Utilization of poly(methacrylic acid)‐rice straw graft copolymers for <scp>P</scp>b²⁺ ions removal from wastewater: Synthesis, characterization, and adsorption studies

Abstract Rice straw bio waste was converted into a high‐performance adsorbent for Pb 2+ ions removal by grafting it with methacrylic acid using microwave irradiation. For this purpose, six levels of poly(MAA)‐rice straw graft copolymers having different graft yields % with increasing order and designated as (PMAARSGC‐I to PMAARSGC‐VI) were prepared and characterized using FTIR, SEM, XRD, TGA, zeta potential and BET analysis. Different factors affecting the Pb 2+ removal expressed as adsorption capacity such as pH, extent of grafting, treatment time, and lead ions concentrations were studied in detail. Various kinetics models (pseudo‐first‐order, pseudo‐second‐order, Elovich, and intraparticle diffusion), isothermal (Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich) and thermodynamic studies have been applied. The results demonstrated that (a) FT‐IR, SEM, XRD, TGA, zeta potential, and BET analysis confirmed the formation of carboxyl groups onto the graft copolymer, (b) the adsorption capacity increased with increasing the Pb 2+ concentration and extent of grafting within the range studied; pH from 1 to 6; and the adsorption time up to 60 min then leveled off afterward, (c) maximum adsorption capacity of poly(MAA)‐rice straw graft copolymer was found to be 118 mg/g at pH 6, 200 mg/L lead ions concentration, adsorption time, 60 min, and 0.1 g adsorbent, (d) the kinetic and isothermal studies revealed that the privilege of Elovich model and pseudo‐second‐order rate equation as well the Langmuir model with more R 2 value. The calculated thermodynamic parameters indicated that the adsorption process was achievable, spontaneous, and exothermic at 298–318 K. Finally, the preliminary adsorption mechanism representing the interaction between the adsorbent and adsorbate has been projected.