Modified Macadamia nutshell nanocomposite for selective removal of hexavalent chromium from wastewater

The present study highlights the synthesis of a polypyrrole (Ppy) composite based on Macadamia nutshells (AMN) and binary metal oxides (Mn-Cu oxide) for the selective removal of Cr(VI) from aqueous solution. Ppy/AMN-Mn-Cu oxide nanocomposite was synthesized via in-situ oxidative polymerization of pyrrole monomer using FeCl₃ as an oxidant in the present of AMN-Mn-Cu oxide composite. The physicochemical properties of Ppy/AMN-Mn-Cu oxide nanocomposite were studied using XRD, FTIR, EDS, SEM, TGA, XPS, TEM, BET and zeta sizer. It was found that the adsorption of Cr(VI) was highly dependent on the pH of the solution and a maximum adsorption capacity of 199.2 mg/g was achieved under optimized conditions (adsorbent dose = 0.1 g/L, solution pH = 2, contact time = 30 min and temperature 298 K). The adsorption was found to follow the pseudo-second-order model and Langmuir isotherm was the best fit for experimental data. Thermodynamic parameters deduced the adsorption process to be endothermic and spontaneous. The adsorbent was selective for Cr(VI) adsorption in the presence of co-existing ions. AMN-Mn-Cu oxide-Ppy nanocomposite was successfully reused for six adsorption-desorption cycles without losing its original adsorption capacity.