An Efficient,Visible‐Light‐Driven,Hydrogen Evolution Catalyst NiS/ZnxCd1−xS Nanocrystal Derived from a Metal–Organic Framework

Photocatalytic water splitting for hydrogen production using sustainable sunlight is a promising alternative to industrial hydrogen production. However, the scarcity of highly active, recyclable, inexpensive photocatalysts impedes the development of photocatalytic hydrogen evolution reaction (HER) schemes. Herein, a metal–organic framework (MOF)‐template strategy was developed to prepare non‐noble metal co‐catalyst/solid solution heterojunction NiS/Zn_xCd_1−xS with superior photocatalytic HER activity. By adjusting the doping metal concentration in MOFs, the chemical compositions and band gaps of the heterojunctions can be fine‐tuned, and the light absorption capacity and photocatalytic activity were further optimized. NiS/Zn_0.5Cd_0.5S exhibits an optimal HER rate of 16.78 mmol g⁻¹ h⁻¹ and high stability and recyclability under visible‐light irradiation (λ>420 nm). Detailed characterizations and in‐depth DFT calculations reveal the relationship between the heterojunction and photocatalytic activity and confirm the importance of NiS in accelerating the water dissociation kinetics, which is a crucial factor for photocatalytic HER.     

Construction of CoS2/Zn0.5Cd0.5S S-Scheme Heterojunction for Enhancing H2 Evolution Activity Under Visible Light

In the field of photocatalysis, building a heterojunction is an effective way to promote electron transfer and enhance the reducibility of electrons. Herein, the S-scheme heterojunction photocatalyst (CoS₂/Zn_0.5Cd_0.5S) of CoS₂ nanospheres modified Zn_0.5Cd_0.5S solid solution was synthesized and studied. The H₂ evolution rate of the composite catalyst reached 25.15 mmol g⁻¹ h⁻¹, which was 3.26 times that of single Zn_0.5Cd_0.5S, whereas pure CoS₂ showed almost no hydrogen production activity. Moreover, CoS₂/Zn_0.5Cd_0.5S had excellent stability and the hydrogen production rate after six cycles of experiments only dropped by 6.19 %. In addition, photoluminescence spectroscopy and photoelectrochemical experiments had effectively proved that the photogenerated carrier transfer rate of CoS₂/Zn_0.5Cd_0.5S was better than CoS₂ or Zn_0.5Cd_0.5S single catalyst. In this study, the synthesized CoS₂ and Zn_0.5Cd_0.5S were both n-type semiconductors. After close contact, they followed an S-scheme heterojunction electron transfer mechanism, which not only promoted the separation of their respective holes and electrons, but also retained a stronger reduction potential, thus promoting the reduction of H⁺ protons in photocatalytic experiments. In short, this work provided a new basis for the construction of S-scheme heterojunction in addition to being used for photocatalytic hydrogen production.     

An Efficient,Visible‐Light‐Driven,Hydrogen Evolution Catalyst NiS/ZnxCd1−xS Nanocrystal Derived from a Metal–Organic Framework

Photocatalytic water splitting for hydrogen production using sustainable sunlight is a promising alternative to industrial hydrogen production. However, the scarcity of highly active, recyclable, inexpensive photocatalysts impedes the development of photocatalytic hydrogen evolution reaction (HER) schemes. Herein, a metal–organic framework (MOF)‐template strategy was developed to prepare non‐noble metal co‐catalyst/solid solution heterojunction NiS/Zn_xCd_1?xS with superior photocatalytic HER activity. By adjusting the doping metal concentration in MOFs, the chemical compositions and band gaps of the heterojunctions can be fine‐tuned, and the light absorption capacity and photocatalytic activity were further optimized. NiS/Zn_0.5Cd_0.5S exhibits an optimal HER rate of 16.78 mmol g^?1 h^?1 and high stability and recyclability under visible‐light irradiation (λ>420 nm). Detailed characterizations and in‐depth DFT calculations reveal the relationship between the heterojunction and photocatalytic activity and confirm the importance of NiS in accelerating the water dissociation kinetics, which is a crucial factor for photocatalytic HER.     

An Efficient and Stable MoS2/Zn0.5Cd0.5S Nanocatalyst for Photocatalytic Hydrogen Evolution

Photocatalytic hydrogen evolution by water splitting is highly important for the application of hydrogen energy and the replacement of fossil fuel by solar energy, which needs the development of efficient catalysts with long-term catalytic stability under light irradiation in aqueous solution. Herein, Zn_0.5Cd_0.5S solid solution was synthesized by a metal–organic framework-templated strategy and then loaded with MoS₂ by a hydrothermal method to fabricate a MoS₂/Zn_0.5Cd_0.5S heterojunction for photocatalytic hydrogen evolution. The composition of MoS₂/Zn_0.5Cd_0.5S was fine-tuned to obtain the optimized 5 wt % MoS₂/Zn_0.5Cd_0.5S heterojunction, which showed a superior hydrogen evolution rate of 23.80 mmol h⁻¹ g⁻¹ and steady photocatalytic stability over 25 h. The photocatalytic performance is due to the appropriate composition and the formation of an intimate interface between MoS₂ and Zn_0.5Cd_0.5S, which endows the photocatalyst with high light-harvesting ability and effective separation of photogenerated carriers.     

Isolated Electron Trap-Induced Charge Accumulation for Efficient Photocatalytic Hydrogen Production

The solar-driven evolution of hydrogen from water using particulate photocatalysts is considered one of the most economical and promising protocols for achieving a stable supply of renewable energy. However, the efficiency of photocatalytic water splitting is far from satisfactory due to the sluggish electron-hole pair separation kinetics. Herein, isolated Mo atoms in a high oxidation state have been incorporated into the lattice of Cd_0.5Zn_0.5S (CZS@Mo) nanorods, which exhibit photocatalytic hydrogen evolution rate of 11.32 mmol g⁻¹ h⁻¹ (226.4 μmol h⁻¹; catalyst dosage 20 mg). Experimental and theoretical simulation results imply that the highly oxidized Mo species lead to mobile-charge imbalances in CZS and induce the directional photogenerated electrons transfer, resulting in effectively inhibited electron-hole recombination and greatly enhanced photocatalytic efficiency.     

Engineering a Self-Grown TiO2/Ti-MOF Heterojunction with Selectively Anchored High-Density Pt Single-Atomic Cocatalysts for Efficient Visible-Light-Driven Hydrogen Evolution

A photocatalyst TiO₂/Ti-BPDC-Pt is developed with a self-grown TiO₂/Ti-metal–organic framework (MOF) heterojunction, i.e., TiO₂/Ti-BPDC, and selectively anchored high-density Pt single-atomic cocatalysts on Ti-BPDC for photocatalytic hydrogen evolution. This intimate heterojunction, growing from the surface pyrolytic reconstruction of Ti-BPDC, works in a direct Z-scheme, efficiently separating electrons and holes. Pt is selectively anchored on Ti-BPDC by ligands and is found in the form of single atoms with loading up to 1.8 wt %. The selective location of Pt is the electron-enriched domain of the heterojunction, which further enhances the utilization of the separated electrons. This tailored TiO₂/Ti-BPDC-Pt shows a significantly enhanced activity of 12.4 mmol g⁻¹ h⁻¹ compared to other TiO₂- or MOF-based catalysts. The structure-activity relationship further proves the balance of two simultaneously exposed domains of heterojunctions is critical to fulfilling this kind of catalyst.     

水热法制备NiS/Cd1-xZnxS及其高效光催化产氢性能

利用水热法制备 NiS 负载的 Cd1-xZnxS 光催化剂.结果表明：在0.35 mol?L-1 Na2SO3和0.25 mol?L-1 Na2S牺牲剂下,0.5%(摩尔分数, y) NiS/Cd0.3Zn0.7S (1840μmol?h-1)获得最好活性,是Cd0.3Zn0.7S (884μmol?h-1)的2.1倍,高于0.5%(质量分数, w) Pt (1390μmol?h-1)的产氢活性.测得其在λ=420 nm附近的表观量子效率为36.8%. X射线衍射(XRD)、紫外-可见漫反射光谱(UV-Vis DRS)、透射电子显微镜(TEM)以及X射线光电子能谱(XPS)的表征结果表明, NiS作为产氢活性位,转移光生电子,因此提高了光催化产氢活性.     

Rapid Charge Transfer Endowed by Interfacial Ni-O Bonding in S-scheme Heterojunction for Efficient Photocatalytic H2 and Imine Production

Cooperative coupling of H₂ evolution with oxidative organic synthesis is promising in avoiding the use of sacrificial agents and producing hydrogen energy with value-added chemicals simultaneously. Nonetheless, the photocatalytic activity is obstructed by sluggish electron-hole separation and limited redox potentials. Herein, Ni-doped Zn_0.2Cd_0.8S quantum dots are chosen after screening by DFT simulation to couple with TiO₂ microspheres, forming a step-scheme heterojunction. The Ni-doped configuration tunes the highly active S site for augmented H₂ evolution, and the interfacial Ni−O bonds provide fast channels at the atomic level to lower the energy barrier for charge transfer. Also, DFT calculations reveal an enhanced built-in electric field in the heterojunction for superior charge migration and separation. Kinetic analysis by femtosecond transient absorption spectra demonstrates that expedited charge migration with electrons first transfer to Ni²⁺ and then to S sites. Therefore, the designed catalyst delivers drastically elevated H₂ yield (4.55 mmol g⁻¹ h⁻¹) and N-benzylidenebenzylamine production rate (3.35 mmol g⁻¹ h⁻¹). This work provides atomic-scale insights into the coordinated modulation of active sites and built-in electric fields in step-scheme heterojunction for ameliorative photocatalytic performance.     

Triplet–Triplet Annihilation Upconversion for Photocatalytic Hydrogen Evolution

The solar generation of hydrogen by water splitting provides a promising path for renewable hydrogen production and solar energy storage. Upconversion of low-energy photons into high-energy photons constitutes a promising strategy to enhance the light harvesting efficiency of artificial hydrogen production systems. In the present study, upconversion micelles are integrated with Cd_0.5Zn_0.5S to construct solar energy conversion systems. The upconversion micelle is employed to upconvert red photons to cyan photons. Cd_0.5Zn_0.5S is sensitized by upconverted cyan light to produce hydrogen, but not by incident red light without triplet–triplet annihilation upconversion (TTA-UC). The performance of the upconversion photocatalytic system was dramatically affected by the concentration of Cd_0.5Zn_0.5S and the irradiation intensity. This novel system was able to produce about 2.3 μL hydrogen after 5 h of red light (629 nm) irradiation (2.4 mW cm⁻²). The present study provides a candidate for applications using low-energy photons for solar hydrogen generation.     

Metal Cation Valency Dependence in Morphology Evolution of Cu2−xS Nanodisk Seeds and Their Pseudomorphic Cation Exchanges

A crucial parameter in the design of semiconductor nanoparticles (NPs) with controllable optical, magnetic, electronic, and catalytic properties is the morphology. Herein, we demonstrate the potential of additive metal cations with variable valency to direct the morphology evolution of copper-deficient Cu_2−xS nanoparticles in the process of seed-mediated growth. In particular, the djurleite Cu_1.94S seed could evolve from disk into tetradecahedron in the presence of tin(IV) cations, whereas they merely formed sharp hexagonal nanodisks with tin(II) cations. In addition to djurleite Cu_1.94S, the tin(IV) cations could be generalized to direct the growth of roxbyite Cu_1.8S and covellite CuS nanodisk seeds into tetradecahedra. We further perform pseudomorphic cation exchanges of Cu_1.94S tetradecahedra with Zn²⁺ and Cd²⁺ to produce polyhedral zinc sulfide (ZnS) and cadmium sulfide (CdS) NPs. Moreover, we achieve Cu_1.8S/ZnS and Cu_1.94S/CdS tetradecahedral heterostructures via partial cation exchange, which are otherwise inaccessible by traditional synthetic approaches.     

Photocatalytic hydrogen production using Me/Cd<Subscript>0.3</Subscript>Zn<Subscript>0.7</Subscript>S (Me = Au,Pt, Pd) catalysts: Transformation of the metallic catalyst under the action of the reaction medium

The activity and stability of Me/Cd_0.3Zn_0.7S (Me = Au, Pt, Pd) photocatalysts in the course of hydrogen production from water under the action of visible radiation have been investigated. The mechanism of activation and deactivation of the catalysts have been elucidated for the first time using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. An increase in the hydrogen evolution rate is observed for all of the catalysts at the early stages of testing. The highest hydrogen evolution rate, 5.4 μmol/min, is afforded by the 1%Pt/Cd_0.3Zn_0.7S catalyst. The activity of the Au/Cd_0.3Zn_0.7S and Pt/Cd_0.3Zn_0.7S catalysts becomes constant 7.5–9 h after the beginning of the photocatalytic test, while in the case of Pd/Cd_0.3Zn_0.7S the hydrogen evolution rate increases over the initial 6 h and then decreases. These specific features of the catalysts likely correlate with the initial state of the metals on the support surface. In particular, supported palladium is in the form of PdO, while gold and platinum are in the metallic state. The Au/Cd_0.3Zn_0.7S and Pt/Cd_0.3Zn_0.7S photocatalysts are activated due to metal encapsulation; the 1%Pd/Cd_0.3Zn_0.7S catalyst, due to the partial reduction of PdO to PdO _x . The 1%Pd/Cd_0.3Zn_0.7S catalyst is deactivated because of the aggregation of nanoparticles of the cadmium sulfide–zinc sulfide solid solution.     

Photopolymerization of water-soluble acrylic monomers induced by colloidal CdS and Cd x Zn1 − x S nanoparticles

Photocatalytic activity of CdS and Cd _x Zn_1−x S nanoparticles in the polymerization of acrylamide and acrylic acid in aqueous solutions has been found. It has been shown that the most probable way of the photogeneration of primary radicals is the reduction of an adsorbed monomer by the conduction band electrons of the semiconductor nanoparticles, a monomer oxidation by the valence band holes and atomic hydrogen addition to a monomer being complementary photoinitiation routes. A correlation between the composition of Cd_xZn_1-xS nanoparticles and their photocatalytic activity in the acrylamide polymerization has been established. It has been shown that an increase in the quantum yield of the photopolymerization in a sequence СdS < Cd_0.75Zn_0.25S < CdS_0.5Zn_0.5S < Cd_0.3Zn_0.7S originates from a concurrent increase of the conduction band potential of the semiconductor nanoparticles. A kinetic equation of the photocatalytic acrylamide polymerization has been derived. Quantum yields of the photoinitiation have been found to be as small as 10⁻⁴ to 10⁻³.     

Coordination-Induced N−H Bond Splitting of Ammonia and Primary Amine of CuI−MOFs

We report a porous three-dimensional anionic tetrazolium based Cu^I−MOF 1 , which is capable of cleaving the N−H bond of ammonia and primary amine, as well as the O−H bond of H₂O along with spontaneous H₂ evolution. In the gas-solid phase reaction of 1 with ammonia and water vapor, Cu^I−MOF 1 was gradually oxidized to NH₂−Cu^II−MOF and OH−Cu^II−MOF, through single-crystal-to-single-crystal (SCSC) structural transformations, which was confirmed by XPS, PXRD and X-ray single-crystal diffraction. Density functional theory (DFT) demonstrated that Cu^I−MOF could lower N−H bond dissociation free energy of ammonia through coordination-induced bond weakening and promote H₂ evolution by the reduction potential of 1 . To our knowledge, this is the first example of MOFs that activate ammonia and amine in gas-solid manner.     

Bemerkungen zu den Reaktionen mit Quecksilberrhodanid-Ion

Zusammenfassung Die Krystallform und die Farbe der reinen Verbindungen Zn-, Cd-, Co- und Cu[Hg(CNS)₄] werden beschrieben.Es wird gezeigt, daß die Empfindlichkeit des Zn-, Cd-, Co- und Cu-Nachweises gesteigert werden kann, wenn man statt des Behrens-Reagens reines, festes (NH₄)₂[Hg(CNS)₄] gebraucht. Die Empfindlichkeit des Nachweises der Ionen ist in Tabelle 5 (S. 69) zu finden.Bei gleichzeitiger Fällung von Zn^.. und Co^.., Zn^.. und Cu^.., Cd^.. und Co^.. und Cd^.. und Cu^.. entstehen intensiv gefärbte Substitutionsmischkrystalle, deren Löslichkeit im Wasser geringer ist, als die der reinen Komponenten. Durch diese Eigenschaften der sich bildenden Mischkrystalle kann bekanntlich die Empfindlichkeit des Nachweises der Ionen Cu^.., Co^.., Zn^.. und Cd^.. noch weiter gesteigert werden.Eine Neubestimmung der Empfindlichkeiten wurde vorgenommen (Tabelle 6, S. 70).     

Semiconductive Copper(I)–Organic Frameworks for Efficient Light‐Driven Hydrogen Generation Without Additional Photosensitizers and Cocatalysts

As the first example of a photocatalytic system for splitting water without additional cocatalysts and photosensitizers, the comparatively cost‐effective Cu₂I₂‐based MOF, Cu‐I‐bpy (bpy=4,4′‐bipyridine) exhibited highly efficient photocatalytic hydrogen production (7.09 mmol g⁻¹ h⁻¹). Density functional theory (DFT) calculations established the electronic structures of Cu‐I‐bpy with a narrow band gap of 2.05 eV, indicating its semiconductive behavior, which is consistent with the experimental value of 2.00 eV. The proposed mechanism demonstrates that Cu₂I₂ clusters of Cu‐I‐bpy serve as photoelectron generators to accelerate the copper(I) hydride interaction, providing redox reaction sites for hydrogen evolution. The highly stable cocatalyst‐free and self‐sensitized Cu‐I‐bpy provides new insights into the future design of cost‐effective d¹⁰‐based MOFs for highly efficient and long‐term solar fuels production.     

Photocatalytic production of hydrogen in systems based on Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>S/Ni<Superscript>0</Superscript> nanostructures

A relation was established between the composition of Cd _x Zn_1–x S nanoparticles and their ability to accumulate excess negative charge during irradiation. The rate of expenditure of the accumulated charge depends on the composition of the nanoparticles and is determined by their electric capacitance. A correlation was found between the photocatalytic activity of the Cd _x Zn_1–x S nanoparticles in the release of hydrogen from solutions of Na₂SO₃, their composition, and their capacity for photoinduced accumulation of excess charge. It was shown that Ni⁰ nanoparticles photodeposited on the surface of Cd _x Zn_1–x S are effective cocatalysts for the release of hydrogen. It was found that Zn^II additions in photocatalytic systems based on Cd _x Zn_1–x S/Ni⁰ nanostructures have a promoting action on the release of hydrogen from water–ethanol mixtures. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 1, pp. 8–16, January-February, 2009.     

A Semi‐Conductive Copper–Organic Framework with Two Types of Photocatalytic Activity

Based on the newly designed ligand 4′‐(3,5‐dicarboxyphenyl)‐4,2′:6′,4′′‐terpyridine (DCTP), a unique semi‐conductive 3D framework {[Cu^ΙCu^ΙΙ₂(DCTP)₂]NO₃?1.5 DMF}_n ( 1 ) with a narrow band gap of 2.1 eV, was obtained and structurally characterized. DFT calculations with van de Waals correction employed to explore the electronic structure of 1 , clearly revealed its semi‐conductive behavior. Furthermore, we found that 1 exhibits a superior band alignment with water to produce hydrogen and degrade organic pollutants. Without adding any photosensitizers, 1 displays an efficiently photocatalytic hydrogen production in water based on the photo‐generated electrons under UV/Vis light. 1 also exhibits excellent photo‐degradation of methyl blue under visible‐light owing to the strong oxidization of excited holes. It is the first example of MOFs with doubly photocatalytic activities related to photo‐generated electrons and holes, respectively.     

Substituent Effect to Fine-Tune Energy Levels of Atom-Precise [MoOS3]2− Modified Copper(I) Thiolate Clusters Boosting Recyclable Photocatalysis

The propulsion of photocatalytic hydrogen (H₂) production is limited by the rational design and regulation of catalysts with precise structures and excellent activities. In this work, the [MoOS₃]²⁻ unit is introduced into the Cu^I clusters to form a series of atomically-precise Mo^VI−Cu^I bimetallic clusters of [Cu₆(MoOS₃)₂(C₆H₅(CH₂)S)₂(P(C₆H₄−R)₃)₄] ⋅ xCH₃CN (R=H, CH₃, or F), which show high photocatalytic H₂ evolution activities and excellent stability. By electron push-pull effects of the surface ligand, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of these Mo^VI−Cu^I clusters can be finely tuned, promoting the resultant visible-light-driven H₂ evolution performance. Furthermore, Mo^VI−Cu^I clusters loaded onto the surface of magnetic Fe₃O₄ carriers significantly reduced the loss of catalysts in the collection process, efficiently addressing the recycling issues of such small cluster-based catalyst. This work not only highlights a competitively universal approach on the design of high-efficiency cluster photocatalysts for energy conversion, but also makes it feasible to manipulate the catalytic performance of clusters through a rational substituent strategy.     

Enhancing Built-in Electric Fields for Efficient Photocatalytic Hydrogen Evolution by Encapsulating C60 Fullerene into Zirconium-Based Metal-Organic Frameworks

High-efficiency photocatalysts based on metal-organic frameworks (MOFs) are often limited by poor charge separation and slow charge-transfer kinetics. Herein, a novel MOF photocatalyst is successfully constructed by encapsulating C₆₀ into a nano-sized zirconium-based MOF, NU-901. By virtue of host-guest interactions and uneven charge distribution, a substantial electrostatic potential difference is set-up in C₆₀@NU-901. The direct consequence is a robust built-in electric field, which tends to be 10.7 times higher in C₆₀@NU-901 than that found in NU-901. In the catalyst, photogenerated charge carriers are efficiently separated and transported to the surface. For example, photocatalytic hydrogen evolution reaches 22.3 mmol g⁻¹ h⁻¹ for C₆₀@NU-901, which is among the highest values for MOFs. Our concept of enhancing charge separation by harnessing host-guest interactions constitutes a promising strategy to design photocatalysts for efficient solar-to-chemical energy conversion.     

Cu2O/CeO2 Photo-electrochemical Water Splitting: A Nanocomposite with an Efficient Interfacial Transmission Path under the Co-action of a p–n Heterojunction and Micro-mesocrystals

Cu₂O is an ideal p-type material for photo-electrochemical (PEC) hydrogen evolution, although serious electron–hole recombination and photocorrosion restrict its further improvement for PEC activity. In this work, CeO₂ nanoparticles (NPs) self-assemble on the surface of Cu₂O octahedra, thus successfully forming a Cu₂O/CeO₂ structure in which p–n heterojunctions and micro-mesocrystals (m-MCs) work together. The optimum Cu₂O/CeO₂ composite, without the use of any cocatalyst, exhibits a fivefold higher photocurrent density (4.63 mA cm⁻² at 0 V vs. the reversible hydrogen electrode) than that of Cu₂O octahedra, which is better than most Cu₂O-based photocathodes without cocatalyst and even comparable with advanced Cu₂O-based photocathodes. The hydrogen production of the optimal Cu₂O/CeO₂ (Faradaic efficiency of ∼100 %) is 17.5 times higher than that of pure Cu₂O octahedra, and the photocurrent shows almost no decay under the 12 h stability test. The delicately designed Cu₂O/CeO₂ structure in this work provides reference and inspiration for the design of cathodes materials.