Photoinduced hydrogen evolution in an artificial system containing photosystem I, hydrogenase, methyl viologen and mercaptoacetic acid

Hydrogen evolution was detected in an artificial system composed of light-harvesting unit of purified photosystem I, catalyst of hydrogenase, methyl viologen and electron donor under radiation. Absorption spectral features confirmed that electron transfer from electron donors to proton was via a photoinduced reductive process of methyl viologen.     

Photoinduced hydrogen evolution in an artificial system containing photosystemⅠ,hydrogenase,methyl viologen and mercaptoacetic acid

Hydrogen evolution was detected in an artificial system composed of light-harvesting unit of purified photosystem I,catalyst of hydrogenase,methyl viologen and electron donor under radiation.Absorption spectral features confirmed that electron transfer from electron donors to proton was via a photoinduced reductive process of methyl viologen.     

Photoinduced hydrogen evolution with water soluble bisviologen linked zinc porphyrin and hydrogenase

Water soluble bisviologen linked zinc porphyrin (ZnP(C₄V_AC₄V_B)₄) was synthesized and characterized. The quenching processes of the photoexcited singlet state and triplet state of ZnP(C₄V_AC₄V_B)₄ were measured by using fluorescence lifetime and laser flash photolysis. The photoexcited singlet state of the zinc porphyrin was quenched by the bonded bisviologen. Photoinduced hydrogen evolution with ZnP(C₄V_AC₄V_B)₄ and hydrogenase was observed under steady state irradiation.     

Blocking backward reaction on hydrogen evolution cocatalyst in a photosystem II hybrid Z-scheme water splitting system

Photocatalytic Z-scheme water splitting is considered as a promising approach to produce solar hydrogen. However, the forward hydrogen production reaction is often impeded by backward reactions. In the present study, in a photosystem II-integrated hybrid Z-scheme water splitting system, the backward hydrogen oxidation reaction was significantly suppressed by loading a PtCrOx cocatalyst on a ZrO₂/TaON photocatalyst. Due to the weak chemisorption and activation of molecular hydrogen on PtCrOx, where Pt is stabilized in the oxidized forms, Pt^II and Pt^IV, hydrogen oxidation is inhibited. However, it is remarkably well-catalyzed by the metallic Pt cocatalyst, thereby rapidly consuming the produced hydrogen. This work describes an approach to inhibit the backward reaction in the photosystem II-integrated hybrid Z-scheme water splitting system using Fe(CN)₆^3?/Fe(CN)₆^4? redox couple as an electron shuttle.     

高效稳定的Al~(3+)偶联多层Eosin Y敏化TiO_2光催化制氢体系研究

通过Al3+偶联制备了多层EosinY敏化的TiO2催化剂,其光催化制氢性能优于Fe3+偶联的催化剂.在水体系、甲醇-水体系中,以三乙醇胺(TEOA)作电子给体,采用原位载Pt,考察了催化剂在可见光(λ420nm)下的制氢活性与稳定性.结果表明,含水0.5%(体积分数)的体系、载铂量为1.0%时,显示了较高的活性和良好的稳定性,20h的平均量子效率为20.5%,转换数为220.较高的活性和稳定性初步归结于Al3+水解趋势较Fe3+小,且催化剂在甲醇中比在水中更稳定,进一步的研究正在进行中.     

Syntheses and structures of magnesium pyridine thiolates--model compounds for magnesium binding in photosystem I

Novel magnesium pyridine-2-thiolates were prepared by using alkane elimination chemistry. The resulting complexes display a metal coordination environment composed of sulfur/nitrogen bonding from the intramolecularly stabilized mercaptopyridine ligand, in addition to coordination by the oxygen centers from two THF donors. The compounds are well-suited model compounds for the magnesium centers in Photosystem I, in which magnesium, situated in the central chlorophyll ligand, is bound to sulfur from a nearby methionine residue. All compounds were characterized by (1)H, (13)C NMR, and IR spectroscopy, in addition to Xray crystallography.     

An EPR/ENDOR study of the asymmetric hydrogen bond between the quinone electron acceptor and the protein backbone in Photosystem I

Hydrogen bonding to the photoaccumulated secondary acceptor radical anion A₁^√− in photosystem (PS) I has been studied using pulsed Q-band ENDOR spectroscopy. With deuterated quinone in protonated PS I particles it is demonstrated that the observed radical anion has only one hydrogen-bond hyperfine coupling (hfc) tensor with tensor components above the 2 MHz range. Below 2 MHz the protein matrix protons dominate and a second weak H-bond could not be detected. The spectral resolution of pulsed Q-band ENDOR is critically required to separate the signals of the H-bond proton from those of the primary chlorophyll acceptor, A₀^√−, which cannot be avoided to be formed to some extent in the photoaccumulation procedure. The determined H-bond hfc tensor of A₁^√− is found to be close to axial symmetry with a small isotropic component, as expected from a predominantly dipolar electron–proton spin interaction in a hydrogen-bond. The principal tensor components are A=(+)7.7, MHz A=(−)4.9 MHz, A_iso=(−)0.7 MHz. The magnitude of the dipolar tensor corresponds to an unusually short H-bond which can be estimated from the point-dipole approximation (1.5±0.1 Å). Based on previous studies with A- and B-branch specific site-directed mutants of the A₁ site of PS I and the chosen photoaccumulation protocol, the observed A₁^√− radical anion can be assigned to the Q_K–A site of the A-branch. The observed H-bond hfc tensor is compared to those determined for related quinone radical anions observed in frozen protic solution as well as in the Q_A site of type II bacterial reaction centers.     

Stabilization of the structure and unctions of a photosystem i submembrane fraction by immobilization in an albumin-glutaraldehyde matrix

The effect of immobilization in an albumin-glutaraldehyde crosslinked matrix on the structure and activity of a photosystem I submembrane fraction has been studied. The photosynthetic activity recovered after immobilization was between 35 and 45% of the oxygen-uptake rates of the native material. Resulting oxygen uptake activities found in immobilized photosystem I preparations with methylviologen as acceptor were as high as 270 μmol O₂ (mg Chl h)^-1, An enhancement of photosystem I electron transfer, which is produced by incubation of thylakoid membranes at temperatures above 30 °C, was detected in native submembrane fractions, but not in the immobilized preparations. It is suggested that the increased activity at high temperature results from conformational modifications not allowed in the immobilization matrix. The insensitivity of immobilized photosystem I particles to prolonged storage at 4°C and to strong light exposure, as well as their high electron-transfer rates, demonstrates that the immobilization procedure used can be successfully applied to submembrane fractions.     

三维百合花状的CoNi2S4作为先进的双功能电催化剂用于氢析出和氧析出反应

为简化电解水催化剂的合成过程和优化电解水操作系统, 双功能电解水催化剂的研究, 特别是在碱性条件下同时具有优异催化氢析出和氧析出反应性能的双功能电催化剂的研究尤为重要. 其中, 过渡金属硫化物, 特别是 CoNi 硫化物, 被报道有与氢化酶类似的催化活性中心, 从而具有优异的催化氢析出和催化氧析出反应性能. 虽然有关对过渡金属硫化物的研究很多, 但主要集中在具有一维纳米线和二维纳米片形貌结构的过渡金属硫化物. 不幸的是, 这些形貌结构的过渡金属硫化物在电催化过程中容易聚集和受限于电荷传输能力. 三维纳米结构的材料具有较大的比表面积以分布更多的活性位点和拥有良好的电子传输能力, 所以, 开发三维纳米结构的过渡金属硫化物材料可能是改进其催化电解水性能的一个好途径. 本文采用简单的两步水热法, 通过硫化合成的 CoNi 前体得到了长于泡沫镍上的三维百合花状的 CoNi2S4(Co-Ni2S4/Ni). 它只需要 54 mV 的过电位即可获得 10 mA cm-2的催化氢析出反应电流, 是最好的碱性催化氢析出反应电极材料之一. 它在驱动 100 mA cm-2的催化氧析出反应电流时也只需要 328 mV 的过电位. 另外, 把 CoNi2S4/Ni 分别作为阴极和阳极组装成双电极碱性水电解槽时, 它只需要 1.56 V 的电压即可获取 10 mA cm-2的催化全电解水电流并具有良好的催化全电解水稳定性.扫描电子显微镜、透射电子显微镜和 N2吸脱附曲线测试结果表明, 该三维百合花状的 CoNi2S4/Ni 的表面粗糙度高和拥有多孔特性. 多孔结构的 CoNi2S4/Ni 可提供更多可接触的催化活性位点, 也有利于催化过程中的电解质和生成的气体的扩散与传递. 交流阻抗图谱测试结果表明, CoNi2S4/Ni 具有良好的电子传输能力. 另外, 不同于前期对尖晶石结构的硫化物 AB2S4的研究结果, XPS 结果表明, CoNi2S4/Ni 中含有 Niб+和 Sб-活性物种, 表明 CoNi2S4具有与活性氢化酶类似的活 性中心. Niδ+和 Sδ-可分别作为氢氧根和质子的接收体, 协助促进吸附的水分子的分离, 从而提高材料的催化性能. 所以, Niδ+和 Sδ-活性物种的出现, 大比表面积的三维百合花状多孔结构和良好的电荷传输能力等特性集合于 CoNi2S4/Ni 上使得CoNi2S4/Ni 具有优异的催化氢析出和催化氧析出反应性能.     

Fabrication of an electrode-viologen-hydrogenase heterogeneous system and the electrochemical hydrogen evolution

An indium tinoxide (ITO) electrode was chemically modified by one layer of viologen (VIO) deri vative, which possessed a persistent and reproducible electrochemical response. A monolayer of a thermal stable hydrogenase from Thiocapsa roseopersic ina was stabilized on a synthesized poly-l-lysine subphase surface and transferred on to the electrode for fabrication of an ITO-VIO-hydrogenase heterogeneous system. Electrochemical properties of both the ITO-VIO monolayer and the heterogeneous ITO-VIO-hydrogenase system have been investigated. Hydrogen evolution could be measured by potentiostating the VIO-hydrogenase-covered ITO electrode to “electroplate” [(VIO⁺)_n]_surf and a large increase in hydrogen evolution was observed when using an electrolytesolution containing sodium dithionite. We discuss the possible electron transfer process.     

Kilogram-scale synthesis of carbon quantum dots for hydrogen evolution,sensing and bioimaging

A facile, low-cost, green, kilogram-scale synthesis of high quality CQDs were synthesized. The throughput of CQDs is 1.4975 kg in one pot and the as-prepared CQDs have a highly crystalline hexagonal structure with remarkable solubility, stability, and biocompatibility. It showed outstanding electrocatalytic activity, Fe³⁺ sensitivity and good biocompatibility.     

Kilogram-scale synthesis of carbon quantum dots for hydrogen evolution,sensing and bioimaging

The development of large-scale synthetic methods for high quality carbon quantum dots (CQDs) is fundamental to their applications. However, the macroscopic preparation and scale up synthetic of CQDs is still in its infancy. Here, we report a facile, green, kilogram-scale synthesis of high quality fluorescent CQDs derived from poplar leaves via a one-step hydrothermal method. Notably, the throughput of CQDs can reach a level up to as high as 1.4975 kg in one pot. The structure and properties of the as-prepared CQDs were assessed through TEM, XRD, XPS and various spectroscopic methods. The obtained high quality CQDs with a photoluminescent quantum yield of 10.64% showed remarkable stability in aqueous media, rich functional groups, high photostability, consistent photoluminescence within biological pH range and low cytotoxicity. On account of these good properties, we demonstrated the multifunctional application to electrocatalytic water splitting, Fe³⁺ sensing and bioimaging. It showed remarkable electrocatalytic activity, Fe³⁺ sensitivity and good biocompatibility. This study provides a green, facile, inexpensive and large-scale method for producing high quality CQDs, which provides application value for large-scale production of CQDs.     

原位Raman光谱揭示中性条件下硫化钼结构变化对其电催化析氢反应的促进作用

硫化钼是析氢反应(HER)有前途的电催化剂. S-或Mo物种均被认为是形成吸附氢触发HER反应的活性位, 但Mo中心和S配体间相互作用的本质仍不清楚. 另外, 采用中性的水作为质子源用于产氢, 来开发低成本的水裂解催化剂体系为研究者高度关注, 但人们很少研究中性水条件下HER反应的机理. 本文采用原位电化学Raman光谱对所合成的硫化钼中Mo-Mo和S-S物种在中性条件下的结构变化进行了监测. 结果显示, 归属于端位S-S物种的谱带随着Mo-Mo, Mo3-μ3S和Mo-S振动谱带频率而同步变化, 表明Mo-Mo键与端位S-S键起着协同作用, 从而有利于氢气的生成. 这可能是通过三核Mo3-μ3S物种的内部重组而确认的. 本文所揭示的HER反应中金属-配体相互作用的本质与作用表明了一个不同的反应机理, 而以往的机理认为, S或Mo活性位独立起作用而促进HER反应的进行.     

1T相MoS2的制备及在电催化分解水析氢反应中的应用

二硫化钼(MoS₂)已成为电化学析氢反应(HER)中铂催化剂的廉价替代品。1T-MoS₂是MoS₂的金属相，由于其具有优异的导电性和更多的电化学活性位点，因此成为了比2H-MoS₂更具前景的理想催化剂材料。本文综述了1T相MoS₂的制备及在HER中的应用。首先，比较了1T-MoS₂和2H-MoS₂几何结构及电子结构的差异，从“自上而下”及“自下而上”的角度概述了1T-MoS₂常用制备方法，总结1T-MoS₂及1T-MoS₂基材料在HER领域的应用；最后指出现阶段关于1T-MoS₂的研究中仍存在的一些关键问题。     

Coulometric generation of hydrogen ions by oxidation of mercury in methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone

Mercury(II)-chloride reacts with anhydrous methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone in a precise stoichiometry ratio (1:2), and weakly ionized compounds of mercury with ketones are formed and equivalent quantity of HCl is released. The application of a mercury anode for the quantitative generation of H⁺ ions in 0.25 M sodium perchlorate in anhydrous methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone has been investigated. Current/potentials curves for the solvents, titrated bases, indicator and mercury showed that in these solvents mercury is oxidized at potentials much more negative than those for the titrated bases and other components present in the solution. The protons generated in this way have been used for the titration of some organic bases, with either visual or potentiometric end-point detection. The oxidation of mercury in methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone and the reaction of mercury ions with these solvents have been found to proceed with 100% current efficiency.     

Synthesis, characterization, and photocatalytic activity for hydrogen evolution of nanocrystalline mesoporous titania prepared by surfactant-assisted templating sol-gel process

Nanocrystalline mesoporous titania was synthesized via a combined sol-gel process with surfactant-assisted templating method, treated under various calcination conditions, and evaluated for its photocatalytic activity through photocatalytic hydrogen evolution from an aqueous methanol solution. In this synthetic method, applied surfactant template molecules functioned as both mesopore-forming and gelation-assisting agents. The resulting products were methodically characterized by TG-DTA, XRD, N₂ adsorption-desorption, diffuse reflectance UV-Vis spectra, SEM, and TEM analyses. The partial phase transformation from anatase to rutile occurred beyond calcination temperature of 600 °C and anatase-rutile transition kinetics was also investigated. The calcination conditions and crystalline phases existing in the products exerted significant effect on the photocatalytic hydrogen evolution activity. The activity of the synthesized titania treated under appropriate calcination conditions was considerably higher than that of commercial titania powders, Ishihara ST-01 and Degussa P-25. It is clearly seen that the introduction of mesopore into titania photocatalyst substantially improved the photocatalytic performance.     

基于镧和铬共掺杂钛酸锶产氢光催化剂构建Z机制全分解水体系（英文）

光催化剂的晶体结构、电子结构、表面结构等都会对自身性质产生决定性的作用,因此认识和理解光催化材料自身结构和光催化性能之间的内在联系有助于设计合成更高效的光催化剂以及光催化复合体系.本文通过聚合络合法和溶胶凝胶水热法分别制备了镧和铬共掺杂的光催化剂,标记为和在碘化钠或甲醇作为牺牲试剂的产氢反应中,担载Pt的样品显示了光催化活性,而担载Pt的样品活性很低,甚至无活性.我们将这两种材料分别作为产氢光催化剂与三氧化钨耦合构建Z机制全分解水体系.研究发现,只有体系观察到了氢气和氧气的产生.在第一个10 h的循环反应中,产生的摩尔比为3.7,明显高于水分解为2的化学计量比.这是因为在反应起始时加入的是Na I,质子还原产氢反应占据了主导.随着氢气的不断产生,部分I-被氧化成了IO_3-,而IO_3-的存在就可以驱动氧气的产生,由于溶液中氧化还原电的共存就可以持续驱动氢气和氧气的同时生成.为了测试体系的稳定性,我们将前面产生的气体完全抽空后又进行第二次10 h的循环反应,总共进行三次循环反应.在第一次循环过程中氢气、氧气生成速率分别为9.1和2.4mmol h~(–1),第二次循环其速率分别为9.9和3.7mmol h~(–1),第三次循环速率分别达到10.4和4.9mmol h~(–1).此外,通过三次循环后摩尔比为2.1,接近水分解的化学计量比.结合紫外可见漫反射光谱和Mott-Schottky曲线可以确定两种样品的能带位置.从能带位置示意图可知,两种样品都具有足够负的导带电势还原质子产氢以及足够正的价带电势氧化水产氧.需要指出的是样品的导带电势比样品的导带电势更负,这意味着前者的导带电势更有利于还原质子产氢.霍尔效应测试的结果表明,两种样品均显示出n型半导体的特征,此外样品显示出比样品更快的载流子迁移率以及更高的载流子浓度.因此,两种样品不同的导带位置以及不同的载流子迁移率和载流子浓度很可能是造成两者光催化性能具有显著差异的主要原因.