The Study Of On-line Reduction And Analytical Method For Nitroaromatic Compounds

Among various nitroaromatic compounds trinitrotoluene(TNT), dinitrotoluene(DNT) and picric acid(PA) are the primary representatives of high explosives. In addition to their explosive nature, nitroaromatics are also considered as environmental contaminants and are toxic to living organisms. As a result, it is significant to develop a simple, rapid and efficient method for the detection of nitroaromatics. A number of analytical techniques are available for the determination of nitroaromatics including gas chromatography, fluorescence, surface plasmon resonance, surface enhanced Raman spectroscopy, chemiluminescence and electrochemistry. However, the stratographic and spectroscopic methods require expensive and bulky instrument and the electrochemical methods often lack of high sensitivity. As an alternative to these techniques, the electrochemiluminescence(ECL) represents a perfect combination of electrochemistry and spectroscopy. It eliminates the background disturbance of electrochemical methods and takes advantages of the high sensitivity of spectroscopic detection and the simplicity of electrochemical instrumentation.Herein, an electrochemical flow cell was fabricated with poly(dimethylsiloxane)(PDMS) to achieve the combination of electrochemical reduction and in-situ ECL detection. An integrative method was developed for the sensitive detection of the nitroaromatics including 4-nitrotoluene, 2,4-dinitrotoluene and TNT. The main contents of the thesis were given as follows:1. This paper studied the electrochemical reduction products and mechanism of nitroaromatics. The optimized electrochemical reduction condition was confirmed to be 0.05mol/L Na2SO4 by studying the effect of different electrolytes on the cyclic voltammetry of nitroaromatics. The reduction products were proved to be the corresponding aminoaromatics, which was evidenced by HPLC, UV and HPLC-MS. The reduction mechanism was preliminarily investigated and it was found that the presence of oxygen was critical for the reduction process, suggesting that the reductive oxygen species O2·-, OH· could be involved in the NACs reduction process.2. The reaction between aminoaromatics and Ru(bpy)32+ was investigated. The ECL intensities obtained from 1.0 × 10-6 mol/L of the 4-aminotoluene, 2,4-diaminotoluene and 2,4,6-triaminotoluene were respectively about 30.0 %, 40.0 % and 70.0 % of that obtained for 2-(Dibutylamino) ethanol(DBAE) at same concentration. The limit of detection(LOD) down to the nmol/L level can be readily achievable by using the ECL electrode. These LOD figures are substantially lower than that are achievable in the solution phase ECL experiment, which could be attributed to the enrichment of aminoaromatics on the surface of the ECL electrode.3. The flow cell was designed to allow the electrochemical reduction and in-situ ECL detection occur in the same solution phase. The copper mesh electrode was arranged directly underneath the ECL electrode to ensure the reduced products could be immediately detected in-situ. An electrolytic solution consists of 33.3 mmol/L Na2SO4 and 16.7 mmol/L phosphate buffer solution(PBS, p H 7.0) was found to be optimum for both the electrochemical reduction of the nitroaromatics and the ECL detection.4. The surface of copper mesh became rough after the electrodeposition of copper nanoparticles, which led to a substantial increase in the specific surface area of the reduction working electrode. At the same time, copper nanoparticles possessed high catalytic activity. Therefore, the reduction efficiency highly enhanced by the electrochemical activity of the copper mesh electrode increased.