Photooxidation mechanism of nitrogen-containing compounds at TiO 2/H 2O interfaces: an experimental and theoretical examination of hydrazine derivatives

Abstract

The photocatalytic oxidation of oxalyldihydrazide, N, N ′-bis(hydrazocarbonyl)hydrazide, N, N ′-bis(ethoxycarbonyl)hydrazide, malonyldihydrazide, N-malonyl-bis[( N ′-ethoxycarbonyl)hydrazide] was examined in aqueous TiO 2 dispersions under UV illumination. The photomineralization of nitrogen and carbon atoms in the substrates into N 2 gas, NH 4 + (and/or NO 3 −) ions, and CO 2 gas was determined by HPLC and GC analysis. The formation of carboxylic acid intermediates also occurred in the photooxidation process. The photocatalytic mechanism is discussed on the basis of the experimental results, and with molecular orbital (MO) simulation of frontier electron density and point charge. Substrate carbonyl groups readily adsorb on the TiO 2 surface, and the bonds between carbonyl group carbon atoms and adjacent hydrazo group nitrogen atoms are cleaved predominantly in the initial photooxidation process. The hydrazo groups were photoconverted mainly into N 2 gas (in mineralization yields above 70%) and partially to NH 4 + ions (below 10%). The formation of NO 3 − ions was scarcely recognized.