Test study and molecular dynamics simulation of Fe3+ modified TiO2 absorbing automobile exhaust

Feng Lai; Hongliang Zhang; Kongfa Zhu; Man Huang

doi:10.1371/journal.pone.0263040

Abstract

With the growth of the economy, the number of automobiles on the road is fast growing, resulting in substantial environmental pollution from exhaust gas emissions. In the automobile factory, some improvements have been achieved by constructing devices to degrade automobile exhaust. However, although most of the vehicle exhaust emissions have met the national standards, the exhaust gas is superimposed at the same time period due to the increasing traffic volume, making the exhaust emissions seriously reduce the air quality. Therefore, the scholars in the road field began to study new road materials to degrade vehicle exhaust, which has gradually become one of the effective ways to reduce automobile exhaust. Photocatalyst materials have been widely concerned because of their ability to oxidize harmful gases by solar photocatalysis. Yet, the effect has been not satisfactory because of the small light response range of photocatalyst material, which restricts the catalytic effect. In this study, this paper attempts to use Fe³⁺ to modify the TiO₂, which is one of the main photocatalytic materials, to expand the range of light reaction band and to improve the degradation effect of automobile exhaust. The degradation effects of ordinary TiO₂ and modified TiO₂ on automobile exhaust were compared by test system in the laboratory. The results show that the modified TiO₂ can effectively improve the performance of vehicle exhaust degradation. Moreover, the molecular dynamics method was used to establish the channel model of TiO₂, and the dynamic process of automobile exhaust diffusion and absorption was simulated. The diffusion law and adsorption process of different types of automobile exhaust gas such as NO, CO, and CO₂ in the TiO₂ channel were analyzed from the molecular scale through the radial concentration distribution and adsorption energy.

Citation: Lai F, Zhang H, Zhu K, Huang M (2022) Test study and molecular dynamics simulation of Fe³⁺ modified TiO₂ absorbing automobile exhaust. PLoS ONE 17(1): e0263040. https://doi.org/10.1371/journal.pone.0263040

Editor: Mahendra Singh Dhaka, Mohanlal Sukhadia University, INDIA

Received: September 26, 2021; Accepted: January 11, 2022; Published: January 26, 2022

Copyright: © 2022 Lai et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the manuscript and its Supporting Information files.

Funding: The authors(FL, HZ, KZ, MH)greatly acknowledge the financial support from the Natural Science Basic Research Plan in Guangdong Provincial Communication Department (No. [2016]611). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

1. Introduction

With the improvement of the economic level and the rapid development of automobile manufacturing industry, the number of automobiles has increased rapidly, resulting in substantial environmental pollution from automobile emissions [1]. Also, the automobile exhaust is the one of the main cause of weather disaster smog. Smog is mainly composed of carbon monoxide, sulphur and nitrogen oxides, which can be produced by incomplete burned fuel with the car moving [2]. Hong, Y. found that automobile exhaust contributed significantly to air pollution and haze, accounting for about 38% [3]. Similarly, Wang, F.C., using Fault Tree Analysis (FTA), indicated that the vehicle exhaust emissions had the great impacts on urban smog, with the contribution ratio reaching 38.4% [4]. Air pollution could cause some harm to respiratory and immune functions of the human body, reducing lung function and increasing the incidence rate of chronic bronchitis and asthma. Automobile exhaust mainly contains carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO, NO₂) and particulate pollutants. In many air quality monitoring centers in big cities, automobile exhaust has become the primary air pollutant.

How to lessen the environmental pollution caused by automotive emissions has become a hot topic among scholars. In addition to build vehicle devices, improving road materials to reduce the impact of exhaust on the environment has become a new direction. At present, nano photocatalytic materials have been used as new materials for air purification due to their good photocatalytic activity, chemical stability and recyclability. The main photocatalyst materials are semiconductor oxides (ZnO, TiO₂, SnO₂, ZrO₂) and semiconductor sulfides (CdS, PdS). Among them, TiO₂ is widely used because it has many advantages, such as fast degradation rate, mild reaction conditions, low price, non-toxic [5,6]. However, the bandgap of TiO₂ is about 3.2eV and an corresponding excitation wavelength is 387nm, and it belongs to the ultraviolet region, which only make up less than 5% of the solar spectrum. Therefore, it is necessary to modify it to expand the range of light reaction band and to improve the catalytic effect.

There are many ways to modify the TiO₂, such as metal ion doping, noble metal deposition, composite with other semiconductors, modification in its thin film by post treatment, etc. Among them, the noble metal deposition method is to deposit Ru, Pt, Au on the surface of TiO₂. This modified way can obviously improve the degradation rate of some organic compounds, but the cost is relatively high. The semiconductor composite method is to grind and dissolve the semiconductor with a narrow bandgap and high conduction band position and disperse it in a continuous matrix with wide bandgap photocatalyst materials. Through recombination, the separation and expansion of charge can be promoted. However, it is necessary to adjust the ratio of the two materials in order to obtain the optimal bandgap, which increases the difficulty of the method and is not conducive to its popularization and application. The properties of titanium dioxide films, such as optical and electrical properties, can be tailored by post treatment in various thermal atmospheric conditions, primarily including thermal annealing in air and vacuum, to improve the catalytic efficiency, and the treated film is widely applied as optical window in Cd-based and electron transport layer in perovskite solar cells [7–10]. Although its modification effect is superior, its procession is complicated and requirements on equipment is complex. The method of doping metal ions can cause lattice distortion, form defects, affect the motion of electron-hole pairs, change the band structure of TiO₂, and finally change the photocatalytic activity of TiO₂. In previous studies, this method is widely used because of its simplicity and economy.

El-Bahy, Z.M., et al compared the effect of TiO₂ doped with lanthanide ion (La³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, and Yb³⁺) on photodegradation and pointed out that lanthanide ions can improve the photocatalytic effect of TiO₂, especially Gd³⁺ [11]. Doping TiO₂ with Fe³⁺, Mo⁵⁺, Ru³⁺, Os³⁺, Re⁵⁺, V⁴⁺and Rh³⁺ also improved the photocatalytic effect, in contrast, Co³⁺ and Al³⁺ had opposite effect, which decreased the photoactivity [12]. Further, Wang, X.C., et al. studied the promoting effect of multi‑transition metals (Mo, Ce, Cu, Fe, W, Zr, P) doped with TiO₂, indicating the catalytic effects of transition metals doped with TiO₂ following the order of Mo > Fe≈Zr > Cu > W > P > Ce [13]. Choi, W. et al. [14] studied the photocatalytic properties of TiO₂ doped with 21 transition metals. The results showed that compared with other transition metal ions, Fe³⁺ and Cu ions doping broaden the range of light responded in a certain range, and make the TiO₂ powder have better catalytic activity. The TiO₂ doped with iron ions largely determines its optical properties [15]. TiO₂ doped with Fe³⁺ ions showed better light absorption in the UV and visible regions due to the reduction in band gap energy compared to pure TiO₂ [16]. The presence of Fe³⁺ doping in TiO₂ crystal lattice causes the shifted absorption edge towards longer wavelengths where the maximum of solar energy light is located to enhanced response to the visible-light region [10]. In order to study the purification effect of photocatalytic material TiO₂ on automobile exhaust gas, Kuang, D.L. [17] et al. mixed different amounts of Fe³⁺into TiO₂ and calcined at 500°C, and then X-ray diffraction measurement and infrared spectrum analysis were carried out. The results showed that the purification efficiency of modified TiO₂ was higher than that of undoped TiO₂. For example, the purification rate of CO and hydrocarbon increased by 0.6% and 2.3% respectively. This is because Fe³⁺ can capture electrons and holes at the same time, which reduces the recombination probability of electron-hole pairs.

In addition to experiments, molecular dynamics (MD) simulation is also introduced in the study of photocatalytic materials absorbing automobile exhaust, because it is the computer simulation of a real molecular system, which can obtain the data that is difficult or impossible to obtain in experiments. Based on mechanical theory and computing technology, MD simulation can simulate and predict the composition, structure, inherent properties and performance of materials. Many scholars have used MD to simulate the physical and chemical properties of TiO₂ and obtain the process information. Predota, M. et al. [18,19] studied the adsorption of water molecules on rutile TiO₂ (110) surface by the MD method. Koparde, V. N. and Cummings, P. T. [20] also used the MD simulation to study the adsorption of water molecules on rutile and anatase titanium dioxide nanoparticles. Lin, H. F. et al. [21] studied the adsorption of CO on TiO₂ particles with different crystal forms (rutile and anatase). The simulation result showed that at different temperatures, CO showed stronger adsorption on anatase.

2. Preparation of modified TiO₂ powder

10g Fe₂O₃(99.5% purity) powder and 990g TiO₂(99.8% purity) powder (the mass ratio is 1:99) were weighed on a precision electronic balance, and the mixed powder was poured into the agate pot of the ball mill. At the same time, some ball-milled balls with a diameter of 1cm were added as the ball milling medium. The mass ratio of the ball-milled beads and the target powder was about 1:1. The rotational speed was set at 300r/min, and the ball milling lasted for about 20h. And then the mixed powder was taken out from the ball mill and put into muffle furnace. Since the nano-TiO₂ is amorphous without photocatalytic activity, it needs to be heat treated to obtain polycrystalline TiO₂ in order to improve its catalytic activity [22]. From the research of Abdullah, SA, et al. about nano-TiO₂ after annealing at different temperatures, it indicates that there were more crystalline phase (mainly including anatase phase and rutile phase) and the proportion of crystalline phases was optimal at 500°C, which can lead to the increase in catalytic activity [23]. In addition to temperature, calcination time is also important. If the time is too long, the structure of titanium dioxide gradually changes from anatase to rutile phase with low photocatalytic activity and the particle size increases. However, if the time is too short, less crystallization phase is not conducive to catalysis. Therefore, according to previous studies and preliminary tests, the heat-treated methods of nano-TiO₂ is as follow. The temperature was turned to 500°C at the speed of 8°C/min, lasting the temperature for 4h. After that, the target powder was cooled to room temperature and taken out for use (as shown in Fig 1) [22].

Download:

Fig 1. Ball mill and modified TiO₂ powder.

https://doi.org/10.1371/journal.pone.0263040.g001

The ball milling method for preparing modified TiO₂ can make iron oxide and titanium dioxide interact to achieve the purpose of ion doping. In the process of ball milling, there is a strong collision between TiO₂ powders, and plastic deformation occurs, resulting in large stress and strain, which makes the lattice of TiO₂ seriously distorted. At the same time, a lot of heat is released during the ball milling process, and the strong mechanical force can make Fe³⁺ separated from Fe₂O₃ and diffuse into the distorted lattice of TiO₂. In addition, ball milling can reduce the particle size of TiO₂, to obtain iron modified nano TiO₂ powder with a large specific surface area. The method has the advantages of low threshold, simple process and large-scale continuous production.

3.Test study

The test process was as follows: firstly, the room temperature was adjusted to the initial test temperature through air conditioning, then the fan was turned on to prevent gas stratification, and the cover plate was closed. The sealing ring between the cover plate and the tail gas reaction chamber was used to ensure the tightness of the equipment. Secondly, the switch of exhaust gas supply source was turned on to introduce a certain amount of automobile exhaust into the reaction chamber about 10 min. When the vehicle exhaust reached the initial concentration, the switch of exhaust gas was turned off and then the incandescent light was turned up to start the degradation test. The test device is shown in Fig 2. The exhaust gas concentration in the test process was read and recorded by the automobile exhaust gas analyzer every 10 minutes. The test lasted for 60 minutes, so as to analyze the variation law of automobile exhaust gas concentration with time.

Download:

Fig 2. The test device of automobile exhaust.

https://doi.org/10.1371/journal.pone.0263040.g002

4. Test method and molecular dynamics simulation method of absorbing automobile exhaust gas

In this study, the commercial software Materials Studio was used to establish the TiO₂ pore model to simulate the adsorption of automobile exhaust (CO, NO₂ and NO). There are three crystal structures of TiO₂ in nature: brookite, anatase and rutile [24]. Among them, the thermal stability of TiO₂ with brookite structure and anatase structure is not good, so rutile type TiO₂ is mainly used in industry. In the XRD spectra made by other scholars of Fe³⁺ modified nano titanium dioxide, the structure of unmodified titanium dioxide is amorphous, and gradually changes to a crystalline structure (anatase and rutile) with the doping of iron ions [16]. Table 1 and Fig 3 show Lattice constants and Cell model of TiO₂.

Download:

Fig 3. Cell model of TiO₂.

https://doi.org/10.1371/journal.pone.0263040.g003

Download:

Table 1. Lattice constants of TiO₂.

https://doi.org/10.1371/journal.pone.0263040.t001

In crystallography, Miller indexes are commonly used to determine the cutting index of a single cell by determining three edges as the coordinate system. Taking the lattice side length as the unit, the intercept of a plane on the three axes of the cell rectangular coordinate system is measured, which is expressed as Miller index (h k l). The cutting index of the cell determines the bare atoms on the surface, which directly affects the surface properties of the crystal.

In nature, the main Miller indexes of TiO₂ are (1 0 0) (0 1 0) (0 0 1). From previous studies, the crystal face index (1 0 0) of TiO₂ is most extensive. Therefore, this paper used the crystal face index to cut TiO₂. When cutting, the thickness was set to 10 Å and the model was transformed from 2D to 3D by adding a vacuum layer. Then, the supercell tool in the build module of materials studio was used to establish the TiO₂ supercell model (Fig 4) with a ×b ×C = 5 ×7 ×1 repetitions, so as to expand the original cell of TiO₂. Finally, the size of the supercell was about 55 Å× 53 Å× 10 Å to realize the contact with automobile exhaust in a larger area and to obtain more reasonable simulation results. According to the composition and mass ratio of each component in automobile exhaust, at the same time, considering the feasibility of molecular dynamics simulation, the number ratio of main components of automobile exhaust was determined as CO: NO: NO₂: SO₂: C₂₀H₁₂ = 90:4:8:2:2.

Download:

Fig 4. The supercell model of TiO₂.

https://doi.org/10.1371/journal.pone.0263040.g004

TiO₂ powder usually has some microporous structure, which is conducive to adsorption of automobile exhaust. Based on this, through the build layer tool in Materials Studio software, this paper built the pore model unit of TiO₂ absorbing automobile exhaust gas by superposition in the order of TiO₂, automobile exhaust and TiO₂, as shown in Fig 5. Compared with unmodified TiO₂, Fe³⁺ ion modified TiO₂ is different in that the trivalent Fe replaces the tetravalent Ti atom, which leads to the imbalance of charge and shows strong external activity.

Download:

Fig 5. The pore model of TiO₂ absorbing automobile exhaust.

https://doi.org/10.1371/journal.pone.0263040.g005

The setting of several important parameters in the simulation process: inorganic TiO₂ and organic gases were both included in the model, so, compass force field which can not only calculate metal inorganic compounds but also analyze organic compounds was adopted in this study. In the model, because the number of particles remained unchanged and the pore volume remained constant, the constant volume and temperature (NVT) ensemble was selected to simulate the absorption of vehicle exhaust gas by TiO₂ at a certain temperature. After the size of a single box was determined, a reasonable cut-off radius which refers to the effective interaction distance between atoms should be set in the simulation process. Generally, the cut-off radius should not be greater than half of the box size to avoid repeated calculation [25,26]. So, in this paper, the cut-off radius was set as 15.5 Å, which can avoid repeated calculation and achieve good simulation accuracy.

In order to get the equilibrium of the dynamic simulation quickly, the energy optimization of the channel model was carried out and the model was preliminarily optimized. At the same time, before MD simulation, the upper and lower TiO₂ molecular layers were fixed, and the pore model was fully relaxed to simulate the adsorption of TiO₂ on automobile exhaust, which made the simulation closer to the real situation. The NVT ensemble and compass II force field were used to calculate the MD equilibrium of 100 PS at a standard atmospheric pressure at 298K and 333K respectively, and the simulation results at ambient temperature and high temperature were obtained respectively.

After molecular dynamics calculation, the equilibrium adsorption model of automobile exhaust gas by titanium dioxide was obtained. Fig 6 shows the comparison of adsorption effects of unmodified TiO₂ and Fe³⁺ ion modified TiO₂ on automobile exhaust gas from the perspective of visualization after MD equilibrium. It can be seen that most of the automobile exhaust molecules orderly approach to the surface of TiO₂. The CO molecule changed from a disordered state to "standing" on the surface of TiO₂, and the C atom end was close to TiO₂, and the O atom end was far away from TiO₂. The main reason is that there are 10 valence electrons in the CO molecule, which form three chemical bonds: one σ bond and two π bond. One of the two π bonds is a coordination bond, and the bonding electrons are completely provided by O atoms. C atoms in CO molecules have a slightly negative charge, which makes the arc electron pairs on C atoms easily enter the empty orbits of other atoms and form coordination bonds.

Download:

Fig 6. Adsorption on exhaust molecules of unmodified and modified TiO₂ on automobile exhaust before and after MD equilibrium in TiO₂ channel.

(a) Unmodified TiO₂ before MD (b) Unmodified TiO₂ before MD (c) Modified TiO₂ after MD.

https://doi.org/10.1371/journal.pone.0263040.g006

Therefore, in the reaction, CO is an electron pair donor and can form complexes with some atoms with empty orbitals. However, for NO and NO₂, O atoms are closer to the surface of TiO₂, and N atoms are slightly separated. There is no obvious regularity in the distribution of SO₂ in the pore.

5. Results and discussion

5.1. Analysis of test result

In order to effectively analyze the degradation effect of powder on automobile exhaust, the degradation efficiency was used as the evaluation index. and the degradation ratio of exhaust gas was evaluated in different periods. The calculation formula is shown in Eq (1) [27], and the calculation results are shown in Table 2. (1) Where D is the degradation ratio of gas in the target stage, C_before is the initial concentration, C_after is the end concentration.

Download:

Table 2. Concentration variation and degradation ratio of vehicle exhaust gas.

https://doi.org/10.1371/journal.pone.0263040.t002

It can be seen from Table 2 and Fig 7 that, compared with the blank group, ordinary TiO₂ powder has some degradation effect on CO, NO, NO₂ and C_xH_y in automobile exhaust. After 60 min, the degradation efficiency of these gas reached 7.89%, 40.74%, 10.87% and 9.93%, respectively. It can be seen that TiO₂ powder had good degradation effect on NO. At the same time, a part of NO₂, C_xH_y and CO was also degraded. After TiO₂ modified by Fe³⁺ions, the degradation effect of NO was significantly improved (increase by 51.57%). Due to its extrinsic bandgap with low energy, Fe³⁺ incorporated into the crystal structure of TiO₂ promotes electron-hole separation, and deposits active sites on the surface of TiO₂, thus improving the adsorption of small molecular weight of NO with fast diffusion velocity [28]. Also, there is some positive effect about the degradation of CO (increase by 10.11%). Yet, there is no significant improvement in the degradation of other gases, such as NO₂, C_xH_y. During the process of automobile exhaust degradation, the concentration of NO₂ and CO₂ increases first and then decreased. The main reason is that, in the first half, the modified TiO₂ powder oxidizes harmful gas NO and CO into NO₂ and non-toxic CO₂, and the amount of NO₂ andCO₂ generated by oxidation may be more than that of purified NO₂ and CO₂, so the concentration is going up slightly [29–31]. In the latter half, the NO₂ and CO₂ are photocatalyzed into organic matter or salts, thus reducing the concentration.

Download:

Fig 7. Variation curve of concentration of automobile exhaust.

(a) Concentration variation of NO during degradation process. (b) Concentration variation of NO₂ during degradation process. (c) Concentration variation of C_xH_y during degradation process. (d) Concentration variation of CO during degradation process. (e) Concentration variation of CO₂ during degradation process.

https://doi.org/10.1371/journal.pone.0263040.g007

5.2. Simulation analysis of automobile exhaust diffusion in the pore of TiO₂

Diffusion analysis is a statistical analysis of the migration of materials in space caused by the thermal movement of a large number of molecules and atoms. The molecular diffusion coefficient is often used to characterize the diffusion velocity. The molecular diffusion coefficient which is often used to characterize the diffusion rate is the proportional constant of the concentration difference between two points and the distance, when a component molecule is transferred from a high concentration place to a low concentration place. For a long time, one-sixth of the slope of the MSD curve is the diffusion coefficient of the system. Therefore, in MS software, the MSD is used to analyze the diffusion velocity of the system, and the calculation formula is Eq (2) [32–35]. (2) Where r(t) is the displacement of particles at time t (m); r(0) is the displacement of particles at the initial time (m); < > is the average of all atoms in the system.

The diffusion velocity of different types of automobile exhaust molecules in the modified and unmodified TiO₂ channels are shown in Figs 8 and 9, respectively. It can be seen from the figure that the diffusion velocity of CO molecules with the smallest molecular weight was the fastest. The second was NO and NO₂, and the diffusion rates of these two gases were very close. The third was C₁₂H₁₂, which had the largest molecular weight because the heavy molecule slowed down the diffusion velocity due to its large volume and weight. The molecule of the gas with the slowest diffusion speed was SO₂, and this law was consistent in the modified and unmodified TiO₂ channels. It shows that the adsorption powder of TiO₂ for SO₂ molecules was weaker than other exhaust molecules. From the energy point of view, the diffusion process is caused by energy gradient, and it is also the process of system transition from the unsteady state (high energy) to steady-state (low energy). It also reflects the change of various forces when the system tends to be stable.

Download:

Fig 8. Diffusion velocity of automobile exhaust gas in modified TiO₂ channel at ambient temperature (298K).

https://doi.org/10.1371/journal.pone.0263040.g008

Download:

Fig 9. Diffusion velocity of automobile exhaust gas in unmodified TiO₂ channel at ambient temperature (298K).

https://doi.org/10.1371/journal.pone.0263040.g009

At the same time, the diffusion velocity of CO, NO, NO₂ and C₁₂H₁₂ molecules in the modified TiO₂ channel was faster than that in the unmodified TiO₂ channel, while the adsorption of SO₂ molecules had almost no change. The results show that the modification of TiO₂ improved its attraction to most automobile exhaust molecules and promoted the directional diffusion of these molecules to the surface of TiO₂. This is due to the incorporation with Fe³⁺, there are more active sites on the surface of titanium dioxide, which accelerates the adsorption of exhaust gas molecules, thus promoting the diffusion of exhaust gas molecules on the crystal surface [36].

5.3. Radial concentration analysis of automobile exhaust on TiO₂ surface

The concentration distribution of the molecule on the crystal surface is an important index of the adsorption of the molecule by the crystal. The closer the adsorption distance and the higher the concentration, the better the adsorption effect between the molecule and crystal [37]. In MD simulation, the radial distribution function (g(r)), which can be explained as the ratio of local density to average density bulk density of the system, is often used to characterize the cross-sectional concentration distribution of particles.

In this study, the geometric center of the TiO₂ layer was used as the reference point to calculate the distance between automobile exhaust molecules and TiO₂. The shorter the distance and the higher the concentration, the better the absorption effect of automobile exhaust, and the less easy to release. The calculation formula of the radial distribution function is Eq (3) [38]. (3) where N is the total number of molecules (number); T is the total calculation time (steps); δ_r is the designed difference in the distance; and △N is the number of molecules within the interval of r→r+δ_r.

Fig 10 shows the radial distribution concentration of automobile exhaust on the surface of TiO₂ powder under three conditions (unmodified TiO₂, TiO₂ modified by Fe³⁺ on the surface of 50% Ti atom and TiO₂ modified by Fe³⁺ on surface of 100% Ti atom). It can be seen that after modification, the radial concentration of automobile exhaust absorption at the same position in the TiO₂ channel has been significantly increased, and the order of concentration is 100% Fe^{3 +} modified TiO₂ > 50% Fe^{3 +} modified TiO₂ > unmodified TiO₂. Especially, the difference was more obvious in the near end of TiO₂. This may be attributed to the fact that the titanium dioxide fully modified by iron ions with low bandgap promotes the separation of electron/hole and further improves the catalytic efficiency [39]. This phenomenon shows that Fe^{3 +} can effectively improve the adsorption of TiO₂ powder to automobile exhaust, and the more complete the modification, the better the effect.

Download:

Fig 10. Radial relative concentration of automobile exhaust on different types of TiO₂ surface.

https://doi.org/10.1371/journal.pone.0263040.g010

5.4. Calculation and analysis of adsorption energy of automobile exhaust on TiO₂ surface

In the previous section, the improvement effect of modified TiO₂ on automobile exhaust gas adsorption was analyzed from the perspective of radial relative concentration, and the adsorption strength was determined from the perspective of distance and concentration. This section will quantitatively analyze the absorption effect of modified TiO₂ on automobile exhaust from the perspective of energy.

When the automobile exhaust gas is adsorbed in the TiO₂ channel, the two independent systems of vehicle exhaust and TiO₂ gradually become a whole system, and refer to other systems, the reduction of system energy is considered as the adhesion work [40]. In other words, the adhesion work is the difference between the total energy of a whole-body (formed by adsorption of automobile exhaust and TiO₂) and the sum of the surface energy of vehicle exhaust and TiO₂ respectively before adsorption. The larger the adhesion work value between automobile exhaust and TiO₂, the more difficult the automobile exhaust to separate from the surface of TiO₂, which means that the adsorption is more difficult to be destroyed [41,42]. The calculation method is shown in Eq (4). (4) where W_adhension represents the work of adhesion at the interface (mJ m^-2). E_total represents the interfacial potential energy of TiO₂ and automobile exhaust after molecular dynamic adsorption equilibrium (kcal mol^-1). E_gas is the potential values of the automobile exhaust after MD simulation (kcal mol^-1). E_TiO2 are the potential values of the TiO₂ after MD simulation (kcal mol^-1). A represents the Connolly area of the interface (Å²). △E represents the Variation value of automobile exhaust gas during the adsorption process (kcal mol^-1).K = 695 [43] is the conversion coefficient for units.

After the MD equilibrium calculation of the two-phase interface model of automobile exhaust (gas) and TiO₂ (solid), the model of TiO₂ adsorption on automobile exhaust was built. And it is shown in Fig 11(a). The interface model was divided into two parts: TiO₂ model and automobile exhaust model. The energy function of force module in Materials Studio software was used to calculate the energy of interface model (a), the disassembled TiO₂ model (b) and automobile exhaust model (c) respectively, so as to calculate the adhesion work between TiO₂ and automobile exhaust gas using the above formula. The calculation results are shown in Table 3. The results present that the adhesion work between the automobile exhaust and TiO₂ was obviously improved. The 50% Fe³⁺ and 100% Fe³⁺modified TiO₂ increased about 40% and 73%, respectively. The incorporation of Fe³⁺ into the structure of TiO₂, causing the reduction of the bandgap, the prevention of recombination of electron/hole and extension of the life of charge separation, increases the number of active points and absorbs more exhaust molecules, which results in the increase of adhesion work [36]. Therefore, Fe³⁺ modification is beneficial to enhance the adsorption capacity of TiO₂ on automobile exhaust, thus improving the degradation effect.

Download:

Fig 11. Disassembled model after MD equilibrium.

(a) Automobile exhaust in TiO₂ channel (b) TiO₂ (c) Automobile exhaust.

https://doi.org/10.1371/journal.pone.0263040.g011

Download:

Table 3. Calculation of adhesion work.

https://doi.org/10.1371/journal.pone.0263040.t003

6. Conclusions

In this study, Fe³⁺ was used to modify the photocatalyst material TiO₂. Through the absorption test of automobile exhaust and the diffusion and absorption of automobile exhaust gas in the TiO₂ channel simulated by molecular dynamics method, it is proved that the modification can effectively improve the degradation effect of TiO₂ on automobile exhaust. The conclusions are as follows:

Test results show that the modification of TiO₂ can obviously improve the degradation effect of NO in automobile exhaust, but it is not obvious to improve the degradation effect of other exhaust gases such as CO and NO₂.
MD simulation shows that the diffusion velocity of most automobile exhaust molecules in the modified TiO₂ channels is faster than that in the unmodified TiO₂ channels, which indicates that the modification of TiO₂ improves the attraction of most automobile exhaust molecules and promotes the directional diffusion of automobile exhaust molecules to the surface of TiO₂.
Through MD simulation and analysis of the radial concentration and the adsorption energy of exhaust molecules in the TiO₂ channel, it is concluded that Fe^{3 +} modification of TiO₂ powder is beneficial to improve the adsorption of automobile exhaust molecules, and the more the modification, the better the effect.

Supporting information

S1 File. S1 File contains the original data for Figs 8–10.

https://doi.org/10.1371/journal.pone.0263040.s001

(XLSX)

References

1. Rahman MM, Kim KH. Exposure to hazardous volatile pollutants back diffusing from automobile exhaust systems. J Hazard Mater. 2012; 241–242: 267–278. pmid:23072984
- View Article
- PubMed/NCBI
- Google Scholar
2. Tavares JR, Sthel MS, Campos LS, Rocha MV, Lima GR, da Silva MG, et al. Evaluation of pollutant gases emitted by ethanol and gasoline powered vehicles. Procedia Environ Sci. 2011; 4: 51–60.
- View Article
- Google Scholar
3. Hong Y, Li CL, Li XL, Ma YJ, Zhang YH, Zhou DP, et al. Analysis of compositional variation and source characteristics of water-soluble ions in PM_2.5 during several winter-haze pollution episodes in Shenyang, China. Atmosphere (Basel). 2018; 9: 280.
- View Article
- Google Scholar
4. Wang FC, Zheng PM, Dai JL, Wang H, Wang RQ. Fault tree analysis of the causes of urban smog events associated with vehicle exhaust emissions: A case study in Jinan, China. Sci Total Environ. 2019; 668: 245–253. pmid:30852201
- View Article
- PubMed/NCBI
- Google Scholar
5. Waldner G, Pourmodjib M, Bauer R, Neumann SM. Photo-electrocatalytic degradation of 4-chlorophenol and oxalic acid on titanium dioxide electrodes. Chemosphere. 2003; 50: 989–998. pmid:12531704
- View Article
- PubMed/NCBI
- Google Scholar
6. Daghrir R, Drogui P, Robert D. Photoelectrocatalytic technologies for environmental applications. J Photochem Photobiol A Chem. 2012; 238: 41–52.
- View Article
- Google Scholar
7. Agarwal R, Himanshu , Patel SL, Verma M, Chander S, Ameta C, et al. Tailoring the physical properties of titania thin films with post deposition air and vacuum annealing. Opt Mater (Amst). 2021; 116: 111033.
- View Article
- Google Scholar
8. Agarwal R, Himanshu , Patel SL, Chander S, Ameta C, Dhaka MS. Vacuum annealing level evolution of titania thin films: Functionality as potential optical window in solar cells. Mater Lett. 2020; 277: 128368.
- View Article
- Google Scholar
9. Agarwal R, Himanshu , Patel SL, Chander S, Ameta C, Dhaka MS. Understanding the physical properties of thin TiO₂ films treated in different thermal atmospheric conditions. Vacuum. 2020; 177: 109347.
- View Article
- Google Scholar
10. Tsang CHA, Li K, Zeng YX, Zhao W, Zhang T, Zhan YJ, et al. Titanium oxide based photocatalytic materials development and their role of in the air pollutants degradation: Overview and forecast. Environ Int. 2019; 125: 200–228. pmid:30721826
- View Article
- PubMed/NCBI
- Google Scholar
11. El-Bahy ZM, Ismail AA, Mohamed RM. Enhancement of titania by doping rare earth for photodegradation of organic dye (Direct Blue). J Hazard Mater. 2009; 166; 138–143. pmid:19097702
- View Article
- PubMed/NCBI
- Google Scholar
12. Paola AD, Garc´ıa-López E, Marc`I G, Mart´ın C, Palmisano L, Rives V, et al. Surface characterisation of metal ions loaded TiO₂ photocatalysts: structure–activity relationship. Appl Catal B. 2004; 48: 223–233.
- View Article
- Google Scholar
13. Wang XC, Zhang XJ, He MY, Song YJ, Li CQ, Wang H. Promoting effect of multi‑transition metals on the NO reduction by NH₃ over TiO₂ catalyst studied with in situ DRIFTS. Res Chem Intermediat. 2020; 46: 1663–1684.
- View Article
- Google Scholar
14. Choi W, Termin A, Hoffmann MR. The role of metal ion dopants in quantum-sized TiO₂: correlation between photoreactivity and charge carrier recombination dynamics. J Phys Chem. 1994; 98: 13669–13679.
- View Article
- Google Scholar
15. Kissoum Y, Mekki DE, Bououdina M, Sakher E, Bellucci S. Dependence of Fe doping and milling on TiO₂ phase transformation: optical and magnetic studies. J Supercond Nov Magn. 2020; 33: 427–440.
- View Article
- Google Scholar
16. Zedek R, Djedjiga H, Megherbi M, Belkaid MS, Ntsoenzok E. Effects of slight Fe(III)-doping on structural and optical properties of TiO₂ nanoparticles. J Solgel Sci Technol. 2021; 100: 44–54.
- View Article
- Google Scholar
17. Kuang DL, Pei JZ, LI R, Ma SW, Ouyang H, Ni ZJ. The application research of modified nano titanium dioxide in automobile exhaust purification (in Chinese). Materials Review. 2014; 28(20): 18–22.
- View Article
- Google Scholar
18. Predota M, Bandura AV, Cummings PT, Kubicki JD, Wesolowski DJ, Chialvo AA, et al. Electric double layer at the rutile (110) surface (1): Structure of surfaces an d interfacial water from molecular dynamics by use of ab initio potentials. J Phys Chem B. 2004; 108: 12049–12060.
- View Article
- Google Scholar
19. Predota M, Cummings PT, Wesolowski DJ. Electric double layer at the rutile (110) surface (3):Inhomogeneous viscosity and diffusivity measurement by computer simulations. Journal of Physical Chemistry C. 2007; 111: 3071–3079.
- View Article
- Google Scholar
20. Koparde VN, Cummings PT. Molecular dynamics study of water adsorption on TiO₂ nan particles. J Phys Chem C. 2007; 111: 6920–6926.
- View Article
- Google Scholar
21. Lin HF, Lin HM, Hsu SL. Molecular simulation for gas adsorption at TiO₂ (rutile and anatase) surface. Nanostruct Mater. 1999; 12 (1/ 2/ 3/ 4): 357–360.
- View Article
- Google Scholar
22. Cui SC, Li R, Ma WS, Li MM, Cui JX, Pei JZ. Preparation, photocatalytic properties investigation and degradation rate study on nano-TiO₂ aerogels doped with Fe³⁺ for automobile emission purification. Mater Res Express. 2018; 5 (11): 115513.
- View Article
- Google Scholar
23. Abdullah SA, Sahdan MZ, Nafarizal N, Saim H, Cik Rohaida C. H, Adriyanto F. XRD and Raman spectroscopy study on the effects of post-annealing temperature of TiO₂ thin films. 2019 IEEE International Conference on Sensors and Nanotechnology, SENSORS and NANO, Penang, Malaysia. 2019; 8940092.
24. Kim DW, Enomoto N, Nakagawa Z, Kawamura K. Molecular dynamic simulation in titanium dioxide polymorphs: rutile, brookite, and anatase. J Am Ceram Soc. 2010; 79.4(2010): 1095–1099.
- View Article
- Google Scholar
25. Chen Z.L. Theory and practice of molecular simulation. Beijing: Chemical Industry Press; 2007.
26. L Yuan S. Molecular Simulation-Theory and Experiment. Beijing: Chemical Industry Press; 2016.
27. Cui SC, Xie BW, Li R, Pei JZ, Tian YF, Zhang JP, et al. g-C₃N₄/CeO₂ binary composite prepared and its application in automobile exhaust degradation. Materials. 2020; 13: 1274. pmid:32168856
- View Article
- PubMed/NCBI
- Google Scholar
28. Nasr M, Eid C, Habchi R, Miele P, Bechelany M. Recent progress on titanium dioxide nanomaterials for photocatalytic applications. ChemSusChem. 2018; 11: 3023–3047. pmid:29984904
- View Article
- PubMed/NCBI
- Google Scholar
29. Han YH, Zhang JJ, Zhao Y. Visible-light-induced photocatalytic oxidation of nitric oxide and sulfur dioxide: Discrete kinetics and mechanism. Energy. 2016; 103: 725–734.
- View Article
- Google Scholar
30. Yuan Y, Zhang JY, Li HL, Li Y, Zhao YC, Zheng CG. Simultaneous removal of SO₂, NO and mercury using TiO₂-aluminum silicate fiber by photocatalysis. Chem Eng J. 2012; 192: 21–28.
- View Article
- Google Scholar
31. Seifvand N, Kowsari E. Synthesis of mesoporous Pd-doped TiO₂ templated by a magnetic recyclable ionic liquid for efficient photocatalytic air treatment. Ind Eng Chem Res. 2016; 55: 10533–10543.
- View Article
- Google Scholar
32. Amirjalayer S, Tafipolsky M, Schmid R. Molecular dynamics simulation of benzene diffusion in mof‐5: importance of lattice dynamics. Angew Chem Int Edit. 2007; 46(3): 463–466. pmid:17131450
- View Article
- PubMed/NCBI
- Google Scholar
33. Chockalingam R, Natarajan U. Dynamics of conformations, hydrogen bonds and translational diffusion of poly (methacrylic acid) in aqueous solution and the concentration transition in MD simulations. Mol Phys. 2015; (ahead-of-print): 1–13.
- View Article
- Google Scholar
34. Dubbeldam D, Beerdsen E, Vlugt TJH, Smit B. Molecular simulation of loading-dependent diffusion in nanoporous materials using extended dynamically corrected transition state theory. J Chem Phys. 2005; 122(22): 224712. pmid:15974708
- View Article
- PubMed/NCBI
- Google Scholar
35. Hofmann D, Fritz L, Ulbrich J, Paul D. Molecular simulation of small molecule diffusion and solution in dense amorphous polysiloxanes and polyimides. Comput Theor Polym S. 2000; 10(5): 419–436.
- View Article
- Google Scholar
36. Chen JR, Qiu FX, Xu WZ, Cao SS, Zhu HJ. Recent progress in enhancing photocatalytic efficiency of TiO₂-based materials. Appl Catal A-Gen. 2015; 495: 131–140.
- View Article
- Google Scholar
37. Liu JZ, Yu B, Hong QZ. Molecular dynamics simulation of distribution and adhesion of asphalt components on steel slag. Constr Build Mater. 2020; 255: 119332.
- View Article
- Google Scholar
38. Ding GY, Yu X, Dong FQ, Ji ZZ, Wang JY. Using silane coupling agent coating on acidic aggregate surfaces to enhance the adhesion between asphalt and aggregate: a molecular dynamics simulation. Materials. 2020; 13: 5580. pmid:33297522
- View Article
- PubMed/NCBI
- Google Scholar
39. Liu M, Qiu XQ, Masahiro M, Kazuhito H. Energy-level matching of Fe(III) ions grafted at surface and doped in bulk for efficient visible-light photocatalysts. J Am Chem Soc. 2013; 135: 10064–10072. pmid:23768256
- View Article
- PubMed/NCBI
- Google Scholar
40. Hu B, Huang WK, Yu JL, Xiao ZC, Wu KH. Study on the adhesion performance of asphalt-calcium silicate hydrate gel interface in semi-flexible pavement materials based on molecular dynamics. Materials. 2021; 14: 4406. pmid:34442934
- View Article
- PubMed/NCBI
- Google Scholar
41. Xiong Y, Zhang C, Duan M, Chen J, Fang SW, Li J, et al. Insight into organic pollutant adsorption characteristics on a g‑C₃N₄ surface by attenuated total reflection spectroscopy and molecular dynamics simulation. Langmuir. 2021; 37: 7655–7667. pmid:34129343
- View Article
- PubMed/NCBI
- Google Scholar
42. Ma Y, Lu GW, Shao CJ, Li XF. Molecular dynamics simulation of hydrocarbon molecule adsorption on kaolinite (0 0 1) surface. Fuel. 2019; 237: 989–1002.
- View Article
- Google Scholar
43. Zhang HL, Huang M, Hong J, Lai F, Gao Y. Molecular dynamics study on improvement effect of bis(2-hydroxyethyl) terephthalate on adhesive properties of asphalt-aggregate interface. Fuel. 2020; 285. pmid:32952206
- View Article
- PubMed/NCBI
- Google Scholar

[ref1] 1. Rahman MM, Kim KH. Exposure to hazardous volatile pollutants back diffusing from automobile exhaust systems. J Hazard Mater. 2012; 241–242: 267–278. pmid:23072984
View Article
PubMed/NCBI
Google Scholar

[2] View Article

[3] PubMed/NCBI

[4] Google Scholar

[ref2] 2. Tavares JR, Sthel MS, Campos LS, Rocha MV, Lima GR, da Silva MG, et al. Evaluation of pollutant gases emitted by ethanol and gasoline powered vehicles. Procedia Environ Sci. 2011; 4: 51–60.
View Article
Google Scholar

[6] View Article

[7] Google Scholar

[ref3] 3. Hong Y, Li CL, Li XL, Ma YJ, Zhang YH, Zhou DP, et al. Analysis of compositional variation and source characteristics of water-soluble ions in PM_2.5 during several winter-haze pollution episodes in Shenyang, China. Atmosphere (Basel). 2018; 9: 280.
View Article
Google Scholar

[9] View Article

[10] Google Scholar

[ref4] 4. Wang FC, Zheng PM, Dai JL, Wang H, Wang RQ. Fault tree analysis of the causes of urban smog events associated with vehicle exhaust emissions: A case study in Jinan, China. Sci Total Environ. 2019; 668: 245–253. pmid:30852201
View Article
PubMed/NCBI
Google Scholar

[12] View Article

[13] PubMed/NCBI

[14] Google Scholar

[ref5] 5. Waldner G, Pourmodjib M, Bauer R, Neumann SM. Photo-electrocatalytic degradation of 4-chlorophenol and oxalic acid on titanium dioxide electrodes. Chemosphere. 2003; 50: 989–998. pmid:12531704
View Article
PubMed/NCBI
Google Scholar

[16] View Article

[17] PubMed/NCBI

[18] Google Scholar

[ref6] 6. Daghrir R, Drogui P, Robert D. Photoelectrocatalytic technologies for environmental applications. J Photochem Photobiol A Chem. 2012; 238: 41–52.
View Article
Google Scholar

[20] View Article

[21] Google Scholar

[ref7] 7. Agarwal R, Himanshu , Patel SL, Verma M, Chander S, Ameta C, et al. Tailoring the physical properties of titania thin films with post deposition air and vacuum annealing. Opt Mater (Amst). 2021; 116: 111033.
View Article
Google Scholar

[23] View Article

[24] Google Scholar

[ref8] 8. Agarwal R, Himanshu , Patel SL, Chander S, Ameta C, Dhaka MS. Vacuum annealing level evolution of titania thin films: Functionality as potential optical window in solar cells. Mater Lett. 2020; 277: 128368.
View Article
Google Scholar

[26] View Article

[27] Google Scholar

[ref9] 9. Agarwal R, Himanshu , Patel SL, Chander S, Ameta C, Dhaka MS. Understanding the physical properties of thin TiO₂ films treated in different thermal atmospheric conditions. Vacuum. 2020; 177: 109347.
View Article
Google Scholar

[29] View Article

[30] Google Scholar

[ref10] 10. Tsang CHA, Li K, Zeng YX, Zhao W, Zhang T, Zhan YJ, et al. Titanium oxide based photocatalytic materials development and their role of in the air pollutants degradation: Overview and forecast. Environ Int. 2019; 125: 200–228. pmid:30721826
View Article
PubMed/NCBI
Google Scholar

[32] View Article

[33] PubMed/NCBI

[34] Google Scholar

[ref11] 11. El-Bahy ZM, Ismail AA, Mohamed RM. Enhancement of titania by doping rare earth for photodegradation of organic dye (Direct Blue). J Hazard Mater. 2009; 166; 138–143. pmid:19097702
View Article
PubMed/NCBI
Google Scholar

[36] View Article

[37] PubMed/NCBI

[38] Google Scholar

[ref12] 12. Paola AD, Garc´ıa-López E, Marc`I G, Mart´ın C, Palmisano L, Rives V, et al. Surface characterisation of metal ions loaded TiO₂ photocatalysts: structure–activity relationship. Appl Catal B. 2004; 48: 223–233.
View Article
Google Scholar

[40] View Article

[41] Google Scholar

[ref13] 13. Wang XC, Zhang XJ, He MY, Song YJ, Li CQ, Wang H. Promoting effect of multi‑transition metals on the NO reduction by NH₃ over TiO₂ catalyst studied with in situ DRIFTS. Res Chem Intermediat. 2020; 46: 1663–1684.
View Article
Google Scholar

[43] View Article

[44] Google Scholar

[ref14] 14. Choi W, Termin A, Hoffmann MR. The role of metal ion dopants in quantum-sized TiO₂: correlation between photoreactivity and charge carrier recombination dynamics. J Phys Chem. 1994; 98: 13669–13679.
View Article
Google Scholar

[46] View Article

[47] Google Scholar

[ref15] 15. Kissoum Y, Mekki DE, Bououdina M, Sakher E, Bellucci S. Dependence of Fe doping and milling on TiO₂ phase transformation: optical and magnetic studies. J Supercond Nov Magn. 2020; 33: 427–440.
View Article
Google Scholar

[49] View Article

[50] Google Scholar

[ref16] 16. Zedek R, Djedjiga H, Megherbi M, Belkaid MS, Ntsoenzok E. Effects of slight Fe(III)-doping on structural and optical properties of TiO₂ nanoparticles. J Solgel Sci Technol. 2021; 100: 44–54.
View Article
Google Scholar

[52] View Article

[53] Google Scholar

[ref17] 17. Kuang DL, Pei JZ, LI R, Ma SW, Ouyang H, Ni ZJ. The application research of modified nano titanium dioxide in automobile exhaust purification (in Chinese). Materials Review. 2014; 28(20): 18–22.
View Article
Google Scholar

[55] View Article

[56] Google Scholar

[ref18] 18. Predota M, Bandura AV, Cummings PT, Kubicki JD, Wesolowski DJ, Chialvo AA, et al. Electric double layer at the rutile (110) surface (1): Structure of surfaces an d interfacial water from molecular dynamics by use of ab initio potentials. J Phys Chem B. 2004; 108: 12049–12060.
View Article
Google Scholar

[58] View Article

[59] Google Scholar

[ref19] 19. Predota M, Cummings PT, Wesolowski DJ. Electric double layer at the rutile (110) surface (3):Inhomogeneous viscosity and diffusivity measurement by computer simulations. Journal of Physical Chemistry C. 2007; 111: 3071–3079.
View Article
Google Scholar

[61] View Article

[62] Google Scholar

[ref20] 20. Koparde VN, Cummings PT. Molecular dynamics study of water adsorption on TiO₂ nan particles. J Phys Chem C. 2007; 111: 6920–6926.
View Article
Google Scholar

[64] View Article

[65] Google Scholar

[ref21] 21. Lin HF, Lin HM, Hsu SL. Molecular simulation for gas adsorption at TiO₂ (rutile and anatase) surface. Nanostruct Mater. 1999; 12 (1/ 2/ 3/ 4): 357–360.
View Article
Google Scholar

[67] View Article

[68] Google Scholar

[ref22] 22. Cui SC, Li R, Ma WS, Li MM, Cui JX, Pei JZ. Preparation, photocatalytic properties investigation and degradation rate study on nano-TiO₂ aerogels doped with Fe³⁺ for automobile emission purification. Mater Res Express. 2018; 5 (11): 115513.
View Article
Google Scholar

[70] View Article

[71] Google Scholar

[ref23] 23. Abdullah SA, Sahdan MZ, Nafarizal N, Saim H, Cik Rohaida C. H, Adriyanto F. XRD and Raman spectroscopy study on the effects of post-annealing temperature of TiO₂ thin films. 2019 IEEE International Conference on Sensors and Nanotechnology, SENSORS and NANO, Penang, Malaysia. 2019; 8940092.

[ref24] 24. Kim DW, Enomoto N, Nakagawa Z, Kawamura K. Molecular dynamic simulation in titanium dioxide polymorphs: rutile, brookite, and anatase. J Am Ceram Soc. 2010; 79.4(2010): 1095–1099.
View Article
Google Scholar

[74] View Article

[75] Google Scholar

[ref25] 25. Chen Z.L. Theory and practice of molecular simulation. Beijing: Chemical Industry Press; 2007.

[ref26] 26. L Yuan S. Molecular Simulation-Theory and Experiment. Beijing: Chemical Industry Press; 2016.

[ref27] 27. Cui SC, Xie BW, Li R, Pei JZ, Tian YF, Zhang JP, et al. g-C₃N₄/CeO₂ binary composite prepared and its application in automobile exhaust degradation. Materials. 2020; 13: 1274. pmid:32168856
View Article
PubMed/NCBI
Google Scholar

[79] View Article

[80] PubMed/NCBI

[81] Google Scholar

[ref28] 28. Nasr M, Eid C, Habchi R, Miele P, Bechelany M. Recent progress on titanium dioxide nanomaterials for photocatalytic applications. ChemSusChem. 2018; 11: 3023–3047. pmid:29984904
View Article
PubMed/NCBI
Google Scholar

[83] View Article

[84] PubMed/NCBI

[85] Google Scholar

[ref29] 29. Han YH, Zhang JJ, Zhao Y. Visible-light-induced photocatalytic oxidation of nitric oxide and sulfur dioxide: Discrete kinetics and mechanism. Energy. 2016; 103: 725–734.
View Article
Google Scholar

[87] View Article

[88] Google Scholar

[ref30] 30. Yuan Y, Zhang JY, Li HL, Li Y, Zhao YC, Zheng CG. Simultaneous removal of SO₂, NO and mercury using TiO₂-aluminum silicate fiber by photocatalysis. Chem Eng J. 2012; 192: 21–28.
View Article
Google Scholar

[90] View Article

[91] Google Scholar

[ref31] 31. Seifvand N, Kowsari E. Synthesis of mesoporous Pd-doped TiO₂ templated by a magnetic recyclable ionic liquid for efficient photocatalytic air treatment. Ind Eng Chem Res. 2016; 55: 10533–10543.
View Article
Google Scholar

[93] View Article

[94] Google Scholar

[ref32] 32. Amirjalayer S, Tafipolsky M, Schmid R. Molecular dynamics simulation of benzene diffusion in mof‐5: importance of lattice dynamics. Angew Chem Int Edit. 2007; 46(3): 463–466. pmid:17131450
View Article
PubMed/NCBI
Google Scholar

[96] View Article

[97] PubMed/NCBI

[98] Google Scholar

[ref33] 33. Chockalingam R, Natarajan U. Dynamics of conformations, hydrogen bonds and translational diffusion of poly (methacrylic acid) in aqueous solution and the concentration transition in MD simulations. Mol Phys. 2015; (ahead-of-print): 1–13.
View Article
Google Scholar

[100] View Article

[101] Google Scholar

[ref34] 34. Dubbeldam D, Beerdsen E, Vlugt TJH, Smit B. Molecular simulation of loading-dependent diffusion in nanoporous materials using extended dynamically corrected transition state theory. J Chem Phys. 2005; 122(22): 224712. pmid:15974708
View Article
PubMed/NCBI
Google Scholar

[103] View Article

[104] PubMed/NCBI

[105] Google Scholar

[ref35] 35. Hofmann D, Fritz L, Ulbrich J, Paul D. Molecular simulation of small molecule diffusion and solution in dense amorphous polysiloxanes and polyimides. Comput Theor Polym S. 2000; 10(5): 419–436.
View Article
Google Scholar

[107] View Article

[108] Google Scholar

[ref36] 36. Chen JR, Qiu FX, Xu WZ, Cao SS, Zhu HJ. Recent progress in enhancing photocatalytic efficiency of TiO₂-based materials. Appl Catal A-Gen. 2015; 495: 131–140.
View Article
Google Scholar

[110] View Article

[111] Google Scholar

[ref37] 37. Liu JZ, Yu B, Hong QZ. Molecular dynamics simulation of distribution and adhesion of asphalt components on steel slag. Constr Build Mater. 2020; 255: 119332.
View Article
Google Scholar

[113] View Article

[114] Google Scholar

[ref38] 38. Ding GY, Yu X, Dong FQ, Ji ZZ, Wang JY. Using silane coupling agent coating on acidic aggregate surfaces to enhance the adhesion between asphalt and aggregate: a molecular dynamics simulation. Materials. 2020; 13: 5580. pmid:33297522
View Article
PubMed/NCBI
Google Scholar

[116] View Article

[117] PubMed/NCBI

[118] Google Scholar

[ref39] 39. Liu M, Qiu XQ, Masahiro M, Kazuhito H. Energy-level matching of Fe(III) ions grafted at surface and doped in bulk for efficient visible-light photocatalysts. J Am Chem Soc. 2013; 135: 10064–10072. pmid:23768256
View Article
PubMed/NCBI
Google Scholar

[120] View Article

[121] PubMed/NCBI

[122] Google Scholar

[ref40] 40. Hu B, Huang WK, Yu JL, Xiao ZC, Wu KH. Study on the adhesion performance of asphalt-calcium silicate hydrate gel interface in semi-flexible pavement materials based on molecular dynamics. Materials. 2021; 14: 4406. pmid:34442934
View Article
PubMed/NCBI
Google Scholar

[124] View Article

[125] PubMed/NCBI

[126] Google Scholar

[ref41] 41. Xiong Y, Zhang C, Duan M, Chen J, Fang SW, Li J, et al. Insight into organic pollutant adsorption characteristics on a g‑C₃N₄ surface by attenuated total reflection spectroscopy and molecular dynamics simulation. Langmuir. 2021; 37: 7655–7667. pmid:34129343
View Article
PubMed/NCBI
Google Scholar

[128] View Article

[129] PubMed/NCBI

[130] Google Scholar

[ref42] 42. Ma Y, Lu GW, Shao CJ, Li XF. Molecular dynamics simulation of hydrocarbon molecule adsorption on kaolinite (0 0 1) surface. Fuel. 2019; 237: 989–1002.
View Article
Google Scholar

[132] View Article

[133] Google Scholar

[ref43] 43. Zhang HL, Huang M, Hong J, Lai F, Gao Y. Molecular dynamics study on improvement effect of bis(2-hydroxyethyl) terephthalate on adhesive properties of asphalt-aggregate interface. Fuel. 2020; 285. pmid:32952206
View Article
PubMed/NCBI
Google Scholar

[135] View Article

[136] PubMed/NCBI

[137] Google Scholar

Figures

Abstract

1. Introduction

2. Preparation of modified TiO2 powder

3.Test study

4. Test method and molecular dynamics simulation method of absorbing automobile exhaust gas

5. Results and discussion

5.1. Analysis of test result

5.2. Simulation analysis of automobile exhaust diffusion in the pore of TiO2

5.3. Radial concentration analysis of automobile exhaust on TiO2 surface

5.4. Calculation and analysis of adsorption energy of automobile exhaust on TiO2 surface

6. Conclusions

Supporting information

S1 File. S1 File contains the original data for Figs 8–10.

References

2. Preparation of modified TiO₂ powder

5.2. Simulation analysis of automobile exhaust diffusion in the pore of TiO₂

5.3. Radial concentration analysis of automobile exhaust on TiO₂ surface

5.4. Calculation and analysis of adsorption energy of automobile exhaust on TiO₂ surface