Synergetic enhancement of Cr(VI) removal from aqueous solutions using polyaniline@Ni(OH)2 nanocomposites adsorbent

Abstract

Novel polyaniline@Ni(OH)2 nanocomposites, designated as PANI@Ni(OH)2 NCs, were synthesised by depositing Ni(OH)2 nonoparticles onto 2-napthalene sulfonic acid doped PANI nanotubes surface. Characterization tools confirmed the presence Ni(OH)2 nanoaprticles onto the reactive PANI nanotubes surface. Greater surface area (26.85 m2/g), and multiple sorption sites of PANI@Ni(OH)2 NCs facilitated higher performance towards removing Cr(VI) from aqueous solution when compared with its PANI nanotubes counterpart. Acidic pH (optimum pH-4.0) and nanocomposite dosage at and above 0.5 g/L yielded the highest Cr(VI) recovery from aqueous solutions. Kinetic experiments with PANI@Ni(OH)2 demonstrated fast Cr(VI) removal and the kinetic mechanism followed with pseudo-second-order kinetic model. Sorption isotherm data for Cr(VI) removal using PANI@Ni(OH)2 fitted well with both linear and non-linear Freundlich isotherm model, whereas a maximum of 625 mg/g Cr(VI) removal capacity was obtained at 25 °C using linear Langmuir isotherm model. Assessment of thermodynamic data with enthalpy change, ΔH0 = 17.895 KJ/mol and entropy change, ΔS0 = 0.135 KJ/mol/K suggested the endothermic and spontaneous nature of the Cr(VI) removal with PANI@Ni(OH)2. Cations and anions commonly present as co-existing ions in industrial wastewater showed negligible impact on abatement of Cr(VI) using PANI@Ni(OH)2. Surface complexation and reduction of noxious Cr(VI) species to less poisonous Cr(III) species onto PANI@Ni(OH)2 surface were identified as the major Cr(VI) removal mechanism associated with the present nanocomposite structures. Meanwhile, using this present simple synthetic route, a number of polymer/metal oxide and/or hydroxide nanocomposite structures can be fabricated for various applications.