Solvothermal preparation of copper(II) porphyrin-sensitized mesoporous TiO2 composites: enhanced photocatalytic activity and stability in degradation of 4-nitrophenol

Four new copper(II) porphyrins CuPp(1, 2, 3, 4) with a different number of peripheral ester groups were synthesized and used to sensitize the mesoporous TiO2 under solvothermal condition, and accordingly, four mesoporous CuPp(1, 2, 3, 4)/TiO2 composites were obtained. These composites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, BET nitrogen adsorption–desorption isotherms (BET), UV–vis diffuse reflectance spectroscopy (UV–vis-DRS), and Fourier-transform infrared spectroscopy (FT-IR). The results showed the crystal structure and morphology of mesoporous TiO2 were not affected by the porphyrin existence on its surface. The photocatalysis properties of mesoporous TiO2 and CuPp(1, 2, 3, 4)/TiO2 have been evaluated by conducting the photocatalytic degradation of 4-nitrophenol (4-NP) under visible-light irradiation, and the result showed their higher photocatalytic activities and the order is: CuPp(4)/TiO2 > CuPp(3)/TiO2 > CuPp(2)/TiO2 > CuPp(1)/TiO2 ≫ TiO2. The probable reasons are their large surface area and different number of peripheral groups in CuPp, which separate electron–hole pairs efficiently. The repetition test of CuPp(1, 2, 3, 4)/TiO2 composites demonstrated that they still maintained superior photocatalytic activity over six recycles.