Preparation of titanium dioxide/activated carbon composites using supercritical carbon dioxide

The penetration of titanium tetraisopropoxide (TTIP) dissolved in supercritical CO2 into the nano-spaces of an activated carbon was studied for the preparation of a TiO2-coated activated carbon. The conversion of TTIP to TiO2 through thermal decomposition was confirmed by evolved gas analysis during heat treatment under a N2 flow. Acetone was detected in the evolved gas, which suggested that some isopropoxide groups in TTIP reacted with the carbonyl groups on the activated carbon surface. This chemical reaction with carbon is expected to be advantageous for favorable attachment to the carbon surface. The crystallite size of anatase in the TiO2/carbon composites was 4.1 nm, as estimated from the X-ray diffraction pattern, which almost corresponded to the graphene crystallite size; La (3.3–3.4 nm), as estimated from both the Raman spectrum and X-ray diffraction pattern. As the size of the crystallite prepared by bulk condensation of TTIP was more than 15 nm, these results confirmed that the anatase crystals were present in the carbon pores. Also, it was suggested that the crystal growth of TiO2 was influenced by the carbon nano-spaces.