Maleated carboxymethyl starch biopolymer for efficient methylene blue adsorption: Synthesis, characterization, and performance evaluation

Le résumé fourni par la source

The increasing discharge of dye-contaminated wastewater from textile and chemical industries poses serious environmental concerns due to the toxicity, persistence, and poor biodegradability of synthetic dyes such as methylene blue (MB). Conventional dye removal techniques often suffer from limited efficiency, high operational costs, and environmental drawbacks. In this study, a novel bio-based adsorbent, maleated carboxymethyl starch (M.CMS), was developed through surface functionalization of carboxymethyl starch via esterification with maleic anhydride, introducing maleate and additional carboxyl (–COOH) functional groups onto the starch backbone. This specific surface modification increases the density of negatively charged adsorption sites and enhances the interaction between the adsorbent surface and cationic dye molecules. The synthesized material was characterized using FT-IR spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), confirming successful maleate grafting, reduced crystallinity, and increased surface roughness. Batch adsorption experiments were performed to evaluate MB removal under varying conditions of pH, temperature, dye concentration, contact time, and adsorbent dosage. The modified M.CMS exhibited a high removal efficiency of 98.2% within 20 min for a 20 ppm MB solution at neutral pH, significantly outperforming unmodified Carboxy Methyl Starch (CMS). Adsorption kinetics and equilibrium data followed the pseudo-second-order kinetic model and Langmuir isotherm, indicating monolayer chemisorption. Thermodynamic analysis revealed that the adsorption process is spontaneous and endothermic, with improved performance at elevated temperatures. The enhanced adsorption mechanism is primarily attributed to electrostatic interactions and hydrogen bonding between the maleate/carboxyl functional groups of M.CMS and MB molecules. These results demonstrate that the surface-modified starch biopolymer is a cost-effective, biodegradable, and highly efficient green adsorbent with strong potential for scalable wastewater treatment applications, particularly for the removal of cationic dyes.

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