Highly selective adsorption performance and mechanism of basic amino acids by modified cation resin: Batch experiments and DFT calculation

Basic amino acids have been a major concern due to poor removal and high generation potential for nitrogenous disinfection by-products in drinking water treatment. Conventional cation exchange resins struggle to effectively eliminate basic amino acids owing to their inferior selectivity. In this work, a novel magnetic cation exchange resin (noted as MCER resin) was designed for the selective adsorption of basic amino acids. Batch experiments were conducted to investigate the removal efficiency for basic amino acids (histidine, arginine) and influencing factors (pH, ionic strength). Notably, MCER resin was superior in the removal of histidine (68.5%) and arginine (90%), which significantly reduced the generation of disinfection by-products (DBPs). It exhibited higher resistance to the interference of cations (Na+, Ca2+) at different levels and displayed a promising application potential for simultaneous removal of hardness. The adsorption for histidine and arginine reached equilibrium within 140 min and was well defined by pseudo-first order and intra-particle diffusion kinetic models. Furthermore, the reusability of MCER resin was elucidated after five consecutive adsorption-desorption cycles and the selective adsorption mechanism was determined through various pathways such as electrostatic attraction, hydrogen bonding and ion exchange, as evidenced by XPS and DFT calculations.