Synthesis of semiconductor-MOF heterostructure photocatalysts has attracted considerable attention for their thermal stability, controllable crystallinity, and enhanced photocatalytic activity. In this work, the hollow nanostructure of anatase TiO₂ was prepared by etching SiO₂ from core–shell SiO₂@TiO₂ nanoparticles. ZIF-8, one of the metal-organic frameworks (MOFs), was hybrid synthesized on the surface of hollow TiO₂ and formed double-shell hollow nanoparticles. The photocatalytic activity of the double-shell hollow TiO₂@ZIF-8 nanoparticles toward methylene blue (MB) under UV light irradiation was processed, and the highest photocatalytic efficiency of 99.1% was shown compared with TiO₂ and SiO₂@TiO₂ nanoparticles. This study suggests a promising approach to achieve an advanced photocatalytic performance toward dye degradation using MOFs for the surface engineering of semiconductors.

TiO₂ and core–shell SiO₂@TiO₂ nanoparticles were synthesized by sol-gel process at different calcination temperatures. Mesoporous hollow TiO₂ composites were prepared by etching SiO₂ from SiO₂@TiO₂ nanoparticles with alkali solution. X-ray diffraction (XRD), Scanning electron microscope (SEM),Transmission electron microscope (TEM), and N₂ adsorption–desorption isotherms, and Roman and Diffuse reflectance spectroscopy (DRS) were employed to characterize the synthesized materials. The effects of different calcination temperatures on the morphology, crystallinity, phase composition, and photocatalytic activity of the prepared materials were investigated in detail. It was found that the calcination temperature altered the phase structure, crystallinity, morphology, specific surface area, and porous structure. Additionally, it was verified that SiO₂ could inhibit the transfer of TiO₂ from anatase phase to rutile phase under high temperature calcination (850 °C). The hollow TiO₂ calcined at 850 °C showed the highest photocatalytic efficiency of 97.5% for phenol degradation under UV irradiation.

ZnFe₂O₄ microspheres were prepared by solvothermal method, and a novel ZnFe₂O₄@TiO₂ core-shell composite photocatalyst was prepared by ultrasonic (denoted as ZT-x) and mechanical stirring (denoted as ZTM-1.2). The morphology, structure, magnetic, and optoelectronic properties of the catalyst were investigated comprehensively, and the degradation performance of the catalyst was explored through the photocatalytic degradation of Rhodamine B (RhB) under UV light. The concentration of RhB was 10 mg/L, and the catalyst concentration was 0.3 g/L. ZT-1.2 showed the best photocatalytic degradation activity, and the degradation rate of RhB reached 97.3% within 60 min. The degradation ability of the catalyst was further evaluated by Methylene blue (MB), Methyl orange (MO), Phenol, and Ofloxacin (OFX). ZT-1.2 also exhibited excellent stability. The improved catalyst degradation performance was attributed to constructing a Z-type heterojunction. Moreover, the low-efficiency degradation of ZTM-1.2 was caused by catalyst agglomeration and low TiO₂ loading, confirming the superiority of the ultrasonic method and providing a new method for the preparation of magnetically recoverable TiO₂-based core-shell photocatalyst.