Polypyrrole modified zirconium (IV) phosphate nanocomposite: An effective adsorbent for Cr(VI) removal by adsorption-reduction mechanism

Abstract

A novel polypyrrole modified α-zirconium phosphate (PPY–ZrPO4) nanocomposite was synthesized by in situ oxidative polymerization method followed by the microwave irradiation process and then used for removal of hexavalent chromium. The physico-chemical properties of polypyrrole (PPY), α-zirconium phosphate (ZrPO4), and PPY-ZrPO4 were characterized by FTIR, XRD, Raman, Zeta potential, N2 adsorption-desorption isotherm, FESEM, TEM, TGA-DTA, and XPS techniques. The XRD data confirmed that our nanocomposite is crystalline in nature and the FTIR, Raman, and TGA data confirmed that organic PPY polymer interacts with ZrPO4 to form PPY-ZrPO4 nanocomposite. FESEM and TEM images of nanocomposite revealed that spherical PPY polymer agglomerate on the surface of ZrPO4 nanoparticles. The various adsorption parameters were optimized by batch adsorption experiment. The maximum removal of Cr(VI) (∼98.8%) occurred in 80 min of equilibrium time. The Cr(VI) adsorption followed the pseudo-second-order kinetic model and Langmuir isotherm model with a R2 value of 0.99 and a maximum adsorption capacity of 62.5 mg g−1. The thermodynamic data (ΔS = 0.102 kJ mol−1 K−1, ΔH = 29.35 kJ mol−1) revealed the spontaneity, endothermic nature, and feasibility of the adsorption process. XPS analysis indicated the simultaneous adsorption of Cr(VI) and in situ chemical reduction to less toxic Cr(III). The –N = and –NH– groups present on the surface of the material were responsible for in situ chemical reduction. Reusability studies showed a greater removal efficiency of ∼80% even after five adsorption-desorption cycles. Hence, the PPY-ZrPO4 nanocomposite could be used as a promising adsorbent for the removal of Cr(VI) from water.