Visible-light Photocatalytic H2 Evolution Research Articles

Efficient activity and stability of ZnWO4/CdS composite towards visible-light photocatalytic H2 evolution

Photocatalytic H2 evolution by water-splitting is a prospective technology of clean energy producing, which can deal with the problems of energy and environment. A novel efficient ZnWO4/CdS photocatalyst was fabricated with the significantly effective performance of photocatalytic H2 evolution. The ZnWO4/CdS composites exhibit the promoting photocatalytic evolution activity of 792.7 μmol/h and the outstanding stability in the following reactions of 12 h. The excellent photocatalytic performance of ZnWO4/CdS composites is mainly ascribed to the efficient separation of carriers and migration of electrons from CdS to ZnWO4 via their intimate contact interfaces. Moreover, the photocatalytic mechanism, which the analysis on XPS spectrum and radical-trapping experiments provide clues for is demonstrated to explicate the enhanced performance of the ZnWO4/CdS photocatalyst. This work provides a new design of ZnWO4/CdS photocatalysts for more efficient utilization of solar energy and some new perspectives for explicating the migration process of carriers.

Synthesis of hierarchically mesoporous polymeric carbon nitride with mesoporous melamine as a precursor for enhanced photocatalytic performance

Constructing mesoporous structure in polymeric carbon nitride (CN) is an effective way to enhance the photocatalytic performance, but rare work achieved this through controlling morphologies of raw materials because of their easy fusion on calcination. Herein, mesoporous melamine (MMA) comprising nanorods was prepared via facile acid processing on commercial MA (CMA), with ~40 times increased specific surface area. By jointly using MMA and the gas template (NH4Br) as the precursor for the first time, hierarchically mesoporous CN (HMCN) was simply synthesized with much thinner nanosheets, ~4 times higher specific surface area, stronger photoabsorption, and faster charge separation than bulky CN. On this account, HMCN exhibits much higher photoactivity in H2 production and for environmental purification. Its visible-light photocatalytic H2 evolution rate, 1412 μmol g–1 h−1 is ~8.9 times that of bulky CN, and reactive oxygen species generation rates are prominently higher than those of CN. The chemical stability of HMCN in the photoreactions is satisfactory. This work provides a simple way to prepare MMA and a novel strategy to synthesize HMCN, which may guide synthesis of other mesoporous CN-based photocatalysts.

Fabrication of a NiCo2O4/Zn0.1Cd0.9S p-n heterojunction photocatalyst with improved separation of charge carriers for highly efficient visible light photocatalytic H2 evolution

Photocatalytic hydrogen (H2) evolution is a greatly promising strategy for solar to H2 conversion. However, photocatalytic activity of single photocatalyst is limited due to the fast recombination of photogenerated charge carriers. Recently, various heterojunction photocatalysts have been constructed to improve photocatalytic activity. Herein, a novel NiCo2O4/Zn0.1Cd0.9S (NCO/ZCS) p-n heterojunction photocatalyst was fabricated via a simple calcination method. The optimized NiCo2O4 content is 3 wt%, and corresponding NCO/ZCS shows the maximum H2 evolution rate of 34.4 mmol g−1 h−1 under visible light irradiation, which is over 4.9 times higher than that of pure ZCS, and has the apparent quantum efficiency of 58.8% at 420 nm. The improved photoactivity of NCO/ZCS can be attributed to the construction of NCO/ZCS p-n heterojunction. In addition, a possible mechanism for photocatalytic H2 evolution of NCO/ZCS p-n heterojunction was proposed.

CoSe2 Clusters as Efficient Co-Catalyst Modified CdS Nanorod for Enhance Visible Light Photocatalytic H2 Evolution

CoSe2, as a kind of co-catalyst, would replace noble metals element to dope pure CdS. The CoSe2/CdS photocatalyst could be synthesized by simple physical mixing. With the introduction of CoSe2, especially 30% CoSe2/CdS, hydrogen production would be about 500 μmol within 5 h, five times that of pure CdS under the same conditions. The CoSe2/CdS photocatalyst could bear four cycles of hydrogen evolution and sustain the hydrogen production, with a minor decrease. In other words, the electron transition velocity would surge along with the introduction of CoSe2 particles. The CoSe2 could be deemed as the predator and exit of electrons to inspire the detachment of the hole-electron pairs and relieve the recombination of the hole-electron pairs.

Plasmonic Ag nanoparticles decorated SrTiO3 nanocubes for enhanced photocatalytic CO2 reduction and H2 evolution under visible light irradiation

Herein, Ag decorated SrTiO3 nanocomposites (ASTO) were fabricated by solvothermal strategy. The resultant ASTO nanocomposites possess the broad plasmonic resonance absorption for visible light, achieving the obvious visible light photocatalytic CO2 reduction and H2 evolution performance. CO, CH4 and H2 were detected for CO2 reduction, but the photocatalytic system exhibits a high CO selectivity. The A0.5STO achieves the largest CO generation amount of 80.24 μmol·g−1. Moreover, the ASTO nanocomposite also shows an enhanced visible light photocatalytic H2 evolution rate of 264.5 μmol·g−1·h−1. The remarkable photocatalytic reduction performance should belong to the improved visible light absorption capacity benefitted from the localized surface plasmon resonance, and the improved electron extraction and transfer between Ag and STO in ASTO nanocomposite. Admittedly, the abundant reactive electrons over ASTO nanocomposites achieved efficient photocatalytic CO2 reduction and H2 evolution performance under visible light. Finally, photocatalytic reduction mechanism was investigated. The work provides a feasible controlled synthesis approach to fabricate plasmonic Ag decorated perovskite nanocomposite, achieving efficient visible light photocatalytic CO2 reduction and H2 generation.

Fabrication of ZnO/N-rGO composite as highly efficient visible-light photocatalyst for 2,4-DCP degradation and H2 evolution

Abstract Nitrogen-doped reduced graphene oxide (N-rGO) has been successfully hybridized with ZnO nanorods via solvothermal method. The physicochemical properties of the composite are investigated via different techniques. The optical and electrochemical analysis including photocurrent response, and electrochemical impedance spectroscopy revealed that ZnO/N-rGO nanocomposite exhibited increased visible-light absorption and improved charge separation leading to the enhanced photocatalytic activities for the degradation of 2,4-dichlorophenol (2,4-DCP) under visible-light illumination (≥420 nm). Photocatalytic experimental results indicated that the present nanocomposite photocatalyst showed significantly higher visible-light photocatalytic H2-evolution activity (13.7 μmol h−1) than the pure ZnO nanorods (3.1 μmol h−1).

Effect of the intra- and inter-triazine N-vacancies on the photocatalytic hydrogen evolution of graphitic carbon nitride

We developed a new method to introduce N-vacancies of graphitic carbon nitride (GCN, typically in the Melon structure) at the inter-triazine sites and investigated how the visible-light photocatalytic H2 evolution of GCN is affected by the N-vacancies at the intra- and inter-triazine sites of GCN. Theoretical and experimental results show that these N-vacancies of GCN create singly-occupied defect states within the band gap acting as a trap for photogenerated electrons and act as the reaction sites for H+ reduction. Compared with the intra-triazine N-vacancy, the inter-triazine N-vacancy exhibits stronger electron localization leading to a more efficient H2 evolution. The photocatalytic reaction rate of GCN with inter-triazine N-vacancies is 9 times higher than that of “defect free” GCN, and 2.2 times higher normalized reaction rates than GCN with intra-triazine N-vacancies. The catalysis mechanism and the method to prepare melon with inter-triazine N-vacancies can be extended to explore new photocatalysts with high activities.

A direct one-step synthesis of ultrathin g-C3N4 nanosheets from thiourea for boosting solar photocatalytic H2 evolution

Two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets, as the promising photocatalyst with fascinating properties, have become a “rising star” in the field of photocatalysis. Although g-C3N4 nanosheets exfoliated from the bulk g-C3N4 powders are extensively emerged, developing a simple synthetic approach is still full of challenge. To this end, here we report a direct polymerization strategy to fabricate the ultrathin g-C3N4 nanosheets, that is only heating treatment of thiourea in air without addition of any template. The photocatalytic activities of as-prepared samples were evaluated by photoreduction of water to hydrogen (H2) using triethanolamine as sacrificial agent and Pt as co-catalyst under visible-light irradiation (λ > 420 nm). As a result, our few-layered g-C3N4 nanosheets with an average thickness of 3.5 nm exhibit a superior visible-light photocatalytic H2 evolution rate (HER) of 1391 μmol g−1 h−1 and a remarkable apparent quantum efficiency of 6.6% at 420 nm. Eventually, the HER of as-fabricated ultrathin g-C3N4 nanosheets is not only much higher than the dicyandiamide-derived g-C3N4 or melamine-derived g-C3N4, but also greater than the thermal-oxidation etched g-C3N4 nanosheets under the same condition.

Self-assembly of triptycene-based polymer on cadmium sulfide nanorod to construct core-shell nanostructure for efficient visible-light-driven photocatalytic H2 evolution

Triptycene covalent polymer (TCP) was fabricated with CdS nanorod to form a novel core-shell nanorod CdS@TCP via a facile in-situ synthesis. A 7 nm thick shell composed of amorphous TCP was homogeneously anchored on the surface of CdS-NR by a self-assembly process, yielding a one-dimensional heterostructure. Characterizations exhibit that CdS@TCP with high surface area can provide abundant surface active sites and intimate contact interfaces for absorbing H2O molecules. The CdS@TCP core-shell nanocomposite as a non-noble metal photocatalyst shows significantly enhanced photocatalytic H2 production activity and excellent photostability. The CdS@TCP-4 indicates the highest photocatalytic H2 evolution rate of 104.51 mmol h−1 g−1, which is approximately 16.2 times than that of pure CdS-NR. Besides, the photoelectrochemical performances of CdS@TCP are measured by using transient photocurrent response, EIS Nyquist plots, open circuit potential as well as Mott-Schottky plots. The improved visible light photocatalytic H2 evolution performance of CdS@TCP is due to its large surface area, and the formation of intimate coaxial heterojunction with n-n type, which can broaden light absorption range, boost the transfer of photoexcited charge carriers, and suppress the photocorrosion of CdS-NR.

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.

A Z-scheme Bi2MoO6/CdSe-diethylenetriamine heterojunction for enhancing photocatalytic hydrogen production activity under visible light

Recently, cadmium selenide (CdSe) has been deeply studied because of its excellent photocatalytic hydrogen (H2) production performance. However, pure CdSe has poor stability and severe photocorrosion, which seriously affect its application prospect. In this work, we successfully deposit Bi2MoO6 on an inorganic-organic CdSe-diethylenetriamine (DETA) hybrid to design Bi2MoO6/CdSe-DETA composites by an in situ solvothermal method. The morphology, crystal structure, electrochemical properties, H2 evolution performance and the photostability of Bi2MoO6/CdSe-DETA composites are explored using various techniques. The results show that the as-prepared Bi2MoO6/CdSe-DETA composites exhibit excellent photocatalytic performance and photostability under visible light irradiation. Among them, the Bi2MoO6/CdSe-DETA hybrid system exhibits excellent photocatalytic H2 production performance (5.92 mmol g-1 h-1), which is approximately 3.6 and 1.8 times higher than that of pure CdSe and CdSe-DETA, respectively. After 4 cycles, the photocatalyst still maintains high H2 production. This study develops a new type of photocatalyst that can respond to visible light. This provides an effective way to solve the energy problem by using solar energy.

Defect-mediated electron–hole separation in an inorganic–organic CdSxSe1−x–DETA solid solution under amine molecule-assisted fabrication and microwave-assisted method for promoting photocatalytic H2 evolution

Inorganic–organic CdSxSe1−x–DETA solid solution shows high visible light photocatalytic H2 evolution activity.

Facile fabrication of oxygen and carbon co-doped carbon nitride nanosheets for efficient visible light photocatalytic H2 evolution and CO2 reduction.

In this study, to overcome the low charge transportation efficiency and poor visible light absorption ability, and achieve highly efficient photocatalytic applications, carbon nitride nanosheets with oxygen and carbon co-doping were successfully designed and fabricated. The resultant carbon nitride nanosheets exhibited efficient photocatalytic H2 evolution and CO2 reduction performance, highlighting the efficacy of such a strategy. The highest H2 evolution rate could reach 698.43 μmol g-1 h-1, higher than that for graphitic carbon nitride (GCN). For CO2 reduction, the photocatalytic system shows a high CO selectivity, and MG3.0 achieves the largest CO generation amount of 55.2 μmol g-1. This enhanced photocatalytic reduction performance could be attributed to oxygen and carbon co-doping, which achieves fast electron extraction and transfer, and improved visible light absorption ability. It should be noted that the excessive addition of glucose in the synthesis process could enhance conductivity and promote visible light absorption of carbon nitride, but suppress the H2 evolution and CO2 reduction ability. Simultaneously, the photocatalytic reduction mechanism is discussed. This work confirms that a carbon nitride semiconductor with oxygen and carbon co-doping could be easily prepared by this strategy, achieving efficient photocatalytic applications.

Hyperstable chromium(iii)/manganese(ii) bimetallic wheel clusters with visible photoactivity.

Two new chromium and manganese bimetallic nanoclusters, [Cr8-xMnx(OH)8-x(H2O)x(OOCC6H5)16, x = 1.11] (1) and [Cr4Mn4O4(OOCC6H5)12·3CH3CN·H2O] (2), have been synthesized in a one-pot solvothermal reaction in this work. Under visible irradiation, cluster 1 can produce an increased photocurrent and exhibits significant visible-light-driven photocatalytic activity for H2 evolution in an aqueous system. Most importantly, it exhibits ultrahigh stability in both acid and base aqueous solutions, making it an excellent synthon for preparing functional materials.

Enhanced photoexcited carrier separation in CdS–SnS2 heteronanostructures: a new 1D–0D visible-light photocatalytic system for the hydrogen evolution reaction

CdS–SnS2 1D–0D core–shell heteronanostructures were designed for an efficient visible-light photocatalytic H2 evolution reaction.

Highly efficient Cu induced photocatalysis for visible-light hydrogen evolution

Coinage metal (Au, Ag, Cu) induced photocatalysis has emerged as a promising strategy in developing visible-light responsive photocatalysts. Though much progress has been made, yet researchers in this field faced great challenges from both low efficiency and rigorously relying on noble metal Au. In this work, a series of Cu/SrTiO3 with gradually increased Cu particle size from 2.8 to 7.7 nm were successfully prepared with in situ multistep photodeposition method. A highly efficient visible-light photocatalytic H2 evolution is achieved over 0.5 wt% Cu/SiTiO3 with an average Cu particle size of 3.9 nm, which reaches 5 fold as compared with its counterpart Au. As far as we know, it is the first time that Cu induced visible-light photocatalytic water splitting show prominently superior activity than that of Au under the same conditions. Further study reveals that the increase of Cu particle size effectively mitigates Fano interference between interband transition and localized surface plasmon resonance (LSPR), which extends the photo-induced carriers lifetime. The discovery here is supposed to ignite great research interests in exploring efficient and nonprecious Cu induced visible-light photocatalysis.

Excellent visible light photocatalytic H2 evolution activity of novel noble-metal-free Ni12P5/CdS composite

Novel noble-metal-free Ni12P5/CdS composite was designed and synthesized by a hydrothermal method. The photocatalytic H2 generation activity of the as-prepared Ni12P5/CdS is 1.93 fold of that of pure CdS under visible light (λ > 420 nm) irradiation. The enhanced activity of Ni12P5/CdS is ascribed to the improved separation efficiency of photocarriers over a direct Z-scheme mechanism. It provides a potential strategy to improve the photocatalytic H2 evolution activity of CdS greatly by loading noble-metal-free Ni12P5 as electron co-catalyst via direct Z-scheme mechanism.

Hierarchically CdS–Ag2S nanocomposites for efficient photocatalytic H2 production

Hierarchically nanostructured CdS composed of 4.7 nm-thick self-assembled ultrathin nanosheets was synthesised through a microwave-assisted solvothermal method. Ag2S nanoparticles (NPs) were deposited at the edge of the CdS nanosheets by an in situ ion exchange strategy. The hierarchically CdS–Ag2S nanocomposites exhibited a high visible light photocatalytic H2 evolution rate of 375.6 μmol h−1 g−1, which was 11.5 times higher than that of pure CdS. Given the difference in work functions between CdS and Ag2S, electrons diffused from the CdS side to the Ag2S side until the Fermi levels align after their contact. When the CdS–Ag2S was illuminated, the photogenerated electrons on the conduction band of the CdS further migrated to Ag2S. Considering the lower overpotential of Ag2S, the electrons more easily participated in the reduction of protons. Meanwhile, the holes on the valence band of CdS reacted with the hole sacrificial agent (triethanolamine). In this process, the photogenerated electron–hole pairs realised effective separation. The introduction of Ag2S also enhanced the utilisation of infrared light and increased the temperature of CdS surface.

Black phosphorus supported Ni2P co-catalyst on graphitic carbon nitride enabling simultaneous boosting charge separation and surface reaction

Rational design and engineering of highly active co-catalysts made of stable and earth-abundant elements is essential to boost the photocatalytic water splitting performances. This paper reports a 2D-black phosphorus (BP) supported Ni2P (2D-Ni2P@BP) as a non-precious heterostructure co-catalyst coupled with a 2D porous graphitic carbon nitride nanosheet (CN NSs) photocatalyst to induce visible light photocatalytic hydrogen production. The resulting 2D-Ni2P@BP/CN composite structure exhibits a remarkable visible light photocatalytic H2 evolution activity of 858.2 μmol h−1 g−1, revealing ∼50- and ∼5-fold enhancement compared to that of a pristine CN reference and Pt/CN sample, respectively. The dramatic advancement in H2 evolution could be ascribe to the superior hydrogen evolution reduction (HER) activity of Ni2P@BP. The excellent HER activity arises from the synergetic effect between BP and Ni2P in which BP, with its superior electron mobility, is believed to accelerate the charge separation/transfer by mediating the photogenerated electrons from CN NSs to the surface of the catalytically active sites of Ni2P, while Ni2P promotes the surface reduction reaction by lowering the H2-evolution overpotential. It is considered that this work provides a new paradigm for designing advanced, stable, and cost-effective photocatalyst systems for the practical implementation of solar hydrogen production.

Graphitic carbon nitride nanosheets prepared by gaseous molecules assembling for enhanced photocatalytic performance

Graphitic carbon nitride (g-C3N4), a new two-dimensional (2D) polymeric semiconductor, is considered as one of the most promising candidates for visible-light photocatalytic H2 evolution. The synthesis of thin-layered g-C3N4 is a facile approach to enhancing its photocatalytic properties. Here, a novel, cost-efficient, and time-saving strategy is reported to obtain 2D g-C3N4. In this equipment, bulk g-C3N4 and thin-layered g-C3N4 (denoted as G-CN) assembled from gaseous molecules were obtained simultaneously. The thin-layered g-C3N4 possesses more negative conduction-band minimum (~ 0.18 eV) relative to the bulk counterparty, leading to stronger redox ability. What is more, the carrier mobility and separation efficiency are both improved. As a result, the water splitting performance and photodegradation efficiency for methylene blue on thin-layered g-C3N4 are dramatically improved. The H2 evolution rate and half-time of photodegradation obtained by kinetic fitting reached 48.83 μmol h−1 and about 1.5 h, which is much more superior to that of bulk g-C3N4. Generally, the present work may bring out new thinking to synthesize thin-layered 2D materials.