Electrochemical Analysis And Application In Environmental Pollutants Based On Nanocomposites Modified Electrode

Nanocomposites of silver nanoparticles decorated multi-walled carbon nanotubes(MWCNT) were synthesized by depositing silver nanoparticles on the oxidized MWCNT surfaces. The morphology and microstructure of Ag/MWCNT nanocomposites were characterized by transmission electron microscopy (TEM), X-ray diffractometer(XRD) and photo-electron energy spectrum(XPS). The electrochemical properties of nanocomposites modified electrode was studied by cyclic voltammetry and square voltammetry technique. Based on the excellent conductivity, high catalytic performance and large ratio surface, the nanocomposites modified electrode were successfully applied for the determination of environmental pollutants, which offered sensitive, fast, and low cost determination methods for environmental analysis. The main contents are listed as following:(1) The well dispersed and size-controlled Ag nanoparticles decorated multi-walled carbon nanotubes (MWCNT) were synthesized by a simple chemical plating method. The oxidized MWCNT surfaces could get a more controlled and specific nucleation of Ag nanoparticles, and NaOH was used as both reducing reagent and pH adjuster to control the size of Ag nanoparticles. The as-prepared nanocomposites were characterized by transmission electron microscopy, X-ray diffraction and cyclic voltammetry. Randles-Sevcik plot suggested that the reaction of the nanocomposites in alkaline solution was a diffusion-controlled process, and the diffusion coefficient of1.09×10-4cm2s-1was obtained. A novel architecture was designed by controllable electrodeposition of silver nanoparticles doped chitosan(SNP-CS) hydrogel film. The as prepared SNP-CS film presents excellent ability to facilitate the diffusion and electron transfer process of the negatively charged redox couple [Fe(CN)6]3-/[Fe(CN)6]4-benefiting from positively charged chitosan in acidic solutions.(2) Silver nanoparticles decorated multi-walled carbon nanotubes (Ag/MWCNT) were used to detect p-nitrophenol by electrochemical technique. Experimental results indicated that these nanocomposites had a favorable catalytic ability for the reduction of p-nitrophenol(p-NP). The reduction of p-NP was a two-step process:reduction of p-NP to para-hydroxylaminophenol, and para-hydroxylaminophenol to para-nitrosophenol. The first reduction step of p-NP was a process of needing protons, but the second reduction step was a process of releasing protons. Thus, acidic medium conducive to the reduction of p-NP to para-hydroxylaminophenol, and alkaline medium in favor of the reduction of para-hydroxylaminophenol to para-nitrosophenol. Under optimum conditions, the voltammetric determination of p-nitrophenol was performed with a linear range of3.0×10-6to1.2×10-4mol L-1in acidic medium(pH=3) and3.5×10-5to1.4×10-4mol L-1in alkaline medium(pH=10), respectively.(3) Silver nanoparticle coated multi-walled carbon nanotubes (MWCNT) and silver nanoparticles doped chitosan(SNP-CS) hydrogel film were used to fabricate modified electrodes for the determination of trichloroacetic acid(TCAA). Electrochemical measurements showed that these composites had favorable catalytic ability for the reduction of trichloroacetic acid. Square wave voltammetric(SWV) technique and amperometric technique were applied to develop TCAA sensors. The square wave voltammetric determination of TCAA was performed with a linear range of5.0×10-6-1.2×10-4mol L-1and a detection limit of1.9×10-6mol L-1(S/N=3). The amperometric determination of TCAA was performed with a linear range of3.0<10-6-5.6×10-5mol L-1and a detection limit of1.1×10-6mol L-1. The proposed methods established a new way for fast, simple and selective analysis of TCAA in the presence of a great amount of dichloroacetic acid (DCAA) or monochloroacetic acid(MCAA).(4) Silver nanoparticles coated multi-walled carbon nanotubes (Ag/MWCNT) were used to fabricate a modified electrode. The electrochemical properties of Ag/MWCNT composites were characterized by electrochemical measurements. The results showed that these composites had a favorable catalytic ability for the reduction of hydrogen peroxide. Square wave voltammetric(SWV) technique was applied to detect hydrogen peroxide. Under optimum conditions, the voltammetric determination of hydrogen peroxide was performed with a linear range of5.0×10-6-8.0×10-5mol L-1and a detection limit of1.7×10-6mol L-1.