(371g) Ionophore-Decorated Magnetic Graphene Oxide As a Composite Adsorbent for Precious Metal Recovery
Herein, a multifunctional adsorbent (CE-rGO-Fe3O4) was successfully synthesized and used as a selective lithium ion (Li+) adsorbent. The adsorbent was decorated with crown ethers (CE) as Li+-specific ionophores, magnetite (Fe3O4) for its easy separation and recyclability, and graphene oxide (GO) as a two-dimensional, high-aspect ratio support of the CE and Fe3O4.
The GO was prepared by oxidizing graphite powder through a modified Hummerâ??s method. The Fe3O4 nanoparticles were then immobilized on the surface of the GO through a solvothermal technique which also partially reduced the GO nanosheets (rGO-Fe3O4). Alkyne moieties were grafted on the rGO-Fe3O4 surface using 4-ethynylaniline The alkyne terminals in 4-ethynylaniline served as â??clickableâ? CE-specific attachment sites. Meanwhile, Li+-selective CE (i.e. 2-hydroxymethyl-12-Crown-4 Ether) was prepared via a two-step mesylation-azidation reaction to obtain 2-(azidomethyl)-12-Crown-4 Ether. The azidated CE was then â??clickedâ? on the alkyne- rGO-Fe3O4 at 60 Â°C via the 1,3 cycloaddition click chemistry reaction.
The synthesized composite adsorbent (12CE4-rGO-Fe3O4) was characterized using Transmission Electron Microscopy (TEM), Boehm Titration, X-ray Diffraction Spectrometry (XRD), Fourier-Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA), Raman Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS). TEM was used to observe 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 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-rGO-Fe3O4) as indicated by the Fe2p signals whereas 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 adsorption results show the Langmuir-type Li+ uptake of the 12CE4-rGO-Fe3O4, with the maximum Li+ uptake at 7.33 mg g-1. The results also show that the material has high selectivity towards Li+ as compared to the other cations. The integration of magnetite allowed the easy separation and recyclability of the adsorbent. Overall results demonstrate the suitability of the 12CE4-rGO-Fe3O4 for long-term Li+ adsorption application.
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and future Planning (2015R1A2A1A15055407) and by the Ministry of Education (No. 2009-0093816).