Nanoplate-assembled hierarchical cake-like ZnO microstructures: solvothermal synthesis, characterization and photocatalytic properties

Abstract

Employing NH₄BF₄ as a fluoride source, novel hierarchical cake-like ZnO microstructures have been fabricated by a simple, template-free, environmentally-friendly DMF (N,N-dimethylformamide)-mediated solvothermal route. The products were characterized by XRD, SEM, TEM and nitrogen adsorption–desorption and PL. The SEM and TEM results indicated that the hierarchical cake-like ZnO were assembled from numerous tiny nanoplates. DMF acted as solvent and structure-directing agent to guide the formation of ZnO nuclei and the self-assembled preferential growth from smaller building units (nanoplates) to larger cake-like ZnO microstructures. The as-prepared samples, ZnO or ZnOHF could be regulated by altering the two major reaction parameters (the amount of DMF and fluoride source). Time-dependent morphological evolution results revealed that self-assembly and Ostwald ripening were the main formation mechanism for the hierarchical ZnO microstructure. Furthermore, the photocatalytic activity of the as-prepared ZnO samples was evaluated by the degradation of Rhodamine B (RhB) under UV light irradiation. Such hierarchical cake-like ZnO microstructures showed an excellent photocatalytic activity. Additionally, the cake-like ZnO microstructures were chemically stable, and the efficiency remained almost the same after being recycled five times.