Efficient Removal of Heavy Metals from Polluted Water with High Selectivity for Mercury(II) by 2‑Imino-4-thiobiuret−Partially Reduced Graphene Oxide (IT-PRGO) Fathi S. Awad, †,‡ Khaled M. AbouZeid, † Weam M. Abou El-Maaty, ‡ Ahmad M. El-Wakil, ‡ and M. Samy El-Shall* ,† † Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284, United States ‡ Chemistry Department, Faculty of Science, Mansoura University, Mansoura 35516, Egypt * S Supporting Information ABSTRACT: A novel chelating adsorbent, based on the chemical modification of graphene oxide by functionalization amidinothiourea to form 2-imino-4-thiobiuret− partially reduced graphene oxide (IT-PRGO), is used for the effective extraction of the toxic metal ions Hg(II), Cu(II), Pb(II), Cr(VI), and As(V) from wastewater. FTIR and Raman spectroscopy, XRD, and XPS confirm the successful incorporation of the amidinothiourea groups within the partially reduced GO nanosheets through nucleophilic substitution reactions with the acyl chloride groups in the chemically modified GO. The IT-PRGO adsorbent shows exceptional selectivity for the extraction of Hg(II) with a capacity of 624 mg/g, placing it among the top of carbon-based materials known for the high capacity of Hg(II) removal from aqueous solutions. The maximum sorption capacities for As(V), Cu(II), Cr(VI), and Pb(II) are 19.0, 37.0, 63.0, and 101.5 mg/g, respectively. The IT-PRGO displays a 100% removal of Hg(II) at concentrations up to 100 ppm with 90%, 95%, and 100% removal within 15, 30, and 90 min, respectively, at 50 ppm concentration. In a mixture of six heavy metal ions containing 10 ppm of each ion, the IT-PRGO shows a removal of 3% Zn(II), 4% Ni(II), 9% Cd(II), 21% Cu(II), 63% Pb(II), and 100% Hg(II). A monolayer adsorption behavior is suggested based on the excellent agreement of the experimental sorption isotherms with the Langmuir model. The sorption kinetics can be fitted well to a pseudo-second-order kinetic model which suggests a chemisorption mechanism via the amidinothiourea groups grafted on the reduced graphene oxide nanosheets. Desorption studies demonstrate that the IT-PRGO is easily regenerated with the desorption of the metal ions Hg(II), Cu(II), Pb(II), Cr(VI), and As(V) reaching 96%, 100%, 100%, 96%, and 100%, respectively, from their maximum sorption capacities using different eluents. The IT-PRGO is proposed as a top performing remediation adsorbent for the extraction of heavy metals from waste and polluted water. KEYWORDS: partially reduced graphene oxide, heavy metal ions, amidinothiourea, wastewater, adsorption, removal of Hg(II), removal of Pb(II), removal of Cr(VI) 1. INTRODUCTION There are growing public health and environmental concerns regarding the condition of clean water all around the world. 1,2 Water contamination by many pollutants, especially heavy metals, pose many public health and environmental concerns as reported in the list of hazardous substances compiled by the US EPA. 3 Metal ions such as Hg(II), Cu(II), Pb(II), As(V), and Cr(VI) have high toxicity and nonbiodegradable properties. 4,5 The accumulation of these heavy metals in the human body can lead to several severe and chronic disorders such as impairment of pulmonary function, renal damage, emphysema, hemoptysis, hypertension, chest pain, skeletal malformation in fetuses, tremors, and impaired cognitive skills. 6,7 Thus, there is a critical need to extract these toxic metal ions from polluted and wastewater. Various processes and techniques have been developed for the extraction of heavy metals from polluted water such as chemical precipitation, coagulation, flotation, reverse osmosis, electrochemical methods, membrane filtration, ion exchange, irradiation, and adsorption. 8−10 Adsorption by chelating resins is proven to be the most effective method for the extraction of metal ions from polluted and wastewater. Several types of materials such as zeolites, 11 clay, 12 mesoporous carbon, 13 polymers, 14 metal−organic frameworks (MOFs), 15,16 and covalent organic frameworks (COFs) 17,18 have been utilized for the possible removal of toxic ions. However, most of these materials are characterized by either low efficiency or complicated postsynthesis modifications with long processing time and prohibitive cost making their practical use for wastewater treatment less likely. Therefore, it is important to Received: July 11, 2017 Accepted: September 7, 2017 Published: September 7, 2017 Research Article www.acsami.org © XXXX American Chemical Society A DOI: 10.1021/acsami.7b10021 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX