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 N-2. Its photocatalytic activity was determined by the balance between the surface area and crystallinity. The best sample was obtained after calcination at 650 degrees C, giving 4-nitroaniline conversion of similar to 100% and p-phenylenediamine selectivity of similar to 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. (c) 2012 Elsevier Inc. All rights reserved.