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

TLDR

The study develops a rapid synthetic strategy to construct ZnO@ZIF‑8 heterostructure photocatalysts for selective reduction of Cr(VI) in dye solutions. ZnO@ZIF‑8 core–shell heterostructures were fabricated by in‑situ ZIF‑8 growth on ZnO colloidal spheres within 8–60 min, yielding a ~30 nm ZIF‑8 shell of polyhedral crystals whose thickness and morphology are tuned by 2‑methylimidazole concentration, thereby controlling Zn²⁺ release and coordination kinetics. The resulting ZnO@ZIF‑8 heterostructures exhibit size‑selective photocatalysis, with 2‑methylimidazole concentration governing core–shell formation, leading to enhanced selective reduction of Cr(VI) in the presence of methylene blue and offering a general route for rapid fabrication of such core–shell photocatalysts.

Abstract

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(2+) 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.