Rapid Construction of ZnO@ZIF‑8 Heterostructures with Size-Selective Photocatalysis Properties

To selectively remove heavy metal from dye solution, inspired by the unique pore structure of ZIF-8, we developed a synthetic strategy for rapid construction of ZnO@ZIF-8 heterostructure photocatalyst for selective reduction of Cr­(VI) between Cr­(VI) and methylene blue (MB). In particular, ZnO@ZIF-8 core–shell heterostructures were prepared by in situ ZIF-8 crystal growth using ZnO colloidal spheres as template and zinc source within 8–60 min. The shell of the resulting ZnO@ZIF-8 core–shell heterostructure with a uniform thickness of around 30 nm is composed of ZIF-8 crystal polyhedrons. The concentration of organic ligand 2-methylimidazole (Hmim) was found to be crucial for the formation of ZnO@ZIF-8 core–shell heterostructures. Different structures, ZnO@ZIF-8 core–shell spheres and separate ZIF-8 polyhedrons could be formed by altering Hmim concentration, which significantly influences the balance between rate of Zn<sup>2+</sup> release from ZnO and coordinate rate. Importantly, such ZnO@ZIF-8 core–shell heterostructures exhibit size-selective photocatalysis properties due to selective adsorption and permeation effect of ZIF-8 shell. The as-synthesized ZnO@ZIF-8 heterostructures exhibited enhanced selective reduction of Cr­(VI) between Cr­(VI) and MB, which may find application in the dye industry. This work not only provides a general route for rapid fabrication of such core–shell heterostructures but also illustrates a strategy for selectively enhanced photocatalysis performance by utilizing adsorption and size selectivity of ZIF-8 shell.