A simple and highly efficient route for the preparation of p-phenylenediamine by reducing 4-nitroaniline over commercial CdS visible light-driven photocatalyst in water

Highly efficient photocatalytic reduction of 4-nitroaniline to p-phenylenediamine over a commercial CdS photocatalyst was observed under visible light irradiation (lambda >= 420 nm) in water. The conversion of 4-nitroaniline and the selectivity of p-phenylenediamine were similar to 100% and similar to 98% after 9 min of visible light irradiation, respectively. The photoreduction efficiency of 4-nitroaniline over the CdS photocatalyst remained above 95% in the 5th cycle of testing. Its photocatalytic activity was much higher than those of nitrogen-doped TiO2 and commercial TiO2 photocatalysts. Further experimental results revealed that the ammonium formate and N-2 atmosphere were indispensable for the photocatalytic reduction of 4-nitroaniline over the CdS photocatalyst. On the basis of the results of electron spin resonance, photoexcited electrons and .CO2- radicals were detected in the present system. These species had strong reductive powers, and were therefore able to efficiently reduce 4-nitroaniline to p-phenylenediamine.