Photocatalytic H2 Evolution Activity Research Articles

Micro-tailored g-C3N4 enables Ru single-atom loading for efficient photocatalytic H2 evolution

Loading single atom (SA) cocatalysts onto semiconductors offers great potential for improving the photocatalytic performance. Here, we report a simple micro-tailoring strategy that cuts g-C3N4 into small pieces and oligomers. Defects, boundaries, dopants and terminal groups created could confine Ru SAs stably onto the framework, ensuring uniform dispersion of Ru SAs on the tailored g-C3N4. The as-prepared composite, the tailored g-C3N4 loaded with Ru SAs, showed a dramatic increase photocatalytic activity for H2 evolution (4052.1 μmol h−1 g−1) compared to the composite of the non-tailored g-C3N4 loaded with Ru (394.3 μmol h−1 g−1). The enhanced catalytic activity was achieved by the metal-support interaction between the Ru atoms and the tailored g-C3N4, which could manipulate local charge distribution, thus promoting the adsorption of intermediates and enabling efficient charge transfer. In addition, atomic Ru-sites could provide directional charge transfer channels and targeting sites to facilitate rapid photo-introduced charge transfer and water reduction reaction. The proposed strategy provides a facile and feasible way for the construction of atomically dispersed catalysts for efficient photocatalytic H2 evolution and other reactions.

Ionic‐Liquid‐Assisted Precursor Route Syntheses of Highly Dispersed Supertetrahedral T3 In‐S/Se Clusters for Photocatalytic Hydrogen Production

AbstractHerein, two pure inorganic isostructural supertetrahedral T3 cluster based compounds with different ratio of S : Se, namely [Bmmim]6[In10QCl4](MIm)2 (Q=S9.5Se6.5 (In‐S/Se‐1), S2Se14 (In‐S/Se‐2), Bmmim=1‐butyl‐2,3‐dimethylimidazolium, MIm=1‐methylimidazole), have been obtained via an ionic‐liquid‐auxiliary precursor approach. Single‐crystal X‐ray diffraction (SCXRD) characterization showed that their structures are comprised of a discrete supertetrahedral T3 [In10QCl4]6− cluster charge‐balanced via six [Bmmim]+ cations. Importantly, the T3 clusters of In‐S/Se‐1 and In‐S/Se‐2 can be highly dispersed in dimethyl sulfoxide (DMSO). As a result, the T3 clusters uncovered more active sites after being dispersed, thereby exhibiting∼6 times of hydrogen generation rate of that in the solid state. Furthermore, benefitting from higher visible‐light absorption, larger driving force from conduction band (CB) and rapider photogenerated carrier migration, the photocatalytic H2 evolution activity was monotonically improved with increasing of the Se concentration in the T3 clusters. This work provides an alternative strategy for obtaining novel hybrid metal chalcogenide crystalline compounds for efficient energy conversion.

Physical properties and photocatalytic activity of pulverized Ga-doped La5Ti2Cu0.9Ag0.1O7S5 powder

The photocatalytic activity of rod-like Ga-doped La5Ti2Cu0.9Ag0.1O7S5 (Ga-LTCA) particles exhibiting the one-dimensional conductivity is considered to be determined by the particle length relative to the charge carrier diffusion length (a few micrometers at most). In this work, Ga-LTCA particles with length of approximately 1 µm and a clear rod-like structure were prepared by thermal sulfidation, ball-milling, and post-annealing in sulfur vapor. Despite the small particle size and neat morphology, however, the photocatalytic H2 evolution activity of the resultant Ga-LTCA was lowered, indicating that the degradation of the crystallinity during the ball-milling treatment was detrimental to the activity.

Construction of MOFs/g-C3N4 composite for accelerating visible-light-driven hydrogen evolution

In this work, we researched the effect of PCN-222 (M = Ni, Fe, Co) (PM) with different metal ligands on their photocatalytic performance. Compared with PFe and PCo, PNi has the highest photocatalytic hydrogen evolution efficiency due to the narrowest bandgap and the highest conduction band (CB) position. Furthermore, PCN-222(M)/g-C3N4 (PM/CN) heterojunctions was synthesized by one-pot solvothermal method in which PNi/CN displayed the most outstanding photocatalytic activity for H2 evolution. PNi/CN-1 displayed the highest photocatalytic activity. Its hydrogen evolution rate is 19.3 and 3.7 times higher than that of PNi and CN, respectively. A mechanism is proposed to expound the roles of PNi and the enhancement of visible-light photocatalytic performance of the PNi/CN. This work presents a new perspective for the development of high performance photocatalysts for hydrogen production under visible-light driven.

Rapid high-temperature hydrothermal post treatment on graphitic carbon nitride for enhanced photocatalytic H2 evolution

Hydrothermal treatment has been widely employed for material synthesis and modification. In this work, with the help of the homemade microreactor, a rapid high-temperature hydrothermal post treatment (RHTHTPT) process with fast heat transfer and short processing time was elaborately designed for graphitic carbon nitride (g-C3N4). Taking advantage of high temperature and short duration time during RHTHTPT process, the RHTHTPT-derived g-C3N4 reached up to a high product yield over 80%. The RHTHTPT-derived g-C3N4 showed an enhanced photocatalytic H2-evolution activity about 5.1 times that of pristine g-C3N4 under visible-light irradiation (λ > 400 nm). With systematic characterizations and the tracking of gas-liquid-solid products by RHTHTPT, it was found that the RHTHTPT could effectively enlarge the specific surface area to increase the active sites for photocatalytic H2-evolution reaction, abundant amino groups and the insertion of oxygen-containing functional groups in the surface of g-C3N4 could realize efficient carriers separation, both of which gave rise to the improved photocatalytic H2-evolution performance. This work develops a promising hydrothermal strategy to regulate the in-plane structure of g-C3N4 and brings a deeper understanding for the correlation between RHTHTPT-induced structure modification with photocatalytic ability, and therefore further provides some guidelines for directionally designing the special structures of g-C3N4 as well as other potential materials by hydrothermal modification.

EDTA-dominated hollow tube-like porous graphitic carbon nitride towards enhanced photocatalytic hydrogen evolution

Graphite carbon nitride (g-C3N4) as metal-free photocatalyst has been widely studied recently in photocatalytic water reduction, which is considered as one of the promising routes to realizing the hydrogen energy-based society in the future. The generally used preparation process based on thermal polymerization of precursors easily brought the formation of aggregated nanosheets morphology, severely limiting its photocatalytic activity. Herein, the hollow tube-like morphology with porous surface was elaborately obtained by ethylene diamine tetraacetic acid (EDTA)-involved hydrothermal treatment of melamine precursor. The hollow and porous features shortened the migration distance of photo-generated carriers, trapped the incident lights, and provided more photocatalytic reactive sites, then realizing the enhanced photocatalytic H2-evolution activity up to 7.1 times that of pristine g-C3N4. The presence of EDTA acted as the pivotal role to control the recrystallization process of melamine and its derivative, cyanuric acid, and thus to determine the framework formation of the hollow tube-like microstructure. Moreover, complete thermal decomposition of cyanuric acid during the thermal polymerization of precursors was responsible for the hollow and porous features. This work extends the morphology regulation cognition of g-C3N4 based on hydrothermal treatment of precursors, and is expected to bring deep understanding and feasible strategies to design morphology-dominated highly-efficient g-C3N4 photocatalysts.

Facile Synthesis of Monodisperse Pt Nanoparticles on Graphitic Carbon Nitride for High‐Performance Photocatalytic H2 evolution

AbstractGraphitic carbon nitride decorated with appropriate co‐catalysts has attracted widespread attention owing to its excellent photocatalytic H2 evolution activity. Herein, monodisperse Pt nanoparticles are synthesized by a facile method and anchored on graphitic carbon nitride (PCN) via self‐assembly route. Among the different Pt content, the 3 % Pt‐loaded PCN (Pt/PCN3) hybrid reveals highest photocatalytic activity for water splitting with the H2 evolution rate of 2.02 mmol g−1 h−1, about 4 times higher than that of Pt‐PCN by traditional photo‐deposition way. This work provides a new strategy for constructing high‐performance Pt‐based co‐catalysts on PCN to boost its photocatalytic activity.

K–I co-doped crystalline carbon nitride with outstanding visible light photocatalytic activity for H2 evolution

Heteroatomic doping is an effective way to optimize the electronic structure of carbon nitride to boost photocatalytic performance. However, the extra introduced defects could result in the decrease of its crystallinity. In this work, crystalline K–I co-doped carbon nitride (K–I–CCN) was simply synthesized from molten salt ionthermal post-calcination in nitrogen atmosphere. Structure characterization results indicate that compared to K–CCN synthesized from conventional molten salt heat treatment in air, nitrogen heating atmosphere is more conductive for the formation of homogeneous pore structure of the catalyst, which has larger surface area and pore volume, while could repairing some defects and resulting in better polymerization crystallization. In addition, except the implanting of K, I doping is still retained after nitrogen heat treatment, thus forming K–I co-doping structure. Due to the positive charge effect of K–I co-doping, K–I–CCN has a narrower band gap, higher surface charge density and stronger charge transport, so it performs significantly enhanced photocatalytic H 2 evolution activity from water splitting. • Low defect crystalline K–I–CCN was prepared by post molten salt heat treatment in nitrogen. • Nitrogen inhibits decomposition of I–CN, and the retained I and introduced K form co-doped structure. • K–I co-dopants have positive effect and inject electrons into CCN. • K–I–CCN has more optimized pore structure, light absorption and carrier transport than K–CCN. • K–I–CCN performs significantly enhanced photocatalytic H 2 production from water splitting.

High-Stability Ti3C2-QDs/ZnIn2S4/Ti(IV) Flower-like Heterojunction for Boosted Photocatalytic Hydrogen Evolution.

The practical application of photocatalytic H2-evolution is greatly limited by its sluggish charge separation, insufficient active sites, and stability of photocatalysts. Zero-dimensional (0D) Ti3C2 MXene quantum dots (MQDs) and amorphous Ti(IV) have been proven to be potential substitutes for noble co-catalyst to accelerate the separation of photogenerated electron-hole pairs and prevent the self-oxidation of photocatalysts, leading to better photocatalytic H2-evolution performance with long-term stability. In this study, amorphous Ti(IV) and MQDs co-catalysts were successfully deposited on ZnIn2S4 (ZIS) microspheres composed of ultra-thin nanosheets via a simple impregnation and self-assembly method (denoted as MQDs/ZIS/Ti(IV)). As expected, the optimal MQDs/ZIS/Ti(IV) sample exhibited a photocatalytic H2-evolution rate of 7.52 mmol·g−1·h−1 and excellent photostability without metallic Pt as the co-catalyst in the presence of Na2S/Na2SO3 as hole scavenger, about 16, 4.02 and 4.25 times higher than those of ZIS, ZIS/Ti(IV), and MQDs/ZIS, respectively. The significantly enhanced photocatalytic H2-evolution activity is attributed to the synergistic effect of the three-dimensional (3D) flower-like microsphere structure, the amorphous Ti(IV) hole co-catalyst, and a Schottky junction formed at the ZIS–MQDs interface, which offers more active sites, suppresses self-photocorrosion, and photo-generates the charge recombination of ZIS.

Promoted charge separation on 3D interconnected Ti3C2/MoS2/CdS composite for enhanced photocatalytic H2 production

The construction of heterojunction has been regarded as an effective way to promote photocatalytic H2 evolution activity, in which an intimately interfacial contact between the materials forming heterojunction is a positive effect on enhancing activity. Herein, a ternary 3D interconnected nanocomposite Ti3C2/MoS2/CdS was synthesized by a hydrothermal method. MoS2 nanosheet with a vertically aligned structure grew on the surface of multi-layered Ti3C2 to form 3D Ti3C2/MoS2 with tightly interfacial contact, which works as a cocatalyst for enhancing photocatalytic H2 evolution. CdS as a photocatalyst covered the surface of Ti3C2/MoS2 to absorb light energy. Benefitting to the synergistic effect between Ti3C2 and MoS2, the Ti3C2/MoS2 further accelerates electron transfer and inhibits the recombination of carriers. The H2 evolution rate of Ti3C2/MoS2/CdS reaches 15.2 mmol h−1 g−1 and the apparent quantum yield is 42.1% at λ = 420 nm. The result provides a useful insight for developing cocatalysts with new nanostructures via controlled interfacial engineering.

Design of noble metal-free NiTiO3/ZnIn2S4 heterojunction photocatalyst for efficient visible-light-assisted production of H2 and selective synthesis of 2,5-Bis(hydroxymethyl)furan

In this work, the development of noble metal-free NiTiO3/ZnIn2S4 (1:0.25 (S1), 1:0.5 (S2), 1:1 (S3), and 1:2 (S4)) heterojunction photocatalysts possessing optimal band edge positions suitable for efficient production of H2 from water and in situ reduction of biomass derivative, 5-hydroxymethylfurfural (HMF) to value-added 2,5-Bis(hydroxymethyl)furan (BHMF) in the absence of any external reducing agent is presented. The electron microscopy analysis of these heterojunctions revealed that ZnIn2S4 nanosheets are decorated uniformly over the surface of NiTiO3 microrods. Interestingly, heterojunction, S3 having NiTiO3/ZnIn2S4 (1:1) showed the best photocatalytic activity with a high H2 generation rate of 4.43 mmol g−1h−1 which is about eight times higher than that of pure ZnIn2S4. Further, the photocatalytic H2 evolution activity of S3 was coupled with in situ reduction of biomass derivative, HMF to obtain value-added chemical, BHMF with > 99% yield along with 100% selectivity. This high photocatalytic activity of S3 is aided by the Z-scheme heterojunction between NiTiO3 and ZnIn2S4. Moreover, photocatalyst, S3, showed excellent photostability and retained the catalytic activity for several cycles of reuse. Overall, this work represents a unique demonstration of H2 generation and high yield production of an important commodity chemical, BHMF from biomass-derivative and provides a greener path for harvesting solar energy and its conversion to chemical energy.

The Fabrication of Pd Single Atoms/Clusters on COF Layers as Co-catalysts for Photocatalytic H2 Evolution.

The particle size of co-catalysts significantly affects the activity of semiconductors in photocatalysis. Herein, we report that the photocatalytic H2 evolution (PHE) activity of a visible light responsive covalent organic framework (COF) layer supported on SiO2 nanoparticles was greatly promoted from 47.7 to 85.5 μmol/h by decreasing the particle size of the Pd co-catalyst from 3.3 nm to single atoms/clusters. A PHE rate of 156 mmol gCOF-1 h-1 and apparent quantum efficiency up to 7.3% were achieved with the Pd SAs/Cs co-catalyst. The relationship between the activity of Pd in H2 dissociation, proton reduction, and PHE rate suggests that the promotion effect of Pd SAs/Cs is mainly attributed to their enhancement in charge separation of COF layers rather than proton reduction. Furthermore, a photoactive film was fabricated and steady production of H2 was achieved under visible light irradiation and static conditions. The optimization of the particle size of co-catalysts provides an efficient method for enhancing the photocatalytic activity of semiconductors.

Synergistically Modulating Geometry and Electronic Structures of a Chalcogenide Photocatalyst via an Ion-Exchange Strategy.

Maneuvering the architecture and composition of semiconductors is essential to optimizing their performance in photocatalytic solar-to-fuel conversion. Here, we show that ion exchange, having a disparate mechanism with direct nucleation and growth of semiconductor crystals, can provide a new platform for rational control over the geometry and electronic structures of chalcogenide semiconductor photocatalysts. As a demonstration, the ZnSe nanocubes possessing a hollowed architecture and doped with a controllable amount of Ag+ ions are accessed via sequential ion exchange. The kinetics of the exchange reaction offers a knob for regulating the electronic structures of the Ag-doped ZnSe hollow cubes and, hence, their functions in light harvesting and photogenerated charge separation. Such synergistically geometric and optoelectronic modulation of ZnSe brings an order of magnitude enhancement in photocatalytic H2 evolution activity relative to commercial ZnSe powders. Our study corroborates that ion exchange may open up new horizons for judicious fabrication and engineering of semiconductor-based photocatalyst materials.

Photocatalysis over NH2-UiO-66/CoFe2O4/CdIn2S4 double p-n junction: Significantly promoting photocatalytic performance by double internal electric fields

Providing sufficient driving force for charge separation is a critical requirement in photocatalytic H2 evolution (PHE), but it remains challenging to precisely adjust the charge separation. Herein, we address this challenge by constructing a NH2-UiO-66/CoFe2O4/CdIn2S4 (NU6/CFO/CIS) double p-n junction with double internal electric fields. Compared with p-n junction with single internal electric field, double p-n junction enables photocatalysts with dual carrier transfer channels, faster carrier separation rate and stronger redox capacity. Additionally, PHE rate is related to the mass of photocatalyst used and a different photocatalyst weight may lead to a different PHE rate. When an excessive amount of photocatalyst is used, most of the photocatalyst cannot adsorb sufficient light and the photocatalytic rate is lower when normalized by the unit photocatalyst mass. Therefore, the effect of photocatalyst mass on PHE rate and apparent quantum yield are investigated in depth. The 25% NU6/2% CFO/CIS double p-n junction exhibits comparable PHE activity, its activity is about 13.5 times and 2.5 times higher than that of CIS and 2% CFO/CIS single p-n junction. In-situ XPS, density functional theory calculations, and Pt ion probe method are used to confirm where the photogenerated charges go and where they react, which is very in accordance with the “double p-n junction with double internal electric fields” mechanism. This work not only provides some ideas for the design of high-efficiency photocatalysts, but also offers a reference for the photocatalytic performance evaluation system.

Palladium-copper nanodot as novel H2-evolution cocatalyst: Optimizing interfacial hydrogen desorption for highly efficient photocatalytic activity

Noble metal palladium (Pd) is well-known as excellent photocatalytic cocatalyst, but its strong adsorption to hydrogen causes its limited H2-evolution activity. In this study, the transition metal Cu was successfully introduced into the metallic Pd to weaken its hydrogen-adsorption strength to improve its interfacial H2-evolution rate via the Pd-Cu alloying effect. Herein, the ultrasmall Pd100−xCux alloy nanodots (2−5 nm) as a novel H2-evolution cocatalyst were integrated with the TiO2 through a simple NaH2PO2-mediated co-deposition route. The resulting Pd100−xCux/TiO2 sample shows the significantly enhanced photocatalytic H2-generation performance (269.2 μmol h−1), which is much higher than the bare TiO2. Based on in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) and density functional theory (DFT) results, the as-formed Pd100−xCux alloy nanodots can effectively promote the separation of photo-generated charges and weak the adsorption strength for hydrogen to optimize the process of hydrogen-desorption process on Pd75Cu25 alloy, thus leading to high photocatalytic H2-evolution activity. Herein, the weakened H adsorption of Pd75Cu25 cocatalyst can be ascribed to the formation of electron-rich Pd after the introduction of weak electronegativity Cu. The present work about optimizing electronic structure for promoting interfacial reaction activity provides a new sight for the development of the highly efficient photocatalysts.

Synthesis of a Zr4(embonate)6-cobalt based superstructure for photocatalytic hydrogen production.

Herein, we report an efficient method to construct cage-based MOF materials with exposed metal active sites for catalysis. By employing Zr4L6 (L = embonate) cages as precursors for assembly with N-containing ligands and Co2+ ions, a new Zr4L6-Co based chain structure (PTC-318) has been generated through two-step reactions. Interestingly, in the absence of a photosensitizer, PTC-318 exhibits notable photocatalytic activity for H2 evolution under visible-light irradiation.

Facile synthesis of novel NH2-MIL-53(Fe)/AgSCN heterojunction composites as a highly efficient photocatalyst for ciprofloxacin degradation and H2 production under visible-light irradiation

A novel NH2-MIL-53(Fe)/AgSCN composite photocatalyst was successfully prepared by a one-step chemical precipitation method, the composite show high photocatalytic activity for antibiotics degradation and H2 evolution under visible light irradiation.

Facile solvothermal assisted g-C3N4post-grafting with aromatic amine dyes for effective photocatalytic hydrogen evolution

Dye grafted g-C3N4using covalent bondsviaa Schiff base chemical reaction exhibit much higher photocatalytic activity for H2evolution.

Manipulation of charge carrier flow in Bi4NbO8Cl nanoplate photocatalyst with metal loading.

Separation of photoexcited charge carriers in semiconductors is important for efficient solar energy conversion and yet the control strategies and underlying mechanisms are not fully established. Although layered compounds have been widely studied as photocatalysts, spatial separation between oxidation and reduction reaction sites is a challenging issue due to the parallel flow of photoexcited carriers along the layers. Here we demonstrate orthogonal carrier flow in layered Bi4NbO8Cl by depositing a Rh cocatalyst at the edges of nanoplates, resulting in spatial charge separation and significant enhancement of the photocatalytic activity. Combined experimental and theoretical studies revealed that lighter photogenerated electrons, due to a greater in-plane dispersion of the conduction band (vs. valence band), can travel along the plane and are readily trapped by the cocatalyst, whereas the remaining holes hop perpendicular to the plane because of the anisotropic crystal geometry. Our results propose manipulating carrier flow via cocatalyst deposition to achieve desirable carrier dynamics for photocatalytic reactions in layered compounds.

Enhanced H2 evolution of visible light active SnO2@Mg nanoflower

Developing a catalyst with a highly effective composite for hydrogen (H2) evolution has been recognised as a promising path toward evidence in modern energy and environmental remediation solutions. Herein, tin oxide (SnO2) based nanoflower photocatalysts were developed using the Sol-Gel process and then decorated with magnesium (Mg). These Mg interactions improve photogenerated charge carrier mobility, transfer, and separation, hence increasing visible light H2 evolution performance. As an outcome, the photocatalytic SnO2@Mg (10 wt%) nanocomposite had much better visible-light photocatalytic H2 evolution activity (26 µmol g−1/h−1) than pure SnO2 (3 µmol g−1/h−1). Besides, photocurrent density has increased to 38 µA cm−2, which is nearly 12 times higher than bare SnO2 (3 µA cm−2).