臭氧超声波联合降解除草剂2，4-D（Ⅱ）降解路径的探讨

利用臭氧超声波联合工艺对苯氧羧酸类除草剂2,4-D进行降解研究,在前文探讨臭氧超声波之间协同效应的基础上,确定其中间产物种类主要有2,4-二氯苯酚、苯醌、氢醌以及小分子酸如顺丁烯二酸、草酸、甲酸、乙酸等.在不同实验条件下,分别对反应溶液里的主要中间产物和离子浓度变化进行分析,研究2,4-D在臭氧超声波联合作用下的反应路径,并初步讨论其降解机理.     

OMC/g-C_3N_4复合材料可见光催化2,4-氯酚的研究

将有序介孔碳材料(OMC)按照一定的质量比例(0.01、0.02、0.04、0.08)加入石墨型氮化碳材料(g-C3N4)再低温煅烧获得了介孔碳/石墨型氮化碳复合材料(OMC/g-C3N4)。可见光下光催化降解2,4-氯酚的实验结果表明,有序介孔碳材料提高了复合材料的吸附和光催化性能,去除吸附作用后,样品0.04-OMC/g-C3N4的光催化效率为纯氮化碳的3.68倍。降解产物的气相色谱-质谱分析结果表明2,4-氯酚的降解主要是被羟基自由基脱氯和甲基化成其他中间后再被逐步分解完全矿化,Langmuir-Hinshelwood模型分析结果表明其光催化降解过程符合为一级反应动力学。     

臭氧降解土壤2,4-D污染物的动力学分析

为了控制土壤有机物污染,对负载污染物2,4-D(2,4-二氯苯氧乙酸)的模拟土壤柱进行臭氧化修复研究,通过考察羟基自由基抑制剂的加入、土壤粒径的影响以及混合气体中臭氧产生量的影响,分析了2,4-D污染土壤的臭氧修复动力学,研究了土壤含水量对动力学的影响。研究结果表明,液膜内羟基自由基、气液相臭氧、土壤颗粒表面的活性位均对降解2,4-D发挥作用。经过合理简化和假设,推导可知2,4-D降解符合拟一级动力学,对实验数据采用拟一级动力学进行拟合,相关系数均大于0.9。基于土壤含水量,提出动力学模型。实际的实验数据指出在土壤质量含水量低于9.38%范围内,拟一级动力学速率常数和水分含量之间基本符合二次多项式关系。     

臭氧降解土壤2，4-D污染物的动力学分析

为了控制土壤有机物污染,对负载污染物2,4-D（2,4-二氯苯氧乙酸）的模拟土壤柱进行臭氧化修复研究,通过考察羟基自由基抑制剂的加入、土壤粒径的影响以及混合气体中臭氧产生量的影响,分析了2,4-D污染土 壤的臭氧修复动力学,研究了土壤含水量对动力学的影响。研究结果表明,液膜内羟基自由基、气液相臭氧、 土壤颗粒表面的活性位均对降解2,4-D发挥作用。经过合理简化和假设,推导可知2,4-D降解符合拟一级动 力学,对实验数据采用拟一级动力学进行拟合,相关系数均大于0.9。基于土壤含水量,提出动力学模型。实际的实验数据指出在土壤质量含水量低于9.38%范围内,拟一级动力学速率常数和水分含量之间基本符合二次多项式关系。     

共存物质对O3/H2O2工艺降解2,4-D的影响(Ⅱ)氯和过氧化氢动力学分析

为了模拟实际水体中复杂的水质环境,在去离子水配制的溶液里加入少量无机盐、有机物,以及用自来水、地表水配制2,4-D溶液,采用O3/H2O2工艺处理水溶液中2,4-D污染物,通过跟踪反应液内氯离子和过氧化氢的浓度变化,考察共存物质对脱氯和过氧化氢产生分解的影响.实验结果表明,脱氯量小于2,4-D去除量,2,4-D降解过程...     

电-生物体系的运行方式对二氯酚还原降解的影响

废水中较高浓度的2,4-二氯酚(2,4-DCP)以溶解态和胶体2种形态存在。研究了间歇式电辅助微生物体系(IEMS)和连续式电辅助微生物体系(CEMS)对较高浓度2,4-DCP的还原降解效果。结果表明CEMS对溶解性2,4-DCP的降解符合零级反应动力学特征,动力学常数为0.245 h-1,对2,4-DCP降解中间产物邻氯酚(2-CP)和对氯酚(4-CP)的降解也为零级反应,动力学常数分别为0.048、0.081 5 h-1。IEMS在停止电辅助期间对胶体态2,4-DCP的水解效率远高于CEMS,2个体系均为零级反应,动力学常数分别为0.083 4、0.027 1 h-1。较高浓度的2,4-DCP宜采用IEMS处理。     

腐殖质/铁氧化物协同促进2,4-D微生物厌氧降解

构建"铁/腐殖质还原菌(Comamonas koreensis,CY01)、腐殖质模式物、铁氧化物、2,4-D"厌氧反应体系,研究2,4-D转化效率与转化途径,探讨2,4-D转化促进机制。结果表明,CY01对2,4-D的直接脱氯效果微弱,蒽醌-2,6-二磺酸钠(AQDS)与针铁矿(α-FeOOH)的加入可有效促进2,4-D厌氧转化,25 d时降解率提高2倍,达33.3%。CY01/AQDS/α-FeOOH/2,4-D体系中,AQDS、Fe(Ⅲ)及2,4-D微生物还原3种过程同时存在,AQDS和Fe(Ⅲ)充当电子穿梭体,加速胞内电子向胞外2,4-D的转移,协同促进2,4-D还原脱氯。本研究可为难降解有机氯农药污染土壤的修复研究提供借鉴。     

2,4-二氯甲苯光氯化反应动力学

研究了以氯气和2,4二-氯甲苯为原料制取2,4二-氯亚苄基二氯,讨论了2,4二-氯甲苯侧链光氯化反应温度对产物收率的影响;用气相色谱仪分别测定了在343 K、373 K及403 K 3个不同温度下反应体系中各组分摩尔分数随反应时间的变化;导出氯化反应过程的动力学模型为dxC/dt=-kxC,3个不同温度下k值分别为0.096、0.120、0.192 h-1。实验数据与动力学模型拟合的结果相吻合。     

TiO2光催化降解2,4-二氯酚动力学及机理的研究

以TiO2作为催化剂,500 W汞灯作为光源,对水体中2,4-二氯酚（2,4-DCP）的光催化降解特性进行了研究。实验结果表明,TiO2光催化降解2,4-DCP效果较好,降解的最佳pH为7,催化剂的最佳投加量为200 mg·L-1。2,4-DCP的初始浓度越小,光催化的效率越高。在初始浓度为5 mg·L-1时,光催化1 h的降解率达90%。在实验的四种不同初始浓度（5 mg·L-1、10 mg·L-1、20 mg·L-1、40 mg·L-1）下,2,4-DCP的光降解速率常数近似与其初始质量浓度成一级反应动力学关系。结合高效液相色谱、气相色谱-质谱的测定结果以及Cl-、COD的变化,认为2,4-DCP的主要降解过程为：脱氯-开环-矿化、中间产物相互作用-进一步矿化。     

2,4-D高效降解菌的筛选及其降解特性

2,4-二氯苯氧乙酸(2,4-D)是一类广泛除草剂,但其大量施用导致环境残留已对生态环境造成严重威胁。从山东某农药厂污水处理站二沉池污泥中筛选出一株高效降解菌,命名为ZQ,能以2,4-D为唯一碳源和能源生长,基于其形态,生化特性及16S r RNA基因序列分析,鉴定为Achromobacter sp.。优化其降解100 mg/L 2,4-D条件,结果表明最佳降解条件为:温度35℃,p H=8.0,接种量为2%。同时,不同初始浓度下2,4-D的降解动力学研究表明ZQ对2,4-D的降解符合一阶动力学模型。当2,4-D浓度为100 mg/L时,降解半衰期大约为10.80 h。菌株ZQ还可以其他6种常见苯氧羧酸类农药作为唯一碳源生长。结果证明Achromobacter sp.作为生态修复苯氧羧酸类农药生物强化菌具有潜在的适用性。     

Degradation of 2,4-D By Ozone And Light

The decomposition of 2,4-dichlorophenoxyacetic acid in aqueous solutions has bsen studied using ozone and ultraviolet radiation at different pH, ozone production, and initial concentration of pesticide. A mathematical model which incorporates the rate of mass transfer of ozone, the oxidation kinetics of 2,4-D and the kinetics of formation and oxidation of the intermediates was used. A global rate constant was calculated and an empirical equation which correlated that constant with ozone production, initial concentration of 2,4-D and pH at the same temperature was determined.     

Treatment of Water Contaminated with Chlorinated Organic Herbicide 2,4-D by an Ozone/Gamma Process

Radiation-induced degradation of 50 ppm 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated in different ozonation times. Co-60 gamma-source was used as a gamma-source with a dose rate of 0.07 kGy/h. Ozonized samples were irradiated for the 0.2 kGy dose. It is observed that irradiation enhances the degradation of 2,4-D with ozone. The amount of passed ozone from samples is between 0.0695 g/L and 8.33 g/L with a flow rate of ozone at 0.078 L/min (10 g/h), from 10 s to 1200 s with the ozone generator. Aliphatic acids and chloride were determined with ion chromatography. Formaldehyde, dissolved oxygen, pH and total acidity were also measured. Both species and amounts of radiolytic intermediates were determined. 2,4-dichloro phenol (2,4-DCP) is one of the toxic intermediates of 2,4-D observed with GC/MS and it decomposes at further ozonation times. It is observed that combination of ozone/gamma irradiation is more effective for degradation of 2,4-D and its intermediate 2,4-DCP. Chloride ions are observed as completely released with combined processes at lower ozonation times although nearly 98% are released with 20 min' ozonation. Intermediate 2,4-DCP decomposes at earlier ozonation times than 2,4-D.     

球形红细菌降解2,4-二硝基甲苯的途径及酶学性质

采用气相色谱-质谱联用仪(GC-MS)分析了球形红细菌降解2,4-二硝基甲苯(2,4-DNT)的中间代谢产物,分析了可能的降解途径,讨论了培养基中2,4-DNT的初始质量浓度、溶液pH值及反应温度对3种酶的酶比活力影响。结果表明,当2,4-DNT的初始质量浓度为40 mg/L时,培养72h后,可以检测到5种物质:2,4-二硝基甲苯、4-氨基-2硝基甲苯、2-氨基-4硝基甲苯、4-硝基-1,2-二(三甲基硅烷)苯、1,2,4-三(三甲基硅烷)苯,其可能的降解途径为2,4-DNT首先还原为4-氨基-2-硝基甲苯和2-氨基4-硝基甲苯,再进一步转化为4-硝基-1,2-羟基苯,然后氧化为1,2,4-三羟基苯,之后开环生成β-酮己二酸,最终降解为小分子物质。硝基还原酶、邻苯二酚2,3-双加氧酶和邻苯二酚1,2-双加氧酶的酶比活力最适宜温度分别为35、30、35℃,最适宜pH值分别为7.0、8.0、7.0,最适宜培养基初始2,4-DNT质量浓度均为40mg/L。     

Electro-oxidation of diclofenac at boron doped diamond: Kinetics and mechanism

Diclofenac is a common anti-inflammatory drug. Its electrochemical degradation at boron doped diamond electrode was investigated in aqueous solution. The degradation kinetics and the intermediate products were studied. Results showed that electro-oxidation was effective in inducing the degradation of diclofenac with 30 mg/L initial concentration, ensuring a mineralization degree of 72% after a 4 h treatment with the applied bias potential of 4.0 V. The effects of applied bias potential and addition of NaCl on diclofenac degradation were investigated. Different degradation mechanisms of diclofenac were involved at various applied bias potentials. With the addition of NaCl, some chlorination intermediates including dichlorodiclofenac were identified, which lead to the total organic carbon increase compared with the electrolysis process without NaCl addition at the reaction initial period. The main intermediates including 2,6-dichlorobenzenamine, 2,5-dihydroxybenzyl alcohol, and benzoic acid are identified at the time of 2 h. 1-(2,6-Dichlorocyclohexa-2,4-dienyl)indolin-2-one were also identified. These intermediates disappeared gradually with the extension of reaction time. Small molecular acids were identified finally. Based on these results, a degradation pathway of diclofenac was proposed.     

Peat adsorption of herbicide 2,4-D from wastewaters

The possibility of utilizing peat as adsorbent for removal of the pesticide 2,4-D from contaminated wastewaters has been evaluated in this investigation. Batch tests were conducted at different conditions of initial solute concentration, pH, particle size of adsorbent, temperature and ratios of weight of adsorbent to solution volume, in order to determine the optimum range of these variables for the adsorption operation. Removal ratios for the 2,4-D of the order of 90% were obtained under optimum conditions. The adsorption of 2,4-D in peat is described adequately by the Freundlich isotherm. Continuous tests, utilizing adsorption columns, were then conducted in order to determine the design parameters for a proposed treatment plant. The column tests were adequately correlated by the Bohart-Adams equation.     

Photodecomposition of 2,4-dichlorophenoxyacetic acid

Three types of reactor operation, flow-differential, flow-integral, and batch-recycle were employed to study the kinetics of the photolysis and oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D). The flow-through annular reactor was irradiated with a polychromatic lamp located at the axis of the annulus. Using aqueous solutions of pollutant-level concentrations (5-50 ppm), the initial rate was found proportional to the light abosrbed and otherwise independent of 2,4-D and dissolved oxygen concentrations.Using thin-layer chromatographic and spectroscopic analytical methods, 2,4-dichlorophenol (2,4-DCP) was identified as one of the photolysis products. Measurements were also made of the initial rate and rate at finite conversions for 2,4-DCP. The results were consistent with a rate equation based upon a photo-activation process followed by formation of peroxides.Of particular significance was the autocatalytic effect of intermediates on the rate of disappearance of 2,4-D. One such catalytic agent was 2,4-DCP.Carbon dioxide was produced as the final oxidation product when either 2,4-D or 2,4-DCP was the reactant. The amount of CO₂ formed proved that the aromatic ring was ruptured. This suggests the possibility of employing photochemical oxidation for reducing refractory, aromatic pollutants into fragments more susceptible to biological oxidation.     

Degradation Pathway of Ozone Oxidation of Phenols and Chlorophenols as Followed by LC-MS-TOF

ABSTRACT

This contribution summarizes the temporal intermediates produced during the ozonation of phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol, as followed by liquid chromatography coupled to a time of flight mass spectrometer (LC-MS-TOF). A 2 × 10^?3 M solution of the phenolic compounds was ozonated in a sintered glass reactor at an ozone dose of 0.14 mg/min (O₂/O₃ flow 10 mL/min). Identified intermediates showed that catechol pathway was the predominant route for phenol oxidation with acrylic acid being the end product. Hydroxylative dechlorination of 2-chlorophenol also gave catechol, and the reaction products were similar to that of phenol. Hydroxylation and ring opening via the 4-chlorocatechol pathways were the predominant route for the ozonation of 4-chlorophenol, while 2,4-dichlorophenol followed both hydroxylation and hydroxylative dechlorination mechanism. Several novel intermediates and coupling products were identified and reaction schemes leading to breakdown products are provided for each phenolic compound.     

溶液初始pH值对2,4-D臭氧直接反应动力学的影响

引言 目前,农药被大量研制及施用,由此带来的农药污染越来越受到人们的重视.含氯苯氧梭酸类除草剂2,4-D(2,4-二氯苯氧乙酸)是一种使用较广、应用较早的除草剂.2,4-D自然降解较慢,由于具有非挥发性和可溶性,易导致地下水或地表水污染,水体中已经可以检测到2,4-D的存在.     

Oxidation of herbicides by in situ synthesized hydrogen peroxide and fenton’s reagent in an electrochemical flow reactor: study of the degradation of 2,4-dichlorophenoxyacetic acid

This paper reports an investigation of H₂O₂ electrogeneration in a flow electrochemical reactor with RVC cathode, and the optimization of the O₂ reduction rate relative to cell potential. A study of the simultaneous oxidation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by the in situ electrogenerated H₂O₂ is also reported. Experiments were performed in 0.3 M K₂SO₄ at pH 10 and 2.5. Maximum hydrogen peroxide generation rate was reached at −1.6 V versus Pt for both acidic and alkaline solutions. Then, 100 mg L⁻¹ of 2,4-D was added to the solution. 2,4-D, its aromatic intermediates such as chlorophenols, chlororesorcinol and chlorinated quinone, as well as TOC were removed at different rates depending on pH, the use of UV radiation and addition of Fe(II). The acidic medium favored the hydroxylation reaction, and first order apparent rate constants for TOC removal ranged from 10⁻⁵ to 10⁻⁴ s⁻¹. In the presence of UV and iron, more than 90% of TOC was removed. This value indicates that some of the intermediates derived from 2,4-D decomposition remained in solution, mainly as more biodegradable light aliphatic compounds.