Ethylenediamine-functionalized ZIF-8 for modification of chitosan-based membrane adsorbents: Batch adsorption and molecular dynamic simulation

In the current investigation, the incorporation of ethylenediamine (EDA)-modified ZIF-8 (zeolitic imidazolate framework) nanostructures into the chitosan/polyvinyl alcohol (CS/PVA) membrane adsorbents was explored for the elimination of reactive green 19 (RG) from aqueous solutions. Characterization of the synthesized EDA-modified ZIF-8 nanostructures and the membranes was carried out using XRD, SEM, BET and ATR-FTIR analyses. The CHN calculated the deacetylation degree of chitosan as 93%. To attain the maximum removal efficiency, three affecting operational parameters, including pH, adsorbent dosage, and initial concentration of dye, were optimized using the central composite design technique. The optimal conditions were resulted as; pH of 4, the adsorbent mass of 0.047 g, and the initial concentration of 70 mg L⁻¹. Afterwards, the isothermal, kinetic, and thermodynamic studies were done under the optimal conditions attained. The outcomes displayed that the equilibrium and rate of reactive green 19 adsorption on the CS/PVA/EDA-modified ZIF-8 membrane surface obeyed the Freundlich isotherm and the pseudo-second order kinetic model, respectively. The adsorption capacity was found as 144.61 mg g⁻¹. Furthermore, the entropy change (ΔS) and the enthalpy change (ΔH) for the adsorption were equal to 0.28 (kJ mol⁻¹ K⁻¹) and 4.83 (kJ mol⁻¹), respectively. Negative values of ΔG° confirmed the spontaneity of the adsorption. Molecular dynamic simulation results showed that the interaction energies of CS/PVA/EDA-modified ZIF-8 membrane + RG system surpassed that of the CS/PVA + RG, which was in agreement with the adsorption performance results.