Sensitive Determination Of Bromate,Iodate And Ammonia By Using Electrochemically Modified Electrodes

In this paper, composite sensitive membranes which were composited with organic polymers, nanoparticles and metal heteropoly salt were successful modified to the surface of glassy carbon electrode, quartz crystal and silver palladium interdigital electrodes. Attention was focus on four research work as follow.(1) Through electro-polymerization and deposition, a silicotungstic heteropoly- anion composite film supported by a poly(o-phenylenediamine) mesh containing acidified MWNTs was successfully modified on a glassy carbon electrode, which forming a Si W12/Po PD/MWNTs/GCE. Scanning electron microscopy(SEM) and cyclic voltammetry(CV) were employed to characterize the different composite films. The electrochemical behaviors of Br O3- on the surfaces of different modified electrodes have been investigated, indicating that the proposed Si W12/Po PD/MWNTs/GCE exhibites excellent electrocatalytic reduction activity to bromate. The mechanism is that the bromate anion is firstly adsorbed to the surface of the electrode through electrostatic interaction, then accepts electron lost from Si W12 and H+ on the surface, resulting in its stepwise reduction to HBr O, Br2, and Br-. In 0.20 mol/L of phosphate buffer solution(p H=2.0) at a scanning rate of 150 m V/s, the modified electrode showed excellent electrochemical response property to Br O3- with a linear range of 1.0×10-8~1.0×10-4 mol/L and a detection limit of 7 ×10-9 mol/L. The electrode possessed good selectivity, reproducibility and stability, which can be well applied to determination of bromate content in real water samples with a recovery rate of 98.4~104.1%. The accuracy of the electrode was also comparable to that of a traditional ion chromatographic method, which met the national standard for requirement of bromate detection in water, indicating that the proposed method was of valuable in practical application on fields of food safety and environmental protection.(2) GCE/MWNTs/PPD modified electrode was successfully prepared by deposition of MWNTs and electro-polymerization of polypyrindine on the surface of GCE. Scanning electron microscopy(SEM) was used for characterize the different composite films, wihle cyclic voltammetry(CV) was employed to study the electrochemical behavior of IO3-and Br O3- on surface of the modified electrode. The experimental results shown that GCE/MWNTs/PPD exhibits excellent property of electrocatalytic reduction for IO3- and Br O3-based on the mechanism that IO3- and Br O3- were firstly electrostatic adsorbed to the surface of the modified electrode and then both of them captured H+ and electron to form I- and Br-. The perfect liquid medium for the modified electrode to electrochemical analysis IO3-and Br O3- was hydrochloric acid, whose concentration has a positive impact on efficiency of electrocatalytic reduction for IO3- and Br O3- by GCE/MWNTs/PPD with both substrates not affect each other among the process of detection. the modified electrode showed excellent linear range of 1.0×10-7 ~ 7.0×10-5 mol/L for Br O3- and 3.0×10-6 ~ 2.0×10-3 mol/L for IO3-. Recoveries for detection of iodate were 91.42% ~ 114.41%, and 93.24% ~ 101.91% for Br O3-. The accuracy of the modified electrode comparabled with UV-visible spectrophotometry and ion chromatography showed great value in the field of food safety and environmental protection.(3) Through Electrostatic self-assembly, ?-cyclodextrin(?-CD) and polyvinyl alcohol(PVA) were successfully modified on the surface of quartz crystal for assembling into an ammonia sensor in this paper. Experimental results shown that response performance of sensor modifying with mixture of ?-CD and PVA better than these two substances alone, witch was more significant when the ratio of PVA/?-CD is 1: 4. The modified electrode showed excellent electrochemical response property to ammonia with a linear range of 60 ~ 2940 ppm and a detection limit of 45 ppm. Recovery of the modified electrode varied between 98.42% to 114.42% wicth comparable with UV- visible spectrophotometry. High accuracy made the sensor have great value in theory and practice in the field of environmental monitoring and protection.(4) An ammonia gas sensors Pt/MWNTs/APIE by coating multi-walled carbon nanotubes(MWNTs) and platinum(Pt) nanoparticles composites on the interdigital electrode surface and a complete gas detection system were successful prepared. Nanocomposites were characterized by TEM, the length is asymmetrical to MWNTs after high temperature acidification and diameter of Pt nanoparticles varied between 20 nm to 60 nm. Experimental results show that Pt/MWNTs/APIE sensor displays a good response to NH3. The best response was performed when volume mixing ratio of MWNTs and Pt nanoparticles was 1: 0.5 in Pt/MWNTs/APIE sensor. Ambient temperature hardly affected detection of ammonia by Ag-Pd / MWNTs / Pt, but environment humidity has a greater impact on its work. A relatively wide linear range of detection NH3 was obtained between 50 ppm and 500 ppm with a recovery of Pt/MWNTs/APIE sensor for NH3 varied between 99.60% ~ 109.20%. Besides, the sensor exhibited excellent stability in 84 d and good reproducibility...