Visible-light photocatalytic SiO2/TiO2−xCx/C nanoporous composites using TiCl4 as the precursor for TiO2 and polyhydroxyl tannin as the carbon source

Abstract

We report an architecturally controlled synthesis of SiO₂/TiO_2−xC_x/C nanoporous composites that exhibit high absorption capability and efficient visible-light photocatalytic activity. The nanoporous composites are composed of silica particles as the cores and TiCl₄ as the precursor for the TiO₂ shell. Tannin is used as the binding agent between the core and the precursor shell, the carbon source, and the porosity promoter. The structure, crystallinity, morphology, and other physical–chemical properties of the samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microcopy (HRTEM), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption isotherm measurements, UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL). The chemical contents of the SiO₂/TiO_2−xC_x/C nanoporous composites were also analyzed by energy dispersive X-ray spectra (EDX). The formation mechanism of the nanoporous composites was extensively discussed. Methylene blue (MB) solutions were used as model wastewater to evaluate the adsorption and photocatalytic activity of the samples under natural sunlight and visible light. Fourier transform-infrared spectroscopy (FT-IR) and mass spectrometry (MS) were used to investigate the photodegradated species on the photocatalysts and in solution, respectively. The SiO₂/TiO_2−xC_x/C nanoporous composite samples exhibit remarkably enhanced visible-light photoactivity than Degussa P25 and pure TiO₂, and can be readily collected for reuse by gravitational sedimentation.