Construction of S-scheme p-n heterojunction between protonated g-C3N4 and α-MnS nanosphere for photocatalytic H2O2 production and in situ degradation of oxytetracycline

Photocatalytic H2O2 production is a green and sustainable technology, which still exposes the issues of excessive dependence on organic electron donors and pure O2, and lacking effective use. It is necessary to develop more efficient and more economical photocatalysis system for H2O2 production. Here, we construct a S-scheme p-n heterojunction from the p-type MnS and the n-type protonated g-C3N4 (PCN) semiconductors for photocatalytic H2O2 production and achieve the in situ use of H2O2 for oxidative degradation of oxytetracycline (OTC). The PCN/MnS composite synthesized by a one-step method well maintains a nanosphere structure of α-MnS and load the PCN on the sphere surface to form a heterojunction with strong interaction. PCN/MnS exhibits the improved photogenerated charge separation and electron transfer efficiency. An optimal photocatalyst can produce 669.6 μM of H2O2 for 6 h without using the electron donors and the pure O2 gas. The mechanism proposed the contribution of a S-scheme p-n heterojunction forms between PCN and MnS. The electrons in conduction band (CB) of MnS are responsible for the major single-electron reduction of •O2- radicals and the auxiliary two-electron reduction of O2 for H2O2 production, while the holes in valence band (VB) of PCN further promote the separation of photocarriers. The photogenerated H2O2 can be effectively used as an in-situ oxidant to achieve 82.2% degradation of OTC in water within 80 min. The •O2- radicals which originate from the in situ decomposition of H2O2 over PCN/MnS mainly contribute to the OTC oxidation.