Eco-Friendly Synthesis of ZnO Nanoparticles Using Zeolitic Imidazolate Framework-7 for Methylene Blue Removal: Experimental and Theoretical Analysis

Abstract

Industrial dye contamination in water sources presents serious threats to both human health and the environment. Adsorption technology has gained popularity for wastewater treatment due to its simplicity, cost-effectiveness, and use of environmentally friendly materials. This study investigates the desorption of methylene blue (MB) dye using zinc oxide nanoparticles (ZnO-NPs) synthesized from ZIF-7 (Zn(BIM)₂; BIM = Benzimidazole) with a sodalite zeolitic topology. The green synthesis of ZnO-NPs was characterized using X-ray powder diffraction with Rietveld refinement (space group = P63/mmc, a = b = 3.252 (2) Å; c = 5.207 (4) Å, α = β = 90°, and γ = 120°), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) techniques, revealing a surface area of (29.93 g/m²), nanoscale size (3 nm), and surface hydroxyls. Under optimal conditions (pH 7, 10 mg/L dye concentration, 0.02 g adsorbent dose), ZnO-NPs achieved an adsorption efficiency of 94.7% for MB. Adsorption capacity increased from 62.7 mg/g at 298 K to 85.16 mg/g at 328 K, with isotherm analysis showing physical adsorption as the primary mechanism (adsorption energies <40 kJ/mol). Modeling revealed MB molecules adsorbed nonparallel to the ZnO-NP surface.