Structural, optical and catalytic properties of ZnO-SiO2 colored powders with the visible light-driven activity

Abstract A set of samples of novel colorized zinc oxide-nanosilica composites was synthesized and analyzed. The color and optical properties are directly dependent on ZnO concentration in the composites. Visible light-driven (λ = 550 nm) catalytic activity on the degradation of pharmaceuticals was tested and indicated that the most active sample with 9 mmol of ZnO per 1 g of SiO2 was ca. 13 times (toward propanolol), 24 times (toward carbamazepine) and ca. 37 times (toward metoprolol) more effective than blank (catalyst-free photolysis) decontamination. Besides showing a typical charge transfer band on the UV–Vis spectra, all the samples demonstrated a visible light absorbance at ca. 500 nm. Due to the diminution of ZnO particles size, the sample with the minimal concentration of zinc oxide exhibited pronounced luminescence at the region of >500 nm. The microscopy confirmed the decrease of ZnO agglomerated crystalline phase with diminution of ZnO concentration over SiO2 matrix. XPS studies provided information about the chemical species contributing to the formation of nanocomposites, including the presence of some unexpected trace elements, and also the surface effects of incorporating ZnO nanoparticles into SiO2 matrix also. With the help of elemental analysis, certain impurities in ZnO were identified, which might be responsible for the outstanding optical and catalytic behavior of the samples. The toxicity results confirmed that applied process can be used for detoxification of wastewater.