BS ISO 22197-2:2011 pdf download – Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for air-purification performance of semiconducting photocatalytic materials Part 2: Removal of acetaldehyde
5 Principle This part of ISO 22197 concerns the development, comparison, quality assurance, characterization, reliability, and design data generation of photocatalytic materials (Reference [3] in the Bibliography). The method described is intended to obtain the air-purification performance of photocatalytic materials by exposing a test piece to model polluted air under illumination by ultraviolet (UV) light (Reference [4] in the Bibliography). Acetaldehyde (CH 3 CHO) is chosen as a typical volatile organic compound (VOC) with lower molecular mass and offensive odour. The test piece, put in a flow-type photoreactor, is activated by UV illumination, and adsorbs and oxidizes gas-phase acetaldehyde to form carbon dioxide (CO 2 ) and other oxidation products. The air-purification performance is determined from the amount of acetaldehyde, in percent, adsorbed by the test piece, in micromoles (µmol). The simple adsorption by the test piece (not due to photocatalysis) is evaluated by the tests in the dark. However, some test pieces adsorb acetaldehyde very strongly, and a stable concentration of acetaldehyde may not be attained in the designated time of test. The photocatalytic activity may depend on physical and chemical properties of pollutants mainly due to the adsorption process involved. For a better evaluation of air purification performance of photocatalytic materials, it is recommended to combine one or more suitable test methods as described in other parts of ISO 22197.
6 Apparatus
6.1 Test equipment The test equipment enables a photocatalytic material to be examined for its pollutant-removal capability by supplying the test gas continuously, while providing photoirradiation to activate the photocatalyst. It is the same as that used in the test method for the removal of nitric oxide (ISO 22197-1) and consists of a test gas supply, a photoreactor, a light source, and pollutant-measurement equipment. Since low concentrations of pollutants are to be tested, the system shall be constructed with materials of low adsorption and resistant to ultraviolet (UV) radiation (e.g. acrylic resin, borosilicate glass). An example of a testing system is shown in Figure 1.
6.2 Test gas supply
The test gas supply provides air polluted with model contaminant at a predetermined concentration, temperature and humidity, and supplies it continuously to the photoreactor. It consists of flow regulators, a humidifier, gas mixers, etc. The flow rate of each gas should be within 5 % of the designated value, which is easily attained by using thermal mass-flow controllers with knowledge of the temperature and gas type at calibration in accordance with ISO 6145-7. The expression of gas flow rate in this part of ISO 22197 is that converted to the standard state (0 °C, 101,3 kPa, and dry-gas basis). Typical capacities of flow controller for pollutant gas, dry air and wet air are 100 ml/min, 1 000 ml/min and 1 000 ml/min, respectively. The standard acetaldehyde gas before dilution, normally balanced with nitrogen in a cylinder, shall have a volume fraction of 50 µl/l to 250 µl/l. Synthetic air (N 2 + O 2 , such as that supplied in cylinders) shall be used for dilution when the CO 2 from acetaldehyde is also measured.
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 a 5,0 mm ± 0,5 mm thick air layer. 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 illumination [Figure 2 b)]. Quartz or borosilicate glass that absorbs minimal light at wavelengths longer than 300 nm should be used for the window.