咔唑基共价有机框架用于光催化析氢

光催化析氢反应是获得高纯氢气的一种具有广阔应用前景的技术. 目前, 开发经济高效、 经久耐用的催化剂仍然是一个巨大的挑战. 我们以3,3'',6,6''-四醛-9,9''-双咔唑和3,7-二氨基二苯并[b,d]噻吩-5,5-二氧化物为基本构建单元, 通过经典的席夫碱反应, 合成了供体-受体型咔唑基共价有机框架(CZ-COF), 对其结构进行了表征, 并探究了其光催化析氢性能. CZ-COF展现了优异的光催化活性, 平均产氢速率为31 μmol·h^-1.     

Electrochemical Properties of a Rhodium(III) Mono-Terpyridyl Complex and Use as a Catalyst for Light-Driven Hydrogen Evolution in Water

Molecular hydrogen (H₂) is considered one of the most promising fuels to decarbonize the industrial and transportation sectors, and its photocatalytic production from molecular catalysts is a research field that is still abounding. The search for new molecular catalysts for H₂ production with simple and easily synthesized ligands is still ongoing, and the terpyridine ligand with its particular electronic and coordination properties, is a good candidate to design new catalysts meeting these requirements. Herein, we have isolated the new mono-terpyridyl rhodium complex, [Rh^III(tpy)(CH₃CN)Cl₂](CF₃SO₃) (Rh-tpy), and shown that it can act as a catalyst for the light-induced proton reduction into H₂ in water in the presence of the [Ru(bpy)₃]Cl₂ (Ru) photosensitizer and ascorbate as sacrificial electron donor. Under photocatalytic conditions, in acetate buffer at pH 4.5 with 0.1 M of ascorbate and 530 μM of Ru, the Rh-tpy catalyst produces H₂ with turnover number versus catalyst (TON_Cat*) of 300 at a Rh concentration of 10 μM, and up to 1000 at a concentration of 1 μM. The photocatalytic performance of Ru/Rh-tpy/HA^–/H₂A has been also compared with that obtained with the bis-dimethyl-bipyridyl complex [Rh^III(dmbpy)₂Cl₂]⁺ (Rh2) as a catalyst in the same experimental conditions. The investigation of the electrochemical properties of Rh-tpy in DMF solvent reveals that the two-electrons reduced state of the complex, the square-planar [Rh^I(tpy)Cl] (Rh^I-tpy), is quantitatively electrogenerated by bulk electrolysis. This complex is stable for hours under an inert atmosphere owing to the π-acceptor property of the terpyridine ligand that stabilizes the low oxidation states of the rhodium, making this catalyst less prone to degrade during photocatalysis. The π-acceptor property of terpyridine also confers to the Rh-tpy catalyst a moderately negative reduction potential (Ep_c(Rh^III/Rh^I) = −0.83 V vs. SCE in DMF), making possible its reduction by the reduced state of Ru, [Ru^II(bpy)(bpy^•−)]⁺ (Ru⁻) (E_1/2(Ru^II/Ru⁻) = −1.50 V vs. SCE) generated by a reductive quenching of the Ru excited state (*Ru) by ascorbate during photocatalysis. A Stern–Volmer plot and transient absorption spectroscopy confirmed that the first step of the photocatalytic process is the reductive quenching of *Ru by ascorbate. The resulting reduced Ru species (Ru⁻) were then able to activate the Rh^III-tpy H₂-evolving catalyst by reduction generating Rh^I-tpy, which can react with a proton on a sub-nanosecond time scale to form a Rh^III(H)-tpy hydride, the key intermediate for H₂ evolution.     

钴、碳共掺杂氮化碳的制备及其光催化分解水产氢性能

针对氮化碳可见光利用率低和在光催化过程中光生电子与空穴易于复合的缺点,通过钴、碳共掺杂提升其光催化性能。以尿素为前驱体,维生素B12（VB12）为钴源和碳源,将二者的混合物进行一步煅烧,制备钴、碳共掺杂氮化碳（CNCoC）。结果表明,钴、碳共掺杂对氮化碳的微观形貌、骨架结构和官能团都没有造成明显影响;但是增大了产物的比表面积,调节了产物的能带结构,增加了其对可见光的吸收。更重要的是,相比于单一元素碳的掺杂,钴、碳共掺杂具有协同作用,能够更有效地提升光生电子和空穴的分离和传递效率。因此,加入6 mg VB12制备的CNCoC-6的可见光光催化分解水产氢速率达到了56.1 μmol·h^-1,是纯氮化碳（CN）的3.05倍;而碳掺杂氮化碳（CNC-6）的产氢速率仅为CN的2.55倍。     

Regulating Charge-Transfer in Conjugated Microporous Polymers for Photocatalytic Hydrogen Evolution

Bandgap engineering in donor–acceptor conjugated microporous polymers (CMPs) is a potential way to increase the solar-energy harvesting towards photochemical water splitting. Here, the design and synthesis of a series of donor–acceptor CMPs [tetraphenylethylene (TPE) and 9-fluorenone (F) as the donor and the acceptor, respectively], F_0.1CMP , F_0.5CMP , and F_2.0CMP , are reported. These CMPs exhibited tunable bandgaps and photocatalytic hydrogen evolution from water. The donor–acceptor CMPs exhibited also intramolecular charge-transfer (ICT) absorption in the visible region (λ_max=480 nm) and their bandgap was finely tuned from 2.8 to 2.1 eV by increasing the 9-fluorenone content. Interestingly, they also showed emissions in the 540–580 nm range assisted by the energy transfer from the other TPE segments (not involved in charge-transfer interactions), as evidenced from fluorescence lifetime decay analysis. By increasing the 9-fluorenone content the emission color of the polymer was also tuned from green to red. Photocatalytic activities of the donor–acceptor CMPs ( F_0.1CMP , F_0.5CMP , and F_2.0CMP ) are greatly enhanced compared to the 9-fluorenone free polymer ( F_0.0CMP ), which is essentially due to improved visible-light absorption and low bandgap of donor–acceptor CMPs. Among all the polymers F_0.5CMP with an optimum bandgap (2.3 eV) showed the highest H₂ evolution under visible-light irradiation. Moreover, all polymers showed excellent dispersibility in organic solvents and easy coated on the solid substrates.     

ZnO/ZnS Heterostructured Nanorod Arrays and Their Efficient Photocatalytic Hydrogen Evolution

Semiconducting heterostructures have been widely applied in photocatalytic hydrogen evolution due to their variable band gaps and high energy conversion efficiency. As typical semiconducting heterostructures, ZnO/ZnS heterostructured nanorod arrays (HNRAs) have been obtained through a simple anion‐exchange process in this work. Structural characterization indicates that the heterostructured nanorods (HNRs) are all composed of hexagonal wurtzite ZnO core and cubic zinc‐blende ZnS shell. As expected, the as‐obtained one‐dimensional heterostructures not only lower the energy barrier but also enhance the separation ability of photogenerated carriers in photocatalytic hydrogen evolution. Through comparisons, it is found that 1D ZnO/ZnS HNRAs exhibit much better performance in photocatalytic hydrogen evolution than 1D ZnO nanorod arrays (NRAs) and 1D ZnS NRAs. The maximum H₂ production is 19.2 mmol h^?1 for 0.05 g catalyst under solar‐simulated light irradiation at 25 °C and the corresponding quantum efficiency is 13.9 %, which goes beyond the economical threshold of photocatalytic hydrogen evolution technology.     

Harvesting Solar Light with Crystalline Carbon Nitrides for Efficient Photocatalytic Hydrogen Evolution

Described herein is the photocatalytic hydrogen evolution using crystalline carbon nitrides (CNs) obtained by supramolecular aggregation followed by ionic melt polycondensation (IMP) using melamine and 2,4,6‐triaminopyrimidine as a dopant. The solid state NMR spectrum of ¹⁵N‐enriched CN confirms the triazine as a building unit. Controlling the amount and arrangements of dopants in the CN structure can dramatically enhance the photocatalytic performance for H₂ evolution. The polytriazine imide (PTI) exhibits the apparent quantum efficiency (AQE) of 15 % at 400 nm. This method successfully enables a substantial amount of visible light to be harvested for H₂ evolution, and provides a promising route for the rational design of a variety of highly active crystalline CN photocatalysts.     

Conjugated Polymers: Catalysts for Photocatalytic Hydrogen Evolution

Conjugated polymers, comprising fully π‐conjugated systems, present a new generation of heterogeneous photocatalysts for solar‐energy utilization. They have three key features, namely robustness, nontoxicity, and visible‐light activity, for photocatalytic processes, thus making them appealing candidates for scale‐up. Presented in this Minireview, is a brief summary on the recent development of various promising polymer photocatalysts for hydrogen evolution from aqueous solutions, including linear polymers, planarized polymers, triazine/heptazine polymers, and other related organic conjugated semiconductors, with a particular focus on the rational manipulation in the composition, architectures, and optical and electronic properties that are relevant to photophysical and photochemical properties. Some future trends and prospects for organic conjugated photocatalysts in artificial photosynthesis, by water splitting, are also envisaged.     

Defect Engineering of MoS2 and Its Impacts on Electrocatalytic and Photocatalytic Behavior in Hydrogen Evolution Reactions

Molybdenum disulfide (MoS₂) has been regarded as a favorable photocatalytic co‐catalyst and efficient hydrogen evolution reaction (HER) electrocatalyst alternative to expensive noble‐metals catalysts, owing to earth‐abundance, proper band gap, high surface area, and fast electron transfer ability. In order to achieve a higher catalytic efficiency, defects strategies such as phase engineering and vacancy introduction are considered as promising methods for natural 2H‐MoS₂ to increase its active sites and promote electron transfer rate. In this study, we report a new two‐step defect engineering process to generate vacancies‐rich hybrid‐phase MoS₂ and to introduce Ru particles at the same time, which includes hydrothermal reaction and a subsequent hydrogen reduction. Compositional and structural properties of the synthesized defects‐rich MoS₂ are investigated by XRD, XPS, XAFS and Raman measurements, and the electrochemical hydrogen evolution reaction performance, as well as photocatalytic hydrogen evolution performance in the ammonia borane dehydrogenation are evaluated. Both catalytic activities are boosted with the increase of defects concentrations in MoS₂, which ascertains that the defects engineering is a promising route to promote catalytic performance of MoS₂.     

稀土离子掺杂对纳米TiO2光催化制氢活性的影响

采用溶胶-凝胶技术制备了纳米TiO2和一系列稀土离子掺杂的TiO2光催化剂,通过X射线衍射、透射电镜及N2吸附等技术对其进行了表征,考察了样品光催化分解水制氢的性能.结果表明,稀土离子掺杂有效抑制了TiO2粒子的生长,提高了粒子的分散性,增大了催化剂的比表面积,从而大幅度提高了其光催化分解水制氢的性能.其中,Gd3 掺杂的TiO2样品粒径最小,分散性最好,比表面积最大(是未掺杂TiO2的35倍).掺杂离子的电子构型对样品的光催化制氢活性有较大影响,具有全空电子构型的La3 和半充满电子构型的Gd3 掺杂的样品具有较高的光催化制氢活性(分别是未掺杂TiO2的3.69倍和3.72倍).     

Bimodal Heterogeneous Functionality in Redox-Active Conjugated Microporous Polymer toward Electrocatalytic Oxygen Reduction and Photocatalytic Hydrogen Evolution

The designing and development of heterogeneous catalysts for conversion of renewable energy to chemical energies by electrochemical as well as photochemical processes is at the forefront of energy research. In this work, two new donor–acceptor-based redox-active conjugated microporous polymers (CMPs) (TAPA-OPE-mix and TAPA-OPE-gly) are synthesized through Schiff base condensation reaction using a microwave synthesizer. Notably, the asymmetric and symmetric bola-amphiphilic nature of the OPE struts results in distinct nanostructuring and morphologies in the CMPs. Interestingly, both CMPs show impressive heterogeneous catalytic activity toward electrochemical O₂ reduction and photocatalytic H₂ evolution reactions, and therefore, act as bimodal electro- and photocatalytic porous organic materials. Furthermore, the redox-active property of the CMPs is exploited for in situ generation and stabilization of platinum nanoparticles (Pt), and these Pt@CMPs exhibit significantly enhanced photocatalytic activity.     

层状K-Fe-Ti金属氧化物上光催化分解水制氢

 采用高温固相反应法合成了层状K-Fe-Ti金属氧化物催化剂,用X射线衍射、扫描电子显微镜、透射电子显微镜和紫外-可见漫反射光谱等手段对催化剂进行了表征,并通过光催化分解水制氢反应对催化剂的活性进行了评价. 结果表明,合成原料中K+的含量和固相反应温度都会影响催化剂的晶相结构; 催化剂中八面体配位的Fe3+使其具有显著的可见光吸收特性,但增加合成原料中Fe3+的量仅增加孤立的Fe2O3物种; 在草酸的偶合作用下,正交晶相的催化剂光催化分解水的产氢速率高于四方晶相的催化剂,但后者的产氢速率稳定性高于前者.     

A Cocatalyst that Stabilizes a Hydride Intermediate during Photocatalytic Hydrogen Evolution over a Rhodium‐Doped TiO2 Nanosheet

The hydrogen evolution reaction using semiconductor photocatalysts has been significantly improved by cocatalyst loading. However, there are still many speculations regarding the actual role of the cocatalyst. Now a photocatalytic hydrogen evolution reaction pathway is reported on a cocatalyst site using TiO₂ nanosheets doped with Rh at Ti sites as one‐atom cocatalysts. A hydride species adsorbed on the one‐atom Rh dopant cocatalyst site was confirmed experimentally as the intermediate state for hydrogen evolution, which was consistent with the results of density functional theory (DFT) calculations. In this system, the role of the cocatalyst in photocatalytic hydrogen evolution is related to the withdrawal of photo‐excited electrons and stabilization of the hydride intermediate species; the presence of oxygen vacancies induced by Rh facilitate the withdrawal of electrons and stabilization of the hydride.     

氧掺杂氮化碳纳米片的制备及其光解水制氢性能

以草酸为氧源,二聚氰胺和尿素为原料,采用两步热聚合方式合成氧掺杂氮化碳纳米片催化剂(CNO)。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、紫外-可见吸收光谱(UV-Vis)、X射线光电子能谱分析(XPS)、荧光光谱(PL)及电化学测试等技术对催化剂进行结构表征分析。在可见光照射下通过分解水制氢反应对CNO的光催化还原性能进行评价。结果表明,草酸中的O元素通过取代氮化碳三嗪环结构中N原子直接键合到sp~2杂化碳上,形成O掺杂CNO。经O掺杂改性后的氮化碳具有良好的层状堆积结构,可见光吸收性明显提高,同时禁带宽度降低。O掺杂的引入加速了光生电子-空穴对的分离和传输,能大幅度提高氮化碳的光催化分解水制氢性能,在可见光照下达88.6μmol·h~(-1),是未掺杂CN的3.91倍。     

A Heterogeneous Photocatalytic Hydrogen Evolution Dyad: [(tpy

The development of an artificial heterogeneous dyad by covalently anchoring a hydrogen‐evolving molecule catalyst to a semiconductor photosensitizer through a bridging ligand is highly challenging. Herein, we adopt the inorganic–organic hybrid CdS–DETA NSs (DETA=diethylenetriamine, NSs=nanosheets) as initial matrix to successfully construct an imine bond (‐CH=N‐) linked heterogeneous dyad [CdS?N=CH?Ni] through the condensation reaction between the amino groups of CdS–DETA and the aldehyde group of the water reduction molecular catalyst, [(tpy‐CHO)₂Ni]Cl₂ (tpy=terpyridine). The [CdS?N=CH?Ni] enables a turnover number (TON) of about 43 815 versus Ni catalysts and an initial turnover frequency (TOF) of approximately 0.47 s^?1 in 26 h under visible‐light irradiation (λ>420 nm). The apparent quantum yield (AQY) reaches (9.9±0.8) % at 420 nm. Under optical conditions, the [CdS?N=CH?Ni] can achieve a considerable amount of hydrogen production, 507.1±27 μmol H₂ for 6 h, which is 1.27 times that generated from the mechanically mixed system of CdS–DETA NSs and [(tpy‐CH=NR)₂Ni]Cl₂ ( III ) under otherwise identical conditions. Furthermore, its TON value based on Ni species is also higher than that of the mixed system of CdS–DETA and III .     

High‐Resolution Electrochemical Mapping of the Hydrogen Evolution Reaction on Transition‐Metal Dichalcogenide Nanosheets

High‐resolution scanning electrochemical cell microscopy (SECCM) is used to image and quantitatively analyze the hydrogen evolution reaction (HER) catalytically active sites of 1H‐MoS₂ nanosheets, MoS₂, and WS₂ heteronanosheets. Using a 20 nm radius nanopipette and hopping mode scanning, the resolution of SECCM was beyond the optical microscopy limit and visualized a small triangular MoS₂ nanosheet with a side length of ca. 130 nm. The electrochemical cell provides local cyclic voltammograms with a nanoscale spatial resolution for visualizing HER active sites as electrochemical images. The HER activity difference of edge, terrace, and heterojunction of MoS₂ and WS₂ were revealed. The SECCM imaging directly visualized the relationship of HER activity and number of MoS₂ nanosheet layers and unveiled the heterogeneous aging state of MoS₂ nanosheets. SECCM can be used for improving local HER activities by producing sulfur vacancies using electrochemical reaction at the selected region.     

Hydrophilic Conjugated Materials for Photocatalytic Hydrogen Evolution

Photocatalytic hydrogen evolution is viewed as a promising green strategy to utilize the inexhaustible solar energy and provide clean hydrogen fuels with zero‐emission characteristic. The nature of semiconductor‐based photocatalysts is the key point to achieve efficient photocatalytic hydrogen evolution. Conjugated materials have been recently emerging as a novel class of photocatalysts for hydrogen evolution and photocatalytic reactions due to their electronic properties can be well controlled via tailor‐made chemical structures. Hydrophilic conjugated materials, a subgroup of conjugated materials, possess multiple advantages for photocatalytic applications, thus spurring remarkable progress on both material realm and photocatalytic applications. This minireview aims to provide a brief review of the recent developments of hydrophilic conjugated polymers/small molecules for photocatalytic applications, and special concern on the rational molecular design and their impact on photocatalytic performance will be reviewed. Perspectives on the hydrophilic conjugated materials and challenges to their applications in the photocatalytic field are also presented.     

Graphitic Carbon Nitride/Nitrogen‐Rich Carbon Nanofibers: Highly Efficient Photocatalytic Hydrogen Evolution without Cocatalysts

An interconnected framework of mesoporous graphitic‐C₃N₄ nanofibers merged with in situ incorporated nitrogen‐rich carbon has been prepared. The unique composition and structure of the nanofibers as well as strong coupling between the components endow them with efficient light‐harvesting properties, improved charged separation, and a multidimensional electron transport path that enhance the performance of hydrogen production. The as‐obtained catalyst exhibits an extremely high hydrogen‐evolution rate of 16885 μmol h^?1 g^?1, and a remarkable apparent quantum efficiency of 14.3 % at 420 nm without any cocatalysts, which is much higher than most reported g‐C₃N₄‐based photocatalysts even in the presence of Pt‐based cocatalysts.     

One‐pot Synthesis of CdS Nanocrystals Hybridized with Single‐Layer Transition‐Metal Dichalcogenide Nanosheets for Efficient Photocatalytic Hydrogen Evolution

Exploration of low‐cost and earth‐abundant photocatalysts for highly efficient solar photocatalytic water splitting is of great importance. Although transition‐metal dichalcogenides (TMDs) showed outstanding performance as co‐catalysts for the hydrogen evolution reaction (HER), designing TMD‐hybridized photocatalysts with abundant active sites for the HER still remains challenge. Here, a facile one‐pot wet‐chemical method is developed to prepare MS₂–CdS (M=W or Mo) nanohybrids. Surprisedly, in the obtained nanohybrids, single‐layer MS₂ nanosheets with lateral size of 4–10 nm selectively grow on the Cd‐rich (0001) surface of wurtzite CdS nanocrystals. These MS₂–CdS nanohybrids possess a large number of edge sites in the MS₂ layers, which are active sites for the HER. The photocatalytic performances of WS₂–CdS and MoS₂–CdS nanohybrids towards the HER under visible light irradiation (>420 nm) are about 16 and 12 times that of pure CdS, respectively. Importantly, the MS₂–CdS nanohybrids showed enhanced stability after a long‐time test (16 h), and 70 % of catalytic activity still remained.     

Hierarchical MoS2@TiO2 Heterojunctions for Enhanced Photocatalytic Performance and Electrocatalytic Hydrogen Evolution

Hierarchical MoS₂@TiO₂ heterojunctions were synthesized through a one‐step hydrothermal method by using protonic titanate nanosheets as the precursor. The TiO₂ nanosheets prevent the aggregation of MoS₂ and promote the carrier transfer efficiency, and thus enhance the photocatalytic and electrocatalytic activity of the nanostructured MoS₂. The obtained MoS₂@TiO₂ has significantly enhanced photocatalytic activity in the degradation of rhodamine B (over 5.2 times compared with pure MoS₂) and acetone (over 2.8 times compared with pure MoS₂). MoS₂@TiO₂ is also beneficial for electrocatalytic hydrogen evolution (26 times compared with pure MoS₂, based on the cathodic current density). This work offers a promising way to prevent the self‐aggregation of MoS₂ and provides a new insight for the design of heterojunctions for materials with lattice mismatches.