BiOBr/protonated graphitic C3N4 heterojunctions: Intimate interfaces by electrostatic interaction and enhanced photocatalytic activity

In this work, enhanced photocatalytic activity of BiOBr/graphitic C3N4 heterojunctions for degradation of Rhodamine B (RhB) were obtained by the protonation pretreatment of graphitic C3N4 with hydrochloric acid. A possibly electrostatic interaction between protonated graphitic C3N4 (pg-C3N4) and BiOBr provided a closely intimate interface in the heterojunction, which was demonstrated by the results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This tight coupling was favorable for the charge transfer between pg-C3N4 and BiOBr, and therefore promoted the effective separation of photogenerated electron–hole pairs. The effect of composition in heterojunctions on photocatalytic activity was investigated, and the optimal photocatalyst with a BiOBr/pg-C3N4 mass ratio of 7:3 showed a superior activity, which was 35.03 and 33.72 times higher than that over pg-C3N4 and BiOBr, respectively. Radical trap experiments confirmed that the holes and superoxide radical species were the main reactive species in the RhB photodegradation process. Moreover, the stability of BiOBr/pg-C3N4 heterojunction was also tested and the RhB degradation efficiency declined by only 9.6% after seven successive cycles.