Efficient Remediation of an Aquatic Environment Contaminated by Cr(VI) and 2,4-Dinitrophenol by XG-g-Polyaniline@ZnO Nanocomposite

Xanthan gum (XG) grafted polyaniline@zinc oxide nanocomposite (XGP@ZnO) was synthesized by an oxidative free-radical graft copolymerization reaction. The synthesized nanocomposite was approved by different analytical processes such as Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. The material was further employed for efficient remediation of aqueous solutions contaminated by Cr(VI) and 2,4-dinitrophenol (2,4-DNP) under batch operations. Solution pH values of 2.0 and 4.0 were found to be optimum pH for the adsorption of Cr(VI) and 2,4,-DNP, respectively. On the basis of higher R 2 value and lower χ 2 value, equilibrium data was found to be best fitted by the Langmuir model followed by the Redlich–Peterson model using nonlinear regression analysis. The maximum monolayer adsorption capacity was found to be 346.18 mg g –1 for Cr(VI) and 123.15 mg g –1 for 2,4-DNP. With a higher R 2 and low χ 2 value, pseudo-second-order model was established as the best model to describe the equilibrium data suggesting the chemical adsorption to be the rate-determining step. The value of Δ H ° (+13.06 kJ mol –1 ) for Cr(VI) and (+10.28 kJ mol –1 ) for 2,4-DNP and negative value of Δ G ° (−1.56 to −3.00 kJ mol –1 ) for Cr(VI) and (−1.75 to −2.94 kJ mol –1 ) for 2,4-DNP in the temperature range of 30–60 °C indicated the overall adsorption process to be endothermic and spontaneous in nature. The mechanism involved in the removal of Cr(VI) and 2,4-DNP was electrostatic adsorption coupled reduction which is also evident from EDX analysis.