Exploration On The Mechanism Of Detection And Remove Of Arsenic And Fluorine Ions In Groundwater

The drinking water polluted by heavy metal ions has seriously threatened the environment, human health, and the development of society. It has put forward more challenges for the development of economy and the progress of the society. Thus, water pollution problems, especially the determination and treatment of pollutants have drawn more attention. Heavy metal ions pollution takes a great part in water pollution, especially arsenic pollution. In China, arsenic pollution distributes in the West and North and has a connection with many kinds of cancers. Therefore, it is of important scientific significance to evaluate of heavy metal pollution, monitor process of pollution and to protect regional groundwater resources security. However, it is always challengeable for us to robust and accurate analysis in the environmental analysis because of heavy metal pollutants under these condition, such as complex background, trace, multi-component and species diversity in groundwater. Although the nanomaterials have been widely applied in chemically modified electrode for their unique physicochemical properties, especially gold, platinum and silvery nanoparticles, there still are some issues unsolved, such as particle size effect and crystallographic plane effect. Meanwhile, how to remove pollutants in the drinking water to realize the water purification is another issue.To solve the above problems, the aim of this dissertation is to study how the crystallographic plane of Au nanoparticles and the particle size of platinum nanoparticles to affect their electrochemical behavior in detection of arsenic. Otherwise, how to remove superfluous fluorine ions in the groundwater has also been studied. The details are described as follows:(1). A direct evidence of enhanced sensitivity on Au (111) facet through a comparative study of gold nanocubic, nanooctahedra, and nanorhombic dodecahedra toward detection of arsenic has been reported. To compare the detection activity of the differently shaped Au nanoparticles, the obtained sensitivity toward As (III) needs to be normalized to the corresponding EC As values. Au Octahedra nanoparticles were found to exhibit the highest sensitivity, followed by those of mechanism based on binding energies and deposition progress. Au-As mode plays an important part in the Au…As(OH)3 interaction. This mechanism based on Au deposition progress also accounts for the phenomenon the sensitivity will decrease when the concentration of As(Ⅲ) reaches a certain level. The electrochemical behavior of Au modified electrodes toward detection of As(III) exhibits a strong relationship with their crystallographic orientation. A new way might be provided to enhance the sensitivity toward the detection of arsenate.(2). The size of the platinum nanoparticles is increased through a Cu-UPD-Pt replacement method by layer-by-layer growth. Then, the ECAs are calculated by integrating the hydrogen adsorption in H2SO4 solution. After considering the ECAs, we have demonstrated that the platinum size has an affection on the detection of As(Ⅲ). As the size of Pt nanoparticles increases from 2.3 to 5.5 nm, the sensitivity decreases, which is caused by the change of the binding energy. The extremely low binding energy of the surface impedes reaction by blocking the active sites with strong adsorbed intermediates and with the formation of the inactive PtO during the anodic oxygen-transfer reaction. More importantly, this work presents an important insight into a new route to realize the improved sensitivity in electrochemical sensing of As(Ⅲ) through the change of the particle size.(3). A novel NaLa(SO4)2-ZrO2 adsorbent with high sorption capacity for fluoride was prepared through the coprecipitation method in this study, and its preparation conditions were optimized. The results of sorption experiments including sorption kinetics, isotherms, and the effect of solution pH showed that the sorption of fluoride on the NaLa(SO4)2-ZrO2 adsorbent was fast and pH-dependent. Especially, the adsorbent had high sorption capacity up to 133mg g-1 for fluoride. Fourier transform infrared (FTIR) analysis and XPS measurement showed that the hydroxyl groups and the SO42- ions on the adsorbent surface were involved in the fluoride adsorption.