ISO 17168-1:2025

International
Standard
ISO 17168-1
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 1:
Removal of nitric oxide
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 . 3
5 Principle . 3
6 Apparatus . 3
6.1 Test equipment .3
6.2 Test gas supply .4
6.3 Photoreactor .5
6.4 Light source .6
6.5 UV sharp cut-off filter .6
6.6 Analyser of pollutants .6
7 Test piece . 6
8 Procedure . 6
8.1 General aspects .6
8.2 Pretreatment of test piece .6
8.3 Pollutant removal test . .8
8.4 Elution test .9
9 Calculation . 9
9.1 Calculation method.9
9.2 Amount of NO adsorption by the test piece .9
x
9.3 Amount of NO removed by the test piece .10
9.4 Amount of NO formed by the test piece .10
9.5 Amount of NO desorbed from the test piece .10
x
9.6 Net amount of NO removed by the test piece .10
x
9.7 Nitrogen eluted from the test piece .10
9.8 Recovery of washing with water .11
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
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
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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 17168-1:2018), 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 is based on ISO 22197-1, a test method for air purification performance of photocatalytic
materials under UV light, and is intended to provide a testing method to determine the performance of
indoor-light-active photocatalytic materials with regards to the removal of nitric oxide, enabling swift
distribution of photocatalytic products and thus contributing to a safe and clean environment.

v
International Standard ISO 17168-1:2025(en)
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
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 nitric oxide, 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 certain test pieces that contain a large
amount of adsorbent, due to unattained adsorption equilibrium. 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 7996, Ambient air — Determination of the mass concentration of nitrogen oxides — Chemiluminescence method
ISO 10304-1, Water quality — Determination of dissolved anions by liquid chromatography of ions — Part 1:
Determination of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate
ISO 10523, Water quality — Determination of pH
ISO 14605, Fine ceramics (advanced ceramics, advanced technical ceramics) — Light source for testing
semiconducting photocatalytic materials used under indoor lighting environment
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
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 following terms and definitions 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/
3.1
photocatalyst
substance that performs one or more functions based on oxidation and reduction reactions under
photoirradiation, including decomposition and removal of air and water contaminants, deodorization, and
antibacterial, self-cleaning and antifogging actions; a type of functional fine ceramics
3.2
indoor light
light from an artificial light source for general lighting service that does not include sunlight
3.3
indoor-light-active photocatalyst
photocatalyst (3.1) that performs under indoor light (3.2) irradiation
3.4
photocatalytic material
material in which or on which the photocatalyst is added by, for example, coating, impregnation or mixing
Note 1 to entry: Photocatalytic materials are intended primarily for use as building and road construction materials
to obtain the above-mentioned functions.
3.5
zero-calibration gas
air in which common pollutants are below 0,01 µl/l
Note 1 to entry: Zero-calibration gas is prepared from indoor air using a laboratory air purification system or supplied
as synthetic air in a gas cylinder.
3.6
standard gas
diluted gas of known concentration supplied in cylinders and certified by an accredited laboratory
3.7
test gas
mixture of air and pollutant(s) of known concentration prepared from the standard gas (3.6) or the zero-
calibration gas (3.5), or from the standard gas (3.6) only, to be used for the performance test of a photocatalytic
material (3.4)
3.8
purified water
water with a specific conductivity lower than 1 µS/cm, prepared by the ion exchange method or distillation
3.9
dark conditions
test conditions of no light illumination by the light source for testing and room lighting
Note 1 to entry: Usually, the test gas (3.7) is supplied for comparison with the illuminated reaction.

4 Symbols
f air-flow rate converted into that at the standard state (0 °C, 101,3 kPa) (l/min)
ϕ nitric oxide concentration at the reactor exit (µl/l)
NO
ϕ supply concentration of nitric oxide (µl/l)
NOi
ϕ nitrogen dioxide concentration at the reactor exit (µl/l)
NO2
φ concentration of nitrogen oxides (ϕ + ϕ ) at the reactor exit (µl/l)
NOx NO NO2
ρ nitrite ion concentration in the eluent from the test piece (mg/l)
NO2-
ρ nitrate ion concentration in the eluent from the test piece (mg/l)
NO3-
t time of adsorption, removal or desorption operation (min)
n amount of NO adsorbed by the test piece (µmol)
ads x
n amount of NO desorbed from the test piece (µmol)
des x
n amount of NO removed by the test piece (µmol)
NO
n amount of NO formed by the test piece (µmol)
NO2 2
n amount of NO removed by the test piece (µmol)
NOx x
n amount of nitrogen eluted from the test piece (µmol) [w , w are the first and second elution,
w 1 2
respectively]
V volume of collected washings (ml) [w , w are the first and second elution, respectively]
w 1 2
η fractional recovery of nitrogen
w
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
[2]
illumination by indoor light . Nitric oxide (NO) is chosen as a typical air pollutant that gives non-volatile
[2]
products on the photocatalyst . The test piece, placed in a flow-type photoreactor, is activated by indoor-
[3]
light illumination, and adsorbs and oxidizes gas-phase NO to form nitric acid (or nitrate) on its surface . A
part of the NO is converted to nitrogen dioxide (NO ) on the test piece. The air purification performance is
determined from the amount of the net removal of nitrogen oxides (NO ) (= NO removed – NO formed). The
x 2
simple adsorption and desorption of NO by the test piece (not due to photocatalysis) is evaluated by tests
in the dark. Although the photocatalytic activity is reduced by the accumulation of reaction products, it is
[4]
usually restored by washing with water . The elution test provided gives information about the ease of
regeneration and material balance of the pollutants.
The results of an interlaboratory test are given in Annex A.
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
consists of a test gas supply, a photoreactor, a light source, a UV sharp cut-off filter and pollutant meas
...