Ultrafine TiO₂ acts as a catalyst in the presence of ultraviolet light which initiates the reaction with atmospheric pollutants. Some of Cristal’s CristalACTiV™ Ultrafine TiO₂ grades show activity also in the visible spectrum, although at a reduced level compared to UV irradiation. The TiO₂, when suitably incorporated into formulated products, provides phtocatalytic reaction at the surface where the coatings material is applied. Depending on the formulation parameters, de-polluting functionality (degradation of airborn pollutants such as nitrogen oxides - NOx) and self-cleaning functionality (destabilization of the organic components of the particles of dirt sticking on the exposed surfaces) can be achieved. Other additional benefits can also be realized, such as control of mildew and bacterial levels, thanks to optimized formulations and choice of photocatalytic TiO₂.
Cristal supplies the active ingredient, a specific form of ultrafine titanium dioxide, that must be formulated into suitable coating systems and applied to various surfaces, such as concrete, building facades, paving blocks, tiles and many others. In these instances, through the photocatalytic activity of the TiO₂, atmospheric pollutants such as oxides of nitrogen (NOx) or oxides of sulphur (SOx) are degraded.
Ultrafine TiO₂ is not degraded by the reactions described. Being a catalyst, it remains in the original formulation, ensuring a continuous activity.
Photocatalytic TiO₂ drives a chemical reaction that adds new functions to formulations:
|Self-Cleaning - The organic interface between the surface and adsorbed species is broken down. The adsorbed species can then be more easily washed away by rinsing or rain.
Depollution - Pollutants, such as oxides of nitrogen and sulfur present in vehicle exhaust and VOCs (Volatile Organic Compounds), are altered once they contact the surface to form less harmful molecules.
De-odorizing - Toxic and unpleasant odors can be neutralized.
Cristal produces a range of Ultrafine Titanium Dioxide products to serve the emerging Photocatalysis market.
These products are manufactured through chemical processes and display a range of surface morphologies and particle size distributions. CristalACTiV™ Photocatalytic TiO₂ in powder form can be suitably formulated and incorporated into exterior coatings, building and construction materials and transportation infrastructure products for roads, pavings and noise barriers. Cristal has experience in the formulation and testing of these materials containing photocatalytic powders as the active ingredient. Photocatalytic functionality as described above can also be beneficial in many other applications such as plastics, textiles, roof tiles, etc.
Cristal offers three aqueous stable colloidal dispersions of Ultrafine TiO₂, stabilized with acid or base, to provide sols CristalACTiV™ S5-300A, S5-300B and PC-S7. These sols can either be introduced as components of photocatalytic formulations to achieve an optimal dispersion of the Ultrafine TiO₂ particles or used to apply Ultrafine TiO₂ particles onto a surface in order to render it photocatalytic.
Cristal was one of eight partners in PICADA, a European Union-funded project designed to develop a range of materials for depollution and to evaluate their effects on a large scale. PICADA, Photocatalytic Innovative Coverings Applications for Depollution Assessment, is within the scope of the European programme called Competitive and Sustainable Growth. It began on January 1, 2002 and ended in 2005. For more information, visit www.picada-project.com.
Borough of Camden, London, UK
In 2006, Cristal carried out a trial on depolluting paving stones on Southampton Row, Bloomsbury in conjunction with Imperial College London consultants and Camden Council. For this particular trial, specially designed TiO₂ was incorporated into the paving slabs and these were laid down the length of the street at either side of the road covering approximately 1,200 sqm. Using a chemilluminescence NOx monitor, the trial concluded that the pollution in the area was reduced by up to 20%.
In Manila, Cristal conducted a trial in conjunction with a major local paint producer that supplied the paint for coating a MRT rail station. The trial also involved a consultant specializing in pollution monitoring. The paint formulation is the result of Cristal’s extensive R&D activity in photocatalysis. The measured NOx reduction in the vicinity of the painted walls showed that each treated square meter removes up to 80g of NOx per year.
During 2007, a depolluting trial was carried out in an indoor car park in Paris, belonging to a major construction company. Due to the very low lighting levels in the area, two specialist paints were used, employing a very active photocatalyst within the matrix of the coating. The trial was run for approximately 12 months and the nitrate accumulation was an indication of the NOx reducing performance of the coating. Samples from the area were collected monthly and analyzed for nitrate buildup alongside blank paint samples from the same area. The analysis demonstrated that the levels of NOx in the area were reduced by between 53% and 99% depending on paint type and lighting levels.
Central St. Martins College of Art & Design, London, UK
A depolluting trial was conducted with Camden Council and Kings College in a courtyard behind the college. Background data of pollutants in the area were collected for a period of one year prior to a transparent coating being applied to the wall surface. Chemilluminescence monitoring of NO, NO₂ and NOx was employed in order to record the pollution levels. Two detection probes were placed at different distances from the wall surface to detect the changes in pollution levels. Parallel pollution monitoring was performed in a nearby area to establish an ongoing baseline of air quality levels as a basis of comparison. Meteorological data such as wind speed and direction, rain fall, temperature and humidity were also continuously monitored every 15 minutes. Monitoring of the area continued for nearly two years after the application of the photocatalytic coating. The results from this trial show NOx reductions of 35 – 65% depending upon the time of the year and local weather conditions. The treatment showed the capacity of removing up to 200g/m2/year of NOx.
CristalACTiV™ is the key ingredient in Boysen’s KNOxOUT™ paint. CristalACTiV photocatalytic technology uses ultrafine titanium dioxide (TiO₂) to absorb energy from light and transform ordinary water vapor into hydroxyl and peroxyl radicals at the surface of the TiO₂.
A great advantage of this photocatalytic reaction is that the ultrafine TiO₂ is not consumed in the reaction, but is merely a catalyst that continuously generates free radicals as long as there is sufficient light, air and moisture. Additionally, this reaction gives the paint self-cleaning and anti-bacterial properties.
Learn more about CristalACTiV in KNOxOUT paints by visiting www.knoxoutpaints.com and www.knoxout.eu.