Visible-light Photocatalytic H2 Production Research Articles

Interlayer Potassium Single-Atom-Coordinated g-C3N4 for Significantly Boosted Visible Light Photocatalytic H2 Production.

In recent years, graphitic carbon nitride (g-C3N4) has attracted considerable attention because it includes earth-abundant carbon and nitrogen elements and exhibits good chemical and thermal stability owing to the strong covalent interaction in its conjugated layer structure. However, bulk g-C3N4 has some disadvantages of low specific surface area, poor light absorption, rapid recombination of photogenerated charge carriers, and insufficient active sites, which hinder its practical applications. In this study, we design and synthesize potassium single-atom (K SAs)-doped g-C3N4 porous nanosheets (CM-KX, where X represents the mass of KHP added) via supramolecular self-assembling and chemical cross-linking copolymerization strategies. The results show that the utilization of supramolecules as precursors can produce g-C3N4 nanosheets with reduced thickness, increased surface area, and abundant mesopores. In addition, the intercalation of K atoms within the g-C3N4 nitrogen pots through the formation of K-N bonds results in the reduction of the band gap and expansion of the visible-light absorption range. The optimized K-doped CM-K12 nanosheets achieve a specific surface area of 127 m2 g-1, which is 11.4 times larger than that of the pristine g-C3N4 nanosheets. Furthermore, the optimal CM-K12 sample exhibits the maximum H2 production rate of 127.78 μmol h-1 under visible light (λ ≥ 420 nm), which is nearly 23 times higher than that of bare g-C3N4. This significant improvement of photocatalytic activity is attributed to the synergistic effects of the mesoporous structure and K SAs doping, which effectively increase the specific surface area, improve the visible-light absorption capacity, and facilitate the separation and transfer of photogenerated electron-hole pairs. Besides, the optimal sample shows good chemical stability for 20 h in the recycling experiments. Density functional theory calculations confirm that the introduction of K SAs significantly boosts the adsorption energy for water and decreases the activation energy barrier for the reduction of water to hydrogen.

Construction of an all-organic S-scheme heterostructure based on PEDOT immobilized g-C3N4 nanosheets by electrostatic self-assembly with enhanced visible-light photocatalytic hydrogen production

Inspired by photosynthesis in nature, exploring all-organic S-scheme heterojunction photocatalysts for efficient H2 production is of great significance in addressing energy shortage issues. In this paper, poly(3,4-ethylenedioxythiophene) (PEDOT) immobilized g-C3N4(CN) nanosheets were constructed by an electrostatic self-assembly strategy to obtain an all-organic S-scheme heterojunction, significantly enhancing the visible-light photocatalytic H2 production performance of g-C3N4. The optimized 5PEDOT/CN exhibits the highest H2 production rate of 3.15 mmol g−1h−1, a 31.5-fold enhancement over pristine CN. According to the staggered energy band positions of two components and the results of electron spin resonance tests, the S-scheme heterojunction electron-transfer mechanism is confirmed, which greatly facilitates the spatial charge separation and retains the strong reducing ability of high-energy potential electrons for efficient photocatalytic H2 production. Based on the results of FT-IR spectra, XPS spectra, fluorescence spectra, hydroxyl radical tests and time-resolved photoluminescence spectra, it is confirmed that the significantly improved photocatalytic activity is mainly attributed to the enhanced charge separation by the S-scheme heterojunction and the tightly contacted interface dependent on N···S interactions in PEDOT immobilized CN nanosheet heterojunctions, along with the enhanced visible-light absorption ability. This work presents a novel approach to the design and fabrication of all-organic S-scheme heterojunction photocatalysts for solar-light-driven energy production.

Linker Engineering of Sandwich-Structured Metal-Organic Framework Composites for Optimized Photocatalytic H2 Production.

While the microenvironment around catalytic sites is recognized to be crucial in thermocatalysis, its roles in photocatalysis remain subtle. Herein, a series of sandwich-structured metal-organic framework (MOF) composites, UiO-66-NH2 @Pt@UiO-66-X (X means functional groups), have been rationally constructed for visible-light photocatalytic H2 production. By varying -X groups of UiO-66-X shell, the microenvironment of Pt sites and photosensitive UiO-66-NH2 core can be simultaneously modulated. Significantly, the MOF composites with identical light absorption and Pt loading present distinctly different photocatalytic H2 production rates, following -X group sequence of -H > -Br > -NA (naphthalene) > -OCH3 > -Cl > -NO2 . UiO-66-NH2 @Pt@UiO-66-H demonstrates H2 production rate up to 2708.2μmol g-1 h-1 , ∼222 times that of UiO-66-NH2 @Pt@UiO-66-NO2 . Mechanism investigations suggest that the variation of -X group can balance the charge separation of UiO-66-NH2 core and proton reduction ability of Pt, leading to the optimal activity of UiO-66-NH2 @Pt@UiO-66-H at the equilibrium point. This article is protected by copyright. All rights reserved.

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 of multi-interfacial charge transfer paths in the NiS/CdS@CuS composite for efficient and broadband visible light photocatalytic H2 production

Broad-spectrum response and high charge separation are two important prerequisites and also challenges for a photocatalyst to achieve excellent activity. Herein, we developed a closely-contacted NiS/CdS@CuS hybrid photocatalyst to construct multi-interfacial charge transfer paths to address these two challenges. Different from previously reported, limited charge transfer for the CdS system, the synergy between photoinduced interfacial charge transfer (IFCT) at the intimate CdS/CuS interface and the superior H2 production cocatalyst (NiS) enables a multi-interfacial charge transfer, which greatly accelerates charge separation and achieves broadband H2 production. The optimal NiS/CdS@CuS composite exhibits the high H2 production activity of 25.02 mmol g−1 h−1 with an apparent quantum efficiency of 27.21% at 420 nm. This activity is even higher than that of the optimized Pt/CdS system. The creation of photoinduced IFCT allows the photocatalytic H2 production of CdS extended to 610 nm. Multiple comparison systems are constructed to understand the reaction mechanisms and highlight the importance of synergy between the three components. This work supplies a paradigm for fabricating efficient H2 production photocatalyst with both enhanced charge transfer dynamics and expanded light response range.

Advanced Functional Carbon Nitride by Implanting Semi-Isolated VO2 Active Sites for Photocatalytic H2 Production and Organic Pollutant Degradation.

It is critical to facilitate surface interaction for liquid-solid two-phase photocatalytic reactions. This study demonstrates more advanced, efficient, and rich molecular-level active sites to extend the performance of carbon nitride (CN). To achieve this, semi-isolated vanadium dioxide is obtained by controlling the growth of non-crystalline VO2 anchored into sixfold cavities of the CN lattice. As a proof-of-concept, the experimental and computational results solidly corroborate that this atomic-level design has potentially taken full advantage of two worlds. The photocatalyst comprises the highest dispersion of catalytic sites with the lowest aggregation, like single-atom catalysts. It also demonstrates accelerated charge transfer with the boosted electron-hole pairs, mimicking heterojunction photocatalysts. Density functional theory calculations show that single-site VO2 anchored into the sixfold cavities significantly elevates the Fermi level, compared with the typical heterojunction. The unique features of semi-isolated sites result in a high visible-light photocatalytic H2 production of 645µmol h-1 g-1 with only 1wt% Pt. They also represent an excellent photocatalytic degradation for rhodamine B as well as tetracycline, surpassing the activities obtained from many conventional heterojunctions. This study presents exciting opportunities for the design of new heterogeneous metal oxide for a variety of reactions.

Carbon layers on Pt/TiO2 induced dramatic promotion of photocatalytic H2 production: a combined experimental and computation study

Noble metal nanoparticles (NMNPs) modified semiconductors play important roles in heterogeneous catalysis. However, for the ultra-small NMNPs (<5 nm) on TiO2, the problems of easy agglomeration and quick deactivation highlight the need for highly efficient protection of ultra-small NMNPs. Here, we introduce a novel structure of carbonized liquid crystals (CLCs) protected Pt NPs on TiO2, which involves in-situ photo-reduction of chloroplatinic acid to ultra-small Pt NPs in lamellar liquid crystals. According to the results of morphological structures, CLCs changed the contact type of Pt/TiO2 from ‘face-contact’ to ‘point-contact’, which was consistent with our simulation results. Compared with the bare Pt/TiO2, the visible-light photocatalytic H2 production rate of C–Pt/TiO2 exhibited 1.75-fold enhancement under the protection of CLCs (26.73 mmol g−1 h−1vs. 15.26 mmol g−1 h−1). Especially, the marriage of CLCs and the traditional Pt/TiO2 photocatalyst achieved long-term stability, which remained 87% of the original rate at the sixth cycle.

Improved performance of visible-light photocatalytic H2-production and Cr(VI) reduction by waste pigeon guano doped g-C3N4 nanosheets

In this study, waste pigeon guano (PG) was re-utilized as an ideal biomass adulterant to improve the photocatalytic activity of the pristine graphitic carbon nitride (g-C3N4). Waste PG and melamine were employed as precursors to fabricate a novel porous multielement-doped g-C3N4 (CN-PG-S) nanosheets photocatalyst via in situ thermal polycondensation coupled with thermal exfoliation strategy. The CN-PG-S owned abundant uniformly porous structures, superior conductivity, and excellent photocatalytic abilities, resulting in highly-efficient H2-production (1950 μmol g–1 h–1) and Cr(VI) reduction (99.1%) under visible light, which increased by 22.9-folds and 5.3-folds more than that of pristine g-C3N4. The non-metallic (P, S, and O) and metallic elements in CN-PG-S played a crucial role in expanding the visible-light absorption range and promoting the separation-migration of photogenerated electron-hole pairs. And the uniformly porous nanosheet structure of CN-PG-S shortens the diffusion paths of photogenerated carriers and exposes more active sites for photocatalytic reactions. This study proposed an eco-friendly resources integration strategy of waste PG to prepare excellent CN-PG-S photocatalysts for highly-efficient H2-production and Cr(VI) reduction.

Covalent Organic Framework/g-C3N4 van der Waals Heterojunction toward H2 Production.

Photocatalytic water splitting into H2 is the most economic and environmentally friendly strategy for H2 production, and rationally constructing a heterojunction retains enormous influence on a photocatalytic system. Herein, 2D/2D covalent organic framework/graphitic carbon nitride (COF/CN) van der Waals heterojunctions were readily prepared via an ultrasonic method for high-efficiency visible-light photocatalytic H2 production. The photocatalytic H2 production performance of optimized COF/CN composites can reach up to 449.64 μmol·h-1, which is approximately 5 times that of pure CN (89.08 μmol·h-1). The characterization and experimental studies reveal that the synergistic effect between COF and CN contributes to promoting the interfacial migration and spatial separation of photoinduced e--h+ pairs, further boosting the photocatalytic hydrogen production activity. This work may open a new window to design and fabricate effective heterojunction photocatalysts for photocatalytic energy conversion.

Green synthesis of Fe2O3 deposited g-C3N4: Addition of rGO promoted Z-scheme ternary heterojunction for efficient photocatalytic degradation and H2 evolution reaction

Construction of heterojunction photocatalysts with robust charge separation, efficiency light utilization and better charge transportation are hotspot in photocatalytic energy and environmental remediation applications. Herein, we have prepared the Z-scheme ternary heterojunction (rGO/g-C3N4/Fe2O3) photocatalysts using green tea extract assisted hydrothermal method for visible-light active photocatalytic degradation and H2 production. The heterojunction formation provides the more active sites for photocatalytic redox reaction in comparison with pure photocatalysts, which was confirmed by BET analysis. Moreover, elemental trapping experiment, photocurrent analysis, and band alignment derived from valance band XPS, clearly revealed that, the prepared photocatalyst shows Z-scheme charge separation. Photocatalytic activity demonstrated that, the prepared Z-scheme heterojunction exhibits 97 and 94% of degradation efficiency against methylene blue (MB) and ciprofloxacin (CIP) model organic pollutants. Moreover, the ternary heterojunction photocatalyst exhibits almost 100% of recycling efficiency towards H2 production even at 5th cycle with 20,786 μmol/g. Hence, we hope that this green synthesis approach would provide the new way to prepare the heterojunction photocatalysts for energy and environmental remediation applications.

Fabrication and enhanced visible-light photocatalytic H2 production of B-doped N-deficient g-C3N4/CdS Hybrids with robust 2D/2D hetero-interface interaction

2D layered photocatalysts with proper electronic structure have sparked much attention in the field of visible-light photocatalysis for H2 production. Herein, by simply calcining the mixture of ultrathin g-C3N4 (CNN) and NaBH4, heteroatom B and N defect were simultaneously introduced into g-C3N4. The obtained modified g-C3N4 (BDCNN) was further coupled with 2D flower-like CdS nanosheet. The optimal 2D/2D BDCNN/CdS-15% heterojunction behaved ideal photocatalytic activity for H2 revolution by water splitting, and the highest H2 revolution rate was as high as 1013.8 μmol g−1 h−1, which was 6.7 times, 2 times, and 5.8 times of the corresponding values of pristine CNN, BDCNN and CdS respectively. It was evidenced that the band structure of 2D/2D BDCNN/CdS-15% was well tuned for better visible-light adsorption and higher separation efficiency of photo-induced carriers for enhancing H2 revolution performance. The achievement in this study provided informative principles for exploring g-C3N4 based heterojunctions with higher H2-production performance.

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.

ZnO-based heterostructure constructed using HKUST-1 for enhanced visible-light photocatalytic hydrogen evolution

ZnO is a promising candidate for photocatalysts, whereas suffered from low activity due to the insufficient visible-light absorption and rapid recombination of photogenerated charges. In order to improve the visible-light catalytic activity of unmodified ZnO, a ZnO/Cu2O/CuO (ZCC) heterostructure photocatalyst constructed from in-situ growth of Cu-based MOF (HKUST-1) on ZnO nanosheets by in-situ growth was designed for photocatalytic H2 evolution, which exhibited excellent visible-light H2 production rate of 467.1 μmol h−1 g−1. It was confirmed that the enhanced photoactivity was mainly attributed to the wide visible-light absorption range and improvement of active sites. The construction of heterostructure promoted the migration and separation of photogenerated charges and enhanced the synergistic effect between the multicomponent hybrid semiconductor materials. This work highlights the design of using MOFs as precursor to construct metal oxide heterostructures with ZnO nanosheets for visible-light photocatalytic H2 production.

G-C3N4/CoTiO3 S-scheme heterojunction for enhanced visible light hydrogen production through photocatalytic pure water splitting

Photocatalytic hydrogen (H2) production via water splitting in the absence of sacrificial agents is a promising strategy for producing clean and sustainable hydrogen energy from solar energy. However, the realization of a photocatalytic pure water splitting system with desirable efficiency is still a huge challenge. Herein, visible light photocatalytic H2 production from pure water splitting was successfully achieved using a g-C3N4/CoTiO3 S-scheme heterojunction photocatalyst in the absence of sacrificial agents. An optimum hydrogen evolution rate of 118 μmol·h−1·g−1 was reached with the addition of 1.5 wt% CoTiO3. The remarkably promoted hydrogen evolution rate was attributed to the intensified light absorption coupled with the synergistic effect of visible light responsive CoTiO3, the promoted efficiency in charge separation, and the reserved strong redox capacity induced by the S-scheme charge transfer mechanism. This work provides an alternative to visible light-responding oxidation photocatalysts for the construction of S-scheme heterojunctions and high-efficiency photocatalytic systems for pure water splitting.

Robust visible-light photocatalytic H2 evolution on 2D RGO/Cd0.15Zn0.85In2S4–Ni2P hierarchitectures

Unique 2D ternary hierarchitectures constructed from reduced graphene oxide nanosheets grown with ultrathin Cd0.15Zn0.85In2S4 nanosheets and Ni2P nanoparticles exhibited an outstanding capability for visible-light photocatalytic H2 production.

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.

Metal–organic framework with atomically dispersed Ni–N4 sites for greatly-raised visible-light photocatalytic H2 production

The depletion of traditional fossil fuels and related environmental issues have increased the demand for clean and sustainable energy resources to achieve carbon neutrality. Active, robust and cheap photocatalysts are required for large-scale photocatalytic H2 evolution reaction (p-HER), which transforms solar energy into chemical energy. Here we report the decoration of Ni-imidazole framework (NiIm) with CdS nanorods for p–HER. The p–HER rate of CdS/NiIm hybrid sharply increased by about 14.23 times to 21,712 µmol h−1 g–1 when compared with that of CdS alone. Physicochemical characterizations and theoretical calculations reveal strong interactions at the CdS/NiIm interface and the presence of numerous Ni–N4 active sites on NiIm leading to the significant performance enhancement. This work demonstrates that NiIm acts as an affordable and abundant co-catalyst that remarkably enhances the p–HER, and enlightens the further development in the design and preparation of metal−organic framework-based materials for various applications in photocatalysis and related subjects.

Optical band gap modification of Ce/ZnO for visible light photocatalytic H2 production from aqueous methanol solution

Ce (0.5, 1, 2 and 3 mol%) incorporated ZnO crystallites along with bare ZnO were prepared by solution free mechanochemical method and characterized with powder XRD, HR-TEM, SEM, EDX, XPS, UV–visible and Photoluminescence (PL) spectra. The visible light photocatalytic performance of these materials was investigated for H2 evolution with the aqueous 10 vol% methanol solution under one sun conditions using solar simulator. X-ray diffraction data suggests the hexagonal wurtzite structure for Ce incorporated ZnO crystallites and due to incorporation of Ce4+ ion there is expansion in the lattice constants of ZnO, which is attributed to decreases in crystallite size. UV–visible spectra propose the decrease in optical band gap of Ce incorporated ZnO with the increase of Ce content up to 3 mol%. The XPS analysis supports the incorporation of Ce4+ in Ce/ZnO. The PL spectra suggest that, with the insertion of Ce ions into ZnO, intensity of green emission band increases, which reflects the low recombination rate of photogenerated charge carriers which is responsible for higher photocatalytic H2 production. Extent of hydrogen production is affected by calcination temperature of Ce/ZnO. 2 mol% Ce incorporated ZnO calcined at 600 °C produces 43μmolh−1g−1 of hydrogen.

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.

Bimetallic Ni–Co nanoparticles confined within nitrogen defective carbon nitride nanotubes for enhanced photocatalytic hydrogen production

This work for the first time reports bimetallic Ni–Co and monometallic (Ni and Co) nanoparticles (NPs)-engineered carbon nitride nanotubes with nitrogen vacancies (V-CNNTs) for visible-light photocatalytic H2 generation application. The bimetallic Ni–Co NPs have an average size of less than 5 nm and are homogenously dispersed along the nanochannels of V-CNNTs. The composition of the bimetallic NPs plays an essential role to maximize photocatalytic activity. With the optimal Ni/Co atom ratio of 3:1, Ni–Co/V-CNNTs nanohybrids yielded a H2 production rate of 4.19 μmol/h, which is higher than those of monometallic counterparts and V-CNNTs. The intimately loaded Ni–Co NPs and incorporated nitrogen vacancies enhance the photocatalytic performance through extended light absorption, abundant active sites, strong metal-support interaction, and efficient charge carrier transfer along the axial direction. This study presents a stable and highly efficient hybrid as a promising photocatalyst for visible light photocatalytic H2 production through water splitting.