Synthesis of core-shell TiO2@g-C3N4 hollow microspheres for efficient photocatalytic degradation of rhodamine B under visible light

Core-shell composites with titanium dioxide (TiO 2 ) hollow microsphere as the core and graphitic carbon nitride (g-C 3 N 4 ) as the shell were fabricated via a two-step self-assembly procedure with the assistance of ultrasonic dispersion. The as-prepared composite samples with different g-C 3 N 4 contents (0–20%) were thoroughly characterized and the photocatalytic activity was evaluated by the photocatalytic degradation of Rhodamine B (RhB) in aqueous solution under visible light. A g-C 3 N 4 layer of approximately 80   nm was successfully coated on the surface of TiO 2 hollow microspheres with a diameter of 1–3   μm, forming a heterostructure with close interfacial contact. The TiO 2 @g-C 3 N 4 composite exhibited significantly enhanced photocatalytic activity as compared with pure TiO 2 hollow microspheres. At an optimum weight ratio of g-C 3 N 4 to TiO 2 (15   wt.%), the photocatalytic activity of the composite sample was almost 3 times higher than that of reference TiO 2 hollow microspheres. Moreover, the results of recycling test indicated that the TiO 2 @g-C 3 N 4 composite had excellent stability. A possible photocatalytic reaction mechanism of TiO 2 @g-C 3 N 4 composite was proposed, in which superoxide radical anions played the major role in the oxidation of RhB, and the separation of photogenerated charge carriers across the heterostructure interface inhibited electron-hole recombination, thus enhancing the photocatalytic activity.