Nanometric Heterostructures for Photocatalytic Degradation: Mechanisms, Preparation, and Applications—A Review

Nanomaterials are the subject of an increasingly growing number of investigations. Due to their unique characteristics, they have found wide applications in disciplines like electronics, catalysis, and medicine. In the field of catalysis, one can mention their application for the photocatalytic removal of various contaminants, both inorganic (e.g., toxic chromates) and organic (pesticides, dyes, pharmaceuticals, etc.). Such applications are important because the contamination of the natural environment is constantly growing. Distinct nanomaterials, such as quantum dots, have been widely utilized for photo-based wastewater treatment, but the current research activity is directed toward investigations of combined nanometric heterostructures which exhibit additional and useful properties in comparison with standalone components. However, the preparation of such heterostructures may be demanding and more complicated than that of standalone components, and the mechanism of improved photocatalytic performance may vary among different types of heterostructures. The aim of this review is to fill the existing gap in the literature and present mechanisms (type-II, Z-scheme, and S-scheme), methods of preparation (sol–gel, hydrothermal, solvothermal, sonochemical methods, and others), and applications of nanometric heterostructures in the photocatalytic degradation of organic pollutants.