散射光下铁(III)-丙酮酸盐配合物还原铬(VI)的研究

研究了在散射光下铁(III)-丙酮酸盐配合物对铬(V I)的光还原反应;考察了溶液pH、铁(III)、丙酮酸钠、铬(V I)浓度对反应的影响;分析了铬(V I)光还原反应的动力学。实验结果表明:铁(III)-丙酮酸盐配合物体系能在较弱的散射光下还原铬(V I)。在铬(V I)浓度为19.2μm o l/L、铁(III)浓度为10.0μm o l/L、丙酮酸钠浓度为240μm o l/L、pH为3.0、光照240m in的条件下,铬(V I)的还原率达到99.7%。从表观动力学方程的反应级数看,铁(III)的级数(0.83)最高,铁(III)浓度是影响铬(V I)光还原反应速率的主要因素,铁(II)是铬(V I)光还原的主要还原剂。     

Preparation, characterization and application of CuCrO2/ZnO photocatalysts for the reduction of Cr(VI)

The delafossite CuCrO₂ elaborated by sol-gel from 40 nm diameter colloid is optically active in the visible region. It is characterized physically and photoelectrochemically. The microstructure is fairly homogenous with a mean crystallite size of ca. 2 μm. The optical gap (1.30 eV), determined from the diffuse reflectance, is well suited to the sunlight spectrum. The Mott Schottky plot is characteristic of P-type conductivity with a flat band potential of -0.26 V_SCE. As application, the photoreduction of chromate is successfully achieved in air-equilibrated suspension CuCrO₂/ZnO (1/1). CuCrO₂ is photoactivated by visible light and the electrons in the conduction band (-1.34 V_SCE) are injected to ZnO. In the presence of salicylic acid, a conversion of Cr(VI) to Cr(III) of 57% is obtained under optimal conditions (pH 3 at 25℃, 5×10^-4 mol/L) because of the HCrO₄^- dark adsorption onto ZnO (4HCrO₄^- + 3C₇H₆O₃ + 18O₂ + 16H⁺ → 4Cr³⁺ + 21CO₂ + 19H₂O, ΔG⁰ = -557 kcal/mol). Prolonged illumination is accompanied by a deceleration in the photoactivity owing to the competitive water reduction, an issue of energetic concern. The hetero-system exhibits self sensitization for hydrogen production with an evolution rate of 149 μmol/(hr·g).     

Photoreduction of parathion ethyl †

Photodegradation of parathion ethyl in presence of unsaturated biomolecules takes place by sufficient reduction of the phenyl nitro group. Main products are N,0‐dialkenyl hydroxylamino, cis/trans azo, and azoxy derivatives of parathion.     

水体汞光还原研究进展

汞的光还原是影响水生系统汞迁移转化的重要过程.光还原产生的溶解性气态汞会通过水气界面向大气挥发.该过程可以减轻水体汞负荷,降低汞被甲基化的风险,对全球汞循环具有重要意义.水生系统中汞的光还原过程十分复杂,影响因素较多,是汞环境地球化学行为研究的重点和热点.目前科学家在这方面已做了大量研究,但许多结论与建议还存在争议,对其还原机制也还不清楚.本文总结了近年来水体汞光还原过程的研究进展;分析了水生系统中影响汞光还原过程的主要因素;评述了水汞光还原研究存在的问题;提出了水体汞光还原的研究焦点与方向.     

散射光下铁(Ⅲ)-丙酮酸盐配合物还原铬(Ⅵ)的研究

研究了在散射光下铁（Ⅲ）-丙酮酸盐配合物对铬（Ⅵ）的光还原反应;考察了溶液pH、铁（Ⅲ）、丙酮酸钠、铬（Ⅵ）浓度对反应的影响;分析了铬（Ⅵ）光还原反应的动力学。实验结果表明：铁（Ⅲ）-丙酮酸盐配合物体系能在较弱的散射光下还原铬（Ⅵ）。在铬（Ⅵ）浓度为19．2μmol／L、铁（Ⅲ）浓度为10．0μmol／L、丙酮酸钠浓度为240μmol／L、pH为3．0、光照240min的条件下,铬（Ⅵ）的还原率达到99．7％。从表观动力学方程的反应级数看,铁（Ⅲ）的级数（0．83）最高,铁（Ⅲ）浓度是影响铬（Ⅵ）光还原反廊速率的主要因素．铁（Ⅱ）是铬（Ⅵ）光还原的主要还原剂。     

铁(III)-丙酮酸盐配合物光解引发水中铬(Ⅵ)还原

初步研究了含有Fe(III)及丙酮酸盐的溶液在高压汞灯照射下对铬(VI)的光还原反应.考察了溶液pH值、Fe(III)浓度、丙酮酸钠浓度、Cr(VI)浓度对反应的影响.分析了光还原反应的动力学及反应机制.结果表明:铁丙酮酸盐体系能光还原Cr(VI);最佳pH为3.0;Cr(VI)光还原的初始速率随着加入的铁(III)、丙酮酸盐、Cr(VI)初始浓度的增加而增加;实验条件下的表观动力学方程为:-dCCr(VI)/dt=0.021[Cr(VI)]0.39[Fe(III)]1.05[CH3COCOONa]0.39;Fe(III)-丙酮酸盐配合物光解产生的Fe(II)是Cr(VI)的主要还原剂.     

Response of diazotrophic cyanobacterium Nostoc carneum under pesticide and UV-B stress

A study was under taken, under controlled laboratory conditions, to investigate the influence of non-ionizing radiation (UV-B) and an organochlorine pesticide on the growth, photosynthetic pigments, protein content and DCPIP photoreduction of a cyanobacterium Nostoc carneum. Test algae was isolated from rice field soils of Sambalpur, Western Orissa, India and grown in nitrogen free BG 11 culture medium. Culture of algae from log phase of growth was treated with 5 ppm of the insecticide, Endodhan and UV-B (20 mW m⁻²) for 2 h daily, separately and in combination of insecticide and UV-B radiation. Algal samples treated with UV-B and pesticide separately showed distinct inhibitory effects on growth, pigments, protein content and DCPIP reduction of the test samples. However, when pesticide treated samples were subjected to UV-B exposure, the effect showed additive as well as synergetic effect. Experiment conducted to check the ability of the organism to recover from the stress, exposed for various time periods, suggest their ability to partially recover from the stress.     

Geochemical and biological controls on trace metal transport in an acid mine impacted watershed

Water samples collected in an acid mine impacted watershed indicated that the concentrations of dissolved trace metals were diurnally influenced by mineral saturation, which is controlled primarily by pH and water temperature. Measurements taken suggested that these variations only occur at sample locations immediately downstream from the confluence of acidic and alkaline waters. It is at these locations where initial mineral precipitation occurred and where subtle changes in solubility were most affected, increasing trace metal removal when both the rate of photosynthesis (influencing pH in headwaters) and water temperature were at a maximum. The role of iron photoreduction (increased midday production of ferrous iron) on overall Cu, Mn, and Zn transport was also evaluated, but found to be inconclusive. Iron photoreduction may however influence adsorption and/or coprecipitation of trace metals through associated changes in oxidation state, solubility, and mineralogy of various iron colloids, which are produced upon the neutralization of acidic, metal enriched water. Furthermore, measured values of copper and zinc were compared to relative USEPA chronic criterion for exposure to continuous concentration (CCC) of metals by the calculation of a “toxicity unit” (TU). It was found that average values of both copper and zinc only exceeded the CCC (TU>1) in the acid mine-impacted Leona Creek. In general, zinc toxicity decreased while copper toxicity increased downstream of the confluence of the mine impacted Leona Creek and background Lion Creek (sampled at Lake Aliso), indicating a significant source of zinc in upstream, non mine-impacted samples.     

Cr(Ⅵ)在Fe(Ⅲ)-柠檬酸盐体系中紫外光还原研究

研究了在紫外光照射下,Fe(Ⅲ)-柠檬酸盐溶液对Cr(Ⅵ)的光还原反应.同时,考察了溶液pH值、Fe(Ⅲ)浓度、柠檬酸盐浓度、Cr(Ⅵ)初始浓度对光还原效率的影响,并分析了光还原反应的动力学.研究结果表明,Fe(Ⅲ)-柠檬酸盐体系能光还原Cr(Ⅵ),在pH为2.0～6.0的范围内,Cr(Ⅵ)的还原率随着溶液初始pH值的降低而增大.当pH值为2.0、Fe(Ⅲ)浓度为10μmol·L-1、柠檬酸盐浓度为250μmol·L-1及Cr(Ⅵ)初始浓度为19.2μmol·L-1时,光照反应8min后Cr(Ⅵ)的最大还原率达到100%,但当pH值增加到6.0时,Cr(Ⅵ)的最大还原率下降到19%;当Cr(Ⅵ)的初始浓度在9.6～96.0μmol·L-1的范围内时,Cr(Ⅵ)光还原反应的初始速率随着Fe(Ⅲ)、柠檬酸盐(cit3)、Cr(Ⅵ)初始-浓度的增加而增加.表观动力学方程为:-dCCr(Ⅵ)/dt=0.1019[Cr(Ⅵ)]0.[Fe(Ⅲ)]0.[cit3]0..536-25     

海藻-过渡金属-光三元体系还原转化Se(Ⅵ)研究

以海洋绿藻(Tetraselmis levis,Chlorella autotrophica,Dunaliella salina,Nannochloropsis sp.,Tetraselmis subcordiformis)、硅藻(Phaeodactylum tricornutum)、红藻(Porphyridium purpureum)和过渡金属(铁、锰、铜)构建海藻-光二元体系、过渡金属-光二元体系、海藻-过渡金属-光三元体系,对比分析不同海藻、不同过渡金属、海藻与过渡金属耦合引发光化学过程,对Se(Ⅵ)还原转化的贡献率.二元和三元体系均可光还原转化Se(Ⅵ)为Se(Ⅳ).铁、铜、锰通过自身的光氧化还原过程诱发Se(Ⅵ)/Se(Ⅳ)的氧化还原;海藻的光化学活性首次被证实,表面壁可吸附富集海水中还原性的有机物、Se(Ⅵ)/Se(Ⅳ)和过渡金属,改变其氧化还原电位,提供光反应场所;Se(Ⅵ)的光还原转化率依海藻和过渡金属的种类、浓度不同而异;海藻浓度的提高、海藻与过渡金属的耦合作用有利于光还原转化率的提高.通过三元体系的光还原转化,Se(Ⅵ)/Se(Ⅳ)比值为1.17～2.85,接近海洋真光层Se(Ⅵ)/Se(Ⅳ)实际浓度比,即海藻和过渡金属引发的光化学过程对硒的价态分布起决定性作用.