Polyethylenimine grafted H₂O₂-oxidized cellulose membrane as a novel biosorbent for Cr(VI) adsorption and detoxification from aqueous solution

A novel biosorbent PEI-HOCM was successfully prepared by grafting polyethyleneimine (PEI) onto H₂O₂-oxidized cellulose membrane (HOCM). The whole systhesis process occurred in aqueous solution and was environmentally friendly without any toxic cross-linkers involved. ATR-FTIR, XPS and titration analysis confirmed that the hydroxyl groups of cellulose were oxidized to carbonyl groups by H₂O₂ and PEI was successfully introduced to the HOCM. The PEI-HOCM had positively charged surface (+ 20.6 to + 86.6 mV) at the measured pH range 3–9 according to the zeta potential analysis. The adsorption of Cr(VI) on the PEI-HOCM obeyed the pseudo-second-order kinetic model and Langmuir isotherm model. Its maximum equilibrium adsorption capacity was 147.06 mg/g at 25 °C, which was much higher than that of cellulose membrane (CM, 30.61 mg/g). According to the obtained results from the intraparticle diffusion, Body kinetic and diffusion-chemisorption models, film diffusion was the rate-limiting step and chemical adsorption was the main mechanism of Cr(VI) adsorption. The Cr(VI) adsorbed on the PEI-HOCM was completely reduced to Cr(III), suggesting that PEI-HOCM was not only useful for Cr(VI) removal but also good for its detoxification. The competitive uptakes from coexisting components (Na⁺, Mg²⁺, Ca²⁺, phenol, Cl⁻ and NO₃⁻) were insignificant except H₂PO₄⁻ and SO₄²⁻ which reduced the Cr(VI) uptake with a efficiency loss of 22–41%. Ionic strength had little effect on the adsorption in the range of 0–1000 mg/L NaCl. After five adsorption/desorption cycles, the PEI-HOCM still retained good adsorption capacity. More importantly, it can be separated easily after adsorption, which will greatly benefit the wastewater treatment by simplifying the separation procedure and reducing costs.