ISO 17168-2:2025

International
Standard
ISO 17168-2
Second edition
Fine ceramics (advanced ceramics,
2025-11
advanced technical ceramics) —
Test method for air-purification
performance of semiconducting
photocatalytic materials under
indoor lighting environment —
Part 2:
Removal of acetaldehyde
Reference number
© ISO 2025
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 2
5 Principle . 2
6 Apparatus . 3
6.1 Test equipment .3
6.2 Test gas supply .4
6.3 Photoreactor .4
6.4 Light source .4
6.5 UV sharp cut-off filter .4
6.6 Analytical system for acetaldehyde . .4
6.7 Analytical system for CO .6
7 Test piece . 6
8 Procedure . 6
8.1 General aspects .6
8.2 Pretreatment of test piece .7
8.3 Preparation for the test .7
8.4 Pretest .7
8.5 Test of acetaldehyde removal and CO conversion .7
8.6 Test of acetaldehyde removal (when CO concentration cannot be measured) .8
9 Calculation . 9
9.1 Calculation method.9
9.2 Removal percentage and removed quantity of acetaldehyde .9
9.3 Conversion to CO .10
10 Test method for test pieces with lower performance .11
11 Test report .11
Annex A (informative) Results of an interlaboratory test .12
Bibliography . 14

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
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with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
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Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
This second edition cancels and replaces the first edition (ISO 17168-2:2018), which has been technically
revised.
The main changes are as follows:
— normative reference to ISO 24448 added to Clause 2 and 6.4.
A list of all parts in the ISO 17168 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
A photocatalyst is a substance that performs decomposition and removal of contaminants, self-cleaning,
antifogging, deodorization and antibacterial actions under photoirradiation. Its application has expanded
considerably in recent years. The application of photocatalysts for indoor spaces has increasingly been
sought as a solution to indoor environmental problems. Since conventional photocatalysts are responsive
only to ultraviolet light, studies have been made to develop an indoor-light-active photocatalyst that makes
effective use of indoor light, which room lights mainly emit, and thus demonstrates high photocatalytic
performance indoors. The development has recently led to the commercialization of various indoor-light-
active photocatalytic products, and there has been demand for the establishment of test methods to evaluate
the performance of this type of photocatalyst.
This document, with ISO 17168-1 and ISO 22197-2 as the basis, is intended to provide a testing method to
determine the performance of indoor-light-active photocatalytic materials with regards to the removal of
acetaldehyde, a representative lower aliphatic volatile organic compound (VOC), enabling swift distribution
of photocatalytic products and thus contributing to a safe and clean environment.

v
International Standard ISO 17168-2:2025(en)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Test method for air-purification performance
of semiconducting photocatalytic materials under indoor
lighting environment —
Part 2:
Removal of acetaldehyde
WARNING — The use of this document can involve hazardous materials, operations and equipment.
It is necessary to check that there are no leaks from the gas flow paths, and to properly dispose
of exhaust gas and wastewater. This document does not purport to address all of the safety or
environmental problems associated with its use.
1 Scope
This document specifies a test method for the determination of the air-purification performance, with regards
to removal of acetaldehyde, of materials that contain a photocatalyst or have photocatalytic films on the
surface, usually made from semiconducting metal oxides such as titanium dioxide or other ceramic materials,
by continuous exposure of a test piece to the model air pollutant under illumination from indoor light.
This document is applicable for use with different kinds of materials, such as construction materials
in flat sheet, board or plate shape, which are the basic forms of materials for various applications. This
document also applies to materials in honeycomb form, and to plastic or paper materials containing
ceramic microcrystals and composites. This document does not apply to powder or granular photocatalytic
materials.
This test method is usually applicable to photocatalytic materials produced for air purification. This
method is not suitable for the determination of other performance attributes of photocatalytic materials, i.e.
decomposition of water contaminants, self-cleaning, antifogging and antibacterial actions.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 4224, Ambient air — Determination of carbon monoxide — Non-dispersive infrared spectrometric method
ISO 14605, Fine ceramics (advanced ceramics, advanced technical ceramics) — Light source for testing
semiconducting photocatalytic materials used under indoor lighting environment
ISO 16000-3, Indoor air — Part 3: Determination of formaldehyde and other carbonyl compounds in indoor and
test chamber air — Active sampling method
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
ISO 17168-1, Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for air purification
performance of semiconducting photocatalytic materials under indoor lighting environment — Part 1: Removal
of nitric oxide
ISO 24448, Fine ceramics (advanced ceramics, advanced technical ceramics) — LED light source for testing
semiconducting photocatalytic materials used under indoor lighting environment
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 17168-1 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Symbols
f air-flow rate converted into that at the standard state (0 °C and 101,3 kPa) (l/min)
ϕ acetaldehyde volume fraction at the reactor exit (µl/l)
A
ϕ acetaldehyde volume fraction at the reactor exit under dark conditions (µl/l)
AD
ϕ volume fraction of acetaldehyde in the test gas (µl/l)
A0
ϕ CO volume fraction generated by indoor-light irradiation (µl/l)
CO2 2
ϕ CO volume fraction at the reactor exit under indoor-light irradiation (µl/l)
CO2,L 2
ϕ CO volume fraction at the reactor exit under dark conditions (µl/l)
CO2,D 2
ϕ CO volume fraction in the dark before indoor-light irradiation (µl/l)
CO2,Dpost 2
ϕ CO volume fraction in the dark after indoor-light irradiation (µl/l)
CO2,Dpre 2
n quantity of acetaldehyde removed by the test piece (µmol)
A
n quantity of CO converted from acetaldehyde per hour (μmol/h)
CO2 2
R removal percentage, by test piece, of acetaldehyde (%)
A
R conversion from acetaldehyde to CO (%)
CO2 2
5 Principle
This document deals with the development, comparison, quality assurance, characterization, reliability and
[1]
design data generation of photocatalytic materials . 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 indoor-light. Acetaldehyde (CH CHO) is chosen as a typical volatile organic compound (VOC)
[2]
with lower molecular mass and offensive odour . The test piece, placed in a flow-type photoreactor, is
activated by indoor-light illumination, and adsorbs and oxidizes gas-phase acetaldehyde to form carbon
[3]
dioxide (CO ) and other oxidation products . The air-purification performance is determined from the
amount of acetaldehyde removed by the test piece (μmol). The simple adsorption by the test piece (not due
to photocatalysis) is evaluated by the tests in the dark. However, some test pieces are very absorbent, and
it is possible that a stable volume fraction of acetaldehyde is not attained in the designated test time. The
photocatalytic activity depends on the physical and chemical properties of pollutants, mainly due to the
adsorption process involved. For a better evaluation of the air purification performance of photocatalytic
materials, it is recommended that one or more suitable test methods are combined, as provided in other
parts of the ISO 17168 series.
The results of an interlaboratory test are given in Annex A to demonstrate the validity of this test method.

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 a test method for the removal of nitric oxide (see ISO 17168-1) and consists of a test gas
supply, a photoreactor, a light source, a UV sharp cut-off filter and pollutant measurement equipment. Since
low-volume fractions of pollutants are to be tested, the system shall be constructed with materials of low
adsorption and resistant to ultraviolet (UV) radiation. An example of a testing system is shown in Figure 1.
Key
1 test gas supply
2 air compressor
3 air-purification system
4 standard gas (pollutant)
5 pressure regulator with a gauge
6 mass-flow controller
7 humidifier
8 gas mixer
9 four-way valve
10 photoreactor
11 test piece
12 airtight optical window
13 light source
14 sharp cut-off filter
15 analyser
16 vent
Figure 1 — A schematic of the testing equipment

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 and so on. The flow rate of each gas shall be within 5 % of the designated value,
which is easily attained by using thermal mass-flow controllers with knowledge of temperature and gas
type at calibration in accordance with ISO 6145-7. The expression of gas flow rate in this document is that
converted to the standard state (0 °C, 101,3 kPa). 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 + O , such as supplied in cylinders) shall be used for dilution when the CO from
2 2 2
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
airtight 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 shall be used for the window.
6.4 Light source
A cool white halophosphate fluorescent lamp and a UV sharp cut-off filter in accordance with ISO 14605 or
LED light source in accordance with ISO 24448 shall be used. The test piece shall be illuminated uniformly
through the window by the light source. When testing honeycomb-form photocatalysts, the light source
shall illuminate 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 illuminance
at the test piece surface is 6 000 lx ± 300 lx. The illuminance along the length of the test piece shall also be
constant within ±5 %. The illuminance shall be measured with an illuminance meter which conforms to
ISO 14605 in the case of using halophosphate fluorescent lamps or to ISO 24448 in the case of using LED
light source. The reactor and light source shall be shielded from external light. The parts around the light
source, such as luminaire and shielding device, shal
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