Photocatalytic Reduction of CO2 over TiO2 Nanotube Arrays Covered with Si Thin Film

In the current study, the composite structure of Si(thin film)TiO2(nanotube arrays) has been fabricated via annealing amorphous TiO2(nanotube arrays, synthesized by anodizing titanium foil) on which was coated by Si film through chemical vapor deposition (CVD) method, and the photocatalytic reduction of CO2 for hydrocarbon compounds (such like formic acid) conversion on as-prepared Si/TiO2 structure has been initially investigated as well. The structure of Si/TiO2 nanotube arrays was characterized by X-ray powder ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectra (Raman) and transmission electron microscopy (TEM). The length, diameter and wall thickness of as-prepared TiO2 nanotube arrays were measured at about 270 nm, 70 nm and 16 nm, respectively. The thickness of the crystallized Si film was tested at around 300 nm. The amount total organic carbon as well as formic acid produced in the liquid phase was detected by high performance liquid chromatography (HPLC) and total organic carbon analyzer (TOC). It was found that the photocatalytic property was enhanced obviously after Si deposition. The TOC content increased from 21.2 mg.L-1 to 29.5 mg.L-1 under Xe lamp irradiation with 400 nm cut filter for 2 h. The improvement of photocatalystic property may due to the high light adsorption and low photogenerated electron and hole recombination of the heterojunction of Si and TiO2. The photocatalytic circulating experiment