N-methylene phosphonic chitosan aerogels for efficient capture of Cu²⁺ and Pb²⁺ from aqueous environment

In this paper, N-methylene phosphonic acid chitosan (NPCS-PEI) was synthesized from chitosan, phosphorous acid, formaldehyde and hyperbranched polyethyleneimine (PEI), and Cu²⁺ and Pb²⁺ removal performance was examined in aqueous solution. NPCS-PEI exhibited three-dimensional porous architectures, with a specific surface area of 490.61 m²/g. The effects of pH, initial concentration, adsorption time, temperature and ionic strength on the adsorption capacity were investigated. The adsorption kinetics indicated that Cu²⁺ and Pb²⁺ adsorption onto NPCS-PEI follows a pseudo-second-order model. The adsorption isotherms agree well with the Langmuir isotherm model, and the maximum adsorption capacities of Cu²⁺ and Pb²⁺ on the NPCS-PEI are approximately 276.12 and 645.16 mg/g, respectively. The adsorption efficiency of NPCS-PEI remained above 85% after 5 adsorption-desorption successive cycles. Moreover, the NPCS-PEI aerogels had selective adsorption toward Cu²⁺. The FTIR and XPS analysis proved that amino, hydroxyl, and phosphonic acid groups were involved in the chelation with metal ions.