Adsorptive performance of a novel polyacrylamide@vermiculite/lignin composite for uranyl ion removal from water

A novel polyacrylamide@vermiculite/lignin (PAA@VL) ternary composite was synthesized for the removal of UO₂²⁺ ions from aqueous solutions. FT-IR and SEM-EDX analyses confirmed the functional groups, heterogeneous layered morphology, and successful UO₂²⁺ adsorption of the composite. Bulk experiments showed that the adsorption process was affected by pH, initial concentration, dosage, temperature, and contact time. Isotherm studies showed that Langmuir and Freundlich models described the process well and that the maximum adsorption capacity was 2.15 mol kg^-1. The high UO₂²⁺ removal performance of PAA@VL is attributed to the synergistic effect of its components, the abundant adsorptive sites, and a strong affinity for UO₂²⁺ ions. Thermodynamic findings indicate that a negative Gibbs energy (ΔG° = -55.0-54.4 kJ mol^-1) suggests the adsorption process is spontaneous, a negative entropy change (ΔS° = -16.8 J mol^-1 K^-1) indicates a reduction in surface disorder on the composite, and a negative enthalpy value (ΔH° = -59.7 kJ mol^-1) suggests the adsorption process is exothermic. The PAA@VL ternary composite shows strong potential as an efficient and sustainable adsorbent for UO₂²⁺ removal.