Significant Improvement of Photocatalytic Activity of TiO2/g–C3N4 Composite Synthesized by the Aiding of Hydrothermal Method.

g–C₃N₄ nanosheets were first synthesized by calcining the mixture of hydrochloric acid-pretreated melamine and ammonium chloride. Then, by the aiding of solvothermal method and hydrofluoric acid as morphology modifier, 001-TiO₂/g–C₃N₄ (TCN-X, X = 5 , 3, 2, 1) nanocomposites were synthesized using g–C₃N₄ nanosheets and tetrabutyl titanate, with the mass ratio of g–C₃N₄ to TiO₂ was 5:1, 3:1, 2:1 and 1:1, respectively. The as-synthesized samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption method, ultraviolet–visible diffuse reflectance spectrum, photoluminescence spectrum, etc. Their photocatalytic properties were evaluated under visible light irradiation with rhodamine B (RhB) as the target pollutant. The results reveal that the TCN-3 composites had a large specific surface area of 67.38 m²/g and consisted of g–C₃N₄ nanosheets and anatase TiO₂ crystals about 10–20 nm in size. The (001) crystal planes of TiO₂ can be easily observed in TCN-X composites. All TiO₂/g–C₃N₄ composites exhibited excellent photocatalytic activity compared with the pure g–C₃N₄ did. The photocatalytic property of TCN-X samples varied with the mass ratio of g–C₃N₄to TiO₂, and TCN-3 presented the optimum photocatalytic performance. In total, 50 mg of TCN-3 completely degraded 50 mL and 100 mL of RhB solution (10 mg/L) in 15 min and 40 min, respectively. The reaction rate constant of TCN-3 was 6.7 times as large as that of pure g–C₃N₄. TCN-3 also presented outstanding activity for the photocatalytic degradation of the colorless tetracycline solution. The significant improvement in photocatalytic activity of TCN-3 was attributed to the evenly distribution of TiO₂ on g–C₃N₄, the enhanced specific surface area and the construction of 001-TiO₂/g–C₃N₄ heterojunction between the g–C₃N₄ nanosheets and the (001) crystal planes of anatase TiO₂, which greatly reduced the recombination rate of the photo-generated electron and hole. In this work, the g–C₃N₄ nanosheets were obtained by simple mixing and calcination of ammonium chloride and acid-treated melamine. Then, using tetrabutyl titanate as the precursor and hydrofluoric acid to expose the 001 crystal face of TiO₂, 001-TiO₂/g–C₃N₄ composite materials with different mass ratios were synthesized by simple hydrothermal method. The composite exhibited excellent photocatalytic performance and degraded RhB within 15 min. The rate constant of TiO₂/g–C₃N₄ composite is 6.7 times that of pure g–C₃N₄. [ABSTRACT FROM AUTHOR]