Zr4+-modified chitosan coated nZVI enhance the removal of Cr(VI) by adsorption-reduction interaction

Abstract

In order to solve the problems of poor mechanical properties and stability of chitosan and easy agglomeration and oxidation of nano zero-valent iron, Zr4+ crosslinked chitosan-coated nano zero-valent iron composites (CS-Zr@nZVI) were prepared for Cr(VI) removal from wastewater. The Zr-O, Zr-N and chitosan characteristic peaks in FTIR spectrum and the nZVI characteristic peaks in XRD pattern confirmed its successful synthesis. SEM and TEM showed that nZVI was dispersed on the surface of CS-Zr@nZVI, which solved the problem of easy agglomeration of nZVI. CS-Zr@nZVI has a wide operating pH range (pH= 2.0–10.0), high pHpzc, good stability and regeneration ability. The removal of Cr(VI) by CS-Zr@nZVI accords with pseudo-second-order kinetic model and Langmuir isotherm model, and it is a spontaneous, disordered and endothermic process. The maximum adsorption capacity was 344.82 mg g−1 at 318 K and pH = 2.0. At the dosage of 1.0 g L−1, CS-Zr@nZVI can treat 134.56 mg L−1 chromium-containing wastewater (pH = 3.5) to meet the discharge standard, which proves that CS-Zr@nZVI has the application prospect of removing Cr(VI). The main mechanisms of Cr(VI) removal by CS-Zr@nZVI are electrostatic interaction, ion exchange, reduction, complexation and co-precipitation. XPS analysis showed that 84.87 % of Cr(VI) was reduced to Cr(III). The above results provide a reference for the design of efficient Cr(VI) removal materials.