A new insight into the photocatalytic reduction of 4-nitroaniline to p-phenylenediamine in the presence of alcohols

Photoreduction of 4-nitroaniline to p-phenylenediamine over TiO2, ZnO, PbBi2Nb2O9 and CdS photocatalysts in the presence of CH3OH was investigated under light irradiation (hv >= band gap) upon purging with N-2. Compared with PbBi2Nb2O9 and CdS,TiO2 and ZnO showed photocatalytic activities for the photoreduction of 4-nitroaniline. Electron spin resonance analysis results revealed that a methanol radical could be detected in the present of TiO2 and ZnO. Its formation was attributed to the reaction between the hydroxyl radical and CH3OH molecule. The species had strong reductive ability, and therefore could reduce 4-nitroaniline to p-phenylenediamine. Other alcohols (C2H5OH and i-C3H7OH) were also found to be efficient additives for the photoreduction of 4-nitroaniline. The results of the H-2-labeled experiments indicated that the p-phenylenediamine formation was formed by the hydrogen transfer reaction between the 4-nitroaniline and H2O molecules. A mechanism was proposed to explain the photoreduction of 4-nitroaniline to p-phenylenediamine in the present alcohols. (c) 2012 Elsevier B.V. All rights reserved.