Abstract
The adsorption of lithium ions(Li+) and the separation of lithium isotopes have attracted interests due to their important role in energy storage and nuclear energy, respectively. However, it is still challenging to separate the Li+ and its isotopes with high efficiency and selectivity. A novel cellulose-based microsphere containing crown ethers groups (named as MCM-g-AB15C5) was successfully synthesized by pre-irradiation-induced emulsion grafting of glycidyl methacrylate (GMA) and followed by the chemical reaction between the epoxy group of grafted polymer and 4′-aminobenzo-15-crown-5 (AB15C5). By using MCM-g-AB15C5 as adsorbent, the effects of solvent, metal ions, and adsorption temperature on the adsorption uptake of Li+ and separation factor of 6Li/7Li were investigated in detail. Solvent with low polarity, high adsorption temperature in acetonitrile could improve the uptake of Li+ and separation factor of lithium isotopes. The MCM-g-AB15C5 exhibited the strongest adsorption affinity to Li+ with a separation factor of 1.022 ± 0.002 for 6Li/7Li in acetonitrile. The adsorption isotherms in acetonitrile is fitted well with the Langmuir model with an ultrahigh adsorption capacity up to 12.9 mg·g−1, indicating the unexpected complexation ratio of 1:2 between MCM-g-AB15C5 and Li+. The thermodynamics study confirmed the adsorption process is the endothermic, spontaneous, and chemisorption adsorption. As-prepared novel cellulose-based adsorbents are promising materials for the efficient and selective separation of Li+ and its isotopes.
Highlights
Lithium has been used widely as an important component in energy storage devices [1] due to its low atomic weight, high energy density, and high reactivity
After analyzing the chemical structure of resultant microcrystalline cellulose microspheres (MCM)-g-AB15C5, we proposed that besides that the ring of crown ether provides a complexing interaction with Li+, the pseudoheterocyclic structure of side groups in the AB15C5 perhaps formed during the adsorption in acetonitrile due to the self-assembly of crown ethers, which could complex with Li+ as well [36]
In order to determine the separation factor of lithium isotopes, the resultant MCM-g-AB15C5 was treated in nitric acid, and the digested solution is diluted with ultrapure water to reduce the concentration of Li+ to ppb level, and a high resolution ICP-MS (Element XR, Thermo Scientific, Waltham, MA, USA) was used to measure the lithium isotope ratio in the samples, at least one hundred data were collected during the measurement to give an average value of isotope ratio, each sample was repeated three times to give an average value and the standard deviation of separation factor is 0.2%
Summary
Lithium has been used widely as an important component in energy storage devices [1] due to its low atomic weight, high energy density, and high reactivity. The oxidized carbon nanotubes were modified with hydroxy-dibenzo-14-crown-4 ether and the resultant adsorbents had the adsorption capacity of 2.11 mg·g−1 [10]. (AB15C5) was produced by chemical modification, which had an adsorption capacity of 5.4 mg·g−1 and a separation factor of 1.049 ± 0.002 [11], and they found that AB15C5 ligand has better complexing ability with Li+ and good selectivity for the lithium isotopes than those of B15C5. They prepared a novel AB15C5 grafted mesoporous silica via atomic transfer radical polymerization.
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