Ag-coated SiO2@TiO2 (Ag-SiO2@TiO2) core-shell nanocomposites were synthesized by a two-step method, which combined hydrothermal process and photodeposition. The morphology, structure, composition, and optical properties of the Ag-coated SiO2@TiO2 nanocomposites were extensively characterized by field-emission scanning microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectra (FT-IR spectra). The anatase TiO2 nanoparticles (5-10 nm) with high surface area were loaded on SiO2 spheres (200-300 nm) in the form of SiO2@TiO2 core-shell nanoparticle with a porous shell of controlled thickness (10–30 nm). Ag nanoparticles of different mass concentrations were photodeposited on SiO2@TiO2 core-shell structure with particle sizes of about 10-20 nm. The results showed that Ag nanoparticles increased the photocatalytic activity of SiO2@TiO2 core-shell nanoparticle improved the degradation of phenol and methylene blue under UV irradiation. The experimental results showed that Ag nanoparticles with mass concentrations of 6% had the highest photocatalytic activity on SiO2@TiO2 core-shell nanoparticles.

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After the core-shell SiO2@TiO2 nanoparticles (CSTNs) were synthesized by hydrothermal method, we investigated the influence of different molar ratios of Ti/Si on morphology, structure, and photocatalytic activity of the CSTNs. It was found that the CSTNs showed different size and surface morphology as the Ti/Si molar ratio changed. Besides, the TiO2 and the CSTN had the anatase phase after hydrothermal process and calcination at 450°C for 2 h. The N2 adsorption-desorption isotherms demonstrated the CSTNs with the molar ratio of Ti/Si increased from 1 : 1 to 8 : 1 can be categorized as type IV with hysteresis loop of type H2 and showed to be mesoporous materials. In addition, the CSTNs with the Ti/Si molar ratio of 5 : 1 had the highest surface area of 176.79 m2/g. Surface charges showed the isoelectric point (IEP) of the CSTNs ranged between silica (IEP at pH 3.10) and titania (IEP at pH 5.29). Since the molar ratio of Ti/Si increased from 1 : 1 to 8 : 1 by degradating both colorless organic pollutant of phenol and colored substances of methylene blue (MB) under UV irradiation, the photocatalytic activity of CSTNs exhibited higher photodegradation efficiency compared with TiO2. What is more, the experimental results also showed the CSTNs with Ti/Si molar ratio of 5 : 1 had the highest photocatalytic activity and showed higher photocatalytic efficiency compared with other TiO2-SiO2 composites reported for photodegradation of phenol and MB.