Insight into the role of Fe in the synergetic effect of persulfate/sulfite and Fe₂O₃@g-C₃N₄ for carbamazepine degradation

In this work, the role of Fe in the synergetic effect of persulfate/sulfite and Fe₂O₃@g-C₃N₄ (FCN) for carbamazepine (CBZ) degradation was studied. Unexpectedly, Fe₂O₃ in FCN plays very different roles for sulfite [S(IV)] and persulfate (PS) activation. Specifically, since photo-generated holes (h⁺) can transform S(IV) into SO₄^-, and photo-generated electrons (e^-) can accelerate Fe(III) reduction which promotes transition metal based S(IV) activation, a synergetic effect of photocatalysis and Fe is observed in FCN/S(IV)/vis system. In contrast, in FCN/PS/vis system, both Fe(III)/Fe(II) cycle and PS activation compete for e^-. Since PS is a stronger electron acceptor, Fe(III) reduction by e^- is limited. Therefore, the contribution of Fe₂O₃ in FCN/S(IV)/vis system is 3 times higher than that in FCN/PS/vis system. Initial pH affects CBZ removal by changing surface charge of catalysts and oxidants species, while the effect varies for different catalysts and oxidants. This study provides new insight into the synergetic effect of photocatalysis and transition metal for SO₄^- generation, which contributes to catalyst design for environmental application.