(197b) Crown Ether-Decorated Phosphazene-Modified Magnetic Graphene Oxide As a Composite Adsorbent Material for Selective Lithium Ion Recovery from Seawater

Lithium is an important component for energy storage devices due to its high energy density property. Precipitation from brine pools is the common method for lithium harvesting, but the surging demand pushed for alternative recovery sources. Herein, a multi-functional adsorbent was successfully synthesized and used as a Li⁺ selective adsorbent material. The composite adsorbent was decorated with crown ethers (CE) as Li⁺-selective ionophores, magnetite (Fe₃O₄) to aid the material separation and recyclability, and graphene oxide (GO) as a two-dimensional, high-aspect ratio support material for the CE and magnetite. The GO support decorated with magnetite (rGO-Fe₃O₄) was synthesized through a modified Hummers’ method and solvothermal process. This was followed by grafting hydroxyl moieties (OH-rGO-Fe₃O₄), epoxidation, and azidation (Azide-HCTP-rGO-Fe₃O₄) wherein the azide terminals served as “clickable” CE-specific attachment sites. On the other hand, Li⁺-selective CE (i.e. 2-hydroxymethyl-12-Crown-4 Ether) was modified to introduce an alkyne-functional group. The alkyne-CE was then “clicked” on the Azide-HCTP-rGO-Fe₃O₄ via the 1,3-cycloaddition click chemistry reaction. The synthesized composite adsorbent material (12CE4-HCTP-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). XPS results revealed the presence of the Fe₃O₄ (12CE4-HCTP-rGO-Fe₃O₄) and the successful attachment of the CEs via click reaction. The adsorbent material was systematically tested to determine the Lithium adsorption capacity and adsorption kinetics. The selectivity of the composite adsorbent material was tested using seawater as the feed solution. Repeated material adsorption-desorption experiments were done to determine the material stability. Thus, the integration of both magnetite and CE on the GO support material resulted to the Li⁺-selective, magnet-responsive composite adsorbent material which is suitable for long-term Li⁺ adsorption application.

This research was supported by the National Research Foundation of Korea (NRF) under the Ministry of Science and ICT (No. 2017R1A2B2002109) and the Ministry of Education (No. 22A20130012051(BK21Plus)).