P-n heterostructured TiO2/NiO double-shelled hollow spheres for the photocatalytic degradation of papermaking wastewater

P-n heterostructured TiO2/NiO double-shelled hollow spheres were prepared through sol–gel and hydrothermal processes. TiO2/NiO nanomaterials were comprehensively characterized, and the results reveal that a cubic-structured NiO layer is successfully grown on the surface of the anatase TiO2 hollow sphere to achieve a p-n heterostructure. The thickness of TiO2 shell is ∼20 nm, and that of NiO shell is 10–25 nm. Compared with the pure TiO2 hollow spheres, the prepared p-n heterostructures display a considerably higher photocatalytic activity for papermaking wastewater degradation under UV light irradiation. The chemical oxygen demand removal rate of papermaking wastewater reaches 98.1% after 6 h of photodegradation with DSTN2 as the photocatalyst. The enhanced photocatalytic activity is due to the synergetic effects of p-n heterostructures and the large specific surface area of the catalyst; these effects may promote the separation of photogenerated electron–hole pairs.