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Photocatalytic pigments
Photocatalysis
Effectiveness and function of the PS-Photonox system
Photocatalysis is a natural reaction in the presence of light, water and oxygen. The reaction is supported by a catalyst
(PS-Photonox) accelerated and activated by the energy of UV light ("Photo").
When PS-Photonox is exposed to UV light, electron-hole pairs are created that enable reduction and oxidation reactions through the formation of adsorbed radicals on the surface. These radicals are extremely reactive species and are able to break down the pollutants that hit or are absorbed by the photocatalytic surface.
The degradation reaction converts harmful substances such as nitrogen oxides, sulfur oxides, VOC (volatile organic compounds) into harmless substances.
The catalyst (PS-Photonox) is not consumed by this reaction, which ensures a continuous process for the life of a photocatalytic surface.
Titanium dioxide is a raw material that is widely used in various applications. It is the white pigment that colors most of the items that we see and use in our daily life. Coatings, wall paints, plastics and paper
are just a few examples of TiO2 to achieve white color as well as to achieve the required level of opacity. In addition to being found in white colored materials, titanium dioxide is a key component when opacity is needed. Special qualities of TiO2 are used in ceramics, electronics, cosmetics and even in pharmaceuticals and food as well as in catalytic applications for industrial processes.
Photocatalytic TiO2 has specific properties and is different from the pigmented version. The morphology and properties of the ultrafine particles have been developed to achieve the best catalytic activity and to enable optimal incorporation into a variety of matrices. Specific photocatalysts are developed at Pigmentsolution GmbH for use in paints, varnishes, cement-bound materials or for direct application to surfaces (e.g. on filter media for air treatment systems).
Why photocatalysis?
Photocatalytic surfaces can drastically reduce local NOx values
Performance effect over time, quantitatively assessed periods
Computational Fluid Dynamics calculations enable the definition of optimal surfaces to be treated
Photocatalytic coatings are inexpensive and easy to apply.
A useful tool to aid in NOx reduction in areas of air quality underachievement
Photocatalytic materials are also effective at breaking down organic stains, molds and algae that accumulate in exposed areas. The self-cleaning effect has been repeatedly demonstrated on building exterior facades, on coated structures and on traffic infrastructures
Air pollution, and especially NOx pollutants, remain a major concern in developed and emerging regions.
The problem is forcing local authorities to take action.
Photocatalysis can be helpful as a new and proven solution on site to comply with the legal upper limits.
Design, construction and estate management firms can differentiate their projects or businesses with little
Care and cleaning agents.
Pigmentsolution supports the developers of coating systems with their accredited laboratories.
Photocatalytic pigments
The following pollutants and gases are broken down:
• Pollutant gas pollution from indoor use, as z. B. outgassed from furniture or carpets or from cigarette consumption
arise: formaldehyde / acetaldehyde.
• Pollutant gas pollution, such as that caused by industrial plants and car traffic, i.e. primarily nitrogen oxides.
• Greasy soiling such as B. stearates.
• Bacteria and mold spores can also be significantly reduced by using photocatalysis.
• Formulations with photocatalytic pigments are able to pick up organic pollution through the influence of light
to decompose effectively at the molecular level. Decomposition products can be washed away and washed away by rain. The settlement
moss and algae are strongly inhibited outdoors. The application is basically on all closed or open-pored
can be used on mineral substrates.
Photocatalytic self-cleaning describes a property of surfaces that have been coated with photocatalysts, for example nanoparticles made of titanium dioxide (TiO2). When exposed to (sun) light, organic materials are decomposed on the surface. The surfaces stay clean and have an antimicrobial effect. On some of these surfaces, water does not form droplets but a thin layer, so that the eye does not see fogging on these surfaces (“superhydrophilic surface”).
How it works using the example of titanium dioxide
The method is based on photocatalysis. Titanium dioxide (TiO2) is a semiconductor; Light generates electron-hole pairs in it if the energy of the photons is greater than the band gap Eg (internal photoelectric effect). The electrons or holes in the titanium dioxide can diffuse to the surface and generate radicals there, which lead to the decomposition of organic substances. The holes in particular have a high oxidative effect; OH radicals are formed from water (H2O). Organic substances are thereby decomposed; The end products are CO2 and water.
The band gap of anatase, the most efficient form of TiO2 for photocatalysis, is 3.2 eV (with the less efficient rutile crystal structure approx. 3.0 eV), this corresponds to a light wavelength of approx. 390 nm Photocatalysis requires ultraviolet light. Since the UV range only makes up a small part of sunlight, efforts are being made to reduce the band gap of anatase by doping and thus to use a larger area of the sunlight spectrum.
The superhydrophilic properties of the surfaces come about through oxygen vacancies on the TiO2 surface. OH groups are bound at these points, which lead to good wetting with water.
Photonox: additive in the facing formwork of paving stones
The "Photonox" concrete test body was examined for the breakdown of NO in the gas phase and was used for 5 days before the measurement
1 mW / cm2 UV-A light pre-irradiated.
Breakdown of NOx
The photocatalytic NO oxidation is measured in an apparatus in which air (relative humidity 50%) with a content of 1 ppm NO and a flow rate of 3 L / min is passed over a sample measuring 50 x 100 mm2. The analysis is carried out with a NO / NO2 analyzer, which has a fluorescence detector with a detection limit of 1 ppb NO. The irradiation takes place with UV (A) lamps, the light intensity on the sample surface being 1 mW / cm2.
Evaluation:
The irradiation power is 1 mW / cm2, which corresponds to a total power of 50 mW for a sample size of 50 cm2.
With an average irradiation wavelength of 350 nm:
50 mW = 1.47 x 10-7 molhν / s
The continuous measuring apparatus is operated at a flow rate of 3 L / min. The following applies to an ideal gas:
24 L gas = 1 mol (at p = 1 bar and 25 °)
ie 1 mol of gas flows over the sample in 8 min. Of this, 1 ppm is NO, so 10-6 mol NO flow over the sample. During this time will
the sample is irradiated with 1.47 x 10-7 molhν / sx 60 s / min x 8min = 70 x 10-6 molhν.
With a complete breakdown of the metered NO, the photon efficiency ζ would be:
ζ = 10-6 mol NO / 70 x 10-6 molhν = 0.0143 = 1.43%
be. If a reduction of x ppm NO is measured, the photon efficiency is calculated according to the following formula:
ζx = x (ppm) * 1.43 (% / ppm)
Results:
Photonox
NO degradation: 0.159 ppm (beginning)
Photon efficiency ζ = 0.23%
NO degradation: 0.148 ppm (end)
Photon efficiency ζ = 0.21%
NOx degradation: 0.102 ppm (beginning)
Photon efficiency ζ = 0.146%
NOx degradation: 0.0565 ppm (end)
Photon efficiency ζ = 0.081%
NO2 formation: 0.057 ppm (beginning)
Photon efficiency ζ = 0.082%
NO2 formation: 0.0915 ppm (end)
Photon efficiency ζ = 0.13%
The test conditions used here correspond to the ISO 22197-1 standard (1 ppm NO, 3 L / min air flow, 50% relative humidity (RH), 1 mW / cm2 UV (A) irradiation). Thus, from the data measured here, according to the ISO standard
22197-1, the degraded amount of NO can be calculated in μmol:
n NO = 3L min-1 / 22.4 L mol-1 x (C NO, in - C NO, out) x 300 min
For "Photonox":
C NO, in - C NO, out = 0.148 ppm, i.e., 0.148 μL / L
n NO = 5.95 μmol (in 5 h irradiation time)
The amount of degraded NOx is calculated in the same way:
n NOx = 3L min-1 / 22.4 L mol-1 x (C NOx, in - C NOx, out) x 300 min
For "Photonox":
C NOx, in - C NOx, out = 0.0565 ppm, that is, 0.0565 μL / L
n NOx = 2.3 μmol (in 5 h irradiation time)
and finally the amount of NO2 formed:
n NO2 = 3L min-1 / 22.4 L mol-1 x (C NO2, in - C NO2, out) x 300 min
For "Photonox":
C NO2, in - C NO2, out = 0.0915 ppm, that is, 0.0915 μL / L
n NO = 3.7 μmol (in 5 h irradiation time)
These results can be compared directly with those shown in Appendix A of ISO 22197-1
Test data are compared.
Alternatively, the following calculation is often done:
The molecular weight of NO is 30 g mol-1, the illuminated surface is 0.005 m2.
The degradation of 1 μmol corresponds to 30 μg or 6 mg / m2.
The Photonox test body breaks down 5.95 μmol in 5 hours, ie 1.19 μmol / h or 7.14 mg NO / m2h.
A value of more than 5.0 mg NO / m2h can be regarded as an excellent degradation performance.
Summary evaluation of the results
With an efficiency of ζ = 0.21% (NO degradation end value), the Photonox test specimen examined here shows very good activity for the photocatalytic degradation of NO in the gas phase.
Our rating scale: sufficient: 0.01% <ζ <0.05%, satisfactory: 0.05% <ζ <
0.1%, good: 0.1% <ζ <0.2%, very good: 0.2% <ζ <0.5%, excellent: ζ> 0.5%).