Photocatalytic self-cleaning coatings are a significant market for nanoparticulate titanium dioxide (TiO2). The market in Japan alone is valued at over $1 billion per annum.
Self-cleaning coatings based on photocatalysts are currently suitable mainly for exterior use for inorganic surfaces and coatings, but photocatalytic materials operating at the wavelength of visible light are also widely studied. Industries impacted by self-cleaning photocatalytic coatings include:
• Architectural glass and construction (including road)
• Medical (self-disinfecting coatings)
• Food production and packaging
• Water purification
• Air purification (indoor)
• Solar coatings.
Nanoparticles
Photocatalysts boost chemical reactions under irradiation with light. This is particularly true for the decomposition of organic substances such as fats, oils or even microbes. The catalytic efficiency is considerably enhanced by the utilization of nanoscale photocatalysts; with TiO2 the most commonly used photocatalyst. Nanostructured TiO2 possesses high specific surface area, high pore volume and pore size, high activity, and low density. These properties increase the accessible surface area and mass transfer for organic pollutant adsorption, resulting in better photocatalytic performance, since photocatalytic reactions are based on chemical reactions on surfaces.
Applications make use of the self-cleaning, anti-fogging, anti-microbial or water cleaving properties. In indoor environments, most surfaces, e.g.. ceramic tiles, windows glass or paper, are gradually covered with organic matter such as oils, dirt, and smoke residue and become fouled. Transparent TiO2 coatings can be completely unobtrusive, causing no readily discernable changes in the substrate colour or transparency, but they can
Markets
Nano-TiO2 surfaces (coated with 10-20nm layer of TiO2) are commercially available and have been used in (mainly in the Japanese and European markets) in water and air purification, self-cleaning glass, concrete products and a variety of coatings applications. These coatings greatly benefit building maintenance, especially for skyscrapers, as they reduce the need for costly surface cleaning. Various types of surfaces with TiO2 can be covered to make them self-cleaning under sunlight as well as room light. Thus, surfaces based on paints, ceramics, glass, cementitious materials containing active photocatalytic titania nanoparticles have widespread applications to create environmentally clean areas within their proximity. Numerous applications have been developed from utilizing the photocatalytic reaction of TiO2:
• Self-Sanitizing Surface: Photocatalyst coating is utilized as a hygienic coating to reduce bacteria and virus contamination. This coating removes the organic matter necessary for bacteria growth. The strong oxidation mechanism also eliminates any bacteria by causing lesion of cell membrane and lysing of cell content.
• Self-Cleaning Coating: Building’s exterior surface benefit from these sustainable photocatalytic coatings by eliminating any contaminants that are causing the building to become dirty such as the oil content from car exhausts and any mold or mildew stains.
• Reduce Indoor Air Pollution and Sick Building Syndrome: Photocatalyst coating and products control Sick Building Syndrome by removing Volatile Organic Compounds emitted from building material and furniture and create a purer space for comfortable living and working conditions.
• Reduction of Air Pollution: Photocatalytic oxidation reduces hydrocarbon waste produced from industrial factories burning fossil fuel or coal.
• Waste Water Treatment: Photocatalysts can replace chlorine to be more effective and a much safer alternative oxidation methods to water purification. Photocatalytic oxidation can remove bacteria, organic toxins, dioxins, and other chemicals in water systems without introducing other chemicals.
Figure 1: Mechanism of photocatalytic NOx oxidation on active concrete road.
Figure 2: Jubilee Church in Rome, the outside coated with nanophotocatlytic TiO2 coatings. Photocatalytic titanium dioxide is energized by UV and accelerates the decomposition of organic particulates and airborne pollutants such as nitrous oxide (NOx).
Photocatalytic coatings have been applied to numerous buildings in Japan including Chuba International Airport Terminal. Photocatalyst coatings have been proven to combat Bird Flu and SARS infections in high risk areas. Hundreds of hospitals and thousands of buildings in Asia and recently in Europe were coated to protect property against deadly infections and environmental pollution damage. The market for photocatalytic technology in Japan has experienced significant growth in the last decade and was worth around $1 billion in sales in 2012 (Photocatalysis Industry Association of Japan). The general sales volume for clean-up technologies has increased greatly in recent years, such as photocatalytic air-purifiers, especially in Asia.
Companies & products
Companies producing self-cleaning photocatalytic nanocoatings include:
• BioshieldTech: NuTiO brand of American designed, engineered and manufactured Nano Hygienic TiO2 Titanium Dioxide (UV-PCO) technology.
• Caparol: CapaSan interior paint with a photocatalytic effect
to improve the indoor air quality.
• Carrier Corp: patent for photocatalytic air filters.
• Cristal: CristalACTiV™ product range.
• Daikin Ltd.: photocatalytic air-purifying filters.
• FN Nano, Inc.: FN® photocatalytic coatings
• Fujita: photocatalytic coatings on roads.
• Green Earth Nanoscience, Inc.: The company has an easy to apply, green, environment friendly, transparent coating for exterior applications. The photocatalyst coating is a water-based coating containing Titanium dioxide (TiO2).
• Green Millennium Inc.: The company produces photocatalytic coating for a range of applications.
• Hiranuma Industries: total organic carbon analyzer with a photocatalytic reactor.
• Hitachi Home and Life Solution: photocatalytic air purifier units.
• Italcementi Group: TX Active® is a photocatalytic self-cleaning cement coating.
• JFE Building Materials: photocatalytic steal plates for construction.
• KRONOS, Inc.: KRONOClean 7000 range of photocatalytic coatings.
• Mitsubishi Electric: deodorization/decomposition of ethylene in refrigeration.
• Mitsubishi Plastics: Hishi Wall™ Partition movable partitions with a photocatalytic coating.
• Nippon Soda: titania pre-coating on window blinds.
• Panahome: Produce KIRATECH photocatalytic tiles for exterior walls.
• Pilkington: Pilkington Activ™ is a range of self-cleaning solar control glass products.
• PPG: SunClean Self-Cleaning Glass.
• Saint-Gobain: EverClean TiO2-based photocatalytic coating technology.
• Sekisuo Plastic: polycarbonate plates coated with titania photocatalyst on both sides
• Sumitomo Metal Industries: photocatalytic treatment of water.
• Taiyo Kogoyo: TiO2 Photocatalytic Membrane:.
• Toshiba Lightec: lighting device with titania photocatalyst.
• Toto Ltd.: photocatalytic coatings for construction.
• UBE Industries: photocatalytic fiber cartridge for decomposition of dioxin and sterilization in water treatment.
