In situ hydrothermal synthesis of g-C 3 N 4 /TiO 2 heterojunction photocatalysts with high specific surface area for Rhodamine B degradation

Semiconductor-based photocatalysis is a promising method for degradation of environmental pollutants, but the activity of most widely used photocatalysts such as titania (TiO2) is still unsatisfactory under visible light. Herein, we synthesized a highly efficient visible-light-responsive heterojunction catalysts based on graphitic carbon nitride (g-C3N4) and TiO2. The g-C3N4/TiO2 heterojunction composites with high specific surface area were prepared via in situ hydrothermal synthesis followed by calcination, using titanium tetrachloride (TiCl4) and melamine as precursors. Interesting, HCl from the hydrolysis of TiCl4 served as the proton source to acidify the melamine. The g-C3N4/TiO2 heterojunction composites exhibited higher photocatalytic performance for decomposition of Rhodamine B (RhB) than pure g-C3N4 or TiO2 under visible light irradiation. The high activity can be ascribed to the high specific surface area (up to 115.6 m2 g−1) of the g-C3N4/TiO2 composites and a synergistic heterojunction structure between TiO2 and g-C3N4. Moreover, the photocatalytic performances of the g-C3N4/TiO2 composites rely on the content of melamine in the synthesis precursors: with an optimum melamine content (3 g for 0.5 mL of TiCl4), the sample showed the highest photocatalytic performance, which is superior to pure TiO2 and g-C3N4 by a factor of 18.7 and 3.5, respectively. Active species trapping experiments revealed that superoxide radicals and photogenerated holes played crucial roles in the photocatalytic reactions. The results will provide new ideas for the smart design and development of g-C3N4-based highly active photocatalysts with ultrahigh specific surface area for environmental and energy applications.