Detection of nitrobenzene, DNT, and TNT vapors by quenching of porous silicon photoluminescence

The detection of nitroaromatic molecules in air by the quenching of the pho toluminescence of porous silicon (porous Si) films has been explored. Detec tion is achieved by monitoring the photoluminescence (PL) of a nanocrystall ine porous Si film on exposure to the analyte of interest in a flowing air stream. The photoluminescence is quenched on exposure to the nitroaromatic, presumably by an electron-transfer mechanism. Detection limits of 500 part s-per-billion (ppb), 2 ppb, and 1 ppb were observed for nitrobenzene, 2,4-d initrotoluene (DNT), and 2,4,6-trinitrotoluene (TNT), respectively (exposur e times of 5 min for each, in air). Specificity for detection is achieved b y catalytic oxidation of the nitroaromatic compound. A platinum oxide (PtO2 ) or palladium oxide (PdO) catalyst at 250 degrees C, placed in the carrier gas line upstream of the porous Si detector, causes oxidation of all the n itroaromatic compounds studied. The catalyst does not oxidize benzene vapor , and control experiments show no difference in the extent of PL quenching by benzene with or without an upstream catalyst. The PL quenching by NO2, r eleased in the catalytic oxidation of nitroaromatic compounds, is less effi cient than the quenching of the intact nitroaromatic compound. This provide s a means to discriminate nitro-containing molecules from other organic spe cies.