(200f) Ionophore-Decorated Magnetic Graphene Oxide As a Composite Adsorbent Material for Heavy Metal Ion Sequestration

Heavy Metal (HM) ion contamination of water resources from human activities represents a major global concern. These ions must be reduced to an acceptably low level according to increasingly stringent environmental regulations. Due to the hazard of the HM contamination of water, there has been a growing interest in the development of materials that are capable of removing low concentrations of HM ions from contaminated waters. Adsorbent materials with a strong affinity and high adsorption capacity for the targeted metal ions need to be developed for HM removal from aqueous sources. In addition, multi-functional adsorbent materials which can aid in its efficient recovery after use, is highly desirable.

A multi-functional adsorbent was successfully synthesized and used as an HM adsorbent. The composite material was decorated with crown ethers (CE) for HM ion-selective removal, magnetite (Fe₃O₄) for material recovery and recyclability, and graphene oxide (GO) as a two-dimensional, high-aspect ratio support material for the CE and magnetite. The GO was prepared by oxidizing graphite powder through a modified Hummers’ method. The magnetite nanoparticles were immobilized on the surface of the GO via the solvothermal process (rGO-Fe₃O₄). Alkyne moieties were grafted on the rGO-Fe₃O₄ surface via diazonium chemistry using 4-ethynylaniline. The alkyne terminals in 4-ethynylaniline served as “clickable” CE-specific attachment sites. On the other hand, the CE (i.e. 1-Aza-18-Crwon-6) was modified in order to introduce an azide-functional group. The azide-CE was then “clicked” on the Alkyne-rGO-Fe₃O₄ at 60 °C via the 1,3 cycloaddition click chemistry reaction.

The synthesized composite adsorbent material (CE-rGO-Fe₃O₄) was characterized using Boehm Titration, Transmission Electron Microscopy (TEM), X-ray Diffraction Spectrometry (XRD), Thermogravimetric Analysis (TGA), Fourier-Transform Infrared Spectroscopy (FT-IR), Raman Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS). Boehm Titration was used to quantity the amount of oxygenous groups on GO. The morphology of the adsorbent was examined under TEM, which revealed the presence of Fe₃O₄ NPs on the GO surface. The XRD and FTIR were used to confirm the presence of different functional groups on the GO support, which were consistent with the TGA results. Raman Spectroscopy also reflected the degree of functionalization of the GO-based materials by quantifying the changes in the D- and G-bands and their corresponding I_D/I_G ratios. XPS was utilized to monitor the changes in the chemical states of the elements present in the adsorbent material upon subsequent modification and functionalization. XPS results revealed the presence of the Fe₃O₄ in the adsorbent (CE-rGO-Fe₃O₄) as indicated by the Fe2p signals. On the other hand, the successful attachment of the CEs via click reaction was confirmed with the presence of the peak attributed to the triazole functional group found in the N1s spectra. The adsorbent material was systematically tested in order to determine the heavy metal adsorption capacity and selectivity, and finally the material recyclability performance.

This research was supported by NRF funded by the Ministry of Science, ICT and future Planning (2017R1A2B2002109 and 2015R1A2A1A15055407) and the Ministry of Education (2009-0093816).