| With the rising number of cars,the air pollution caused by vehicle exhaust intensifies and the nitrogen oxide which is most difficult to degrade in vehicle exhaust increases the harm to human body and environment gradually.The new photocatalytic technology is widely used in sterilizatin,exhaust gas and sewage disposal because of advantages of less secondary pollution,mild reaction and low energy consumption.In this paper,the modified nano-TiO2 powder and silica sol were prepared and the powder was evenly dispersed in silica sol to obtain dispersion,then the dispersion was applied in cement pavement in different typies to give pavement the function of photocatalytic degradation of nitrogen oxides,and reduce environment pollution caused by vehicle exhaust.The wide band gap width and low quantum conversion effciency of nano-TiO2 limit its practice application in visible light,urea and Fecl3 used as doping source were applied to modify nano-TiO2 and the photocatalytic activity and crystal properties of nano-TiO2 were respectively evaluated by methyene blue degradation rate and XRD.The effect of element content,calcination temperature and calcination time on properties of doped samples was investigated by single factor variable method,the results show that the photocatalytic activity of Fe-doped samples declines because of the formation of iron compounds and the photocatalytic activity of N-doped samples intensified compared with pure nano-TiO2.The best mixed solution(calcination temperature 700℃,calcination time 5h,N content 1%)was obtained through orthogonal design on the basis of single factor experiments,and the degradation rate of optimum sample was 49.88%.The elemental silicon hydrolysis method using ammonia and sodium silicate as catalyst was used to prepare silica sol,and the effects of silicon dosage,catalyst dosage,reaction time and reaction temperature on reaction rate and properties of silica sol were investigeted firstly.Then the preparation technic was opimized through the orthogonal design and the silica sol of conversion rate 87.2%and silica content 24.8%was made.The nano-TiO2 powder was dispered into the silica sol and the effects of ultrosonic time,ultrosonic power,concentration of silica sol,TiO2 content and four kinds of dispersants on dispersion properties was investigated in order to determine the type and dosage of dispersant and dispersion process.On the basis of aforementioned experiments,the optimum dispersion method(ultrasonic time 120min,ultrasonic power 100W,SHMP dosage 0.3%and silica sol concentration 0.5%)was obtained and the absorbance of dispersion made in optimum method was 3.07.The results of absorbance,SEM and SPM show that powders of optimum dispersion disperse evenly and had small particle size.In addition,the results of FI-IR show that components of dispersion combine in physical ways not chemical ways.The cement specimens carrying nano-TiO2 were prepared through direct-mixing method,spreading method and spraying method and the photocatytic activity was investigated by NO photodegradation rate.The results show that the NO degradation rate of specimens made with three methods increases with the augment of nano-TiO2,and the NO photodegradation rate of specimens made with direct-mixing method and spreading method is lower because of the coverage with concrete and the uneven dispersion.Meanwhile,the NO photodegradation rate of spraying specimens is as high as 74.7%with 0.3g TiO2.In the following experiments,the effects of environmental factors such as gas flow,NO concentration and the kind of light source on NO photodegradation rate were investigated,and the results showed that the photocatalytic properties of specimens under the irradiation of 280nm UV lamp,360nm UV lamp and visible light lamp were all excellent.In additon,the NO photodegradation rate decreased with the increase of NO concentrarion and gas flow rate,and the NO photodegradation rate was as high as 97.1%under the gas flow rate of 0.6L/min. |
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