Photocatalytic H2 Generation Research Articles

Enhanced photocatalytic hydrogen evolution under visible-light using C, N co-doped mesoporous TiO2 nanocrystals templated by ionic liquids

Introducing heteroatoms into TiO2 photocatalysts is an effective way to improve its visible-light driven photocatalytic performance. However, the strategies to realize it always require hazardous reagents and/or high temperature. Herein, we put forward a facile and environmentally benign strategy for synthesizing C, N co-doped mesoporous TiO2 nanocrystals. The preparation consists of microwave heating of a simple mixture of H2O, imidazolium-based ionic liquid (IL) and tetrabutyl titanate and subsequent heat-treatment. During the synthesis, the IL acts as reaction solvent, microwave absorbent, C and N sources, and structure-directing agent. Such a strategy not only simplifies the synthesis by avoiding the employment of additional reactants and structure-directing agents towards constructing TiO2 with small sizes, well-developed mesoporous structure and abundant C, N dopants in the lattices, but also lows down the post-processing temperature, which can relieve the secondary growth of TiO2 grains. Benefiting from the mesoporous structure and heteroatom co-doping, the synthesized material shows high specific-surface area, excellent hydrophilicity, elevated valence-band edges, abundant defect levels and narrowed band-gap, which contribute to the improved visible-light absorption, reduced photogenerated electron-hole recombination, and rapid charge transfer and surface-catalyzed reactions. As a result, the material exhibits higher photocatalytic H2 generation performance under the visible-light irradiation than many conventional types of doped TiO2. Besides, the formation mechanism of this TiO2 and the relationships of IL with the morphology and co-doping process have been revealed. This work highlights great potential of IL-assisted microwave synthesis in developing heteroatoms co-doped TiO2 with enhanced photoactivity and application in the solar energy conversion.

Single-Atom-Based Catalysts for Photocatalytic Water Splitting on TiO2 Nanostructures

H2 generation from photocatalytic water splitting is one of the most promising approaches to producing cost-effective and sustainable fuel. Nanostructured TiO2 is a highly stable and efficient semiconductor photocatalyst for this purpose. The main drawback of TiO2 as a photocatalyst is the sluggish charge transfer on the surface of TiO2 that can be tackled to a great extent by the use of platinum group materials (PGM) as co-catalysts. However, the scarcity and high cost of the PGMs is one of the issues that prevent the widespread use of TiO2/PGM systems for photocatalytic H2 generation. Single-atom catalysts which are currently the frontline in the catalysis field can be a favorable path to overcome the scarcity and further advance the use of noble metals. More importantly, single-atom (SA) catalysts simultaneously have the advantage of homogenous and heterogeneous catalysts. This mini-review specifically focuses on the single atom decoration of TiO2 nanostructures for photocatalytic water splitting. The latest progress in fabrication, characterization, and application of single-atoms in photocatalytic H2 generation on TiO2 is reviewed.

Defected tungsten disulfide decorated CdS nanorods with covalent heterointerfaces for boosted photocatalytic H2 generation

Owing to their intrinsic and pronounced charge carrier transport when facing the formidable challenge of inhibiting severe surface charge recombination, one-dimensional (1D) CdS nanostructures are promising for advancing high-yield hydrogen production. We herein demonstrate an efficient strategy of boosting interfacial carrier separation by heterostructuring 1D CdS with defective WS2. This process yields solid covalent interfaces for high flux carrier transfer that differ distinctively from those reported structures with physical contacts. As a nonnoble cocatalyst, WS2 can accept photogenerated electrons from CdS, and the sulfur vacancies existing at its edges can effectively trap electrons as active sites for H2 evolution. Moreover, due to its strong negative property, the H+ from the aqueous solution can gather around WS2. WS2 possesses a lower reaction barrier than CdS, which expedites the kinetic process for the reaction. The optimized sample exhibits a high photocatalytic H2 evolution rate of 183.4 µmol/h (10 mg photocatalyst), which is as far as we know among the top in the records for CdS-based photocatalysts. We believe this present work will be inspiring in addressing the interfacial charge carrier transfer by constructing covalent heterointerfaces.

Anchoring highly-dispersed ZnCdS nanoparticles on NiCo Prussian blue Analogue-derived cubic-like NiCoP forms an S-scheme heterojunction for improved hydrogen evolution

This study used a facile hydrothermal technique to obtain a novel ZnCdS/NiCoP S-scheme heterojunction for highly photocatalytic H2 generation, Notably, phosphatization was used to derive the cubic NiCoP from a Prussian blue analog ZnCdS nanoparticles are simple to disperse on the surface because NiCoP has a cubic characteristic, which easily transfers interface charges, and consequently accelerates surface reaction kinetics. Furthermore, the ZnCdS/NiCoP-3% composite exhibited the highest photocatalytic H2 generation performance of 582.98 µmol with an apparent quantum yield (AQY) of 7.93% at 450 nm in the lactic acid aqueous solution, which is approximately 4.16 and 500-fold higher than that of the pure ZnCdS and NiCoP, respectively. Additionally, outstanding photostability was achieved after 20h of the four cycling experiments. Consequently, the peachy photocatalytic hydrogen evolution can be imputed for establishing S-scheme heterojunction, maintaining doughty redox capacity and achieving spatial separation of charges, thereby vastly restraining the fast recombination of photoexcitation. Furthermore, the photoluminescence (PL) spectroscopy and hydroxyl radical (OH) capture experiments further proved the S-scheme mechanism. Therefore, this study provides a neoteric perspective establishing S-scheme photocatalytic systems for solar energy conversion.

Flash dual-engineering of surface carboxyl defects and single Cu atoms of g-C3N4 via unique CO2 plasma immersion approach for boosted photocatalytic activity

Single transition metal atom embedding and functional group defect engineering is commonly utilized to optimize the electronic band structure of g-C3N4. However, most dual modification method suffers from the destruction of structure and active sites. Herein, single atom Cu and carboxyl group dual-endowed g-C3N4 nanosheets with a tunable bandgap were prepared by employing a facile CO2 plasma method. Experiments and density functional theory calculation show that the dual modification leads to a decreased bandgap and reconstructed local charge distribution to promote the separation of photogenerated charge carriers. As a result, the optimal Cu–CN–CO2-6min perform well in photo-Fenton degradation of dye and photocatalytic generation of H2. The synergy mechanism can be ascribed to the local imbalance electronic environment, in which single-atom Cu sites serve as H2 evolution center, and the carboxyl defect sites provide separate derivative site for various free radicals. The unique CO2 plasma method developed here can be completed in minutes with merits of environmental-friendless and waste-free, thus provides a promising route not only for the precise complex multiple modification of photocatalysts, but also for the sustainable industrial use of carbon dioxide.

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.

Single-Atom Photocatalysis: Surface-Defect Engineered TiO2 Anatase As a Tunable Platform for Hosting Co-Catalysts Atoms

Single‐atom (SA) or single‐site catalysis (SACs) has over the past years become an increasingly fascinating topic in the catalysis field. SACs have allowed new approaches in heterogeneous catalysis, minimized the use of precious metals, and enabled an unprecedented control over atomistic effects, resulting in improved active sites, and at the same time enabled the design of metal–support interfaces with a high level of structural and chemical control [1,2]. A diverse range of supports and features is known to stabilize isolated metal atoms, notably through pinning at electronic and/or structural defects associated with coordinatively unsaturated sites. However, it is still difficult to create a high density of thermally stable support sites, and hence the fabrication and control of high SA loading remains a challenge [1,2].In this work, an atomic‐scale defect engineering approach to form and control traps for SA sites as co‐catalyst for photocatalytic H2 generation is described. The control over defect types and density can be monitored by electron paramagnetic resonance spectroscopy (EPR) as the most precise method to study atomic scale defects [3]. Thin sputtered TiO2 layers are used as a model photocatalyst, and compared to the more frequently used (001) anatase sheets. To form stable SA co-catalysts, the TiO2 layers are reduced in Ar/H2 under different conditions (leading to different but defined Ti3+‐Ov surface defects), followed by immersion in a dilute solution containing Pt ion in this study. HAADF‐STEM results show that only on the thin‐film substrate can the density of SA sites be successfully controlled by the degree of reduction by annealing. An optimized SA‐Pt decoration can enhance the normalized photocatalytic activity of a TiO2 sputtered sample by a great extent in comparison to a conventional nanoparticle‐decorated TiO2 surface. Most interestingly, in the follow up work based on DFT calculations and experimental data we show that Pd single atom outperforms Pt as the most active co-catalyst for photocatalytic H2 evolution [4]. HAADF‐STEM, XPS, and EPR investigation jointly confirm the atomic nature of the decorated Pt and Pd on TiO2. Importantly, the density of the relevant surface exposed defect centers—thus the density of SA sites, which play the key role in photocatalytic activity—can be precisely optimized.[1] Sh. Mohajernia et al. Adv. Mater. 2020, 32 (16).[2] A. Wang, J. Li, and T. Zhang, Nat. Rev. Chem., 2(6).[3] Sh. Mohajernia et al. J. Mater. Chem. A, 2020, 8(1432)[4] G. Cha et al. iScience, 2021, 8 (24). Figure 1

Enhanced Photocatalytic Hydrogen Evolution from Water Splitting on Ta2O5/SrZrO3 Heterostructures Decorated with CuxO/RuO2 Cocatalysts.

Photocatalytic H2 generation by water splitting is a promising alternative for producing renewable fuels. This work synthesized a new type of Ta2O5/SrZrO3 heterostructure with Ru and Cu (RuO2/CuxO/Ta2O5/SrZrO3) using solid-state chemistry methods to achieve a high H2 production of 5164 μmol g–1 h–1 under simulated solar light, 39 times higher than that produced using SrZrO3. The heterostructure performance is compared with other Ta2O5/SrZrO3 heterostructure compositions loaded with RuO2, CuxO, or Pt. CuxO is used to showcase the usage of less costly cocatalysts to produce H2. The photocatalytic activity toward H2 by the RuO2/CuxO/Ta2O5/SrZrO3 heterostructure remains the highest, followed by RuO2/Ta2O5/SrZrO3 > CuxO/Ta2O5/SrZrO3 > Pt/Ta2O5/SrZrO3 > Ta2O5/SrZrO3 > SrZrO3. Band gap tunability and high optical absorbance in the visible region are more prominent for the heterostructures containing cocatalysts (RuO2 or CuxO) and are even higher for the binary catalyst (RuO2/CuxO). The presence of the binary catalyst is observed to impact the charge carrier transport in Ta2O5/SrZrO3, improving the solar to hydrogen conversion efficiency. The results represent a valuable contribution to the design of SrZrO3-based heterostructures for photocatalytic H2 production by solar water splitting.

Effects of Preparation Conditions on the Efficiency of Visible-Light-Driven Hydrogen Generation Based on Ni(II)-Modified Cd0.25Zn0.75S Photocatalysts.

Hydrogen as an environmentally friendly fuel can be produced by photocatalytic procedures from aqueous systems, utilizing H2S, an industrial side-product, by conversion and storage of renewable solar energy. Although composites of CdS and ZnS prepared by co-precipitation are very efficient in heterogeneous photocatalytic H2 generation, the optimal conditions for their synthesis and the effects of the various influencing factors are still not fully clarified. In this work, we investigated how the efficiency of Cd0.25Zn0.75S composites modified with Ni(II) was affected by the doping method, Ni-content, hydrothermal treatment, and presence of a complexing agent (ammonia) used in the preparation. The composition, optical, and structural properties of the photocatalysts prepared were determined by ICP, DRS, XRD, TEM, and STEM-EDS. Although hydrothermal treatment proved preferable for Ni-free composites, Ni-modification was more efficient for untreated composites precipitated from ammonia-containing media. The best efficiency (14.9% quantum yield at 380 nm irradiation, 109.8 mmol/g/h hydrogen evolution rate) achieved by surface modification with 0.1–0.3% Ni(II) was 15% and 20% better than those for hydrothermally treated catalyst and similarly prepared Pt-modified one, respectively. Structural characterization of the composites clearly confirmed that the Ni2+ ions were not embedded into the CdS-ZnS crystal lattice but were enriched on the surface of particles of the original catalyst in the form of NiO or Ni(OH)2. This co-catalyst increased the efficiency by electron-trapping, but its too high amount caused an opposite effect by diminishing the excitable surface of the CdS-ZnS particles.

Plasmonic TiN nanobelts assisted broad spectrum photocatalytic H2 generation

The conversion of solar energy in a wide spectrum region to clean fuel, H2, remains a challenge in the field of photocatalysis. Herein, plasmonic TiN nanobelts, as a novel cocatalyst, were coupled with CdS nanoparticles to construct a 0D/1D CdS/TiN heterojunction. Utilization of the localized surface plasmon resonance (LSPR) effect generated from TiN nanobelts was effective in promoting light absorption in the near-infrared region, accelerating charge separation, and generating hot electrons, which can effectively improve the photocatalytic H2 generation activity of the 0D/1D CdS/TiN heterojunction over a wide spectral range. Furthermore, owing to the high metallicity and low work function, an ohmic-junction was formed between the CdS and TiN, favoring the transfer of hot electrons generated from TiN nanobelts the CdS nanoparticles, followed by the reaction with water to generate H2. Consequently, the 0D/1D CdS/TiN heterojunction demonstrated H2 generation activity even under light irradiation at 760 nm, while the pure CdS and Pt nanoparticles modified CdS presented no activity. This work opens a new insight into coupling plasmonic cocatalysts to realize full spectrum H2 production.

Novel 3D-flower shaped KTaO3 perovskite for highly efficient photocatalytic and H2 generation ability

Treatment of industrial wastewater is one of the biggest challenges that mankind is facing today to prevent environmental pollution and its associated adverse effects on human health. Environmentalists across the world have given a clarion call for dye degradation, wastewater treatment and their effective management in our surrounding habitats. Despite significant progress in the development of new water treatment technologies, new materials haven’t matured enough for large scale industrial applications. Hence, the development of new scalable and sustainable multifunctional materials having the potential to treat wastewater and generate energy is the need of the hour. In this direction, novel 3D-flower shaped KTaO3 (3D-F-KT) material has been synthesized using areca seed powder as a green fuel. This new material has been successfully applied for the treatment of industrial wastewater contaminated with Rose Bengal. The efficiency of the material was analysed using several parameters like catalytic loading, dye concentration, kinetic and scavenging experiments, photostability, effect of co-existing ions and recyclability. In addition, the material was subjected to optical studies and H2 generation, making it a highly versatile multifunctional material, exhibiting a degradation efficiency of 94.12% in a short span of 150 min and a photocatalytic H2 generation efficiency of 374 µmol g−1 through water splitting. With an immense potential, KTaO3 presents itself as a multifunctional catalyst that can be scaled up for a variety of industrial applications ranging from wastewater treatment to energy generation and storage.

Porous CoxP nanosheets decorated Mn0.35Cd0.65S nanoparticles for highly enhanced noble-metal-free photocatalytic H2 generation

Incorporating 2D transition-metal phosphides into visible-light-driven semiconductors is fascinating for advancing novel photocatalysts. In this paper, porous CoxP nanosheets prepared by phosphating Co(OH)2 nanosheets are coupled with Mn0.35Cd0.65S nanoparticles for significantly boosted photocatalytic H2 evolution performance. The optimal CoxP/Mn0.35Cd0.65S hybrids show an excellent visible-light H2 production rate of 7188.9 μmol g−1h−1 upon visible light with an apparent quantum yield (AQY) of 18.9% at 420 nm. The H2 production rate of the 5% CoxP/Mn0.35Cd0.65S sample is about 257 times bare CdS and even 18 times higher than pristine Mn0.35Cd0.65S. This dramatic photocatalytic H2 generation activity is mainly ascribed to the efficient charge transfer and abundant active sites by introducing the porous CoxP nanosheets. The photocatalytic mechanism of the CoxP/Mn0.35Cd0.65S composites is investigated by the photoluminescence (PL), time-resolved photoluminescence (TRPL), electrochemical, and photoelectrochemical (PEC) tests. This work presents a viable strategy to design a 2D/0D hybrid system containing porous cobalt phosphides nanosheets and MnCdS solid solutions for noble-metal-free photocatalytic application.

Donor-acceptor carbazole-based conjugated microporous polymers as photocatalysts for visible-light-driven H2 and O2 evolution from water splitting

Although novel donor–acceptor conjugated microporous polymers (D-A CMPs) that absorb visible light broadly and allow the efficient isolation of photoinduced electrons and holes are being sought for water splitting photocatalysis, their elusive energy band structures have made it a challenge to produce both H2 and O2 simultaneously. In this paper, for the first time, we develop a series of semiconducting D-A CMPs with various sulfur and nitrogen contents and degrees of conjugation for effective photocatalytic H2 and O2 generation from water. Here, we used a carbazole (Cz) moiety as the donor, and pyrene (Py), triphenyltriazine (TPT), benzothiadiazole (BT), and thiazolylthiazole (TzTz) as the acceptors. The resulting D-A CMPs had large surface areas (up to 1530 m2 g–1) and high thermal stabilities (Td10: up to 623 °C; char yield: up to 83 wt%). Moreover, the Cz-TzTz CMP provided an excellent hydrogen evolution rate (HER), reaching 15.3 mmol g–1 h–1 in the presence of ascorbic acid as the sacrificial electron donor, but without the need for an additional Pt co-catalyst. Interestingly, the Cz-TPT CMP provided an excellent oxygen evolution rate (OER) of 3.38 mmol g–1 h–1 when using AgNO3 as a sacrificial electron acceptor; this value is competitive with those of most previously reported organic photocatalysts. These highly active CMP-based photocatalysts appear to be useful materials for solar energy harvesting and conversion.

Assembling Ti3C2 MXene into ZnIn2S4-NiSe2 S-scheme heterojunction with multiple charge transfer channels for accelerated photocatalytic H2 generation

Exploring effective photocatalysts to promote water splitting into solar fuels remains a great challenge due to the fast charge recombination. Herein, the ZnIn2S4(ZIS)-NiSe2 S-scheme heterojunctions anchored on Ti3C2 MXene (MX) with multiple internal electric fields were rationally fabricated for effective photocatalytic H2 generation. Indeed, under the intense synergy between Schottky barrier and S-scheme heterojunctions, the optimized photocatalyst exhibits the highest hydrogen evolution rate of 23.51 mmol/g/h with an apparent quantum yield of 10.9% at 450 nm monochromatic light, which is about 23.51-fold of the pure ZnIn2S4. The formation of Schottky barrier between ZnIn2S4 and MX could achieve the transfer of the electrons from ZIS to MX via the Schottky-junction interface, while an internal electric field in S-scheme heterojunctions allows the migration of electrons from NiSe2 to ZIS. In this regard, multiple internal electric fields with vibrant kinetics are constructed between the ZnIn2S4, NiSe2 and MX, which facilitates the favorable charge separation, thus leading to the isolated construction of electron-enriched H2-evolution sites (MX) and hole-accumulated oxidation sites (NiSe2), respectively. It is expected that the coupling of S-scheme heterojunctions and Schottky barrier in this work could provide a better understanding of the rational design of highly-efficient ternary hybrid photocatalysts for promoted H2 evolution.

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.

Fabricating Ti3C2 MXene cocatalyst supported NiAl-LDH/g-C3N4 ternary nanocomposite for stimulating solar photocatalytic H2 production

The development of effective nanotextures for photocatalytic H2 generation has been the focus of extensive study aimed to alleviate the associated energy and environmental problems. The intrinsic power of natural photosynthesis may be significantly replicated by constructing Z-scheme-based charge-transfer heterostructures. In this study, a two-dimensional Ti3C2 MXene supported NiAl-LDH/g-C3N4 heterojunction for increased photocatalytic H2 production under visible light has been examined in terms of design and fabrication. A modified hydrothermal technique was used to create a composite of NiAl-LDH/Ti3C2/g-C3N4 and the effect of variables including catalyst loading, sacrificial reagents, and irradiation time was investigated. The photocatalytic activity of NiAl-LDH/Ti3C2/g-C3N4 composite for H2 evolution reached to 720 µmol/g, which is 2, 1.4, and 1.2 times greater than g-C3N4, NiAl-LDH/g-C3N4, and Ti3C2/g-C3N4 samples, respectively. This obvious augmented activity was due to the formation of Z-scheme heterojunctions which contributed to maximize oxidation/reduction reaction and facilitating separation and migration of photoinduced electron-hole pairs in the presence of Ti3C2 MXene. Furthermore, using Triethanolamine with 100 mg catalyst loading, highest H2 yield was attained due to more attachment of reactants over the catalyst surface with minimum light diffusions effects. The stable layered structure, switchable property of layered composites and high interface contact area of the composite was discovered to play crucial roles in boosting the photocatalytic efficiency for H2 production.

Insight into Interfacial Charge Transfer during Photocatalytic H2 Evolution through Fe, Ni, Cu and Au Embedded in a Mesoporous TiO2@SiO2 Core‐shell

AbstractThe efficiency of charge transfer at the interface of transition metals loaded on TiO2 as well as the active reduction site undoubtedly define the kinetics of H2 production. Here, we report the interfacial charge process of various transition metals (Fe, Ni, Cu, and Au) embedded in mesoporous core‐shell nanostructures, which provides further insight into the photocatalytic H2 evolution. Au was found to be the most active cocatalyst for the H2 evolution. Au nanoparticles (NPs) collect electrons and become a very efficient reduction site, promoting both charge separation and H2 evolution. The scavenging capacity of Au was found to be the highest compared to other NPs. Cu(I), which is as active as Au, but at a higher loading, also shows an ability for electron scavenging and acts as an active site under UV excitation, or rather injects electrons into the TiO2 conduction band under visible excitation. Ni(II) NPs were found to be involved in charge‐carrier separation through hole collection and their contribution to hydrogen evolution is expected to be limited to visible absorption and electron injection. The same behavior occurs with Fe(III), however, it is less efficient for H2 generation due to the weak charge‐carrier lifetime. We show that only Cu(I) could compete with noble metals such as Au, presenting electron‐scavenging behavior. Understanding the charge‐carrier dynamics will help design a very efficient system for photocatalytic H2 generation system.

Ultrathin Two-Dimensional ZnIn2S4/Nix-B Heterostructure for High-Performance Photocatalytic Fine Chemical Synthesis and H2 Generation.

Photocatalytic H2 evolution coupled with organic transformation provides a new avenue to cooperatively produce clean fuels and fine chemicals, enabling a more efficient conversion of solar energy. Here, a novel two-dimensional (2D) heterostructure of ultrathin ZnIn2S4 nanosheets decorated with amorphous nickel boride (Nix-B) is prepared for simultaneous photocatalytic anaerobic H2 generation and aromatic aldehydes production. This ZnIn2S4/Nix-B catalyst elaborately combines the ultrathin structure advantage of the ZnIn2S4 semiconductor and the cocatalytic function of Nix-B. A high H2 production rate of 8.9 mmol h-1 g-1 is delivered over the optimal ZnIn2S4/Nix-B with a stoichiometric production of benzaldehyde, which is about 22 times higher than ZnIn2S4. Especially, the H2 evolution rate is much higher than the value (2.8 mmol h-1 g-1) of the traditional photocatalytic half reaction of H2 production with triethanolamine as a sacrificial agent. The apparent quantum yield reaches 24% at 420 nm, representing an advanced photocatalyst system. Moreover, compared with traditional sulfide, hydroxide, and even noble metal modified ZnIn2S4/M counterparts (M = NiS, Ni(OH)2, Pt), the ZnIn2S4/Nix-B also maintains markedly higher photocatalytic activity, showing a highly efficient and economical advantage of the Nix-B cocatalyst. This work sheds light on the exploration of 2D ultrathin semiconductors decorated with novel transition metal boride cocatalyst for efficient photocatalytic organic transformation integrated with solar fuel production.