Photocatalytic concretes - The interface between photocatalysis and cement chemistry

Concrete materials are ubiquitous in the developed world due to their versatility and cost-effectiveness as a construction material, but their great potential for increased functionality remains underdeveloped. As supports for photocatalysts, these structures offer viable solutions for the reduction of atmospheric pollutant concentrations, the source of which is often associated with urbanisation and the built infrastructure. This paper addresses (i) the photocatalytic mechanisms applicable to atmospheric depollution, (ii) the influence of doping, and (iii) the application of TiO2-based photocatalysts to concrete. Modifications to TiO2 will be discussed which can improve its activation in visible light and, in the treatment of NOx, improve catalytic selectivity towards nitrate rather than the more toxic NO2. The influence of the chemistry of cements on catalyst performance during both concrete placement and in service will also be addressed and some attention will be given to alternative strategies for introducing the photocatalyst to the concrete.