Experimental and computational evaluation of ZIF-67 based nanoadsorbents for efficient removal of acid red 37 from...

Zeolitic imidazolate framework ZIF-67, (Z) and its nanocomposite CuO/Co₃O₄NP@ZIF-67, (CCZ) were synthesized, characterized, and applied for the removal of Acid Red 37 (AR37) from aqueous media. A dual approach combining experimental studies (adsorption kinetics, isotherms, thermodynamics) with computational simulations (geometry optimization, molecular dynamics, adsorption locator) was used to validate structure and adsorption mechanisms. (CCZ) exhibited higher adsorption capacity (65.61 mg/g) than pristine (Z) (59.14 mg/g). The adsorption data collectively indicates a complex mechanism. For (Z), the process is endothermic with a significant enthalpy change (ΔH° = 25.8 KJ/mol), laying within a borderline region between physisorption and chemisorption. In contrast, adsorption onto the (CCZ) composite is also endothermic but with a much lower enthalpy change (ΔH° = 3.48 KJ/mol), firmly classifying it as a physisorption process. For both materials, kinetics followed the pseudo-second-order model, indicating a favorable adsorption process. This, combined with their distinct isotherm behaviors (Temkin for (Z) and Dubinin-Radushkevich for (CCZ)). Together, this evidence supports a mechanism of chemically enhanced physisorption, where strong, specific non-covalent interactions govern the rate and capacity, without the high enthalpy change of classic chemisorption. While the removal efficiency of (CCZ) was much higher than (Z), both materials demonstrated excellent recyclability, maintaining high efficiency for at least five adsorption-desorption cycles. Computational studies supported these findings: geometry optimization clarified the ordered Z framework, CuO/Co₃O₄ layered surface, and planar dye structure; molecular dynamics simulations over 1000 ps confirmed the (CCZ)'s thermal and dynamic stability; and adsorption locator analysis revealed strong dye binding via hydrogen bonding, van der Waals interactions, and multiple active sites. Collectively, (CCZ) emerges as a sustainable adsorbent for wastewater remediation.