Efficient adsorption and reduction of Cr(VI) by Zr4+ cross-linked magnetic chitosan/polyaniline composite

In this work, Zr4+ cross-linked magnetic chitosan/polyaniline (Fe3O4 @CTS-Zr-PANI) composite was synthesized for the first time and used to remove Cr(VI) from aqueous solution. The presence of C--C bonds (benzenes and quinones), Zr-O and Zr-N in its FTIR spectrum confirmed the successful synthesis of it. The introduction of polyaniline enhances the stability of chitosan under acidic conditions and its ability to reduce Cr(VI). The addition of zirconium enables ion exchange and electrostatic adsorption to work together to remove Cr(VI). The maximum monolayer adsorption capacity is 491.43 mg g-1 at 298 K (pH=2.0). The adsorbent has excellent stability and regeneration ability, and the adsorption efficiency is still as high as 90.63% after six adsorption cycles. Real chromium-containing wastewater (Cr(VI) 241.21 mg L-1, pH= 3.5) was treated with a dosage of 0.08 g adsorbent, and its residual chromium concentration could not be detected. The removal of Cr(VI) by Fe3O4 @CTS-Zr-PANI mainly includes electrostatic adsorption, ion exchange, reduction and complexation. XPS showed that 86.9% of Cr(VI) was reduced to Cr(III) by-OH groups of CTS and C-N groups of PANI at pH= 2.0. Then, Cr (III) was removed by complexing with COO-groups of CTS and C-N groups of PANI.