若干因素对催化光还原水产氢的量子收率的影响

研究了pH对Prof(前黄素)-MV~(2 )(甲基紫精)-EDTA(乙二胺四乙酸二钠)-K_2PtCl_4,Prof-Rh(bpy)_3~(3 )-TEOA(三乙醇胺)-K_2PtCl_4以及Ru(bpy)_3~(2 )-Rh(bpy)_3~(3 )-TEOA-K_2PtCl_4三个体系的产氢量子收率(ΦH_2)的影响。表明前一体系的最佳pH范围是4.0—5.0,后两个体系为7.5—8.1,还研究了光敏剂(PS)浓度对ΦH_2的影响,当PS浓度超过某一极限值时,ΦH_2随PS浓度增加而降低。在MV~(2 )-EDTA-K_2PtCl_4催化体系中,使用吸收光谱重叠的两种光敏剂(Prof和Ru(bPy)_3~(2 )一般导致ΦH_2的下降;但当其中一种PS的浓度超过极限值时,使用两种光敏剂所得的ΦH_2结果较单独使用其中任何一种要好。     

羰基四(对磺酸基苯基)卟啉钌(Ⅱ)的合成及光解水产氢的研究

金属卟啉在绿色植物的光合作用中起着重要的电子传递功能,在光解水产氢的研究中被用做光敏剂.在筛选金属卟啉光敏剂的研究中,通过改变卟啉环上的取代基和中心离子,将能改善其光敏性能.Okura等曾研究以羰基四苯基卟啉钌[Ru(CO)TPP]为光敏剂的光解水产氢体系,但由于Ru(CO)TPP不溶于水,故采用表面活性剂将其分散在水中,进行光敏效应的研究.我们合成了一种水溶性的钌卟啉化合物Ru(CO)TPPS,通过电子吸收光谱、红外光谱、核磁共振谱及元素分析等确定结构,并对Ru(CO)TPPS-K_2PtCl_6-TiCl_3复合光解水产氢体系进行了研究.实验结果表明,该体系的酸性水溶液在光照条件下,有较好的释氢性能和较高的转化数.     

Co2+.nbpy-Ru(bpy)2+3-抗坏血酸体系光照放氢和乙炔还原反应机理的研究

本文进一步研究了Co~(2+)·nbpy-Ru(bpy)_3~(2+)-抗坏血酸的体系光照放氢以及乙炔等底物的还原反应。发现C_2H_2和C_2H_4都是放氢反应的抑制剂,C_2H_2则几乎全抑制了体系的放氢。因此,可以认为乙炔等底物的还原以及放氢是在同一活性中心上发生的。C_3D_3的加氢实验指出,C_2H_3侧配位于Co~I上发生顺位加氢反应。由动力学实验得知,乙烯生成的初速与溶液的pH值的关系呈高斯型;对乙炔分压为一级反应;对Co(bPy)~(2+)浓度为零级反应。初步讨论了光助单电子转移反应以及乙炔加氢的可能机理。     

介绍一个简易的光解水制氢示范实验

近年来,国际上关于 Ru(bipy)_3~(2+)/MV~(2+)/EDTA/Pt水溶液体系光致产氢的研究已有报道。其中Ru(bipy)_3~(2+)为光敏剂,MV~(2+)为电子中继物,EDTA为电子源,胶态铂为催化剂。为了使学生了解当前有关这类化学现象的基本原理、操作、进展及其中的电子传递过程,在教学中开出本实验是受到欢迎的。但是,文献中的这些实验是从研究角度出发的,它们在设备、试剂及用量、催化剂制作、光源等方面都有一定的要求。为了使一些条件比     

基于非贵金属镍的金属有机大环的光解水放氢性能

将具有NN(氮氮)双齿配位点的席夫碱配体L2(L2=1,4-苯二-2′-吡啶腙)与镍构筑得到一例[2+2]型金属有机大环[Ni_2(L_2)_2(CH_3CN)_4](ClO_4)_4·4CH_3CN(2),并将其用于可见光条件下的光解水产氢研究。该非贵金属光催化体系由催化剂、光敏剂(荧光素,Fl)和电子牺牲剂(三乙胺)三部分组成。相比于具有相同配位环境的单核配合物[Ni(L_1)_2(CH_3CN)_2](ClO_4)2(1,L1=3-甲酰基苯-2′-吡啶腙),金属有机大环2作为催化剂具有较高的光催化活性,其产氢TON值可以达到3 100 molH_2·molcat-1,归因于荧光素分子可能与金属有机大环2形成超分子配合物,提高了光致电子转移效率。     

Rh(DMF)TPPS.5H2O的合成及光助还原水放氢的研究

为筛选光解水产氢的光敏剂, 用改进的方法, 分别合成了Rh4(CO)12和meso-四(对苯磺酸钠)卟啉(TPPS), 并在N,N-二甲基甲酰胺(DMF)中反应, 得到组成为Rh(DMF)TPPS.5H2O的新配合物, 用元素分析, 红外, 拉曼光谱, 质子核磁共振, 电子顺磁共振及热重分析, 确定了配合物的结构和Rh的价态, 并进行了Rh(DMF)TPPS-TiCl3-K2PtCl6三组份复合体系的放氢实验, 结果表明铑体系较诸钌体系有更高的放氢效率.     

Fe(Ⅲ)-邻菲啰啉配合物光还原的研究及其在铁分析中的应用

实验发现,在散射光中Fe(Ⅱ)-phen配合物能发生显著的光还原反应,当向体系中加入EDTA后则可阻止Fe(phen)_3~(2+)的生成,用汞灯液内照射Fe~(3+)-phen及Fe~(3+)-phen-EDTA体系,6分钟内能将100μgFe~(3+)还原成Fe(phen)_3~(2+)。这种光化学还原法已用于水及合成氨触媒的铁价态分析。触媒分析结果与推荐值一致。     

直接Z型LaNiO3/Mn0.2Cd0.8S异质结催化剂光解水产氢性能及机理探究

以LaNiO_3纳米颗粒为基质,在水热法制备CdS的过程中引入Mn~(2+)离子,原位合成直接Z型LaNiO_3/Mn_(0.2)Cd_(0.8)S异质结光催化剂。分别采用场发射扫描电镜、X射线衍射、X射线光电子能谱、紫外可见漫反射光谱、氮气吸附-脱附测试以及电化学测试等分析方法对制备的催化剂进行表征。在光解水产氢测试中,LaNiO_3/Mn_(0.2)Cd_(0.8)S异质结光催化剂在5 h的H_2产量达到1 190.3μmol,相较于CdS和Mn_(0.2)Cd_(0.8)S,其H_2产量分别提高了 25倍和10倍。荧光和电化学实验证实,Mn~(2+)的引入能够有效地促进光生载流子的分离,同时LaNiO_3/Mn_(0.2)Cd_(0.8)S之间异质结的构筑能有效地促进光生载流子在界面间的迁移、分离,从而促进其光解水产氢效率和稳定性的提高。结合一系列表征和活性测试结果提出直接Z型光解水反应机理,很好地阐述了其光解水产氢活性和稳定性的增强。     

铝-铜铁试剂配合物氢催化波

在示波极谱仪上,0.5M(NH_4)_2SO_4底液中,pH=4.5时,Al~(3+)-Cup体系在-1.31V(VS.SCE)产生较大的还原电流,浓度在7.4×10~(-7)-3.0×10~(-5)M,与峰电流有线性关系。-1.31V的峰电流是Al-Cup配合物的氢催化波。在试验条件下,配合比为1:3,质子化的Al~(3+)-Cup配合物吸附于电极上还原,产生氢气。释出的配合物再从溶液中的NH~+_4获得质子,吸附于电极产生催化电流。     

面式、经式异构体的钴-氨基硫脲配合物作为催化剂应用于可见光催化分解水产氢（英文）

近年来,作为替代贵金属铂催化剂的铁、钴和镍等非贵金属配合物分子催化剂,由于合成容易、结构调控方便以及具有良好的催化活性等特点,成为均相光催化分解水产氢领域的研究热点.其中,钴配合物具有结构简单、成本低廉、容易合成以及具有理想的氧化还原电位等优势,更是光催化分解水产氢领域的优先研究对象.由于稳定性及溶解度的问题,在已报道的研究工作中,大部分钴配合物测试环境均在有机溶剂或有机溶剂/水混合溶剂中.因此,寻找水溶性良好的钴配合物催化剂成为了目前的均相光催化分解水产氢领域的研究焦点之一.在此之前,氨基硫脲配合物已经广泛用于生物和制药等研究,例如:抗氧化、抗菌以及抗病毒等领域.而在人工光合产氢领域采用氨基硫脲配合物作为催化剂的例子则比较罕见.在该项研究中,我们报道了一对水溶性较好(40 mg mL~(–1),20°C)且具有几何异构特征的八面体钴-氨基硫脲配合物作为光、电催化质子还原产氢的分子催化剂.这对几何异构体分别为:面式异构体[Co(Htsc)_3]Cl_3·3H_2O(C1,Htsc=氨基硫脲配体)和经式异构体[Co(Htsc)_3]Cl_3·4H_2O(C2).我们将几何异构体C1和C2作为水还原分子催化剂,与有机光敏剂荧光素一起构筑了不含贵金属成分的光催化分解水产氢体系.在三乙胺作为牺牲剂及纯水环境中,体系展现出了良好的光催化制氢性能.可见光照15 h后,体系产氢相对于催化剂的TON接近900.对比实验结果表明,具有这对几何异构的C1和C2具有相似的光催化产氢性能,暗示其催化机理的相似性.汞中毒实验结果表明,光催化分解水产氢过程中并没有钴纳米胶体形成,可以确定这是一个均相光催化分解水产氢体系.在纯水环境下,我们将C1和C2与传统的钴配合物(钴肟配合物:[Co(dmgH)_2pyCl](dmg H=丁二酮肟,py=吡啶);联吡啶钴配合物:[Co(bpy)_3Cl_2](bpy=2,2'-联吡啶))的催化活性进行对比.结果表明,催化剂C1和C2展现出了较强的光催化产氢活性.此外,电催化实验表明,在乙腈中且乙酸作为质子源的条件下,C1和C2具有相同的电催化活性,过电位接近640毫伏,催化转化频率(TOF)为每秒210.同时,在pH=7的磷酸盐缓冲溶液中,C1和C2也同样表现出对水分子的电催化产氢性能,过电势为560毫伏.这是当前第一例具有几何异构体的分子催化剂对光、电催化产氢体系影响的工作.     

Determination of dissolved hexavalent chromium in river water, sea water and waste water

Summary A simple and reliable method for the determination of dissolved hexavalent chromium in aquatic systems is described. Chromium(VI) is quantitatively coprecipitated with lead sulfate from weakly acidic (pH 3.5) sample solutions. It is determined by graphite furnace atomic absorption spectroscopy at 357.9 nm. The detection limit of the method is 0.3 g/l at a 95% confidence level. Relatively high concentrations of chromium(III) do not interfere in the determination of hexavalent chromium. High chloride (> 6 g/l) or sulfate (> 800 mg/l) concentrations cause a significant decrease in the Cr(VI) recoveries. These interferences are mutually influenced.The sulfate interference is reduced, but not eliminated in the presence of high chloride concentrations, while chloride interferences are eliminated in the presence of a sufficient sulfate concentration in the original sample. Chromium(VI) is recovered quantitatively from river water and effluent samples, but its recovery from sea water is incomplete (83%), due to interferences by sulfate during the coprecipitation procedure.

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Bestimmung von gelöstem Chrom(VI) in Fluß-, Meer- und Abwasser

Zusammenfassung Eine einfache und zuverlässige Methode zur Chrom(VI)-bestimmung in wäßrigen Systemen wurde ausgearbeitet. Dabei wird Chrom(VI) aus schwach saurer Lösung (pH 3,5) mit Bleisulfat mitgefällt und mit Hilfe der Graphitofen-AAS bei 357,9 nm bestimmt. Die Nachweisgrenze liegt bei 0,3 g/l bei 95% Vertrauensbereich. Relativ hohe Konzentrationen an Chrom(III) stören nicht. Hohe Gehalte an Chlorid (> 6 g/l) oder Sulfat (> 800 mg/l) können zu beträchtlichen Minderbefunden an Cr(VI) führen. Diese Störungen beeinflussen sich gegenseitig. So wird die Störung durch Sulfat in Gegenwart großer Chloridmengen herabgesetzt, aber nicht ganz eliminiert, während die Chloridstörung durch genügend Sulfat beseitigt wird. Chrom(VI) konnte aus Fluß- und Abwasser quantitativ wiedergefunden werden, aus Meerwasser nur zu 83% (wegen der Störung durch Sulfat bei der Mitfällung).

     

Charge-on-spring polarizable water models revisited: from water clusters to liquid water to ice

The properties of two improved versions of charge-on-spring (COS) polarizable water models (COS/G2 and COS/G3) that explicitly include nonadditive polarization effects are reported. In COS models, the polarization is represented via a self-consistently induced dipole moment consisting of a pair of separated charges. A previous polarizable water model (COS/B2), upon which the improved versions are based, was developed by Yu, Hansson, and van Gunsteren. To improve the COS/B2 model, which overestimated the dielectric permittivity, one additional virtual atomic site was used to reproduce the water monomer quadrupole moments besides the water monomer dipole moment in the gas phase. The molecular polarizability, residing on the virtual atomic site, and Lennard-Jones parameters for oxygen-oxygen interactions were varied to reproduce the experimental values for the heat of vaporization and the density of liquid water at room temperature and pressure. The improved models were used to study the properties of liquid water at various thermodynamic states as well as gaseous water clusters and ice. Overall, good agreement is obtained between simulated properties and those derived from experiments and ab initio calculations. The COS/G2 and COS/G3 models may serve as simple, classical, rigid, polarizable water models for the study of organic solutes and biopolymers. Due to its simplicity, COS type of polarization can straightforwardly be used to introduce explicit polarization into (bio)molecular force fields.     

A water calorimetric determination of absorbed dose to water

To realize a more accurate determination of the water absorbed dose, a basic quantity in radiation dosimetry, water absorbed dose calorimeters are being developed. They allow the dose to be measured according to its definition. A calorimeter type is described which permits the application of horizontally directed beams of different types of radiation.It is shown that the use of water calorimeters for the determination of the dose under reference conditions can cause substantial errors if the results are not corrected for the influence of heat conduction in the water.     

FTIR study of water clusters in water–triethylamine solutions

The FTIR study presented in this work, on water dissolved in triethylamine (TEA), reveals the formation of water clusters in the TEA liquid phase at tenths of water molar concentrations. In the OH stretching region, the FTIR spectra of water in TEA show, at high frequencies, a narrow band at 3682 cm⁻¹ and, at low frequencies, a wide band that can be resolved into four peaks with maxima at 3249 cm⁻¹, 3348 cm⁻¹, 3440 cm⁻¹ and 3545 cm⁻¹. The results have been rationalised assuming the formation of clusters containing tens of three- and four-coordinated water molecules. TEA molecules surrounding the clusters are hydrogen bonded to one OH of the water molecules at the surface, leaving dangling protons. Further, the analyses of the spectra suggest that, in the used range, the water cluster mean size does not depend strongly on the water concentration.     

The dynamic crossover in water does not require bulk water

Many of the anomalous properties of water may be explained by invoking a second critical point that terminates the coexistence line between the low- and high-density amorphous states in the liquid. Direct experimental evidence of this point, and the associated polyamorphic liquid-liquid transition, is elusive as it is necessary for liquid water to be cooled below its homogeneous-nucleation temperature. To avoid crystallization, water in the eutectic LiCl solution has been studied but then it is generally considered that "bulk" water cannot be present. However, recent computational and experimental studies observe cooperative hydration in which case it is possible that sufficient hydrogen-bonded water is present for the essential characteristics of water to be preserved. For femtosecond optical Kerr-effect and nuclear magnetic resonance measurements, we observe in each case a fractional Stokes-Einstein relation with evidence of the dynamic crossover appearing near 220 K and 250 K respectively. Spectra obtained in the glass state also confirm the complex nature of the hydrogen-bonding modes reported for neat room-temperature water and support predictions of anomalous diffusion due to "worm-hole" structure.     

The permittivity of water and water vapor in saturation states

The applicability of several well-known equations describing the dependences of the relative permittivities of liquid water and water vapor on their densities and temperature is analyzed. An original semiempirical equation was suggested to relate the permittivity of equilibrium vapor to that of the liquid phase. The temperature intervals within which the equations under consideration described experimental data most accurately were established. The results were used to tabulate the calculated permittivities of water and water vapor in saturation states.     

Strategy for pesticide control in ground water and drinking water

Summary The analysis of pesticides is quite difficult and expensive. It is shown in this paper which analytical methods and systems have to be used for pesticide-monitoring in ground water and drinking water. Clear identification, control of positive results, quantitative determination, accuracy and precision are very important points for pesticide analysis.