结冰过程对溶解性有机质典型组分还原Cr(Ⅵ)的影响

研究了结冰过程对溶解性有机质(DOM)的4种典型组分草酸、酒石酸、苹果酸和柠檬酸还原Cr(Ⅵ)的影响.结果表明,在低浓度下Cr(Ⅵ)在水溶液中不能被4种有机酸所还原;而在冰中,不同的有机酸对Cr(Ⅵ)的去除均有促进作用,且去除效果随着有机酸浓度的增大逐渐增强.4种有机酸的作用效果强弱顺序为草酸酒石酸苹果酸柠檬酸.通过使用不同浓度的无机盐和无机酸可以改变冰表面上类似液体层的厚度来抑制Cr(Ⅵ)的还原,作用效果与无机盐种类无关.溶液的初始pH值和有机酸结构是影响Cr(Ⅵ)还原的重要因素.实验条件下冷冻浓缩效应的富集倍数至少可达10~3,对冰中草酸去除Cr(Ⅵ)有明显的促进作用.     

硅酸镁锂的有机改性及对Cr(Ⅵ)的吸附特性

采用水热法合成了硅酸镁锂(Laponite), 然后利用十六烷基三甲基溴化铵(CTMAB)对其进行有机改性, 研究了改性后的有机硅酸镁锂(CTMABL)对Cr(Ⅵ)的吸附特性. 结果表明, 改性后样品的比表面积和孔容积变小而平均孔径增大. CTMABL样品的d₍₀₀₁₎值从改性前的1.23 nm增加到1.79 nm, 表明CTMAB进入Laponite层间. 随着溶液pH值的提高, CTMABL对Cr(Ⅵ)的吸附效率明显下降; pH<8.5时, CTMABL颗粒表面电势为正, 能够与Cr(Ⅵ)阴离子发生静电吸引从而提高吸附效率. 随着固液比增加, 对Cr(Ⅵ)的去除效率迅速上升, 当固液比达到4 g/L后去除效率趋于稳定. 离子强度对Cr(Ⅵ)吸附过程的影响不明显. CTMABL对Cr(Ⅵ)的吸附符合准二级动力学模型, 吸附传质速率受膜扩散和颗粒内扩散过程共同影响. 等温吸附过程符合Langmuir模型, 热力学分析结果表明吸附过程是一个自发的吸热反应. 综合分析认为表面配合作用是主要的吸附机制, 同时静电引力在吸附过程中起到了促进作用.     

钠盐溶液中U(Ⅵ)的电化学电子转移与晶化研究

采用循环伏安法分析钠盐溶液中U(Ⅵ)的电化学行为, 恒电位电化学还原处理U(Ⅵ), 利用交流阻抗谱分析电化学还原反应中的过程动力学特性, 利用X射线衍射、 扫描电子显微镜和电子能谱等方法分析了U(Ⅵ)的电化学晶化. 结果表明, 在钠盐溶液中, U(Ⅵ)可通过电化学反应先还原成低价的U(V)并进一步还原为U(Ⅳ), U(Ⅳ)一步氧化为U(Ⅵ), U(Ⅳ)/U(Ⅵ)之间的电化学转化过程受扩散控制, 且U(Ⅵ)的电化学电子转移易受环境pH值的影响; 恒电位还原4 h时, 溶液中U(Ⅵ)的去除率可达90%, U(Ⅵ)的结晶固化产物主要以固态的(UO₂)₆O₂(OH)₈·6H₂O(水铀矿) 和UO₂的形式附着在工作电极上.     

Ag/NH2-MIL-125(Ti)的构建及可见光还原水中Cr(Ⅵ)

开发高效、稳定的复合光催化材料是当前环境领域的迫切需求。 本文采用溶剂热协同紫外光还原法成功制备了复合光催化材料Ag/NH₂-MIL-125(Ti),并通过X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱(EDS)、紫外-可见漫反射光谱(UV-Vis DRS)及X射线光电子能谱(XPS)等技术手段对其形貌、结构及光学性质进行分析,考察了Ag/NH₂-MIL-125(Ti)可见光(λ≥420 nm)催化还原Cr(Ⅵ)的性能,并优化了催化剂用量、Cr(Ⅵ)浓度、空穴捕捉剂种类及用量等条件。 结果表明,在最佳条件下,Ag/NH₂-MIL-125(Ti)具有良好的吸附及光催化还原Cr(Ⅵ)性能,其吸附及光催化还原率是NH₂-MIL-125(Ti)的3.11倍,Ag/NH₂-MIL-125(Ti)特殊的“芝麻饼”形貌以及Ag⁰与NH₂-MIL-125(Ti)之间形成的异质结有助于增强复合材料的光催化还原Cr(Ⅵ)的性能。 同时,通过条件实验,提出了光催化还原过程中主要的活性物种以及Cr(Ⅵ) 的还原机理。 本研究将为金属有机骨架(MOFs)复合材料在可见光催化环境修复领域的应用提供理论依据和实验参考。     

低相对分子质量有机酸对α-FeO(OH)吸附As(Ⅲ)的影响

制备并表征了α-FeO(OH),探究了4种低相对分子质量有机酸(LMW)对α-FeO(OH)吸附As(Ⅲ)的影响,并阐明了机理。 单一和混合LMW对α-FeO(OH)吸附As(Ⅲ)均有抑制作用,4种LMW的影响大小顺序为:草酸(OA)>柠檬酸(CA)>乳酸(LA)、水杨酸(SA)。 混合LMW的影响为:OA会加剧CA对α-FeO(OH)吸附As(Ⅲ)的影响,而SA几乎不起作用。 当ρ(As(Ⅲ))较低,LMW通过与α-FeO(OH)的静电引力、与α-FeO(OH)表面的铁离子形成配合物、生成沉淀从而影响α-FeO(OH)对As(Ⅲ)的吸附;当ρ(As(Ⅲ))较高,LMW还通过阻碍As(Ⅲ)在α-FeO(OH)上的扩散和沉淀作用产生影响。 实验结果为土壤中As(Ⅲ)的迁移转化、污染治理提供技术支撑。     

凹凸棒黏土负载纳米TiO2-Fe3O4吸附剂的制备及Cr(Ⅵ)的脱除

采用溶胶-凝胶法、一锅反应法制备了负载纳米TiO₂和Fe₃O₄的凹凸棒黏土(TiO₂-Fe₃O₄-ATP)吸附剂,并进行了模拟废水中Cr(Ⅵ)的吸附及脱附性能的研究。 通过扫描电子显微镜(SEM)、X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)和EDS等分析方法对ATP负载纳米TiO₂-Fe₃O₄前后结构进行了表征,考察了物料配比及吸附时间、pH值、温度、投加量和初始质量浓度对Cr(Ⅵ)吸附率的影响。 结果表明,吸附剂在Ti元素含量与负载总量的摩尔比为3：4时吸附效果最佳。 当吸附剂质量为0.6 g,Cr(Ⅵ)离子初始质量浓度小于0.8 mg/L时,pH=6,温度20 ℃,吸附剂对Cr(Ⅵ)的吸附率为79.8%。 TiO₂-Fe₃O₄-ATP吸附剂对Cr(Ⅵ)离子吸附满足Freundlich模型。 在20~40 ℃ 条件下,吸附过程ΔG<0、ΔS=-43.55 J/(mol·K)、ΔH=-14.36 kJ/mol,表明该吸附是个自发、熵减、放热的过程。 吸附过程符合准二级动力学模型,吸附速率控制步骤以表面化学反应为主。 TiO₂-Fe₃O₄-ATP吸附剂在循环使用4次后,吸附率仍能达到65%以上。     

纸上层析法鉴定植物组织中的非挥发性有机酸

(1)本文分别用戊醇-蚁酸-水和丁醇-蚁酸-水为溶剂测定了酒石酸等七种有机酸的 R_f 值。除草酸外,所有结果与文献记录基本符合。在本文实验的温度范围内(30±4°)温度变化对有机酸的 R_f 值并无显著影响。(2)由于草酸的严重拖尾现象,在一般的操作用量下,草酸试液浓度在0.5M 以下不能生成有固定 R_f 值的斑点。因此草酸 R_f 值必须以0.5M 以上的浓试液进行试验,并须以最高处的深浓斑点作为计算根据。(3)对植物组织中非挥发性有机酸的纸上层析,本文建议用两种 R_f 值相互验证,并用浓试液与稀试液作比较试验,所得结果比较明确可靠。(4)用本方法在蓖麻叶中检出了酒石酸,柠檬酸,苹果酸和延胡索酸四种非挥发性有机酸。在荷叶中检出了葡萄糖酸,酒石酸,柠檬酸,苹果酸,草酸和琥珀酸六种非挥发性有机酸。     

ZnO@ZIF-8核壳微球的制备及对U(Ⅵ)的吸附性能

利用ZnO诱导制备了ZnO@ZIF-8复合微球材料并将其用于溶液中U(Ⅵ) 的去除. 研究表明, 制备的ZnO@ZIF-8复合微球的直径为1~7 μm, pH=4时, 在水溶液中对U(Ⅵ) 的吸附量最大, 达到145.32 mg/g, 吸附机理可能与铀酰离子与复合材料之间的配位作用和氢键作用相关. 考虑到复合微球中用于U(Ⅵ) 吸附的有效成分ZIF-8的含量仅为12.6%, 以ZIF-8含量计算, 该材料对U(Ⅵ) 的单位吸附量高达1137 mg/g.     

山楂汁树脂柱层析过程中主要有机酸变化规律探讨

利用高效液相色谱法测定山楂汁经过树脂柱层析处理后流出液中草酸、酒石酸、苹果酸、柠檬酸、琥珀酸5种单一有机酸含量,探讨山楂汁中主要有机酸在树脂吸附与解吸附过程中的变化规律,为降酸后果汁口感的改变原因提供依据。5种有机酸达到饱和的先后顺序:琥珀酸,草酸,苹果酸,酒石酸,柠檬酸;吸附过程中5种有机酸总含量与总滴定酸含量分别降低26.71%和40.54%;在吸附阶段,有机酸对树脂吸附位点存在竞争性,出现柠檬酸作为洗脱液将其他有机酸洗脱的现象;由于不完全解吸附,树脂吸附能力随树脂柱层析次数的增加而降低。     

基于离子交换-电导检测法对酿酒葡萄中有机酸含量进行分析

建立了离子色谱法测定酿酒葡萄中乳酸、丙酸、苹果酸、酒石酸、草酸、柠檬酸、琥珀酸和抗坏血酸的方法。样品经提取、脱色、过滤后以自动淋洗液发生器生成的1.5~30 mmol/L KOH为淋洗液洗脱,抑制电导检测器检测。考察了共存非测定离子及相邻离子间的干扰,结果表明非测定无机离子对测定无干扰。8种有机酸在一定浓度范围内与其峰面积呈良好的线性关系,检出限为0.064~0.25 mg/L,加标回收率为89.5%~96.2%。该方法用于宁夏贺兰山东麓酿酒葡萄中8种有机酸分析,8种有机酸均被检出,以苹果酸和酒石酸含量最高,柠檬酸次之,其它酸含量均较低。酿酒葡萄为典型的酒石酸型水果。     

Determination of ten organic acids by low pressure liquid chromatography

Summary Organic acids, such as lactic, malic and citric acids, are involved in primary metabolism of all living organisms. Their presence in food products contributes to the flavour and their equilibrium with inorganic cations defines to a large extent the acidity of the food preparations. A resin cation-exchanger device, normally used for separating amino-acids, can be adapted for characterizing 10 organic acids: formic, propionic, fumaric, succinic, lactic, malic tartaric, citric, and oxalic. Two monitoring systems were used, one of them based on specific iron III salt coloration with hydroxy-acids.     

Polymeric sensors for determination of anions of organic acids

New polymeric electrochemical sensors based on various neutral and charged organic ionophores were suggested. The new sensors have a high sensitivity to anions of various organic acids (acetic, oxalic, lactic, malic, succinic, tartaric, and citric) in a wide concentration range. The selectivity and the detection limit of the developed sensors with respect to anions of the acids were studied.     

高效液相色谱法测定铬超富集植物李氏禾根系分泌物中的有机酸

建立了高效液相色谱（HPLC）测定Cr超富集植物李氏禾根系分泌物中低相对分子质量有机酸的分析方法。采用XSelect HSS T3色谱柱（250 mm×4.6 mm,5 μm,Waters）,以40 mmol/L磷酸二氢钾-磷酸缓冲溶液（pH=2.40）作流动相,流速1.0 mL/min,柱温25℃,在波长205 nm处检测。该方法在13 min内简便快速地分离出8种有机酸（草酸、酒石酸、苹果酸、乳酸、甲酸、乙酸、马来酸和柠檬酸）,且峰形良好。有机酸的检出限（LOD）为0.12~12.32 mg/L;草酸的加标回收率为73.15%,其他有机酸的加标回收率为94.54%~109.98%。李氏禾的根系分泌物中各有机酸含量分别为酒石酸（130.90±1.44）μg/g（根干重）、苹果酸（1031.34±4.38）μg/g（根干重）、乳酸（65.54±1.01）μg/g（根干重）、马来酸（0.96000±0.00367）μg/g（根干重）和柠檬酸（201.50±1.13）μg/g（根干重）。该方法简便快速,灵敏可靠,适用于植物根系分泌物样品中有机酸的测定。     

Dissolution of kaolinite induced by citric, oxalic, and malic acids

Kaolinite is a dominant clay mineral in the soils in tropical and subtropical regions, and its dissolution has an influence on a variety of soil properties. In this work, kaolinite dissolution induced by three kinds of low-molecular-weight organic acid, i.e., citric, oxalic, and malic acids, was evaluated under far-from-equilibrium conditions. The rates of kaolinite dissolution depended on the kind and concentration of organic acids, with the sequence R(oxalate)>R(citrate)>R(malate). Chemical calculation showed the change in concentration of organic ligand relative to change in concentration of organic acid in suspensions of kaolinite and organic acid. The effect of organic acid on kaolinite dissolution was modeled by species of organic anionic ligand. For oxalic acid, L(2-)(oxalic) and HL(-)(oxalic) jointly enhanced the dissolution of kaolinite, but for malic and citric acids, HL(-)(malic) and H2L-(citric) made a higher contribution to the total dissolution rate of kaolinite than L(2-)(malic) and L(3-)(citric), respectively. For oxalic acid, the proposed model was R(Si)=1.89x10(-12)x[(25x)/(1+25x)]+1.93x10(-12)x[(1990x1)/(1+1990x1)] (R2=0.9763), where x and x1 denote the concentrations of HL(oxalic) and L(oxalic), respectively, and x1=10(-3.81)xx/[H+]. For malic acid, the model was R(Si)=4.79x10(-12)x[(328x)/(1+328x)]+1.67x10(-13)x[(1149x1)/(1+1149x1)] (R2=0.9452), where x and x1 denote the concentrations of HL(malic) and L(malic), respectively, and x1=10(-5.11)xx/[H+], and for citric acid, the model was R(Si)=4.73x10(-12)x[(845x)/(1+845x)]+4.68x10(-12)x[(2855x1)/(1+2855x1)] (R2=0.9682), where x and x1 denote the concentrations of H2L(citric) and L(citric), respectively, and [Formula: see text] .     

Potentiometric determination of the total acidity and concentration of citric acid in wines

The method of potentiometric titration with a copper electrode is used for the determination of the total acidity and concentration of citric acid (CA) in identifying the adulteration of wines. The procedure is suitable for the determination of citric acid in wines in the range from 0.1 to 3.5 g/L in the presence of 30-fold amounts of tartaric, acetic, malic, succinic acids and a 10-fold amount of oxalic acid after the separation of organic carboxylic acids on an AV-17-8 anion exchanger. The procedure was developed and certified for the potentiometric determination of the mass fraction of citric acid in table wines and wine materials with an error not exceeding 20%. The criteria (mass fraction of citric acid, the percentage of citric acid in the total acidity, and the shape of the curves of potentiometric titration) were proposed for revealing the adulteration of the acid composition of wines.     

LC Determination of Trace Short-Chain Organic Acids in Wheat Root Exudates Under Aluminum Stress

A novel and reliable high-performance liquid chromatographic method for trace short-chain organic acids measurement in wheat root exudates under aluminum stress has been optimized and validated. The chromatographic separation of the short-chain organic acids (citric, oxalic, malonic, succinic, tartaric, malic, and acetic acids) was achieved with Bio-rad Aminex HPX-87H cation exchange resin column. These seven organic acids were identified and quantified in 25 min. Well-shaped peaks were obtained for trace organic acids using dilute sulfuric acid as mobile phase. Under optimum conditions, Bio-rad Aminex HPX-87H column showed distinct advantages of the ability to well separate different short-chain organic acids (especially for tartaric and malic acids, as well as malonic and acetic acids) in wheat root exudates under aluminum stress, and offered accurate and precise results for the analysis of these organic acids. This HPLC method can efficiently eliminate the aluminum’s interference and is quite suitable to the trace detection of trace organic acids in wheat root exudates under aluminum stress.

     

逐级提取-高效液相色谱法快速测定植物组织中8种有机酸

针对植物组织中草酸存在的不同形态,建立了水和稀盐酸作为提取介质的逐级提取方法,获得了水溶态和酸溶态草酸及乙醇酸、乙醛酸、酒石酸、苹果酸、乙酸、柠檬酸、琥珀酸等有机酸。采用Hypersil ODS (200 mm×4.6 mm, 5 μm)色谱柱,以5 mmol/L磷酸二氢钾水溶液(pH 2.8)作为流动相,在进样量5 μL、检测波长210 nm、柱温30 ℃的条件下,通过分时段控制流速实现了8种有机酸的快速分离,同时去除了盐酸对酸溶态草酸测定的干扰。本方法精确灵敏、回收率高、重复性好,可应用于实际样品的测定分析。     

LC Determination of Trace Short-Chain Organic Acids in Wheat Root Exudates Under Aluminum Stress

A novel and reliable high-performance liquid chromatographic method for trace short-chain organic acids measurement in wheat root exudates under aluminum stress has been optimized and validated. The chromatographic separation of the short-chain organic acids (citric, oxalic, malonic, succinic, tartaric, malic, and acetic acids) was achieved with Bio-rad Aminex HPX-87H cation exchange resin column. These seven organic acids were identified and quantified in 25 min. Well-shaped peaks were obtained for trace organic acids using dilute sulfuric acid as mobile phase. Under optimum conditions, Bio-rad Aminex HPX-87H column showed distinct advantages of the ability to well separate different short-chain organic acids (especially for tartaric and malic acids, as well as malonic and acetic acids) in wheat root exudates under aluminum stress, and offered accurate and precise results for the analysis of these organic acids. This HPLC method can efficiently eliminate the aluminum’s interference and is quite suitable to the trace detection of trace organic acids in wheat root exudates under aluminum stress.     

Analysis of Organic Acids Accumulated in Kochia Scoparia Shoots and Roots by Reverse.phase High Performance Liquid Chromatography Under Salt and Alkali Stress

Introduction K.ScopariaisanannualintheChenopodiaceae family.Itsseedscontainabout15%oilandhavebeen usedintraditionalChinesemedicinetotreatdiuresis andskindisease[1].Thecrudeproteincontentof K.Scopariaseedlingsistwiceasmuchasthatin maize.Thisplantisalsorich…