Synthesis Of Micro-and Nano-structured Metal Oxides And Comparative Studies In Electrochemical Detection Of Heavy Metal Ions

High development of socialist modernization has facilitated the strength of our national economy, along with many environmental concerns, especially the water pollution. Heavy metal ions have a detrimental risk to all the lives on the earth even at a very low concentration, including plants, animals and our human beings due to the properties of biodegradable. Therefore, it is urgent and necessary to explore a method, which is simple, fast and effective, for the analysis of heavy metal ions. Up to now, large quantities of analytical techniques have been developed for the analysis of heavy metal ions in water. Among the current developed strategies, electrochemical method has been extensively accepted as a useful way for the analysis of heavy metal ions, which offers advantages in terms of easy to operate, fast analysis speed, and low cost. Micro-and nano-structured metal oxides has drawn much researching interests owing to their excellent properties, including catalytic efficiency, magnetic properties and adsorption performance, which have been extensively explored in the field of electrochemical determination of heavy metal ions. In the past, electrochemical method was aimed at higher sensitivity with lower limit of detection (LOD) and a reasonable mechanism based on adsorption performance and the Brunauer, Emmett and Teller specific surface areas (BET) was widely provided. However, so far, the inherent relationship between electrochemical behavior and adsorption performance is still not clear, that is, reasonable explanation at the atomic level is still not proposed so far. Furthermore, the mechanism at the atomic level is of great importance for further development of micro-and nano-structured metal oxides in electrochemical determination of heavy metal ions with high sensitivity. Therefore, our study focus on synthesis of micro-and nano-structured metal oxides with different crystal phases and highly concerning the role of crystal phases in electrochemical detection of heavy metal ions. With our combination of adsorption experiment and crystalline structure, our work reveal the relationship between electrochemical behaviors and crystal phases. The major work in our study can be summarized and shown as follows:On the one hand, we successfully synthesized micro-structured iron oxide with different crystal phases (α-and γ-Fe2O3), and then applied as electrode materials for electrochemical determination of heavy metal ions, including Cu(Ⅱ), Pb(Ⅱ) and Hg(Ⅱ) under optimized experimental conditions. Their electrochemical performance were explored and compared to deeply understand the role of crystal phase. The interferences of the other four heavy metal ions and humic acid (HA) toward Pb(Ⅱ) were also performed. Finally, reasonable explanations were provided based on the crystalline structures of iron oxide with different crystal phases. The differences in electrochemical determination of heavy metal ions on α-and γ-Fe2O3modified electrodes can be known by highly considering vacant cation sites, superparamagnetic relaxation, the interaction between heavy metal ions and iron oxide with different crystal phases and surface hydroxyl groups.On the other hand, we successfully prepared manganese dioxide nanorods with different crystal phases (α-, β-and γ-MnO2) via a simple hydrothermal method and then applied as electrode sensing materials for the electrochemical determination of heavy metal ions. Their electrochemical behaviors were explored and compared to deeply understand the role of crystal phase. In order to investigate the relationship between the adsorption/desorption performances and the electrochemical behavior, the desorption and adsorption experiments were carried out. Furthermore, reasonable explanation based on crystal structures of α-,β-and γ-MnO2was provide, which was built by Diamond3.1d. Finally, α-, β-and γ-MnO2modified Au electrodes were applied in the electrochemical detection of As(Ⅲ) under mild experimental conditions. The result indicated that the stripping behaviors toward As(Ⅲ) also had a close relationship with the crystal phases.