Separation Of Photogenerated Charge Carriers Research Articles

Ultrasonically aided selective stabilization of pyrrolic type nitrogen by one pot nitrogen doped and hydrothermally reduced Graphene oxide/Titania nanocomposite (N-TiO2/N-RGO) for H2 production.

Herein, we report the simultaneous doping of nitrogen on TiO2 and reduced graphene oxide (N-TiO2/N-RGO) with exclusive stabilization of pyrrolic type nitrogen on RGO network by ultrasonic conditions followed by hydrothermal method for efficient photocatalytic H2 production. Interestingly, during synthesis of N-TiO2/N-RGO composite, pyrrolic type nitrogen in RGO has been exclusively stabilized as confirmed by XPS analysis. The exclusive stabilization of pyrrolic nitrogen changed the optical and electronic properties of N-TiO2/N-RGO nanocomposites by giving two π-electrons to the system for extended conjugation, which enhanced the optical absorption and charge carrier separation efficiency as confirmed by UV-Vis DRS and PL studies. Notably, N-TiO2/N-RGO nanocomposite demonstrated. This enhanced photocatalytic activity can be ascribed to synergetic action of N-TiO2 and N-RGO in optical and photogenerated charge carrier separation. Moreover, the plausible mechanism for exclusive stabilization of pyrrolic type nitrogen and enhanced photocatalytic activity were also proposed.

Boosting molecular oxygen activation ability in self-assembled plasmonic p-n semiconductor photocatalytic heterojunction of WO3/Ag@Ag2O

In recent years, many efforts have been devoted to boost molecular oxygen activation in semiconductor. This is because the reactive oxygen species (ROS) induced by molecular oxygen activation have been confirmed to play a great role in environmental remediation. Herein, we proposed a self-assembled plasmonic p-n heterojunction of WO3/Ag@Ag2O with enhanced molecular oxygen activation ability under visible and near-infrared (NIR) light irradiation. The prepared p-n heterojunction is favorable for the migration and separation of photo-generated hot charge carriers, which can promote the transformation of molecular oxygen to ROS with enhanced photocatalytic performance for norfloxacin (NOR) decomposition. The trapping experiments and Electron spin response (ESR) spectra demonstrate that both superoxide (O2−) and singlet oxygen (1O2) are the main functional ROS for NOR degradation. The yield amount of O2− in the prepared hybrid catalyst is higher than that of pristine catalyst from nitrotetrazolium blue chloride (NBT) degradation. The sustainable generation of 1O2 is mainly ascribed to the charge transfer and energy transfer. Fluorescence spectra method is employed to confirm the generation of hydrogen peroxide (H2O2). The intermediates of NOR degradation are identified by LC/MS, and the possible degradation pathway is proposed in detail. A reasonable charge transfer pathway for the ultra-high hot charge carrier separation is studied. In addition, the as-prepared hybrid composite shows excellent photocatalytic performance for the degradation of rhodamine B (RhB) and ciprofloxacin (CIP). This study provides a promising avenue for fabrication of semiconductor with boosting molecular oxygen activation.

Enhanced CdS quantum dots loading density and charge transport by Sn4+ doping improve the photoelectrochemical performance of TiO2 nanosheets with highly exposed {001} facets

In this paper, the Sn4+ doping has been demonstrated to be an effective strategy to fundamentally enhance the photon absorption, improve the charge transport and increase the surface quantum-dots loading density of TiO2 nanosheets with highly exposed {001} facets, thereby improve their photoelectrochemical performance. The Sn4+ doped TiO2 (STO) nanosheet arrays with different doping concentrations are prepared by a facile one-pot hydrothermal method. And the STO nanosheet arrays (9 mM) enhance light absorption and decrease electron transport resistance, thus improving the photoelectrochemical properties due to the generation of doping energy level and mixed-cation composition of SnxTi1-xO2. Furthermore, after sensitizing CdS quantum-dots, the light absorption intensity of the CdS/STO films increases and the light absorption range extends to visible light region. Remarkably, compared to the pristine TiO2 NSs, the amount of surface active reaction sites of STO NSs increases arising from Sn4+ doping process, which is beneficial to sensitize more uniform and dense CdS quantum-dots on the surface of STO NSs, thereby increasing the heterojunction areas and enhancing the visible light absorption. Additionally, the CdS/STO photoelectrodes show the maximum photocurrent density of 5.71 mA cm−2 at 0 V versus Ag/AgCl, which is 11.4 and 1.7 times higher than those of TiO2 and CdS/TiO2 photoelectrodes respectively, due to the enhanced visible light absorption ability, increased heterojunction areas and superior photogenerated charge carrier separation and transport properties.

Enhanced gas-phase photocatalytic removal of aromatics over direct Z-scheme-dictated H3PW12O40/g-C3N4 film-coated optical fibers

Environmentally benign photocatalytic oxidation is one of the most promising approaches to remove volatile, highly toxic and refractory aromatics, and the key points of gas-phase photocatalytic oxidation of aromatics are to develop efficient photocatalysts and design suitable photoreactors. Here, the custom-designed H3PW12O40/g-C3N4 film-coated optical fiber photoreactor is demonstrated for gas-phase simulated sunlight photocatalytic removal of aromatics including benzene, toluene and m-xylene. At relative humidity of 73% and air atmosphere, the H3PW12O40/g-C3N4 film-coated optical fibers with H3PW12O40 doping level of 3.2% exhibit remarkably higher photocatalytic removal efficiency of benzene, toluene and m-xylene than that of the g-C3N4 film, and apparent rate constant of the H3PW12O40/g-C3N4 film for benzene, toluene and m-xylene removal is 2.42, 1.75 and 3.67 times higher than that of g-C3N4 film. The enhanced photocatalytic activity of the H3PW12O40/g-C3N4 film is ascribed to direct Z-scheme-dictated charge carrier migration mechanism, imparting not only superior photogenerated charge carrier separation ability but also undiminished redox capability of the photogenerated electrons and holes; additionally, the increased contact area of catalyst film with the substrates and improved light harvesting ability give rise to the important contribution to gas-phase photocatalytic removal of aromatics. Moreover, the catalyst film exhibits excellent adhesion, stability and recyclability, and the activity loss is negligible after total thirty times’ catalytic runs.

Enhanced photocatalytic H2 production over dual-cocatalyst-modified g-C3N4 heterojunctions

Ag nanoparticles (NPs) were deposited on the surface of g-C 3 N 4 (CN) by an in situ calcination method. NiS was successfully loaded onto the composites by a hydrothermal method. The results showed that the 10 wt%-NiS/1.0 wt%-Ag/CN composite exhibits excellent photocatalytic H 2 generation performance under solar-light irradiation. An H 2 production rate of 9.728 mmol·g −1 ·h −1 was achieved, which is 10.82-, 3.45-, and 2.77-times higher than those of pure g-C 3 N 4 , 10 wt%-NiS/CN, and 1.0 wt%-Ag/CN composites, respectively. This enhanced photocatalytic H 2 generation can be ascribed to the co-decoration of Ag and NiS on the surface of g-C 3 N 4 , which efficiently improves light harvesting capacity, photogenerated charge carrier separation, and photocatalytic H 2 production kinetics. Thus, this study demonstrates an effective strategy for constructing excellent g-C 3 N 4 -related composite photocatalysts for H 2 production by using different co-catalysts. g-C 3 N 4 co-decorated with Ag nanoparticles and NiS co-catalysts exhibits enhanced migration and separation of photoexcited charge carriers and, thus, improved photocatalytic H 2 generation owing to Ag and NiS serving as electron acceptors, surface-active sites, and H 2 -evolution co-catalysts.

Quantum Dots as Photocatalysts for Bicarbonate Reduction to Solar Fuels: Formate Production from CuS, CuInS2, and CuInS2/ZnS

ABSTRACTIn this study, non-cadmium-based quantum dots were synthesized and used as catalysts for the photochemical reduction of bicarbonate to value-added formic acid. Three types of quantum dots (CuS, CuInS2, and CuInS2/ZnS) were chosen because of they feature environmentally benign properties, possess wide optical absorption, and exhibit excellent photocatalytic activity. All three photocatalysts exhibited excellent efficiency in the photo-reduction of bicarbonate to formic acid, with CuInS2/ZnS showing the highest photon to formate conversion efficiency of 6.07 ± 0.07%. We attribute these exceptional results to their smaller bandgap leading to enhanced visible light absorption and the application of an appropriate hole scavenger that prolongs photo-generated charge carrier separation. To the best of our knowledge, the application of quantum dots in photocatalysis is still quite limited; this report describes the highest apparent quantum efficiency (AQE) to date.

Two-dimensional Sn2Ta2O7 nanosheets as efficient visible light-driven photocatalysts for hydrogen evolution

Two-dimensional Sn2Ta2O7 nanosheets with a thickness of ~ 10 nm were successfully prepared through a novel tantalic acid-based solid-state reaction method at reduced temperature. The as-obtained samples were characterized by powder X-ray diffraction (XRD), ultraviolet–visible (UV–Vis) diffuse reflectance spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) analysis. The photocatalytic performance of Sn2Ta2O7 nanosheets was evaluated by photocatalytic water splitting for hydrogen evolution under visible light irradiation (λ ≥ 400 nm). The Sn2Ta2O7 nanosheets with a large surface area of 25.9 m2·g−1 showed higher H2 production activity, which was about 4.4 times higher than that of bulk Sn2Ta2O7 in lactic acid aqueous solutions using Pt as a co-catalyst. The improved photocatalytic performance mainly benefited from the nanosheet structure, which provided abundant surface active sites and facilitated the photogenerated charge carrier separation efficiently. This work may open up new opportunity to develop novel nanostructured tantalum-based semiconductors with improved catalytic performance for solar energy conversion.

Strategy for improving the visible photocatalytic H2 evolution activity of 2D graphitic carbon nitride nanosheets through the modification with metal and metal oxide nanocomponents

The semiconductor based photocatalytic water splitting is a promising approach for the production of environmentally friendly, clean, and cost-effective hydrogen fuel by utilizing the solar energy. Graphitic carbon nitride (g-C3N4) has emerged as an excellent material to produce hydrogen via photocatalytic water splitting reactions, however the limited visible light absorption and fast charge recombination restricts the further real practical applications. Fabrication of multicomponent g-C3N4 based heterostructured photocatalytic system is an effective strategy to enhance the charge separation and thereby photocatalytic efficiency. Here, a new g-C3N4-Au-In2O3 ternary system with efficient photogenerated charge carrier separation is successfully designed. The morphology, structure, phase and electronic environments of g-C3N4, Au and In2O3 in the composite were studied by different characterization methods. As expected, the optimized g-C3N4-Au-In2O3 catalyst shows excellent photocatalytic H2 evolution rate. The improved photocatalytic H2 evolution rate could be attributed to the formation of heterojunctions between g-C3N4, Au and In2O3 components; improved visible light harvesting via surface plasmon resonance (SPR) effect of metal Au nanoparticles (NPs); and effective photogenerated electron-hole pairs separation. The proposed work is expected to provide a new concept to fabricate g-C3N4 based ternary heteronanostructures with metal NPs and metal oxide semiconductors not only to a photocatalytic applications but also opens up to variety of optoelectronic applications.

Fabrication of nanoheterostructures of boron doped ZnO-MoS2 with enhanced photostability and photocatalytic activity for environmental remediation applications

In this work, we have developed two dimensional (2D) nanosheets-nanoparticles (0D) nanoheterostructures of boron-doped ZnO nanoparticles loaded over MoS2 nanosheets with enhanced photocatalytic activity for pollutant removal. A series of nanoheterostructures with varying amount of MoS2 nanosheets were prepared using facile hydrothermal method and characterized by x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) techniques to confirm there successful synthesis. The optimized nanoheterostructure photocatalyst with 1 wt% of MoS2 nanosheets (BZM1) exhibits superior photocatalytic activity for pollutant removal under visible light illumination. The superior photocatalytic activity of BZM1 nanoheterostructure has been supported by photoluminescence (PL) studies which show the remarkably decreased PL intensity signifying the low recombination rate of photogenerated charge carriers. In addition, the formation of 0D-2D heterojunction plays a significant role in enhancing the photocatalytic activity by accelerated photogenerated charge carriers separation in space and ultimately improved photocatalytic activity. Furthermore, the plausible photocatalytic mechanism has been discussed in detail on the basis of active species trapping experiment which validate the significant role of holes and hydroxyl radicals in degradation process. Overall, this work paves way for the facile fabrication of 0D-2D nanoheterostructures for diverse applications.

Revealing the role of kapok fibre as bio-template for In-situ construction of C-doped g-C3N4@C, N co-doped TiO2 core-shell heterojunction photocatalyst and its photocatalytic hydrogen production performance

For the first time, C-doped g-C3N4@C, N co-doped TiO2 core-shell heterojunction photocatalyst was successfully prepared by an in-situ one-pot hydrothermal bio-template approach, assisted by calcination treatment at 500 °C. Kapok fibre was used as a bio-templates and in-situ C doping in g-C3N4 and TiO2 during the formation of core-shell heterojunction photocatalyst. Moreover, the used of urea as g-C3N4-precursor also contribute to band-gap narrowing by an in-situ carbon and nitrogen doping in TiO2. Various characterisation techniques were employed to understand the effect TiO2 precursor concentration on the evolution of core-shell nanostructure heterojunction photocatalyst that can affect and boost the catalytic activity. The detailed understanding of the concurrent growth of C-doped g-C3N4 (CCN) and C, N co-doped TiO2 mechanism, as well as the formation of core-shell nanostructures heterojunction formation, are also proposed in this study. Our finding indicated that the bio-template core-shell nanostructure heterojunction photocatalysts showed a dramatic increase in photoinduced electron-hole separation efficiency as demonstrated by the photoelectrochemical and photoluminescence analyses. The enhancement in photogenerated charge carrier separation and narrower band gap resulted in superior photocatalytic activities with the highest rate of hydrogen production was recorded by CCN/T-1.5 sample (625.5 μmol h−1 g−1) in methanol aqueous solution. The well-developed interconnected heterojunction formation with appropriate CCN and TiO2 contents in core-shell nanoarchitectures system is a prime factor for the future design of a highly efficient visible-light-driven photocatalyst.

C/N Vacancy Co‐Enhanced Visible‐Light‐Driven Hydrogen Evolution of g‐C3N4 Nanosheets Through Controlled He+ Ion Irradiation

Graphitic carbon nitride (g‐C3N4) is reported to be a promising metal‐free semiconductor for photocatalytic water splitting. However, the performance of g‐C3N4 is substantially limited by its insufficient visible‐light absorption and low photogenerated charge carrier separation efficiency. In this work, an innovative method (ion irradiation) to efficiently introduce both defined C‐ and N‐vacancies (VC and VN) simultaneously into g‐C3N4 nanosheets are explored. Unlike traditional chemical methods, by controlling He+ ion fluence, tunable vacancy concentrations are able to be obtained in g‐C3N4. Defect‐engineered g‐C3N4 shows highly improved performance under optimized conditions, the defective g‐C3N4 exhibits a significantly higher (2.7‐fold) hydrogen evolution rate of 1271 µmol g−1 h−1 than that of the g‐C3N4 nanosheets under visible light (λ > 420 nm) illumination. Meanwhile, the defective g‐C3N4 exhibits a significantly enhanced (threefold) photocurrent density as photoanodes for photoelectrochemical (PEC) water splitting. Further characterizations show that the enhanced visible light absorption and an extended charge carrier lifetime, can be ascribed to the presence of C‐ and N‐ vacancies. These experimental results are in line with density functional theory (DFT) calculations. Therefore, the present work shows that defect‐engineering on g‐C3N4 using ion irradiation technique, is an effective, controllable, and defined approach to improve the photocatalytic and PEC water splitting performance of g‐C3N4.

Snowflake-like Cu2S/Zn0.5Cd0.5S p–n heterojunction photocatalyst for enhanced visible light photocatalytic H2 evolution activity

Abstract Building a p–n heterojunction can accelerate the separation and transfer of photoinduced charges, which is considered to be a promising approach to constructing photocatalysts with excellent H2 evolution activities. Herein, novel snowflake-like Cu2S/Zn0.5Cd0.5S heterojunction photocatalysts were successfully synthesized. Compared to the pure Cu2S and Zn0.5Cd0.5S, the as-synthesized Cu2S/Zn0.5Cd0.5S showed remarkably improved H2 evolution rate. Cu2S/Zn0.5Cd0.5S with a Cu2S content of 3 wt% showed the optimized H2 evolution rate of 4923.5 µmol g−1 h−1 in Na2S–Na2SO3 solutions, and the corresponding apparent quantum efficiency is 30.2% at 420 nm. The experimental results indicate that the enhanced H2 evolution rates can be attributed to the fabrication of the p–n heterojunction between Cu2S and Zn0.5Cd0.5S, effectively boosting photogenerated charge carriers separation and transfer. Moreover, a plausible mechanism was proposed.

Gold nanoparticle decorated bismuth sulfide nanorods for enhanced photoelectrochemical hydrogen production

The design of photo-electrodes with good light absorption, effective photo-generated charge carrier separation and fast charge transportation are key parameters for photoelectrochemical (PEC) hydrogen generation.

ZnO/Ag/Ag2WO4 photo-electrodes with plasmonic behavior for enhanced photoelectrochemical water oxidation.

Ag-based compounds are excellent co-catalyst that can enhance harvesting visible light and increase photo-generated charge carrier separation owing to its surface plasmon resonance (SPR) effect in photoelectrochemical (PEC) applications. However, the PEC performance of a ZnO/Ag/Ag2WO4 heterostructure with SPR behavior has not been fully studied so far. Here we report the preparation of a ZnO/Ag/Ag2WO4 photo-electrode with SPR behavior by a low temperature hydrothermal chemical growth method followed by a successive ionic layer adsorption and reaction (SILAR) method. The properties of the prepared samples were investigated by different characterization techniques, which confirm that Ag/Ag2WO4 was deposited on the ZnO NRs. The Ag2WO4/Ag/ZnO photo-electrode showed an enhancement in PEC performance compared to bare ZnO NRs. The observed enhancement is attributed to the red shift of the optical absorption spectrum of the Ag2WO4/Ag/ZnO to the visible region (>400 nm) and to the SPR effect of surface metallic silver (Ag0) particles from the Ag/Ag2WO4 that could generate electron–hole pairs under illumination of low energy visible sun light. Finally, we proposed the PEC mechanism of the Ag2WO4/Ag/ZnO photo-electrode with an energy band structure and possible electron–hole separation and transportation in the ZnO/Ag/Ag2WO4 heterostructure with SPR effect for water oxidation.

Sol-gel synthesis of new ZnFe2O4/Na-bentonite composites for simultaneous oxidation of RhB and reduction of Cr(VI) under visible light irradiation

To improve the photogenerated charge carrier separation and stability of ZnFe2O4, we prepared new ZnFe2O4/Na-bentonite composites using Na-bentonite as the carrier via a sol-gel method. The composition, surface morphology and optical properties of samples were characterized by XRD, TEM, XPS, FTIR and UV–vis DRS analysis. The results of TEM and XPS show that the ZnFe2O4 nanoparticles spread on the thin layers of Na-bentonite due to intercalation with Na-bentonite. The simultaneous effect of the Cr(VI)-RhB wastewater system was investigated by ZnFe2O4/Na-bentonite composites, the removal rate are 88.6% for Cr(VI) and 94.2% for RhB in 120 min, which is 1.3-fold higher of Cr(VI) reduction than that of the individual ones. Based on experimental results of PL and reactive species involved in the removal of RhB and Cr(VI), the enhanced photocatalytic activity of the new ZnFe2O4/Na-bentonite composite could be due to visible-light adsorption ability, larger interfacial area, as well as effective transfer and prolonged charge-hole separation.

Highly efficient visible-light-assisted photocatalytic hydrogen generation from water splitting catalyzed by Zn0.5Cd0.5S/Ni2P heterostructures

Development of heterostructured photocatalysts which can facilitate spatial separation of photo-generated charge carriers is crucial for achieving improved photocatalytic H2 production. Consequently, herein, we report the synthesis of Zn0.5Cd0.5S/Ni2P heterojunction photocatalysts with varying amount of Ni2P, 0.5 (S1), 1 (S2), 3 (S3), 5 (S4) and 10wt% (S5) for the efficient visible-light-assisted H2 generation by water splitting. The heterostructures were characterized thoroughly by PXRD, FE-SEM, EDS, HR-TEM and XPS studies. FE-SEM and HR-TEM analyses of the samples unveiled the presence of Zn0.5Cd0.5S microspheres composed of smaller nanocrystals with the surface of the microspheres covered with Ni2P nanosheets and the intimate contact between the Zn0.5Cd0.5S and the Ni2P. Further, visible-light-assisted photocatalytic investigation of the samples showed excellent water splitting activity of the heterostructure, Zn0.5Cd0.5S/1wt%Ni2P (S2) with very high H2 generation rate of 21.19 mmol h−1g−1 and the AQY of 21.16% at 450 nm with turnover number (TON) and turnover frequency (TOF) of 251,516 and 62,879 h−1 respectively. Interestingly, H2 generation activity of S2 was found to be about four times higher than that of pure Zn0.5Cd0.5S (5.0 mmol h−1g−1) and about 240 times higher than that of CdS/1wt%Ni2P. The enhanced H2 generation activity of S2 has been attributed to efficient spatial separation of photogenerated charge carriers and the presence of highly reactive Ni2P sites on the surface of Zn0.5Cd0.5S microspheres. A possible mechanism for the enhanced photocatalytic H2 generation activity of Zn0.5Cd0.5S/1wt%Ni2P (S2) has been proposed and is further supported by photoluminescence and photocurrent measurements. Furthermore, the catalyst, S2 can be recycled for several cycles without significant loss of catalytic activity and photostability. Remarkably, the H2 generation activity of S2 was found to be even higher than the reported examples of ZnxCd1-xS doped with noble metal cocatalysts. Hence, the present study highlights the importance of Zn0.5Cd0.5S/Ni2P heterostructures based on non-noble metal co-catalyst for efficient visible-light-driven H2 production from water splitting.

Facile Fabrication of Novel Hetero-Structured Organic–Inorganic High-Performance Nanocatalyst: A Smart System for Enhanced Catalytic Activity toward Ciprofloxacin Degradation and Oxygen Reduction

In this study, a novel organic–inorganic polyaniline/silver/silver molybdate (PANI/Ag/Ag2MoO4) heterojunction nanocatalyst has been fabricated by in situ depositing Ag2MoO4 on p-type PANI to explore two different catalytic properties, e.g., photocatalytic degradation of antibiotic ciprofloxacin (CIP) and electrocatalytic reduction of oxygen. After hybridization of Ag2MoO4 with PANI, the p-n heterojunction developed and consequently z-scheme induced efficient photogenerated charge carrier separation and migration occur due to the internal electric field developed at the heterojunction interface. Compared with pure Ag2MoO4, the heterojunction nanocomposite possessed significantly enhanced photocatalytic activity as evidenced by the degradation of Congo Red (CR) dye under UV light irradiation. The optimum composite with 20 wt % PANI nanorods exhibited paramount photocatalytic activity over all the composites. Subsequently, 99.99% of CIP removal was achieved with this optimal composite within 40 min. On the o...

Facile fabrication of BiOCl/RGO/protonated g-C3N4 ternary nanocomposite as Z-scheme photocatalyst for tetracycline degradation and benzyl alcohol oxidation

A novel ternary BiOCl/RGO/PCN nanocomposite was successfully fabricated through coupling-protonated g-C3N4 (PCN) sheets with GO by electrostatic attraction, followed by in situ synthesis of BiOCl layers on the surface on PCN/GO via hydrothermal reaction and simultaneously achieving the reduction in GO. The as-prepared BiOCl/RGO/PCN composite exhibited significantly enhanced photoactivities toward the degradation of representative antibiotic tetracycline and selective aerobic oxidation of benzyl alcohol compared to pristine g-C3N4, protonated g-C3N4, pure BiOCl and binary BiOCl/PCN composite under simulated solar light irradiation. The structure–property relationship was explored by several effective characterization techniques. The results show that RGO coordinated well with two semiconductors of BiOCl and PCN, and BiOCl/RGO/PCN composite with closely contacted interface exhibited broad optical adsorption range and effective photogenerated charge carrier separation efficiency, which are attributed to the improved photocatalytic performance. The results also demonstrate that a Z-scheme charge process was formed between BiOCl and PCN with RGO serving as electron transfer medium to promote the fast transporting of photoinduced electrons. Therefore, more photoinduced electrons and holes could retain in the CB of PCN and in the VB of BiOCl with strong redox ability, respectively, which is beneficial to the further effective generation of active radicals participating in photocatalytic reaction. This work provides a promising Z-scheme ternary photocatalyst with facile synthetic method and potential application in environmental pollution elimination and green oxidative organic transformation.

Manganese oxide at cadmium sulfide (MnOx@CdS) shells encapsulated with graphene: A spatially separated photocatalytic system towards superior hydrogen evolution

Exploring novel, high-efficiency and durable catalysts is of vital importance to expedite current research on photocatalytic H2 evolution and address the energy and environmental issues. Herein, we rationally designed and synthesized a novel MnOx@CdS@GR photocatalyst with spatially separated dual co-catalysts for efficient visible-light-driven hydrogen production activity. In this spatially separated photocatalytic system, reduced graphene oxide (GR) and MnOx nanoparticles were anchored on the outer and inner surfaces of CdS shells acting as electron and hole collectors, respectively. The composition, microstructure and optical properties of the samples were thoroughly investigated. Photoluminescence spectra and photocurrent response as well as electrochemical impedance spectra were employed to reveal the separation and transfer ability of photo-generated charge carriers in the spatially separated MnOx@CdS@GR catalyst. Benefit from the synergistic effect including boosted light absorption capacity, enlarged specific surface area and increased separation and transfer efficiency of electron/hole pairs, the MnOx@CdS@GR exhibited superior H2 evolution performance, and the optimized H2-evolution rate reached a value of 5.45 mmol h−1 g−1, which is approximately 7.2 times than that of bare CdS. Moreover, this novel catalyst also displayed a long-term stability without apparent debasement in H2 evolution activity. Finally, the photocatalytic mechanism was proposed and discussed.

Metal-induced Z-scheme CdS/Ag/g-C3N4 photocatalyst for enhanced hydrogen evolution under visible light: The synergy of MIP effect and electron mediator of Ag

Efficient photogenerated charge carriers separation and wide absorption wavelength range are important factors for improving photocatalytic performance and application potential of photocatalysts. Applying metal-induced photocatalysis and Z-scheme photocatalysis are two efficient ways to achieve the above aims. Herein, a metal-induced Z-scheme CdS/Ag/g-C3N4 photocatalyst was prepared for photocatalytic H2 evolution under visible light irradiation. X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), scanning electron microscopy (SEM), high resolution field emission scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance (UV–vis DRS), photoluminescence spectrum (PL), transient photocurrent and electrochemical impedance spectroscopy (EIS) were performed to characterize the structures, optical and electrochemical properties. Results demonstrated that CdS/Ag/g-C3N4 (Ag 3 wt%, g-C3N4 15 wt%) exhibited superior photo-response performance and more efficient photogenerated carriers separation, compared to the counterparts. Owing to the desired properties of CdS/Ag/g-C3N4, high H2 evolution rate of 1376.0 μmol /h∙g in lactic acid scavenger solution was achieved, which was 3.12 and 1.76 times of those of CdS and CdS/g-C3N4. The roles of Ag on CdS/Ag/g-C3N4 were discussed, and it was believed that both metal-induced surface plasmon resonance effect and the Z-scheme electron mediator mechanism synergistically contributed to the enhanced performance. Possible mechanisms for photoelectrons transfer and photocatalytic H2 evolution were proposed.