A study on adsorption of Cr (VI) by modified rice straw: Characteristics, performances and mechanism

In this study, aminated rice straw-grafted-poly (vinyl alcohol) (A-RS/PVA) was first used to remove Cr (VI) from aqueous solution. The A-RS/PVA was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), element analysis and zeta potential measurement. Batch adsorption experiments showed that the Elovich model and the Freundlich isotherm model fitted the adsorption data very well, and the Cr (VI) adsorption capacity of A-RS/PVA was up to 140.39 mg g−1 at initial pH 2.0 and 60 °C, much larger that of original rice straw (34.90 mg g−1). The thermodynamic parameters such as free energy change ΔG, enthalpy change ΔH and entropy change ΔS were evaluated and it has been found that the reaction was spontaneous and endothermic in nature. The effects of initial pH, coexisting anions and reusability were also investigated. Moreover, X-ray photoelectron spectroscopy (XPS) analysis revealed that about 57.4% of the chromium adsorbed on A-RS/PVA had turned into less toxic trivalent chromium. The possible adsorption mechanism was proposed based on the experimental data and analysis results finally.