Enhanced degradation of p-nitrophenol in soil in a pulsed discharge plasma-catalytic system.

A pulsed discharge plasma-TiO(2) catalytic (PDPTC) system was developed to investigate the degradation of p-nitrophenol (PNP) in soil. The effects of TiO(2) amount, soil pH and air moisture on PNP degradation were evaluated, and PNP degradation processes were predicted with Gaussian 03W combined with density functional theory (DFT). Experimental results showed that 88.8% of PNP could be smoothly removed in 10 min in the PDPTC system with the specific energy density of 694 J g(soil)(-1), compared with 78.1% in plasma alone system. The optimum TiO(2) amount was 2% in the present study, and higher TiO(2) amount exhibited an inhibitive effect. Alkaline soil was favorable for PNP removal. The increase of air moisture to a certain extent could enhance PNP removal. A DFT calculation presented that there was a high preference for the -ortho and -para positions with respect to the functional -OH group of PNP molecule for OH radicals attack. The main intermediates were hydroquinone, benzoquinone, catechol, phenol, benzo[d][1,2,3]trioxole, acetic acid, formic acid, NO(2)(-), NO(3)(-) and oxalic acid. The generation of hydroxylated intermediates, NO(2)(-) and NO(3)(-) suggested that the experimental results were consistent with those of the theoretical prediction.