Review and Perspective on Rational Design and Interface Engineering of g-C3N4/ZnO: From Type-II to Step-Scheme Heterojunctions for Photocatalytic Applications

Heterostructuring the g-C3N4 (GCN) with wide gap oxide photocatalysts is of prominent interest as they can harvest photons spanning the UV–visible region. In this regard, GCN/ZnO have garnered remarkable attention due to their admirable structure, optical, dimensional anisotropy, and electronic properties. The 2D sheet-like structure of GCN can serve as a suitable substrate for the growth of distinct ZnO nanostructures under the multitude of reaction conditions. This review focuses on the progress in the rational design and interface engineering of GCN/ZnO to from Type-II and Z/S-scheme heterojunctions, followed by their relevant photocatalytic applications toward H2 evolution, CO2 reduction, pollutant degradation, and bacteria inactivation. The mechanism underlying the crystallization of GCN and ZnO together with their intimate contact in the composite are emphasized under the light of diverse preparation methods. The modification of GCN/ZnO with cocatalysts such as metals, alloy, semiconductors, and carbon materials to form ternary systems to highlight their advancements. The gap analysis and future prospectus of this intricate heterostructure concerning the challenges in synthetic approaches and the charge carrier dynamics are discussed. This review envisages the development of efficient GCN/ZnO-based heterostructures for multiscale applications.