Graft copolymerization of acrylonitrile onto recycled newspaper-cellulose based adsorbent for heavy metals removal

Abstract

Finding a good selection of solid sorbent becomes one of the greatest problems in the adsorption technique. In this study, adsorptive recycled newspaper (RNP)-based adsorbent was prepared with acrylonitrile initiated by ceric ammonium nitrate by graft copolymerization. The grafted recycled newspaper was used to remove heavy metals, such as chromium, Cr(VI); nickel, Ni(II); and copper, Cu(II), from aqueous solutions. The effects of grafting process of acrylonitrile onto the RNP, such as acrylonitrile concentration, ceric ammonium nitrate concentration, and reaction time, were investigated. The physicochemical properties of the grafted RNP was characterized by using Fourier transform infrared (FTIR), scanning electron microscope coupled with energy dispersive X-ray spectroscope (SEM-EDX), thermal gravimetric analysis (TGA), differential thermogravimetry (DTG), and X-ray diffraction (XRD) analysis. The adsorption capacity of the heavy metals was evaluated as a function of pH, initial concentrations of Cr(VI), Ni(II) and Cu(II), and contact time. Under pH 2 conditions, adsorption of Cr(VI) was optimal at 60 ppm for 360 minutes, with 15.1 mg/g of adsorption capacity. Meanwhile, for the adsorption of Cu(II), the optimal conditions were observed at pH 7 for 80 ppm over a period of 180 minutes, achieving 25.4 mg/g of adsorption capacity. The highest adsorption capacity for Ni(II) adsorption was 317.5 mg/g, which was achieved at pH 5 for a period of 60 minutes at 100 ppm of the initial Ni(II) concentration. Then, the equilibrium isotherms were conducted using Langmuir and Freundlich models. The findings showed that both Cr(VI) and Cu(II) were best fitted with the Langmuir model, which reflected the monolayer adsorption mechanism. Meanwhile, for the adsorption of Ni(II), the equilibrium coefficient was well suited with the Freundlich model, indicating that the adsorption had occurred based on the multilayer adsorption mechanism. The kinetic studies have been conducted by measuring the Pseudo-firstorder and Pseudo-second-order for three types of heavy metals. The result showed that the adsorption kinetics of Cu(II) and Ni(II) were best fitted with the Pseudo-firstorder, indicating the physisorption reaction. Meanwhile, the adsorption of Cr(VI) fitted with the Pseudo-second-order related to the chemisorption. This study concluded that the graft copolymerization of acrylonitrile on RNP improved efficiency by 52%, 57% and 56% for Cu(II), Ni(II) and Cr(VI) respectively relative to the pristine RNP.