Mr. Prairie et al., AN INVESTIGATION OF TIO2 PHOTOCATALYSIS FOR THE TREATMENT OF WATER CONTAMINATED WITH METALS AND ORGANIC-CHEMICALS, Environmental science & technology, 27(9), 1993, pp. 1776-1782
Laboratory experiments were performed to investigate TiO2 photocatalys
is for treating water contaminated with dissolved metals (Ag, Au, Cd,
Cr, Cu, Hg, Ni, and Pt) and a variety of organics (e.g., methanol, for
mic acid, salicylic acid, EDTA, phenol,and nitrobenzene). It was found
that only those metals with half-reaction standard reduction potentia
ls more positive than 0.3 V (vs normal hydrogen electrode) can be trea
ted using TiO2 as the photocatalyst. Kinetic data illustrating the syn
ergism between oxidation and reduction are presented. Experiments usin
g singly substituted benzenes as electron donors show that the rate of
reduction of Cr(VI) is correlated with Hammett sigma constants. Photo
efficiencies approaching 85% were measured for the conversion of Cr(VI
) to Cr(III) using citric acid as the reductant. In contrast, photoeff
iciency was only 4% when oxidizing salicylic acid using O2 as the oxid
ant. It is concluded that efficient designs of photocatalytic systems
for wastewater treatment must take into account both oxidation and red
uction processes.