(287d) Ionophore-Decorated Phosphazene-Functionalized Magnetic Graphene Oxide As a Composite Adsorbent Material for Selective Lithium Ion Recovery
Herein, a multi-functional adsorbent was successfully synthesized and used as a Li+ selective adsorbent material. The composite adsorbent material was decorated with crown ethers (CE) as Li+-selective ionophores and magnetite (Fe3O4) to aid the material separation and recyclability, on 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 Hummersâ method. Solvothermal process was utilized in order to immobilize the magnetite nanoparticles on the surface of the GO (rGO-Fe3O4). Hydroxyl moieties were grafted on the surface of rGO-Fe3O4 via diazonium chemistry using 4-aminobenzyl alcohol (OH-rGO-Fe3O4). The hydroxyl functional group in 4-aminobenzyl alcohol was utilized as the attachment sites for the Hexachlorocyclotriphosphazene (HCTP) in which the remaining 5 P-Cl bonds were utilized for further functionalization using glycidol in order to introduce the epoxide functional groups. Epoxide ring opening reaction was subsequently performedÂ to introduce the azide moieties on the support material (Azide-HCTP-rGO-Fe3O4). The azide terminals served as âclickableâ CE-specific attachment sites. On the other hand, Li+-selective CE (i.e. 2-hydroxymethyl-12-Crown-4 Ether) was modified in order to introduce an alkyne-functional group. The alkyne-CE was then âclickedâ on the Azide-HCTP-rGO-Fe3O4 at 60 Â°C 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). Boehm Titration was used to quantity the amount of oxygen functional groups present in the synthesized materials. TEM was used to examine the morphology of the adsorbent, which revealed the presence of Fe3O4 NPs on the surface of the GO nanosheets. The XRD spectrum and FTIR conservatively confirmed the presence of different functional groups on the GO support, which was also consistent with the TGA results. Raman Spectroscopy also reflected the degree of functionalization of the GO-based materials as indicated by the changes in the D- and G-bands and their corresponding ID/IG ratios. The changes in the chemical states of the elements present in the adsorbent upon subsequent modification and functionalization was also confirmed via XPS. XPS results revealed the presence of the Fe3O4 in the adsorbent (12CE4-HCTP-rGO-Fe3O4) as indicated by the Fe2p signals, while the attachment of the HCTP was confirmed by the presence of N1s and P2p 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 Lithium adsorption capacity and selectivity, and finally the material recyclability performance. Thus, the integration of both magnetite and CE into the GO support material resulted in the production of a Li+-selective, magnet-responsive composite adsorbent material which is suitable for long-term Li+ adsorption application.
This research was supported by NRF funded by the Ministry of Science, ICT and future Planning (2017R1A2B2002109) and the Ministry of Education (2009-0093816).