Removal of carcinogenic hexavalent chromium from aqueous solutions using newly synthesized and characterized polypyrrole– titanium(IV)phosphate nanocomposite Umair Baig a,b , Rifaqat Ali Khan Rao c , Asif Ali Khan d,⇑ , Mohd Marsin Sanagi e , Mohammed Ashraf Gondal b,a,⇑ a Center of Excellence for Scientific Research Collaboration with MIT, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia b Laser Research Group, Physics Department & Center of Excellence in Nanotechnology, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia c Environmental Research Laboratory, Department of Applied Chemistry, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh 202002, UP, India d Analytical and Polymer Research Laboratory, Department of Applied Chemistry, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh 202002, UP, India e Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia (UTM), 81310 Johor Bahru, Johor, Malaysia highlights  Synthetic nano-adsorbent were synthesized for the removal of Cr(VI).  Equilibrium isotherm data were analyzed using Langmuir and Freundlich isotherms.  The pseudo-second-order model described adequately the adsorption kinetics data.  The adsorption and desorption studies suggested 100% desorption of Cr(VI) ions. graphical abstract article info Article history: Received 12 April 2015 Received in revised form 4 June 2015 Accepted 7 June 2015 Available online 11 June 2015 Keywords: Polymer Nanocomposite Synthetic adsorbent Hexavalent chromium abstract This paper reports the synthesis of polypyrrole–titanium(IV)phosphate (PPy–TiP) nanocomposite as a synthetic adsorbent for the adsorptive removal of Cr(VI) ions from aqueous solutions. Facile in situ chem- ical oxidative polymerization of pyrrole in presence of titanium(IV)phosphate (TiP) formed PPy–TiP nanocomposite. The prepared PPy–TiP nanocomposite was characterized by FT-IR, FE-SEM, TEM, EDAX and BET analysis. A strong interaction between PPy and TiP particles was observed, and the nanocompos- ite showed remarkable adsorption of Cr(VI) ions from aqueous solutions. In order to optimize the condi- tions for maximum adsorption of Cr(VI) ions, batch process was used and the effects of contact time, initial concentration, pH, point of zero charge measurement and adsorbent doses were investigated. The equilibrium isotherm data were fitted using Langmuir and Freundlich isotherms. The adsorption pro- cess based on the thermodynamic parameters was spontaneous and endothermic. Dubinin– Radushkevich (D–R) isotherm was used to calculate the mean free energy, which showed that the adsorp- tion process involves chemical forces, hence chemical in nature. The kinetics data were evaluated using the pseudo-first-order and pseudo-second order kinetics model, and it was found that data was best fit- ted by the pseudo-second-order model for adsorption of Cr(VI) supporting that the adsorption mainly http://dx.doi.org/10.1016/j.cej.2015.06.031 1385-8947/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding authors at: Center of Excellence for Scientific Research Collaboration with MIT, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia. Tel.: +966 3 8602351/8603274; fax: +966 3 8604281 (M.A. Gondal). Tel.: +91 571 2720323 (A.A. Khan). E-mail addresses: asifkhan42003@yahoo.com (A.A. Khan), magondal@kfupm.edu.sa (M.A. Gondal). Chemical Engineering Journal 280 (2015) 494–504 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej