Abstract
This paper revealed an interesting phenomenon. The photo-catalytic activity in terms of NOx removal of cement pastes prepared with white cement (WC) and nano-TiO2 (P25) was found to be superior to those prepared with ordinary Portland cement (OPC) and P25. Even by simply mixing P25 with anhydrous WC and OPC (without hydration), the same performance was observed. The UV-Vis diffuse reflectance spectra (DRS) of WC and OPC clearly showed that OPC was able to absorb much higher amounts of light within the range of 200–800 nm compared with WC. Also, the electrochemical impedance spectroscopy analysis pointed to a higher charge transfer resistance on the surface of OPC/P25 dry mixtures. Furthermore, the OPC/P25 dry mixtures displayed a much lower photoluminescence (PL) intensity. All the results suggest that the higher photocatalytic NOx removal ability harboured by the WC/P25 mixtures is due to both the lower light absorption capacity and the lower charge transfer resistance of WC.
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