Engineering Sepiolite–Alginate Hydrogel Beads for Efficient Malachite Green Remediation: Synthesis, Characterization, Adsorption Performance, and Advanced Molecular Modeling

Abstract

This study presents the development of sustainable sepiolite–alginate (Sep@alg) hydrogel beads for the efficient removal of malachite green (MG) from aqueous media. The composite was synthesized via calcium-mediated ionic crosslinking of the alginate network, facilitating the formation of Sep@alg hydrogel beads. XRD, TGA/DTG, FTIR, SEM, STEM and XRF analyses confirmed the successful integration of sepiolite without altering its fundamental crystalline framework. Batch adsorption tests demonstrated a remarkable maximum capacity of 476 mg/g, with the equilibrium data best described by the Sips isotherm model and pseudo-second-order kinetics. Thermodynamic parameters revealed that the adsorption process is endothermic and spontaneous, with ΔG° decreasing at higher temperatures. Advanced molecular modeling, including Density Functional Theory (DFT) and Monte Carlo simulations, provided detailed insights into the interaction mechanisms, highlighting a strong adsorption energy of −377.75 kcal/mol. Additionally, Molecular Dynamics (MD) simulations clarified the spatial distribution and concentration profiles of MG within the hydrogel network. These findings demonstrate that Sep@alg beads are an eco-friendly, low-cost, and high-capacity adsorbent for sustainable wastewater treatment.