Efficient Photocatalytic H2 Generation Research Articles

Effect of precursors on Cu particle distribution in g-C3N4 nanosheets towards efficient photocatalytic degradation and H2 generation

N-rich precursors govern the thermal polymerization formation of graphitic carbon nitride (g-C3N4) based catalysts towards enhanced photocatalytic performance. In this paper, Cu components were introduced in superior thin g-C3N4 nanosheets using the thermal polymerization copper acetate and bulk g-C3N4 created by different precursors including melamine, dicyandiamide, and thiourea, such as melamine-g-C3N4 (MCN), dicyandiamide-g-C3N4 (DCN), and thiourea-g-C3N4 (TCN). The performance of Cu-g-C3N4 nanosheets depended strongly on the precursors of bulk g-C3N4 samples. The well-developed Cu nanoparticles with clear lattice fringes were observed in the sample prepared using MCN (sample Cu-MCN) while the crystallinity of Cu nanoparticles became worse in the sample prepared using DCN (sample Cu-DCN). Interestingly, Cu clusters were homogeneously distributed in superior thin g-C3N4 nanosheets in the case of using TCN (sample Cu-TCN) because of S components in thiourea affected the thermal polymerization. The photocatalytic activity of Cu-TCN was drastically improved compared with other Cu-g-C3N4 samples. The photocatalytic hydrogen production rate of Cu-TCN with 1% of Cu components was 4035.6 μmol g-1 h-1. Cycle stability test indicated that sample Cu-TCN revealed high stability, in which the H2 generation rate was retained 95% of their initial value after 5 cycles. These results supply efficient approaches for the study and application of g-C3N4 based photocatalysts.

Bismuth nanocluster loaded on N-doped porous carbon with “memory catalysis” effect for efficient photocatalytic H2 generation and uranium(VI) reduction

Photocatalytic hydrogen production and uranium reduction can solve the problems of energy crisis and environmental pollution. Here, bismuth nanocluster loaded on N-doped porous carbon (Bi0/NC) with “memory catalysis” effect was prepared through a Bi-MOF precursor pyrolysis strategy for H2 generation and UO22+ reduction. The photocatalyst achieved an enhanced H2 production rate of 12.8 mmol g−1 h−1 and an improved UO22+ removal ratio of 95.9 %, which was 3.2 and 1.8 times as pristine carbon material, respectively. Moreover, both the H2 generation and UO22+ reduction showed a sustained activity under dark condition. Improved activity is ascribed to the optimized electronic property and the enhanced charge separation in Bi0/NC, which can be proved by the DFT calculation of projected density of state, Fermi level and charge density difference. This work provides a new strategy to realize the continuous H2 generation and U(VI) reduction in day and night.

Natural Wollastonite-Derived Two-Dimensional Nanosheet Ni3Si2O5(OH)4 as a Novel Carrier of CdS for Efficient Photocatalytic H2 Generation

Ni3Si2O5(OH)4 rods (NS) were synthesized via a hydrothermal method, employing natural wollastonite as a template. The hierarchical Ni3Si2O5(OH)4 rods exhibited vertically oriented nanosheets, resulting in a substantial increase in the specific surface area (from 2.24 m2/g to 178.4 m2/g). Subsequently, a CdS/Ni3Si2O5(OH)4 composite photocatalyst (CdS/NS) was prepared using a chemical deposition method. CdS was uniformly loaded onto the surface of the Ni3Si2O5(OH)4 nanosheets, successfully forming a heterojunction with Ni3Si2O5(OH)4. The CdS/NS photocatalyst in the presence of lactic acid as a sacrificial agent demonstrated an impressive H2 production rate of 4.05 mmol h−1 g−1, around 40 times higher than pure CdS. The photocorrosion of CdS was effectively solved after loading. After four cycles, the performance of CdS/NS remained stable, showing the potential for sustainable applications. After photoexcitation, electrons moved from Ni3Si2O5(OH)4 to the valence band of CdS, where they interacted with the holes via an enhanced interface contact. Simultaneously, electrons in CdS transitioned to its conduction band, facilitating hydrogenation. The enhanced performance was attributed to the improved CdS dispersion by Ni3Si2O5(OH)4 loading and efficient photogenerated carrier separation through the heterojunction formation. This work provides new perspectives for broadening the applications of mineral materials and developing heterojunction photocatalysts with good dispersibility and recyclability.

(Invited) Towards Broadband Photocatalysis

Forming nanomaterials junctions and using plasmons represent two important, promising strategies for realizing broadband photocalysis in strategically important applications such as solar fuels and photocatalytic degradation of pollutants. In this talk, I will present some of our recent work on the rational design of nanohybrids and their applications in solar fuels and photocatalysis. One example is about the in situ synthesis of plasmonic Ag nanoparticles (AgNPs) and Ag-MOF. The intimate and stable interface between the AgNPs and Ag-MOF and hot electron transfer from the plasmonic AgNPs to MOF led to highly efficient visible-light photocatalytic H2 generation in aqueous solution, which surpasses most of reported MOF-based photocatalytic systems. This work sheds light on effective electronic and energy bridging between plasmonic NPs and MOF.

S vacancies engineering ZnIn2S4 nanosheets for boosted photocatalytic hydrogen evolution

2D-layered ZnIn2S4 nanosheets (ZIS NSs) have been considered as a promising photocatalysts to produce H2. Nevertheless, the carrier recombination of 2D ZnIn2S4 is still severe, which limits its photocatalytic efficiency and practical applications. Herein, the defective ZnIn2S4 nanosheets with S vacancies (DZIS NSs) is fabricated via an easy one-step solvothermal process only by changing the used solvent without a complex physical or/and chemical secondary treatment, which can realize efficient photocatalytic H2 generation. The resultant DZIS NSs show enhanced photocatalytic hydrogen evolution reaction (HER) activity and well stability after 5 cycles. And the photocatalytic HER rate of DZIS NSs is up to 5437 μmol−1 h−1 g−1, nearly 2.6 times of pristine ZIS NSs (2090 μmol−1 h−1 g−1). The experimental data suggest that the excellent photocatalytic HER performance of DZIS NSs is attributable to the existence of S vacancies, which can form a S defect energy level under the lower conduction band (CB), offering abundant active sites for hydrogen activation, extending the visible light absorption range and narrowing the bandgap of DZIS NSs. Such defect engineering strategy opens new avenues for other sulfide photocatalysts to further boost photocatalytic activity.

Transition metal anchored on red phosphorus to enable efficient photocatalytic H2 generation.

Transition metal (TM) single atom catalysts (SACs) are of great potential for photocatalytic H2 production because of their abundant catalytic active sites and cost-effectiveness. As a promising support material, red phosphorus (RP) based SACs are still rarely investigated. In this work, we have carried out systematic theoretical investigations by anchoring TM atoms (Fe, Co, Ni, Cu) on RP for efficient photocatalytic H2 generation. Our density functional theory (DFT) calculations have revealed that 3d orbitals of TM locate close to the Fermi level to guarantee efficient electron transfer for photocatalytic performances. Compared with pristine RP, the introduction of single atom TM on the surface exhibit narrowed bandgaps, resulting in easier spatial separation for photon-generated charge carriers and an extended photocatalytic absorption window to the NIR range. Meanwhile, the H2O adsorptions are also highly preferred on the TM single atoms with strong electron exchange, which benefits the subsequent water-dissociation process. Due to the optimized electronic structure, the activation energy barrier of water-splitting has been remarkably reduced in RP-based SACs, revealing their promising potential for high-efficiency H2 production. Our comprehensive explorations and screening of novel RP-based SACs will offer a good reference for further designing novel photocatalysts for high-efficiency H2 generation.

Role of Efficient Charge Transfer at the Interface between Mixed-Phase Copper-Cuprous Oxide and Conducting Polymer Nanostructures for Photocatalytic Water Splitting.

Photocatalytic hydrogen generation from water splitting is regarded as a sustainable technology capable of producing green solar fuels. However, the low charge separation efficiencies and the requirement of lowering redox potentials are unresolved challenges. Herein, a multiphase copper-cuprous oxide/polypyrrole (PPy) heterostructure has been designed to identify the role of multiple oxidation states of metal oxides in water reduction and oxidation. The presence of a mixed phase in PPy heterostructures enabled an exceptionally high photocatalytic H2 generation rate of 41 mmol h-1 with an apparent quantum efficiency of 7.2% under visible light irradiation, which is a 7-fold augmentation in contrast to the pure polymer. Interestingly, the copper-cuprous oxide/PPy heterostructures exhibited higher charge carrier density, low resistivity, and 6 times higher photocurrent density compared to Cu2O/PPy. Formation of a p-p-n junction between polymer and mixed-phase metal oxide interfaces induce a built-in electric field which influences directional charge transfer that improves the catalytic activity. Notably, photoexcited charge separation and transfer have been significantly improved between copper-cuprous oxide nanocubes and PPy nanofibers, as revealed by femtosecond transient absorption spectroscopy. Additionally, the photocatalyst demonstrates excellent stability without loss of catalytic activity during cycling tests. The present study highlights a superior strategy to boost photocatalytic redox reactions using a mixed-phase metal oxide in the heterostructure to achieve enhanced light absorption, longer charge carrier lifetimes, and highly efficient photocatalytic H2 and O2 generation.

Oxygen-contained amorphous MoSx cocatalyst by one-step photodeposition to enhance H-adsorption affinity for efficient photocatalytic H2 generation

Oxygen-contained amorphous MoSx cocatalyst by one-step photodeposition to enhance H-adsorption affinity for efficient photocatalytic H2 generation

Silver nanoparticle enhanced metal-organic matrix with interface-engineering for efficient photocatalytic hydrogen evolution

Integrating plasmonic nanoparticles into the photoactive metal-organic matrix is highly desirable due to the plasmonic near field enhancement, complementary light absorption, and accelerated separation of photogenerated charge carriers at the junction interface. The construction of a well-defined, intimate interface is vital for efficient charge carrier separation, however, it remains a challenge in synthesis. Here we synthesize a junction bearing intimate interface, composed of plasmonic Ag nanoparticles and matrix with silver node via a facile one-step approach. The plasmonic effect of Ag nanoparticles on the matrix is visualized through electron energy loss mapping. Moreover, charge carrier transfer from the plasmonic nanoparticles to the matrix is verified through ultrafast transient absorption spectroscopy and in-situ photoelectron spectroscopy. The system delivers highly efficient visible-light photocatalytic H2 generation, surpassing most reported metal-organic framework-based photocatalytic systems. This work sheds light on effective electronic and energy bridging between plasmonic nanoparticles and organic semiconductors.

Efficient photocatalytic H2 generation over In2.77S4/NiS2/g-C3N4 S-scheme heterojunction using NiS2 as electron-bridge

Herein, In2.77S4/NiS2 heterojunction was firstly synthesized through an in-situ solvothermal method, then it was introduced to the surface of g-C3N4 to construct a ternary In2.77S4/NiS2/g-C3N4 S-scheme heterojunction via a simple physical solvent evaporation process. The investigation shows that the ternary In2.77S4/NiS2/g-C3N4 heterojunction exhibits an excellent light harvesting ability from 200 nm to 800 nm for the metallic-like NiS2 and the narrower bandgap of In2.77S4, it also has a better charge carrier separation and migration property compared to single and binary components. According to the photocatalytic tests, the photocatalytic H2 production rate over 20 wt% In2.77S4/NiS2/g-C3N4 can attain 7481.7 μmol·g−1·h−1, 52.5, 33.8 and 28.5 times higher than that of g-C3N4, In2.77S4 and In2.77S4/g-C3N4 respectively. Further investigation shows that the charge carriers transfer between g-C3N4 and In2.77S4 follows a S-scheme transfer route on the basis of the photoelectrochemical tests and density functional theory (DFT) calculations. In addition, NiS2 as an electron-bridge can further improve the charge transfer between the interface of g-C3N4 and In2.77S4, making more useful electrons and holes with strong REDOX capacity participating the surface reactions. What’s more, In2.77S4/NiS2 can also induce more electrochemical active sites, which can lead to a faster surface H2 releasing kinetics by reducing the overpotential of H2 evolution. This work offers an effective method for the designing novel g-C3N4-based S-scheme heterojunctions by introducing a charge-bridge to facilitate the charge carrier transfer between different photocatalysts.

Facilitated charge transfer in ZnIn2S4@CuInP2S6 heterojunctions towards efficient photocatalytic H2 generation

Accelerating charge separation and migration in semiconductor photocatalysts is the key for acquiring high performance in the photocatalytic hydrogen generation reaction. In this work, a new ZnIn2S4/CuInP2S6 hetero-structured system (ZIS/CIPS) is designed and constructed. Owing to the presence of face-to-face hetero-interface with high charge-transport capability, the photocatalytic hydrogen generation rate of ZIS/CIPS dramatically enhanced (76.2 μmol h−1) under the visible-light irradiation, which is up to 13 and 190 times compared to that of ZnIn2S4 and CuInP2S6 (CIPS), respectively.

(Invited) Towards Broadband Solar Fuel Production

Combining nanomaterials of different properties into nanohybrids can potentially lead to improved properties/performance or multiple functions. In particular, forming nanomaterials junctions and using plasmons represent two important, promising strategies for realizing broadband photocalysis in strategically important applications such as solar fuels and photocatalytic degradation of pollutants in our environments. In this talk, I will present some of our recent work on the rational design and realization of nanohybrid materials as well as their applications in solar fuel and photocatalysis. For instance, the construction of homojunctions of nanoplates made of metal–organic frameworks (MOF) led to broadened light absorption and increased photoactivity. The well-defined MOF homojunction was prepared by a facile one-pot synthesis route directed by hollow transition metal nanoparticles. The homojunction is enabled by two concentric stacked nanoplates with slightly different crystal phases. The enhanced charge separation in the homojunction was visualized by in-situ surface photovoltage microscopy. The as-prepared nanostacks displayed a visible-light-driven carbon dioxide reduction with very high carbon monooxide selectivity, and excellent stability. Another example is about the in situ synthesis of plasmonic Ag nanoparticles (AgNPs) and Ag-MOM (metal organic matrix) using one-step facile approach. The intimate and stable interface between the AgNPs and Ag-MOM and hot electron transfer from the plasmonic AgNPs to MOM led to highly efficient visible-light photocatalytic H2 generation in aqueous solution, which surpasses most of reported MOF-based photocatalytic systems. This work sheds light on effective electronic and energy bridging between plasmonic NPs and metal organic matrix.Related

Zn-P bond induced S-scheme heterojunction for efficient photocatalytic tetracycline degradation synergistic H2 generation

A Zn-P bond oriented black phosphorus/CuInZnS S-scheme heterojunction was successfully constructed for tetracycline (TC) degradation and synergistic H2 generation. An enhanced photocatalytic H2 revolution rate of 2056.0 μmol/h/g was achieved with triethanolamine (TEOA) as the hole sacrifice agent, which was nearly two times higher than that of CuInZnS (CIZS) and 170 times that of black phosphorus (BP). To further improve the hole utilization rate and reduce the energy consumption, an appropriate amount of TC was added instead of TEOA, and an improved photocatalytic H2 generation rate of 1921.2 μmol/g was obtained with the synergistic degradation of TC by 82%. The types of heterojunctions and the transfer process of carriers were investigated by the combination of Mott-Schottky curves, Ultraviolet photoelectron spectroscopy, UV–vis diffuser reflectance spectra, and density functional theory. The results showed that a S-scheme heterojunction is built in BP/CIZS, which maintained the high redox ability of electron-hole pairs based on the successful separation of carriers. In addition, the novel Zn-P bond provided a charge transport channel and catalytic reaction active center upon photocatalysis. The design and application of photocatalysts proposed in this work offered a new idea for the coordinated resolution of environmental purification and energy conversion problems.

Black magnetic Cu-g-C3N4 nanosheets towards efficient photocatalytic H2 generation and CO2/benzene conversion

Copper (Cu) clusters are incorporated into graphitic carbon nitride (g-C3N4) via a two-step thermal polymerization process, forming a superior thin black g-C3N4 nanosheets based Cu cluster composite (Cu-g-C3N4) with highly efficient charge transfer characteristic and enhanced photocatalytic activity. The Cu–N bonding is formed through intercalation of copper atoms (using Cu (II) acetylacetonate as Cu source) into dicyandiamide-based supramolecular precursor via mechano-chemical reaction, and the Cu atoms and the N atoms are bonded together in two ways: between one Cu atom and four coordinated N atoms (that comes from adjacent carbon nitride layers) and between one central Cu atom and the three N atoms from identical carbon nitride layer forming an in-plane system. Enhanced ferromagnetism of black Cu-g-C3N4 nanosheets is found for the first time, opening the way to deepen the understanding of the material in novel undiscovered applications and to generate fundamental knowledge of ferromagnetism of Cu incorporated g-C3N4 composite material. This black Cu-g-C3N4 nanosheets composite reveals enhanced visible-light-responsive photocatalytic hydrogen generation (526 μmolg-1h−1) as well as excellent CO (5.0 μmolg-1h−1) and CH4 generation (2.4 μmolg-1h−1) efficiency. Moreover, outstanding conversion rate (90.4 %) and high selectivity to phenol (99.1 %) are obtained in visible-light-driven benzene oxidation application.

Synergetic effect of bismuth vanadate over copolymerized carbon nitride composites for highly efficient photocatalytic H2 and O2 generation

The development of copolymerized carbon nitride (CN)-based photocatalysts may support advances in photocatalytic overall water splitting. However, the recombination of charge carriers is the main bottleneck that reduces its overall photocatalytic activity. To overcome this problem, the construction of heterojunction technology has emerged as an effective approach to reduce the charge carrier recombination, thereby improving charge separation and transport efficiency. In this work, an innovative heterojunction was prepared between Quinolinic acid (QA) modified CN (CN-QAx) and novel nanorod-shaped bismuth vanadate (BiVO4) (BiVO4/CN-QAx) for overall water splitting through a simple in-situ solvent evaporation technique. The obtained results show that the synthesized samples have efficient and improved activities for releasing H2 (862.1 μmol/h) and O2 (31.58 μmol/h) under visible light irradiation. Furthermore, an exceptional apparent quantum yield (AQY) of 64.52 % has been recorded for BiVO4/CN-QA7.0 at 420 nm, which might be due to the substantial isolation of photoinducedcharge carriers. Therefore, this work opens up a new channel toward efficient CN-based photocatalysts in the sustainable energy production processes.

Rational regulation of vacancy species to manage migration paths of carriers in MoS2/TiO2 heterojunctions for efficient photocatalytic H2 generation

Photocatalytic water splitting to produce hydrogen (H2), as one means to solve environmental pollution and energy shortage, is limited by the serious recombination of photogenerated electrons and holes, resulting in low solar energy conversion efficiency. Thus, steering the behaviors of charge carriers by rationally designing their transport pathway is essential, which can effectively suppress the recombination of electrons and holes. Herein, we designed a MoS2/TiO2 heterojunction with different vacancy species to manage the migration paths of photogenerated charge carriers. As demonstrated by experimental characterizations and density functional theory (DFT) calculations, oxygen and sulfur vacancies can induce defect energy levels in heterostructures, which can capture photogenerated holes and electrons, respectively, resulting in substantially promoted charge separation efficiency and longer lifetime of electrons. As expected, the optimized photocatalyst shows a stable H2 production rate of 1.41 mmol g−1 h−1, which is significantly better than that of the bare MoS2/TiO2 heterojunction. This finding informs the significance in rational design of the nanostructures for promoting the photocatalytic performance.

Molecular Engineering of Robust Starburst-Based Organic Photosensitizers for Highly Efficient Photocatalytic Hydrogen Generation from Water

Six donor–donor−π–acceptor (D–D−π–A) triphenylamine-based starburst organic dyes with different electron-donating moieties and thiophene-based π-linkers were synthesized and characterized. Their photophysical and electrochemical properties, together with their photocatalytic hydrogen evolution performance as photosensitizers (PSs), were investigated. Distinctive and prolonged hydrogen evolution performances of these PSs under visible-light irradiation from water in their platinized TiO2 composites were demonstrated: a turnover number (TON) of up to 24 900 (252 h) with 1560 μmol (37.6 mL) hydrogen produced, an initial turnover frequency (TOFi) of 1130 h–1, initial activity (Activityi) of 705 mmol g–1 h–1, and initial apparent quantum yield (AQYi) of 12.1%. To the best of our knowledge, according to the TOF and TON values, the designed PS system is one of the most efficient and robust photocatalytic H2 generation systems adopting a TiO2-anchoring molecular PS in the literature. The results showed that the starburst triarylamine donor moiety with phenothiazine functionality and the alkyl chain on the thiophene π-linker could boost the performance and longevity of the photocatalytic system, providing a powerful strategy for the development of starburst-based highly efficient and robust D–D−π–A organic photosensitizers in the future.

Fabrication of Ni2P Cocatalyzed CdS Nanorods with a Well-Defined Heterointerface for Enhanced Photocatalytic H2 Evolution

Developing non-noble metal photocatalysts for efficient photocatalytic hydrogen evolution is crucial for exploiting renewable energy. In this study, a photocatalyst of Ni2P/CdS nanorods consisting of cadmium sulfide (CdS) nanorods (NRs) decorated with Ni2P nanoparticles (NPs) was fabricated using an in-situ solvothermal method with red phosphor (P) as the P source. Ni2P NPs were tightly anchored on the surface of CdS NRs to form a core-shell structure with a well-defined heterointerface, aiming to achieve a highly efficient photocatalytic H2 generation. The as-synthesized 2%Ni2P/CdS NRs photocatalyst exhibited the significantly improved photocatalytic H2 evolution rate of 260.2 μmol∙h−1, more than 20 folds higher than that of bare CdS NRs. Moreover, the as-synthesized 2%Ni2P/CdS NRs photocatalyst demonstrated an excellent stability, even better than that of Pt/CdS NRs. The photocatalytic performance enhancement was ascribed to the core-shell structure with the interfacial Schottky junction between Ni2P NPs and CdS NRs and the accompanying fast and effective photogenerated charge carriers’ separation and transfer. This work provides a new strategy for designing non-noble metal photocatalysts to replace the noble catalysts for photocatalytic water splitting.

Unique Mo2C–CdS–Co@C heterojunction integrated with redox cocatalysts and multiple active sites for efficient photocatalytic H2 generation

Photocatalytic water-splitting has encouraged great interest to obtain renewable H2 fuel via the transformation of solar energy. Although significant progress has been achieved, realizing efficient H2 evolution reaction (HER) with non-noble-metal photocatalysts is still challenging. Herein, we report a facile synthesis of Mo2C–CdS–[email protected] heterojunction by anchoring CdS and Mo2C nanoparticles onto [email protected] micro-flowers. The [email protected] micro-flowers were composed of graphitic carbon nanoflakes partially embedded with Co, CoOx, Co9S8 nanocrystals and obtained through the carbonization of metanilic-anion intercalated Co(OH)2 precursor. Due to excellent visible-light harvesting capacity, efficient charge transmission and isolation caused by the existence of superior electron mediator (graphitic carbon) together with oxidation (CoOx) and reduction (Co, Co9S8, Mo2C) cocatalysts, as well as the plentiful H2-evolving active sites originating from the metal (Co), metal sulfide (Co9S8), and metal carbide (Mo2C), the Mo2C–CdS–[email protected] hybrid micro-flowers delivered an exceptional HER (λ > 400 nm) activity of 760.58 μmol h−1 (10 mg), approximately 32 and 15 folds that of pristine CdS and platinum (3 wt%)-decorated CdS, respectively. Moreover, both the cycling and long-term photocatalytic tests confirm that the Mo2C–CdS–[email protected] possesses an outstanding durability for H2 production. The study results might inspire the rational integration of cocatalysts to simultaneously optimize the charge trapping and H2-evolving kinetics for strengthening the photocatalytic HER activity efficiently.

Zn-P Bond Induced Direct S-Scheme Heterojunction for Efficient Photocatalytic Tetracycline Degradation Synergistic H2 Generation

Zn-P Bond Induced Direct S-Scheme Heterojunction for Efficient Photocatalytic Tetracycline Degradation Synergistic H2 Generation