Chitosan/modified sidr (Ziziphus spina-christi) tree leaves biocomposite for removal of methylene blue dye: characterization, adsorption optimization, isotherms, and kinetics

This study targets the development of a sustainable and effective adsorbent (henceforth, CHA/STL-HS) for the removal of methylene blue (MB) by combining chitosan (CHA) with modified sidr (Ziziphus spina-christi) tree leaves (STL) using sulfuric acid (H₂SO₄, HS). The physicochemical properties of CHA/STL-HS were analyzed using techniques such as FESEM-EDX, CHNS-O, XRD, BET, and FTIR. Response surface methodology (RSM) was applied to optimize the adsorption efficiency of CHA/STL-HS, taking into account variables such as pH (4–10), CHA/STL-HS dose (0.02–0.08 g), and time (10–60 min). The acquired data of MB adsorption by CHA/STL-HS were well-matched with the Freundlich and pseudo-first-order models. Remarkably, CHA/STL-HS exhibited an outstanding adsorption ability of 546.98 mg/g. The significant adsorption of MB onto CHA/STL-HS is primarily attributed to electrostatic interaction between the MB cation and the acidic groups of CHA/STL-HS, alongside n-π interactions and hydrogen bonding. The current research highlights the potential of integrating biomass (STL-HS) into biopolymer (chitosan) to generate an adsorbent that exhibits promise in eliminating cationic dye from contaminated aquatic environments.