Fine ceramics (advanced ceramics, advanced technical ceramics) - Test method for antibacterial activity of semiconducting photocatalytic materials under indoor lighting environment (ISO 17094: 2014).

Test not accreditted yet in our laboratory.

A photocatalytic activated by indoor light is a substance that performs many functions, including an antibacterial action, based on oxidation and reduction reactions produced by artificial light sources used in the indoor lighting environment.

ISO 17094 describes a test method to determine the antibacterial activity of materials that contain a photocatalytic component activated by exposure to indoor light or that have active photocatalytic surface films in indoor lighting environments, by measuring the survival of bacteria after a period of exposure to indoor light. It is designed to test different types of photocatalytic materials activated with indoor artificial lighting and used in building materials in the form of flat sheets, plates or boards. This standard does not include the analysis of powdered, granular or porous photocatalytic materials, nor is it applicable to fabrics or textiles.

The method is used to obtain the antibacterial activity of photocatalytic materials activated by indoor light by contacting a test piece with two bacteria (Staphylococcus aureus and Escherichia coli), under indoor lighting conditions. The test piece is placed in a Petri dish and the bacterial suspension is inoculated onto the test piece. Subsequently, a cover film is placed on the suspension and a humidity conservation glass on the Petri dish. The Petri dish containing the test piece is exposed to indoor artificial light. After exposure, the test bacteria are recovered from the test piece and the cover film using a washing solution and the viable bacteria in the suspension in serial dilutions are counted.

The customer must specify the circumstances where the materials are used, in order to irradiate the material with one intensity or another of radiation. The standard indicates an illuminance or illumination level of 1000 lx ± 50 lx, but indicates that this luminance can be adapted between 100 lx ± 5 lx and 3000 lx ± 150 lx to take into account the actual conditions of use of the photocatalytic material. Furthermore, depending on the actual conditions of use, two ultraviolet light cut-off conditions can be selected: Condition A (interior lighting that transmits optical radiation of more than 400 nm) and Condition B (interior lighting that transmits optical radiation of more than 380 nm).

The exposure time to indoor lighting indicated by the standard is 8 hours. However, the standard also specifies that this time of exposure to indoor lighting can be adapted between 4 and 24 hours to take into account the real conditions where the photocatalytic material will be used, so the applicant must choose it.

For this test, square pieces of the test material measuring 50 ± 2 mm x 50 ± 2 mm, and whose thickness should not exceed 10 mm, are used. Both pieces treated with the photocatalytic material are used, as well as control pieces, with the same characteristics, but without the photocatalytic treatment. The number of test pieces is 15 for each test bacteria (9 untreated pieces and 6 pieces treated with the photocatalytic material). The pieces are used in the following groups: 3 units without photocatalytic product to quantify the inoculum control; 3 units with photocatalytic product and another 3 units without photocatalytic product to keep in the same test chamber without exposure to artificial interior lighting; and 3 units with photocatalytic product and another 3 units without photocatalytic product to keep in the same test chamber with exposure to artificial interior lighting. Therefore, to carry out the complete test, the client must send a minimum of 30 test pieces (18 pieces not treated with the photocatalytic material + 12 pieces treated with the photocatalytic material). However, it is always recommended to send twice the number of pieces required (60 pieces: 36 without photocatalytic and 24 with photocatalytic treatment).

Once the exposure test of the test material to the inoculums and artificial interior lighting has been carried out, the bacteria existing on each of the surfaces are quantified, and the value of the antibacterial activity of the photocatalyst activated with interior light is calculated.

It is recommended to complement this test method with the ISO 22551: 2020 standard for the determination of the bacterial reduction rate of semiconductor photocatalytic materials in indoor lighting environments. This test simulates the conditions of the indoor lighting environment, using bacterial suspensions suspended in a dispersion medium that simulates human sebum.