Thiocarbohydrazide Cross-Linked Oxidized Chitosan and Poly(vinyl alcohol): A Green Framework as Efficient Cu(II), Pb(II), and Hg(II) Adsorbent Mudasir Ahmad, † Kaiser Manzoor, † Ranjana Ray Chaudhuri, ‡ and Saiqa Ikram* ,† † Department of Chemistry Faculty of Natural Sciences, Jamia Millia Islamia, New Delhi, 110025, India ‡ Department of Regional Water Studies, TERI University, New Delhi, 11007, India * S Supporting Information ABSTRACT: The macroporous thiocarbohydrazide cross- linked chitosan-poly(vinyl alcohol) framework (TCPF), prepared via the condensation reaction of thiocarbohydrazide and the oxidized products of chitosan (OCS) and poly(vinyl alcohol) (OPVA) is reported with selective and efficient adsorption of Cu(II), Pb(II), and Hg(II). The adsorption of Cu(II), Pb(II), and Hg(II) onto TCPF was studied through batch adsorption experiments, and the adsorption data were analyzed by using various models. The Langmuir model fits best with the experimental values which yields adsorption capacities of 47.16 mg g -1 , 47.39 mg g -1 , and 52.63 mg g -1 for Cu(II), Pb(II), and Hg(II), respectively. The calculated thermodynamic parameters ΔG o , ΔS o , and ΔH o suggest that the adsorption of Cu(II), Pb(II), and Hg(II) is thermodynami- cally favorable and thus a spontaneous process which follows pseudo-second-order kinetics. The plot of qt versus t 1/2 suggests that intraparticle diffusion is not only the rate- controlling step but also the positive value of the intercept in Pb(II) and Hg(II) plots. This indicates that several steps are operational in the adsorption mechanism. Furthermore, the excellent recycle performances also were achieved with desorption and regeneration efficiencies close to 97-99%, permitting the recovery of both metal ions and TCPF. Finally, the complete soil degradability which can be attained in approximately 90 days makes the whole process environmentally friendly and economically feasible. 1. INTRODUCTION Industrial processes have been the cause of various environ- mental problems. Among these is the generation of wastewater containing heavy metal contaminants which are highly toxic, persistent, and bioaccumulative. Therefore, this wastewater must be treated before its reuse or disposal on land or in water bodies. 1 Exposure to Cu(II), Pb(II), and Hg(II) causes cardiovascular problems, 2 abdominal pain 3 , and impairment in the central nervous system, respectively, as witnessed by the Minamata. 4,5 Various remedial methods have been used for removal of toxic metals such as chemical precipitation, ion exchange, membrane filtration, electrolytic methods, reverse osmosis, and adsorption. 6-11 In recent years bioadsorbents have gained much attention due to their natural availability, as well as being eco-friendly and cost-effective. Chitosan (CS) with glucosamine (poly-β-(1→4)-2-amino-2-deoxy-D-glucose) residues has been widely used as a bioadsorbent, 12-14 due to the presence of high content of hydroxyl and primary amine groups. 15,16 For over a decade ago researchers have been interested in the chemical modification of CS. CS modified with 2,5-dimercapto-1,3,4-thiodiazol, 17 1,2 ethylene disulfide, 18 thiosemicarbazide, 19 barbital immobilized chitosan, 11 and iodine/bromide and sulfuric acid modified chitosan based adsorbents are analyzed for the successful removal of heavy metal ions. 20 CS and its derivatives as adsorbents have showed limited dissolution, high swelling, and low mechanical proper- ties. Chemical cross-linking is used to overcome these problems. It causes a decrease in solubility in water and other common organic solutions. It also causes a decrease in swelling, controls the leaching and thereby improves mechanical stability. 21 In general, the common documented cross-linking reagents are glutaraldehyde and epichlorohydrin. 22 These cross- linking reagents have shown a high risk of carcinogenicity, toxicity, and immunogenicity to living systems for decades. 23,24 This work is intended to fill the knowledge gaps and, to the best of our knowledge, to investigate for the first time the Received: January 26, 2017 Accepted: May 24, 2017 Article pubs.acs.org/jced © XXXX American Chemical Society A DOI: 10.1021/acs.jced.7b00088 J. Chem. Eng. Data XXXX, XXX, XXX-XXX