Decontamination and disinfection of wastewater by photocatalysis under UV/visible light using nano-catalysts based on Ca-doped ZnO

Abstract Nano-catalysts based on ZnO-Ca x% (with x = 0, 0.1, 0.3, 0.5, 0.7, and 1.0 mol % Ca 2+ ) were synthesized with a bio-friendly adaptation of the sol-gel method using gelatin as template. These materials were characterized by Fourier Transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Micro-Raman, transmission electron microscopy (TEM), scanning electron microscopy (SEM), N 2 physisorption, photoacoustic absorption spectroscopy (PAS), and photoluminescence spectroscopy (PL). The Raman results indicated that the signal, attributed to an E 1 (LO) mode at 580 cm −1 , was characteristic of oxygen vacancies that decreased with the increased Ca 2+ content in doped oxides. This agreed with the PL results, which showed that the green emission centered at 510 nm and attributable to structural defects in ZnO decreased for Ca-doped ZnO. Our oxides are constituted by nanoparticles with rod-like and spherical morphologies. All the nano-catalysts exhibited the band gap characteristics of semiconductor materials around 3.0 eV. ZnO-Ca 1.0% exhibited the best photocatalytic performance for degradation of Methyl Orange (MO) model dye, degrading about 82% after 240 min of UV–Vis irradiation at pH 7.0. The reaction mechanism was influenced by hydroxyl ( OH) and superoxide (O 2 - ) radicals and mainly by active holes (h + ). This doped oxide also demonstrated efficiency in wastewater disinfection against heterotrophic bacteria and total coliforms, exhibiting a potential use as an antimicrobial agent for the treatment of hospital wastewater. Furthermore, our nanoparticles did not show significant cytotoxic effects on L929 fibroblast cells.