Study On Au Microwire Electrode For The Electrochemical Detection Of Arsenic In Groundwater

The pollution of heavy metal ions in water has seriously threatened the environment, human health, and social development. Thus, it becomes extremely important and necessary to measure and monitor heavy metal ions. And their accurate analysis in groundwater is of important scientific significance for evaluation of heavy metal pollution, monitoring process of pollution, protection of regional groundwater resources security. However, it is always a challenge for robust and accurate analysis in the environmental analysis because of heavy metal pollutants with complex background, trace, multi-component and species diversity in groundwater. Although the nanomaterials have been widely applicated in in chemically modified electrode for their unique physicochemical properties, there still are some issues to resolve, such as the unclear function of nanomaterials as sensing interfaces, poor anti-interference and stability, electrode surface fouling, awful performance in complicated environment.Based on the above problems, the dissertation aims to design and fabricate the simple and robust electrochemical sensor with ultramicroelectrode to investigate the heavy metal ions in complicated groundwater. And the scientific mechanism of nanomaterials in electroanalysis has been further demonstrated. The details are described as follows:(1) An efficient sensor with gold micro wire electrode was fabricated and further successfully realized the robust and accurate detection of As(Ⅲ) in groundwater in Togtoh region of Inner Mongolia, northern China. Considering the complicated conditions of Togtoh water, the efficiency of Au microwire electrode was systematically evaluated by a series of interference tests, and no obvious interference on the determination of As(Ⅲ) was observed. Besides, the Au microwire electrode offered the favorable stability and reproducibility.(2) Since the interference of HA with high concentration in Togtoh region on the electroanalysis of As(Ⅲ), the interference mechanism of nature organic materials was demonstrated in combination with the electrochemical method and spectroscopic technique (FTIR and XPS). The interference mechanism was suggested to be derived from two part:HA molecules can interact with Au microwire electrode surface through adsorption or adhesion, thus masking the efficient binding sites; The interaction of HA with As(Ⅲ) by hydrogen bonding and slight physical adsorption decrease the activity of As(Ⅲ) in solution. The introduction of Fe(Ⅲ) on the effect of HA was also investigated. The results indicated that Fe(Ⅲ) can interact with HA to form HA-Fe(Ⅲ) complexes and their interaction was stronger than that of HA-As(Ⅲ). The co-existed Fe(Ⅲ) in groundwater can efficiently eliminate the influence of HA on As(Ⅲ) detection. It offered a deep understanding on the elimination of the interference in electroanalysis toward inorganic arsenic and provided a novel strategy to investigate the interference and to realize the robust and accurate detection of inorganic arsenic.(3) The molybdenum oxide (MoOx) was electrochemically deposited onto the surface of Au microwire electrode in a simple manner. The MoOx-Au microwire electrode was further realized the sensitively electrochemical detection of As(Ⅲ) in mild condition (pH5.0). Moreover, the interference of Cu(Ⅱ) on the determination of As(Ⅲ) was carefully examined. Although two distinct anodic peaks for As(Ⅲ)(-0.09V) and Cu(Ⅱ)(0.29V) are observed on MoOx-Au microwire electrode, there is an obvious potential of380mV between the two anodic peaks. The results demonstrated that the electrochemical detection of As(Ⅲ) can be realized without the interference from Cu(Ⅱ). The excellent stability and reproducibility of the MoOx-Au microwire electrode was observed. These evaluations demonstrated that the MoOx-Au microwire electrode was feasible to determine As(Ⅲ) in mild condition.(4) Well-arranged porous CO3O4nanosheets and layered CO3O4were synthesized via a simple hydrothermal process and calcination. A case study with Pb(Ⅱ) was established to explore their adsorption capacity and electrochemical performance. Based on the different adsorption behavior of porous and layered CO3O4, the mechanism in "adsorbing and releasing" of nanomaterials as sensing interfaces was successfully demonstrated, that is, target metal ions can be adsorbed onto the surfaces of the nanomaterials and released onto the electrode surface, thus improving the electrochemical performance of metal ions. It was of benefit for the design and fabrication of the highly sensitive sensors with high adsorptive nanomaterials.