A tetrazole-based metallogel induced with Ag+ ion and its silver nanoparticle in catalysis

A tetrazole-based ligand forms a supramolecular metallogel in the presence of Ag+ in aqueous solution at basic condition. The silver-induced metallogel has been characterized by SEM, TEM, XRD and rheometry. The metallogel exhibits a fiber structure. Upon standing, silver nanoparticles grow in the gel. TEM confirmed that the particles are exclusively formed in the gel fibers. The size of the silver nanoparticles formed on the gel fibers is dependent to the concentration of silver during gel formation. The silver nanoparticles show a face-centered cubic crystalline structure. The silver nanoparticles can effectively catalyze reduction of 4-nitrophenol by sodium borohydride in aqueous solution. The formation of Ag+-induced metallogels does not strongly depend on anions. According to DFT calculations, two silver cations are coordinated to nitrogen at the tetrazole moiety. The other silver cation is coordinated to the nitrogen of the pyridine and coordinated to the oxygen of the amide moiety. Furthermore, the rheological properties of the Ag+-tetrazole-based metallogel were strongly dependent on the concentration of AgClO4.