Construction Of Novel Chemically Modified Carbon Ionic Liquid Electrode And Application

Ionic liquids (ILs) are ionic compounds that consist of ions entirely, and exit in liquid state at ambient or even far below ambient temperatures. ILs have been widely used in the study of electrochemical sensors due to their unique chemical and physical properties, such as good conductivity, high chemical and thermal stability, wide electrochemical windows etc.. ILs can be not only used as solvent and electrolyte but also used to modify electrodes. The sensor can be used in wide areas and have advantages at sensitive, productive etc.. In this thesis, the carbon ionic liquid electrode is constructed by using ionic liquid as binder, which is modified to apply in biological and environmental sensing. The creative works of this thesis are summarized as follows:1. The electrocatalytic reduction of hydrogen peroxide (H₂O₂) was investigated using an electrode that was obtained by electrodeposition of Prussian blue (PB) on a carbon ionic liquid electrode (CILE). The electrochemical reduction of H2O2 in buffer of pH 7.4 was performed using cyclic voltammetry and the amperometric I-t curve technique. A PB-modified CILE was applied to detect H2O2 at -0.10 V (versus the Ag/AgCl electrode). The linear dynamic range is from 0.05 to 6.0 mM, the detection limit is 1.0μM (S/N=3). The electrode displays good stability, a response time of <5 s, and better electrocatalytic activity towards H2O2. The ease and low cost of fabrication along with its high sensitivity and renewable surface make the CILE widely applicable in the electroanalytical sensing.2. In this paper, a hydroxyapatite modified carbon ionic liquid electrode (HAP-CILE) for the simultaneous determination of lead and cadmium was developed. The hydroxyapatite which combines with ionic liquid plays an important role in remarkable responses of metals. Trace analysis of the selected heavy metals was performed by square-wave anodic stripping voltammetry (SWASV). The oxidation of two metals yielded well-defined, separated square-wave peak currents. The peak currents at about -0.34 V for Pb2+ and -0.88 V for Cd2+ were measured. The affecting factors containing supporting electrolyte, pH of solution, accumulation time, deposition potential, amount of hydroxyapatite and possible interferences were investigated. The sensor exhibited linear behavior in the range of 1×10^-9-1×10^-7mol L^-1for lead and cadmium (correlation coefficients: 0.995 and 0.997, respectively) with detection limits of 2×10¹⁰ mol L^-1 for lead and 5×10^-10 mol L^-1 for cadmium. The results indicate that the sensor is sensitive and effective for the simultaneous determination of lead and cadmium.3. A novel amperometric sensor for determination of nitrite was fabricated by electropolymerizing methylene blue (MB) on multiwall carbon nanotubes (MWNTs) modified carbon ionic liquid electrode (PMB/MWNT-CILE). The presence of MWNTs in the carbon ionic liquid elecrode could enhance the surface coverage amount of PMB and decrease the degradation of PMB, and promote the electron transfer rate. The effects of pH of the electrolyte, amount of MWNT, electropolymerization cycles and applied potential on the sensitivity of the sensor have been systemically investigated. The proposed sensor showed electrocatalytic activity for the oxidation of nitrite in 0.1 M phosphate buffer solution (pH 4.0) and the oxidation peak occurred at low overpotential (0.768 V versus Ag/AgCl). The catalytic peak current was found to be linear with the nitrite concentration in the range of 0.5–67.9μM, with a correlation coefficient of 0.9997, using amperometric measurements. The sensor showed a fast response to nitrite (less than 5 s). The sensor also exhibited good reproducibility and stability.