Wheat straw-based amidoximated bioadsorbent for heavy metal removal: Synthesis, Experimental design, Isotherms, and Kinetics

Abstract In this research, 3-(trimethoxysilyl)propyl methacrylate (MPS) silane agent was applied to modify the extracted wheat straw (WS) cellulose as a natural biopolymer. Polyacrylonitrile (PAN) was attached to the MPS-modified WS (MPS-WS) via in-situ polymerization to form PAN-WS biocomposite. AO-WS amidoxime biocomposite adsorbent was synthesized through amidoxime reaction and tested for its ability to remove Pb(II) ions. The adsorbent was characterized using field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The FTIR results confirmed that the alkaline treatment removed the hemicellulose and lignin groups and that the silane agent successfully bonded to the WS cellulose. The thermal stability of WS was enhanced by the MPS-WS composite due to the attachment of acrylonitrile polymer chains. The Taguchi method was employed to investigate the effects of agitation speed, Pb(II) initial concentration, and adsorbent dosage on the adsorption capacity. The ANOVA results indicated that increasing the adsorbent dosage and decreasing the pollutant's initial concentration significantly improved the adsorption efficiency. The optimal conditions yielded maximum adsorption capacity of 22.26 mg/g for the AO-WS bioadsorbent. The kinetic and isotherm studies revealed that the pseudo-second-order kinetic model and the Dubinin-Radushkevich isotherm fit the experimental data best.