Electron-hole Pairs Research Articles

A novel ZnO-TiO2-Bi2WO6/Carboxymethyl chitosan composite with high antimicrobial activity and visible-light catalytic degradation of ethylene towards banana preservation in hot and humid environments

In order to solve the problem of significantly shortened storage time of bananas in hot and humid environment (e.g., 30 °C and 90 % relative humidity), this paper reports the preparation of ZnO-TiO2-Bi2WO6 (ZTB) ternary heterojunction antimicrobial photocatalysts composite carboxymethyl chitosan film (ZTB/CMCS). ZTB were prepared by hydrothermal method and composited with CMCS by surface deposition method to construct ZTB/CMCS edible nano-preservation film. It is noteworthy that the ZTB/CMCS composite film exhibited excellent antibacterial efficiency (>99.99 %) against E. coli and S. aureus suspensions (106 CFU/mL) after 24 h of incubation at 37 °C. Time-resolved photoluminescence (TRPL) spectroscopy showed that the incorporation of Zinc oxide nanoparticles (ZnO NPs) into the ZTB structure led to a decrease in fluorescence lifetime. Moreover, the interfacial interaction between ZnO and TiO2/Bi2WO6 inhibited the recombination of photogenerated electron-hole pairs, promoting carrier separation and improving photocatalytic activity. The combination of high antibacterial activity, photocatalytic degradation of ethylene and inhibition of gas exchange provided multiple protections for fruit preservation. Therefore, this work provides a novel, effective and safe method for prolonging the preservation of bananas in hot and humid environments.

Synergistic photocatalytic degradation of TC-HCl by MIL-53(Fe)/CoWO4 composite and PMS under visible light

A series of novel MIL-53(Fe)/CoWO4 composites were synthesized by combining MIL-53(Fe) and CoWO4 nanoparticles via solvothermal method. The structural characterizations showed that CoWO4 nanoparticles were uniformly distributed on the surface of hexagonal bipyramid MIL-53(Fe). Combining XPS and Mott-Schottky plots, a Z-scheme heterojunction was formed between MIL-53(Fe) and CoWO4, resulting in a significant improvement in the electron-hole pair separation efficiency. UV–vis diffused reflectance spectra indicated that the optical arrange of MIL-53(Fe)/CoWO4 composites were expanded to visible light. The photocatalytic degradation experiments under visible light irradiation showed that MIL/CWO-60 synergistically with PMS degraded 90.5 % of TC-HCl within 50 min. The XRD spectra of used and unused composites were identical, indicating good stability in four consecutive cycles. Electron paramagnetic resonance (EPR) and free radicals trapping experiment revealed that active species included O2−, SO4−, h+, OH and 1O2, and mechanism of the synergistic degradation of TC-HCl by MIL-53(Fe)/CoWO4 composites and PMS was proposed.

In situ thermal-assisted photocatalytic decarboxylation of high-concentration biomass-derived fatty acids to alkanes

Heating is a straightforward method to increase reaction rates to meet industrial production, yet photocatalysis seldom incorporates it because their intrinsic driving force depends on the separation of photogenerated carriers, which is rarely affected by temperature. Here, we report a temperature-dependent photocatalytic decarboxylation strategy for producing long-chain n-alkanes from biomass-derived fatty acids using only the photothermal effect of the SnS catalyst. Under concentrated light irradiation without any external heating, and by employing high boiling-point solvents to reach optimal reaction temperatures (∼254 °C), Cn-1 n-alkane allows a very high concentration output (∼0.5 M for stearic acid to n-heptadecane) in a single operation, which is far beyond the capacity limit of conventional photocatalysis, typically no more than the mM levels. Mechanistic studies suggest that the in-situ heat brings the standing C-chain at low temperature down onto the SnS surface, increasing strain on the C-COO- bonds and facilitating reaction with photo-induced hole-electron pairs. We demonstrate that the majority of the incident light energy, when converted to heat, accelerates the photocatalytic decarboxylation.

Single-atom Rh[sbnd]S bond on defective CdZnS for enhanced photocatalytic hydrogen production

It is highly necessary but challenging to modify sulfides at the atomic scale to boost the separation of electron-hole pairs for enhanced photocatalytic performance. In this regard, single Rh atoms (Rh1) are assembled on CdZnS support with S vacancy defects (def-CZS) through RhS bond, creating a highly efficient photocatalyst. The optimized Rh1/def-CZS achieves an outstanding hydrogen evolution activity (30,512 μmol h−1 g−1), 4.32 and 3.34 folds enhancement that of CZS and def-CZS, respectively. The defective CZS support provides abundant S vacancy defects for Rh atom anchoring, where Rh bonds with neighboring S atoms (RhS). Theoretical calculations suggest that Rh can not only act as new H generation-release sites, but also optimize electron distribution around S defects simultaneously through the RhS bond, facilitating the separation of electron-hole pairs. Furthermore, in line with DFT results, in situ Raman confirms Rh (RhH) and electron-rich S atoms (SH) two main sites for proton reduction during hydrogen evolution.

Recent advances in photocatalytic degradation of persistent organic pollutants: Mechanisms, challenges, and modification strategies

Ecosystems and human health are seriously threatened by persistent organic pollutants (POPs), which are hazardous, resistant to environmental degradation, and have the capability of bioaccumulating. The sources, ecological dispersion, and potential adverse impacts of POPs are investigated in this study, which further highlights the urgent need to develop successful remediation technologies. As it can use light energy to promote degradation, photocatalysis is a promising approach among other methods. The review explores many evolved photocatalyst materials, such as those based on nanomaterials, metal-organic frameworks (MOFs), carbon, and hybrids, highlighting their characteristics and functions in the removal of pollutants. Enhancing photocatalytic performance through modification techniques such as surface changes, doping, and co-catalyst insertion is explored. The focus is on the degrading mechanisms specific to POPs and further examines the basic ideas and processes of photocatalysis. Despite its enormous significance, environmental stability, electron-hole pair recombination, and limited light absorption are some of the obstacles that photocatalysis faces. Finally, this analysis calls for novel materials and optimization techniques to overcome existing constraints and enhance the effectiveness of POP removal, highlighting future directions for photocatalyst research.

Enhanced Photoelectrochemical Water Splitting of In2S3 Photoanodes by Surface Modulation with 2D MoS2 Nanosheets.

Photoanodes with ample visible-light absorption and efficient photogenerated charge carrier dynamics expedite the actualization of high-efficiency photoelectrochemical water splitting (PEC-WS). Herein, we fabricated the heterojunction nanostructures of In2S3/MoS2 on indium-doped tin oxide glass substrates by indium sputtering and sulfurization, followed by the metal-organic chemical vapor deposition of 2D MoS2 nanosheets (NSs). The photocurrent density of In2S3/MoS2 was substantially enhanced and higher than those of pristine In2S3 and MoS2 NSs. This improvement is due to the MoS2 NSs extending the visible-light absorption range and the type-II heterojunction enhancing the separation and transfer of photogenerated electron-hole pairs. This work offers a promising avenue toward the development of an efficient photoanode for solar-driven PEC-WS.

Synthesis of Self-Assembled Mesoporous ZnO Microspheres Designed for Microwave-Assisted Photocatalytic Degradation of Tetracycline.

Microwave-assisted photocatalysis offers a novel approach for degrading antibiotics, while the mechanism of enhancement of microwave-induced photocatalysis remains poorly understood. In this study, tetracycline (TC) was degraded using the method of microwave-assisted photocatalysis with a ZnO catalyst, which was synthesized by the combination of hydrothermal and calcination methods. The self-assembled mesoporous ZnO catalyst exhibited superior catalytic activity in degrading TC. It is found that the degradation efficiency of TC by the ZnO catalysts with microwave-assisted photocatalysis is 4.27 times higher than that of photocatalysis alone. Of particular significance, we found that the optical absorption range of ZnO increased and the band gap decreased when microwave was introduced into the photocatalytic system. Semi-in situ photochemical tests demonstrated that more photogenerated electron-hole pairs were detected under microwave, thus further improving the photocatalytic activity of ZnO. The separation efficiency and charge transfer efficiency of photogenerated electron-hole pairs also improved due to the increase of oxygen vacancies in the synergistic effect. Meanwhile, h+ and ·OH were the main active species in the degradation system. The mechanism of microwave-induced photocatalysis is illustrated, and an efficient way for degrading antibiotic is provided in this work.

In-Situ Construction of Atomic-Level Fe-O Bond Bridges within Fe2N/g-C3N4 Heterojunction for Efficient Visible-Light-Driven Photocatalytic H2 Production.

The limited active sites and faster photogenerated electron-hole pair recombination rate of g-C3N4 restrict its application in photocatalytic H2 production. Constructing heterojunctions has been shown to improve the spatial (directional) separation of photogenerated electrons and holes. However, due to interface mismatch in traditional heterojunction structures and a lack of precise electron transport channels, the photocatalytic efficiency is limited. Here, we developed a two-step calcination approach to create an Fe2N/g-C3N4 heterojunction linked by Fe-O bonds (named as Fe-OCN). The newly formed Fe-O bonds within the heterojunction can act as atomic-level interface electron transfer channels, directly transferring the photogenerated electrons of g-C3N4 to the reactive center Fe2N, significantly improving the charge transfer rate and utilization, thus promoting visible-light-driven photocatalytic H2 production. The optimal Fe-OCN achieved a H2 production rate of 5986.29 μmol g-1 h-1 under visible light, 13.44 times higher than that of the OCN due to efficient charge separation and transfer capabilities. This work provides a constructive reference for the design and synthesis of organic-inorganic heterojunction with chemically bonded interfaces, establishing quick electron transfer channels, and achieving targeted electron transfer.

Bionic Leaf: Ultrahigh energy efficiency in a defect Engineered MoS2 based photo induced charging of flexible Zn-Air battery

Introducing solar energy directly into flexible energy storage systems is an environmentally friendly, efficient, and low-cost strategy. Herein, we constructed a photoelectrode based on flexible carbon cloth (CC) to promote the oxygen evolution reaction (OER) and effectively reduce the charging voltage of flexible zinc-air batteries (ZABs), inspired by the photosynthesis process in leaves. The implementation of sulfur vacancies (VS) and oxygen doping in nanoscale molybdenum disulfide (MoS2) effectively enhances the separation efficiency of photo-generated electron-hole pairs, and adjusts its band structure to improve the oxidation capability. The constructed photocathode with defect-rich MoS2 (D-MoS2) exhibits a low overpotential of 235 mV at 10 mA cm−2 for OER. The sandwich flexible ZABs based on D-MoS2 achieve a low charge voltage around 1.3 V and an ultra-high energy efficiency greater than 90 % under illumination at 0.1 mA cm−2. This strategy provides a new insight for the application of light energy in smart wearable energy storage devices.

Performance study of GaN-based betavoltaic nuclear batteries with 3D interfaces

This study presents a design of a 3D interface simulation model featuring an inverted pyramid structure. Our objective is to forecast the performance of GaN-based betavoltaic nuclear batteries with the PN junction 3D interface structures comparing a practical machining process. Initially, we computed the electron-hole pairs (EHPs) generation rate in GaN materials irradiated by both 63Ni and 147Pm sources using Geant4. Furthermore, we employed COMSOL Multiphysics, a finite element analysis software, to simulate the EHPs transport phenomena within the battery and investigate the influence of structural parameters on the output performance. Despite maintaining thicknesses of the P- and N-regions and consistent doping concentrations (Hp-GaN, Hn-GaN, Na, and Nd) as constants, the simulation results revealed notable disparities in the short-circuit current density (Jsc), open-circuit voltage (Voc), and maximum output power density (Pmax) among batteries irradiated with various radioactive sources. Subsequently, we investigated the output performance of the nuclear battery by altering parameters such as the number of inverted pyramid structures, junction depth, and type of radioactive source. Our investigation revealed that selecting 63Ni as the radioactive source, with Na at 1017 cm−3, Nd at 1014 cm−3, a junction depth of 0.1 μm, and inverted pyramid structures of 25, resulted in the following battery performance parameters: a short-circuit current density (Jsc) of 0.648 μA/cm2, an open-circuit voltage (Voc) of 2.3481 V, and a maximum output power density (Pmax) of 1.2949 μW/cm2. Substituting the radioactive source with 147Pm, the average short-circuit current density, Jsc, increased to 56.865 μA/cm2, and the maximum output power density, Pmax, increased to 94.975 μW/cm2, It's a significant enhancement in output performance.

Facile preparation of Co-doped ZnIn2S4 nanosheets for highly efficient photocatalytic hydrogen peroxide production

Utilizing solar energy to produce hydrogen peroxide from oxygen and water offers an appealing and sustainable approach. In this work, Co-doped ZnIn2S4 nanosheets were effectively synthesized through a chemical precipitation method, and the morphological structure, band structure and pathways for hydrogen peroxide production were investigated. The results indicate that Co doping significantly enhances the photocatalytic efficiency of ZnIn2S4 in producing hydrogen peroxide. The sample with the 2 % doping concentration exhibited the highest rate, with a detected hydrogen peroxide concentration of 535.53 µM in the solution after 100 minutes of exposure to visible light, which is 4.29-fold higher than that of undoped ZnIn2S4. Further analysis revealed that the improved performance mainly originated from better spectral response, faster photogenerated carrier transport, and lower recombination frequency of photogenerated electron-hole pairs.

Template-synthesized CdWO4/Cd0.5Zn0.5S hollow microsphere photocatalyst for high-efficient hydrogen evolution under visible light

Photocatalytic water splitting for hydrogen production is a promising strategy for renewable energy. While Cd1-XZnXS catalysts display high photocatalytic hydrogen evolution efficiency in pure water, they are limited by severe photocorrosion and rapid recombination of electron–hole pairs. In this study, HGM (hollow glass microspheres) was used as the support template, Cd0.5Zn0.5S and CdWO4 were successively coated on the template by hydrothermal method. The tightly packed heterojunction interface between the coatings ensures efficient electron transport and suppresses the recombination of electron-hole pairs. Under visible light irradiation, when the theoretical mass ratio of Cd0.5Zn0.5S to CdWO4 is 4:1, the Cd0.5Zn0.5S/CdWO4-25% hollow microsphere photocatalyst exhibits the highest hydrogen evolution rate, reaching 41.40 mmol g−1 h−1, which is approximately 3.4 times higher than the hydrogen evolution rate of pure Cd0.5Zn0.5S (12.31 mmol g−1 h−1). This research provides a novel approach for the design and synthesis of efficient and stable photocatalysts.

Effect of substrate temperature on In2S3 thin films using nebulizer spray pyrolysis method for photodetector applications

In this work, Indium Sulfide (In2S3) thin films were prepared using an economical nebulizer spray pyrolysis technique by various substrate temperatures from 250 °C to 375 °C in steps of 25 °C to evaluate their photo sensing properties. X-ray diffraction (XRD) patterns confirm the presence of In2S3 with face centered cubic structure for all substrate temperatures. The densely packed small spherical grain-sized particles were observed for In2S3 films deposited at 350 °C using Field emission scanning electron microscope (FESEM) analysis. The optical bandgap values were decreased from 3.16 eV to 2.28 eV, with increment in coating temperatures from 250 °C to 350 °C. The high intensity Photoluminescence (PL) peak is observed at 480 nm for the film coated at 350 °C is due to higher rate of electron–hole pair recombination. The photo sensing analysis revealed that the In2S3 thin films deposited at 350 °C, has the maximum responsivity (R) of 9.09 × 10−2 A W−1, detectivity (D*) of 8.25 × 1010 Jones, and external quantum efficiency (EQE) of 21.2%. Increasing the substrate temperature results in a significant enhancement of photo sensing characteristics.

WO3@MOF heterostructure in-situ transformed and deposited on La-Bi2WO6-BiFeWOx composite with enhanced photocatalytic performance for degradation of harmful and toxic substances produced by tobacco

Nowadays, tobacco is widely cultivated, and there are millions of people who smoke around the world. The cultivation of tobacco, along with the handling of cigarettes and the consumption of tobacco products, can produce numerous harmful and toxic substances. Many researchers are working diligently to eliminate these harmful and toxic substances. However, the results have been minimal. In this paper, we successfully prepared a novel La-Bi2WO6-BiFeWOx-WO3@MOF using hydrothermal and in-situ transformation methods. All samples were thoroughly investigated using various characterization techniques, including XRD, SEM, TEM, XPS, UV–Vis absorption spectra, transient photocurrent responses, and electron spin resonance. Furthermore, La-Bi2WO6-BiFeWOx-WO3@MOF was utilized as a catalyst for the degradation of harmful and toxic substances produced by tobacco, including phenol, nicotine, benzopyrene, and nitrosamines. The results indicate that La-Bi2WO6-BiFeWOx-WO3@MOF exhibits efficient separation and transfer of photo-generated electron-hole pairs under visible light irradiation. La-Bi2WO6-BiFeWOx-WO3@MOF also exhibits excellent photocatalytic activity, efficiently degrading phenol (98.62%), nicotine (92.41%), benzopyrene (81.74%), and nitrosamine (98.23%). Furthermore, the effects of varying catalyst dosage, phenol concentration, and pH values, as well as the degradation of nicotine, benzopyrene, and nitrosamine by La-Bi2WO6-BiFeWOx-WO3@MOF, were also investigated. The main active radicals are ·OH and ·O2– during the degradation process. Finally, a potential degradation mechanism for phenol, nicotine, benzopyrene, and nitrosamine by La-Bi2WO6-BiFeWOx-WO3@MOF is proposed.

Hierarchical Equations of Motion for Quantum Chemical Dynamics: Recent Methodology Developments and Applications.

ConspectusQuantum effects are critical to understanding many chemical dynamical processes in condensed phases, where interactions between molecules and their environment are usually strong and non-Markovian. In this Account, we review recent progress from our group in development and application of the hierarchical equations of motion (HEOM) method, highlighting its ability to address some challenging problems in quantum chemical dynamics.In the HEOM method, the bath degrees of freedom are represented using effective modes from exponential decomposition of the bath correlation function. Complex spectral densities and low temperature simulations often require a larger number of modes, making the simulations very expensive. Recent advances, such as the barycentric spectral decomposition (BSD) technique, can significantly reduce the number of effective modes, allowing to handle complex spectral densities and enabling simulations at very low temperatures, including near-zero temperature dynamics.Another key improvement in the computational efficiency is the use of tensor network methods like matrix product states and hierarchical tensor networks. These techniques allow for efficient HEOM propagation with thousands of effective modes, crucial for simulating large molecular systems interacting with multiple baths. This combination enables simulations of excitation energy transfer (EET) in systems like the Fenna-Matthews-Olson (FMO) complex and even larger systems with experimentally determined spectral densities.The versatility of the HEOM method is demonstrated through applications to a wide range of chemical dynamics problems. Simulations of EET and related ultrafast spectroscopy are first briefly covered. Applications of the HEOM to quantum tunneling effects in proton transfer reactions are then presented. Early works have studied the non-Kramers dependence of the rate constant as a function of bath friction due to deep tunneling and revealed vibrationally nonadiabatic dynamics within the so-called nontraditional view of proton transfer reactions. A recent work on the large kinetic isotope effects in soybean lipoxygenase also indicated that many quantum correction approximations to classical transition-state theory may fall short in describing deep tunneling effects.Charge transport and separation dynamics in organic semiconductors are another area where the HEOM method has been instrumental. We first demonstrate that the HEOM provides a unified description of both band-like and thermally assisted charge carrier transport in organic materials. The effect of non-nearest neighbor transitions is then investigated by combining generalized master equations with exact memory kernels. The HEOM method also enables simulation of charge separation in organic photovoltaics (OPVs) and reveals how factors such as external electric fields, entropy, and charge delocalization influence the charge separation barrier and dynamics.Moreover, HEOM has been applied to investigate hydrogen atom scattering on the Au(111) surface and vibrational energy relaxation at molecule-metal interfaces. These studies provide deeper insights into how electron-hole pair excitations and temporary charge transfer states influence the nuclear motion, offering a new framework for simulating nonadiabatic dynamics on metal surfaces.In summary, the HEOM method has developed into a robust tool for simulating quantum effects in condensed phases. Future developments in algorithm efficiency and computational power will likely expand its applicability to even more complex systems.

Design of novel Z-scheme g-C3N4/TiO2/CuCo2O4 heterojunctions for efficient visible light-driven photocatalyic degradation of rhodamine B

One of the most important environmental challenges that needs to be resolved is the industrial discharge of synthetic dyes. Graphitic carbon nitride (g-C3N4), Titanium dioxide (TiO2) and flower-like copper oxide (CuO)/copper cobaltite (CuCo2O4) nanocomposites were synthesized in order to synthesis an effective visible light driven photocatalyst that could degrade Rhodamin B (Rh.B) dye under simulated solar light irradiation. The SEM and TEM results verifies that the flower-like CuO/CuCo2O4 (CCO) structure and g-C3N4/TiO2 (g-CN/TO) generated a smart hybrid structure with superior g-CN distribution. According to the photocatalytic studies, g- C3N4/TiO2/CuO/CuCo2O4 (g-CN/TO/CCO) shows good photodegradation of Rh.B dye (99.9%) in minmal times (1 h) in CCO: g-CN/TO (2:1) ratio by Z-Scheme mechanism. The enhanced visible light absorption and effective electron-hole pair separation provided by the synergistic dispersion of CuO/CuCo2O4 and g-C3N4 can be attributed to the improved photocatalytic performances. These novel insights into g-CN/TO/CCO based photocatalysts are useful for treating industrial effluent.

Visible-light-driven photocatalytic for degrading tetracycline wastewater by BiOI/Bi2O3 Z-scheme heterojunction

Direct Z-scheme heterojunctions can exhibit enhanced redox capacity in redox reactions compared to conventional heterojunctions. In this study, BiOI/Bi2O3 Z-scheme heterojunctions were synthesized by a facile co-precipitation and calcination method using BiOI as a precursor, and its photocatalytic activity was investigated by degrading tetracycline antibiotics in aqueous environment. Under visible light, the degradation efficiency of tetracycline reached 80.01 % and the photocatalytic degradation rate constant reached 0.0116 min−1 when the molar ratio of Bi and I in BiOI/Bi2O3 composites was 1:1, which were 2.8 and 4.8 times higher than that of pristine BiOI (0.0041 min−1) and Bi2O3 (0.0024 min−1), respectively. The heterojunctions exposed excellent stability that maintained at 78.80 % after four cyclic tests. The ascendant photocatalytic performance can be attributed to the formation of direct Z-scheme heterojunctions, which improves the separation and transfer efficiency of the photogenerated electron-hole pairs, and ·O2- is the main active substance in the degradation process. This research provides a green and convenient method for preparing photocatalytic heterojunctions, which is conducive to promoting the development of photocatalytic degradation of refractory pollutants under visible light.

Construction of Z‐type heterojunction Bi4Ti3O12/g‐C3N4 with pyroelectric effect for enhanced photocatalytic performance

AbstractPhotocatalytic technology has been widely studied, discussed, and tested as a feasible wastewater degradation technology. The present study demonstrated the preparation of g‐C3N4 material using solid‐state sintering method and the construction of Bi4Ti3O12/g‐C3N4 heterostructure via hydrothermal method. This direct contact Z‐type heterojunction improves the wide bandgap of Bi4Ti3O12 monomer, enhances its photoresponsiveness, and thus improves its photocatalytic performance. During the process of photocatalytic experiments, an environment of cold and hot fluctuations were created, and the pyroelectric effect was utilized to induce self‐polarization of the material and formed an internal electric field. It improves the transport ability of electron–hole pairs and suppresses their recombination in the transport path. According to the degradation experiment results, the degradation efficiency of pyroelectric synergistic heterojunction photocatalysis reached 88.7%, which was 2.27 times that of Bi4Ti3O12. It proves that the photocatalysis by pyroelectric synergistic heterojunction has good application prospects.

Piezoelectric field accelerating charge transfer in Z-scheme heterojunction 2D-KNbO3/1D-CdS for efficient piezo-photocatalytic H2 evolution and TCH degradation

The piezo-phototronic effect utilizes the piezoelectric polarization field to tune the photogenerated carrier separation and transport performance in heterojunctions, which portrays a promising strategy for addressing energy shortage and environmental pollutants. Herein, a novel Z-scheme piezoelectric semiconductor heterojunction, 2D-KNbO3/1D-CdS-x (KNCS-x), was fabricated using hydrothermal and solvothermal methods, resulting in enhanced redox capacity. Under the simultaneous light and strain, KNCS-15 exhibits the highest piezo-photocatalytic activity, with degradation rates of tetracycline hydrochloride degradation rate constant, H2O2 as well as H2 production rates being 1.806 × 10−2s−1, 45.56 mM·h−1·g−1 and 8.87 mmol·h−1·g−1, respectively, which are 1.4, 2.4 and 1.9 times of photocatalysis alone, and 9.8, 9.2 and 9.8 times of piezocatalysis alone. DFT calculations, EPR and PALS indicate that the Z-scheme structure realizes effective separation of electron-hole pairs with strong redox ability and a higher carrier concentration. The enhanced catalytic activity is attributed to the introduction of piezoelectric potential, which facilitates improved spatial separation of electrons with high reduction and holes with high oxidation potential.

Composites Based on Electrodeposited WO3 and TiO2 Nanoparticles for Photoelectrochemical Water Splitting.

Photoelectrochemically active WO3 films were fabricated by electrodeposition from an acidic (pH 2), hydrogen-peroxide-containing electrolyte at -0.5 V vs. SCE. WO3-TiO2 composites were then synthesized under the same conditions, but with 0.2 g/L of anatase TiO2 nanoparticles (⌀ 36 nm), mechanically suspended in the solution by stirring. After synthesis, the films were annealed at 400 °C. Structural characterization by XRD showed that the WO3 films exhibit the crystalline structure of a non-stoichiometric hydrate, whereas, in WO3-TiO2, the WO3 phase was monoclinic. The oxidation of tungsten, as revealed by XPS, was W6+ for both materials. Ti was found to exist mainly as Ti4+ in the composite, with a weak Ti3+ signal. The efficiency of the WO3 films and composites as an oxygen evolution reaction (OER) photo-electrocatalyst was examined. The composite would generate approximately three times larger steady-state photocurrents at 1.2 V vs. SCE in a neutral 0.5 M Na2SO4 electrolyte compared to WO3 alone. The surface recombination of photogenerated electron-hole pairs was characterized by intensity-modulated photocurrent spectroscopy (IMPS). Photogenerated charge transfer efficiencies were calculated from the spectra, and at 1.2 V vs. SCE, were 86.6% for WO3 and 62% for WO3-TiO2. Therefore, the composite films suffered from relatively more surface recombination but generated larger photocurrents, which resulted in overall improved photoactivity.