Humic acid-assisted synthesis of Ag/Ag2MoO4 and Ag/Ag2WO4 and their highly catalytic reduction of nitro- and azo-aromatics

Herein, Ag/Ag 2 MoO 4 and Ag/Ag 2 WO 4 have been prepared via a humic acid-assisted precipitation-calcination process and used as catalysts for the hydrogenation reduction of nitro- and azo-aromatic compounds. The Ag/Ag 2 MoO 4 and Ag/Ag 2 WO 4 composites were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) and Raman spectroscopies, UV–vis-NIR diffuse reflectance spectroscopy (DRS), and nitrogen adsorption-desorption analyses. Metallic Ag nanoparticles were in situ generated during the annealing process and spatially confined in the Ag 2 MoO 4 or Ag 2 WO 4 matrix, which effectively inhabited the particle agglomeration of silver. The Ag/Ag 2 MoO 4 and Ag/Ag 2 WO 4 catalysts displayed good performance toward the hydrogenation reduction of 4-nitrophenol, 2-nitroaniline, and rhodamine B in terms of rapid conversion and long term durability.