Experimental and Molecular Simulation Study of Methyl Orange Adsorption on ZIF-67

Efficient removal of organic dye pollutants remains challenging owing to the limited adsorption capacity and poor reusability of most conventional adsorbents. Herein, rhombic-dodecahedral zeolitic imidazolate framework-67 (ZIF-67) was successfully fabricated via a facile aqueous strategy. The obtained ZIF-67 exhibited a high BET specific surface area of 1842.31 m² g^-1, with a maximum Langmuir adsorption capacity of 156.74 mg g^-1 toward methyl orange (MO). The adsorption kinetics successfully followed the pseudo-second-order model, and the material maintained 88.9% dye removal efficiency after six ethanol-regeneration cycles. Common inorganic anions (HCO₃^- and SO₄^2-) presented a distinct inhibitory effect on MO adsorption. Static electrostatic potential calculations and hydrated molecular dynamics simulations were further adopted to reveal the interfacial adsorption behavior on typical ZIF-67 (100) and (110) facets. Based on equilibrated trajectories of 40-50 ps, both facet systems exhibited stable temperature and potential-energy fluctuations. The dominant Co-O(MO) radial distribution distances for (100) and (110) facets were determined to be 5.825 Å and 5.775 Å, respectively, both far beyond conventional short-range Co-O coordination lengths. The stronger radial ordering of the (110) facet suggests facet-sensitive interfacial organization, rather than direct Co-O chemical bonding during MO adsorption.