Photocatalytic degradation of organic dyes under visible light on sol-gel derived M/ZnO (M=Cr, Mn, Sn, Fe, Ni, Cu, Co, Ba) catalysts

A series of ZnO photocatalysts were developed by sol-gel method for photocatalytic degradation of dyes in textile wastewater under visible light irradiation. Eight different metal elements (barium, cobalt, copper, chromium, iron, manganese, nickel, and tin) were incorporated into ZnO structure to improve the photocatalytic activity of the samples in the visible region. The synthesized particles were characterized by X-ray diffraction, inductively coupled plasma, N2 adsorption techniques and UV–vis diffuse reflectance spectroscopy. Two different types of dyes, rhodamine B and methylene blue, were used to study the effect of dye structure on degradation rates. The results showed that addition of different metal elements on ZnO structure had remarkable effects on textural and optical properties, crystal structures, and photodegradation rates. The surface area of ZnO increased with the metal ion additives. The band gap energy of the ZnO was reduced by addition of Sn dopant. The diverse photocatalytic trends of metal-doped ZnO samples for both dyes undoubtedly showed the significant and drastic effect of metal dopant on the photocatalytic activity. For photodegradation of both rhodamine B and methylene blue under visible light, Sn doped ZnO showed the highest photocatalytic owing to the decreased band gap of ZnO and suppressed recombination of electron-hole pairs. The pH of the reaction medium had also significant effect on degradation rate. Graphical abstract