Construction of a porous core-shell homojunction for the photocatalytic degradation of antibiotics

The photocatalytic mineralization efficiency of antibiotics is primarily determined by the adsorption ability and photoactivity of the photocatalyst. In this work, we constructed a porous core-shell homojunction by growing amorphous TiO2 onto mesoporous rutile TiO2 crystals (MRCs) to simultaneously enhance the adsorption ability and photoactivity of the catalyst. Tetracycline hydrochloride (TCH) was chosen as a model agent of antibiotics. Scanning electron microscopy, high resolution transmission electron microscopy, N2 adsorption-desorption, and X-ray diffraction experiments were conducted to investigate the physical properties of the prepared samples. Surface photovoltage spectroscopy and X-ray photoelectron spectroscopy were applied to study the charge separation process. The results showed that amorphous TiO2 was homogeneously coated on the MRCs surface, thereby forming a 3D hierarchical porous core-shell morphology. The growth of amorphous TiO2 increased the surface area of the catalyst by 213% and the amount of TCH absorbed by up to 1760%. Moreover, a homojunction was formed at the interface of the MRC core and the amorphous TiO2 shell. The built-in electric field of the homojunction drove photogenerated holes (electrons) migrating from the core to the shell (shell to core) and thus enhanced the charge separation. TCH and the holes simultaneously concentrated in the amorphous TiO2 shell, thereby enhancing the mineralization of TCH.