ISO 10678 Fine Ceramics (Advanced Ceramics, Advanced Technical Ceramics) - Determination of Photocatalytic Activity of Surfaces in Aqueous Media by Decomposition of Methylene Blue

In the standard "ISO 10678 Fine ceramics (advanced ceramics, advanced technical ceramics) - Determination of photocatalytic activity of surfaces in aqueous media by degradation of methylene blue" published by the International Organization for Standardization (ISO), a method is described for determining the photocatalytic activity of surfaces by degradation of the dye molecule methylene blue in aqueous solution using artificial ultraviolet (UV) radiation. This method characterizes the ability of photoactive surfaces to degrade dissolved organic molecules under ultraviolet radiation.

The specified test method is also valid for the assessment of the specific photocatalytic self-cleaning activity of surfaces covered with the relevant coatings. This method is not applicable for characterizing the photoactivity of surfaces in visible illumination in terms of direct fouling, degradation of gaseous molecules and determination of the antimicrobial photoactivity of surfaces. However, correlations can be found between these different types of photocatalytic activity, especially for surfaces showing low photonic efficiency.

For the purposes of this standard, the following terms and definitions apply:

Specific photocatalytic activity is a measure of photochemical conversion. Specific photocatalytic activity is expressed in moles per square meter and per hour.
Photonic efficiency is a measure of the selectivity of incident photons to cause decolorization of methylene blue. Photonic efficiency is expressed as a percentage of the incident photon flux. It is assumed that one photon can cause decolorization of one dye molecule.
Test solution refers to the aqueous methylene blue solution used to determine the photocatalytic activity of surfaces.
The measuring solution, at least 10 percent of the test solution by volume, is used for external determination of optical absorbance using a spectrophotometer.
Conditioning solution refers to the aqueous methylene blue solution used for pre-adsorption of methylene blue onto test surfaces before determining the photocatalytic activity of the surfaces.

When testing, in principle, methylene blue is degraded in an aqueous solution in contact with a potentially photocatalytically active surface by ultraviolet (UV) radiation passing through the solution, the light being unable to induce direct photolysis of the dye. The general result is decolorization of the solution.

The amount of dye remaining in the solution is determined using UV/visible spectroscopy at regular intervals throughout the UV radiation period. A reference measurement is performed with the same sample without UV radiation or with the same sample in a second vessel with the photoactive surface protected from the incident light beam by a cover. The results are used to calculate the specific degradation rates and the corresponding photonic efficiencies of the tested surface.

Major apparatus used in the tests include:

General: Apparatus to be in contact with the methylene blue solution should be constructed of materials that have little or no tendency to adsorb this dye on their surface, e.g. glass, stainless steel, polyethylene, polypropylene, polyacrylate, low organic emission silicones. The test arrangement should show a minimum of stray light.
The measuring device is: two test cylinders or two test cells, each consisting of a container with a sample holder, fixed to the sample surface with a suitable adhesive.
Glass panel: Used to cover the measuring cell, which exhibits minimum absorbance in the spectral emission region of the UV radiation light source.
UV radiation light source: A narrow-band emitter in the wavelength range, for example, between 320 nm and 400 nm (UV-A)
UV radiometer (sensor): To measure the V radiation intensity, the UV radiation is calibrated close to the characteristics of the light source.
UV/vis-spectrophotometer: Calibrated in the measuring range between 600 nm and 700 nm for the determination of methylene blue concentration.
Measuring cells: For spectrophotometers made of glass or plastic with an optical length of 10 mm and a transmittance of more than 80 percent (600 nm to 700 nm).

Aqueous methylene blue solutions are used for both measurement and conditioning. Methylene blue solutions are freshly prepared from stock solutions stored in the dark using distilled water without any other additives. The initial methylene blue concentration for the test solution is prepared at 10 plus/minus 0,5 µmol/L. The conditioning solution is prepared at a concentration of 20 plus/minus 1 µmol/L.

The geometric surface area of the sample should be between 100 plus/minus 1 mm2 and 1500 plus/minus 15 mm2. The sample should first be cleaned in accordance with the manufacturer's instructions.

Among the numerous tests, measurements, analyses and evaluation studies carried out for businesses in various sectors, our organization also provides testing services defined in the standard “ISO 10678 Fine ceramics (advanced ceramics, advanced technical ceramics) - Determination of photocatalytic activity of surfaces in aqueous media by the degradation of methylene blue” with its trained and expert staff and advanced technological equipment.