【作者】 周建红；

【导师】 司士辉；

【作者基本信息】 中南大学 ， 分析化学， 2011， 博士

【摘要】 重金属离子和杀虫剂等环境污染物是危害人体健康安全的重要因素,如何对环境污染物进行快速测定和有效处理一直是国内外研究的热点。TiO2在重金属的光催化还原、光催化沉积和传感器的制作应用等方面有着很大的发展潜力。纳米二氧化钛(TiO2)、二氧化锆(ZrO2)等金属氧化物容易在电极上成膜,而且成膜后的性能稳定,因而可利用这些纳米金属氧化物修饰电极来进行电分析,有利于快速、现场获得相关数据,以利于对环境污染物处理过程中的机理进行分析；并且可以利用它的催化和强吸附性能,可用作修饰电极来对环境污染物进行电化学分析,以期提高检测的选择性和灵敏度。本论文将纳米技术、膜制备技术和电化学分析理论和方法有机地结合起来,致力于构建TiO2、ZrO2等纳米金属氧化物材料修饰电极,应用于光催化还原重金属离子的机理研究和环境污染物的检测分析。其主要内容如下：一、纳米TiO2修饰电极研究TiO2对重金属离子的光催化还原行为采用石英晶体微天平(QCM)和微分脉冲伏安法(DPV)等技术作如下三方面的研究：1.纳米TiO2光催化沉积铋机理的现场研究：QCM、DPV方法以及电流时间法现场研究了Bi(Ⅲ)在纳米TiO2表面的吸附及光化学还原过程。首次采用新型的分析方法估算了氧化态和还原态铋的质量比,得出如下结果：Bi(Ⅲ)借助于纳米TiO2的表面羟基发生吸附,其吸附过程符合准二级动力学反应,反应的速率常数为13.3g·mol-1·min-1；饱和吸附量为267.5 mg(Bi)/g(TiO2)。Bi(Ⅲ)的吸附和光还原速率均受溶液的浓度和pH值影响。另外,有机物作为空穴清除剂对光还原速率有很大的影响,甲酸是光催化还原Bi(Ⅲ)的最有效的空穴清除剂,在紫外光照和空穴清除剂的作用下,光化学沉积的物质包括氧化态Bi(ⅡⅠ)和零价铋,其质量比约为7.48：1。2.纳米TiO2修饰电极研究重金属离子在络合剂存在的情况下,TiO2的光催化还原行为：研究了乙二胺四乙酸二钠(EDTA)对光催化还原以汞为代表的重金属离子的影响：采用现场QCM技术,DPV和循环伏安法(CV)来研究EDTA在TiO2表面对光催化还原汞的影响。在不同的pH下,EDTA对TiO2吸附Hg(Ⅱ)和光催化还原Hg(Ⅱ)的影响过程进行了详细的研究。根据现场研究汞吸附到TiO2表面的QCM响应和准二级动力学模型,估算出吸附的速率常数和饱和吸附量分别为4.71×10.6 g·m0l-1·min-1和46.36 mg(Hg(II))/g(Ti02).光催化还原汞的量受溶液的pH值和EDTA与Hg(II)的摩尔比的影响。当摩尔比为1：1时,最有利于光催化还原汞。关于甲酸和EDTA对光催化还原汞的作用进行了比较研究,其光催化还原机制得以进一步地阐明。3.纳米TiO2复合膜修饰电极研究TiO2在光催化还原重金属离子过程中与有机物之间的相互作用：采用QCM现场技术和DPV方法,以及红外光谱和扫描电镜(SEM)作为辅助手段研究了纳米TiO2和壳聚糖(CS)在光催化还原汞过程中的相互作用。结果显示Ti02.CS.TiO2与CS(1:1,质量比)的复合膜对汞离子的静态饱和吸附量分别为46.36(mg Hg(Ⅱ)/g Ti02),120(mg Hg(Ⅱ)/g CS)和75(mg Hg(Ⅱ)/ (1/2 g TiO2和1/2 g CS)).纳米纳米TiO2对CS具有固定和保护其免受UV分解的作用是由于形成氢键的作用；同时CS的加入有利于Ti02对汞的吸附还原作用；在有空穴清除剂存在的情况下,光催化还原汞的过程中,TiO2几乎不会光催化分解CS。二、修饰电极溶出伏安法检测环境污染物含量1.修饰电极溶出伏安法快速测定重金属离子：(1)重金属络合剂(N,N’-哌嗪二硫代氨基甲酸钠,BDP)掺杂碳糊修饰电极(BDP/CPE)阳极溶出伏安法测定痕量汞。BDP能与重金属离子形成螯合物,将其制作成掺杂BDP的CPE电极,对汞离子具有富集作用。考察了BDP/CPE测定汞离子的优化条件,通过将富集介质和溶出介质分开的方法使得实验的灵敏度和选择性得以明显提高。该修饰电极测定汞的线性范围为2～20μg·L-1,检出限为1μg·L-1(S/N=3),常见的干扰离子Pb2+、Cd2+、Cu2+和Zn2+浓度为汞离子浓度的500倍时均对其测定峰电流没有影响,应用于实际样品自来水和人发丝中的汞含量测定,其回收率分别为97%-103%和95%-107%。(2)采用同位镀铋方法,同时检测水溶液或发丝中的多种金属离子Zn2+、Cd2+、Pb2+和Cu2+,溶出电流与浓度的线性范围分别为20～100μg·L-1、5～50μg·L-1、5～50μg·L-1和20～100μg·L-1；检出限分别为10μg·L-1、2μg·L-1、2μg·L-1和10μg·L-1(S/N=3).并比较了铋膜电极和汞膜电极在测定铜离子含量中的差别。2.TiO2纳米管光化学沉积汞膜修饰电极吸附溶出伏安法(AdSV)测定有机药物含量利用Ti基体电极采用阳极氧化法制得TiO2纳米管,然后采用光催化还原汞离子制得汞膜修饰TiO2/Ti电极AdSV测定磺胺嘧啶(SDZ)。研究结果表明：在优化的条件下,吸附SDZ 5min后于B-R缓冲溶液(pH=2)中溶出峰电流在1.0×10-8～1×10-6M SDZ范围内具有良好线性,检测限为4.35×10-9 M,测定牛奶中的SDZ,其回收率为95%-108%。从而实现快速、灵敏和选择性较好地测定SDZ。3.自组装单层膜电沉积氧化锆修饰电极溶出伏安法测定对硫磷含量：在巯基自组装单层膜(SAM)上电沉积ZrO2纳米粒(ZNPs)修饰金电极,从而制得一种新的传感器,在没有介体的条件下,采用方波溶出伏安法(SWV)来直接测定对硫磷的含量。在优化的SWV操作参数下测定对硫磷,得到了线性相关的浓度范围为0.005-1.0μg·ml-1,该方法的检测限为0.8 ng·ml-1 (S/N=3)。ZNPs在自组装单层修饰金电极上显示了可接受的重现性(RSD4.16%,n=10)和良好的稳定性。该修饰电极应用于实际样品的测定得到令人满意的结果。更多还原

【Abstract】 Heavy metal ions and pesticides were the major environmental problem threatening our health and even our lives, so it is critical to develop fast, simple, and sensitive method for analysis and treatment of these pollutes. Nano-titania has great potential to be used as modified electrode in photocatalytic reduction or photodeposition of heavy metals ions and adsorption of environmental pollutes. TiO2 could form stable film on the electrode and could be employed to explore the mechanism of its photocatalytic reduction of heavy metal ions. At the same time, the catalytic and strong adsorpted performance of TiO2 could enhance the sensitivity while determining of environmental pollutes. The paper combined with the nanotechnology, film fabrication technology, the theory and method of electro-analytical chemistry to employ novel nano-TiO2 and nano-ZrO2 modified electrode. The modified electrodes were used to determine the mechanism of photocatalytic reduction of heavy metal ions and the contents of environmental pollutes. The main work could be summarized as follows:1. Study on the behavior of photocatalytic reduction heavy metal ions with nano-TiO2 modified electrode.With the in-situ technology quartz crystal microbalance (QCM), differential pulse voltammetry (DPV), three main parts were studied:(1) In-situ techniques of QCM, DPV were employed to investigate the adsorption of Bi(III) ions and the photocatalytic deposition processes of Bi at the surface of nanocrystalline TiO2. It was obtained that the adsorption of Bi(III) ions onto nanocrystalline TiO2 accorded with the pseudo-second-order reaction and the reaction rate constant k was about 13.3 g·mol-1·min-1. In addition, the photocatalytic deposition of Bi onto the surface of TiO2 was further investigated. It was found that photocatalytic deposition rate at the surface of TiO2 was enhanced by increasing pH value or initial concentration of Bi(III) ions. The influence of organic hole-scavegeners on the photocatalytic deposition of Bi was obtained that formic acid might be the best hole-scavegener for the photocatalytic reduction of Bi. The mass ratio between the Bi(III) and Bi metal deposition were calculated as 7.48:1.(2) In-situ techniques QCM, DPV and cyclic voltammetry (CV) were employed to investigate the effect of disodium ethylenediamine tetraacetate (EDTA) on photocatalytic reduction of mercury onto nanocrystalline TiO2. Effects of EDTA on adsorption of Hg(II) and its photocatalytic reduction processes at the surface of TiO2 at different pH value solutions had been studied in detail. From the in-situ response to the adsorption of Hg(II) onto TiO2, the reaction rate and saturation adsorption amount were estimated about 4.71×10-6 g·mol-1·min-1 and 46.36 mg(Hg(Ⅱ))/g(TiO2) respectively via the model of pseudo-second-order kinetics. The photocatalytic reduction of Hg at the surface of TiO2 was influenced by pH values and the mole ratio of Hg(II) to EDTA. When the ratio of Hg(Ⅱ) to EDTA was 1:1, it was most favorable for the photocatalytic reduction of mercury. In addition, the effects of HCOOH and EDTA on the reduction of Hg(II) were comparatively investigated and the mechanism on the photocatlytic reduction of mercury was also illustrated.(3) In-situ techniques QCM, DPV and the assistant technology of IR and SEM were employed to study on the interaction of TiO2 and chitosan (CS) while in the photocatalytic reduction of mercury. Results showed that The static saturation adsorption amount of TiO2, CS, and the composition of TiO2 and CS to Hg(Ⅱ) were about 46.36 (mg Hg(II)/g TiO2),120 (mg Hg(Ⅱ)/g CS) and 75 (mg Hg(II)/(1/2 g TiO2 and 1/2 g CS), respectively. Nanocrystalline TiO2 could protect CS from the UV-light; the addition of CS was favorable for the adsorption of mercury and increased the rate of photocatalytic reduction of mercury; TiO2 hardly decomposed CS when hole-scavenger was used to assist photocatalytic reduction of mercury.2. Modified electrode with stripping voltammetry method to detect environmental pollutes.(1) Determination of heavy metalsa. Bis-(dithiocarbamate) piperazine (BDP) made by ourselves was employed to prepare BDP doped carbon paste modified electrode (BDP/CPE). BDP/CPE was employed to determine the content of trace mercury with stripping voltammetry method. With the activity of complex with heavy metals, BDP could be used to enrich mercury ions. The optimum conditions such as the time of enrichment and the amount of BDP are investigated. Under the optimized condition, the enrichment of Hg(II) with BDP enhanced the sensitivity and selectivity of the determination of mercury. A linear adsorptive stripping voltammetric response over the concentration range from 2 to 20μg·L-1 was obtained under the optimized operational parameters. The limit of detection was 1μg·L-1 (S/N=3). Several metal ions Pb2+, Cd2+, Cu2+and Zn2+with the concentration 500 times of the mercury ions, showed almost no influence on the peak current of the mercury ions. With the standard additions, the mercury in the spiked water and the hair was determined with the recovery were 97%～103%and 95%～107%respectively.b. With the isochronous bismuth plating method, Zn2+, Cd2+, Pb2+, Cu2+in piked water or hair could be determined synchronously. A linear stripping voltammetric response over the concentration range of Zn2+, Cd2+, Pb2+, Cu2+were 20-100μg·L-1,5～50μg·L-1,5～50μg·L-1 and 20-100μg·L-1, respectively. The limit of detection were 10μg·L-1,2μg·L-1,2μg·L-1and 10μg·L-1 (S/N=3) respectively. At the same time, it was compared with the determination of copper using bismuth or mercury film electrode.(2) A method for the determination of sulfadiazine (SDZ) in milk was proposed by the adsorptive stripping voltammetry (AdSV) based on photocatalytic reduction of Hg film onto the TiO2 nanotube modified titanium electrode. Under the optimized conditions:After enrichment of SDZ in electrolyte of Britton-Robinson (B-R) buffer solution, pH of 2.0, for 5 min, the oxidation peak current was linearly proportional with the concentration of SDZ over the range of 1×10-8～1×10-6 M (R2=0.997) with the determination limit of 4.35×10-9M and the recovery results were 95%～108%. It was achieved to determine SDZ rapidly, selectively and sensitively.(3) A self-assembled monolayer (SAM) template was employed for the electrodeposition of zirconia nanoparticles (ZNPs) onto gold electrode. The ZNPs film was highly stable and could selectively adsorb molecules containing organic phosphoric groups. Therefore, a sensor was developed for the determination of parathion (PT) based on the ZNPs electrodeposited on the SAM modified gold electrode. The electrochemistry of PT on the present electrode was studied using CV and square-wave voltammetry (SWV). A linear adsorptive stripping voltammetric response over the concentration range from 0.005 to 1.0μg·ml-1 (after a 2-min adsorption) was obtained under the optimized operational parameters of SWV. The limit of detection was 0.8 ng·ml-1 (S/N=3). The ZNPs modified on SAM surface of gold electrode presented acceptable reproducibility (RSD 4.16%, n=10) and a good stability. The present electrode was also applied for the determination of PT in real samples and the satisfactory results were obtained.更多还原