PHOTOCATALYTIC REDUCTION OF NITROORGANICS OVER ILLUMINATED TITANIUM-DIOXIDE - ELECTRON-TRANSFER BETWEEN EXCITED-STATE TIO2 AND NITROAROMATICS

The present study investigates the steady-state photocatalytic reducti on of methyl viologen and a suite of monosubstituted nitrobenzenes. Re duction was carried out in deoxygenated, illuminated aqueous slurries of titanium dioxide (Degussa P25) in the presence of a sacrificial ele ctron donor, 2-propanol. Langmuir-Hinshelwood plots were obtained for the reduction of each compound and found to be linear, with an average correlation of 0.98 and with a standard deviation on the correlations of 0.02. The concentration independent rates for nitroaromatic reduct ion obtained from these plots were normalized against the rate of meth yl viologen reduction, and the ratio was used to solve for the rate co nstant of nitroaromatic reduction, assuming a bimolecular model. The a ssumptions behind this procedure were tested by the use of the Marcus expression. Using the reorganization energy for the reaction as the fi tting variable, it was possible to fit the measured rates to the predi cted rates with a reorganization energy of 138 kJ/mol.