Photoluminescent Porous Silicon을 이용한 Nitroaromatic Compounds의 탐지

Abstract

Detection of nitroaromatic compounds is desirable since there are approximately 120 million unexploded land mines worldwide. Detection of nitroaromatic compound based on adsorption into polymers has been reported. Chemo-selective polymers on SAW(surface acoustic wave) device, cyclic voltammetry using gold micro-electrode covered with non-volatue electrolyte, and organic polymer has been previously reported to detect TNT vapor. In this study very sensitive detection of TNT (2,4,6-trinitrotoluene), DNT (2,4-dinitrotoluene), NB (nitrobenzene), and PA (picric acid) has been achieved in gas phase with porous silicon films using photoluminescence quenching of the silicon crystallites as a trans- duction mode. Porous silicon films are electrochemically etched from crystalline silicon wafers in an aqueous solution of hydrofluoric acid. We used two types of PSi for detection of nitroaromatic compounds. One is the freshly etched PSi and the other is hydrosilylated PSi. First, fresh porous silicon synthesized from the electrochemical etching described above exhibits strong photoluminescence(PL) at the wavelength around 720 nm. The intensity of PL from the freshly etched porous silicon is decreased upon the exposure of the vapor of NB, DNT, TNT or PA. Flow rate of analyte-saturated air is about 5 L/min. After 30 minute, the percentage of quenching PL is 37%, 45% and 40% in the case of DNT-saturated air (vapor pressure = 200 ppb at 25℃), TNT-saturated air (vapor pressure = 4 ppb at 25℃) and PA-saturated air, respectively. It is interesting to report that 38% of quenching PL for nitrobenzene was observed just in 50 seconds. Secondly, hydrosilylation of PSi has been also investigated with divinyltetraphenylsilole(DVTPS). It is observed that the intensity of emission from porous silicon was decreased after hydrosilylation. The detection of nitroaromatic compounds has been achieved using surface-derivatized porous silicon with divinyltetraphenylsilole. Hydrosilylated PSi shows the PL at 660 nm, which exhibits the blue-shift of the wavelength compared to fresh PSi. The percentage of quenching PL of hydrosilylated PSi after exposure to nitroaromatic compounds for 30 min is 47% for DNT-saturated air, 63% for TNT-saturated air, and 52% for PA-saturated air, respectively. The percentage of quenching PL with nitrobenzene-saturated air is about 45% in 50 seconds. The detection limit on time for the analyte-saturated air is 1 sec. for NB, 1 min. for DNT, and 15 sec. for TNT, respectively. The mechanism of quenching PL is attributed to the electron transfer quenching of quantum-sized nano-crystallites in the porous silicon matrix to analyte. We also observed the chemical oxidation of porous silicon by the nitroaromatics that leads to an irreversible response at long exposure times (＞5min). Partially reversible detection mode for nitroaromatic compounds was observed. Consequently, it has been shown that porous silicon is a versatile substrate for chemical sensing with a large surface area and highly sensitive transduction modes.