Efficient Remediation of an Aquatic Environment Contaminated by Cr(VI) and 2,4-Dinitrophenol by XG‑g‑Polyaniline@ZnO Nanocomposite Rais Ahmad* and Imran Hasan Environmental Research Laboratory, Department of Applied Chemistry, Aligarh Muslim University, Aligarh, 202002, India * S Supporting Information ABSTRACT: 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 di fferent 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 ΔH° (+13.06 kJ mol -1 ) for Cr(VI) and (+10.28 kJ mol -1 ) for 2,4-DNP and negative value of ΔG° (-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. 1. INTRODUCTION Pollution caused by toxic heavy metals and organic compounds has received widespread attention owing to the high toxicity and carcinogenic effects to both the ecological environment and living organisms. 1-10 Cr(VI) has been categorized as one of the toxic heavy metal ions present in effluents produced by various industries such as chemical, mining, aerospace, steel fabrication, and electroplating, etc. 11-20 Dinitrophenolic, a group of persistent organic compounds, has received widespread attention due to its detrimental effects on the environmental and human health. 21,22 2,4-Dinitrophenol (2,4-DNP) has been broadly observed in industrial effluents owing to its extensive use as a crude substance for specialty chemicals or as a median in pharmaceutical dye and textile industries 23-30 which can hinder the biological the cell growth even at low concentration (1 mg L -1 ). The high toxicity and carcinogenicity of 2,4-DNP and Cr(VI) compounds make essential their effective removal from the wastewater streams. Now, it has become of a matter of great concern to remove these pollutants from groundwater as well as industrial wastewater due to the adverse effect on human health. Important methods for scavenging Cr(VI) and 2,4-DNP from contami- nated water include electrocoagulation, adsorption, ultrafiltra- tion, precipitation, ion exchange, and electroflotation. 31-38 Among these methods, the adsorption process has been widely recognized as most efficient for the removal of Cr(VI) and 2,4- DNP from contaminated groundwater 39-43 due to ecofriendly, economic, and simpler operation. 44-46 Among the various polysaccharides, XG was found to have additional high viscosity even at low concentrations, high thermal stability, and higher shelf life. 47 XG (Xanthan gum) is mainly composed of glucose units with added side chains of α-D- mannose. The presence of pH tunable groups such as -COOH and -OH on XG can be utilized to bind various organic and inorganic pollutants through electrostatic interaction. 48 Recently, a conducting polymer with metal oxide nanocomposite has emerged as an attractive alternative for the treatment of wastewater. 49-51 These compounds mainly provide a larger surface area for the adsorption, and interfacial adhesion between the surface of the nanocomposite and metal ions and are also easily tractable and economic. 52,53 Among various conducting polymers polyaniline (PANI) due to presence of abundant amine Received: November 18, 2016 Accepted: March 31, 2017 Article pubs.acs.org/jced © XXXX American Chemical Society A DOI: 10.1021/acs.jced.6b00963 J. Chem. Eng. Data XXXX, XXX, XXX-XXX