THE DECONTAMINATION OF VEHICLE EMISSIONS NOX THROUGH NANO-TIO2 IMMOBILIZED ON THE SURFACE OF CONCRETE AND

ASPHALT ROAD

CHEN Meng College of Traffic, Northeast Forestry University, 26 Hexing Road, Xiangfang District, Harbin, 150040, P.R. China, E-mail:chenmeng623@126.com Abstract: With the increase of the automobile amount, the atmosphere pollution for the automobile emission becomes very serious day by day. In the paper, we have studied vehicle emissions of decontamination by using nanometer titanium dioxide of photocatalysis method in traffic environment. Based on concrete and asphalt road material different characteristic, we used the different matching scheme of TiO2 respectively, and utilized permeability technology and coated film technology to make environmental protection materials of concrete and asphalt nano-TiO2. In order to test degeneration efficiency of the materials, we have carried on the indoor simulation test by a kind of testing system that was designed by us. The test result indicated: Their effective degeneration efficiency may achieve 30% and the photocatalytic activity may achieve 0.01cms-1. On the basis of this research, the productions were used in road environment. The decontamination effect was tested by contrast test in TiO2 spraying section with non-spraying section. The experiment showed that decontamination rate of the productions was from 6% to 12%. Key words: NOx decomposition road surface materials TiO2 immobilization 1 Introduction

Automobile's emission is one of atmosphere sources of pollution, which has been the huge harm to human health. So, various countries have conducted the massive research in the automobile manufacture aspect in order to reduce the automobile exhaust. With automobile inventory rapid increase, its total emissions quantity increases steadily. In view of the fact that automobile emission contacts with the road surface in the first time, it is one feasible method that photocatalyst is immobilized in the road surface to purify automobile pollutants. Road surface materials are mainly divided into two types, cement-based material and bituminous mixture. It focuses on the immobilized method and purification efficiency of nanometer TiO2 of two road materials.

2 The photochemical catalysis material of preparation base on road 2.1 Cement-based nanometecr photohemical catalysis material preparation

The cement material is one kind of inorganic building material that has more structure porous, bigger surface area and better water-wet. Therefore, we use the

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nanometer TiO2 solution and penetration method to prepare cement base photochemical catalysis material. Its steps are followed:

(1)Cement specimen: The manufacture cement test specimen consists of basic material including C40 swan sign cement, the crushed stone and the sand, superplasticizer FDN and air-entraining agent DH-9B.

(2)Matching scheme of TiO2 solution: TiO2 is a kind photocatalyst that has good surface effects and volume effects. But it is easier to agglomerate and reduce photochemical catalysis performance. Meanwhile different content proportion of the TiO2 and the dispersing agent has obvious influence on photochemical catalysis material purifying effect. Therefore, right amount TiO2, dispersing agent content and reasonable dispersed method is a key to preparation TiO2 solution.

In order to obtain the best purifying effect photochemical catalysis material, we use different content TiO2 (1%, 3% and 5%) to make the photochemical test specimen and carry on the best TiO2 content experiment. After determining best TiO2

content, we use different content dispersing agent and TiO2 in order to carry on the best dispersing agent content experiment. In Figure 1, the test shows that photochemical catalysis of material made of 5% content is the best. The purifying rate of the photochemical material whose dispersant is 3% is the highest in Fig 2. It indicates that higher dispersant content is better is not true, and the test proves that the best content dispersant is 3%.

0 1 2 3 4 5 6 70

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Fig.1 Degradation effect of different Nano-TiO2 density on NOx Fig.2 Degradation effect of different dispersant on NOx

At the same time, we prepare nanometer TiO2 solution through synthesis

dispersed method that include dispersant, high speed rotary and ultrasonic wave. In Fig 3, we may discover that Firstly, the ultrasonic wave makes nano-particles dispersed tiny pellet. Secondly, high speed rotary cause the solution mixed in wide range. In addition, the suitable dispersant makes pellet surface adsorb certain high polymer and creates the steric hindrance, which hinders pellet further to grow-up effectively. So the measure improved the nanometer granule dispersity.

(3)Cement-based photochemical catalysis material preparation: Using the cement specimen water-wet and the porosity, we make the nanometer TiO2 solution seeped to the cement specimen by the self-made HIT-GY001 penetrate. Fig 4 shows

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the effect of cement base nanometer TiO2 photochemical catalysis material.

Fig.3 TEM image of TiO2 after dispersed Fig.4 Sample of photocatalysis Nano-TiO2 on concrete material

2.2 Asphalt-based nanometer photochemical catalysis material preparation The asphalt material is a kind of organic high polymer which is composed of

many kinds of mixtures, has compact structure, kisses oil and hates water. But TiO2 is one kind of small molecular inorganic material has water-wet and hates greasiness. Their compatibility is bad. So, we use the TiO2 paint film solution and coated method to prepare asphalt base photochemical catalysis material. Its steps are followed:

(1)Asphalt specimen: Base on "Technical Specifications for Construction of Highway Asphalt Pavements", we select AC-16 to carry on the asphalt specimen preparation that is constituted of MAC-70# asphalt, the sand and the powdered ore.

(2)Nanometer TiO2 paint film fluid configuration: Because the nanometer TiO2 surface has strong activity, which is difficulty in dispersing in organic high polymer material. It causes the crevice present in the surface of pith pavement photochemical catalysis thin film. When air moisture enters the crevice, the high polymer in the thin film may degenerate and embrittle.

The paper takes the silane coupling agent as modifier to carry on modified experiments in order to nanomaterials lipophilic. In Fig5, the peak at 3428cm-1 shows that hydroxyl group is present, C-H is present at 2495cm-1 peak, C=O vibration peak appear at 1722cm-1, Si-O-Si vibration peak is at 1097cm-1, Ti-O peak is present at 540cm-1.The result indicates that the silane coupler is linked with hydroxyl of TiO2 surface by chemical bond form, when changes nanomaterials lipophilic. Afterward, we prepare the nanometer TiO2 paint film fluid using organosilicon modified Epoxy resin as binder, diethylenetriamine as curing agent, acetone as resolver and lipophilic nanometer TiO2 as photocatalyst. In the best matching scheme the photocatalyst content is 5%(profits from cement base nanomaterials best TiO2 amount used).According to the papers (Chen Guo-ping, 2002), the ratio between binder total mass and the mass of the photocatalyst and the cementing agent lumpy is 70-98%, so we selects 70%. The amount of curing agent use is determined by papers (Wang De-zhong, 2001).

(3)Asphalt-based photochemical catalysis material preparation: Firstly, we take the quantity organosilicon modified epoxy resin in the 60ml acetone and carry on the magnetic force agitation for 30 minutes. Secondly, add-on enters lipophilic nanometer into the solution and dispersed 30min under the ultrasonic wave. Finally,

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we join the quota divinyl three amines into the solution to continue the ultrasonic wave to be dispersed about 10 minutes. Afterward, we may prepare the asphalt base photochemical catalysis material (Fig 6).

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Fig.5 Infrared spectrogram of the modified TiO2 Fig.6 Sample of photocatalysis Nano-TiO2 on Asphalt material

3 The simulation application with photochemical catalysis material base on road

In order to test the photochemical catalysis material purifying effect, we use effective purifying rate ( ), the photocatalytic rate (PR) and the photocatalytic activity (PA) to evaluate by a kind of testing system that was designed by us(HAN Xiang-chun, 2005). The experiment is divided into two stages. The first stage of the test is standard specimen purifying effect. Firstly, test roadbed material own adsorption function under closing ultraviolet source. Next the ultraviolet source is opened in order to carry on the nanometer photochemical catalysis material purifying function test. The second stage test purifying effect of wear standard specimen. Because the road surface is wear frequently in the actual driving process, polish the test specimen to some extent to test purifying effect.

( ) 100%in suv bin sb

in bin

C C C CC C

(1)

Where is effective purifying rate, %;Cin represent the initial steady-state pollutant concentration(before turn on the UV source),mg/m3;Csuv represent the pollutant concentration during irradiation phase,mg/m3;Cbin represent the initial steady state pollutant concentration,mg/m3,Csb represent the pollutant concentration at the end of the blank experiment(without irradiation).

rCPR QS

(2)

Where PR is the photocatalytic rate, mgm-2s-1;Cr represent the pollutant concentration removed by the TiO2 effect mg/m3;S represent the sample area exposed to the irradiation; the airflow of ventilator.

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( ) / 2in suv

PRPAC C

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Where PA is the photocatalytic activity,cms-1;Csuv represent the pollutant concentration during irradiation phase,mg/m3.

In table 1, we can find that two kinds of the photochemical catalysis material have good decontaminating effect to NOx discharge by vehicles. But the cement-based photochemical catalysis material is better than the asphalt-based photochemical catalysis material in effective purifying rate and the photocatalytic rate. In purifying NO and the NO2, the photocatalytic rate of the cement-based photochemical catalysis material is 6% higher than the photocatalytic rate of asphalt-based photochemical catalysis material and the reaction rate is 0.07 mg m-2s-1. But the two kinds of the photochemical catalysis material have the same value about 0.01cms-1in the photocatalytic activity. Asphalt-based photochemical catalysis material is made by coated method is reduced the photochemical catalysis function because partial photocatalyst surface is bound duplicate in the cementing agent.

At the same time, we also find that two kinds of wear photochemical catalysis material also had purifying function to NOx. Moreover, wear influence on cement test specimen purification is less than influence on asphalt test specimen. This is mainly because, when penetrate is put into photochemical catalysis material, they can mix fully and better disperse in penetrating agent. Because of good penetrate function agent, can enter carry with nano-TiO2 to penetrate, so that cement nano-TiO2 can enter internal test sample smoothly. At this point the agent has played a carrying role. The carrier is able to significantly increase the penetrating effect and ensure wear purifying effect. But asphalt-based photochemical catalysis material, is different because TiO2 is filmed on the asphalt road, it would have natural shedding after wear, which reduces the road surface photochemical catalysis environmental protection function. However, the bonding ensures nanomaterials limits shedding, and guarantees purifying effect after asphalt road is wear.

Tab 1.NOx purification effect parameter list

NO NO2 photochemical catalysis

material PR PA PR PAcement-based 29.5 0.17 0.011 38.2 0.15 0.008

asphalt-based 23.6 0.06 0.009 29.9 0.09 0.008

cement-based after wear 29.3 0.16 0.010 36.7 0.14 0.008

asphalt-based after wear 20.8 0.03 0.009 24.6 0.06 0.008

4 The practical application with photochemical catalysis material base on road

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In order to examine the practical applying effect in the traffic environment outside, we have tested on the road which is federal highway G11.The test experiment applies contrast test plan. We arrange three air samplers to carry on the synchronized sampling in immobilization and non-immobilization range respectively as well as use the multi-purpose weather stations to gather dynamic data in external environment condition. Finally, we use the UV-Vis spectroscopy (TU-1901) to carry on determination absorbency of gathered sample by N-(1- naphtyl)-cthylcncdiaminc di hydrochloride colorimctric analysis.

The NOx density of the experimental road immobilized nanomaterials and not immobilized nanomaterials has remarkable difference both in the cement road and in the asphalt road from table 2.Meanwhile, the biggest NOx purifying rate may achieve more than 10% and the lowest NOx purifying rate may also achieve 6.56% in the contrast experiment. The test result is obtained in the natural condition affected by wind, temperature, humidity. So, it can fully prove it is feasible that nano-TiO2 can purify vehicle emission pollutant in actual traffic environment.

Tab 2. Degradation effect of different on NOx

Difference decontaminating rate % Test Item

F p Max Min

TiO2 load cement - Non- TiO2 load cement 9.1596 0.0064 12.1 6.56

TiO2 load pitch - Non- TiO2 load pitch 6.8253 0.0047 10.4 7.11

5 Conclusions

According to the characteristic of concrete and asphalt road material, we utilized permeability and coated film technology to make environmental protection materials of concrete and asphalt nano-TiO2.The simulation test shows that two kinds of photochemical catalysis material have good purification function. At last, through comparative test, we obtained purifying rate of vehicle pollutant of the road surface nanometer photochemical catalysis material which is from 6% to 12% under actual outdoor road traffic environment. Therefore, it is feasible nano-TiO2 can purify vehicle emission pollutant in actual traffic environment. Reference Chen Guoping, Li Qijia, etc.(2002). “The film-forming technology of TiO2 film

Photocatalytic[J]”.Journal of Ceramics, 23(1):67-71. HAN Xiangchun,BAI Haiying,etc.(2005). “Design on Testing System for Degrading

Automobile Emission with Photocatalytic Material TiO2[J] ”.Journal of Northeast Forestry University,33(5):89-91.

Wang Dezhong.(2001).“The epoxy resin of production and application [M] ”. Chemical Industry Press, 60-61.

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