Visible-light Photocatalytic H2-production Activity Research Articles

Transient Metal Centers at the Covalent Heterointerface Favor Photocatalytic Hydrogen Evolution.

Semiconductor heterostructures effectively promote the transfer and separation of interfacial photoinduced charges for the photocatalytic process. Herein, we constructed a direct Z-scheme SnSe2/CdS heterojunction photocatalyst. N-type SnSe2 semiconductors are suitable candidate materials for oxidation half-reactions in Z-scheme heterojunctions. The intimate atomic-level interfacial contact through Cd-Se bonds provides a better interfacial charge transport channel for the photoinduced charges. Moreover, the transient Sn4+/Sn0 centers caused by the photoredox process boost the interfacial charge transport/separation at the interface. Besides, the presence of S vacancies acting as electron enrichment centers further enhances the redox ability for hydrogen production. Therefore, the SnSe2/CdS heterostructure showed a superior visible-light photocatalytic H2-production activity of 13.6 mmol·g-1·h-1 using ascorbic acid as a sacrificial agent, which is 9.7 times higher than that of pristine CdS. The apparent quantum yield reaches 10.5% at λ = 420 nm. This work provides a useful way to improve charge transfer in the Z-scheme heterojunction photocatalyst for hydrogen production.

Construction and performance of CdS/MoO2@Mo2C-MXene photocatalyst for H2 production

Nowadays, photocatalytic technologies are regarded as promising strategies to solve energy problems, and various photocatalysts have been synthesized and explored. In this paper, a novel CdS/MoO2@Mo2C-MXene photocatalyst for H2 production was constructed by a two-step hydrothermal method, where MoO2@Mo2C-MXene acted as a binary co-catalyst. In the first hydrothermal step, MoO2 crystals with an egged shape grew on the surface of two-dimensional (2D) Mo2C MXene via an oxidation process in HCl aqueous solution. In the second hydrothermal step, CdS nanorods were uniformly assembled on the surface of MoO2@Mo2C-MXene in ethylenediamine with an inorganic cadmium source and organic sulfur source. The CdS/MoO2@Mo2C-MXene composite with MoO2@Mo2C-MXene of 5 wt% exhibits an ultrahigh visible-light photocatalytic H2 production activity of 22,672 µmol/(g·h), which is ∼21% higher than that of CdS/Mo2C-MXene. In the CdS/MoO2@Mo2C-MXene composite, the MoO2 with metallic nature separates CdS and Mo2C MXene, which acts as an electron-transport bridge between CdS and Mo2C MXene to accelerate the photoinduced electron transferring. Moreover, the energy band structure of CdS was changed by MoO2@Mo2C-MXene to suppress the recombination of photogenerated carriers. This novel compound delivers upgraded photocatalytic H2 evolution performance and a new pathway of preparing the low-cost photocatalyst to solve energy problems in the future.

Enhancing interfacial charge transfer in mesoporous MoS2/CdS nanojunction architectures for highly efficient visible-light photocatalytic water splitting

Mesoporous MoS2-modified CdS nanojunction networks possessing advantageous electronic connectivity and charge transfer behavior at the interfaces deliver highly efficient visible-light photocatalytic H2 production activity from water splitting.

Flux-Assisted Low Temperature Synthesis of SnNb2O6 Nanoplates with Enhanced Visible Light Driven Photocatalytic H2-Production

Foordite SnNb2O6 as a typical layered niobate has gained great attention in photocatalytic applications owing to its narrow band gap and proper conduction and valence band potentials. However, the ever reported methods toward the synthesis of SnNb2O6 nanostructures required either the use of environmentally unfriendly solvents or a prolonged high temperature heat treatment. Herein, we develop a facile flux-assisted low temperature synthesis route for the preparation of SnNb2O6 nanoplates by using H4Nb2O7 and SnCl2 as precursors. The as-obtained SnNb2O6 nanoplates with a thickness of ∼50 nm display improved visible light photocatalytic H2-production activity, which is about 10 times higher than that of a bulk SnNb2O6 sample. The enhanced photocatalytic H2-production activity can be ascribed to its nanoplate-like architecture, larger specific surface area, and better charge transfer efficiency.

Controllable sulphur vacancies confined in nanoporous ZnS nanoplates for visible-light photocatalytic hydrogen evolution.

Controllable sulphur vacancies (Sv) confined in nanoporous ZnS nanoplates (Sv-ZnS) were prepared successfully via rapid heat treatment of ZnS(en)0.5 nanoplates. Sv with controllable concentrations originating from the in situ doping of N atoms endowed Sv-ZnS with a visible-light photocatalytic H2 production activity, having a positive linear correlation with Sv concentration.

Orthorhombic WP co-catalyst coupled with electron transfer bridge UiO-66 for efficient visible-light-driven H2 evolution

The abundant transition metal phosphides co-catalysts on the earth can satisfy the sustainable and clean solar H2 production through photocatalytic water splitting, which is promising to replace the rare precious metals, such as Pt, Au, Pd, Ru and so on. In this paper, we use the temperature-programmed solid phase method to prepare WP nanoparticles. Based on the Density Functional Theory (DFT) calculations, we demonstrate that the WP nanoparticles possess outstanding electrical conductivity and excellent capability to transport electrons. WP nanoparticles are loaded onto the surface of UiO-66 via the ultrasound-assisted impregnation method to induce a highly efficient visible-light photocatalytic H2 production activity of 384 µmol in 5 h, which is 10.67 times than that of pure UiO-66. The catalytic performance is attributed to the excellent metallic conductivity and the favourable Fermi level position of WP nanoparticles. Further studies of PL, TRPL and Mott-Schottky curves, we can not only know that the modification of WP nanoparticles do improve the electron transfer ability, but also that the matched work functions between the EY and UiO-66 provides a feasible thermodynamic path for the transmission of electrons. Our work demonstrates that the earth-abundant transition metal phosphides material have the potential to construct cheaper and high catalytic performance photocatalysts.

A ternary Z-scheme WO3–Pt–CdS composite for improved visible-light photocatalytic H2 production activity

Fabrication of advanced semiconductor system for photocatalytic water splitting into valuable hydrogen energy has attracted a lot of attention worldwide due to the increasing global energy crises. In this work, a ternary WO3–Pt–CdS composite was synthesized through coprecipitation and hydrothermal reactions. The ternary composite (i.e. WO3–Pt–CdS) showed a high hydrogen evolution rate of 390 μmol h−1 g−1 exceeding CdS alone (27 μmol h−1 g−1), WO3–CdS (55 μmol h−1 g−1), and CdS–Pt (135 μmol h−1 g−1). The enhanced photocatalytic activity is mainly attributed to the formation of Z-scheme heterojunction between WO3 and CdS, which results in the effective space charge separation. Meanwhile, the Pt in the as-prepared WO3–Pt–CdS plays an essential role as a bridge for accelerating the charge transportation between WO3 and CdS. This work provides another effective way of developing visible-light-driven photocatalysts for practical application.

Metal-Free 2D/2D Phosphorene/g-C3 N4 Van der Waals Heterojunction for Highly Enhanced Visible-Light Photocatalytic H2 Production.

The generation of green hydrogen (H2 ) energy using sunlight is of great significance to solve the worldwide energy and environmental issues. Particularly, photocatalytic H2 production is a highly promising strategy for solar-to-H2 conversion. Recently, various heterostructured photocatalysts with high efficiency and good stability have been fabricated. Among them, 2D/2D van der Waals (VDW) heterojunctions have received tremendous attention, since this architecture can promote the interfacial charge separation and transfer and provide massive reactive centers. On the other hand, currently, most photocatalysts are composed of metal elements with high cost, limited reserves, and hazardous environmental impact. Hence, the development of metal-free photocatalysts is desirable. Here, a novel 2D/2D VDW heterostructure of metal-free phosphorene/graphitic carbon nitride (g-C3 N4 ) is fabricated. The phosphorene/g-C3 N4 nanocomposite shows an enhanced visible-light photocatalytic H2 production activity of 571 µmol h-1 g-1 in 18 v% lactic acid aqueous solution. This improved performance arises from the intimate electronic coupling at the 2D/2D interface, corroborated by the advanced characterizations techniques, e.g., synchrotron-based X-ray absorption near-edge structure, and theoretical calculations. This work not only reports a new metal-free phosphorene/g-C3 N4 photocatalyst but also sheds lights on the design and fabrication of 2D/2D VDW heterojunction for applications in catalysis, electronics, and optoelectronics.

Zn-vacancy mediated electron-hole separation in ZnS/g-C3N4 heterojunction for efficient visible-light photocatalytic hydrogen production

Vacancy defects play an important role in modifying the electronic structure and the properties of photoexcited charge carriers by introducing additional energy levels and consequently enhanced the photocatalytic activity of photocatalyst. In this work, we report a ZnS/g-C3N4 heterostructure with abundant zinc vacancy defects on the surface of ZnS to emphasis the synergistic promotion on charge separation. The ZnS/g-C3N4 heterostructured photocatalyst possesses low over-potential, extended absorption in the visible light region, and promoted photoinduced electron-hole separation capability. Fluorescence emission spectra and XPS results confirm that existence of abundant zinc vacancies on ZnS. VZn-rich CZV20 (g-C3N4/ZnS-20 wt%) heterojunction exhibits more than 30 times higher photocatalytic H2 evolution rate (713.68 μmol h−1 g−1) than that of pure g-C3N4 (24.09 μmol h−1 g−1) under visible light irradiation and high stability during the prolonged photocatalytic operation. The enhanced photocatalytic performance can be attributed to the intimate interfacial contact between g-C3N4 and ZnS nanoparticles, increasing the light-absorbing capacity and charge separation efficiency of ZnS/g-C3N4 heterojunction. And more importantly, the visible-light photocatalytic H2 production activity can be ascribed to the two-photo excitation in the middle band gap of ZnS. This work demonstrates that appropriate Zn vacancy defects modified ZnS/g-C3N4 heterojunction can be used for highly efficient visible-light photocatalysis.

What is the predominant electron transfer process for Au NRs/TiO2 nanodumbbell heterostructure under sunlight irradiation?

Au nanorods/TiO2 nano-dumbbells photocatalysts exhibited significantly enhanced visible light photocatalytic H2-production activity due to injection of hot electrons of photo-excited Au nanorods to TiO2 nanopaticles, which was confirmed by femtosecond transient absorption spectroscopy. However, it is well known that the electrons were transferred from TiO2 nanopaticles to Au nanorods under UV light irradiation. Considering the practical application, we investigated the photo-catalytic activity of Au nanorods/TiO2 nano-dumbbells photocatalysts under sunlight irradiation. Based on the data analysis, we confirmed the dominant electron transfer direction was from TiO2 nanoparticles to Au nanorods under sunlight irradiation and Au nanorods/TiO2 nano-dumbbells photocatalysts could act as an effective photocatalyst for H2-generation from water even without electron donor due to the efficient charge separation and the spatial separation of reduction and oxidation reaction sites.

Strongly interactive 0D/2D hetero-structure of a ZnxCd1-xS nano-particle decorated phosphorene nano-sheet for enhanced visible-light photocatalytic H2 production.

A novel zero-dimensional (0D)/two-dimensional (2D) hetero-junction of a ZnxCd1-xS nano-particle loaded phosphorene nano-sheet was assembled to achieve highly-efficient visible-light photocatalytic H2 production. Further mechanistic insight into the high performance and strong interaction in this nano-composite provides guidance to design numerous 0D/2D hetero-structures towards various applications in catalysis, electronics and opto-electronics.

Enhanced photocatalytic H2 production on CdS nanorod using cobalt-phosphate as oxidation cocatalyst

Employing visible light responsive semiconductor for photocatalytic hydrogen production by water splitting is an efficient way for utilizing renewable solar energy to solve the depletion of fossil fuel and environmental contamination. Herein, we report enhanced photocatalytic H2-production performance over CdS nanorod using cobalt-phosphate (Co-Pi) as a water oxdation cocatalyst. The optimal Co-Pi modified CdS nanocomposite photocatalyst with the Co-Pi content of 8.4 mol% has a superior visible light H2-production rate of 13.3mmolh−1g−1 with an apparent quantum efficiency of 24.3% at 420nm, which is even higher than that of 1wt% Pt-CdS (11.3mmolh−1g−1) under the same conditions. The enhanced visible-light photocatalytic H2 production activity was attributed to the hole trapping and collecting ability of Co-Pi cocatalyst, which could effectively suppress the recombination of photogenerated electron-hole pairs and increase the electron density for hydrogen production. This work shows a possibility of using earth-abundant Co-Pi as cocatalyst for enhancing photocatalytic H2 production.

Low-temperature solid-state preparation of ternary CdS/g-C3N4/CuS nanocomposites for enhanced visible-light photocatalytic H2-production activity

Low-temperature solid-state method were gradually demonstrated as a high efficiency, energy saving and environmental protection strategy to fabricate composite semiconductor materials. CdS-based multiple composite photocatalytic materials have attracted increasing concern owning to the heterostructure constituents with tunable band gaps. In this study, the ternary CdS/g-C3N4/CuS composite photocatalysts were prepared by a facile and novel low-temperature solid-state strategy. The optimal ternary CdS/g-C3N4/CuS composite exhibits a high visible-light photocatalytic H2-production rate of 57.56μmolh−1 with the corresponding apparent quantum efficiency reaches 16.5% at 420nm with Na2S/Na2SO3 mixed aqueous solution as sacrificial agent. The ternary CdS/g-C3N4/CuS composites show the enhanced visible-light photocatalytic H2-evolution activity comparing with the binary CdS-based composites or simplex CdS. The enhanced photocatalytic activity is ascribed to the heterojunctions and the synergistic effect of CuS and g-C3N4 in promotion of the charge separation and charge mobility. This work shows that the low-temperature solid-state method is efficient and environmentally benign for the preparation of CdS-based multiple composite photocatalytic materials with enhanced visible-light photocatalytic H2-production activity.

AuPd bimetallic nanoparticles decorated Cd0.5Zn0.5S photocatalysts with enhanced visible-light photocatalytic H2 production activity

In this study, novel AuPd bimetallic co-catalyst decorated Cd0.5Zn0.5S photocatalyst was successfully synthesized via an in-situ chemical deposition method. The physical as well as the photophysical properties of the as-obtained AuPd/Cd0.5Zn0.5S samples were characterized by X-ray diffractometry (XRD), Transmission electron microscope (TEM), UV–vis diffuse reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and surface photovoltage spectroscopy (SPV). The AuPd bimetallic co-catalysts showed dramatic photo-generated charge separation efficiency in Cd0.5Zn0.5S sample, and thus significantly enhance the H2 production activity under visible light irradiation. The AuPd/Cd0.5Zn0.5S sample with 0.5 wt% content had the highest catalytic activity, and the corresponding H2 evolution rate is 3.65 mmol g−1 h−1, which was about 12 times as that of pure Cd0.5Zn0.5S sample under visible light irradiation. The photocatalytic activity of the photocatalyst was stable even after 9 cycling photocatalytic experiments. A possible mechanism on the photocatalytic enhancement of AuPd NPs was systematically investigated, which can provide a novel concept for the synthesis of other desirable photocatalytic materials.

Facile synthesis of ultrathin SnNb2O6 nanosheets towards improved visible-light photocatalytic H2-production activity.

Ultrathin SnNb2O6 nanosheets with a thickness of ∼3 nm were synthesized via a facile hydrothermal route using ultrathin K4Nb6O17 nanosheets as the precursor. This ultrathin nanosheets with a large specific surface area of 71.1 m(2) g(-1) showed improved visible-light photocatalytic H2-production activity in lactic acid aqueous solution, which is about 4 and 14 times higher than that of 50 nm-thick SnNb2O6 nanosheets and bulk SnNb2O6 powders, respectively. The higher activity of ultrathin nanosheets was mainly attributed to their larger specific surface area and much better charge transfer efficiency.

Visible light photocatalytic H2-production activity of wide band gap ZnS nanoparticles based on the photosensitization of graphene

Visible light photocatalytic H2 production from water splitting is considered an attractive way to solve the increasing global energy crisis in modern life. In this study, a series of zinc sulfide nanoparticles and graphene (GR) sheet composites were synthesized by a two-step hydrothermal method, which used zinc chloride, sodium sulfide, and graphite oxide (GO) as the starting materials. The as-prepared ZnS-GR showed highly efficient visible light photocatalytic activity in hydrogen generation. The morphology and structure of the composites obtained by transmission electron microscope and x-ray diffraction exhibited a small crystallite size and a good interfacial contact between the ZnS nanoparticles and the two-dimensional (2D) GR sheet, which were beneficial for the photocatalysis. When the content of the GR in the catalyst was 0.1%, the ZG0.1 sample exhibited the highest H2-production rate of 7.42 μmol h−1 g−1, eight times more than the pure ZnS sample. This high visible-light photocatalytic H2 production activity is attributed to the photosensitization of GR. Irradiated by visible light, the electrons photogenerated from GR transfer to the conduction band of ZnS to participate in the photocatalytic process. This study presents the visible-light photocatalytic activity of wide bandgap ZnS and its application in H2 evolution.

An effective quaternary nano-sized Er3+:Y3Al5O12/Pt–PdS/ZnS visible-light photocatalyst for H2 production

The visible-light photocatalytic H2 production activity of Er3+:Y3Al5O12/Pt–PdS/ZnS was evaluated by using Na2S and Na2SO3 as sacrificial reagents. Er3+:Y3Al5O12, Pt and PdS can effectively improve the visible-light photocatalytic activity of ZnS.

Porous P-doped graphitic carbon nitride nanosheets for synergistically enhanced visible-light photocatalytic H2production

Porous P-doped g-C3N4nanosheets prepared by combining P doping and thermal exfoliation exhibit a high visible-light photocatalytic H2-production activity of 1596 μmol h−1g−1and a quantum efficiency of 3.56% at 420 nm.

Hierarchical porous CdS nanosheet-assembled flowers with enhanced visible-light photocatalytic H2-production performance

Hierarchical porous CdS nanosheet-assembled flowers were synthesized by a simple ion-exchange strategy using morphology-analogous Cd(OH)2 and Na2S as precursors. The prepared CdS flowers exhibited high visible-light photocatalytic H2-production activity with a rate of 468.7μmolh−1 and the corresponding apparent quantum efficiency (QE) of 24.7% at 420nm, which exceeded that obtained on CdS nanoparticles by more than 3 times. This enhanced photocatalytic H2-production activity was achieved because the hierarchical organization of nanosheets and porous nanosheet structures can efficiently enhance light-absorption ability and provide a greater number of active adsorption sites. This work shows a great potential of hierarchical porous CdS nanosheet-assembled flowers for photocatalytic H2 production, and also demonstrates that the ion-exchange strategy of Cd(OH)2 intermediates can be extended to the preparation of other porous oxides and sulfides with hierarchical nanostructures.

Fabrication of NiS modified CdS nanorod p–n junction photocatalysts with enhanced visible-light photocatalytic H2-production activity

Production of hydrogen from photocatalytic water splitting has become an attractive research area due to the possibility of converting solar energy into green chemical energy. In this study, novel NiS nanoparticle (NP) modified CdS nanorod (NR) p-n junction photocatalysts were prepared by a simple two-step hydrothermal method. Even without the Pt co-catalyst, the as-prepared NiS NP-CdS NR samples exhibited enhanced visible-light photocatalytic activity and good stability for H2-production. The optimal NiS loading content was determined to be 5 mol%, and the corresponding H2-production rate reached 1131 μmol h(-1) g(-1), which is even higher than that of the optimized Pt-CdS NRs. It is believed that the assembly of p-type NiS NPs on the surface of n-type CdS NRs could form a large number of p-n junctions, which could effectively reduce the recombination rates of electrons and holes, thus greatly enhancing the photocatalytic activity. This work not only shows a possibility for the utilization of low cost NiS nanoparticles as a substitute for noble metals (such as Pt) in the photocatalytic H2-production but also provides a new insight into the design and fabrication of other new p-n junction photocatalysts for enhancing H2-production activity.