Research of new Preventive maintenance materials based on automobile exhaust gas purification and PM2.5 absorption

In order to reduce the harmful gases and particulate matter in the atmospheric environment, alleviate the pollution of automobile exhaust,this paper studies the preventive maintenance seal based on exhaust gas purification and PM2.5 adsorption. The optimal preparation process at the micrometer is determined by the ratio design at the micro-surfacing. Based on wet wheel wear test and rutting deformation test, the influence of environmental protection material content on wear resistance and high temperature stability of micro-surfacing was studied.A set of automobile exhaust pollutant purification test equipment was developed, and the test method was determined. The exhaust purification performance of environmental protection micro-surfacing and the adsorption effect of PM2.5 and 10 particles was studied. The microstructure of environmental protection materials was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the mechanism of tail gas purification and PM2.5 particle adsorption was revealed.The results show that with the increase of nano TiO2/tourmaline composite content, the viscosity and high temperature stability of SBR modified emulsified asphalt evaporation residue are improved, but the ability to resist deformation at low temperature is slightly reduced.When the content of nano-TiO2/tourmaline is 7%,the wear resistance at the micro-surfacing increases by 4%, and the high temperature stability increases by 14.6%.The purification efficiency of various gas components in automobile exhaust by adding nano-TiO2/tourmaline composite micrometer reached 33.3% of hydrocarbons, 46% of carbon monoxide and 92.8% of nitrogen oxides, respectively. The adsorption effect of particulate component PM2.5and10 in automobile exhaust reached 29.9% and 25.2%, respectively.The nano-TiO2 aggregates loaded on the surface of tourmaline particles are uniformly dispersed, and the crystal forms are anatase and rutile. The permanent electric field generated by spontaneous permanent polarization of tourmaline can accelerate the separation of electron-hole pairs and improve the redox ability of nano-TiO2.The permanent electric field of tourmaline and the permanent release of air negative ions can absorb and neutralize the charged suspended particles in the air, so as to achieve the purpose of settlement.


Introduction
Automobile exhaust pollution is an important reason for environmental air pollution problems such as photochemical smog and haze. Automobile exhaust pollutants include nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC) and inhalable particulate matter (PM) [1].Therefore, it is necessary to 2. Raw material 2.1. Modified emulsified asphalt The SBR modified emulsified asphalt provided by Qilu Branch of Sinopec was used in this experiment, and its performance was tested according to the specification requirements [22]. The main technical indexes are shown in table 1.

Coarse aggregate
The coarse aggregate used in the test was the gravel produced in Xinxiang City, Henan Province, and its performance was tested according to the requirements of the regulations [23]. The performance indexes of each particle size group are shown in table 2.

Fine aggregate
The fine aggregate used in the test was stone chips produced in Xinxiang City, Henan Province, and its performance was tested according to the specification requirements [23]. The performance indexes of each particle size group are shown in table 3.

Mineral powder
The ore powder used in the test was ground limestone powder, and its performance was tested according to the requirements of the regulations [24]. The performance is shown in table 4.
(1) In three beakers with 500 ml capacity, 300 ml distilled water and 10 g tourmaline powder were added and stirred in cold water bath (0°C) for 5 min. In the condition of good ventilation, 0.5 ml TiCl 4 reserve solution was absorbed by colloidal dropper, and then slowly dropped into the mixture by scale dropper.
(2) 5 ml of (NH 4 ) 2 SO 4 solution (1.5 mol l −1 ) and 3 ml of HCl (36%∼38% purity) were mixed, and the mixture was slowly dropped into the above reaction system. After full stirring for 15 min, the mixture was heated to 70°C(magnetic stirrer) for 1 h.
(3) Using a certain volume ratio of dilute ammonia, the PH value of the mixture was adjusted to about 4.4, and the reaction was held for 2 h. The test process was shown in figure 1. The reaction solution was filtered by quantitative filter paper, and the precipitation on the filter paper was repeatedly cleaned by distilled water. When no white precipitate was detected by AgNO 3 solution (0.2 mol l −1 ) in the washing solution, that is, there was no Cl − in the washing solution, anhydrous ethanol was used to clean the precipitate on the filter paper once.
(4) The filter paper, together with the filtered precipitation, was put into the vacuum drying box (D2F-6050 drying box) for 1 h. When the sample was completely evaporated into powder by ethanol, the sample was put into the crucible together with the filter paper and placed in the high temperature resistance furnace   3.1.2. Preparation of emulsified asphalt evaporation residues modified by nano TiO 2 /tourmaline composites Nano-TiO 2 /tourmaline composite modified emulsified asphalt is prepared by mechanical method. The specific preparation process is as follows: SBR modified emulsified asphalt with a certain mass is taken in the steel basin, and the steel basin is heated slowly on the electric furnace. The heating setting temperature can be slightly higher than 100°C but should not cause emulsion spill. During the heating process, the glass rod is used to stir uniformly. SBR modified emulsified asphalt first rises and maintains in boiling state at 100°C. There are many bubbles on the surface, which generate, swell and break. When the bubble aggregation is to overflow, accelerated stirring or cooling the steel basin can alleviate bubble aggregation.When the surface of modified emulsified asphalt is no longer bubble aggregation, showing a paste, the moisture in the sample has been little but not evaporated, the temperature of the sample began to rise rapidly. When the temperature of the sample exceeds 105°C, the heating rate of the furnace is adjusted, and the temperature is kept below 140°C. Continue stirring until the surface of the sample is no longer bubble, and then the temperature rises to 163°C and stop heating, that is, the evaporation residue of SBR modified emulsified asphalt is obtained. Keeping the temperature unchanged at 163°C, the high-speed shear head is put into the evaporation residue, and the asphalt is stirred at 2500 r min −1 . The bottom of the head is about 1∼2 cm from the bottom of the basin, so as to avoid premature aging of asphalt caused by local overheating during heating.After stirring for about 5 min, the nano-TiO 2 /tourmaline composite with a certain proportion of the evaporation residue of SBR modified emulsified asphalt was slowly added to the asphalt, and the shear speed was increased to 6500 r min+, and the continuous modification was about 30∼50 min. In the process of modification, because the rotor speed inside the rotor head is great, the vacuum area will be formed below the rotor head. The rotor head will absorb the surrounding asphalt and composite materials, and shear modification is carried out by using the relative speed of the rotor and the stator. The nano-TiO 2 /tourmaline composite can be effectively dispersed in the evaporation residue modified by high-speed shearing, and the expected evaporation residue of emulsified asphalt modified by nano-TiO 2 /tourmaline composite is obtained.

Mix proportion design of MS-3 micro-surfacing
The dosage of modified emulsified asphalt, water and additive cement was preliminarily selected according to the existing mix design experience, and the range of asphalt-aggregate ratio was preliminarily selected through   the state of slurry mixture and the crack of specimen in the mixing test and cohesion test.Based on 100 g aggregate, select 5.9%, 6.2%, 6.5%, 6.8%, 7.1% five groups of oil-stone ratio, water use tap water, dosage 9%, cement 325 ordinary Portland cement, dosage 1.5%. The amount of modified emulsified asphalt can be determined by calculating the evaporation residue content of SBR modified emulsified asphalt.The mixing time was recorded in the mixing test, and the slurry state was observed. The test results are shown in table 5. The mixing test results and phenomenon description show that among the five groups of mixtures with different oil-stone ratios selected in the test, the mixing time of the five groups of test samples meets the requirements of more than 120 s in the specification. However, by observing the slurry state, it is found that the apparent state of asphalt content with oil-stone ratios of 5.9% and 7.1% is not ideal. Five groups of cohesion test samples were prepared according to the five groups of mixture formulations with the oil-stone ratios of 5.9%, 6.2%, 6.5%, 6.8% and 7.1%, and the cohesion values were tested.The test results are shown in figure 4 and table 6.
The initial setting time and open traffic time at the micro-surfacing are related to the cohesion value. Moreover, the forming speed and early strength of the micro-surfacing are both reflected by the value of cohesion within the same time. Therefore, from the test results and phenomenon description of tables 3-4, it can be seen that the cohesion value of the specimen with 5.9% oil-stone ratio is small, which cannot meet the design requirements.The cohesion value of the specimen with the oil-stone ratio of 6.2% is close to the standard design index. The mixture with oil-stone ratio of 6.5% has good molding, and its cohesion value reaches the specification of China, and its test result is the best. The asphalt with the oil-stone ratio of 6.8% and 7.1% completely wrapped the mineral and had good cohesion value, which was primary molding.

Determination of optimum oil-stone ratio
In the design of micro-surfacing mixture ratio, the optimal range of oil-stone ratio is often determined by the wear value of 1 h wet wheel and the amount of adhered sand. The above mixtures with oil-stone ratios of 6.2%, 6.5% and 6.8% were subjected to 1 h wet wheel wear test and load wheel sand adhesion test, respectively. The curve of oil-stone ratio corresponding to 1 h wet wheel wear value and sand adhesion are shown in figure 5.  The optional range of oil-stone ratio can be seen from figures 3-4 of the change curve of 1 h wet wheel wear value and sand adhesion amount. The oil-stone ratio corresponding to the 1 h wet wheel wear value of 540 g m −2 is the minimum oil-stone ratio, and the oil-stone ratio corresponding to the sand adhesion amount of 450 g m −2 is the maximum oil-stone ratio. The optional range of oil-stone ratio is between 6.4% and 6.7%. When the oilstone ratio is 6.5%, the mixing time and cohesion value of the micro-surfacing mixture meet the requirements of the specification, and the molding effect of the specimen is the best. The 6 d wet wheel wear index of the mixture is tested with the selected 6.5% oil-stone ratio, and the results are less than 800 g m −2 , which meets the requirements of the specification. Therefore, the optimum oil-stone ratio is determined to be 6.5%.

Purification of automobile exhaust at micro-surfacing and adsorption of PM2.5
According to the basic concept of air purification test system, relevant instruments were selected, the necessary equipment was processed, and a set of air purification test equipment was produced. The test method of purifying automobile exhaust was determined, and the true use of roads was simulated. The test results of purifying automobile exhaust and adsorbing PM2.5 at the micro-surfacing of nano-TiO 2 /tourmaline composite were tested.
The test method of exhaust gas purification and PM2.5 adsorption test combined with the pavement materials studied in this paper is to connect the inlet and the exhaust port of the vehicle with the guide pipe, open the inlet control valve and the outlet control valve, and launch the vehicle idle running for 1-5 min .close the inlet control valve and the outlet control valve, record the initial exhaust concentration and PM2.5 content in the reaction chamber.The detection device was placed under the Sunlight or turned on the ultraviolet lamp, and the fan was started. The exhaust gas concentration and PM2.5 content were recorded every half hour, and the final data were recorded after 4 h as the final exhaust gas concentration and PM2.5 content. The purification effect of environmental protection pavement materials is evaluated by the purification efficiency index. The purification efficiency is calculated according to the initial and final exhaust concentration or PM2.5 content. The calculation formula of purification efficiency is as follows: In the formula:n is purification efficiency. x and y are the initial and final exhaust concentration or PM2.5 content, respectively.

X-ray diffraction test (XRD)
phase analysis of X-ray diffraction using X-ray diffraction effect in crystal materials for material structure analysis technology. Each crystalline substance has its specific crystal structure, including lattice type, crystal plane spacing and other parameters. When the sample is irradiated by X-ray with sufficient energy, the substance in the sample is excited, and the secondary fluorescence X-ray is generated. The crystal plane reflection follows the Bragg law. The qualitative analysis of the compound can be carried out by measuring the diffraction angle position(peak position), and the quantitative analysis can be carried out by measuring the integral intensity(peak intensity) of the spectral line. The grain size and shape can be detected by measuring the relationship between the spectral line intensity and the angle.

Scanning electron microscope
The ZEISS HD 15/Oxford X-Max N scanning electron microscope was used. There are nine small sample platforms on the loading table of scanning electron microscope, and nine samples can be prepared at the same time. The length, width and height of each sample are best within 2 cm×2 cm×1 cm. The special doublesided adhesive should be attached to the front bearing table of the sample, and then the sample is bonded to the bearing table and wrapped with the same double-sided adhesive.In the preparation of samples in this experiment, appropriate amount of samples were taken with a medicine spoon and evenly spread on the small bearing platform in the center of the loading platform. Appropriate pressure was applied to make the sample powder uniformly fixed on the double-sided adhesive. The unfixed sample powder was blown off with a suction ear ball to ensure the cleanliness of the loading platform and not affect the next scanning electron microscope. The sample preparation is shown in figure 7 and is located at the central loading table.

Test results and analysis
4.1. Effect of nano TiO 2 /tourmaline composite content on properties of evaporative residues of modified emulsified asphalt The samples with composite content of 0%, 1%, 3%, 5% and 7% were prepared. The influence of nano-TiO 2 /tourmaline composite content on the properties of modified emulsified asphalt evaporation residue was studied by three index tests. The properties of modified emulsified asphalt evaporation residue under different dosage are shown in table 7.
It can be seen from table 7 that with the increase in the proportion of nano-TiO 2 /tourmaline composite, the penetration of evaporation residue of SBR modified emulsified asphalt showed a continuous decrease.When the dosage is 7%, the penetration is reduced to the lowest, the relative 0% dosage is reduced by 0.9 mm, and the  reduction is 15.3%. It can be seen that the addition of nano TiO 2 /tourmaline composites increases the viscosity of SBR modified emulsified asphalt evaporation residue; with the increase in the proportion of nano-TiO 2 /tourmaline composite, the softening point of evaporation residue of SBR modified emulsified asphalt showed an increasing trend.When the content is 7%, the softening point rises to the highest, the relative 0% content increased by 4.5°C, increased by 8.3%. It can be seen that the addition of nano-TiO 2 /tourmaline composite can improve the heat resistance and temperature stability of SBR modified emulsified asphalt evaporation residue. With the increase in the proportion of nano-TiO 2 /tourmaline composite, the ductility of evaporation residue of SBR modified emulsified asphalt showed a decreasing trend.When the content is 7%, the ductility is reduced to the lowest, which is 6.1 cm lower than that of 0%, and the decrease is 16.3%. It can be seen that the addition of nano-TiO 2 /tourmaline composite reduces the deformation resistance of evaporation residue of SBR modified emulsified asphalt, but it still meets the specification. It can be seen from table 8 that with the increase of nano TiO 2 /tourmaline content in SBR modified emulsified asphalt, the wet wheel wear value at the micro surface continues to decrease.Therefore, the wet wheel wear value of the doped nano-TiO 2 /tourmaline material on the micro surface is decreased by 4% compared with that of the undoped micro surface, that is, the wear resistance of the doped nano-TiO 2 /tourmaline material is improved by 4%.

Elevated temperature property
The wheel track deformation test specimens were prepared, and the wheel track width deformation rate and rutting depth rate were tested to evaluate the high temperature stability at the micro-surfacing. Different nano-TiO 2 /tourmaline composite content under the micro-surfacing wheel rut deformation test results as shown in table 9.
It can be seen from table 9 that after the addition of nano-TiO 2 /tourmaline composite material, the PLD and PVD of the deformation specimen of the mixture wheel track continuously decrease, with the decrease rates of 14.6% and 7.2%. The decrease of PLD and PVD indicates that the rutting resistance of the micro-surfacing mixture is enhanced and the high temperature stability is improved.Therefore, it can be considered that the addition of nano-TiO 2 /tourmaline composite can improve the high-temperature stability of the microsurfacing by 14.6%.

Purification effect test and analysis of micro-surfacing of composite materials
The mineral aggregate gradation is AC-13 type, and the asphalt is No. 70 A grade asphalt provided by Qilu Branch of Sinopec. The formed volume of rut plate is used as the pavement foundation. The micro-surfacing of 7% nano-TiO 2 /tourmaline composite is paved to make the test sample of exhaust gas purification effect. The mineral aggregate gradation at the micro-surfacing is MS-3 type gradation median, and the modified emulsified asphalt is SBR modified emulsified asphalt.The test equipment was placed in the outdoor sunlight, and the exhaust gas purification test sample was placed in the center of the bottom plate. The handheld gas detector (four in one) and high-precision handheld PM2.5 speed tester were opened and placed in the reaction room. The reaction room and the bottom plate were sealed with polyurethane foam sealant.After the sealant curing, connect the automobile exhaust pipe, the automobile idle running 2∼5 min after closing the inlet and outlet control valve, read the value of the two detectors for the initial value, every half an hour to measure a set of data, after4h to measure the final value, the test site as shown in figure 8, the measured test data are shown in table 10, figure 9. From table 10, it can be seen that the micrometer of doped nano-TiO 2 /tourmaline composite has good automobile exhaust purification and PM2.5 adsorption effect. The purification efficiency of the micro-surfacing on automobile exhaust and PM2.5 particles reached 33.3% of hydrocarbons, 46% of carbon monoxide, 92.8% of nitrogen oxides, 29.9% of PM2.5 and 25.2% of PM10, respectively.  figure 10. Figure 10(a) shows that the particle size of tourmaline powder is different, ranging from 10 m to 100 m. The tourmaline powder used in the experiment is single crystal tourmaline, which is produced in Xinjiang. Due to the limitation of processing and preparation process, it cannot obtain uniform particle size products, but does   not affect the experimental study.It can be seen from figure 10(b) that nano-TiO 2 aggregates are loaded on the surface of tourmaline, and the segments are relatively uniform, and the particle size is uniform and large, which is in the micron level.It shows that the nano-TiO 2 loaded on the tourmaline surface still exists in the form of aggregates, but the dispersion is uniform and does not gather together to form larger aggregates.It can be seen from figure 10(c) that the surface of tourmaline powder is relatively flat and smooth without rough surfaces such as grooves or pits, indicating that the strong attachment of nano-TiO 2 aggregates to the surface of tourmaline  powder may be due to the adsorption force generated by the polarization of tourmaline itself, or the chemical bond between nano-TiO 2 aggregates and tourmaline powder. Figure 10(d) shows that the particle size of nano-TiO 2 aggregates attached to the surface of tourmaline powder is large to1m, small to 0.3 m, indicating that nano-TiO 2 attached to the surface of tourmaline still exists agglomeration phenomenon.Generally, nano-TiO 2 particles agglomerate together to form large particles of 150-300 nm and adsorb together, while the diameter of nano-TiO 2 aggregates loaded on tourmaline powder surface is about 300 nm and evenly distributed.This indicates that this composite method can reduce the aggregation of nano-TiO 2 aggregates and improve their dispersion, thereby promoting the photocatalytic reaction of nano-TiO 2 materials.

Phase analysis
The tourmaline and nano-TiO 2 /tourmaline standard samples were prepared according to the requirements and X-ray diffraction (XRD) was carried out. The diffraction patterns are shown in figures 11 and 12. It can be seen from figure 11  Compared with the standard comparison cards of anatase and rutile TiO 2 , it can be seen that anatase TiO 2 has a characteristic peak at 25.3°, and rutile TiO 2 has a characteristic peak at 27.4°. The enhanced diffraction peak of TiO 2 /tourmaline composites appeared at 26.6°. It is speculated that the diffraction peak of anatase TiO 2 at 25.3°and the characteristic peak of rutile TiO 2 at 27.4°superimposed to form the enhanced diffraction peak of TiO 2 /tourmaline composites at 26.6°. Moreover, the diffraction peaks of TiO 2 /tourmaline composites at 27.9°, 36.5°, 41.5°and 56.6°are close to the characteristic diffraction peaks of rutile TiO 2 . Therefore, it can be seen that TiO 2 attached to the surface of tourmaline is not a single crystal, and anatase and rutile are both.The composite prepared by hydrolysis precipitation method did not change the phase of tourmaline.TiO 2 crystal forms attached to the surface of tourmaline were anatase and rutile.Studies have shown that temperature regulation can directly and effectively promote the transformation of anatase TiO 2 to rutile TiO 2 , and low-valent anions such as Cl − and F − can also promote the transformation of TiO 2 from anatase to rutile [24]. When the temperature is higher than 600°C, some anatase TiO 2 begins to transform to rutile.Therefore, the TiO 2 crystal forms attached to the tourmaline surface are anatase and rutile, which may be due to the fact that the sample preparation process does not filter and wash clean Cl − or the temperature control is not accurate enough during the high temperature calcination at 550°C, which causes the phase transition of TiO 2 and makes some TiO 2 crystal forms change from anatase to rutile.

Mechanism analysis of tail gas purification
After the excitation of nano-TiO 2 by light irradiation, the electron absorption energy transits from the valence band to the conduction band to form an electron-hole pair. Hole can directly oxidize TiO 2 surface materials can also oxidize H 2 O and OH − to generate hydroxyl radicals ·OH, electrons react with O 2 in air to generate oxygen radicals O . 2 · -·OH and O 2 ·have very high oxidation ability, which can react with harmful exhaust pollutants in the air to produce harmless CO 2 and H 2 O.
The spontaneous permanent polarity of tourmaline makes opposite charges appear at both ends, forming electrostatic field around it, which involves the transfer of photogenerated electron-hole pairs to two opposite directions.The existence of the spontaneous electrode has been proved by experiments, which is explained by the orientation of the silicox tetrahedron SiO 4 -4 . The spontaneous electrode of tourmaline is a spontaneous permanent electrode, which is not affected by external electric field and has nothing to do with temperature change.
The purification efficiency of each component of automobile exhaust at the micro-surfacing of doped nano-TiO 2 tourmaline composite reached 33.3% for hydrocarbons, 46% for carbon monoxide and 92.8% for nitrogen oxides, respectively, which was significantly higher than that of single nano-TiO 2 . It shows that the catalytic performance of nano-TiO 2 loaded on the surface of tourmaline has been greatly improved, because tourmaline has its own polarization, forming a permanent electric field around it, which is beneficial to the separation of photogenerated electron-hole pairs and reduces the recombination rate of photogenerated electron-hole pairs, thus improving the photocatalytic performance of TiO 2 .

Analysis of PM2.5 adsorption mechanism
Tourmaline is a multi-element natural mineral, the main chemical composition is SiO 2 , TiO 2 , CaO, K 2 O, LiO, Al 2 O 3 , B 2 O 3 , MgO, Na 2 O, Fe 2 O 3 , FeO, MnO, P 2 O 5 , containing magnesium, aluminum, iron, boron and other 10 kinds of beneficial trace elements to the human body. The electrical effect of tourmaline mainly refers to the secondary thermoelectric effect caused by thermal expansion and piezoelectric effect. Its thermoelectricity is a charged, asy mmetric and non-harmonic vibration. The thermoelectric coefficient K increases nonlinearly with the increase of temperature. The electric field effect of tourmaline is mainly manifested as: the electrolysis effect of electric field on water; electrostatic field adsorption and neutralization of charged ions, tourmaline also has high mechanical and chemical stability, tourmaline does not have saturation limit.
The purification efficiency of PM2.5 and PM10 particles in automobile exhaust at the micrometer of doped nano-titanium dioxide tourmaline composites reached 29.9% and 25.2%, respectively. This is because natural mineral tourmaline as a special structure of polar crystals, itself can produce long-term ions, and permanently release air negative ions and far infrared. Air negative ions can neutralize positively charged suspended particles in the air, resulting in the settlement of suspended particles.Moreover, tourmaline can form an electric field around itself because of its permanent electrode property, and adsorb charged particles in the air.

Conclusion
(1) The addition of nano-TiO 2 /tourmaline composites has a certain effect on the properties of evaporation residue of SBR modified emulsified asphalt, which can increase its viscosity by 15.3%, enhance its heat resistance and temperature stability by 8.3%, but reduce its deformation resistance by 16.3%.
(2) Intermediate value of MS-3 mineral aggregate gradation range specified in specification for microsurfacing. The best oil-stone ratio is 6.5%. The optimum dosage of SBR modified emulsified asphalt is 10.5%. The addition of nano-TiO 2 /tourmaline composite can improve the road performance of microsurfacing to a certain extent, especially the addition of 7% nano-TiO 2 /tourmaline composite can improve the wear resistance of 4% and the high temperature stability of 14.6%.
(3) Based on the research direction of this paper and the design idea of relevant design schemes, a detection device for tail gas purification and PM2.5 adsorption effect is independently developed.The test method and evaluation index for the purification and adsorption of tail gas pollutants by preventive maintenance sealing materials were determined.
(5) The composite method of loading nano-TiO 2 on tourmaline surface reduces the aggregation of nano-TiO 2 aggregates, improves the dispersion of nano-TiO 2 materials, and promotes the catalytic reaction of nano-TiO 2 materials. The nano-TiO 2 loaded on the tourmaline surface contains anatase and rutile, and the tourmaline phase does not change. The experimental reaction process and the combination of the two substances do not change the structure of the two. The two work together and each can exert the material characteristics.
(6) Tourmaline has its own permanent polarization effect. The generated permanent electric field can accelerate the separation of photogenerated electron-hole pairs of TiO 2 , improve its redox ability, and also adsorb charged gas molecules and charged particles in the air.The piezoelectricity and thermoelectricity of tourmaline make it permanently release air negative ions, and neutralize the electricity with positive suspended particles in the air, so that the suspended particles settle.

Data availability statement
All data that support the findings of this study are included within the article (and any supplementary files).
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