Surfactant free stable cobalt oxide nanocolloid in water by pulsed laser fragmentation and its thin films for visible light photocatalysis

[Display omitted] •Pure and stable Co2O3 nanocolloid in water by laser fragmentation.•TEM shows the effects of fragmentation and reshaping of the NPs.•Nanostructured Co2O3 thin films from the nanocolloid by spray deposition.•Annealing of these films enhanced their visible light photocatalysis. Stable, pure nanocolloid of cobalt oxide (Co2O3) in water was prepared by pulsed laser fragmentation in liquid (PLFL) technique. Cobalt oxide powder with black color turned to golden yellow for the nanocolloid after laser fragmentation in water. The structure and morphology of the nanoparticles were analyzed by transmission electron microscopy. Spherical nanoparticles of cobalt oxide (∼10−20 nm) were obtained by PLFL. Nanostructured cobalt oxide thin films were fabricated by spray deposition of the cobalt oxide nanocolloid onto heated glass substrates. Scanning electron microscopy analysis showed that the thin films surfaces were uniform with some porosity, layered nature that had a transformation on thermal treatments. Raman spectroscopic results matched with the peaks for Co2O3 in literature. XPS results of the surface of the films exhibited a difference in oxygen content which was confirmed by XPS mapping. Photocatalytic activities for the as prepared and annealed thin films were studied using methylene blue as a contaminant under irradiation of visible light from a solar simulator. The results showed good visible light photocatalytic activity for the cobalt oxide nanostructured thin films and an enhancement with increase in the annealing temperature as compared to the commercial cobalt oxide powder.