Magnetic carboxymethyl chitosan nanoparticles for palladium and platinum adsorption

Magnetic earboxymethyl chitosan (MCMCS) nanoadsorbent was prepared for adsorption of palladium and platinum. Chitosan was first carboxymethylated and then grafted on the surface of Fe₃O₄ nanoparticles through carbodiimide activation. The results showed that MCMCS had the diameter of about 20 nm, the mass content of Fe₃O₄ of 36%, and the saturation magnetization of 25.74 × 10^-3 A· m²·g^-1. The main adsorption mechanism was the electrostatic attraction of protonated amine groups and Pd(Pt)-Cl anionic complexes at pH 2. The saturated adsorption capacity was 3.2 mmol· g^-1 for Pd and 2.7 mmol·g^-1 for Pt, respectively. The competition adsorption between Pd and Pt was observed, Pd and Pt competed for the same adsorption active sites, and the affinity of MCMCS for Pd was greater than that for Pt. The desorption efficiency of more than 68% for both Pd and Pt was achieved using 0.5 mol·L^-1 thiourea as eluant, while the highest selectivity was observed with 5 mol· L^-1 ammonia.