Insight into the high-efficient functionalization of carbon nanotubes by advanced oxidation using peroxomonosulfate

Abstract

We report a high-efficient approach for functionalizing carbon nanotubes (CNTs) by utilizing peroxomonosulfate (PMS) coupling with Co(II) ions. Compared with UV/Fenton approach (UF-CNT), the PMS/Co(II) procedure enables superior water dispersibility of the functionalized CNTs (PM-CNT). Both morphological and Raman characterizations show that numerous defects are created upon functionalization, leading to intensive tube wall corrosion and truncation. XPS spectra indicate that both UF-CNT and PM-CNT contain large amounts of oxygen-containing groups. The O content in UF-CNT is dominated by hydroxyl and epoxy species. In contrast, carbonyls are more preferentially planted in PM-CNT. First-principles simulations reveal that the PMS/Co(II) functionalization includes two sequential Steps, during which the adsorbed OH species undergo self-dissociation to form epoxies, followed by the breaking of neighboring C-C bonds as well as the formation of carbonyls. We identified that the HO· radical (exist in both two activation processes) could only functionalize the CNTs to the hydroxyl or epoxy stage, while SO4–· radical (only appears in PMS/Co(II) treatment) will facilitate the conversion of epoxy to carbonyl, in excellent agreement with experimental observations. Our results not only shed light on the insights of the PMS/Co(II) functionalization but provide a transferrable strategy for functionalizing other carbon substrates.