Cistus libanotis L. leaves -derived cellulose biosorbent for efficient hexavalent chromium removal: Integrating density functional theory with response surface methodology optimization

Hexavalent chromium (Cr(VI)) is a toxic pollutant with significant environmental and health risks due to its persistence and bioaccumulation in aquatic ecosystems. Traditional remediation methods often encounter challenges related to cost and efficiency. This study investigates Cistus libanotis L. leaf fibers as an eco-friendly and cost-effective bioadsorbent for Cr(VI) removal from aqueous solutions. The fibrous, porous morphology of Cistus libanotis L ., along with its mesoporosity and moderate surface area of 17.02 m 2 /g, was confirmed through Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET)/Barrett-Joyner-Halenda (BJH) analysis. The optimal adsorption conditions, determined using Central Composite Design and Response Surface Methodology (CCD-RSM), included a pH of 5.4, an adsorbent dose of 3 g/L, and a contact time of 60 min, achieving a maximum adsorption capacity of 32.02 mg/g. The Langmuir isotherm and Pseudo-Second Order kinetic models best fit the adsorption process, suggesting monolayer adsorption and chemisorption. Density functional theory (DFT) and Non-Covalent Interaction (NCI) analyses revealed that hydrogen bonding, and van der Waals forces play critical roles in Cr(VI) adsorption. Additionally, the Electron Localization Function (ELF) analysis demonstrated coordination interactions between HCrO₄ − and the π-electrons of the cellulose and hemicellulose benzene rings, further confirming the adsorption mechanism. This study highlights Cistus libanotis L. as a sustainable and efficient bioadsorbent for Cr(VI) removal, offering a promising alternative for environmental remediation. • Developed a cellulose-based biosorbent from Cistus libanotis L leaves for Cr(VI) removal. • Achieved 32.02 mg/g Cr(VI) adsorption efficiency at ambient temperature. • DFT and NCI calculations show cellulose and hemicellulose contribute to adsorption. • Adsorption mechanism involves hydrogen bonding and van der Waals forces. • Optimized adsorption performance using CCD-RSM method.