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 TiO 2 , ZnO, PbBi 2 Nb 2 O 9 and CdS photocatalysts in the presence of CH 3 OH was investigated under light irradiation ( hv   ≥   band gap) upon purging with N 2 . Compared with PbBi 2 Nb 2 O 9 and CdS, TiO 2 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 TiO 2 and ZnO. Its formation was attributed to the reaction between the hydroxyl radical and CH 3 OH molecule. The species had strong reductive ability, and therefore could reduce 4-nitroaniline to p -phenylenediamine. Other alcohols (C 2 H 5 OH and i -C 3 H 7 OH) were also found to be efficient additives for the photoreduction of 4-nitroaniline. The results of the 2 H-labeled experiments indicated that the p -phenylenediamine formation was formed by the hydrogen transfer reaction between the 4-nitroaniline and H 2 O molecules. A mechanism was proposed to explain the photoreduction of 4-nitroaniline to p -phenylenediamine in the present alcohols.