Effect of Cd-doping on the catalytic activity of ZnO nanoflakes in the synthesis of benzimidazoles

Abstract

A set of hierarchical Cd x Zn1−x O nanoflakes (x = 0, 0.01 and 0.03) was prepared by the co-precipitation method using methanol as solvent. The prepared samples were characterized by UV–visible, X-ray diffraction, field emission scanning electron microscopy and energy-dispersive X-ray analysis techniques. The slight red shift in the Cd-doped ZnO confirms the doping of Cd2+ ions into ZnO lattices. The average crystallite size of Cd-doped ZnO nanoflakes was found to be in the range of 10–28 nm. The catalytic activity of Cd-ZnO nanoflakes in conjunction with microwave irradiation was investigated for reactions between o-phenylenediamine with aldehydes. It was found that the presence of Cd content in ZnO promotes rapid and selective synthesis of 2-substituted benzimidazoles under solvent-free conditions. The improvement of the catalytic activity by Cd doping is discussed in the light of the Brunauer–Emmet–Teller method. The catalyst could be reused up to five cycles without any significant loss of catalytic activity.