Broccoli waste protein hydrolysate–modified chitosan with iron sand for methylene blue adsorption from water

Chitosan–amino acid (Chi–AA) and chitosan–amino acid–iron sand (Chi–AA–IS) bead composites were developed as eco-friendly adsorbents for methylene blue (MB) removal from water. Amino acids derived from broccoli protein hydrolysates were incorporated into a chitosan matrix, with iron sand added to enhance structural and adsorption performance. FTIR confirmed the presence of –OH, –NH, and FeO functional groups, while XRD showed reduced crystallinity after modification. Thermal analysis indicated improved thermal stability for Chi–AA–IS due to iron sand incorporation. Adsorption studies revealed distinct behaviors between the composites. Chi–AA exhibited higher experimental uptake under identical conditions, whereas Chi–AA–IS showed faster kinetics and improved site homogeneity. Chi–AA followed the Freundlich isotherm (Qm = 1.756 mg/g), indicating heterogeneous multilayer adsorption, whereas Chi–AA–IS fitted the Langmuir model well, with a higher monolayer capacity (Qm = 4.69 mg/g). Chi–AA–IS reached near-equilibrium within 5 min at pH 10, compared with 30 min at pH 12 for Chi–AA. Regeneration tests showed limited reusability under acidic conditions, although Chi–AA–IS retained comparatively higher performance. Overall, Chi–AA–IS demonstrates strong potential as a low-cost, magnetically assisted adsorbent for rapid dye removal applications requiring short contact times.