CrNbO6 and Sr2CrTaO6 will shift the band edges of conduction band and valence band, resulting in a significant widening of the band gaps, which blue-shifts the absorption edge.Download high-res image (201KB)Download full-size image
Co-reporter:Yawei Wang, Dazhang Zhu, and Xiaoxiang Xu
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 51) pp:
Publication Date(Web):December 7, 2016
DOI:10.1021/acsami.6b14230
Tantalum nitride (Ta3N5) has been considered as a promising candidate for photocatalytic water splitting because of its strong visible-light absorbance as far as 600 nm. However, its catalytic activity is often hampered by various intrinsic/extrinsic defects. Here, we prepared a series of Zr-doped mesoporous tantalum nitride (Ta3N5) via a template-free method and carried out a detailed investigation of the role of Zr doping upon the photocatalytic performance. Various physicochemical properties including crystal structure, optical absorption, and so on were systematically explored. Our results show that doping Zr into Ta3N5 induces an enhancement of oxygen content and a suppression of absorption band around 720 nm, indicating an increase of ON• defects and a decrease of VN••• defects in the structure. Introduction of Zr significantly boosts the photocatalytic oxygen production of Ta3N5. The optimized photocatalytic oxygen production rate approaches 105 μmol h–1 under visible light illumination (λ ≥ 420 nm), corresponding to an apparent quantum efficiency as high as 3.2%. Photoelectrochemical analysis and DFT calculation reveal that the superior photocatalytic activity of Zr-doped Ta3N5 originates from a high level of ON• defects’ concentration, which contributes to a high electron mobility, and a low level of VN••• defects’ concentration, which often act as charge recombination centers.Keywords: microspheres; photocatalyst; Ta3N5; water oxidation; Zr-doped;
Co-reporter:Fangfang Wu;Meilin Lv;Xiaoqin Sun;Yinghao Xie;Hongmei Chen;Dr. Shuang Ni;Dr. Gang Liu; Xiaoxiang Xu
ChemCatChem 2016 Volume 8( Issue 3) pp:615-623
Publication Date(Web):
DOI:10.1002/cctc.201501035
Abstract
Photocatalytic water splitting is an appealing process for solar energy conversions yet it is often limited by the slow oxidation of water to oxygen half-reaction. Here we performed an investigation on N-doped Sr4Nb2O9 as a water oxidation photocatalyst. Our results show that N doping is an effective approach to improve the visible-light response of Sr4Nb2O9. Efficient photocatalytic oxygen production was observed after N doping, and the highest production rate of ∼27 μmol h−1 under visible-light irradiation corresponds to an apparent quantum efficiency of ∼0.31 %. Clear anodic photocurrent can be generated under visible-light illumination, and the flat-band potential was determined to be ∼−1.25 V vs. Ag/AgCl at pH 7. Theoretical calculations reveal that N doping introduces additional valence bands and is responsible for the visible-light response. Variations in light absorption and photo-oxidation performance can be controlled by modifying these valence band positions using different nitridation temperatures.
Co-reporter:Xiaoqin Sun;Shuwei Wang;Dr. Cai Shen; Xiaoxiang Xu
ChemCatChem 2016 Volume 8( Issue 13) pp:2289-2295
Publication Date(Web):
DOI:10.1002/cctc.201600425
Abstract
Introducing foreign elements is an appealing means to endow wide band gap semiconductors with visible-light responses. Here, we investigated a series of Rh-doped Zn2TiO4 as water reduction photocatalysts. Our results show that Rh doping is effective to improve the visible-light response as well as surface hydrophilicity of Zn2TiO4. Efficient photocatalytic hydrogen evolution was observed after Rh doping and was found to be compositional dependent. The best performance was recorded for sample Zn2Ti0.96Rh0.04O4, with an apparent quantum efficiency of ≈0.74 % under full-range irradiation (λ≥250 nm) and ≈0.25 % under visible-light irradiation (λ≥420 nm). The light absorption and surface hydrophilicity are likely the controlling factors for the better activity. Theoretical calculations suggest that Rh doping is responsible for a band gap reduction and is due to a newly formed valence band composed mainly of Rh 4d orbitals at the top of the original valence band. The visible-light activity can be attributed to the electron excitations from this new valence band to the conduction band.
Co-reporter:Yinghao Xie;Yawei Wang; Zuofeng Chen ; Xiaoxiang Xu
ChemSusChem 2016 Volume 9( Issue 12) pp:1403-1412
Publication Date(Web):
DOI:10.1002/cssc.201600193
Abstract
Tantalum nitride (Ta3N5) highlights an intriguing paradigm for converting solar energy into chemical fuels. However, its photocatalytic properties are strongly governed by various intrinsic/extrinsic defects. In this work, we successfully prepared a series of Mg-doped mesoporous Ta3N5 using a simple method. The photocatalytic and photoelectrochemical properties were investigated from the viewpoint of how defects such as accumulation of oxygen and nitrogen vacancies contribute to the catalytic activity. Our findings suggest that Mg doping is accompanied by an accumulation of oxygen species and a simultaneous elimination of nitrogen vacancies in Ta3N5. These oxygen species in Ta3N5 induce delocalized shallow donor states near the conduction band minimum and are responsible for high electron mobility. The superior photocatalytic activity of Mg-doped Ta3N5 can then be understood by the improved electron–hole separation as well as the lack of nitrogen vacancies, which often serve as charge-recombination centers.
Co-reporter:Xiaoqin Sun; Yinghao Xie; Fangfang Wu; Hongmei Chen; Meilin Lv; Shuang Ni; Gang Liu
Inorganic Chemistry 2015 Volume 54(Issue 15) pp:7445-7453
Publication Date(Web):July 14, 2015
DOI:10.1021/acs.inorgchem.5b01042
Layered semiconductor photocatalysts have been found to exhibit promising performance levels, probably linked to their interlayer framework that facilitates separation of charge carriers and the reduction/oxidation reactions. Layered titanates, however, generally demonstrate activities under UV irradiation, and therein lies the strong desire to extend their activity into the visible light region. Here, we investigated a series of layered perovskite by doping Sr2TiO4 with Cr and/or La in the hope to improve their visible light responses. Their crystal structures and other physicochemical properties were systematically explored. Our results show that La and Cr can be successfully accommodated in the layered structure and Cr is an efficient dopant for the extension of visible light absorbance. Much enhanced photocatalytic hydrogen evolution was observed after doping and was found to be composition-dependent. The highest hydrogen production rate approaches 97.7 μmol/h for Sr2Ti0.95Cr0.05O4-δ under full range irradiation (λ ≥ 250 nm) and 17 μmol/h for Sr2Ti0.9Cr0.1O4-δ under visible light irradiation (λ ≥ 400 nm), corresponding to an apparent quantum efficiency of 0.16% and 0.05%, respectively. Theoretical calculation reveals that the improved optical and photocatalytic properties are owing to a newly formed spin-polarized valence band from Cr 3d orbitals. The decreased unit cell parameters, reduced band gaps as well as anisotropic properties of layered architectures are likely the reasons for a better activity. Nevertheless, instability of these compounds in the presence of moisture and CO2 was also noticed, suggesting that protective atmospheres are needed for the storage of these photocatalysts.
Co-reporter:Hongmei Chen, Yinghao Xie, Xiaoqin Sun, Meilin Lv, Fangfang Wu, Lei Zhang, Li Li and Xiaoxiang Xu
Dalton Transactions 2015 vol. 44(Issue 29) pp:13030-13039
Publication Date(Web):08 Jun 2015
DOI:10.1039/C5DT01757B
Separation of photo-generated charges has played a crucial role in controlling the actual performance of a photocatalytic system. Here we have successfully fabricated g-C3N4/TiO2-B nanowire/tube heterostructures through facile urea degradation reactions. Owing to the effective separation of photo-generated charges associated with the type-II band alignment and intimate interfacial contacts between g-C3N4 and TiO2-B nanowires/tubes, such heterostructures demonstrate an improved photocatalytic activity over individual moieties. Synthetic conditions such as hydrothermal temperatures for the preparation of TiO2-B and the weight ratio of TiO2-B to urea were systematically investigated. A high crystallinity of TiO2-B as well as the proper growth of g-C3N4 on its surface are critical factors for a better performance. Our simple synthetic method and the prolonged lifetime of photo-generated charges signify the importance of type-II heterostructures in the photocatalytic applications.
Co-reporter:Meilin Lv, Yinghao Xie, Yawei Wang, Xiaoqin Sun, Fangfang Wu, Hongmei Chen, Shuwei Wang, Cai Shen, Zuofeng Chen, Shuang Ni, Gang Liu and Xiaoxiang Xu
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 39) pp:26320-26329
Publication Date(Web):14 Sep 2015
DOI:10.1039/C5CP03889H
Modification of prototype perovskite compound SrTiO3 by introducing foreign elements has been an appealing means to endow this wide band gap semiconductor with visible light responses. Here we systematically investigated a series of Sr1−xBixTi1−xCrxO3 solid solution compounds prepared by two different synthetic routes, namely, solid state reactions and the hydrothermal method. Their crystal structures as well as other physicochemical properties were explored. Our results showed that a number of important factors such as microstructures, crystallinity, light absorbance and surface compositions etc. are all strongly correlated with the synthetic methods used. The hydrothermal method is generally helpful for morphology controls as well as avoiding Cr6+ defects and Sr segregation at the surface, thereby contributing to a high photocatalytic activity. Better performance normally occurs in samples with a high crystallinity and free of defects like Bi5+. Theoretical calculations suggest that Cr plays an important role in band gap reduction and photocatalytic reactions, while Bi only acts as a constituent cation for the perovskite structure and does not significantly alter the electronic structures near the Fermi level. Our findings have revealed how synthetic routes are relevant to the final photocatalytic properties of a compound, and therefore comparisons among various photocatalysts have to include concerns about their preparation history.
Co-reporter:Xiaoxiang Xu, Gang Liu, Abul K. Azad
International Journal of Hydrogen Energy 2015 Volume 40(Issue 9) pp:3672-3678
Publication Date(Web):9 March 2015
DOI:10.1016/j.ijhydene.2015.01.046
•We have performed in-situ growth of uniform silver nano-particles on AgTaO3.•The Ag@AgTaO3 shows Enhanced photocatalytic performance under UV and visible light.•The Ag@AgTaO3 microstructure is important for the improved activity.Constituting plasmonic-metal nanostructures is an efficient way in the design and development of active photocatalytic systems. Here we demonstrate a simple one-step reduction process that can in situ grow plasmonic silver nanoparticles on the surface of AgTaO3. The exsolution of silver out of AgTaO3 does not seem to have a significant impact on the crystal integrity, whilst its visible light sensitivity is greatly enhanced. Such Ag nanoparticles decorated AgTaO3 system showed improved photocatalytic hydrogen evolution both under visible and full range irradiation.
Co-reporter:Fangfang Wu, Gang Liu, Xiaoxiang Xu
Journal of Catalysis (February 2017) Volume 346() pp:10-20
Publication Date(Web):1 February 2017
DOI:10.1016/j.jcat.2016.11.022
•Introducing Ca into LaTiO2N leads to structural shrinkage and shorter TiO(N) bonds.•The presence of Ca suppresses surface Ti3+ species and segregation of La at the surface.•Ca incorporation increase electron mobility and boosts photocatalytic O2 evolution.•Lifetime of photogenerated charges was extended after Ca substitution.LaTiO2N has been considered a promising candidate for efficient photocatalytic water splitting. However, its photocatalytic activity is often hampered by the presence of structural defects and poor charge mobility. In this work, we introduced Ca into the crystal structure of LaTiO2N via a simple co-precipitation method and investigated the photocatalytic and photoelectrochemical properties for the full range solid solution La1−xCaxTiO2+yN1−y (0 ⩽ x, y ⩽ 1). Our results show that incorporating Ca into LaTiO2N induces a strong structural shrinkage as well as a space group change from I mma to P nma around a middle doping point (x = 0.5). The presence of Ca effectively boosts the photocatalytic oxygen production and aids photocurrent extraction for LaTiO2N. The best photocatalytic activity was achieved for sample La0.3Ca0.7TiO2.7N0.3 with oxygen production rate ∼66.96 μmol/h under visible light illumination (λ ⩾ 420 nm), corresponding to apparent quantum efficiency ∼3.13%. XPS analysis revealed a substantial reduction in surface Ti3+ species and a removal of A-site cation segregation for samples containing Ca. Further photoelectrochemical analysis highlights the critical role of Ca in enhancing the charge mobility of LaTiO2N. The better photocatalytic performance of Ca-modified LaTiO2N can be understood as a result of defect removal, high charge mobility, and improved surface charge migration pathways that considerably prolong the lifetimes of photogenerated charges.Download high-res image (92KB)Download full-size image
Co-reporter:Meilin Lv, Yinghao Xie, Yawei Wang, Xiaoqin Sun, Fangfang Wu, Hongmei Chen, Shuwei Wang, Cai Shen, Zuofeng Chen, Shuang Ni, Gang Liu and Xiaoxiang Xu
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 39) pp:NaN26329-26329
Publication Date(Web):2015/09/14
DOI:10.1039/C5CP03889H
Modification of prototype perovskite compound SrTiO3 by introducing foreign elements has been an appealing means to endow this wide band gap semiconductor with visible light responses. Here we systematically investigated a series of Sr1−xBixTi1−xCrxO3 solid solution compounds prepared by two different synthetic routes, namely, solid state reactions and the hydrothermal method. Their crystal structures as well as other physicochemical properties were explored. Our results showed that a number of important factors such as microstructures, crystallinity, light absorbance and surface compositions etc. are all strongly correlated with the synthetic methods used. The hydrothermal method is generally helpful for morphology controls as well as avoiding Cr6+ defects and Sr segregation at the surface, thereby contributing to a high photocatalytic activity. Better performance normally occurs in samples with a high crystallinity and free of defects like Bi5+. Theoretical calculations suggest that Cr plays an important role in band gap reduction and photocatalytic reactions, while Bi only acts as a constituent cation for the perovskite structure and does not significantly alter the electronic structures near the Fermi level. Our findings have revealed how synthetic routes are relevant to the final photocatalytic properties of a compound, and therefore comparisons among various photocatalysts have to include concerns about their preparation history.
Co-reporter:Hongmei Chen, Yinghao Xie, Xiaoqin Sun, Meilin Lv, Fangfang Wu, Lei Zhang, Li Li and Xiaoxiang Xu
Dalton Transactions 2015 - vol. 44(Issue 29) pp:NaN13039-13039
Publication Date(Web):2015/06/08
DOI:10.1039/C5DT01757B
Separation of photo-generated charges has played a crucial role in controlling the actual performance of a photocatalytic system. Here we have successfully fabricated g-C3N4/TiO2-B nanowire/tube heterostructures through facile urea degradation reactions. Owing to the effective separation of photo-generated charges associated with the type-II band alignment and intimate interfacial contacts between g-C3N4 and TiO2-B nanowires/tubes, such heterostructures demonstrate an improved photocatalytic activity over individual moieties. Synthetic conditions such as hydrothermal temperatures for the preparation of TiO2-B and the weight ratio of TiO2-B to urea were systematically investigated. A high crystallinity of TiO2-B as well as the proper growth of g-C3N4 on its surface are critical factors for a better performance. Our simple synthetic method and the prolonged lifetime of photo-generated charges signify the importance of type-II heterostructures in the photocatalytic applications.
Co-reporter:Meilin Lv, Yawei Wang, Lingwei Lu, Ruinan Wang, Shuang Ni, Gang Liu and Xiaoxiang Xu
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 31) pp:NaN21499-21499
Publication Date(Web):2016/07/04
DOI:10.1039/C6CP03522A
The crystal structure of photocatalysts generally plays a pivotal role in controlling their electronic structure as well as catalytic performance. In this work, a series of double perovskite compounds A2InTaO6 (A = Sr or Ba) and their Ni doped counterparts were investigated with the aim of understanding how doping and structural modification will affect their photocatalytic activity. Our results show that Ni doping is effective in improving the optical absorption of these wide band gap semiconductors and accommodating the Sr cation in the A sites leads to severe structural distortion, i.e. the In(Ni)–O–Ta bond angle deviates largely from 180°. A better photocatalytic performance was observed for samples with Ni doping and Ba in the A sites. The best photocatalytic hydrogen production rate recorded was ∼293.6 μmol h−1 for Ba2In0.9Ni0.1TaO6 under full range irradiation, corresponding to an apparent quantum efficiency of 2.75%. DFT calculations reveal the role of Ni doping by forming additional spin-polarized bands inside the intrinsic band gap of the native perovskite. The better photocatalytic activity of Ba2In0.9Ni0.1TaO6 can then be understood as a result of a reduced band gap as well as a linear In(Ni)–O–Ta bond arrangement that is favorable for the strong metal–oxygen–metal interactions.
