Ordered–Disordered BaZrO(3−δ) Hollow Nanosphere/Carbon Dot Hybrid Nanocomposite: A New Visible-Light-Driven Efficient Composite Photocatalyst for Hydrogen Production and Dye Degradation

[Image: see text] Perovskites form an interesting class of photocatalytic compounds because of their chemical stability and exotic chemistry. Although barium zirconates have been known for a long time, their photocatalytic study in the literature is very limited. Herein, we have studied the effect of structural disorder, oxygen vacancies and carbon dots (CDs) on photocatalytic activity of BaZrO(3−δ) (BZO) hollow nanospheres. High alkaline conditions during hydrothermal synthesis lead to the formation of disordered states as well as oxygen vacancies in BZO and create midgap states within the band gap of BZO. The midgap states further shift its absorption onset toward visible light and their presence and effects have been proved by ultraviolet–visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and electron spin resonance analysis. A composite that consists of CDs shows upconversion photoluminescence and charge-carrier transfer properties to enhance the light absorption of a photocatalyst and its activity. The photocatalytic efficiency of the compounds were examined by H(2) evolution and the degradation of methylene blue (MB) dye. In this study, loading of 3 wt% CDs on BZO shows the highest hydrogen evolution efficiency (670 μmol/h/g) with an apparent quantum yield of ∼4% and the highest MB dye degradation efficiency (∼90%) among all synthesized composites. The synergistic effect of increased visible light absorption along with enhanced photogenerated charge-carrier transfer efficiency in the presence of CDs and oxygen vacancies in BZO contributes to the enhanced photocatalytic efficacy of hybrid nanomaterials under visible light irradiation.