Removal of diclofenac using a 1-hexadecyl-3-methylimidazolium/cellulose composite as an adsorbent

Background The widespread presence of diclofenac (DCF), a nonsteroidal anti-inflammatory drug, in aquatic environments emphasizes notable environmental concerns due to its persistence and ecotoxicity. Methods In this study, a new composite adsorbent (C16mim@cell) was developed by coating nanocrystalline cellulose with the ionic liquid 1-hexadecyl-3-methylimidazolium chloride (C16mim) using an ultrasonic-assisted impregnation method. The resulting composite was characterized using SEM, TEM, FTIR, XRD, TGA, and XPS analysis. The removal of DCF was investigated through batch adsorption experiments. Additionally, periodic density functional theory (DFT) simulations were employed to examine the interaction between DCF and the C16mim@cell surface. Significant Findings The C16mim@cell composite showed rapid DCF removal, reaching equilibrium in <10 min with a maximum adsorption capacity (Q _max) of 78.37 mg. g ⁻¹ at 20 °C. The kinetic data best matched the fractal-like pseudo-first-order (FPFO) model, indicating heterogeneous surface interactions. The Liu isotherm model provided the best fit for the equilibrium data. Thermodynamic analysis confirmed the process is spontaneous and exothermic (ΔH°= -20.74 kJ mol ^-1), driven by physical adsorption. DFT simulations showed that DCF binds to the surface of the adsorbent via π–π stacking, hydrogen bonding, and electrostatic interactions. The composite achieved over 95 % removal efficiency in simulated pharmaceutical effluents and can be fully regenerated using mild saline eluents, maintaining effectiveness through multiple cycles. These results demonstrate C16mim@cell's potential as a fast, reusable, and sustainable method for removing pharmaceutical pollutants from water.