Synthesis of ZnO:Ag core-shell nanoparticles with enhanced photocatalytic properties by single - and two-steps USP

Abstract

Synthesis of ZnO:Ag core-shell nanoparticles were performed by ultrasonic spray pyrolysis (USP) from the corresponding nitrate solutions. Varying relative concentrations of Ag and ZnO precursors and two different equipment installation, allowing either common (single-step) or separate precipitation (two-steps) of Ag and ZnO, were examined in terms of their effect on final microstructure and photocatalytic properties using X-ray powder diffraction (XRPD), scanning and transmission electron microscopy (SEM, TEM, HRTEM), UV-Vis spectroscopy and photocatalytic tests. Formation of phase-pure ZnO:Ag core- shell like particles where ZnO secondary submicron sized particles formed by primary crystals with the size of 5-20 nm were confirmed by TEM analyses. Structural analyses revealed variations in silver distribution and morphology within ZnO core depending on experimental conditions. Samples with fine and uniform silver distribution on ZnO surface display a strong silver-induced enhancement of photocatalytic performance and exhibits a significantly improved photocatalytic activity in the degradation of methyl blue (MB) than that of other noble metal free ZnO systems. Photocatalytic analyses (all samples reached > 45% MB degradation) confirm the all synthesized ZnO:Ag USP systems viability for environmental applications. The best result (93% of dye elimination) is obtained for sample exhibiting maximum available surface, which strongly depends on particle morphology, size and distribution. Moreover, all samples synthesized by single-step USP revealed higher dye elimination with respect to ones with two- steps USP due to favored distribution of silver in microstructure.