| 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. |
