(193z) CBn-Loaded PVC Nanofiber Membrane for Metal Cation Recovery

Erwin C. Escobar^a,c, Grace M. Nisola^a, Lawrence A. Limjuco^a, Rosemarie Ann I. Cuevas^a, Khino J. Parohinog^a, Rey Eliseo C. Torrejos^a, Francis Kirby B. Burnea^b, Jin Yong Lee^b, Seong- Poong Lee^a, Wook-Jin Chung^a,*

^a Department of Energy Science and Technology (DEST), Myongji University, Myongji-ro 116, Cheoin-gu, Yongin-si, Gyeonggi-do, South Korea 17058

^b Department of Chemistry, Sungkyunkwan University, (16419) 2066, Seobu-ro, Gyeonggi-do, South Korea

^c Department of Engineering Science, College of Engineering and Agro-Industrial Technology, University of the Philippines Los Baños, College Laguna, Philippines 4031

Abstract:

The high electron density of the carbonyl rims of the cucurbituril (CBn) family makes them an excellent host for metal cations. This feature of CBns had been exploited in various applications such as organometallic reactions, in situ click reactions, and the formation of molecular capsules. However, CBns had rarely been applied to metal ion recovery. Moreover, CBns that have been studied for this application were used in free form, which raises practical concerns particularly in terms of adsorbent recovery and reuse.

Most immobilization strategies for CBn operate via non-covalent attachments such as ionic grafting onto iron oxide nanoparticles and deposition onto metal surfaces. Although effective to some extent, these immobilization strategies inevitably suffer from reversibility issues and therefore cannot be relied on to hold CBn lastingly. The challenge of CBn immobilization is further compounded by their recalcitrance to chemical modification or introduction of functional groups. So far, strategies that prevailed in this aspect employ harsh reaction conditions and tedious preparation procedures.

In this study, effective tethering of CBns on electrospun polyvinyl chloride (PVC) nanofiber (NF) via nitrene chemistry is proposed. The technique is interestingly simple but effective for the preparation of PVC NF membrane with covalently immobilized CBn. The strategy takes advantage of the spontaneous generation of nitrenes from azido groups as a consequence of UV irradiation. Although immobilized CBn would assume different orientations due to the tendency of nitrene to insert liberally and non-selectively into C-H bonds, their metal cation receptor capability nevertheless remains remarkably potent--- and only slightly weakened--- since the carbonyl rims are essentially unaltered by the covalent bond formation. The tendency for a 2:1 metal to CBn complexation ratio is also retained. As such, the CBn-loaded PVC NF was found capable of selectively capturing target metal ions in water. The CBn-loaded PVC NF may be used in radioactive metal recovery or the treatment of heavy metal-laden water wastes.

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)).