Efficient visible-light-induced photocatalytic reduction of 4-nitroaniline to p-phenylenediamine over nanocrystalline PbBi2Nb2O9

Nanocrystalline PbBi2Nb2O9 was successfully prepared by a modified sol–gel method. The as-prepared nanocrystalline PbBi2Nb2O9 was an active visible-light-driven photocatalyst for the photoreduction of 4-nitroaniline to p-phenylenediamine in aqueous solution upon purging with N2. Its photocatalytic activity was determined by the balance between the surface area and crystallinity. The best sample was obtained after calcination at 650 °C, giving 4-nitroaniline conversion of ∼100% and p-phenylenediamine selectivity of ∼99% after irradiation for 150 min, which was much higher than those of bulk PbBi2Nb2O9 and TiO2−xNx photocatalysts. Further experiments revealed that oxalate anion (as a hole scavenger) was indispensable for the photocatalytic reduction of 4-nitroaniline. Moreover, on the basis of the electron spin resonance analysis result, a mechanism was proposed to explain the photoreduction of 4-nitroaniline over nanocrystalline PbBi2Nb2O9.