Electroanalytical Chemical Study Of Heavy Metal Cadmium Based On Boron-doped Diamond Electrode In Waters

At present, cadmium was detected mainly via the following methods. One is the spectroscopy, the other is the inductively coupled plasma mass spectrometry. The above two methods can meet the test requirements, but still has some problems, such as large equipment, expensive, requires specialized technical personnel to operate, all these problems make it difficult to meet the needs of current analysis, thus, it can only be fixed in the laboratory. The electrochemical analysis method was developed in recent years. Because of its simple equipment, easy operation, high analysis sensitivity, miniaturization, portable, and can be used for real-time water quality detection.Usually, in electrochemical analysis, the key factor affecting the analytical results is the electrode adopted. Generally, in the conventional electrochemical analysis, the most widely used electrodes are hanging mercury drop electrode and mercury film electrode. Although they have high reproducibility and easy-updated surface, the toxic mercury and the need for environmental protection limit the application of the electrode.A new type of environmental protection boron-doped diamond film electrode(Boron-doped diamond, BDD) was adopted as the sensor electrode in this paper. It has many excellent features: very good conductivity, wide electrochemical window, very low background current, high physical and chemical stability, corrosion resistance, etc. The BDD electrode was served as working electrode, saturated calomel electrode as reference electrode and platinum electrode as auxiliary electrode. Such a three-electrode system was adopted in this paper, and the following research contents were done.The electrochemical potential window of BDD electrode was investigated using cyclic voltammograms technique in dilute sulphuric acid solution, and the results showed that the BDD electrode has very wide potential window; The dynamic performance of the BDD electrode was explored by cyclic voltammetric technique, which showed that the reaction on BDD electrode surface is a reversible electrochemical reaction, and the electrochemical reaction kinetics was mainly controlled by the diffusion process, namely the BDD electrode has very excellent dynamic performance; The BDD electrode surface state was characterized by electrochemical impedance spectroscopy technique, and the results showed that when the BDD electrode was 50 min-polarized, potassium ferricyanide and potassium ferrocyanide oxidation-reduction electric has a very fast electron transfer rate on the BDD electrode surface, at this point, the BDD electrode surface was the best.Linear sweep voltammetric technique was used to investigate the optimal applicable to cadmium ion test system, including the perchloric acid, sulfuric acid, sodium sulfate, nitrate, ammonium chloride, acetic acid, sodium acetate, potassium nitrate and hydrochloric acid, and the influence of the different electrolytes on cadmium ion test, and the results showed that the test supporting electrolyte for cadmium ion test was the acetic acid-sodium acetate; Such working parameters as accummulation potential, accummulation time, solution pH, etc were explored on the influence of cadmium ion test using altrasound-assisted square wave scan anodic stripping voltammetry, which showed that the best accummulation potential of-1.4 V, accummulation time of 500 s, the solution pH of 4.67, the step voltage is 5 mV, amplitude of 25 mV and frequency of 20 Hz; The square wave anodic stripping voltammetry was used to investigate the effect of mass transfer way on cadmium ion test with the results that ultrasonic-assisted voltammetry exhibites higher sensitivity than the mechanical mixing; The influence of the scan mode on cadmium ions test was studied, including linear scanning, square wave pulse scanning and the differential pulse scanning, and the results exhibited that the square wave scanning showed the highest sensitivity(4.49 μA L μg-1 cm-2) and the lowest detection limit(1.0 μg L-1); The altrasound-assisted square wave scan anodic stripping voltammetry was adopted to detect cadmium ions in actual water samples without cadmium founded; In addition, the possible interference factors in the solution of cadmium ions were examined with the results showing that the 0.4-fold Pb2+ interference was the most serious, followed by 10-fold Cu2+, whereas 1000-fold K+, 2800-fold Na+, 10-fold Cr3+, 500-fold NH4+ and Ca2+, 700-fold Cl-, 100-fold Mg2+, 3500-fold SO42- and Zn2+ at the same concentration level have no significant affect on the ASV signals of Cd2+.