Thermal diffusion of Co into sputtered ZnO:Co thin film for enhancing visible-light-induced photo-catalytic activity

► ZnO based visible-light photo-catalyst is realized by diffusing Co into ZnO:Co. ► Diffused Co/ZnO:Co narrows its band gap as a visible-light driven photo-catalyst. ► Grain sizes of diffused Co/ZnO:Co affect the absorption edge red-shift. ► Photo-degradation and bacteria inactivation occur on the diffused Co/ZnO:Co.