水体N、P富营养化对氯代苯甲酸光解的影响

发布时间：2018-08-07 19:50

【摘要】：氯代苯甲酸作为一种重要化工原料和中间体被广泛使用,由于具有致癌、致畸、致突变“三致效应”,其排放使地表水体生态环境受到严重污染。光化学转化是有机污染物在水体环境中去除的重要方式。本文针对地表水体严重的富营养化现象,研究水体中氮、磷对氯代苯甲酸光化学降解转化的影响具有重要意义。本文采用TiO2光催化氧化技术降解邻氯苯甲酸,主要包括以下几个部分：(1)首先采用凝胶溶胶法制备TiO2,考察制备过程中各个因素的影响。运用XRD和TG对催化剂进行表征,并用亚甲基蓝测试其光催化活性；(2)利用自制TiO2与商业P25型TiO2在相同实验条件下光催化降解邻氯苯甲酸,根据其去除率来比较两种催化剂的光催化性能,采用催化性能较好的TiO2来进行后续试验。考察光解邻氯苯甲酸过程中初始浓度、催化剂投加量和溶液pH值的影响,确定最佳降解条件；(3)在水体N、P富营养化的情况下考察邻氯苯甲酸的光解效果；(4)利用醇类做为羟基自由基的捕获剂,初步检验羟基自由基理论；(5)采用液质联用来检测邻氯苯甲酸光解的中间产物,以推断邻氯苯甲酸的光解过程。实验结果显示：(1)自制TiO2的晶型受煅烧温度影响显著,其中450-600℃煅烧制备的TiO2为锐钛矿型,对亚甲基蓝光催化降解2.5小时后降解率高达95%左右；(2)在相同实验条件下商业P25型TiO2比自制的TiO2对邻氯苯甲酸光解4小时后,其降解效果差距较大,相对比之下最终选择P25型TiO2作为后续实验的催化剂,确定了光解邻氯苯甲酸的最佳条件,当溶液初始浓度为30 mg/L时催化剂投加量为0.1g/L、溶液初始pH值为3.5；(3)在最佳光解条件下当水体中N、P呈现不同程度的富营养化状态时,均会对邻氯苯甲酸的光解产生抑制作用。其中,溶液中5 mg/L的NO3-使2-CBA的去除率下降了近27%,0.5 mg/L的H2P04-使2-CBA的去除率下降了近25%。(4)实验体系中加入异丙醇导致2-CBA的去除效率明显降低,表明2-CBA光解过程中起主要作用的是羟基自由基,初步验证了羟基自由基理论。(5)通过液质联用的检测结果得知2-CBA光解中间产物为邻氯苯酚,初步推断出2-CBA降解过程为先脱羧而后羟基化。本实验研究为卤代芳香酸类在水体环境中的迁移转化,尤其是在富营养化水体中的光解转化机理提供了重要依据。
[Abstract]:Chlorobenzoic acid, as an important chemical raw material and intermediate, is widely used. Because of its carcinogenic, teratogenic and mutagenic effects, the discharge of chlorobenzoic acid has seriously polluted the ecological environment of surface water. Photochemical transformation is an important way to remove organic pollutants in water environment. In view of the serious eutrophication of surface water bodies, it is of great significance to study the effects of nitrogen and phosphorus on the photochemical degradation and transformation of chlorobenzoic acid. In this paper, the degradation of o-chlorobenzoic acid by TiO2 photocatalytic oxidation is described. The main contents are as follows: (1) TiO2 was prepared by gel sol method, and the influence of various factors in the preparation process was investigated. XRD and TG were used to characterize the catalyst and methylene blue was used to test its photocatalytic activity. (2) the photocatalytic degradation of o-chlorobenzoic acid was carried out under the same experimental conditions using self-made TiO2 and commercial P25 type TiO2. According to the removal rate, the photocatalytic performance of the two catalysts was compared, and the TiO2 with better catalytic performance was used to carry out the follow-up test. The effects of initial concentration, catalyst dosage and pH value of the solution during photolysis of o-chlorobenzoic acid were investigated, and the optimum degradation conditions were determined. (3) the photolysis effect of o-chlorobenzoic acid was investigated under the condition of eutrophication. (4) the hydroxyl radical theory was preliminarily tested by using alcohols as the trapping agent of hydroxyl radical, (5) the intermediate product of photolysis of o-chlorobenzoic acid was detected by liquid-quality coupling to infer the photolysis process of o-chlorobenzoic acid. The results showed that: (1) the crystal type of TiO2 was significantly affected by calcination temperature. The TiO2 prepared by calcination at 450-600 鈩，

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