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* Corresponding author: jincpark@cau.ac.kr
Mock-up Test for NOx Reduction by Photocatalyst Paint for
Indoor Use
Yong Woo, Song1,, Min Young, Kim1,, and Jin Chul, Park2.*
1Graduate School Students, School of Architecture and Building Science, Chung-Ang University, 06974, South Korea
2Professor, School of Architecture and Building Science, Chung-Ang University, 06974, South Korea
Abstract. In this study, the photocatalyst TiO2 was mixed with a general paint and applied on
indoor walls as part of a mock-up test to measure the reduction in the NOx concentration affected
by the on or off state of a UV lamp. The findings may be summarized as follows; the NOx
concentration was reduced by approximately 7% more (0.134 ppm) with the UV lamp on than
when the lamp was off in the indoor space where the paint mixed with TiO2 was applied.
1 Introduction
In recent years, particulate matter (PM10) have received
much public attention due to their effects on health.
Particularly, in Korea, the level of particulate matter is
relatively higher than that in other major OECD
countries. With many people currently spending more
than 90% of their time indoors, particulate matter have
ultimately become a health threat to indoor residents. To
explore one of the methods of reducing particulate
matter, a mock-up test was conducted in this study, to
examine the performance of TiO2-mixed paint for indoor
use in reducing NOx, one of the main precursors to
particulate matter. This study will prove its usefulness,
as a basic study on the reduction of particulate matter, in
the future.
2 Properties of Photocatalysts
2.1. Material Properties of Photocatalysts
A photocatalyst is a material that generates a certain
reaction in response to light, enabling a chemical
reaction induced only by light. In general, photocatalysts
are used in semiconductors. Some of the most well-
known photocatalysts include zinc oxide, cadmium
oxide, tungsten oxide, and titanium oxide. The
classification in accordance with the material properties
of photocatalysts is shown in Table 1 below:
Table 1. Classification physical property of photocatalyst
Representative
properties
Contents
Crystallization
type
Rutile, Anatase, and Brookite exist, and
Rutile is the most stable
Stability
Very stable material that does not dissolve in
acid, alkali, water, and organic solvents under
normal temperature and pressure conditions
Representative
application
Generally used in toothpaste and cosmetics
2.2. Characteristics of TiO2 as Photocatalyst
Of the four types, the photocatalyst that is used most
widely is TiO2, due to its air-purifying, antibacterial,
deodorizing, and other such features. Specifically, the
photocatalyst may be utilized as shown in Table 2:
Table 2. Characteristics of titanium dioxide photocatalyst
Characteristic
Contents
Representative utilization
Antifouling
Degradation and
removal of pollutants by
superhydrophilic action
Automotive coating
Air Cleaning
Removal of nitrogen
oxides and sulfur oxides
in air
Air-purification artificial
plants, Building wall
coating
Antibacterial
Oxidation of organics by
OH radicals
Air-conditioner filter
Deodorization
Removal of VOCs and
odors
Clothes-deodorizing
device
Water
Purification
Wastewater treatment
Factory wastewater and
sewage treatment facility
Air purification of TiO2 photocatalysts is done through
oxidation reactions, and oxidation reactions to NOx used
in this experiment are shown in Table 3.
Table 3.
Photocatalytic oxidation mechanism of nitrogen oxides
Activation
TiO2 + hv* → h+ + e-
Absorption
H2O(g)+Site** →H2Oads, O2(g) + Site** → O2ads
NO(g)+Site** → NOads, NO2(g)+Site** → NO2ads
Hole trapping
H2O + h+ → ㆍOH+H+
Electron trapping
O2+e-→O2-
Hydroxyl attack
NOads+2ㆍOH→NO2ads+H2O
NO2ads+ ㆍOH→HNO3
Superoxide attack
NO+O2-→NO3-
* hv : (UV), **Site : Surface of TiO2
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© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative
Commons Attribution License 4.0
(http://creativecommons.org/licenses/by/4.0/).
3 Mock-Up Test
3.1. Introduction
For the purpose of the study, TiO2 – known for its air-
purifying property – was mixed with a general paint and
applied on the walls inside a mock-up test room (2,675 ×
2,750 × 2,860). To confirm the air-purifying effects of
TiO2, a UV lamp was used, since light energy is not as
readily available in indoor spaces as in outdoor spaces.
After the TiO2-mixed paint was applied on the walls,
NOx, one of the major precursors to particulate matter,
was injected, in the form of a gas, into the room until a
certain level of concentration (2 ppm) was attained.
Thereafter, the changes in the concentration were
measured with the UV lamp turned on and off. The
indoor temperature was set at 25 °C. The details are
shown in Fig. 1 and Table 3.
Fig. 1. Mock-Up Test Plan & 3D Picture
Table 3. Mock-Up Test Summary
Classification
Contents
Test Gas
NO gas
UV Lamp
UV-A BLB lamp, 0.505 mW/cm2
Number of Experiments
UV ON-OFF 3 times, total 6 times
Measurement Interval
1 min
Measurement Instrument
Chemiluminescence instrument
Measurement Time
3 hours after attaining 2 ppm
concentration in test room
3.2. Mock-Up Test Result
Considering the margin of error, three tests were
conducted to use the average value. Fig. 2 shows the
NOx concentration rising to 2 ppm after the precursor
was introduced into the closed mock-up test room
painted with TiO2-mixed paint.
Fig. 2. NOx Concentration Rise Graph
When the NOx concentration reached 2 ppm in the
closed room painted with TiO2-mixed paint, the
introduction of NOx was stopped. Fig. 3 and Table 4
show the reduction in the NOx concentration three hours
after turning the UV lamp on/off. The values indicated
on the graph are the averages taken from three tests, each
conducted with the UV lamp on/off.
Table 4. Mock-Up Test Result
Classification
UV OFF
UV ON
Concentration
difference
Start Concentration
2.028 ppm
2.038 ppm
+0.01 ppm
End Concentration
0.959 ppm
0.825 ppm
-0.134 ppm
Fig. 3. NOx Concentration According to Status of UV Lamp
It was found that in the closed room where TiO2-mixed
paint was applied on the walls, the NOx concentration
was approximately 7% (0.134 ppm) lower with the UV
lamp on than with the lamp off.
4 Conclusions
The findings of this study can be summarized as follows;
In the mock-up test on an internal space where TiO2 with
air-purifying property was mixed with a general paint
and painted on the wall, the reduction in the NOx
concentration was measured to compare the on and off
states of a UV lamp. It was found that in the indoor
space where TiO2-mixed paint was used, the NOx
concentration was approximately 7% (0.134 ppm) lower
with the UV lamp on than with the lamp off.
References
1. Y.K. Jang, Status and Problems of Fine Dust
Pollution, Journal of Environmental Studies, Vol. 58,
2016. 09.
2. S.D. Kim, C.H. Kim, The Physico-chemical
Character of Aerosol Particle in Seoul Metropolitan
Area, The Seoul City Research, Vol. 9, 2008. 09
3. Zhang Jinhui, Li Si, Chen Lang, Pan Yi, Yang
ShuangChun, The progress of TiO2 photocatalyst
coating, IOSR Journal of Engineering, 2, 8, 50-53,
4. Juan Zhao, Xudong Yang, Photocatalytic oxidation
for indoor air purification, Building and
Environment, 38, 645-654, 2003
Acknowledgements
This research was supported by a grant (19SCIP-B146251-02)
from the Infrastructure and Transportation Technology
Promotion Research Program funded by the Ministry of Land,
Infrastructure and Transport of the Korean government.
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