Effect of Iron Oxides in Coal Fly Ash on Nano-size TiO2 Photocatalytic Activity

TiO2 photocatalyst was immobilized on coal fly ash by precipitation method. The titanium hydroxide precipitated on coal fly ash by neutralization of titanium chloride was oxidized by heat treatment in the temperature range of 300-700°C. The crystalline structure of the titanium dioxide is anatase type in this temperature range. The crystallite size of anatase can be increased with raising temperature of heat treatment, with the draw back as the removal ability of NO gas will decrease. When the coal fly ash coated with 10wt% of TiO2 was calcined at the temperature range of 300-400°C for 2 hrs, the crystallite size of anatase appeared about 9nm, and the removal rate of NO gas showed 63-67.5%. The major crystal structure of iron oxides, existing as an impurity in coal fly ash, was magnetite (Fe3O4). Their phase transformation into hematite (Fe2O3) by heat treatment improves the removal rate of NO gas for TiO2-coated coal fly ash.