Co-reporter:Anton Kovalsky, Lili Wang, Gage T. Marek, Clemens BurdaJeffrey S. Dyck
The Journal of Physical Chemistry C 2017 Volume 121(Issue 6) pp:
Publication Date(Web):January 19, 2017
DOI:10.1021/acs.jpcc.6b12231
Temperature-dependent thermal conductivity in the range between 7 and 300 K was measured for CH3NH3PbI3 and CsPbI3 and compared to a Debye model via the Callaway method. Thermal conductivity was found to be extremely low across the whole temperature range for both materials, with CH3NH3PbI3 lower than CsPbI3. Fitting analysis showed that a resonant phonon scattering term can account for the difference in thermal transport behavior between the perovskite with a methylammonium (MA) ion versus a single cesium atom in the cationic A site of the lattice. The resonant frequency associated with this term is in the range of ∼15–30 cm–1, pointing to the rotational degree of freedom of the organic ion. Analysis of the temperature dependence of the possible phonon scattering mechanisms showed that thermal conductivity of both CH3NH3PbI3 and CsPbI3 perovskites was dominated by Umklapp scattering at room temperature, and the rotation of the organic cation may be responsible for suppressing the thermal conductivity of CH3NH3PbI3 in comparison with CsPbI3, particularly at low temperatures, ∼25 K. This work presents the first determination of temperature-dependent thermal conductivity of CsPbI3.
Co-reporter:Mei Yang, Qi Yang, Junbo Zhong, Shengtian Huang, Jianzhang Li, Jiabo Song, Clemens Burda
Applied Surface Science 2017 Volume 416(Volume 416) pp:
Publication Date(Web):15 September 2017
DOI:10.1016/j.apsusc.2017.04.206
•Ag2O was employed to modify BiOF photocatalyst.•The photo-induced charge separation rate has been greatly enhanced.•The solar driven-photocatalytic activity has been greatly boosted.•The separation and transfer of charge are a typical Z-scheme mechanism.Previous studies have well established that the photocatalytic performance of BiOF is greatly inhibited by its inherent drawbacks, which are the wide band gap and high recombination of photo-generated charge carriers. Therefore, it is necessary to promote the photocatalytic activity of BiOF. In this work, a series of novel Ag2O/BiOF composites were prepared by a facile precipitation method and characterized by X-ray diffractometry (XRD), UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), surface photovoltage (SPV) spectroscopy, and electron spin-resonance (ESR) spectroscopy. The photocatalytic characteristics of Rhodamine B (RhB) discoloration under simulated sunlight and visible-light irradiation were studied. The results revealed that the sample with 1.0% molar ratio of Ag/Bi displayed the best photocatalytic performance towards RhB discoloration and all the studied composites in this work displayed a higher photocatalytic activity than the bare BiOF. Based on the results of “band edge potential” of Ag2O and BiOF, SPV and ESR, charge separation and transportation mechanisms are suggested. Under simulated sunlight illumination, the charge separation and transport mechanism of the photo-induced charge pairs followed a Z-scheme.Download high-res image (162KB)Download full-size image
Co-reporter:Shuhao Liu, Lili Wang, Wei-Chun Lin, Sukrit Sucharitakul, Clemens Burda, and Xuan P. A. Gao
Nano Letters 2016 Volume 16(Issue 12) pp:7925-7929
Publication Date(Web):November 29, 2016
DOI:10.1021/acs.nanolett.6b04235
Organometal halide perovskite has emerged as a promising material for solar cells and optoelectronics. Although the long diffusion length of photogenerated carriers is believed to be a critical factor responsible for the material’s high efficiency in solar cells, a direct study of carrier transport over long distances in organometal halide perovskites is still lacking. We fabricated highly oriented crystalline CH3NH3PbI3 (MAPbI3) thin-film lateral transport devices with long channel length (∼120 μm). By performing spatially scanned photocurrent imaging measurements with local illumination, we directly show that the perovskite films prepared here have very long transport lengths for photogenerated carriers, with a minority carrier (electron) diffusion length on the order of 10 μm. Our approach of applying scanning photocurrent microscopy to organometal halide perovskites may be further used to elucidate the carrier transport processes and the vastly different carrier diffusion lengths (∼100 nm to 100 μm) in different types of organometal halide perovskites.Keywords: carrier diffusion length; Halide perovskite; photovoltaics; scanning photocurrent microscopy;
Co-reporter:Xin Guo, Christopher McCleese, Charles Kolodziej, Anna C. S. Samia, Yixin Zhao and Clemens Burda
Dalton Transactions 2016 vol. 45(Issue 9) pp:3806-3813
Publication Date(Web):28 Jan 2016
DOI:10.1039/C5DT04420K
Perovskite films were prepared using single step solution deposition at different annealing temperatures and annealing times. The crystal structure, phases and grain size were investigated with XRD, XPS and SEM/EDX. The prepared films show a typical orientation of tetragonal perovskite phase and a gradual transition at room temperature from the yellow intermediate phase to the black perovskite phase. Films with high purity were obtained by sintering at 100 °C. In addition, the chemical composition and crystal struture of intermediate phase were investigated in detail. FTIR, UV-vis and NMR spectra revealed the occurance of DMF complexes. Interestingly, the intermediate phase could be transformed to the black perovskite phase upon X-ray irradiation. In addition, the recovery of the aged perovskite films from a yellow intermediate phase back to the black perovskite was shown to be viable via heating and X-ray irradiation.
Co-reporter:Xin Guo, Christopher McCleese, Wei-Chun Lin and Clemens Burda
RSC Advances 2016 vol. 6(Issue 65) pp:60620-60625
Publication Date(Web):15 Jun 2016
DOI:10.1039/C6RA09714F
Perovskite films were prepared using one-step solution deposition. The prepared films were degraded for 14 days under ambient atmosphere with controlled humidity of 60 ± 5%. The degraded films showed separated regions of PbI2-rich and methylammonium iodide (MAI)-rich phases. Through X-ray, UV and electron beam irradiation, a fast recovery of perovskite was initiated in the MAI regions and the photoproduct further spread into the PbI2 regions over a time frame of minutes. Ultraviolet and electron beam were also explored as irradiation sources and the same photoinduced perovskite formation was observed in each case. XRD results proved that the photoproduct is indeed tetragonal perovskite MAPbI3. A slower conversion process can be achieved by storing the degraded samples at 25% ± 5% humidity. It is also observed that samples degraded at high humidity can be recovered by thermal annealing at a temperature as low as 35 °C. In this work, recovery of the aged perovskite films from decomposed phases (intermediate phase and PbI2) is shown to be feasible, which paves a new way for sustainable perovskite-based solar cells.
Co-reporter:Buddhadev Maiti, Arun K. Manna, Christopher McCleese, Tennyson L. Doane, Sudha Chakrapani, Clemens Burda, and Barry D. Dunietz
The Journal of Physical Chemistry A 2016 Volume 120(Issue 39) pp:7634-7640
Publication Date(Web):September 21, 2016
DOI:10.1021/acs.jpca.6b05610
Photoinduced cleavage of the bond between the central Si atom in porphyrin macrocycles and the neighboring carbon atom of an axial alkyl ligand is investigated by both experimental and computational tools. Photolysis and electron paramagnetic resonance measurements indicate that the Si–C bond cleavage of Si–phthalocyanine occurs through a homolytic process. The homolytic process follows a low-lying electronic excitation of about 1.8 eV that destabilizes the carbide bond of similar bond dissociation energy. Using electronic structure calculations, we provide insight into the nature of the excited state and the resulting photocleavage mechanism. We explain this process by finding that the electronic excited state is of a charge transfer character from the axial ligand toward the macrocycle in the reverse direction of the ground state polarization. We find that the homolytic process yielding the radical intermediate is energetically the most stable mechanistic route. Furthermore, we demonstrate using our computational approach that changing the phthalocyanine to smaller ring system enhances the homolytic photocleavage of the Si–C bond by reducing the energetic barrier in the relevant excited states.
Co-reporter:Xin Guo;Christopher McCleese;Weiyin Gao
Materials for Renewable and Sustainable Energy 2016 Volume 5( Issue 4) pp:
Publication Date(Web):2016 November
DOI:10.1007/s40243-016-0081-1
This work presents a novel method for preparing perovskite films using a simple processing technique. Perovskite paste was prepared by dispersing an equimolar mix of PbI2 and methyl ammonium iodide powders into terpineol with stirring. From these precursors, perovskite films were fabricated using doctor blading and drying for 24 h at room temperature. The prepared films were then placed into relative humidity (RH) levels of 30, 50, and 70 % to test the moisture stability. The crystal structure, phases, and morphology were investigated with XRD and SEM/EDX. These samples exhibited good stability against long time exposure to moisture for 70 days. The XRD results showed that samples stored at RH 70 % contained only a small amount of hydrate compound after 70 days storage, while in the sample stored at RH 50 %, the formation of PbI2 was observed. The sample at RH 30 % manifested almost no change when stored for the same storage period. We attribute the enhanced moisture stability, compared with the spin-coated samples, to a passivated surface of the perovskite film by terpineol which exhibits a hydrophobic moiety. Time-resolved photoluminescence measurements show that the passivation of surface defect states by the formation of either PbI2 or hydrated compound leads to prolonged charge carrier recombination times.
Co-reporter:Lixia Sang, Yixin Zhao, and Clemens Burda
Chemical Reviews 2014 Volume 114(Issue 19) pp:9283
Publication Date(Web):May 20, 2014
DOI:10.1021/cr400629p
Co-reporter:Lili Wang ; Christopher McCleese ; Anton Kovalsky ; Yixin Zhao
Journal of the American Chemical Society 2014 Volume 136(Issue 35) pp:12205-12208
Publication Date(Web):August 22, 2014
DOI:10.1021/ja504632z
CH3NH3PbI3 perovskite layered films deposited on substrates with and without a titania support structure have been prepared and studied using time-resolved femtosecond transient absorption (fs-TA) spectroscopy in the visible light range (450–800 nm). The electron injection dynamics from the photoexcited perovskite layers to the neighboring film structures could be directly monitored via the transient bleaching dynamics of the perovskite at ∼750 nm and thus systematically studied as a function of the layer-by-layer architecture. In addition, for the first time we could spectrally distinguish transient bleaching at ∼750 nm from laser-induced fluorescence that occurs red-shifted at ∼780 nm. We show that an additional bleach feature at ∼510 nm appears when PbI2 is present in the perovskite film. The amplitudes of the PbI2 and perovskite TA peaks were compared to estimate relative amounts of PbI2 in the samples. Kinetic analysis reveals that perovskite films with less PbI2 show faster relaxation rates than those containing more PbI2. These fast dynamics are attributed to charge carrier trapping at perovskite grain boundaries, and the slower dynamics in samples containing PbI2 are due to a passivation effect, in line with other recently reported work.
Co-reporter:Feng Lu, Tennyson L. Doane, Jun-Jie Zhu and Clemens Burda
Chemical Communications 2014 vol. 50(Issue 6) pp:642-644
Publication Date(Web):28 Oct 2013
DOI:10.1039/C3CC47124A
After ligand exchange with PEG, Au NPs with differently mixed surface functionalities co-exist in the as-synthesized sample. It is found that the poorly grafted nanoparticles can be simply removed using a chromatographic method, and the well grafted nanoparticles can be eluted as a function of the core size.
Co-reporter:Dr. Tennyson Doane;Andrew Chomas;Shriya Srinivasan ; Clemens Burda
Chemistry - A European Journal 2014 Volume 20( Issue 26) pp:8030-8039
Publication Date(Web):
DOI:10.1002/chem.201304885
Abstract
The use of macrocyclic molecules for both imaging and photodynamic therapy (PDT) has proven to be a powerful method for assessing and treating diseases, respectively. However, many potential candidates for these applications rely on rigid organic structures which are hydrophobic and thus lead to possible aggregation in aqueous solutions such as blood. Here, we describe the discovery of noncovalent J-aggregate dimers of the asymmetrically, axially modified silicon phthalocyanine 4 (Pc 4) in aqueous solutions through steady-state and time-resolved spectroscopy. Remarkably, the monomer–dimer equilibrium is dictated by water content and pH, with free monomers resulting in favorable solvation conditions even after formation of the dimer complex. This work sheds light on previous observations of Pc 4 behavior in cells during PDT, and can further elucidate the structure–activity relationship of these important molecules.
Co-reporter:Keng-Chu Lin, Lili Wang, Tennyson Doane, Anton Kovalsky, Sandra Pejic, and Clemens Burda
The Journal of Physical Chemistry B 2014 Volume 118(Issue 49) pp:14027-14036
Publication Date(Web):June 12, 2014
DOI:10.1021/jp5038987
In order to promote the development of solar cells with varying types of sensitizers including dyes and quantum dots, it is crucial to establish a general experimental analysis that accounts for all important optical and electrical losses resulting from interfacial phenomena. All of these varying types of solar cells share common features where a mesoporous scaffold is used as a sensitizer loading support as well as an electron transport material, which may result in light scattering. The loss of efficiency at interfaces of the sensitizer, the mesoporous TiO2 nanoparticle films, the FTO conductive layer, and the supportive glass substrate should be considered in addition to the photoinduced electron transport properties within a cell. On the basis of optical parameters, one can obtain the internal quantum efficiency (IQE) of a solar cell, an important parameter that cannot be directly measured but must be derived from several key experiments. By integrating an optical loss model with an electrical loss model, many solar cell parameters could be characterized from electro-optical observables including reflectance, transmittance, and absorptance of the dye sensitizer, the electron injection efficiency, and the charge collection efficiency. In this work, an integrated electro-optical approach has been applied to SiPc (Pc 61) dye-sensitized solar cells for evaluating the parameters affecting the overall power conversion efficiency. The absorptance results of the Pc 61 dye-sensitized solar cell provide evidence that the adsorbed Pc 61 forms noninjection layers on TiO2 surfaces when the dye immersion time exceeds 120 min, resulting in shading light from the active layer rather than an increase in photoelectric current efficiency.
Co-reporter:Baodong Mao ; Chi-Hung Chuang ; Christopher McCleese ; Junjie Zhu
The Journal of Physical Chemistry C 2014 Volume 118(Issue 25) pp:13883-13889
Publication Date(Web):June 2, 2014
DOI:10.1021/jp500872w
Near-infrared emitting AgInS2/ZnS nanocrystals were synthesized by carefully controlling the growth conditions in a Ag/In/Zn/S solution with less zinc relative to the other precursors. The role of having a smaller amount of zinc (8 atom %) was systematically investigated in an effort to understand the mechanism of the largely red-shifted emission. The AgInS2/ZnS nanocrystals can be transferred to aqueous solutions while retaining the emission intensity. The near-infrared emission and solubility in aqueous solutions make AgInS2/ZnS nanocrystals excellent candidates for bioimaging and photocatalytic applications.
Co-reporter:Yujie Ding, Hao Zhu, Xiaoxia Zhang, Jun-Jie Zhu and Clemens Burda
Chemical Communications 2013 vol. 49(Issue 71) pp:7797-7799
Publication Date(Web):02 Jul 2013
DOI:10.1039/C3CC43926G
A novel fluorescence resonance energy transfer (FRET)-based probe, γ-cyclodextrin modified oleic acid–NaYF4:Yb, Ho upconversion nanoparticles functionalized with a rhodamine B derivative (RBD), has been achieved for Fe3+-sensing in aqueous solution with high sensitivity and selectivity.
Co-reporter:Jinze Lyu; Lizhong Zhu; Clemens Burda
ChemCatChem 2013 Volume 5( Issue 10) pp:3114-3123
Publication Date(Web):
DOI:10.1002/cctc.201300308
Abstract
Adsorption and photodegradation are key steps in environmental air purification. Micropores have been introduced into anatase TiO2 nanocatalysts to enhance the adsorption of pollutant molecules onto the photocatalyst surface, which increases the use of the photoinduced electron–hole pairs. Three nanocomposites have been synthesized with dodecylamine as a pore-forming agent under mild hydrothermal conditions and at varying temperature of preparation. Samples synthesized at 100, 115, and 130 °C, labeled TiO2-100, TiO2-115, and TiO2-130, respectively, provided insights into the effect of crystallinity and micropore area on the removal efficiency of gas-phase organic pollutants. Of the three, TiO2-100 had the largest micropore area (493 m2 g−1) but amorphous phase. TiO2-130 had anatase phase but only mesopores, whereas TiO2-115 had both a relatively large micropore area (258 m2 g−1) and an anatase crystal structure. Toluene was chosen as a model air pollutant. Experiments were performed in a single-pass reactor in the presence of UV irradiation under various experimental conditions, such as varying partial pressures of toluene, contact times, and relative humidities of the mobile gas phase, to approximate realistic conditions for this air purification system. Of the three prototype catalysts, TiO2-115 showed the highest removal and mineralization efficiencies owing to the optimized availability of photogenerated holes and adsorbed toluene. The key parameters for optimized photocatalysis of low-concentration air pollutants are the micropore area and the crystallinity of the photocatalyst.
Co-reporter:Lixia Sang, James L. Gole, Junwei Wang, Jonathan Brauer, Baodong Mao, S. M. Prokes, and Clemens Burda
The Journal of Physical Chemistry C 2013 Volume 117(Issue 29) pp:15287-15294
Publication Date(Web):June 25, 2013
DOI:10.1021/jp402547t
Porous sol–gel generated TiO2 nanocolloids and their corresponding oxynitrides TiO2–xNx are investigated to evaluate the effects that accompany doping with iron (FeII) ions at high doping concentrations. The introduction of FeII at higher concentrations leads to an anatase-to-rutile conversion at room temperature for the seeded oxynitride nanocolloids and to a less crystalline state in the subsurface and bulk as suggested by Raman spectroscopy. Combinations of core level and valence band photoelectron spectroscopy are correlated with the results of density functional theory (DFT) calculations to demonstrate a facile charge transfer from FeII to TiIV, producing TiIII and FeIII, and subsequently the transformation of FeII + TiIII to FeIII + TiII. This process is associated with the detectable formation of Ti(III) and Ti(II) at the surface of the titania-based nanoparticles. With significant visible light absorption, the photocatalytic activities of the iron-seeded titania systems are comparable to that of the iron-doped oxynitride TiO2–xNx as a function of doping concentration. The observations reported herein suggest that the anatase-to-rutile phase transformation and the enhancement of electron transfer can control the visible-light catalytic activity within the doped nanoparticles to form FeII/FeIII-codoped TiO2 nanocolloids.
Co-reporter:Baodong Mao, Chi-Hung Chuang, Feng Lu, Lixia Sang, Junjie Zhu, and Clemens Burda
The Journal of Physical Chemistry C 2013 Volume 117(Issue 1) pp:648-656
Publication Date(Web):December 24, 2012
DOI:10.1021/jp309202g
AgInS2–ZnS (AIZS) nanocrystals (NCs) were synthesized using a simple one-step approach by heating a Ag/In/Zn/S solution to 210 °C providing highly tunable photoluminescence (PL). The incorporation of Zn even at low temperatures (∼150 °C) and the increased cation exchange of silver by zinc at higher temperatures strongly influence the optical properties of the resulting NCs. The correlation between synthesis parameters and resulting optical properties provided insights on the growth and stability of ternary and quaternary semiconductors. Systematic investigation with time-resolved spectroscopy showed distinguishable PL behaviors between developing and fully grown AIZS NCs. Attempts to coat as-prepared AgInS2 NCs resulted in the same PL behavior as the one-step reaction product indicating that Zn readily exchanges with Ag ions even when not directly incorporated in the initial reaction mixture. Even with a low amount of zinc, the fully grown AIZS NCs showed improved PL QYs and single exponential decay behavior with long PL lifetimes. Control of the optical properties of these NCs makes them potentially useful for applications in photovoltaics and bioimaging particularly in light of their nontoxicity.
Co-reporter:Yixin Zhao and Clemens Burda
Energy & Environmental Science 2012 vol. 5(Issue 2) pp:5564-5576
Publication Date(Web):07 Dec 2011
DOI:10.1039/C1EE02734D
The development of copper chalcogenide based nanomaterials as promising candidates for sustainable energy materials, due to their environmental compatibility and low toxicity, is presented and discussed in this review. Different solution syntheses have recently been developed for the low-cost preparation of copper chalcogenide nanocrystals, and their unique properties derived from copper deficiencies were investigated with much progress. The notorious compositional instability and defect formation of copper chalcogenide nanocrystals have been healed by forming donor–acceptor pairs in ternary and quaternary chalcogenide based nanocrystals, especially in copper zinc tin sulfides (CZTS). In addition to their use as light absorbers in solar cells, copper chalcogenide nanocrystals have also been utilized in different applications, such as electrode materials in Li ion batteries and high efficiency counter electrodes in dye/quantum dot sensitized solar cells as well as for NIR photothermal therapy. All relate to their unique copper deficiency properties. The copper chalcogenide based nanomaterials are believed to be sustainable materials for future energy applications once the syntheses and property investigations have led to a more complete understanding of their physics.
Co-reporter:Feng Lu, Tennyson L. Doane, Jun-Jie Zhu, Clemens Burda
Inorganica Chimica Acta 2012 Volume 393() pp:142-153
Publication Date(Web):1 December 2012
DOI:10.1016/j.ica.2012.05.038
Gold nanoparticles (Au NPs) provide a unique platform for biomedical applications. Au NP-based sensors have been widely employed to detect many different chemicals and disease-related biomolecules. Recent research on drug delivery and therapy with Au NPs has also indicated attractive and promising prospects for future applications. In this invited review we will provide an overview of the use of Au NPs for diagnostic sensing and therapy applications.Graphical abstractThis review provides a historical overview of the development of gold nanoparticle synthesis and highlights the recent progress in using gold nanoparticles for the applications in diagnostic sensing and therapy.Highlights► Historical overview of the development of gold nanoparticle synthesis and applications in the field of biomedicine. ► Concise summary of work on gold nanoparticle sensors from the initial work to current state of the art. ► Concise summary of work using gold nanoparticles for drug delivery and therapeutic applications. ► Short overview of the authors’ work in these areas.
Co-reporter:Chi-Hung Chuang and Clemens Burda
The Journal of Physical Chemistry Letters 2012 Volume 3(Issue 14) pp:1921-1927
Publication Date(Web):June 28, 2012
DOI:10.1021/jz300299r
Femtosecond laser spectroscopy has now been a powerful technique for over a decade to investigate charge carrier dynamics in nanoscale optoelectronic systems with a temporal resolution of 100 fs (10–13 s) or better. Both transient absorption and time-resolved photoluminescence spectroscopy are now popular spectroscopic techniques, which are well-established and provide direct insight into the charge carrier dynamics of nanomaterials. In this Perspective, we focus mainly on the developments with regard to studies of semiconductor nanostructures. Controlling the charge carrier dynamics, including hot carrier relaxation, trapping, interfacial carrier transfer, carrier multiplication, and recombination, is essential for successful energy conversion or photocatalysis, to name two major optoelectronic applications. We will show how femtosecond laser spectroscopy evolved into techniques that unveil the dynamic charge carrier properties of semiconductor nanomaterials toward heterostructures and complex nanoarchitectures and that femtosecond time-resolved laser spectroscopy can shine light on the path to novel optoelectronic structures and emergent optoelectronic technologies.
Co-reporter:Yu Cheng ; Joseph D. Meyers ; Ann-Marie Broome ; Malcolm E. Kenney ; James P. Basilion
Journal of the American Chemical Society 2011 Volume 133(Issue 8) pp:2583-2591
Publication Date(Web):February 4, 2011
DOI:10.1021/ja108846h
Efficient drug delivery to tumors is of ever-increasing importance. Single-visit diagnosis and treatment sessions are the goal of future theranostics. In this work, a noncovalent PDT cancer drug-gold nanoparticle (Au NP) conjugate system performed a rapid drug release and deep penetration of the drug into tumors within hours. The drug delivery mechanism of the PDT drug through Au NPs into tumors by passive accumulation was investigated via fluorescence imaging, elemental analysis, and histological staining. The pharmacokinetics of the conjugates over a 7-day test period showed rapid drug excretion, as monitored via the fluorescence of the drug in urine. Moreover, the biodistribution of Au NPs in this study period indicated clearance of the NPs from the mice. This study suggests that noncovalent delivery via Au NPs provides an attractive approach for cancer drugs to penetrate deep into the center of tumors.
Co-reporter:Yixin Zhao, Jeffrey S. Dyck and Clemens Burda
Journal of Materials Chemistry A 2011 vol. 21(Issue 43) pp:17049-17058
Publication Date(Web):30 Aug 2011
DOI:10.1039/C1JM11727K
Significant research effort has recently gone into the synthesis of thermoelectric nanomaterials through different chemical approaches since nanomaterials chemistry became a promising strategy for improving thermoelectric performance. Different thermoelectric nanocrystals, especially PbTe, Bi2Te3 and CoSb3, with various compositions and morphologies have been successfully prepared by solvo/hydrothermal, electrochemical, and ligand-based synthesis methods. Such nanoscale materials show not only substantial reduction in thermal conductivity due to increased phonon scattering at nanoscale grain boundaries and lower densities of phonon states but possibly also an enhancement in thermopower due to electronic quantum size effects. More recently, the notoriously low power factors of thermoelectric nanomaterials prepared by wet chemistry have been significantly improved by using an increasingly cross-disciplinary approach towards the bottom-up synthesis that combines expertise from chemistry, physics, and materials engineering. In this review, we discuss the recent progress and current challenges of preparing thermoelectric nanomaterials with solution-based chemistry approaches.
Co-reporter:Hongying Liu, Xiang Zhang, Ximei Wu, Liping Jiang, Clemens Burda and Jun-Jie Zhu
Chemical Communications 2011 vol. 47(Issue 14) pp:4237-4239
Publication Date(Web):25 Feb 2011
DOI:10.1039/C1CC00103E
Highly fluorescent and water-soluble gold nanoclusters (AuNCs) with near-infrared-emission and Au@AgNCs with yellow-emission were successfully prepared via a rapid sonochemical approach, and the as-prepared AuNCs could be applied in the determination of Cu2+ with a wider detection range and lower detection limit.
Co-reporter:Baodong Mao ; Chi-Hung Chuang ; Junwei Wang
The Journal of Physical Chemistry C 2011 Volume 115(Issue 18) pp:8945-8954
Publication Date(Web):April 20, 2011
DOI:10.1021/jp2011183
Ternary I–III–VI AgInS2 (AIS) semiconductor nanocrystals (NCs) with strong photoluminescence (PL) were synthesized using a one-pot reaction at low temperature. UV–vis absorption and PL spectra red shifted as the AIS NCs grew. Both steady-state and time-resolved PL spectroscopies were used to investigate the influence of surface and intrinsic trap states on the PL behaviors of the prepared AIS NCs. PL lifetimes at different wavelengths in the full spectrum range were measured using a streak camera for each sample toward a systematic kinetic study. We found PL lifetime components that were short-lived from surface states and long-lived from intrinsic states. Surface trap emissions were wavelength- and size-dependent. Besides these PL studies, we report the first measurements using femtosecond transient absorption spectroscopy to investigate the exciton dynamics of the AIS NCs. Because of the abundant intrinsic trap states, these ternary AIS NCs have long-lived excitons, which may provide potential applications in photocatalysis and photovoltaics.
Co-reporter:Chi-Hung Chuang, Tennyson L. Doane, Shun S. Lo, Gregory D. Scholes, and Clemens Burda
ACS Nano 2011 Volume 5(Issue 7) pp:6016
Publication Date(Web):June 14, 2011
DOI:10.1021/nn201788f
Using femtosecond transient absorption and time-resolved photoluminescence spectroscopy, we studied the electron versus hole dynamics in photoexcited quasi-type-II heterostructured nanocrystals with fixed CdTe core radii and varying CdSe shell coverage. By choosing the pump wavelength in resonance with the core or the shell states, respectively, we were able to measure the excited electron and hole dynamics selectively. Both, the core- and the shell-excited CdTe/CdSe nanocrystals showed the same spectral emission and photoluminescence lifetimes, indicating that ultrafast electron and hole transfer across the core/shell interface resulted in the identical long-lived charge transfer state. Both charge carriers have subpicosecond transfer rates through the interface, but the subsequent relaxation rates of the hole (τdec ∼ 800 ps) and electron (τavg ∼ 8 ps) are extremely different. On the basis of the presented transient absorption measurements and fitting of the steady-state spectra, we find that the electron transfer occurs in the Marcus inverted region and mixing between the CdTe exciton and charge transfer states takes place and therefore needs to be considered in the analysis.Keywords: charge transfer; core/shell quantum dots; electron/hole relaxation; femtosecond transient absorption; Marcus theory; type-II heterostructure
Co-reporter:Yixin Zhao ; Jeffrey S. Dyck ; Brett M. Hernandez
Journal of the American Chemical Society 2010 Volume 132(Issue 14) pp:4982-4983
Publication Date(Web):March 24, 2010
DOI:10.1021/ja100020m
The carrier concentration of chemically synthesized Bi2Te3-based nanocrystals (NCs) is for the first time reported to be adjusted by forming ternary Bi2−xSbxTe3 NCs (x = 0.02, 0.05, 0.10, 0.20, 0.50, and 1.50) through partial substitution of Bi with Sb. Carrier concentrations of ternary Bi2−xSbxTe3 NCs were successfully adjusted by a factor of more than 10 controlled by the stoichiometric partial Sb/Bi substitution level. The power factors of the stoichiometric ternary Bi2−xSbxTe3 NCs improved three times compared to the parent Bi2Te3 due to the carrier concentration adjustment.
Co-reporter:James L. Gole, Sharka M. Prokes, O. J. Glembocki, Junwei Wang, Xiaofeng Qiu and Clemens Burda
Nanoscale 2010 vol. 2(Issue 7) pp:1134-1140
Publication Date(Web):21 May 2010
DOI:10.1039/C0NR00125B
Experiments with a porous sol–gel generated TiO2 nanocolloid and its corresponding oxynitride TiO2−xNx are carried out to evaluate those transformations which accompany additional doping with transition metals. In this study, doping with cobalt (CoII) ions is evaluated using a combination of core level and VB-photoelectron and optical spectroscopy, complementing data obtained from Raman spectroscopy. Raman spectroscopy suggests that cobalt doping of porous sol–gel generated anatase TiO2 and nitridated TiO2−xNx introduces a spinel-like structure into the TiO2 and TiO2−xNx lattices. TEM and XPS data complemented by valence band-photoelectron spectra demonstrate that metallic cobalt clusters are not formed even at high doping levels. As evidenced by Raman spectroscopy, the creation of a spinel-like structure is commensurate with the room temperature conversion of the oxide and its oxynitride from the anatase to the rutile form. The onset of this kinetically driven process correlates with the formation of spinel sites within the TiO2 and TiO2−xNx particles. Despite their visible light absorption, the photocatalytic activity of these cobalt seeded systems is diminished relative to the oxynitride TiO2−xNx.
Co-reporter:Junwei Wang, Baodong Mao, James L. Gole and Clemens Burda
Nanoscale 2010 vol. 2(Issue 10) pp:2257-2261
Publication Date(Web):27 Aug 2010
DOI:10.1039/C0NR00313A
Visible-light-responsive nitrogen-doped titanium dioxide nanorods have been synthesized by a hydrothermal method at low temperature. X-Ray diffraction, scanning electron microscopy, UV-vis spectroscopy, and contact angle measurements were used to obtain the crystal structures, morphologies, visible-light absorbance, and hydrophobicity, respectively, of the prepared nanorods. The surface wettability of the samples could be reversibly tuned from hydrophobic to hydrophilic upon visible-light illumination. This switchable surface wettability is crucial since the photocatalytic activity of this nanoscaled catalyst for the decomposition of organic molecules exhibits a strong dependence on the surface wettability.
Co-reporter:Guo-Xi Liang, Ling-Ling Li, Hong-Yin Liu, Jian-Rong Zhang, Clemens Burda and Jun-Jie Zhu
Chemical Communications 2010 vol. 46(Issue 17) pp:2974-2976
Publication Date(Web):05 Mar 2010
DOI:10.1039/C000564A
New water-soluble CdSeTe/ZnS core–shell quantum dots with excellent near-infrared emission were synthesized via an aqueous solution method; they showed strong electrogenerated chemiluminescence and favorable biocompatibility.
Co-reporter:Yajun Ji, Keng-Chu Lin, Hegen Zheng, Chung-Chiun Liu, Laurie Dudik, Junjie Zhu, and Clemens Burda
ACS Applied Materials & Interfaces 2010 Volume 2(Issue 11) pp:3075
Publication Date(Web):October 25, 2010
DOI:10.1021/am100579g
Transparent photocatalytic surfaces are of ever increasing importance for many applications on self-cleaning windows and tiles in everyday applications. Here, we report the formation and photocatalytic testing of a quasi-transparent thin and nanoporous titania films deposited on glass plates. Sputtered Ti thin films were anodized in fluoride-ion-containing neutral electrolytes to form optically semitransparent nanoporous films, which transformed to be completely transparent after thermal annealing. The nanoporous films were studied at different stages, such as before and after anodization, as well as after thermal annealing using scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV−vis and Raman spectroscopy. It was observed that anodization at 20 V of high-temperature deposited titanium films resulted in regular nanopore films with pore diameters of 30 nm. Structural investigations on the transparent nanopore arrays reveal the presence of anatase phase TiO2 even after annealing at 500 °C, which was confirmed by XRD and Raman spectroscopy measurements. The solar-light induced photocatalytic decomposition of stearic acid and photoconductivity characteristics of these nanoporous thin films are also presented.Keywords: photocatalysis; photocurrent; thin film; titania nanopores
Co-reporter:Xiaofeng Qiu, Yixin Zhao, Ian M. Steward, Jeffrey S. Dyck and Clemens Burda
Dalton Transactions 2010 vol. 39(Issue 4) pp:1095-1100
Publication Date(Web):14 Sep 2009
DOI:10.1039/B914644J
Nanostructured PbSe films with different (200)/(111) grain size ratios were prepared by anisotropic growth on glass substrates. Although face centered cubic bulk PbSe is an isotropic material, the thermopower (S), electrical conductivity (σ) and hole mobility of the prepared nanostructured PbSe films show an obvious dependence on the anisotropic parameter, (200)/(111) grain size ratio. The thermoelectric power factor (S2σ) of the nanostructured films is improved with higher (200)/(111) grain size ratio. Temperature-dependent transport measurements suggest that grain boundary scattering dominates in these nanostructured films. Subtle changes in the microstructure are discussed in the light of the effect on grain boundary activation energy (barrier height). A 20% enhancement of the room temperature thermopower (S) at given carrier concentrations is demonstrated for the CBD-grown nanostructured PbSe films compared to single crystal bulk PbSe.
Co-reporter:Yu Cheng, Anna C. Samia, Jun Li, Malcolm E. Kenney, Andrew Resnick and Clemens Burda
Langmuir 2010 Volume 26(Issue 4) pp:2248-2255
Publication Date(Web):August 31, 2009
DOI:10.1021/la902390d
In this feature article, gold nanoparticle conjugates loaded with phthalocyanine-based PDT drugs are prepared and tested for delivery efficiency and PDT efficacy on HeLa cancer cells. It could be shown that the delivery and PDT outcome are strongly affected by the bond that links the drug load to the nanoparticle surface. Whereas labile amino adsorption to the Au nanoparticle surface allows for efficient drug release into the cancer cells and for efficient PDT, a covalent thiol bond to the Au nanoparticle leads to the delivery of the drug into cell vesicles, and no PDT effect is observed. This work highlights the importance of carefully choosing the interaction between drug molecules and the nanoparticle surface.
Co-reporter:Yixin Zhao, Jeffrey S. Dyck, Brett M. Hernandez and Clemens Burda
The Journal of Physical Chemistry C 2010 Volume 114(Issue 26) pp:11607-11613
Publication Date(Web):June 16, 2010
DOI:10.1021/jp102816x
The power factors of chemically synthesized Bi2Te3 and Bi0.5Sb1.5Te3 nanocrystals (NCs) were improved up to 2.4 and 7.8 μW cm−1 K−2, respectively, which are significantly higher than previously reported values for chemically synthesized Bi2Te3 NCs and even comparable to the recently reported highest power factor of 5 μW cm−1 K−2 for Bi2Te3 NCs consolidated by spark plasma sintering. This improvement was achieved by annealing the NCs under argon protection, and the crystal structures and morphologies of these annealed NCs were characterized via XRD, SEM, and TEM measurements. The temperature-dependent thermoelectric properties of these modified NCs were explored on cold-pressed pellets of NCs. Improvement of the thermoelectric performances of the pellets resulted primarily from an increase in electrical conductivity (σ), while only weakly increasing the lattice thermal conductivity (κL), which was still kept lower than bulk values. Hall carrier concentration studies suggest that the improvement of the electrical conductivity is caused primarily by modification of the charge carrier mobility rather than the carrier concentration. A mechanism is proposed to explain a large increase of electrical conductivity by annealing related to a decrease of activation energy for the mobility after the removal of organic capping ligands through annealing.
Co-reporter:Chi-Hung Chuang, Shun S. Lo, Gregory D. Scholes and Clemens Burda
The Journal of Physical Chemistry Letters 2010 Volume 1(Issue 17) pp:2530-2535
Publication Date(Web):August 10, 2010
DOI:10.1021/jz1008399
Femtosecond transient absorption (TA) is used to investigate population dynamics of electronic states in CdTe/CdSe core/shell nanocrystals (NCs) with varying CdSe shell coverage. Upon CdSe shell growth, the CdTe/CdSe NCs show a gradual evolution of surface passivation toward a quasi-type-II charge separation regime. Our results indicate that ultrafast electron transfer (ET) through the interface of CdTe/CdSe NCs becomes measurable as the CdSe shell approaches the quasi-type-II regime which we experimentally determined to be at 0.4 nm (shell) for a 3.4 nm CdTe core. This work reports the first measurement using femtosecond TA to study the electronic states in CdTe/CdSe NCs and spectroscopically observe the evolution of an ultrafast charge transfer (CT) in such a core/shell system. Time-resolved photoluminescence (PL) spectroscopy is used to study the radiative lifetimes of the CdTe/CdSe NCs. One monolayer CdSe coverage leads to longer-lived PL, which is red-shifted by 140 nm compared to the CdTe core PL. It is concluded that this is due to greater electron−hole separation providing a longer-lived CT state.Keywords (keywords): charge separation; core−shell; electron transfer; femtosecond transient absorption; quasi-type-II heterostructure;
Co-reporter:Yixin Zhao and Clemens Burda
ACS Applied Materials & Interfaces 2009 Volume 1(Issue 6) pp:1259
Publication Date(Web):June 3, 2009
DOI:10.1021/am900148d
Bismuth−antimony−telluride alloy, Bi0.5Sb1.5Te3, nanocrystals (NCs) have been synthesized by direct chemical solution synthesis, in which the bismuth and antimony precursors, dissolved in a phenyl ether solution and coordinated with dodecanethiol, directly reacted with tellurium in trioctylphosphine. Transmission electron microscopy and X-ray diffraction (XRD) were used for the structure and morphology characterization of these NCs. Their XRD pattern evolution indicated that the reaction temperature plays a critical role in alloying and crystallization of Bi0.5Sb1.5Te3 NCs. X-ray photoelectron spectrometry was used to study the alloy states and surface oxidation. It is found that the choice of the capping ligands can be important and useful in protecting against the surface oxidation of Bi2Te3-type thermoelectrical nanomaterials.Keywords: Bi0.5Sb1.5Te3; Bi2Te3; nanocrystal; Sb2Te3; thermoelectric; XPS; XRD
Co-reporter:Yixin Zhao;Philip Larimer;RichardT. Pressler Dr.;BenW. Strowbridge Dr. Dr.
Angewandte Chemie International Edition 2009 Volume 48( Issue 13) pp:2407-2410
Publication Date(Web):
DOI:10.1002/anie.200806093
Co-reporter:Yixin Zhao, Xiaofeng Qiu and Clemens Burda
Chemistry of Materials 2008 Volume 20(Issue 8) pp:2629
Publication Date(Web):March 19, 2008
DOI:10.1021/cm703043j
N-Doped titanium oxide nanoparticles (NPs) were synthesized through the hydrolysis of N-substituted titanium isopropoxide precursors and postsynthesis treated by sintering at different temperatures in a nitrogen atmosphere and in air. X-ray diffraction (XRD) results revealed that the presence of oxygen during the sintering also affects the crystallization of the N-doped TiO2 NPs. The air and N2 sintering produced different nitrogen concentrations and visible-light absorbances. The N-doped TiO2 NPs sintered at 200–250 °C in air for 1/2 h produced the best photocatalytic nanoparticles for visible-light decomposition of methylene blue in water. On the other hand, sintering in N2 atmosphere at any temperature provided photocatalysts with about half-the activity for visible-light decomposition of methylene blue compared to the air-sintered NPs. The zeta potential of the N-doped TiO2 NPs solution used in the photocatalytic tests shows that higher sintering temperatures create more negative charges on the NP surface and that the sintering in air creates more negative charges compared to the treatment in N2, due to the carboxylation of organic surface residues. Computational and ATR-FTIR results indicate that the doping of the nitrogen into the matrix occurs as a complexation between the Ti central metal ion and the N atom and not from a covalent Ti−N bond.
Co-reporter:Changjie Mao, Yixin Zhao, Xiaofeng Qiu, Junjie Zhu and Clemens Burda
Physical Chemistry Chemical Physics 2008 vol. 10(Issue 36) pp:5633-5638
Publication Date(Web):30 Jul 2008
DOI:10.1039/B805915B
Nitrogen-doped CeO2nanoparticles were synthesized through a wet-chemical route. Nitrogen has been successfully incorporated into CeO2nanoparticles and the nitrogen-doping level was also successfully controlled. The optical properties due to the different N-doping levels in CeO2nanoparticles were characterized by UV-Vis diffuse reflectance spectroscopy (DRS), which showed a visible-light absorbance shift. The resulting nanoparticles show enhanced visible-light sensitivity and photocatalytic activity compared to undoped CeO2nanoparticles. DFT calculations were performed to explore the effect of nitrogen doping versusoxygen vacancies. The calculations show that the change of the electronic structure upon N-doping CeO2 is quite different from that of N-doped TiO2, which has been studied extensively.
Co-reporter:Smita Dayal;Jun Li;Ying-Syi Li;Hongqiao Wu;Anna C. S. Samia;Malcolm E. Kenney
Photochemistry and Photobiology 2008 Volume 84( Issue 1) pp:243-249
Publication Date(Web):
DOI:10.1111/j.1751-1097.2007.00227.x
Abstract
This study examines the electronic coupling between quantum dots (QDs) and molecules on their surfaces as a function of the modality of their interaction. As a probe, the energy transfer (ET) between CdSe QDs and phthalocyanines (Pcs) was monitored and evaluated with regard to the functionalization of the axial phthalocyanine ligand, bulkiness of the functional group bridging the QD donor and Pc acceptor, and the number of the functionalized axial ligands. New silicon PCs and their conjugates with CdSe QDs were synthesized. The ET efficiency and kinetics were studied by steady state and femtosecond time-resolved absorption spectroscopy. We observed a decrease in ET efficiency with the increase in functional group bulkiness, which could be explained by increasing steric hindrance between the ET pair. In addition, a higher ET efficiency was observed for amino and thiol functionalized Pcs compared to Pcs without functional group on the axial alkyl chain.
Co-reporter:Sidney Clouser;Anna C. S. Samia;Eric Navok;Jarred Alred
Topics in Catalysis 2008 Volume 47( Issue 1-2) pp:42-48
Publication Date(Web):2008 March
DOI:10.1007/s11244-007-9037-0
Nitrogen doped titania nanoparticles were synthesized and deposited as thin films onto glass slides for photodecomposition studies of high molecular weight organics. The decomposition of stearic acid and polyethelyne glycol (PEG) on the nanostructured thin films under visible light irradiation were monitored using FTIR spectroscopy and a decrease in C–H stretch peak area in the 2,700–3,000 cm−1 range was monitored as the organic molecules were photocatalytically destroyed. Conversely, irradiation with visible light only or the whole Xenon lamp spectrum did not result in the degradation of the stearic or PEG coatings on glass in the absence of the nanocatalysts, which demonstrates for the first time visible light photoactivity of nitrogen-doped titania nanoparticle films.
Co-reporter:Bo Liu, Ting Ren, Jian-Rong Zhang, Hong-Yuan Chen, Jun-Jie Zhu, Clemens Burda
Electrochemistry Communications 2007 Volume 9(Issue 4) pp:551-557
Publication Date(Web):April 2007
DOI:10.1016/j.elecom.2006.10.030
The hollow spherical CdSe QD assemblies were synthesized via a sonochemical approach that utilizes β-cyclodextrin as a template reagent in aqueous solution. The hollow nanospheres have an average diameter of 70 nm and are found to consist of an assembly of monodispersed 5 nm sized CdSe quantum dots. Following an electrochemical reaction with persulfate ions, strong electrogenerated chemiluminescence (ECL) was observed from the CdSe nanoassemblies suspended in an aqueous solution of pH ⩽ 7.95. The study indicates that the morphology of the 70 nm nanoassembly plays an important role in generating the stable ECL since individually dispersed quantum dots did not exhibit any significant ECL. The unique ECL intensity and stability of the synthesized spherical nanoassemblies could allow for potential sensor applications of CdSe quantum dots in water.
Co-reporter:Yang Liu, Jin Li, Xiaofeng Qiu, Clemens Burda
Journal of Photochemistry and Photobiology A: Chemistry 2007 Volume 190(Issue 1) pp:94-100
Publication Date(Web):5 July 2007
DOI:10.1016/j.jphotochem.2007.03.017
The antibacterial effect of nitrogen-doped TiO2 and ZrO2 were tested on Escherichia coli and biofilm heterotrophic bacteria under solar light illumination. The rates of photocatalytic inactivation for biofilm bacteria with soluble extracellular polymeric substances (EPS) stripped off and E. coli bacteria were found to be higher than those of the biofilm bacteria with intact EPS. Measurements of both bacterial count and cellular components (carbohydrate and protein) revealed that EPS play an important role in controlling the kinetics of solar-induced photocatalysis. TiO2−xNx and ZrO2−xNx doped with ethylenediamine as the nitrogen source showed improved photoactivity compared with TiO2−xNx using ethanolamine as the nitrogen source.
Co-reporter:Anna C. S. Samia;Smita Dayal
Photochemistry and Photobiology 2006 Volume 82(Issue 3) pp:617-625
Publication Date(Web):30 APR 2007
DOI:10.1562/2005-05-11-IR-525
Quantum dots have emerged as an important class of material that offers great promise to a diverse range of applications ranging from energy conversion to biomedicine. Here, we review the potential of using quantum dots and quantum dot conjugates as sensitizers for photodynamic therapy (PDT). The photophysics of singlet oxygen generation in relation to quantum dot-based energy transfer is discussed and the possibility of using quantum dots as photosensitizer in PDT is assessed, including their current limitations to applications in biological systems. The biggest advantage of quantum dots over molecular photosensitizers that comes into perspective is their tunable optical properties and surface chemistries. Recent developments in the preparation and photophysical characterization of quantum dot energy transfer processes are also presented in this review, to provide insights on the future direction of quantum dot-based photosensitization studies from the viewpoint of our ongoing research.
Co-reporter:Xiaofeng Qiu;Leah N. Austin;Philip A. Muscarella;Jeffrey S. Dyck
Angewandte Chemie International Edition 2006 Volume 45(Issue 34) pp:
Publication Date(Web):21 JUL 2006
DOI:10.1002/anie.200600848
A new strategy to grow thermoelectric nanostructures on a wide variety of substrates is introduced. The synthesis involves the reduction of a selenium precursor to promote nucleation with bismuth ions to produce Bi2Se3 nanostructured films (see picture, scale bar 10 μm) under thermodynamic control. Thermoelectric transport measurements of the nanostructured films were performed from 6 to 300 K.
Co-reporter:Xiaofeng Qiu;Leah N. Austin;Philip A. Muscarella;Jeffrey S. Dyck
Angewandte Chemie 2006 Volume 118(Issue 34) pp:
Publication Date(Web):21 JUL 2006
DOI:10.1002/ange.200600848
Mit einer neuen Strategie können thermoelektrische Nanostrukturen auf vielfältigen Substraten gezüchtet werden. Auf die Reduktion einer Selenvorstufe folgt die Nukleation mit Bismut-Ionen, sodass thermodynamisch kontrolliert Bi2Se3-Filme entstehen (siehe Bild, Maßstab 10 μm). Die thermoelektrischen Transporteigenschaften der nanostrukturierten Filme wurden zwischen 6 und 300 K untersucht.
Co-reporter:Xiaofeng Qiu;Yongbing Lou;Anna C. S. Samia Dr.;Ano Devadoss;James D. Burgess ;Smita Dayal
Angewandte Chemie International Edition 2005 Volume 44(Issue 36) pp:
Publication Date(Web):5 AUG 2005
DOI:10.1002/anie.200501282
Highly uniform, single-crystalline PbTe nanorods with a diameter of 7 nm and an aspect ratio of 7 can be obtained by using a sonoelectrochemical method. The metal ion/ligand ratio controls the purity of the PbTe nanostructures through the redox chemistry of the ions involved in the growth process. Transmission electron microscopy of the nanorods reveals the highly uniform morphology obtained (see picture).
Co-reporter:Xiaofeng Qiu;Yongbing Lou;Anna C. S. Samia Dr.;Ano Devadoss;James D. Burgess ;Smita Dayal
Angewandte Chemie 2005 Volume 117(Issue 36) pp:
Publication Date(Web):5 AUG 2005
DOI:10.1002/ange.200501282
Sehr einheitliche, einkristalline PbTe-Nanostäbchen mit einem Durchmesser von 7 nm und einem Seitenverhältnis von 7 sind mit einer sonoelektrochemischen Methode zugänglich. Das Metallion/Ligand-Verhältnis steuert die Reinheit der PbTe-Nanostrukturen über die Redoxchemie der am Wachstumsprozess beteiligten Ionen. Transmissionselektronenmikroskopische Untersuchungen belegen die sehr einheitliche Morphologie der Nanostäbchen (siehe Bild).
Co-reporter:Tennyson Doane, Clemens Burda
Advanced Drug Delivery Reviews (May 2013) Volume 65(Issue 5) pp:607-621
Publication Date(Web):1 May 2013
DOI:10.1016/j.addr.2012.05.012
The use of nanoparticles (NPs) for enhanced drug delivery has been heavily explored during the last decade. Within the field, it is has become increasingly apparent that the physical properties of the particles themselves dictate their efficacy, and the relevant non-covalent chemistry at the NP interface also influences how drugs are immobilized and delivered. In this review, we reflect on the physical chemistry of NP mediated drug delivery (and more specifically, non-covalent drug delivery) at the three main experimental stages of drug loading, NP–drug conjugate transport, and the resulting cellular drug delivery. Through a critical evaluation of advances in drug delivery within the last decade, an outlook for biomedical applications of nanoscale transport vectors will be presented.The use of nanoparticles for the non-covalent delivery of drugs is promising for the treatment of many diseases, but can only be optimized through an understanding of their fundamental properties. This review explores non-covalent drug delivery during conjugate formation, transport, and delivery.Download high-res image (142KB)Download full-size image
Co-reporter:Feng Lu, Tennyson L. Doane, Jun-Jie Zhu and Clemens Burda
Chemical Communications 2014 - vol. 50(Issue 6) pp:NaN644-644
Publication Date(Web):2013/10/28
DOI:10.1039/C3CC47124A
After ligand exchange with PEG, Au NPs with differently mixed surface functionalities co-exist in the as-synthesized sample. It is found that the poorly grafted nanoparticles can be simply removed using a chromatographic method, and the well grafted nanoparticles can be eluted as a function of the core size.
Co-reporter:Yujie Ding, Hao Zhu, Xiaoxia Zhang, Jun-Jie Zhu and Clemens Burda
Chemical Communications 2013 - vol. 49(Issue 71) pp:NaN7799-7799
Publication Date(Web):2013/07/02
DOI:10.1039/C3CC43926G
A novel fluorescence resonance energy transfer (FRET)-based probe, γ-cyclodextrin modified oleic acid–NaYF4:Yb, Ho upconversion nanoparticles functionalized with a rhodamine B derivative (RBD), has been achieved for Fe3+-sensing in aqueous solution with high sensitivity and selectivity.
Co-reporter:Hongying Liu, Xiang Zhang, Ximei Wu, Liping Jiang, Clemens Burda and Jun-Jie Zhu
Chemical Communications 2011 - vol. 47(Issue 14) pp:NaN4239-4239
Publication Date(Web):2011/02/25
DOI:10.1039/C1CC00103E
Highly fluorescent and water-soluble gold nanoclusters (AuNCs) with near-infrared-emission and Au@AgNCs with yellow-emission were successfully prepared via a rapid sonochemical approach, and the as-prepared AuNCs could be applied in the determination of Cu2+ with a wider detection range and lower detection limit.
Co-reporter:Guo-Xi Liang, Ling-Ling Li, Hong-Yin Liu, Jian-Rong Zhang, Clemens Burda and Jun-Jie Zhu
Chemical Communications 2010 - vol. 46(Issue 17) pp:NaN2976-2976
Publication Date(Web):2010/03/05
DOI:10.1039/C000564A
New water-soluble CdSeTe/ZnS core–shell quantum dots with excellent near-infrared emission were synthesized via an aqueous solution method; they showed strong electrogenerated chemiluminescence and favorable biocompatibility.
Co-reporter:Xin Guo, Christopher McCleese, Charles Kolodziej, Anna C. S. Samia, Yixin Zhao and Clemens Burda
Dalton Transactions 2016 - vol. 45(Issue 9) pp:NaN3813-3813
Publication Date(Web):2016/01/28
DOI:10.1039/C5DT04420K
Perovskite films were prepared using single step solution deposition at different annealing temperatures and annealing times. The crystal structure, phases and grain size were investigated with XRD, XPS and SEM/EDX. The prepared films show a typical orientation of tetragonal perovskite phase and a gradual transition at room temperature from the yellow intermediate phase to the black perovskite phase. Films with high purity were obtained by sintering at 100 °C. In addition, the chemical composition and crystal struture of intermediate phase were investigated in detail. FTIR, UV-vis and NMR spectra revealed the occurance of DMF complexes. Interestingly, the intermediate phase could be transformed to the black perovskite phase upon X-ray irradiation. In addition, the recovery of the aged perovskite films from a yellow intermediate phase back to the black perovskite was shown to be viable via heating and X-ray irradiation.
Co-reporter:Xiaofeng Qiu, Yixin Zhao, Ian M. Steward, Jeffrey S. Dyck and Clemens Burda
Dalton Transactions 2010 - vol. 39(Issue 4) pp:NaN1100-1100
Publication Date(Web):2009/09/14
DOI:10.1039/B914644J
Nanostructured PbSe films with different (200)/(111) grain size ratios were prepared by anisotropic growth on glass substrates. Although face centered cubic bulk PbSe is an isotropic material, the thermopower (S), electrical conductivity (σ) and hole mobility of the prepared nanostructured PbSe films show an obvious dependence on the anisotropic parameter, (200)/(111) grain size ratio. The thermoelectric power factor (S2σ) of the nanostructured films is improved with higher (200)/(111) grain size ratio. Temperature-dependent transport measurements suggest that grain boundary scattering dominates in these nanostructured films. Subtle changes in the microstructure are discussed in the light of the effect on grain boundary activation energy (barrier height). A 20% enhancement of the room temperature thermopower (S) at given carrier concentrations is demonstrated for the CBD-grown nanostructured PbSe films compared to single crystal bulk PbSe.
Co-reporter:Yixin Zhao, Jeffrey S. Dyck and Clemens Burda
Journal of Materials Chemistry A 2011 - vol. 21(Issue 43) pp:NaN17058-17058
Publication Date(Web):2011/08/30
DOI:10.1039/C1JM11727K
Significant research effort has recently gone into the synthesis of thermoelectric nanomaterials through different chemical approaches since nanomaterials chemistry became a promising strategy for improving thermoelectric performance. Different thermoelectric nanocrystals, especially PbTe, Bi2Te3 and CoSb3, with various compositions and morphologies have been successfully prepared by solvo/hydrothermal, electrochemical, and ligand-based synthesis methods. Such nanoscale materials show not only substantial reduction in thermal conductivity due to increased phonon scattering at nanoscale grain boundaries and lower densities of phonon states but possibly also an enhancement in thermopower due to electronic quantum size effects. More recently, the notoriously low power factors of thermoelectric nanomaterials prepared by wet chemistry have been significantly improved by using an increasingly cross-disciplinary approach towards the bottom-up synthesis that combines expertise from chemistry, physics, and materials engineering. In this review, we discuss the recent progress and current challenges of preparing thermoelectric nanomaterials with solution-based chemistry approaches.
Co-reporter:Changjie Mao, Yixin Zhao, Xiaofeng Qiu, Junjie Zhu and Clemens Burda
Physical Chemistry Chemical Physics 2008 - vol. 10(Issue 36) pp:NaN5638-5638
Publication Date(Web):2008/07/30
DOI:10.1039/B805915B
Nitrogen-doped CeO2nanoparticles were synthesized through a wet-chemical route. Nitrogen has been successfully incorporated into CeO2nanoparticles and the nitrogen-doping level was also successfully controlled. The optical properties due to the different N-doping levels in CeO2nanoparticles were characterized by UV-Vis diffuse reflectance spectroscopy (DRS), which showed a visible-light absorbance shift. The resulting nanoparticles show enhanced visible-light sensitivity and photocatalytic activity compared to undoped CeO2nanoparticles. DFT calculations were performed to explore the effect of nitrogen doping versusoxygen vacancies. The calculations show that the change of the electronic structure upon N-doping CeO2 is quite different from that of N-doped TiO2, which has been studied extensively.
Co-reporter:Yubin Chen ; Chi-Hung Chuang ; Keng-Chu Lin ; Shaohua Shen ; Christopher McCleese ; Liejin Guo
The Journal of Physical Chemistry C () pp:
Publication Date(Web):
DOI:10.1021/jp500270d
This work provides new routes for developing efficient photoelectrodes for photoelectrochemical (PEC) water splitting using a low-cost electrophoretic film preparation method. A series of (Cu2Sn)xZn3(1–x)S3 (0 ≤ x ≤ 0.75) quaternary nanocrystals (NCs) with tunable optical band gaps are synthesized. Morphologies including particles, rods, and wires are obtained by tuning the composition of the NCs. (Cu2Sn)0.75Zn0.75S3 (Cu2ZnSnS4) has a pure kesterite structure, but an increase in the Zn content results in a kesterite–wurtzite polytypism. (Cu2Sn)xZn3(1–x)S3 films are fabricated from their colloidal solutions via electrophoretic deposition, and the PEC properties of these films with p-type character have been examined under water-splitting conditions. It is shown that the photocurrent varies as a function of film thickness as well as chemical composition. The produced (Cu2Sn)0.45Zn1.65S3 (x = 0.45) film has the highest photocurrent, and the incident photon to current conversion efficiency is improved compared with previously reported results of Cu2ZnSnS4 photocathodes.
![Silicon,[[3-(dimethylamino)propyl]dimethylsilanolato-kO]hydroxy[29H,31H-phthalocyaninato(2-)-kN29,kN30,kN31,kN32]-, (OC-6-23)- (9CI)](/data/chemimg/474500/135719-28-7.png)
![Silicon,[[3-(dimethylamino)propyl]dimethylsilanolato-kO]hydroxy[29H,31H-phthalocyaninato(2-)-kN29,kN30,kN31,kN32]-, (OC-6-23)- (9CI)](/data/chemimg/474500/135719-28-7_b.png)