2D carbon semiconductors and composites are highly promising photocatalysts.

As the search for efficient catalysts for CO ₂ photoreduction continues, nanostructured perovskite oxides have emerged as a class of high-performance photocatalytic materials. The perovskite oxide candidates for CO ₂ photoreduction are primarily nanostructured forms of titanates, niobates, tantalates and cobaltates. These materials form the focus of this review article because they are much sought-after due to their nontoxic nature, adequate chemical stability, and tunable crystal structures, bandgaps and surface energies. As compared to conventional semiconductors and nanomaterial catalysts, nanostructured perovskite oxides also exhibit an extended optical-absorption edge, longer charge carrier lifetimes, and favorable band-alignment with respect to reduction potential of activated CO ₂ and reduction products of the same. While CO ₂ reduction product yields of several hundred μ mol ⁻¹ h ⁻¹ are observed with many types of perovskite oxide nanomaterials in stand-alone forms, yield of such quantities are not common with semiconductor nanomaterials of other types. In this review, we present current state-of-the-art synthesis methods to form perovskite oxide nanomaterials, and procedures to engineer their bandgaps. This review also presents a comprehensive summary and discussion on crystal structures, defect distribution, morphologies and electronic properties of the perovskite oxides, and correlation of these properties to CO ₂ photoreduction performance. This review offers researchers key insights for developing advanced perovskite oxides in order to further improve the yields of CO ₂ reduction products.

Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered graphitic carbon nitride (g-C₃N₄) and few layered graphitic carbon nitride sheets (g-C₃N₄-S) are synthesized and investigated as an active photoanode material for sunlight driven water splitting.