Protonated g-C3N4 coated Co9S8 heterojunction for photocatalytic H2O2 production

Photocatalytic H2O2 production is an eco-friendly technique because only H2O, molecular O2 and light are involved. However, it still confronts the challenges of the unsatisfactory productivity of H2O2 and the dependence on organic electron donors or high purity O2, which restrict the practical application. Herein, we construct a type-II heterojunction of the protonated g-C3N4 coated Co9S8 semiconductor for photocatalytic H2O2 production. The ultrathin g-C3N4 uniformly spreads on the surface of the dispersed Co9S8 nanosheets by a two-step method of protonation and dip-coating, and exhibits improved photogenerated electrons transportability and e--h+ pairs separation ability. The photocatalytic system can achieve a considerable productivity of H2O2 to 2.17 mM for 5 h in alkaline medium in the absence of the organic electron donors and pure O2. The optimal photocatalyst also obtains the highest apparent quantum yield (AQY) of 18.10% under 450 nm of light irradiation, as well as a good reusability. The contribution of the type-II heterojunction is that the migrations of electrons and holes within the interface between g-C3N4 and Co9S8 matrix promote the separation of photocarriers, and another channel is also opened for H2O2 generation. The accumulated electrons in conduction band (CB) of Co9S8 contribute to the major channel of two-electron reduction of O2 for H2O2 production. Meanwhile, the electrons in CB of g-C3N4 participate in the single electron reduction of O2 as an auxiliary channel to enhance the H2O2 production.