Oxidative Desulfurization of Benzothiophene by Persulfate and Cu-Loaded g-C3 N4 via the Polymerization Pathway

Turning aromatic sulfur impurities to value-added polymers is a promising technology for fuel desulfurization. In this study, Cu(I,II)@g-C3N4 plates prepared via facile calcination show high reactivity in catalytic oxidation of benzothiophene (BT) by persulfate in a mixture of MeCN/H2O (v/v = 50/50). Quenching experiments rule out the primary contributions of SO4•–, •OH, and O2•– to BT oxidation and confirm the presence of carbon-centered radicals during the desulfurization process. XPS and Raman analyses reveal that Cu(I) and graphitic-N are reactive sites for persulfate activation, accompanied with moderate activation of the peroxo group in persulfate via the nonradical pathway. Solid characterizations indicate the formation of polybenzothiophene S,S-dioxide during the oxidation process, which further reveals that the moderately activated persulfate abstracts H from BT to form a BT radical cation, followed by subsequent polymerization of BT radical cations to a BT tetramer, and then the BT tetramer is further oxidized to a BT S,S-dioxide tetramer. The high electrochemical stability and pseudo-capacitive properties of the obtained polymers also imply their high potential to be used for capacitors. This work provides new insight on turning aromatic sulfur impurities in fuels to “treasures”.