Photocatalytic Surfaces: Antipollution and Antimicrobial Effects

Abstract A series of nano and micron particle grade anatase and rutile titanium dioxide pigments have been prepared with various densities of surface treatments, particle size and surface area. Their photocatalytic activities have been determined in a series of paint films and cementitious materials for self‐cleaning, depollution and antimicrobial/‐bacterial activity. The photocatalytic activities have also been examined by rapid assessment methodologies using 2‐propanol oxidation and hydroxyl group analysis. Photo‐oxidation studies on several types of paint films show a clear demarcation between nanoparticle and pigmentary grade titanium dioxide, with the former being more active due to its greater degree of catalytic surface activity. The photosensitivity of titanium dioxide is considered to arise from localized sites on the crystal surface (i.e. acidic OH) and occupation of these sites by surface treatments inhibits photo‐reduction of the pigment by UV radiation and hence the destructive oxidation of the binder is inhibited. The use of photocatalytic titania nanoparticles in the development of self‐cleaning paints and microbiological surfaces is demonstrated. In the former case surface erosion is shown to be controlled by varying the ratio of admixture of durable pigmentary grade rutile (heavily coated) and a catalytic grade anatase nanoparticle. For environmental applications in the development of coatings and cementitious materials for destroying atmospheric pollutants such as nitrogen oxides (NO x ), stable substrates are illustrated with photocatalytic nanoparticle grade anatase. Here porosity of the coatings through calcium carbonate doping is shown to be crucial in the control of the effective destruction of atmospheric NO x gases. Good environmental stability of the coatings is also crucial for long‐term durability and this aspect is examined for a variety of material substrates. For the development of microbiological substrates for the destruction of harmful bacteria/fungi, effective nanoparticle anatase titania is shown to be important, with hydrated high surface area particles giving the greatest activity.