Efficient removal of hexavalent chromium from aqueous solutions by lanthanum crosslinked chitosan/polypyrrole composite

In this work, in order to improve the adsorption capacity of chitosan for Cr(VI), a chitosan-based composite co-modified with lanthanum and polypyrrole (CS-La-PPy) was prepared and its effectiveness in removing Cr(VI) from aqueous solution was investigated. CS-La-PPy was characterized by FT-IR, XRD, BET, SEM, EDS and XPS. The successful synthesis of CS-La-PPy was confirmed by the presence of C=C (pyrrole ring) and La-O in the FT-IR spectrum. The effects of different adsorbent materials, dosage, initial pH, coexisting ions, adsorption time and temperature on the removal of Cr(VI) were investigated by batch experiments. The removal efficiency of 50 mL Cr(VI) with concentration of 150 mg L −1 by CS-La-PPy is 95.28 % at pH=2.0, T = 298 K. The adsorption process is spontaneous, which is consistent with pseudo-second-order kinetic model and Freundlich adsorption isotherm model. The maximum adsorption capacity is 321.96 mg g −1 . XPS analysis showed that the removal mechanism of Cr(VI) by CS-La-PPy was mainly based on the electrostatic adsorption between Cr(VI) and lanthanum, -NH 2 + , and -NH 3 + , the ion exchange between Cr(VI) and Cl − , the reduction of Cr(VI) to Cr(III) by PPy 0 and -OH groups, and the complexation between Cr(III) ions and COO- groups. This work provides a reference for the design and preparation of efficient chitosan-based adsorption materials.