BS ISO 22197-4:2021 pdf download – Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for air-purification performance of semiconducting photocatalytic materials Part 4: Removal of formaldehyde
6.3 Photoreactor
The photoreactor holds a planar test piece within a 50‑mm‑wide trough, with its surface parallel to an optical window for photoirradiation. The reactor shall be fabricated from materials that adsorb little test gas and withstand irradiation of near‑UV light. The test piece shall be separated from the window by an air layer 5,0 mm ± 0,5 mm thick. The test gas shall pass only through the space between the test piece and the window. This gap shall be accurately set up according to the thickness of the test piece, for example by using height‑adjusting plates with different thicknesses, as shown in Figure 2 a). When a filter-type material is tested, an alternative type of test-piece holder shall be used, which holds the test piece while allowing the test gas to pass through the cells of the filter under irradiation [Figure 2 b)]. Quartz or borosilicate glass that absorbs minimal light at wavelengths longer than 300 nm shall be used for the window.
6.4 Light source
The light source shall provide UV irradiation within a wavelength range of 300 nm to 400 nm. Suitable sources include the so-called black light (BL) and black light blue (BLB) fluorescent lamps, with a maximum at 351 nm, as specified in ISO 10677. The test piece shall be irradiated uniformly through the window by the light source. If testing filter-type photocatalysts, the light source shall irradiate one face of the test piece. A light source that requires warming up shall be equipped with a shutter. The distance between the light source and the reactor shall be adjusted so that the UV irradiance (300 nm to 400 nm) at the sample surface is 10 W/m 2 ± 0,5 W/m 2 . The irradiance along the length of the test piece shall also be constant within ±5 %. The UV irradiance shall be measured with a radiometer which conforms to ISO 10677. The reactor shall be shielded from external light if necessary.
6.5 Analytical system
The test gas shall be sampled using a sampling cartridge, pump and flow controller, as specified in ISO 16000‑3. The concentration of formaldehyde shall be determined by 2,4‑dinitorphenylhydrazine‑ derivatised high‑performance liquid chromatography (DNPH‑HPLC). The reagents, equipment and procedure as specified in ISO 16000‑3 shall be used. Other analytical methods that give equivalent or better performance can be used.
7 Test piece
The test piece shall be a flat material or a filter-type 49,0 mm ± 1,0 mm wide and 99,0 mm ± 1,0 mm long. It may be cut to these dimensions from a larger bulk material or coated sheet, or may be specially prepared for the test by coating a pre‑cut substrate. The thickness of the test piece shall ideally be less than 5 mm, in order to minimize the contribution from the side faces. If thicker test pieces are to be tested, the side faces shall be sealed with an inert material before testing. The filter-type test piece shall not be thicker than 20 mm.
8 Procedure
8.1 General aspects The test procedure consists of pretreatment of the test piece, an adsorption process in the dark and measurements of removal of formaldehyde under photoirradiation. An example of the concentration change of formaldehyde during the test is shown in Figure 3. Some test pieces will possibly not give accurate removal of formaldehyde due to lower photocatalytic activity. In these cases, loading of formaldehyde per test piece may be reduced following the procedure in Clause 10.
8.2 Pretreatment of test piece
8.2.1 The test piece shall normally be pretreated according to 8.2.2 and 8.2.3, in this order. When it is anticipated that the test piece will have hydrophobic contamination, 8.2.3 may be followed by 8.2.2. The procedure in 8.2.2 may be omitted if it causes damage to the test piece. If the test pieces are not to be tested immediately after this pretreatment, they shall be kept in an airtight container.