Morphology tuning of assembled Au–Cu nicotinate rings by ligand coordination and their use as efficient catalysts

In this work, cyclic annular Au–Cu nicotinates were synthesized through a facile one-pot method. Cupric nitrate trihydrate, hydrogen tetrachloroaurate and nicotinic acid were used as the initial reactants; nicotinic acid was found to be an excellent ligand. The Au–Cu nicotinate annularity rings were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Specifically, the shape of the assembled Au–Cu nicotinate rings can be readily controlled by changing the ratio of the reactants and the reaction time. The mechanism of growth of the Au–Cu nicotinate annular rings was also investigated; the results of the experiments indicate that the Au–Cu nicotinate annular rings were assembled from ultrathin nanosheets. The Au–Cu nicotinate rings exhibit excellent catalytic activity toward the reduction of nitrophenols (including 2-nitrophenol, 3-nitrophenol, 4-nitrophenol and 4-nitrothiophenol) by sodium borohydride in water. Experimentally, the optimized ratio of the components was found to be Au : Cu : nicotinate close to 1 : 4 : 1. Kinetic rate investigations were carried out for the Au–Cu NRs-catalyzed reactions at different cycles. Importantly for their use as catalysts, the Au–Cu nicotinate rings can be recycled and exhibit good reusability. These results indicate that Au–Cu nicotinate rings are an effective catalyst for environmental wastewater treatment.