Experimental Use of TiO2 Nanoparticles for Reducing Pollutant Depositions on Road Aime' Lay-Ekuakille2, Sabino Maggi3
Filippo Gandolfo1, Dino Erdfeld1
2
Dept. of Innovation Engineering, University of Salento 73100 Lecce, Italy 3 CNR-IRSA, National Research Council, 70100 Bari, Italy
1
Evagrin Srl, Research Division 91018 Salemi, Italy
[email protected]
Abstract — Atmospheric deposition of pollutants is a major challenge for the environmental governance and management of cities. Different depositions could be harmful especially on ground and roads. In particular, in areas were industrial activities are located and/or significant car traffics occur, depositions on roads are harmful for all people especially for pregnant women who will be attacked as well as other people. The main effects are risks of breathing pathologies and possible cancer as a long-term consequence. The main objective of this research is to illustrate the latest achievements in terms of the use of titanium dioxide to be spread on a road as a cover film to neutralize pollutants as NOx, SO x , NH 3 , CO, dusts and aromatic substances. The removal is performed by means of a photocatalytic reaction. The nanoparticles play a key role in this process. The paper show some experimental and interesting results. Index Terms— TiO 2 , nanoparticles, chemical characterization, measurement, road pollutants and depositions, nanotechnology, instrumentation, photocatalysis.
F=
c(0) rs
in which r s is the surface resistance s (m-1) depends only upon the affinity of the surface for the particular pollutant under test. The above flux [2] is connected to vertical dispersion coefficient denoted as K z , so that
F = K z ( z)
F=
c( z ) − c(0) rg ( z )
F c
(1)
with F (g m-2 s-1) as the pollutant deposition flux and c (g m-3) the pollutant concentration. This equation can be parameterized to describe the wet deposition. Using the a specific description [1] in case of concentration c(0) is not too high at the surface and if the trend of sorption is considered proportional to the concentration c(0). At these conditions the concentration flux at the surface is
(3)
(4)
where z
rg ( z ) = ∫
I. INTRODUCTION
Vd =
∂c ∂z
that yields, by means of an integration, to
0
Depositions from emissions sources impact directly on people and lands. Two types of deposition are generally considered in terms of mechanism, that is, dry deposition and wet deposition. With deposition we intend here, deposition of pollutants produced by emission sources, as for instance the uptake at the surface of the earth (dry deposition) and droplet precipitation or impaction on the surface of earth (wet deposition). We start with wet deposition: given the deposition V d ,, it can be defined as
(2)
dz ' Kz (z' )
(5)
With the combination of Eq.2 and Eq.4 we obtain the following:
F=
c( z ) rs + rg ( z )
(6)
that is the overall resistance r(s) to deposition is simply the additive sum of the resistance sequentially encountered by the pollutant in its trajectory to its final destination. We can also express the total resistance as
r ( z )= rs + rg ( z )
(7)
to expressed in terms of deposition velocity through
Vd= ( z)
1 F = r ( z ) c( z )
(8)
The resistance at the surface r s is a function of the physical and chemical properties of the surface and the pollutant and is not easy to assess.
Wet deposition is produced by precipitation scavenging and surface deposition of fog and cloud droplets. Unlike dry deposition, it is a reaction that takes place in lower layers of the planetary boundary lay (PBL). According to [3], the wet flux of a pollutant to the surface is described by the following equation ∞
∫ Λ( z, t )c( x, y, z, t )dz
Wg =
(9)
0
and for gaseous fluids ∞
Wp =
∫ Λ(d
p
, z , t ) c(d p , x, y, z , t ) dz
(10)
0
b c − )(O2 + 3.773 N 2 ) → 4 2 b b c aCO2 + H 2O + 3.773(a + − ) N 2 2 4 2
Ca H bOc + (a +
(14)
where constants a, b, c describe the propellant composition, O 2 + 3.773*N 2 is the oxidant. The soot contains a lot of pollutants but only a few numbers are under specific regulations of different countries; they are: carbon monoxide (CO), unburnt hydrocarbons (HC), oxides of nitrogen (NO x ), and specifically particulate for diesel engines. II. POLLUTION
REDUCTION PHOTOCATALYSIS
WITH
NANOPARTICLES
The use of titanium dioxide (TiO ) to reduce pollutant components is a well-known technique used at least 40 years ago, needing an ultraviolet light produced by sun and/or artificial lightning. There is a great concern about pathologies and impairments [7] [8] related to human exposure to pollutants. TiO can be considered as one of the few and best photocatalyst for the abatement of pollutants in fluids, namely gaseous and aqueous. Its effectiveness has been proved since it is triggered by ultraviolet (UV) light band, and especially around 365 nm as wavelength thanks to its high photoactivity, chemical stability [9] and non toxicity. The proposed chemical solution is based on particle size (nanoparticles) that influences the photocatalytic activities that depend upon surface area, particle size and crystal phase. Therefore, with the reduction of particle size we obtain the decreasing of the bulk recombination of electrons photogenerated and holes pairs at the inner of TiO crystalline, that enhances the photoactivity. The developed product proposed here, Tirex35® [10], is an innovating paint that is different from others [11] [12] because, a part from nitrates produced by the reaction of titanium dioxide with NO 3 , there is a few and negligible production of NO 2 . The product also contains silicates of potassium, high-purity quartziferous inerts and appropriate additives. The proposed paint has been proved and tested in many laboratory according to EN 11247. As it will be illustrated in the next section the rate of abatement of NO x is greater than 35%. The paint is also able to reduce mainly the following pollutants: NO x , SO x , NH 3 , CO, thin dusts, aromatic and polycondensed substances, etc.. The paint exhibits other interesting features as for example, anti- bacteria action and anti-mould due to the oxidation by photocatalysis of specific elements. As recalled in [12], it is difficult to purify (to reduce pollutants) in three-dimensional spaces than in two-dimensional spaces because of two main reasons: the overall amount of requested reactant is higher in three-dimensional spaces than in double – dimensional spaces; the effectiveness of photocatalysis is proved in doubledimensional spaces. That is why the proposed formulation, using nanoparticles, is of interest since it overcomes the above reasons or limitations. TiO has also proved its effectiveness in contaminated land and water purification. For the first case the 2
for particles, where Λ is the washout coefficient and c the concentration expressed, for particles, as a function of the particle diameter d p . The knowledge of the wet flux W (W g or W p ) [4] allows the definition of the wet deposition velocity
Vw =
W ΛH c( x, y, 0, t )
(11)
where the last relationship assumes that the pollutant is uniformly distributed between z=0 and z=H. the wet deposition velocity V w can be calculated by
Vw = wr p0
(12)
where w r is the species-specific washout ratio, that is for example, the concentration of material in surface-level precipitation divided by the concentration of material in surface-level air, and p 0 is 2.8 10-7ms-1 (corresponding to a typical light rainfall of 1 mm h-1), hence V w =28 cm s-1, that yields, for H=1000 m, to
Λ =2.8 10-4 s-1.
Beyond depositions from industrial emissions, depositions on road are also due by car traffics on road. This phenomenon is related to the combustion process of the car motor [5]. The fuel used in cars is a mixture of diverse hydrocarbons, taking into account the presence eventual oxygenated compounds. It is well-know that the general equation of internal combustion engine is the following:
Combustible + Oxidant → Pr oduct of combustion
(13)
The ideal and full combustion reaction is then illustrated by means [6] of the following:
AND
2
2
2
formulation is able for protecting soil and land against abnormal modifications and activities [13] [14]. It also finds application in water purification to avoid surface and subterranean waters to be contaminated [15].
The aforementioned performance on a surface of 150,000 m2 yields to save around 4,500 ton/year of NO x in terms of emissions. The samples taken from the road, as depicted in fig.3, have been characterized in laboratory.
III. EXPERIMENTAL ACTIVITIES AND RESULTS The experimental activities have been performed on roads in Sicily in the period of july and November 2015. The paint has been applied in noctitime conditions so that people can directly use the road in the morning. Fig.1 illustrates the look of the application on road. The color of asphalt changes from dark to light grey because of the nanocrystals encompassed in the interstices and arises as a new look. Fig.3 Samples of treated asphalt.
Fig.1 Features of TiO 2 usage on road: before (left), immediate application (center) and after usage (right).
The following features have been recovered as performances: applied amount: 160-200 gr/m2 application system: high-pressure atomization index of abatement on road: 40-70% percentage of abatement in air: 1.2-9.3%
Fig.4 Attenuation of NO and NO x in the range of photocatalysis using a lamp with UV wavelength.
Fig.2 Current look of the road after treatment with TiO 2 paint.
Changes in road color are not a problem since the efficiency of the application is related to draining asphalt (see fig.2). This latter, even expensive than normal asphalt, allows a complete achievement of the paint performance in a long time. The paint is not indicated, in terms of efficiency and effectiveness, for normal asphalt because its surface is not open and it is easily removed by car traffic on the road. The normal or smooth asphalt does not preserve the nanoparticles of TiO2. Conversely, that allows the reaction on air pollutants producing an air cleaning, reducing targeted pollutants for a long time.
The attenuation of pollutants is immediate according to fig.4 in the photocatalysis range of 45 minutes. That is the confirmation of the effect of nanoparticle within TiO2 formulation with a low production of NO 2 . Different samples have been characterized for road applications with the same and efficient performance. In the event of NO x abatement, the results are nitrates; analogously for targeting SO x , the results are sulfates. The question is: what is worse? air pollution or salts on soil and subsoil? The answer is simple: it is preferable to have salts in soil and subsoil to be removed by rain and recovered in water to be collected in municipal black sewer. Nitrates and sulfates can be retrieved for other utilization using traditional system as for example sewage plants with a special unit called denitrification section: De-nitrification can be carried out using both heterotrophic and autotrophic bacteria. A further interest is the possibility and/or opportunity to retrieve eventual and residual quantity of non converted TiO 2 in salts, that is nitrates and sulfates. That is a matter of further deep research in the field of water treatment or to use this eventual amount for reclaiming contaminated lands. That is a strategy to exploit TiO 2 for a different application than direct emission reduction from combustion process [16].
IV. CONCLUSIONS This paper has illustrated the research carried out with Evagrin research laboratory in cooperation with scientific community. The main scope of the research is to use nanoparticles-based TiO2 paint to reduce and/or remove a large amount of specific pollutants disseminated in the air. A new formulation has been proposed and tested on the field. The innovation paint is able to react with either dry or wet deposition described in the introduction section. The dimension of crystals is essential since it reacts with the wet flux and deposition resistance (dry deposition) respectively. This is a key issue for a major targeting of pollutants. The results show that the efficiency and effectiveness of the formulation is higher than others for road applications. A further unexpected application could be soil reclamation using the eventual unconverted part of titanium dioxide. In any case, retrieval of ultrafine TiO2 particles from suspension after photodegradation process is a hard work, which limits their practical applications. But the control of photodegradation can be made by means of biosensors using beamforming techniques [17]. REFERENCES [1] J.A. Garland, “Dry and wet removal of suphur from the atmosphere”, Atmos. Environ., Vol.12, pp.349-362, 1978. [2] G. Andria, A. Lay Ekuakille, M. Notarnicola, “ Mathematical Models for Atmospheric and Industrial Pollutant Prediction”, XVI IMEKO World Congress , Vienna, Austria, September 2528, 2000 [3] J.H. Seinfeld, “Atmospheric Chemistry and Physics of Air Pollution”, John Wiley, New York, 1986. [4] B.C. Scott, “Theoretical estimates for scavenging coefficient for soluble aerosol as function of precipitation type, rate, and altitude”, Atmos. Environ., Vol.16, pp.1735-1762. [5] A. Lay-Ekuakille, P. Carlucci, A. Ficarella, D. Laforgia, A. Pascali, Measurements of Opacity at Exhaust of Diesel Engine Using Extinction Laser Technique, SPIE2002 Photonics Asia, Shanghai October 2002 (China). [6] J.B. Heywood,”Internal combustion engine fundamentals”, McGraw-Hill, 1988, Singapore. [7] A. Lay-Ekuakille, P. Vergallo, I. Jabłoński, S. Casciaro,F. Conversano, (2016), “Measuring Lung Abnormalities in Images-based CT”, International Journal on Smart Sensing and Intelligent Systems, Vol.9, n.2, pp. 1156-1179. [8] S. Prakash, S. Urooj, A. Lay-Ekuakille, “Breast Cancer Detection using PCPCET and ADEWNN: A Geometric Invariant Approach to Medical X-rays Image Sensors”, IEEE Sensors Journal, Vol.16 n.12, pp.4847-4855, 2016. [9] N. Laugel, et. al., “Composite films of polycations and TiO2 nanoparticles with photoinduced superhydrophilicity”, Journal of Colloid and Interface Science, Vol. 324, pp.127-133, 2008. [10] www.evagrin.it [11] C.R. Dijy, D. Divya, “Reduction of Air Pollution from Vehicles Using Titanium Dioxide”, International Research Journal of Engineering and Technology (IRJET), Vol.2, n. 5, pp.13081314, 2015 [12] K. Hashimoto, H. Irie, A. Fujishima, “ TiO 2 Photocatalysis; A Historical Overviw and Future Prospects”, Japanese Journal of Applied Physics, Vol.44, n.12, pp.8269-8285, 2005.
[13] A. Lay Ekuakille, F. Tralli, M. Tropeano, “Land Modification Measurements Using ERS-2 Satellite Images”, XVI IMEKO World Congress , Vienna, Austria, September 25-28, 2000 [14] V. Bhateja, A. Tripathi, A. Gupta, A. Lay-Ekuakille, (2015),“Speckle Suppression in SAR Images Employing Modified Anisotropic Diffusion Filtering In Wavelet Domain For Environment Monitoring”, Measurement, Vol.74, pp.246254. [15] A. Lay-Ekuakille, I. Palamara, D. Caratelli, F.C. Morabito, Experimental Infrared Measurements for Hydrocarbon Pollutant Determination in Subterranean Waters, Review of Scientific Instruments, Vol. 84, pp. 015103-1 (8 pages) 2013. [16] A. Lay-Ekuakille, M.G. De Giorgi, A. Ficarella, S. Urooj, V. Bhateja, “Detecting environmental features in an experimental combustion chamber of Gas Turbine: advanced imaging process and accuracy”, 6th EnvImeko - Imeko TC19, June 24-25, 2016, Reggio Calabria, Italy [17] A. Lay-Ekuakille, P. Vergallo, D. Saracino, A. Trotta, Optimizing and Post Processing of a Smart Beamformer for Obstacle Retrieval, IEEE Sensors Journal, vol.12, issue 5, pp.1294-1299, 2012
