Abstract
ZnO-SiO2 nanoparticles were synthesized by a sol-gel technique from Zn (NO3)(2)center dot 6H(2)O and tetraethyl orthosilicate. The synthesized samples were further modified by nano-sized Ag from silver nitrate solution through photo-assisted deposition (PAD) and impregnation (Img) routes. The obtained samples were characterized by a series of techniques including X-ray diffraction, UV-vis diffuse reflectance spectroscopy, N-2 adsorption, extended X-ray absorption fine structure, and transmission electron microscopy. The nano-sized Ag metal with a mean diameter (d) of ca. 2 nm having a narrow size distribution was found on the PAD-Ag/ZnO-SiO2 catalyst, whereas the aggregated Ag metal with various sizes were observed on Img-Ag/ZnO-SiO2 catalyst (d = 12 nm). The surface area of the synthesized samples was decreased from 550 to 480 and 350 m(2)/g with ZnO-SiO2, PAD-Ag/ZnO-SiO2, and Img-Ag/ZnO-SiO2, respectively. The UV-visible diffuse reflectance spectra spectra analysis confirmed the lowest band gap of PAD-Ag/ZnO-SiO2 with a value of 2.5, compared to 2.8 and 3.2 with Img: Ag/ZnO-SiO2 and ZnO-SiO2, respectively. The photocatalytic reduction of Hg2+ to Hg-0 was performed by aqueous solution containing formic acid. The obtained results revealed that the photocatalytic activity of the prepared samples increased in the order; ZnO-SiO2 < Img-Ag / ZnO-SiO2<PAD-Ag/ZnO-SiO2. The surface area decreased from 550 to 480 and 450 m(2)/g, while the efficiency of the photocatalytic reduction Hg (II) increased from 30 to 73 and 100%, with the ZnO-SiO2, Img-Ag/ZnO-SiO2 and PAD-Ag/ZnO-SiO2 samples, respectively.