THE EFFECT OF PHOTOCATALYTIC BUILDING MATERIALS IN URBAN DEPOLLUTION Th. Maggos, D. Kotzias, J.G Bartzis, N. Moussiopoulos
Photocatalysis provides a very promising solution for pollutants removal compared with other technologies Pollutants are oxidized Energetically interesting process: a) It operates near ambient temperature b) Use solar energy to initiate photocatalytic reactions O 2 Reduction UV CO 2 e - TiO 2 h + O.- 2 Organic OH. Compound s Oxidation H 2 O UV H 2 O TiO 2 is considered to be the most promising material for the treatment of air pollutants due to its highly strong oxidative ability TiO 2 introduction in building matrix or surface coating could give to the material self cleaning and depolluting activities These are two fields in which Research and Development activities have widely increased the recent years.
Photo-catalytic Innovative Covering Applications for De-pollution Assessment www.picada-project.com The core issue of PICADA, is the development and validation of new building coverings capable of reducing the pollution (air and aesthetic).
PRINCIPLE OF HETEROGENEUS PHOTOCATALYSIS Institute of O 2 Reduction UV CO 2 Conductance band Valence band e - TiO 2 h + O.- 2 Organic OH. Compound s Oxidation H 2 O H 2 O UV The self-cleaning and de-polluting abilities arise from the photocatalytic properties of titanium dioxide which can be introduced either in the building matrix or surface coatings. Such materials, when exposed to solar UV rays, will act as a catalyst for the photoinduced decomposition of organic molecules adsorbed on its surface.
Photo-catalytic Innovative Covering Applications for De-pollution Assessment The main technical and scientific objectives of the project are to: Achieve a better understanding of the processes/mechanisms controlling the photo-catalytic surface reaction regulating the de-soiling and de-polluting activity of the innovative building coverings on NO x, VOC S, O 3 combined pollutants Develop manufacturing and application methods to increase materials performances while reducing their costs. Assessment of the cost and durability performances of the innovative coverings Develop a numerical model for prediction of photo-catalytic behaviour at micro-scale under different exposure conditions Develop a numerical model for predicting the de-soiling and de-polluting activities of the coverings at micro-scale under realistic urban scale climate and environmental exposure conditions ; Validate, through a complete real scale study, results coming from laboratory and scale models Give guidelines to end-users (property owners, municipalities) for a successful exploitation of results.
LIGHT + AIR + RH VOCs + NO X + O 3 POLLUTANTS ADSORPTION AND DEGRADATION DESOILING AND DEPOLLUTING EFFECT O 2 TiO 2 TiO 2 TiO 2 TiO 2 TiO 2 TiO 2 TiO 2 MATERIAL MATRIX In the frame of PICADA project two types of materials were tested: a cement-based mortar an organic translucid film
THE PROJECT WORKPLAN 1. Lab scale tests in order to evaluate the photocatalytic efficiency of the materials on NOx, VOCs and O 3 degradation. Selection of the most promising materials. 2. Macro scale tests of the selected materials in order to validate previous results and perform experiments on more complicated systems 3. Exposure of the selected materials under real environmental conditions. Application on artificial street canyons (Pilot site tests) 4. Real scale tests
1. Lab scale tests Chamber Features Volume.... 0,45m 3 Temperature on sample... 23-30 o C Relative Humitidy...47-56% Airflow on sample surface....0.2m/s Specimen area...780 cm 2 (8 samples) loading factor... 0,14 m 2 /m 3 (JRC, Ispra IT)
Fundamental parameters NO, O 3, NO 2.......~250 ppb U.V lamp.... 300W (Osram ultravitalux) Distance lamp-sample 50cm Irradiation time... 6 hours Total irradiance of U.V.A 6.8 W/m 2
Experimental procedure for the evaluation of air pollutants removal due to photocatalytic oxidation NOx outnox inno (%) in NO removal 100 x x Inside the chamber, the incoming pollutant are consumed by four (4) mechanisms: 1. Sink effect (on the walls of the chamber) 2. Absorption on the surface of the sample 3. Photocatalytically by U.V light 4. Photocatalytically by TiO 2 and U.V light. Therefore, the measurement can give information on the TiO 2 activity provided that the above side effects 1-3 have been calculated.
Chart 3. NO experiment: a)sink b) absorption, photocatalysis on sample A3 (3% TiO2 PC 105) 110 100 % NO concentration 90 80 70 60 50 40 U.V on 84% 77% 70% 30 20 10 0 0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 Tim e NO sink (no U.V) NO sink ( U.V) A3 sam ple + NO (no U.V) A3 sam ple + NO + U.V 8 cementitius and 8 organic translucent samples were tested and the materials with the best photocatalytic efficiency were selected Criteria for the selection: % photocatalytically degradation, the photocatalytic rate and the deposition velocity. The photocatalytic characteristics of the selected materials are described below:
2. Macro-scale tests Institute of Chamber Features Volume.....30m 3 Temperature.... 23 o C Relative humidity........50% Airflow on sample surface...0.13-0.2m/s Specimen area....4m 2 loading factor...0,13 m 2 /m 3 (JRC, Ispra IT)
FUNDAMENTAL PARAMETERS NO, O 3, NO 2.........~250 ppb U.V lamp........4x300w (Osram ultravitalux) Distance lamp-sample..150cm Irradiation time.... 7 hours UVA radiation.4.6 W/m 2 (centre) 2.1 W/m (corner) (JRC, Ispra IT)
Mixture + Organics (Benzene, Toluene) Translucent A (100% TiO2) BENZENE Experiments Tanslucent A (100% TiO2) TOLUENE experiments 110 110 100 100 90 90 80 80 70 70 % Concentration 60 50 % Concentartion 60 50 40 30 20 Sink Sink + U.V Benzene blank Benzene + U.V NO + BENZENE+U.V 40 30 20 Sink Toluene blank Sink + U.V Toluene + U.V 10 10 NO + TOLUENE+U.V 0 0 100 200 300 400 500 600 Time 0 0 50 100 150 200 250 300 350 400 450 50 Time The presence of NO promoted the photocatalytic rate of Toluene while it doesn t seem to affect Benzene 1) + 2. 2 +. 2) VOC + OH.. COx
Tanslucent A (100% TiO2) NO experim ents 110 100 90 80 % Concentration 70 60 50 40 sink sink + UV A (100% TiO2) BLANK A (100% TiO2) Photo A (100% TiO2) NO + TO LUENE U.V A (100% TiO2) NO + BENZENE U.V 30 20 10 0 0 50 100 150 200 250 300 350 400 450 500 The photocatalytic rate of NO decreased with the presence of Benzene or Toluene. The formation of intermediate organic radicals act competitive with NO for the adsorption sites on the TiO 2 surface reduction of NO photocatalytic rate Tim e
3. Application of the selected materials on pilot street cayon Institute of Description of site 3 series of canyon streets at a scale of 1:5 length: 20m, Width: 2m, Height: 5m One street is covered with TiO 2 treated mortar and the other with the similar mortar panels but without TiO 2 (reference) A gas emission source connected to a perforated pipe has been installed in the tested canyon.
3. Application of the selected materials on pilot street cayon Institute of Measurement parameters Gas velocity, temperature and composition from the pollution source were measured partially during the day Continuous NOx measurements on both sides of TiO 2 and reference canyon in the middle axis VOCs sampling twice a day in canyon and background Background NOx and O 3 measurements on the top of the canyon Meteorological parameters (WD, WS, T, RH, solar irradiation)
Measurement time schedule Four weeks measurements in each canyon (9/7 11/8 in TiO 2 canyon) (11/8 3/9 in reference canyon)
4. Real scale tests Institute of