Mechanism of Cu<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mo stretchy="false">(</mml:mo><mml:mi mathvariant="normal">Ⅱ</mml:mi><mml:mo stretchy="false">)</mml:mo></mml:math></inline-formula> adsorption from water by an aminated fiber-based bio-adsorbent

To develop a low-cost and renewable fiber-based biomass adsorbent for efficient removal of copper from wastewater, alligator weed (Alternanthera philoxeroides) was used as the biomass substrate and graft-modified with epichlorohydrin and diethylenetriamine in an N, N-dimethylformamide medium. An aminated network-crosslinked fiber-based adsorbent, namely modified Alternanthera philoxeroides (MAP), was thereby prepared. The material structure and surface properties were comprehensively characterized using morphology observation, functional-group identification, crystal structure analysis, and surface chemical-state analysis. The adsorption behavior of MAP toward Cu2+ in water was systematically investigated, focusing on the effects of adsorbent dosage, contact time, solution pH, initial concentration, and temperature. The results showed that the modified material exhibited a rough and porous surface compared with the relatively smooth pristine biomass. Under the conditions of an initial Cu2+ concentration of 100 mg/L, MAP dosage of 5 g/L, pH 5.5, temperature of 298 K, and contact time of 180 min, the equilibrium adsorption capacity and removal efficiency reached 19.33 mg/g and 95.57%, respectively. Kinetic and isotherm analyses indicated that the adsorption process followed the pseudo-second-order model and the Langmuir isotherm model, with a maximum Langmuir monolayer adsorption capacity of 58.56 mg/g at 298 K. Thermodynamic parameters (ΔG H > 0) revealed that the adsorption was spontaneous and endothermic. Combined analysis of adsorption behavior and changes in surface functional groups and chemical states indicated that Cu2+ removal was mainly attributed to amino-group coordination complexation. Regeneration experiments demonstrated good reusability of the adsorbent, with the removal efficiency remaining ≥ 72.06% after six adsorption–desorption cycles. This study provides a promising low-cost and renewable fiber-based biomass adsorbent option for the treatment of copper-containing wastewater.