ISO 22197-2: 2011 – Test method for air-purification performance of semiconducting photocatalytic materials. Part 2: Removal of acetaldehyde.
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 (CO2) and other oxidation products. Typical test conditions are given below:
|Sample size||5 cm x 10 cm and typically 5 mm thick|
|Suitable sample type||Construction materials in flat sheet, board or plate shape; structured filter materials including honeycomb-form; woven and non-woven fabrics; plastic or paper materials if they contain ceramic microcrystals and composites.|
|Unsuitable sample type||Powder or granular photocatalytic materials|
|Sample pre-treatment||16-24 hr UV irradiation at ≥ 1.5 mW/cm2|
|Test conditions||1 L min-1 of 5 ppmv Acetaldehyde in air, adjusted to 50% RH; time: 3 hours; irradiance: 1 mW/cm2; temp: 25 °C|
|Analytical method||Acetaldehyde: GC-FID|
|Information returned||Amount of acetaldehyde removed (mmol) and % acetaldehyde removed|
Acetaldehyde occurs widely in nature, since it is produced by plants as part of their metabolism and also during the ripening process. It is also a product of combustion (wood, oil, petrol and diesel) and so is a constituent of car exhaust fumes and tobacco smoke. It is a significant industrial chemical which is used in the manufacture of acetic acid, perfumes, flavours, aniline dyes, plastics and synthetic rubber. It is a cancer suspect agent, an irritant and large doses can cause death by respiratory paralysis. It is an important indoor air pollutant as it is released by building materials such as polyurethane foams, adhesives, coatings and inks. Along with formaldehyde and other volatile organic carbons, i.e. VOCs, such as toluene, it is associated with sick building syndrome.
The photocatalytic oxidation of acetaldehyde has been well studied [1-3] using titania photocatalysts, although the reaction pathway, and the major intermediates, are still the subject of debate . Recent work indicates that it is first oxidised to acetic acid and then to formic acid, formaldehyde (the acids being adsorbed onto the surface of the titania) and then, finally to CO2 , i.e.
A typical data set generated, i.e. acetaldehyde removed and carbon dioxide generated, is illustrated below. The hatched areas B and B’ are proportional to the amounts of acetaldehyde removed and carbon dioxide generated, respectively. The key points are the start of contact with the acetaldehyde feed (t=0), UV lights on (↓) and UV lights off (↑).
 M.L. Sauer and D.F. Ollis, J. Catal., 158 (1996) 570.
 Y. Ohko, D.A. Tryk, K. Hashimoto and A. Fujishima, J. Phys. Chem. B, 102 (1998) 2699.
 E. Obuchi, T. Sakamoto and K. Nakano, Chem. Eng. Sci., 54 (1999) 1525.
 B. Hauchercorne, D. Terrens, S. Verbruggen, J. A. Martens, H. Van Langenhove, K. Demeestere and S. Lenaerts, Appl. Catal., B, 106 (2011) 630.
For the best evaluation of air purification performance of photocatalytic materials, it is recommended by ISO to combine one or more of the Air Purification test methods.
These methods are designed to obtain the air-purification performance of photocatalytic materials by exposing a test piece to model polluted air, in a photoreactor, under illumination by ultraviolet (UV) light. The concentration(s) of the analyte(s) of interest are monitored regularly and the concentration versus time data profile(s) are then processed so as to provide one or more measures of the efficiency of the test piece to remove photocatalytically the air-pollutant under test.