Zr⁴⁺ cross-linked chitosan-thiourea composite for efficient detoxification of Cr(VI) ions in aqueous solution

The effective strategy to solve the problems of low mechanical strength, low adsorption efficiency and poor stability of chitosan is to modify it. In this work, Zr⁴⁺ cross-linked chitosan-thiourea (CS-thiourea-Zr) composite was synthesized for the first time and used to remove Cr(VI). CS, ZrO, CN bonds in FTIR spectrum and Zr, S elements in XPS spectrum, SEM-mapping and EDS results verify the successful preparation of CS-thiourea-Zr. The main mechanism of Cr(VI) removal by CS-thiourea-Zr includes electrostatic action, ion exchange, reduction and complexation. The adsorption of Cr(VI) is enhanced by electrostatic adsorption and ion exchange, 80.6 % of the adsorbed Cr(VI) is reduced to Cr(III) by -OH group, and the adsorption of Cr(III) is enhanced by COO- group and CS bond. The maximum adsorption capacity of CS-thiourea-Zr is 246.72 mg g^-1 at 298 K and pH = 2.0. CS-thiourea-Zr has excellent acid-base resistance (suitable pH 2-12) and reusability.