1. Research and Development Department of United Global Pavings
PHOTOCATALYTIC PAVEMENT IN ORDER TO REDUCE AIR POLLUTANTS IN THE ATMOSPHERE OF A CITY
Research and Development Department
of United Global Pavings

2. What is Photocatalysis?
A chemical reaction in which the combined effect of light and a photocatalyst accelerates the decomposing process of a given air pollutant. Consequently, it promotes the removing of the main pollutant components found in our urban areas
Application of photocatalysis, especially photocatalysis using a semiconductor particulate system, points to be the most appropriate method in order to decompose toxic compounds into non-hazardous products, instead of the conventional oxidizing processes

3. Air pollutants
A wide range of pollutants can be removed by photocatalysis: NOx, SOx, volatile organic compounds (VOCs), CO, metil mercaptane, formaldehide, chloride organic compounds, acetaldehide, polyaromatic compounds. 3

4. Mecanism of pollutants removing
Ultra Violet light was the only light capable of carrying out the reaction. But only a small portion of the solar radiation belongs to this light fraction
Progresses in the synthesis of new photocatalysts have achieved an increase in the removal yields also under visible light
Photon absorbed on the semiconductor
It is generated the electron-whole pair
High oxidazing processes 4

5. Mecanism of pollutants removing
When the electron-hole is promoted, oxygen and water in the air form O2- and -OH radicals, respectively. These kinds of radicals have a high oxidizing effect and this way, they oxidize a large amount of pollutants producing CO2 and water. We have to take into account that the amount of CO2 formed is negligible and not relevant for the greenhouse effect and global warming. 5

6. Mecanism of NOx removing
Photocatalytic tile
The pollutant is adsorbed on the surface of the floor tile
The adsorbed pollutant is oxided to an inert component, nitrate ion (NO3-)
The inert component is removed from the surface of the tile
CNO3-(max) = 0,5 molecula·nm-2
(Ohko et al., 2009) 6

7. Titanium dioxide (TiO2)
Natural minerals
rutile
anatase
Applications
As a pigment
To provide whiteness and opacity to paints, plastics, food, medicines, paper, toothpastes…
Cosmetics
Sunscreen
Band gap = 3.2 eV
As a photocatalyst 7

8. Applications of TiO2 as a photocatalyst8

9. Applications of TiO2 as a photocatalyst9

10. Tiles production
The photocatalyst is supplied by one of the biggest company in the production of photocatalyst in the world.
It is a modern photocatalyst which is impregnated with other metal in order to improve its behaviour
The dose of the catalyst has been adjusted after several experiments in order to obtain the highest efficiency for pollutant removal
The addition of the photocatalyst is carried out optimizing pollutant removal yield and manteining mechanic properties of pavement 10

11. Experiments procedure
NOx has been analyzed in order to test the photocatalytic properties of the manufactured tiles
The operation conditions have been limited to ISO , simulating real conditions
Air flow
C NO S tr
Radiation
humidity
1 l/min
1 ppm
300 cm2
18 s
1mW/cm2 %
Experimental equipment used for the tests
Heated analyzer of NOx CLD-700-AL-NO/NOx of ECO PHYSICS 11

12. Test results
In this moment the
lamp is switched on 12

13. Test results, catalyst discrimination
NOx removal test
Sample
Relative humidity
5 %
25 %
50 %
75 %
BE1
NOx removal
64,3
62,2
56,5
52,3
NO oxidize
4,5
BE2
67,4
59,1
52,8
37,4
3,6
5,8
BE3
63,0
53,4
45,5
24,4
1,2
6,1
9,4
BE4
66,3
60,1
50,2
41,5
4,4
Catalyst efficiency is very similar in all cases, 65 % at 5 % humidity.
Catalyst efficiency is highly dependent on humidity.
BE1 catalyst achieves 65 % of efficiency and is the least dependent on humidity, 52% at 75 % humidity. 13

14. Test results, humidity
For BE1 catalyst, the humidity has a slight negative effect on the removal yield of NOx. The highest removal yield (64 %) has achieved with 5 % of relative humidity.
NOx removal yield tends to a minimum of 50 % at high relative humidities.
Since relative humidity in a year has an average of 64 % in New York, a 54 % of NOx removal yield would be reached.
Figure 3. Effect of humidity on NOx removal yield 14

15. Test results, saturation
Pavement behaviour is very stable, keeping around 60 % of NOx removal yield for 81 h.
The tile could work at least for 8 days, without requiring water in order to remove the nitrates which decreases the removal yield. Therefore, Ecosit™ can be used in a place where rain is not frequent.
Figure 4. Effect of saturation time on NOx removal yield 15

16. Extrapolation of test results
NOx removal yield results (64 %) ensure efficient photocatalytic action in order to clean a polluted atmosphere with a concrete tile. The results obtained are within the range other type of materials have achieved in similar uses ( %).
Field tests are limited and their results are different ( %). Nevertheless, results point towards a satisfactory reduction in the amount of air pollutants in urban areas.
16 mg NO/m3 valor máximo 16

17. Conclusions
Photocatalysis is an emergent process supported by 40 years of research and some thousands of scientific publications. It points to be the most aproppiate treatment for air pollutants.
The fact that the photocatalyst can be mixed with the concrete is a very interesting aspect for air pollutants reduction due to the obligatory and spreading use of concrete pavament in urban areas.
Titanium oxide is a non hazardous material.
NOx removal yield of 64 % can be reached under favorable conditions.
Photocatalyst does not deactivate in this application but can be saturated, not before 10 sunny days. In order to avoid it, only cleaning water or rain water is necessary. 17

18. PHOTOCATALYTIC PAVEMENT TO REDUCE AIR POLLUTANTS IN THE ATMOSPHERE OF A CITY
THANKS FOR YOUR ATTENTION
Research and Development Department
of United Global Pavings 18