Photocatalytic co-oxidation of As(III) and Orange G using urea-derived g-C3N4 and persulfate.

Urea was thermally degraded to be transformed into graphitic carbon nitride (g-C3N4), and the fabricated charring compound was aimed to use a photocatalyst for the simultaneous removal of Orange G (OG) and trivalent arsenic (As(III)) through photocatalytic oxidation. This study experimentally revealed that the degradation of OG substantially restricted the oxidation performance for As(III). To mitigate the unwanted inhibition arising from the decomposition of OG, persulfate (PS) was intentionally added, which synergistically expedited the reaction kinetics for governing the oxidation performance for both OG and As(III). Hydroxyl radicals formed in the presence of g-C3N4 become a driving force for PS to expedited sulfate radicals, which substantially increased the oxidation of OG and As(III). The intrinsic structure of g-C3N4 enhancing the photocatalytic stability guaranteed the re-usability of the photocatalyst. For instance, the fabricated photocatalyst in this study exhibited the same oxidation performance at least three times. Despite the intrinsic charring compound (i.e., high porosity), this study reported that the synthesized catalyst did not adsorb As species, therefore, the further treatment is required to remove the oxidized As. Thus, all experimental findings suggest that g-C3N4 derived from urea and PS could synergistically co-oxidize azo dye compound and As(III) from the aqueous phase.