Study On Coating State Characterization And Properties Of 3DOM TiO₂ Fog Seal Material

Nitric oxide（NO）in motor vehicle exhaust is an important precursor of PM2.5.Past studies have mostly used TiO₂ as a photocatalyst to degrade NO in motor vehicle exhaust on the road surface,but the agglomeration effect of nano-TiO₂ tends to lead to a decrease in specific surface area and a significant decrease in degradation efficiency.The group proposed to develop Three-Dimensionally Ordered Macroporous（3DOM）TiO₂ instead of nano-TiO₂ to solve the defects of the large agglomeration effect of nano-TiO₂.The previous experiments demonstrated that the degradation effect of 3DOM TiO₂ fog seal layer on NO was significantly enhanced,and the optimal pore size and doping amount of 3DOM TiO₂ were initially determined,but the microscopic characterization of the fog seal layer material coating state and the optimal parameter selection of external influencing factors were not clear yet.Therefore,this study aimed at the changes in the coating state of 3DOM TiO₂ fog encapsulation materials with different pore sizes,characterized by microscopic experiments and verified by comparison with the previous macroscopic experimental results.And the optimal parameters of influencing factors were determined by photocatalytic performance experiments,and finally the road performance and durability were verified.Firstly,this study used the gel-crystal template method to prepare 3DOM TiO₂ and optimized the preparation method for the problems found in it,and then designed the experimental method for the stability of 3DOM TiO₂ in emulsified asphalt and conducted the stability study.The results showed that the gel crystal template prepared by using 2.5%concentration of 300nm PS microsphere solution was qualified in thickness,and the microspheres were neatly and tightly arranged with good quality.As for the roasting temperature,if the temperature is too low,the formed macroporous structure is not permeable and the pore wall is not firm enough;if the temperature is too high,it will lead to the sintering of the macroporous structure,and subsequent studies cannot be carried out.The optimal roasting temperature is 550℃.The stability of 3DOM TiO₂ in emulsified asphalt can be significantly improved by the intermixing of three dispersing stabilizers,and the stability coefficient is large when the dose is low,and the caking phenomenon will occur when the dose is too high to affect the practical application.The best dispersing stabilizer was determined to be a 1:1 mixture of polyvinyl alcohol and anhydrous calcium chloride at 2%of the mass fraction of emulsified asphalt.Secondly,the crystalline structure of 3DOM TiO₂ materials prepared in this study was verified as anatase type by X-ray diffraction analysis,which is in accordance with the research requirements.In order to characterize the wrapping state of 3DOM TiO₂ fog seal layer materials with different pore sizes（200 nm,300 nm,400 nm,500 nm）,scanning electron microscopy（SEM）,physical adsorption experiments（BET）,and mercury-pressure experiments（MIP）microscopic experimental methods were used.Its effects on the specific surface area,pore size distribution,pore volume and surface micromorphology of 3DOM TiO₂ before and after being coated by emulsified asphalt were investigated.The results show that when the 3DOM TiO₂ photocatalyst is made into a fog seal layer material,there is a significant decrease in the specific surface area of the photocatalytic material under each pore size,and there is mesoporous structure in the material,so when the pore size is 300 nm,its specific surface area value is higher and the degradation performance will also be improved.And the distribution of macropore pore size is basically unchanged,but the pore volume is somewhat reduced,which indicates that there is some loss of photocatalyst after emulsified asphalt coating,but there are still macropore structures on the surface that can participate in gas degradation reaction.Meanwhile,the pore volume of 3DOM TiO₂ fog seal layer materials at 300 nm and 500 nm is relatively larger,and the specific surface area is larger when the pore diameter is 300 nm,so its degradation efficiency is higher at this time.Scanning electron microscopy observed that the 3DOM TiO₂ powder had a clear three-dimensional ordered macropore structure,the photocatalyst formed a coherent macropore structure up and down,and the skeleton of the macropore structure was also more complete,while the remaining 3DOM TiO₂ that could participate in the degradation reaction after being coated by emulsified asphalt was obviously reduced,leading to the reduction of its degradation efficiency.The pore size of 300 nm has more surface clear pore channels and the macroporous structure is relatively complete,which indicates that the photocatalyst can migrate to the surface of the fog seal layer material with the evaporation of water after the emulsification of emulsified asphalt.In conclusion,300 nm is recommended as the best pore size for 3DOM TiO₂ material.Finally,the effects of different sprinkling amounts（0.2,0.4,0.6,0.8 kg/m²）,different emulsified asphalt solid contents（40,50,60%）,different temperatures（20,24,28,32℃）,and different humidity levels（25,35,45,55,65%）on the degradation performance,road performance and durability of 3DOM TiO₂ fog seal material were investigated.The results showed that the degradation efficiency of the photocatalytic materials could be significantly improved with the increase of the sprinkling amount of the fog seal layer materials,but the improvement of the degradation efficiency was not obvious when the sprinkling amount was too large.Appropriately increasing the solid content of emulsified asphalt in the photocatalytic fog seal layer material is beneficial to improve the degradation performance of the material,and the improvement of the degradation efficiency is small.With the increase of temperature,the degradation efficiency of 3DOM TiO₂ fog seal layer material to polluted gas showed a trend of increasing and then decreasing,and the degradation efficiency was at the maximum at 28℃.With the increase of relative humidity of the reaction environment,the efficiency of NO degradation by photocatalytic fog seal layer materials also showed a trend of increasing first and then decreasing,and the degradation efficiency was at the maximum at 35%relative humidity.With the increase of solid content and sprinkling amount,the pendulum value of the specimens slightly decreased,and at the same time,the water permeability of the photocatalytic pavement could be improved and its degradation durability was slightly improved.The greater the solid content of the fog seal layer material its anti-slip durability is worse,but the effect is not significant.The water seepage coefficients of sprinkle fog seal layer materials are low before and after abrasion,which indicates that the materials have good water sealing effect,and there is no significant effect of different temperature and humidity on the road performance and durability.Considering the economic factors and practical applications,it was recommended to use 60%solid content emulsified asphalt as binder,and the sprinkling volume of fog seal material was selected as 0.6 kg/m².The change law of degradation performance of photocatalytic fog seal material under different temperature and relative humidity was clarified,and the best reaction environment temperature was determined to be 28℃and 35%relative humidity.Under the optimal parameters,the degradation efficiency was improved by 8.03%compared with the previous experiments of the group.