The Preparation And Application Of Novel Nanoplatinum Modified Electrodes With High Catalytic Activity

The modified electrodes based on nanomaterials are prepared and applied to the environmental electrochemistry, which is an organic combination of nanotechnology, environmental technology and electroanalytical chemistry. It is a promising research field which is advantage to form the new technology and new method and accelerate the development of environmental electrochemistry.The main work of this paper focuses on one of the most active field where nanotechnology combines with electroanalytical chemistry, preparation and application of novel nanomaterial-modified electrodes. Three methods are applied in this thesis to fabricate nanoplatinum-modified electrodes with high catalytic activity. The emphasis of the study is to apply these modified electrodes to realize the environmental determination and thermodynamic analysis of phenol's electrochemical oxidation. The details are listed below:1. Platinum nanoparticles directly attached to glassy carbon (PtNPs/GC) were successfully fabricated by using an in situ chemical reductive growth method with ascorbic acid was used as reducing agent. The results indicated that many spherical metallic platinum nanoparticles were presented on GC surface. The diameter of these spherical nanoparticles was in the range of 40 to 200 nm. The electrochemical activety of the PtNPs/GC electrode and the electrochemical behavior of L-cysteine (L-cys) on the modified electrodes were studied. It was found that the PtNPs/GC electrode characterized excellent electrochemical feature in improving the electrocatalytic activity for the oxidation of methanol. Excellent redox reaction activity was obtained at high pH value and high temperature. The electrochemical behavior of PtNPs/GC for the L-cys oxidation was apparently higher than those of the bulk platinum electrode. Compared with the response obtained on the bulk platinum electrode, the electrochemical oxidation potential of L-cys on the modified electrode shifted negatively by 0.3 V, and the oxidation peak current of L-cys increased 12 times. The oxidation peak current of L-cys was linear to the L-cys concentration in the range of 1.0×10-7 mol/L to 1.3×10-5 mol/L. The calculated detection limit was 7.6×10-8 mol/L, which could be used to detect L-cys.2. The electrochemical oxidation behavior of phenol, catechol and hydroquinone on PtNPs/GC electrode was investigated by cyclic voltammetry. Various influence factors such as temperature, the pH of electrolyte and the concentration of phenol were examined. The results indicated that the oxidation peak potentials of phenol shifted to more negative values when temperature, pH and the concentration of phenol increased. The peak current increased with temperature and the concentration of phenol. However, the peak current decreased with increasing pH valve between 3 and 7. The peak current increased obviously until pH=7.5, and then decreased with increasing pH value. Activation energy of phenol's electro-oxidation on PtNPs/GC electrode obtained from the experimental data was 14.6 kJ/mol. The thermodynamicanalyses showed that polymerization process took place without any side reaction at 187 K. After 375 K the main reaction tended to be the degradation of phenol with a spontaneous polymerization process on the electrode surface. In addition, the electrolyte and pH did not influence the oxidation mechanism of phenol on platinum surface. Polymerization was the main oxidation process of phenol, which was controlled by the generation rate of catechol and hydroquinone.The electrochemical oxidation of catechol was a diffusion-controlled process. The oxidation peak current increased with temperature. However, the oxidation peak potential decreased with increasing temperature. The electrochemical oxidation mechanisms of catechol in different electrolyte were different. The polymerization of catechol could occur at room temperature and the formed polymer was an electronically conducting polymer. The oxidation process was significantly affected by temperature, the concentration of catechol and electrolyte. The activation energy of hydroquinone's oxidation was 14.0 kJ/mol. The reaction became irreversible with increasing temperature. The logarithm of the oxidation peak current was linear to the reciprocal of the absolute temperature.3. The hemoglobin (Hb) was immobilized on the platinum nanoparticles modified glassy carbon surface successfully. The Hb immobilization was characterized by electrochemical impedance technique. The results indicated that the effect of Hb monolayer was contributed to catalyzing the direct electron transfer of Hb and improving the reduction of hydrogen peroxide (H2O2). The electrocatalytic reduction activity to H2O2 on Hb/PtNPs/GC electrode was apparently higher than those on the PtNPs/GC electrode. The linear relationship existed between the catalytic current and the H2O2 concentration in the range of 5.0×10-6 mol/L to 4.5×10-4 mol/L. The limited detection was 7.4×10-7 mol/L.4. This study has shown that the synthesis of polycatechol/platinum composites could be accomplished using the electrochemical method. A polymerization catechol film with excellent electrochemical activity was obtained by controlling the potential scan range from -0.6 V to 0.8 V. Metallic platinum nanoparticles was introduced in polycatechol film by cyclic voltammetry. The catalytic oxidation of methanol was influenced predominantly by the size and dispersion of platinum particles. The results indicated that the oxidation current of methanol at polycatechol/platinum composites was significantly higher (70%) than that at the platinum directly electrodeposited on the GC surface, illustrating that the polymer had a synergistic effect with platinum particles in improving the catalytic oxidation of methanol. Thus, the obtained composites may be used as novel electrode material with excellent electrochemical feature.5. The electrochemical behavior of formaldehyde was investigated on the polycatechol/platinum composites modified electrode. Various influence factors such as electrolyte, pH value,scan rate and the concentration of formaldehyde were examined by cyclic voltammetry. The results indicated that the polycatechol/platinum composites modified electrode had excellent electrochemical catalytic activity to the oxidation of formaldehyde. The main reaction occurred in 0.5 mol/L H2SO4 solution was the oxidation of formaldehyde to methyl acid. However, formaldehyde could be completely oxided in 0.1 mol/L citrate + 0.2 mol/L Na2HPO4 solution (pH=7.0). The first oxidation peak current was linear to the formaldehyde concentration, which could be used to detecte formaldehyde.