Protonated g-C3N4 coated Co9S8 heterojunction for photocatalytic H2O2 production

Photocatalytic H 2 O 2 production is an eco-friendly technique because only H 2 O, molecular O 2 and light are involved. However, it still confronts the challenges of the unsatisfactory productivity of H 2 O 2 and the dependence on organic electron donors or high purity O 2 , which restrict the practical application. Herein, we construct a type-II heterojunction of the protonated g-C 3 N 4 coated Co 9 S 8 semiconductor for photocatalytic H 2 O 2 production. The ultrathin g-C 3 N 4 uniformly spreads on the surface of the dispersed Co 9 S 8 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 H 2 O 2 to 2.17 mM for 5 h in alkaline medium in the absence of the organic electron donors and pure O 2 . 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-C 3 N 4 and Co 9 S 8 matrix promote the separation of photocarriers, and another channel is also opened for H 2 O 2 generation. The accumulated electrons in conduction band (CB) of Co 9 S 8 contribute to the major channel of two-electron reduction of O 2 for H 2 O 2 production. Meanwhile, the electrons in CB of g-C 3 N 4 participate in the single electron reduction of O 2 as an auxiliary channel to enhance the H 2 O 2 production.