Photocatalytic activation of sulfite by nitrogen vacancy modified graphitic carbon nitride for efficient degradation of carbamazepine

Graphitic carbon nitride with plentiful nitrogen vacancies (NV-g-C3N4) was prepared through a treatment of melamine under a N2 flow, and used for constructing a system of sulfite activation under visible light toward the degradation of carbamazepine. In the presence of Na2SO3 (20 mmol L−1), the use of NV-g-C3N4 (1 g L−1) increased the apparent rate constant for the photodegradation of carbamazepine (42 μmol L−1) to 0.0187 min−1, with an increasing magnitude of 270% in comparison with that obtained by using the conventional g-C3N4 (Bulk-g-C3N4). The enhanced photodegradation of carbamazepine by NV-g-C3N4 was found to be attributed to the efficient trap of photo-generated electrons by nitrogen vacancies, which inhibited the recombination of photo-generated carriers. Therefore, more holes aggregating in the valence band were available for the activation of sulfite anions to produce sulfite radicals. Sulfite radicals were identified as the major reactive species in the investigated photocatalytic system for the degradation of carbamazepine. The degradation pathway of carbamazepine induced by sulfite radicals in the NV-g-C3N4/Na2SO3 system was clarified on the basis of the identification of intermediates by GC- and LCMS. The photocatalytic activation of sulfite by metal free NV-g-C3N4 may be a useful technique for purifying waste-water containing organic pollutants.