Visible light treatment of azo dye-contaminated water by Ni- and Co-doped-ZnO nanoparticles supported on carbon-covered alumina

Metal-ion (Co and Ni)-doped-zinc oxide (ZnO) nanocatalysts were successfully embedded onto carbon-covered alumina (CCA) supports via a simple, green sol–gel technique. The nanocatalysts were characterised by various analytical, microscopic, and spectroscopic techniques. The CCA-embedded nanocatalysts were crystalline with high surface areas and pore volume compared to the free metal-ion–doped-ZnO nanocatalysts while retaining the wurtzite phase of the core ZnO. The influences of the dopant content and the CCA on the optical and dye removal activities of the ZnO were investigated. The materials were photo-catalytically active under visible light irradiation. Congo red and methyl orange dyes were used as model pollutants, and the reactivity followed a pseudo-first-order reaction kinetics. The reaction rate of the CCA-supported nanocatalysts showed doping with Co > Ni. The CCA/metal-ion-doped-ZnO was found to have photocatalytic activities better than the CCA-supported ZnO. HIGHLIGHTS Cost-effective ZnO is activated for visible light-responsive photocatalysis through Co/Ni + CCA incorporation.; XRD and EDX analyses confirmed the existence of Co and Ni in ZnO sites.; Co/Ni ion doping influenced the band gap and photoluminescence lifetime.; ZnO–Co/CCA showed enhanced photodegradation of Congo red to 100% in 150 min and 20 times faster than with bare ZnO.