Fabrication of Amino Functionalized Magnetic Expanded Graphite Nanohybrids for Application in Removal of Ag(I) from Aqueous Solution

Hindawi Journal of Nanomaterials Volume 2017, Article ID 6839474, 11 pages https://doi.org/10.1155/2017/6839474 Research Article Fabrication of Amino Functionalized Magnetic Expanded Graphite Nanohybrids for Application in Removal of Ag(I) from Aqueous Solution Ying-Xia Ma, Yong-Xin Ruan, Dan Xing, Xue-Yan Du, and Pei-Qing La State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Key Laboratory of Nonferrous Metal Alloys and Processing, Ministry of Education, School of Materials Science & Engineering, Lanzhou University of Technology, Lanzhou 730050, China Correspondence should be addressed to Ying-Xia Ma; and Xue-Yan Du; Received 19 September 2016; Revised 21 December 2016; Accepted 25 December 2016; Published 9 February 2017 Academic Editor: Xuping Sun Copyright © 2017 Ying-Xia Ma et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Ethylenediamine functionalized magnetic expanded graphite decorated with Fe3 O4 nanoparticles (MEG-NH2 ) was fabricated by one-pot solvothermal method. The as-prepared MEG-NH2 nanohybrids were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), and Zeta potential analyzer. The effects of Fe3 O4 content in MEG-NH2 nanohybrids, pH, initial concentration, contact time, and dosage on adsorption properties of the MEG-NH2 nanohybrids for Ag(I) from aqueous solution were investigated by batch experiments. The pseudo-first-order and the pseudosecond-order kinetic models were utilized to study adsorption kinetics. The experimental data was also analyzed with Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models. The results show that Ag(I) was reduced to silver in the process of the adsorption by MEG-NH2 nanohybrids; the experimental data was better fitted to pseudo-second-order model and Langmuir isotherm model which revealed that the adsorption process was a chemical adsorption by the formation of silver on the surface of MEG-NH2 nanohybrids. 1. Introduction In recent years, numerous water bodies such as rivers, lakes, and ponds have accommodated a great deal of waste water composed of industrial and domestic sewage. Among various contaminants, heavy metal ions occupy a large proportion. Drainage of high concentration of heavy metal ions is extremely deleterious to living organism and the environment, especially to the existence and development of human beings, which has aroused global concerns. Among heavy metals, sliver is not dietary requirement for organic survival. Englobement of high level of silver is toxic to human cells. Ag(I) is more fatal for fish than copper or mercury [1]. On the other hand, as a precious metal, silver possesses extensive commercial value in various fields for its unique ornament and decoration performance and highest electrical and thermal conductivity along with excellent machinability [2]. Given the above notable properties, the widely technical and industrial usage of silver in photography, brazing, electronic products, electroplation, and so forth heavily accelerates its requirements. However, with surging demand of silver, silver bearing mines that are available for exploitation have reached a steep reduction. Moreover, substantial employment of silver in various industries inevitably creates mass production of silver-containing effluent. To dispose the thorny issue, a large number of measures have been taken, including adsorption, cathodic reduction [3], ion-exchange [4], solvent extraction [5], and so on. During the past decade, adsorption method has attracted much attention in heavy metal removal and recycling [6] for its energy saving, high efficiency, and outstanding selectivity, especially its superiority in disposal of trace metal ions. Currently, various adsorbents have been utilized to treat waste water containing silver ions, such as chitosan [7], ion-imprinted polymers [8], zeolite, chemically 2 modified melamine resins [9], and bioadsorbent [10]. It is somewhat difficult for these traditional adsorbents to separate for resource recycling after adsorption. The magnetic adsorption materials solve the practical problem. Magnetic expanded graphite (MEG) holds lower price and easier preparation properties compared with graphene, carbon nanotubes, and other carbonaceous adsorbents, arousing researchers’ extensive interests [11, 12]. Generally, the synthesis process of MEG with a majority of macropores and favorable magnetic response is composed of oxide intercalation, high temperature expansion, and magnetic loading. The resulting macropores formed in the interlayers, providing passageway for ion diffusion. Acquisition of magnetic performance avoids centrifugation, decompressed filter, and slather usage of expensive percolators. With a weak magnet, it is very simple and effective to separate the material along with target contaminant. Thus, secondary pollution will never occur, and the recovery and recycling of silver are ready to be realized [13]. Nevertheless, it is not ideal for pure MEG to be applied to adsorb silver ions owing to lack of appropriate functional groups. These materials mostly need modification to improve their physicochemical properties. Accordingly, it is necessary to graft suitable functional groups onto surface of MEG to introduce active sites for silver ion adsorption. In this study, using ethylenediamine functionalized magnetic expanded graphite (MEG-NH2 ) nanohybrids with desirable performance composed of magnetism of Fe3 O4 , chemical adsorption of amino groups, and unique ion diffusion channels of EG were synthesized by one-pot solvothermal reaction. In contrast to chemical coprecipitation method [14], the approach prevented oxidation and aggregation of nano-Fe3 O4 . The effects of Fe3 O4 content in MEG-NH2 nanohybrids, pH, initial concentration, contact time, and dosage on the adsorption properties of the MEG-NH2 nanohybrids for Ag(I) were taken into consideration during adsorption experiments. Adsorption kinetics and isotherms were also studied to ascertain the adsorption process. 2. Experimental 2.1. Materials and Chemicals. Natural flake graphite (NFG), 50 BS mesh, with the purity of 99 wt% was supplied by ShanDong Qingdao Tianhe Graphite Company (China). Concentrated sulfuric acid (H2 SO4 ), concentrated nitric acid (HNO3 ), potassium permanganate (KMnO4 ), ferric chloride hexahydrate (FeCl3 ⋅6H2 O), sodium acetate anhydrous, ethanediol, ethylenediamine, ethanol, potassium hydroxide, potassium periodate, and potassium sulfate are all of analytical grades, used as received without any further purification. 2.2. Preparation of Expanded Graphite. Expanded graphite (EG) was (...truncated)