Fabrication of Hollow ZIF-8 Nanocrystals with Aqueous Cu ²⁺ Incorporation for Chemisorptive Methylene Blue Capture

High Resolution Image Download MS PowerPoint Slide Hollow zeolitic imidazolate framework-8 (HZIF-8) represents a compelling class of porous nanomaterials that synergizes the intrinsic microporosity of ZIF-8 with the enhanced surface-to-volume ratios and abundant active sites afforded by hollow architectures. Despite the demonstrated benefits of hollow MOF architectures and Cu incorporation for adsorption, no prior study has coupled hollow ZIF-8 formation with aqueous-phase, room-temperature postsynthetic Cu 2+ cation exchange for dye removal. Herein, we report the facile synthesis of copper-incorporated HZIF-8 through a two-step, predominantly aqueous strategy at ambient temperature. In the first step, tannic acid (TA) serves a dual role, acting as a selective etchant and surface protectant, to convert solid ZIF-8 into hollow structures while preserving the original polyhedral morphology. Systematic variation in the Zn 2+ /2-methylimidazole/water molar ratios enabled precise control over particle size and morphology. In the second step, Cu 2+ ions were incorporated into HZIF-8 via cation exchange in deionized water, without the use of organic solvents or elevated temperatures. The resulting Cu-incorporated HZIF-8 exhibited a Langmuir maximum methylene blue (MB) adsorption capacity (Q max ) of 272 ± 11 mg g –1 (nonlinear Langmuir, R 2 = 0.994), 1.44 times that of undoped HZIF-8 (189 mg g –1; a 44% increase). Adsorption followed the Langmuir isotherm and pseudo-second-order kinetics models, consistent with chemisorption driven by electrostatic interactions, π–π stacking, and Cu–S coordination. This low-solvent, room-temperature approach provides an environmentally benign route to effective MOF-based adsorbents and a useful design template for further development toward wastewater treatment.