Photocatalytic Decomposition Of Water Research Articles

ZnIn2S4/In(OH)3 hollow microspheres fabricated by one-step l-cysteine-mediated hydrothermal growth for enhanced hydrogen production and MB degradation

An intervening barrier for photocatalytic water decomposition and pollutant degradation is the frustratingly quick recombination of e− - h+ pairs. Delicate design of heterojunction photocatalysts by coupling the semiconductors at nanoscale with well-matched geometrical and electronic alignments is an effective strategy to ameliorate the charge separation. Here a facile and environment-friendly l-cysteine-assisted hydrothermal process under weakly alkaline conditions is demonstrated for the first time to fabricate ZnIn2S4/In(OH)3 hollow microspheres with intimate contact, which are verified by XRD, SEM, (HR)TEM, XPS, N2 adsorption-desorption, UV–Vis DRS and photoluminescence spectra. ZnIn2S4/In(OH)3 heterostructure (L-cys/Zn2+ = 4, molar ratio) with a band-gap of 2.50 eV, demonstrates the best photocatalytic performance for water reduction and MB degradation under visible light, outperforming its counterparts (In(OH)3 and ZnIn2S4). The excellent activity of ZnIn2S4/In(OH)3 heterostructure arises from the intercrossed band-edge positions as well as the unique hollow structure with large surface area and wide pore-size distribution, which are beneficial for the efficient charge migration from bulk to surface as well as at the interface between ZnIn2S4 and In(OH)3. This work provides an efficient and eco-friendly strategy for one-pot synthesis of heterostructured composites with intimate contact for photocatalytic application.

Operando NMR study on the effect of photon flux and wavelength on photocatalytic reforming of methanol

Photocatalytic decomposition of water for hydrogen generation is a promising way to obtain clean energy sources, and photon flux together with photon energy play particularly important roles in photocatalytic reactions. However, a study of their effects under real conditions is still limited, thus leaving a gap in our understanding. Herein, an operando NMR technique was proposed to systematically study the effects of photon flux and photon energy on TiO2 and Pd/TiO2-based photocatalytic methanol reforming reactions by changing the irradiation wavelength from 350 to 400 nm. Experimental results showed that the productivity of the methanol oxidation reaction can be obviously influenced by photon flux for the pure TiO2 and Pd/TiO2 sample, but longer wavelengths (lower photon energy) can slow down the reaction. Meanwhile, on the Pd/TiO2 catalyst a significantly enhanced activity in CH3OH oxidation was found at the irradiation with the wavelength of 380 nm, which activity in CH3OH oxidation is even higher than that observed under the irradiation with the wavelength of 365 nm. This enhanced oxidation activity can be attributed to the surface plasmon resonance of the cocatalyst.

Amorphous tungsten phosphosulphide-modified CdS nanorods as a highly efficient electron-cocatalyst for enhanced photocatalytic hydrogen production.

Improving the utilization rate of photogenerated electrons generated by visible light excitation is an important factor to improve the activity of photocatalytic decomposition of water for hydrogen evolution. In this study, amorphous tungsten phosphosulphide nanoparticle (WPS NP)-modified CdS (WPS/CdS) catalysts were successfully prepared by a simple physical mixing method. The activity of the 15% WPS/CdS composite catalyst is the best, and the average hydrogen production rate reached 123 257 μmol g-1 in 5 h, and the highest AQE of 9.15% is derived at 420 nm for the 15% WPS/CdS composite catalyst. Simultaneously, five cycle stability tests were performed on the 15% WPS/CdS composite catalyst, and the results show that the 15% WPS/CdS composite catalyst exhibits a high stability. WPS NPs not only improve the visible light absorption rate, but also provide a large number of exposed active sites for the hydrogen evolution reaction. These active sites can capture photogenerated electrons on CdS NRs quickly, and can be used for the hydrogen evolution reaction quickly, promoting the transmission and separation of photogenerated charges and inhibiting the recombination of photogenerated electron and hole pairs. Thus, the utilization rate of photogenerated electrons generated by visible light is improved, and the activity of the photocatalyst is significantly increased.

Investigation of the mechanism of overall water splitting in UV-visible and infrared regions with SnC/arsenene vdW heterostructures in different configurations.

Monolayer arsenene presents good stability and high photogenic carrier mobility. However, a high photogenic electron and hole pair recombination rate seriously reduces its photocatalytic activity. The photocatalytic activity can be effectively improved by building type II heterostructures. In this work, SnC/arsenene heterostructures in three configurations are studied using first-principles calculations. Their structure, stability, and electronic and photocatalytic properties are investigated. It is found that all SnC/arsenene heterostructures are stable, and form type-II band edges, which effectively promote the transfer of photogenerated electrons from the SnC monolayer to the arsenene sheet. The charge transfer between SnC and arsenene leads to a built-in electric field in the interface region, which is favorable for inhibiting photogenic electron and hole pair recombination. Compared with the monolayer arsenene, the photocatalytic activity is greatly improved and the absorption spectrum of SnC/arsenene heterostructures is expanded. Attractively, these three heterostructures present two different photocatalytic mechanisms. H1 and H3 configurations were taken as examples to study their photocatalytic properties for overall water splitting at varying pH values and external strains. We found that alkaline conditions were more favorable for photocatalysis of SnC/arsenene heterostructures. In particular, H3 can still achieve full photocatalytic water decomposition in the near infrared region. These results show that the SnC/arsenene heterostructures are a prospective material for photocatalysis application.

Unique synergistic effects of ZIF-9(Co)-derived cobalt phosphide and CeVO4 heterojunction for efficient hydrogen evolution

The photocatalytic decomposition of water to produce hydrogen is an important process, through which solar energy can be converted to chemical energy. Non-precious metal phosphides have quietly attracted attention as an emerging inexpensive photocatalyst. In this study, we reported that a CoP/CeVO4 hybrid photocatalyst exhibited high hydrogen evolution efficiency owing to EY (eosin Y) sensitization under visible light irradiation for the first time, and the amount of generated hydrogen reached 444.6 μmol in 5 h. The CoP/CeVO4 nanohybrids were synthesized by a simple chemical precipitation method. The coupling of CoP and CeVO4 with ZIF-9 as a precursor could be completed in one step. The CeVO4 particles were firmly attached to the surface of the CoP particles to form a “small point” to “big point” heterojunction. The results of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, EDX, and transmission electron microscopy showed the formation of CoP and CeVO4 nanoparticles and the structure of the composite. Based on a detailed analysis of the Mott-Schottky plot, the UV-vis diffuse reflectance spectra, photocurrent-time (it) curve, Tafel curve, Nyquist curve (EIS), linear volt-ampere curve (LSV), and steady-state fluorescence spectra were studied. The time-resolved photoluminescence measurements indicated that the reason for the high-efficiency hydrogen evolution of CoP/CeVO4 was that the bands of CoP and CeVO4 were bent due to the existence of the Schottky barrier, and a heterojunction was formed between CoP and CeVO4, which generated an internal electric field and accelerated the charge transfer. In addition, the synergistic effect between CoP and CeVO4 provided a new hydrogen-evolution activity center for each of them. The improved carrier separation efficiency and the decrease in the photo-generated recombination rate led to the excellent photocatalytic hydrogen-evolution activity of the CoP/CeVO4 composite catalyst. This work provides a new strategy for modulating the electronic structure and carrier behavior of transition metal phosphide photocatalysts.

Simultaneous hydrogen production and pollutant degradation by photocatalysis of wastewater using liquid phase plasma

Ethanolamine released from a nuclear power plant was degraded by photocatalytic decomposition using plasma in the liquid phase with metal-incorporated photocatalysts. Metal-incorporated titanium dioxide photocatalysts were employed with carbon nanotubes and carbon nanofibers as a support. The photocatalytic decomposition of ethanol amine-contained water induced the degradation of ethanolamine and H2 evolution, simultaneously. The degradation of ethanolamine and H2 evolution were elevated by incorporating Ni on titanium dioxide nanocrystallites. The rate of H2 evolution in the ethanolamine-containing water was higher than that in pure water, which was attributed to the additional H2 evolution by the photodecomposition of ethanolamine in water.

SrTiO3/TiO2 heterostructure nanowires with enhanced electron-hole separation for efficient photocatalytic activity

Heterostructure is an effective strategy to facilitate the charge carrier separation and promote the photocatalytic performance. In this paper, uniform SrTiO3 nanocubes were in-situ grown on TiO2 nanowires to construct heterojunctions. The composites were prepared by a facile alkaline hydrothermal method and an in-situ deposition method. The obtained SrTiO3/TiO2 exhibits much better photocatalytic activity than those of pure TiO2 nanowires and commercial TiO2 (P25) evaluated by photocatalytic water splitting and decomposition of Rhodamine B (RB). The hydrogen generation rate of SrTiO3/TiO2 nanowires could reach 111.26 mmol·g−1·h−1 at room temperature, much better than those of pure TiO2 nanowires (44.18 mmol·g−1·h−1)and P25 (35.77 mmol·g−1·h−1). The RB decomposition rate of SrTiO3/TiO2 is 7.2 times of P25 and 2.4 times of pure TiO2 nanowires. The photocatalytic activity increases initially and then decreases with the rising content of SrTiO3, suggesting an optimum SrTiO3/TiO2 ratio that can further enhance the catalytic activity. The improved photocatalytic activity of SrTiO3/TiO2 is principally attributed to the enhanced charge separation deriving from the SrTiO3/TiO2 heterojunction.

Preparation of Zn0.5Cd0.5S@Ni-Glycerate composite for photocatalytic water reduction

Large specific surface is beneficial to improve the performance of catalyst in the application of water photolysis. In this work, we designed and successfully prepared the metal compound Ni-Glycerate with a large specific surface area, and combined it with Zn0.5Cd0.5S to form Zn0.5Cd0.5S@Ni-Glycerate core-shell structure nanocomposites. It was revealed that the introduction of nickel-glycerate can promote the separation of photoinduced charges and accelerate the photocatalytic water decomposition reaction. The optimized H2 production rate on Zn0.5Cd0.5S@Nickel-glycerate (3%) can reach 2800 μmol/h/0.1 g, about 6 times that of pure Zn0.5Cd0.5S. This work indicates that the sulfide-metal organic complex can play a synergistic role in the entire photocatalytic reaction.

A Theoretical Perspective on Charge Separation and Transfer in Metal Oxide Photocatalysts for Water Splitting

AbstractSemiconductor‐based photocatalytic decomposition of water is one of the most promising techniques to produce clean and renewable energy in the future. Photogenerated charge separation and transfer is considered as one of the crucial steps controlling the conversion efficiency of solar energy in heterogeneous photocatalysis. Many experimental methods have been developed to enhance the efficiency of this process, such as fabricating junction structures, manipulating exposed facets, and loading suitable cocatalysts. Besides a variety of time and spatial resolved spectroscopic techniques, density functional theory calculations have been widely used to explore the photoinduced charge dynamics due to the advances of relevant theory and methodologies along with the improved computer performance. This article reviews recent theoretical researches mainly by means of density functional theory calculations in the charge separation and transportation in metal oxide photocatalytic systems. We introduce some common theoretical and computational methods for investigating physicochemical properties of photocatalytic materials, discuss the charge mobility in bulk and surface of semiconductors, the interfacial charge transfer in junction structures, and the role of cocatalysts in complex photocatalysts, and then evaluate potential research directions for superior photocatalytic systems on the basis of computational investigation and theoretical comprehension of intrinsic properties.

Density functional theory calculation on two-dimensional MoS2/BiOX (X = Cl, Br, I) van der Waals heterostructures for photocatalytic action

Abstract Bismuth oxyhalide (BiOX)-based heterostructures have attracted much attention due to their promotion effect on photocatalytic performance. Nonetheless, there is a lack of theoretical understanding on the relationship between the BiOX-induced interface and the enhancement of photocatalytic activity. In the present work, density functional theory (DFT) calculations were conducted to investigate the energy band structure, charge transfer and optic properties of layered MoS 2 /BiOX (X = Cl, Br, I) van der Waals (vdW) heterojunctions. All the MoS 2 /BiOX heterojunctions have lower band gaps, smaller effective mass and better light absorption ability than BiOX monolayers. Moreover, electrons transfer from MoS 2 to BiOX, and MoS 2 /BiOX heterojunctions show typical type-II band arrangement. Importantly, MoS 2 /BiOI presents significant performance in the carrier mobility and light absorption ability among the three heterostructures, which can facilitate effective separation of photo-generated electron-hole pairs and enhance photocatalytic activity. It is disclosed that the band edges MoS 2 /BiOX are suitable for the photocatalytic decomposition of water into oxygen. It is especially so for MoS 2 /BiOI which can affect full photocatalytic water splitting. The results clarify why the combination of MoS 2 and BiOX for the generation of MoS 2 /BiOX vdW heterojunctions could result in excellent photocatalytic activity, and disclose why MoS 2 /BiOI is the best among the three for photocatalytic water splitting.

Photocathodic Protection Performance of ZnS-CdS-Ag@TiO2 for 403SS Under Visible Light

Up to date, TiO2 nanotubes have attracted extensive interest in photocatalysts [1], dye-sensitized solar cells [2], photocatalytic decomposition of water into hydrogen [3], and sensors [4]. In addition, some researchers have reported that the photoelectrochemical properties of TiO2 could be applied to the cathodic protection of metals [5-7]. Compared with conventional cathodic protection, the photocathodic protection technology has no need to supply current or sacrificial anodes, and can achieve green and nonpolluting protection of metals [5]. However, there are two key drawbacks to the practical application of photocathodic protection of bare TiO2 films. In this work, an all-solid-state Z-scheme type CdS-Ag@TiO2 nanocomposite was fabricated by pulse electrodeposition and the successive ion layer adsorption and reaction (SILAR) technique. To suppress CdS photocorrosion, a ZnS shell was provided by the SILAR method. The CdS was chosen to sensitize the TiO2, and Ag acted as a transporter of electrons. This nanocomposite shows an impressive photocathodic protection performance for the 403 stainless steel (SS). The morphologies were observed using field-emission scanning electron microscope Hitachi FE-SEM S4800. The results showed that the film possessed a porous network morphology and the network consisted of scrolled-up nanowires. It can be observed that CdS and ZnS particles were uniformly distributed on the nanowire surface. The EDX spectrum and XPS measurement revealed that the ZnS-CdS-Ag@TiO2 films were composed of Ti, O, Ag, Cd, Zn and S. The UV-vis absorption spectra showed that the photoabsorption spectrum of the composite film was expanded into the visible light region. The corrosion performances of 403 stainless steel in a 0.5 M NaCl solution coupled to a titanate film photoanode in 1.0 M NaOH solutions were evaluated by photogenerated potential and electrochemical impedance spectroscopy (EIS). The steel was coupled to the composite photoanode under illumination and dark conditions. Under irradiation, the stabilized potential of 403SS coupled to the composite photoanode was recorded at approximately -1174 mV (vs.SCE). Under dark condition, the composite photoanode still provides the certain cathodic protection for the steel. To further study the corrosion process of 403SS under photocathodic protection, EIS was performed under illumination. It was found that the impedance arc of the 403SS coupled to the composite photoanode was markedly smaller. This may be due to a larger number of photogenerated electrons being transferred from the photoanode to the the surface of 403SS, leading to the cathodic current density increase for the steel. The EIS result revealed composite film could provide a good photocathodic protection effect for 403SS. Acknowledgements This work was supported by the the National Natural Science Foundation of China (Nos. 51801013) and the Natural Science Foundation of Shandong Province of China (ZR2016BP11) and A Project of Shandong Province Higher Educational Science (J16LC18).

(Invited) Confined Molecular Electrocatalyst for Electrochemical and Photoelectrochemical Hydrogen Evolution Reaction

Hydrogen is the most important clean fuels in the future and production of hydrogen from water by solar energy is required. Photoelectrochemical (PEC) and photocatalytic decomposition of water has been studied for long time. Most serious problem of PEC production of hydrogen from water is that while semiconductor electrodes with small energy gap can absorb large fraction of solar energy but unstable, those with large energy gap are stable but can absorb only small fraction of solar energy. This can be solved by using semiconductor of small gap and separating the reaction site from the surface. We have constructed viologen molecular layer on hydrogen terminated Si(111) surface and then Pt complex was introduced within the molecular layer by ion-exchange reaction [1-3]. Significant decrease of overpotential for dark hydrogen evolution reaction (HER) at n-Si electrode was observed by this modification. Further improvement was achieved by constructing multi-viologen-Pt -layers. Viologen layers and Pt species act as electro relay and HER catalyst, respectively. Phoelectrochemical HER at p-Si(111) electrode is also accelerated by the modification with viologen-Pt layers. In situ XAFS study during HER showed that Pt complexes not Pt particles acted as HER catalysts, i.e., confined molecular catalysts, as schematically shown in the figure [3]. The decrease of white line intensity suggests the formation of a hydride complex as an intermediate of HER. The formation of Pt particles may have been inhibited since the complexes are separated by molecular layers. Confined molecular catalyst by viologen-Pt layers for HER was also constructed on indium tin oxide (ITO). While two redox peaks corresponding to viologen dication/ radical cation (V2+/V+•) and viologen radical cation/neutral form (V+•/V0) were observed in cyclic voltammogram (CV) of viologen monolayer modified ITO electrode without Pt complex, no redox peaks but large current due to HER was observed at viologen monolayer modified ITO electrode with Pt complex. Spectroelectrochemical measurements at constant potentials and during potential scan showed stable spectra corresponding to radical cation (V+•) and neutral form (V0) of viologen at potentials between V2+/V+• and V+•/V0 redox peaks and more negative than V+•/V0 redox peak, respectively, at an ITO electrode modified by viologen monolayer without a Pt complex but no absorption peaks corresponding to V+• or V0 at an ITO electrode modified by viologen monolayer with a Pt complex. Time-resolved spectroelectrochemical measurements, however, showed that V+• is formed upon the potentials step to the potentials more negative than V2+/ V+• redox potential and disappeared within ca. 1 ms at the ITO electrode modified by viologen monolayer with Pt complex, confirming that electron is transferred from ITO electrode to proton via viologen moiety and Pt complex [4]. By incorporating various metal complexes, not only HER but also CO2 reduction can be accelerated [5, 6] References [1] T. Masuda, K. Uosaki, Chem. Lett., 33 (2004) 788-789. [2] T. Masuda, K. Shimazu, K. Uosaki, J. Phys. Chem. C, 112 (2008) 10923-10930. [3] T. Masuda, H. Fukumitsu, S. Takakusagi, W.J. Chun, T. Kondo, K. Asakura, K. Uosaki, Adv. Mater., 24 (2012) 268-272. [4] C. Kurniawan, H. Noguchi, T. Masuda, K. Uosaki, Electrochem. Commun., 62 (2016) 56–59. [5] Y. Sun, T. Masuda, K. Uosaki, Chem. Lett., 41 (2012) 328-330. [6] T. Masuda, Y. Sun, H. Fukumitsu, H. Uehara, S. Takakusagi, W.-J. Chun, T. Kondo, K. Asakura, K. Uosaki, J. Phys. Chem. C, 120 (2016) 16200-16210. Figure 1

Effective Electron–Hole Separation Over Controllable Construction of CdS/Co-Ni-P Core/Shell Nanophotocatalyst for Improved Photocatalytic Hydrogen Evolution Under Visible-Light-Driven

In artificial photocatalysis, the slow kinetics of electron–hole transfer and high charge recombination rate have been the Achilles heel of photocatalytic conversion efficiency. Therefore, methods for promoting exciton splitting and charge separation have received sustained attention. Here, Co-Ni-P is used as a molecular cocatalyst, which is designed onto the surface of cadmium sulfide nanorods. CdS-Co-Ni-P constitutes a unique CdS/Co-Ni-P core/shell structure, which is a new type of efficient heterostructure photocatalysts used for photocatalytic decomposition of water to produce hydrogen. The modification strategy maximizes the contact area between the cocatalyst and the reactant, which effectively increases the light absorption capacity of the composite catalyst, reduces the overpotential of generating hydrogen, and accelerates the interface transfer rate of electron–hole pairs, thus achieving better photocatalytic decomposition of water. The reaction kinetics of the reduction is enhanced. Compared with pure CdS of the same quality, the optimal photocatalyst CdS-Co-Ni-P has a hydrogen evolution rate of 9.67 mmol g−1 h−1, which is about 5.3 times that of pure CdS. This work demonstrates that the new and efficient CdS/Co-Ni-P core/shell photocatalyst has great potential for photocatalytic production of H2.

Photocatalytic hydrogen production with purification of wastewater from nuclear power plant under irradiation of liquid phase plasma

Liquid phase plasma process was applied in production of hydrogen and purification of wastewater. Ethanolamine released from a nuclear power plant was degraded by photocatalytic decomposition using the liquid phase plasma with perovskite photocatalysts. Eu-doped CaTiO3 and Eu-doped SrAl2O4 perovskites were compared with that of commercial TiO2 photocatalyst. The photocatalytic decomposition of ethanolamine-contained water induced the degradation of ethanolamine and H2 evolution, simultaneously. The degradation of ethanolamine and H2 evolution were elevated on Eu-doped CaTiO3 perovskite which having less bandgap energy. The rate of H2 evolution in the ethanolamine-containing water was higher than that in pure water, which was attributed to the additional H2 evolution by the photo-decomposition of ethanolamine in water.

0D CoP cocatalyst/ 2D g‐C3N4 nanosheets: An efficient photocatalyst for promoting photocatalytic hydrogen evolution

AbstractIn this work, cobalt phosphide (CoP) nanoparticles were successfully decorated on an ultrathin g‐C3N4 nanosheet photocatalysts by in situ chemical deposition. The built‐in electric field formed by heterojunction interface of the CoP/g‐C3N4 composite semiconductor can accelerate the transmission and separation of photogenerated charge‐hole pairs and effectively improve the photocatalytic performance. TEM, HRTEM, XPS, and SPV analysis showed that CoP/g‐C3N4 formed a stable heterogeneous interface and effectively enhanced photogenerated electron‐hole separation. UV‐vis DRS analysis showed that the composite had enhanced visible light absorption than pure g‐C3N4 and was a visible light driven photocatalyst. In this process, NaH2PO2 and CoCl2 are used as the source of P and Co, and typical preparation of CoP can be completed within 3 hours. Under visible light irradiation, the optimal H2 evolution rate of 3.0 mol% CoP/g‐C3N4 is about 15.1 μmol h−1. The photocatalytic activity and stability of the CoP/g‐C3N4 materials were evaluated by photocatalytic decomposition of water. The intrinsic relationship between the microstructure of the composite catalyst and the photocatalytic performance was analyzed to reveal the photocatalytic reaction mechanism.

Orderly designed functional phosphide nanoparticles modified g-C3N4 for efficient photocatalytic hydrogen evolution

The synthesis of highly efficient and stable photocatalysts has always been one of the key research objects in the field of photocatalysis. Increasing the efficiency of charge separation is an important aspect of improving photocatalytic activity. In this work, the Co-W-P cocatalysts were loaded on g-C3N4, synthesized for the first time and the electron transport routes were appropriately adjusted, which extremely improved efficiency of photocatalytic decomposition of water for hydrogen evolution. A composite photocatalyst with high-efficiency photocatalytic H2 production performance under visible light was obtained by loading the Co-W-P composites on a g-C3N4 nanosheet. It was ascribed to the efficient interfacial electron transfer routes. This has contributed to the synthesis of high-priority and stable photocatalysts. Besides, the composite catalysts were characterized by SEM, TEM, XRD, XPS, UV-vis, BET, transient photocurrent, and FT-IR etc. And a mechanism of photocatalytic hydrogen production was hypothesized.

Effective electron-hole separation over a controllably constructed WP/UiO-66/CdS heterojunction to achieve efficiently improved visible-light-driven photocatalytic hydrogen evolution.

The photocatalytic decomposition of water to produce hydrogen is an important strategy to effectively utilize solar energy and solve the energy crisis. In this study, a highly efficient WP-nanoparticle-modified composite catalyst was successfully prepared. WP nanoparticles have been used as an efficient and acid-stable co-catalyst for the HER owing to their specific electronic structure, metalloid characteristics and catalytic activity. On the one hand, the octahedral spatial structure of UiO-66 not only provides attachment space for CdS and WP nanoparticles, but also effectively reduces the particle size and increases the dispersion of CdS and WP nanoparticles. On the other hand, the potential difference and the matching energy band positions of UiO-66 and CdS provide a feasible thermodynamic path for the transmission of photogenerated electrons. The intimate contact between the abovementioned three compounds resulted in a strong synergistic effect, which improved the efficiency of the photocatalytic H2 production. Under visible-light irradiation, the maximum H2 production in 5 h over the [UiO-66@CdS/WP (10 wt%)] photocatalyst was 395 μmol, which was 26.33 times that of pure CdS. The physical and chemical information of the samples could be obtained through XRD, SEM, TEM, XPS, BET and UV-vis DRS characterizations. Furthermore, based on the photoluminescence spectra, photoelectrochemical experiments and Mott-Schottky curves, we could reasonably explain the separation and transfer mechanisms of the photogenerated electrons and holes. The lower recombination rate of charge, enhanced intensity of light absorption, a short fluorescence lifetime (2.11 ns), a faster electron injection rate (KET = 2.32 × 108 s-1), a larger efficiency of electron injection (ηinj = 49.1%), high photocurrent response, and smaller charge transfer resistance accelerate the efficient separation and transfer of spatial charges, finally enhancing the photocatalytic performance.

2D–2D Heterostructured UNiMOF/g-C3N4 for Enhanced Photocatalytic H2 Production under Visible-Light Irradiation

On the basis of ultrathin two-dimensional (2D) nickel metal organic framework (UNiMOF) nanoflakes and 2D g-C3N4 nanoflakes, fresh visible-light-driven 2D/2D heterostructure catalysts were designed, which were assembled with a simplistic electrostatic self-assembly process. The photocatalytic performance of UNiMOF/g-C3N4 for H2 production was evaluated in visible light. The hydrogen evolution of 25.0% UNiMOF/g-C3N4 (UNG-25.0) heterojunction was 20.03 μmol h–1, which was greater than that of pure g-C3N4. In addition, the UNG composites also presented more excellent photocatalytic activity than that of bulk NiMOF/g-C3N4 (BNG) hybrid. This enhanced performance may depend on cooperative potentiation between UNiMOF and g-C3N4 efficiently lowering recombination of carriers. This work showed that constructing 2D–2D heterojunctions provides a feasible approach to obtain highly capable catalysts for photocatalytic decomposition of water.

Synthesis of hollow core-shell CdS@TiO2/Ni2P photocatalyst for enhancing hydrogen evolution and degradation of MB

During the photocatalytic production of hydrogen gas, close interface with a catalyst is very important. We designed a noble-metal-free photocatalytic system that is spatially separated to produce hydrogen by high frequency visible light. We used a new type of a catalyst consisting of hollow core-shell CdS@TiO2/Ni2P structures prepared using sacrificial template method. Photocatalytic decomposition of water was tested using this catalyst. Hydrogen production yield using 420 nm light was 14.80 mmol/g after 2.5 h and using Xe lamp with AM1.5G filter was 34.78 mmol/g after 2.5 h. Hollow core shell CdS@TiO2/Ni2P particles were more stable than hollow core shell CdS@TiO2/Pt structures because TiO2 protected CdS from photo-corrosion. Combination of CdS and Ni2P increased absorption range of TiO2 at 720 nm. Holes and electrons produced during the photo-reaction can migrate to the CdS on the inside and to the Ni2P on the outside of the TiO2 protective coating. Such design exposes more surface, thus, increases hydrogen production.

High Performance Photocatalytic Based on Ce Doped CoWO4: Controllable Synthesis and Enhanced Photocatalytic Activity

The development of highly active and resource-rich cocatalysts is important for the replacement of precious metals by the realization of large-scale and low-cost photocatalytic decomposition of water to hydrogen production. Here, we report that Ce/CoWO4 has been prepared by the microwave method and has good photocatalytic H2 properties. Under visible light irradiation (≥ 420 nm), the optimized hydrogen yield of the Ce/CoWO4 (10%) photocatalyst was 200.89 µmol, which was three times that of CoWO4. Based on the results of photoelectrochemistry and PL measurements, it is proposed that CeO2 can not only quickly capture photo-generated electrons from excited CoWO4 to improve the efficiency of charge separation, but also promote the reduction of H+–H2. View of its high activity, low cost and ease of preparation, the catalyst is a compound having a high application potential of the photocatalyst. The Ce/CoWO4 was successfully synthesized by the microwave method, and the composite catalyst showed excellent photocatalytic activity in the dye-sensitized system, which was about three times higher than that of CoWO4. The CeO2 on the surface of CoWO4 provided the more active sites and improved the efficiency of photo-generated charge separation. The Ce/CoWO4 composite catalyst is a highly efficient photocatalyst with potential applications.