The Electrochemical Study Of L-Cysteine Assembled Films

In this paper, L-Cysteine (L-Cys) films was assembled on copper surfaces by self-assembly and electrochemical assembly methods. Copper was choosed as basal electrode material because it is cheap and widely used in industry. The condition for pareparing the two different kinds of films were explored respectively, and the two assembled films covered electrodes were used to electrocatalysize Ascorbic acid (AA), respectively. It was found that both of them had obviously electrocatalytic oxidization effect to AA. But the thermal stability of electrochemical assembled films of L-Cys/Cu electrode was better than self-assembled films of L-Cys/Cu electrode. And for the linear detection range, the electrochemical assembly films of L-Cys/Cu electrode were wider than self-assembled films of L-Cys/Cu electrode. There were eight chapers in this paper.In Chapter 1, reagents, solutions, electrochemistry instrument and experimental methods were introducted.In Chapter 2, the forming mechanism, structure and characteristics of molecular self-assembled films were introducted briefly. The classification, the factors and the characterization methods of SAMs were also described briefly. The application of SAMs was summarized. Finally, the research purpose, content and innovations of the subject were put forward.In Chapter 3, the L-Cysteine self-assembled films were prepared on the copper electrodes and characterizated by AC Impedance (AC), Cyclic voltammetry (CV), Difference pulse voltammetry (DPV). The best self- assembled conditions (assembly time, concentration, temperature, and pH) were explored. The influence of scanning rates on the quality of L-Cysteine self- assembled films was also studied, it was shown that oxidation peak currents (Ⅰ) were directly proportional to the square root of the scanning rates. Finally, its stability was investigated; it was found that this electrode had good stability.In Chapter 4, the L-Cysteine electrochemical assembled films were prepared on the copper electrodes and characterizated by AC Impedance (AC), Cyclic voltammetry (CV), Difference pulse voltammetry (DPV). The best electrochemical assembled conditions (circular scanning circles, assembly time, concentration, temperature and pH) were explored. The influence of scanning rates on the quality of L-Cysteine electrochemical assembled films was also studied. It was shown that oxidation peak currents (Ⅰ) were directly proportional to the square root of the scanning rates. Finally, its stability was investigated; it was found that this electrode had good stability.In Chapter 5, The coverage (θ) of L-Cys self-assembled films and the coverage (θ) of L-Cys electrochemical assembled films on copper electrode changing with time were studied by means of electrochemical impedance spectroscopy (EIS) method in this paper, and combined with capacitance value and experience constants (n), the density and homogeneous degree of assembled films in different time were discussed. It was proved that, considerated comprehensively with the coverage, the density and the homogeneous degree of the films, it should be extended the assembly time of the films appropriately in order to get better quality films, the best assembly time of L-Cys self-assembled films was about 24h, and the best assembly time of L-Cys electrochemical assembled films was about 16000s.In Chapter 6, L-Cys/Cu self-assembled films covered electrode was used to electrocatalysize ascorbic acid (AA), and the best pH value, the best static time, the best enrichment potential and the best enrichment time of the electrocatalytic oxidization were discussed, the possible catalytic mechanism was also discussed. It was measured that oxidation peak current and the concentration of AA had a good linear relationship in 1.0×10-4～9.0×10-4mol/L, the related coefficient reached to 0.9961. Finally, it was found that L-Cys/Cu self-assembled films covered electrode had good anti-interference ability to the electrocatalysis of AA.In Chapter 7, L-Cys/Cu electrochemical assembled films covered electrode was used to electrocatalysize AA, and the best pH value, the best static time, the best enrichment potential and the best enrichment time of the electrocatalytic oxidization were discussed, the possible catalytic mechanism was also discussed, it was measured that oxidation peak current and the concentration of AA had a good linear relationship in 2.0×10-5～2.0×10-4mol/L, the related coefficient reached to 0.9945. Finally, it was found that L-Cys/Cu electrochemical assembled films covered electrode had good anti-interference ability to the electrocatalysis of AA.In Chapter 8, research summary and prospect were given.