Efficient Photocatalytic Hydrogen Evolution Research Articles

Self-driven photochemical exfoliation of Fe-coordinated covalent organic frameworks for enhanced solar hydrogen production

Covalent organic frameworks (COFs) have great potential in solar hydrogen production to alleviate environmental pollution and global energy crisis. However, to achieve high H2 yield is still a challenge. Herein, we designed and synthesized two Fe3+-coordinated imine type COFs (Fe-COFs) for photocatalytic H2 production from water splitting. It was surprising to find that with the progress of H2 evolution under visible light, the bulk powders of Fe-COFs (180–250 nm) were gradually stripped into covalent organic nanosheets (Fe-CONs, 0.3–1.9 nm), which in turn efficiently catalyzed H2 production. As such, a self-driven mechanism was established in the catalytic system, and H2 evolution rate increased with the increase of cyclic runs until the thickness of the nanosheet no longer changes in the regeneration and reuse process of the Fe-CON photocatalysts. The optimal Fe-CON catalyst exhibited a record high H2 evolution rate of 67.94 mmol g−1h−1 among the currently reported COFs loaded with other non-noble metals, due to the more exposed active sites, smaller charge-transfer resistance, and stronger separation ability of the photogenerated electrons and holes of Fe-CONs. This work provides the first example for the integration of self-driven photochemical exfoliation of 2D materials and their highly efficient photocatalytic hydrogen evolution

Efficient photocatalytic hydrogen evolution by in situ construction of Nb4+ charge-carrier channels in hollow porous tubular C3N4 and Nb2O5 Z-scheme heterojunctions

Optimizing heterojunction structure is an important way to improve photocatalytic activity. Herein, we report a novel hollow tubular C3N4/Nb4+/Nb2O5 nanoparticle Z-Scheme heterojunction, by introducing Nb4+ ions into Nb2O5 through a reducing atmosphere during C3N4 thermal polymerization. The optimized heterostructure showed outstanding photocatalytic hydrogen evolution activity under both UV–vis (14.93 mmol g−1 h−1) and Vis (5.22 mmol g−1 h−1) lights. The photocatalytic hydrogen evolution activity under UV–vis light is 26.6 and 4.75 times that of bulk C3N4 (CN) and hollow tubular C3N4 (HCN), respectively. The increased photocatalytic activity can be attributed to the larger specific surface area, more active sites, and enhanced light absorption capacity of the composite. Crucially, the introduction of Nb4+ ions as the charge-carrier transport channels in the Z-scheme heterostructure improves the efficiency of photogenerated charge-carrier separation. This study provides a useful design strategy for Z-Scheme photocatalytic heterojunction structures that can utilize solar light more efficiently.

Anchoring Pt single atoms on specific nitrogen vacancies of carbon nitride to accelerate photogenerated carrier transfer

The anchoring sites of metal single atoms are closely related to photogenerated carrier dynamics and surface reactions. Achieving smooth photogenerated charge transfer through precise design of single-atom anchoring sites is an effective strategy to enhance the activity of photocatalytic hydrogen evolution. In this study, Pt single atoms were loaded onto ultra-thin carbon nitride with two-coordination nitrogen vacancies (VN2c-UCN-Pt) and ultra-thin carbon nitride with three-coordination nitrogen vacancies (VN3c-UCN-Pt). This paper investigated the photocatalytic hydrogen evolution performance and photogenerated carrier behavior of Pt single atoms at different anchoring sites. Surface photovoltage measurements indicated that VN2c-UCN-Pt exhibits a superior carrier separation efficiency compared to VN3c-UCN-Pt. More importantly, the surface photovoltage signal under the presence of H2O molecules revealed a significant decrease. Theoretical calculations suggest that VN2c-UCN-Pt exhibits superior capabilities in adsorbing and activating H2O molecules. Consequently, the photocatalytic hydrogen evolution efficiency of VN2c-UCN-Pt reaches 1774 µmol g−1h−1, which is 1.8 times that of VN3c-UCN-Pt with the same Pt loading. This work emphasized the structure–activity relationship between single-atom anchoring sites and photocatalytic activity, providing a new perspective for designing precisely dispersed single-atom sites to achieve efficient photocatalytic hydrogen evolution.

Dual–Acceptor Engineering in Pyrene‐Based Covalent Organic Frameworks for Boosting Photocatalytic Hydrogen Evolution

AbstractThe integration of electron donor (D) and acceptor (A) units into covalent organic frameworks (COFs) has received increasing interest due to its potential for efficient photocatalytic hydrogen (H2) evolution from water. Nevertheless, the advancement of D–A COFs is still constrained by the limited investigations on acceptor engineering, which enables the highly effective charge transfer pathways in COFs to deliver photoexcited electrons in a preferential orientation to enhance photocatalytic performance. Herein, two systems with D–A and D–A–A configurations based on the acceptor molecular engineering strategy are proposed to construct three distinct COFs. Specifically, TAPPy‐DBTDP‐COF merging one pyrene‐based donor and two benzothiadiazole acceptors realized an average H2 evolution rate of 12.7 mmol h−1 g−1 under visible light, among the highest ever reported for typical D–A‐type COF systems. The combination of experimental and theoretical analysis signifies the crucial role of the dual‐acceptor arrangement in promoting exciton dissociation and carrier migration. These findings underscore the significant potential of D–A–A structural design, which is conducive to the efficient separation of photoexcited electrons and holes resulting in superior photocatalytic activities.

Carbon doping and bridging oxygen benefit for g-C3N4 to photocatalytic H2 production from methanol/water splitting: Experiments and theoretical calculations

Water-based homogeneous pre-assembly and thermal polycondensation were used to prepare carbon-doped oxygen-bridged layer-twisted graphite carbon nitride (g-C3N4) heterojunction for highly efficient photocatalytic hydrogen evolution (PHE). Despite the narrow band gap of around 0.91 eV, g-C3N4 heterojunction exhibited an excellent hydrogen evolution rate (563.87 μmolg−1h−1) in 30 % methanol/water solution without precious metal assisting catalysts, 36.85 times higher than g-C3N4. C doping in heptazine ring and bridging O caused the adjacent layer of g-C3N4 to twist by 11° in three-dimensional space. Noticeably, carbon doping in triazine ring was favorable to the establishment of build-in electric field between adjacent layers owing to the delocalized large π bonds. Bridging oxygen acted as a conversion switch for electron storage and transport of photogenerated charge from innerlayer (unmodified layer) with high Fermi level to outlayer (modified layer) with low Fermi level. This work provided an insightful guidance to novel layer-twisted g–C3N4–based photocatalysts for efficient H2 production.

A novel photothermal-assisted FeNi2S4@Mn0.3C0.7S S-scheme heterojunction for enhanced photo-catalytic hydrogen evolution

In addition to the intrinsic driving force of photocatalysis, the external thermal field from the photothermal effect can provide additional energy to the photo-catalytic system to improve the photo-catalytic hydrogen-evolution (PHE) efficiency. Herein, based on the results of density functional theory, we designed and constructed a hollow core–shell FeNi2S4@Mn0.3Cd0.7S (NFS@MCS) S-scheme heterojunction with a photothermal effect, thereby realising a significant enhancement of the PHE performance due to the thermal effect, S-scheme heterojunction and hollow core–shell morphology. As a light collector and heat source, the hollow NFS could absorb and convert photons into heat, resulting in the increased local temperature of photocatalyst particles. Moreover, the S-scheme charge path at the interface not only improved the carrier separation efficiency but also retained a higher redox potential. All these are favourable to increase the PHE activity. The PHE tests show that 0.5 %-NFS@MCS exhibits the highest PHE rate of 17.11 mmol·g−1·h−1, 7.7 times that of MCS. Moreover, through a combination of theoretical calculation and experimental evidence, the PHE mechanism of the NFS@MCS system is discussed and clarified in-depth.

In Situ Construction of Hollow Coral-Like Porous S-Doped g-C3N4/ZnIn2S4 S-Scheme Heterojunction for Efficient Photocatalytic Hydrogen Evolution.

The rational design of visible-light-responsive catalysts is crucial for converting solar energy into hydrogen energy to promote sustainable energy development. In this work, a C─S─C bond is introduced into g-C3N4 (CN) through S doping. With the help of the flexible C─S─C bond under specific stimuli, a hollow coral-like porous structure of S-doped g-C3N4 (S-CN) is synthesized for the first time. And an S-doped g-C3N4/ZnIn2S4 (S-CN/ZIS) heterojunction catalyst is in situ synthesized based on S-CN. S0.5-CN/ZIS exhibits excellent photocatalytic hydrogen evolution (PHE) efficiency (19.25mmol g-1 h-1), which is 2.7 times higher than that of the g-C3N4/ZnIn2S4 (CN/ZIS) catalyst (8.46mmol g-1 h-1), with a high surface quantum efficiency (AQE) of 34.43% at 420nm. Experiments and theoretical calculations demonstrate that the excellent photocatalytic performance is attributed to the larger specific surface area and porosity, enhanced interfacial electric field (IEF) effect, and appropriate hydrogen adsorption Gibbs free energy (ΔGH*). The synergistic effect of S doping and S-scheme heterojunction contributes to the above advancement. This study provides new insights and theoretical basis for the design of CN-based photocatalysts.

Oxidative and selective C–C cleavage of glycerol to glycolaldehyde with atom-like Cu on Cu-TiO2: Photocatalytic water reduction with concurrent glycerol oxidation in sunlight

Concurrent consumption of electrons and holes for the conversion of a biomass component to value added products represents a highly efficient and sustainable approach towards utilizing renewable energy, but difficult to achieve. The integration of hydrogen production with glycerol oxidation presents a novel and sustainable approach towards achieving a circular economy. In the current study, integration of atom-like Cu-clusters onto TiO2 substrate has been achieved using a facile photo-deposition technique (TC-PDO). Also, novel synthetic approaches have been employed to augment the surface coverage of Cu on TiO2 with atom-like clusters of Cu, either by borohydride treatment on TiO2 followed by Cu-deposition (TC-200) or oxygen-vacancy creation by UV illumination followed by Cu-deposition (TC-PDO). Increased dispersion and enhanced electronic integration of Cu with TiO2 lead to a corresponding increase in the efficiency of photocatalytic hydrogen evolution (13.8 mmol/h.g for TC-PDO at pH 9). Several atom-like Cu integrated with each TiO2 particle acts as photocatalytic reactor, and the same enhances electron-hole separation as well as activity. Sustainable aspect was also studied for TC-PDO up to 25 h at pH 9. Concurrently, glycerol oxidation displays the highest selectivity to C2 product (glycolaldehyde with 70 %) with a C–C cleavage. The investigation of this process holds significant potential for the extensive and simultaneous exploitation of electrons and holes in order to achieve water splitting and glycerol oxidation towards selective value-added products formation.

Oxidative and selective C–C cleavage of glycerol to glycolaldehyde with atom-like Cu on Cu-TiO2: Photocatalytic water reduction with concurrent glycerol oxidation in sunlight

Concurrent consumption of electrons and holes for the conversion of a biomass component to value added products represents a highly efficient and sustainable approach towards utilizing renewable energy, but difficult to achieve. The integration of hydrogen production with glycerol oxidation presents a novel and sustainable approach towards achieving a circular economy. In the current study, integration of atom-like Cu-clusters onto TiO2 substrate has been achieved using a facile photo-deposition technique (TC-PDO). Also, novel synthetic approaches have been employed to augment the surface coverage of Cu on TiO2 with atom-like clusters of Cu, either by borohydride treatment on TiO2 followed by Cu-deposition (TC-200) or oxygen-vacancy creation by UV illumination followed by Cu-deposition (TC-PDO). Increased dispersion and enhanced electronic integration of Cu with TiO2 lead to a corresponding increase in the efficiency of photocatalytic hydrogen evolution (13.8 mmol/h.g for TC-PDO at pH 9). Several atom-like Cu integrated with each TiO2 particle acts as photocatalytic reactor, and the same enhances electron-hole separation as well as activity. Sustainable aspect was also studied for TC-PDO up to 25 h at pH 9. Concurrently, glycerol oxidation displays the highest selectivity to C2 product (glycolaldehyde with 70 %) with a C–C cleavage. The investigation of this process holds significant potential for the extensive and simultaneous exploitation of electrons and holes in order to achieve water splitting and glycerol oxidation towards selective value-added products formation.

Fabrication of S-scheme graphdiyne (g-CnH2n-2)/carbon-nitrogen vacancies hollow Ni–Fe prussian blue analogues heterojunction for boosting wide spectrum photocatalytic hydrogen evolution

Efficient photocatalytic hydrogen evolution can be achieved by adjusting the morphology and constructing suitable heterojunction. In this work, an 2D/3D S-scheme graphdiyne (g-CnH2n-2)/carbon-nitrogen vacancies hollow Ni–Fe prussian blue analogues (Ni–Fe–CN PBA) heterojunction (GNF-CN) was prepared for photocatalytic hydrogen evolution. Ni–Fe–CN PBA were prepared by chemical etching and high temperature calcination. The hollow structure can realize multiple reflections of incident light and effectively improve the light utilization efficiency. The CN vacancy changes the band structure of Ni–Fe PBA and enhances its light absorption capacity. Graphdiyne nanosheets (GDY) prepared by load ball milling can increase the active site. The key lies in the construction of an S-scheme heterojunction between GDY and Ni–Fe–CN PBA, which effectively consume useless holes and increase the utilization rate of photogenerated electrons. The S-scheme electron transfer path are proved by DFT calculation, work function and in situ XPS. The GNF–CN–20 showed excellent photocatalytic hydrogen evolution activity (3755.02 μmol h−1 g−1) and photostability compared with GDY (1116.54 μmol h−1 g−1). The present study introduces a novel approach for the construction of an S-scheme heterojunction based on GDY and PBA, enabling wide‐spectrum‐responsive photocatalytic hydrogen evolution.

Protonated Z-scheme CdS-covalent organic framework heterojunction with highly efficient photocatalytic hydrogen evolution

The low efficiency of photocatalytic hydrogen production from water is mainly suffer from limited light absorption, charge separation and water delivery to the active centers. Herein, an inorganic–organic Z-scheme heterojunction (CdS-COF-Ni) is constructed by in-situ growth of CdS nanosheets on the porphyrin-based covalent organic framework with nickel ions (COF-Ni) in the porphyrin centers. A built-in electric field is formed at the interface, which accelerates the separation and transfer of photogenerated charges. Moreover, through the surface protonation treatment in ascorbic acid (AC) solution, the hydrophilicity of the obtained composite is obviously increased and facilitates the transport of water molecules to the photocatalytic centers. Under the synergistic effect of the interfacial interaction and surface protonation treatment, the photocatalytic hydrogen production rate is optimized to be 18.23 mmol h−1 g−1 without adding any cocatalysts, which is 21 times that of CdS. After a series of photoelectrochemical measurements, in situ X-ray photoelectron spectroscopy (XPS) analysis, and density functional theory (DFT) calculations, it is found that the photocatalytic charge transfer pathway conforms to the Z-scheme mechanism, which not only greatly accelerates the separation and transfer of photogenerated charges, but also retains a high reduction capacity for water splitting. This work offers a good strategy for constructing highly efficient organic–inorganic heterojunctions for water splitting.

Modulation of catalyst interfacial electric field and charge transfer promotes NiS-modified CoWO4/ZnIn2S4 S-scheme heterojunction for efficient photocatalytic hydrogen evolution

The strategic post-synthetic modification of engineered S-scheme heterojunctions represents a potent and manipulable approach to significantly enhance photocatalytic activity. This study details the synthesis of innovative photocatalysts via the deposition of NiS nanoparticles onto S-scheme heterojunctions of CoWO4/ZnIn2S4 (CWO/ZIS-NiS), facilitated by solvothermal and photochemical methodologies. Under visible light irradiation, the hydrogen production rate of CWO/ZIS-NiS was 22.304 mmol g−1 h−1, which 14.7 times higher than that of the ZnIn2S4. XPS, EPR, SPV and DFT calculations were used to analyze the charge transfer path and the reasons for the performance improvement of the catalyst. The construction of the S-scheme CoWO4/ZnIn2S4 heterojunction, along with NiS modification to enhance the interfacial electric field (IEF) and act as a reaction center, was identified as the primary reason for the enhanced hydrogen production activity. This work provides guidance for the design of efficient photocatalytic systems using the synergistic effect between cocatalysts and S-scheme heterojunctions.

Dual S-scheme MoS2/ZnIn2S4/Graphene quantum dots ternary heterojunctions for highly efficient photocatalytic hydrogen evolution

The layered chalcogenide ZnIn2S4 (ZIS) exhibits photo-stability and a tunable band gap but is limited in photocatalytic applications, such as hydrogen (H2) production, due to rapid carrier recombination and slow charge separation. To overcome these limitations, we have synthesized a ternary MoS2/ZIS/graphene quantum dots (GQDs) heterojunction, wherein MoS2 and GQDs are strategically attached to ZIS interlaced nanoflakes, enhancing light absorption across the 500–1500 nm range. This heterojunction benefits from dual S-scheme interfaces between MoS2-ZIS and ZIS-GQDs, establishing directed internal electric fields (IEFs). These IEFs accelerate the transfer of photoinduced electrons from the conduction bands of MoS2 and GQDs to the valence band of ZIS, promoting rapid recombination with holes and facilitating efficient catalytic reactions with plentiful photoinduced electrons stemmed from the conduction band of ZIS. As a result, the photocatalytic H2 production rate of the MoS2/ZIS/GQDs heterojunction is measured at 21.63 mmol h−1 g−1, marking an increase of 36.7 times over pure ZIS. This research provides valuable insights into designing novel heterojunctions for improved charge separation and transfer for solar energy conversion applications.

Facile Synthesis of Organic–Inorganic Hybrid Heterojunctions of Glycolated Conjugated Polymer‐TiO2−X for Efficient Photocatalytic Hydrogen Evolution

AbstractThe utilization of the organic–inorganic hybrid photocatalysts for water splitting has gained significant attention due to their ability to combine the advantages of both materials and generate synergistic effects. However, they are still far from practical application due to the limited understanding of the interactions between these two components and the complexity of their preparation process. Herein, a facial approach by combining a glycolated conjugated polymer with a TiO2−X mesoporous sphere to prepare high‐efficiency hybrid photocatalysts is presented. The functionalization of conjugated polymers with hydrophilic oligo (ethylene glycol) side chains can not only facilitate the dispersion of conjugated polymers in water but also promote the interaction with TiO2−X forming stable heterojunction nanoparticles. An apparent quantum yield of 53.3% at 365 nm and a hydrogen evolution rate of 35.7 mmol h−1 g−1 is achieved by the photocatalyst in the presence of Pt co‐catalyst. Advanced photophysical studies based on femtosecond transient absorption spectroscopy and in situ, XPS analyses reveal the charge transfer mechanism at type II heterojunction interfaces. This work shows the promising prospect of glycolated polymers in the construction of hybrid heterojunctions for photocatalytic hydrogen production and offers a deep understanding of high photocatalytic performance by such heterojunction photocatalysts.

2D Porphyrin-Based Covalent Organic Framework/PEG Composites: A Rational Strategy for Photocatalytic Hydrogen Evolution.

Two-dimensional porphyrin-based covalent organic frameworks (2D-por-COFs) have gained significant attention as attractive platforms for efficient solar light conversion into hydrogen production. Herein, we found that introducing transition metal zinc and polyethylene glycol (PEG) into 2D-por-COFs can effectively improve the photocatalytic hydrogen evolution performance. The photocatalytic hydrogen evolution rate of ZnPor-COF is 2.82 times higher than that of H2Por-COF. Moreover, ZnPor-COF@PEG has the highest photocatalytic hydrogen evolution efficiency, which is 1.31 times and 3.7 times that of pristine ZnPor-COF and H2Por-COF, respectively. The filling of PEG makes the layered structure of COFs more stable. PEG reduced the distortion and deformation of the carbon skeleton after the experiment of photocatalytic hydrogen evolution. The layered stacking and crystallization of 2D-por-COFs are also enhanced. Meanwhile, the presence of PEG also accelerates the transfer of excited electrons and enhances the photocatalytic hydrogen evolution activity. This strategy would provide valuable insights into the design of 2D-por-COFs as efficient solid photocatalysts for solar-driven hydrogen production. This article is protected by copyright. All rights reserved.

Single−atom Co anchored on covalent organic framework for remarkable photocatalytic hydrogen evolution efficiency

Single-atom catalysts (SACs) have attracted extensive attention because of their high atomic utilization and superior catalytic activity. Herein, single-atom Co has anchored on the β-ketoenamine-linked covalent organic framework (Tp-Tta COF) pores and used for remarkable photocatalytic hydrogen(H2) production under Ultraviolet–Visible light (UV–Vis light) irradiation. The single-atom Co is visualized by the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC HAADF-STEM), and the C3–Co–N1 coordination structure is demonstrated by X-ray absorption fine structure (XAFS) measurements. The modified Co0.4-SAC/Tp-Tta COF shows a high photocatalytic H2 production of 1798.5 μmol g−1 h−1 and the Apparent quantum yield(AQY) is 3.02% at 420 nm. The improvement of the activity and stability of the photocatalyst is mainly attributed to the incorporation of Co single-atom that boosts the separation efficiency of photogenerated electron-hole pair and provides well-dispersed active sites. This study provides valuable insights into the development of UV–Vis light-responsive photocatalysts at the atomic level.

Rod-like Mn0.2Cd0.8S wrapped in foliated CeO2 promote efficient photocatalytic hydrogen evolution

The Mn0.2Cd0.8S/CeO2 heterojunction is synthesized by means of hydrothermal coupling. Short rod-like Mn0.2Cd0.8S is wrapped in leaf like CeO2 to construct a tight heterointerface, which stimulated the photocatalytic activity to the great extent. Due to the remarkable catalytic and electrochemical properties of Mn0.2Cd0.8S, the CeO2 surface active site is driven. CeO2 has excellent specific surface area, suitable pore volume aperture and Mn0.2Cd0.8S match to optimize the internal interface charge transfer path. At the same time, the heterointerface can coordinate the interface electron flow and promote the H2 reduction ability. The results show that the optimal hydrogen production of Mn0.2Cd0.8S/CeO2 with S-type heterostructure is 291.8 μmol, and the internal lattice and surface morphology of Mn0.2Cd0.8S/CeO2 are not easily damaged due to good catalytic stability. The photocatalytic mechanism of Mn0.2Cd0.8S/CeO2 is studied by finding the short distance interfacial charge transfer path and enriching the photogenerated electrons required for hydrogen evolution.

CdS-based Schottky junctions for efficient visible light photocatalytic hydrogen evolution

Heterojunctions photocatalysts play a crucial role in achieving high solar-hydrogen conversion efficiency. In this work, we mainly focus on the charge transfer dynamics and pathways for sulfides-based Schottky junctions in the photocatalytic water splitting process to clarify the mechanism of heterostructures photocatalysis. Sulfides-based Schottky junctions (CdS/CoP and CdS/1T-MoS2) were successfully constructed for photocatalytic water splitting. Because of the higher work function of CdS than that of CoP and 1T-MoS2, the direction of the built-in electric field is from CoP or 1T-MoS2 to semiconductor. Therefore, CoP and 1T-MoS2 can act as electrons acceptors to accelerate the transfer of photo-generated electron on the surface of CdS, thus improving the charge utilization efficiency. Meanwhile, CoP and 1T-MoS2 as active sites can also promote the water dissociation and lower the H+ reduction overpotential, thus contributing to the excellent photocatalytic hydrogen production activity (23.59 mmol·h−1·g−1 and 1195.8 mol·h−1·g−1 for CdS/CoP and CdS/1T-MoS2)

Enhanced visible light-driven hydrogen evolution in non-precious metal Ni2P/CdIn2S4 S-type heterojunction via rapid interfacial charge transfer

Strong light absorption capacity and effective separation of photogenerated charge are the keys to photocatalytic water decomposition, which is usually solved by constructing heterojunction methods. In this work, a novel n-n interwoven Ni2P/CdIn2S4 S-type heterojunction photocatalyst was prepared by hydrothermal method for efficient photocatalytic hydrogen evolution. After a series of characterization and performance tests, under simulated sunlight irradiation at 6 °C (λ > 420 nm), the hydrogen production of Ni2P/CdIn2S4 composite with the best performance can reach 6 mmol/g/h, which is not only 48 times that of pure CdIn2S4, but also 17.2 times that of the expensive metal Pt (CIS–1Pt). By changing the temperature, the hydrogen production of Ni2P/CdIn2S4 reached 8.7 mmol/g/h at 27.5 °C, while its AQY reached 7.7 % and 6.6 % at 420 nm and 475 nm, respectively. In addition, the possible photocatalytic mechanism was analyzed by band structure and XPS diagram, and it was confirmed that the internal electric field of the S-type heterojunction accelerated the photogenerated charge transition and enhanced the hydrogen evolution ability. This effectively compensated for the limitations of severe carrier recombination and low active sites in CdIn2S4 photocatalysts. Therefore, this work provides some help for the construction of non-precious metal S-type heterojunctions for photocatalytic hydrogen production.

Facile synthesis of CuOx-decorated TiO2 nanoparticles via oxygen-limited pyrolysis of Cu(II) complex for efficient photocatalytic hydrogen evolution

CuOx-decorated TiO2 (CuOx/TiO2) nanoparticles have been prepared by the pyrolysis of Cu(II) complex on TiO2 in an oxygen-limited atmosphere. A solution phase deposition method combined with freeze drying was employed for depositing the 2-methylimidazole-Cu(II) complex onto TiO2 nanoparticles. The effect of decoration of CuOx on TiO2 nanoparticles in terms of the crystal phase, morphology, chemical compositions, surface area, surface elemental states, optical absorption and emission properties, was investigated using a series of characterization tools. The oxygen-limited pyrolysis of 2-methylimidazole resulted in the reduction of partial Ti4+ and Cu2+ ions into Ti3+, Cu+ and Cu0 species, respectively. The surface decoration of CuOx was found to improve the separation and migration of photogenerated electron-hole pairs and increase the life time of excitons. Furthermore, the photocatalytic performance of CuOx/TiO2 nanoparticles was evaluated for hydrogen evolution in aqueous methanol solution under UV–visible light irradiation. The CuOx/TiO2 photocatalyst with the optimal cocatalyst loading achieved hydrogen evolution rate of 4.34 mmol h−1 g−1, with 71- and 5.5-fold enhancement in activity over neat TiO2 and CuOx/P25, respectively. It is expected that the combination of deposition and pyrolysis of 2-methylimidazole-Cu(II) complex could be an effective approach for the decoration of Cu and its oxides on other supports.