Valorization of Tea Waste Into Magnetic Chitosan and Nanoceria Composites for Efficient Congo Red Adsorption: A Comparative Equilibrium, Kinetic, and Mechanistic Study

In the study, tea waste (TW) was valorized through two distinct approaches to investigate the impact of the functionalization mechanism: organic modification with citrate cross‐linked magnetic chitosan‐Fe 3 O 4 nanoparticles (TW@CS) and inorganic modification with cerium oxide nanoparticles (TW@NC). Both TW and the prepared composites were characterized using FT‐IR and SEM, and the composites were employed to remove Congo red (CR) dye from wastewater in batch mode. Functionalization has altered the point of zero charge in opposite directions: from 6.8 for TW to 7.8 for TW@CS and 4.2 for TW@NC, resulting in the highest biosorption capacity at pH 3 for TW and TW@NC and pH 6 for TW@CS, which is a practically useful shift toward near‐neutral effluents. Biosorbent capacities of 38.77, 47.11, and 49.06 mg/g for TW, TW@CS, and TW@NC, respectively, were obtained at a biosorbent dose of 0.05 g/50 mL, a contact time of 90 min, and an initial dye concentration of 50 mg/L at 303 K. The adsorption data showed a good fit to the Langmuir isotherm ( R 2 ≥ 0.982) and pseudo‐second‐order kinetic modeling ( R 2 = 0.999). The work shows that the choice of functionalizing chemistry, not merely its presence, dictates where a tea‐waste sorbent can be deployed.