• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Photo-piezoelectric synergistic degradation of typical volatile organic compounds on BaTiO3

    2022-03-14 09:29:36QinLiuWeinaZhaoZhiminAoTaichengAn
    Chinese Chemical Letters 2022年1期

    Qin Liu,Weina Zhao,Zhimin Ao,Taicheng An

    Guangzhou Key Laboratory of Environmental Catalysis and Pollution Control,Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control,School of Environmental Science and Engineering,Institute of Environmental Health and Pollution Control,Guangdong University of Technology,Guangzhou 510006,China

    ABSTRACT Explore the photo-piezoelectric synergistic micro-mechanism by density functional theory(DFT)calculations at the electronic and atomic level is important.In this work,to understand the synergistic mechanism,atomic and electronic properties of typical piezoelectric and photocatalytic material BaTiO3 were initially investigated with different strains.Subsequently,the adsorption of volatile organic compounds(VOCs)on the BaTiO3(001)surface was determined during the piezoelectric process.In addition,the relationship between deformation ratio,the electronic structure and adsorption energy was understood in the deformation ratio range of 7%-12% for the optimal catalytic effect.The results of charge density differences and Born effective charge reveal the synergistic mechanism of piezoelectric photocatalysis.The built-in electric field formed by polarization results in the enhanced separation of charges,which makes the surface charges aggregation,enhancing the adsorption of VOCs,and benefiting the subsequent photocatalytic degradation.This work can provide significant theoretical guidance for the piezoelectric photocatalytic degradation of pollutants with the optimal strain range.

    Keywords:Photocatalysis Photo-piezoelectric synergistic Polarization Charge separation BaTiO3 Volatile organic compounds(VOCs)

    Volatile organic compounds(VOCs)are one type of the most toxic air pollutants in atmosphere[1,2]and have been attracting intensive attention due to the serious threats to the ecological environment,the global climatic conditions and human health[3,4].The majority of emitted VOCs,such as aldehydes,polycyclic aromatic hydrocarbons(PAHs),alcohols and halohydrocarbons(e.g.,HCHO,C6H6,CH3OH,C2HCl3)[5–8],are linked with the precursors to photo-chemical fumes and other environmental hazards.Therefore,considerable efforts have been made to remove VOCs before releasing to the environment.

    Due to its excellent oxidation and purification capabilities,photocatalytic technology is considered as a highly promising and efficient procedures for VOCs elimination[9–11].ZnO[12],g-C3N4/TiO2[13],Au/TiO2[14]and Fe doped WO3[15]have been reported to degrade VOCsviaultraviolet irradiation.Although such systems have photocatalytic performance,unfortunately the rapid recombination of electron-hole pairs of the semiconductor photocatalysts results in a low photocatalytic efficiency for the practical removal of VOCs[16].New technology is thus urgently required to overcome the shortcoming of the photogenerated carrier recombination during the photocatalytic reaction.

    Numerous attempts have been made to improve the photocatalytic efficiency,including precious metals and aromatic compounds loading[17–19],heterojunctions and Z-scheme constructions[20]and material structure modifiers[21–23].In addition to these methods,the piezoelectric effect has been explored to improve the charge separation[24].Extensive research has been performed on the role of the polarization field in promoting the photocatalytic performance[25–27].The piezoelectric catalytic degradation of organic pollutants under the action of ultrasound have extended the piezoelectric catalytic effects to the field of environmental purification[28,29].Piezo-photocatalytic effects to the system(e.g.,ZnO nanowires[30],ZnSnO3nanowires[31]and CuS/ZnO[32])have demonstrated a favorable degradation effi-ciency of methylene blue(MB).The enhancement is mainly ascribed to the bending and polarization fields generated by alternating ultrasonic vibration,which can reduce the recombination of electrons and holes induced by photo irradiation and subsequently increase the mobility of these charge carriers.However,experimental results only revealed the improvement of the photocatalytic degradation of pollutants due to the piezoelectric effect,while the micro mechanism of the photo-piezoelectric synergistic degradation process remains unclear.

    Recently,BTO(BaTiO3)has been widely used as a typical photopiezoelectric material due to its high dielectric constant[33]and the appropriate energy band gap of 3.2 eV[34].In addition,the BTO structure is highly sensitive to external deformation[35]due to the presence of the mixed ionic covalent chemical bonding for both of the Ba and O atoms and as well as the strong hybridization between the d and p states of the Ti and O atom,respectively.Therefore,BTO has significant piezoelectric effect.Liet al.developed a new hybrid photocatalyst by integrating BTO nanocrystals with Ag2O semiconductor nanoparticles[26].In this hybrid photocatalyst,the piezoelectric effect was combined with photoelectric conversion for Rhodamine B degradation.However,the majority of the aforementioned studies focus solely on the modification of photocatalytic materials,while research on the mechanism underlying the photo-piezoelectric synergistic effect and the corresponding influencing factors is limited.Density functional theory(DFT)is an effective strategy for the deep exploration of the synergistic mechanism.

    Piezoelectric polarization is sensitive to structure deformation/vibration and the adsorption process is extremely important during photocatalytic system.Therefore,in this study,the effect of BTO deformation on the change of electronic structure of tetragonal BTO crystal and the adsorption performance of BTO for typical VOCs were discussed by DFT calculation.We first investigated the relationship between the structural parameter variations and the polarization degree and subsequently predicted the strain ratio with respect to the photocatalytic performance.Therefore,the adsorption of several typical VOCs species on the BTO(001)surface was calculated and the optimal strain ratio for the photopiezoelectric synergistic effect was identified.Results revealed the relationship between the deformation of BTO and the adsorption performance,therefore providing theoretical guidance for the optimum strain range of piezoelectric materials during the photopiezoelectric synergistic process.

    The calculation details are shown in Text S1(Supporting information).The BTO unit was optimizedviathe hybrid Heyd-Scuseria-Ernzerhof(HSE06)functional,with optimized lattice constants ofa=b=3.83 ?A andc=3.82 ?A.This agrees well with the experimental dataa=b=3.95 ?A andc=3.96 ?A[36].Fig.1a presents the crystal structure of BTO,where the blue,green and red spheres represent Ba,Ti and O atoms,respectively.The BTO crystal phase is a regular oxygen octahedral structure,in which the titanium is located approximately in the center of the oxygen octahedron structure.Previous work has demonstrated that the offcentering displacement of Ti4+cation within the oxygen octahedral results in the spontaneous polarization along the(001)axis[37].This indicates that deformations in this direction would produce potential differences.Thus,we focused on the variation of(001)direction bond length with different strain ratio.The unstrained bond length of Ti?O(top)and Ti?O(bottom)in BTO were 1.91 ?A and 1.92 ?A,respectively.Fig.1b depicts the Brillouin region of the optimized BTO structure with its reciprocal lattice as pseudopotential.From this,we can determine the path along high symmetry directions in the reciprocal lattice for the following band structure calculations,which is consistent with previous study[38].

    Fig.1.(a)Crystal structure of the perovskite BaTiO3.Blue,green,and red spheres represent barium,titanium and oxygen atoms,respectively.The white arrow indicates the direction of polarization Ps.(b)Corresponding first Brillouin zone and the selected high-symmetry k-points as marked.Variations in(c)the bond length of Ti?Otop,(d)the offset distance of the central Ti atom,and(e)the band gap(Eg)under different strain ratios.

    Thus,we have identified that the polarization direction is along the(001)axis in BTO.This indicates that the shift of the Ti ion would affect the degree of polarization.Fig.1c presents the trend in Ti?Otopbonding length variations in the BTO structure with respect to the deformation ratio.The strain range is determined by the sum of radii of Ti and O ions[39].The distance of the Ti?Otopbonding length is defined asdTi-O,while the red dot represents the distance ofdTi-Owithout strain.dTi-Odecreases gradually as the compression increases,indicating the gradual increase of the Ti?Otopbond strength.In contrast,an increase in tension would elongatedTi-O,whiledTi-Oreaches the maximum(dTi-O=2.02 ?A)when the tension equals 6%.The tension strain continues to increase and the bond length exhibits a rapid drop to 1.80 ?A when the tensile strain ratio increases from 6% to 7%.After checking the BTO structure,it is found that the Ti is away from the central site.Further increase in the tension results in very slow reduction ofdTi-O.Prior to reachingdTi-Opeak at the tensile strain of 6%,dTi-Olength is observed to be proportional to the strain ratio.The results show that the tensile strain would induce the Ti atoms to shift away from the center along the polarization direction.

    To assess the effect of strain on the electronic structure of BTO and understand the corresponding photo-response properties,the band gap of BTO with different strain ratios was calculated and shown in Fig.1e.The band gap exhibits gradual decrease as the compressive strain ratio changing from 0% to 8%.This agrees with the trend of the bond length variation.The variation in the band gap contrasts to that of the Ti-Otopbond length under tensile strain,where band gap decreases first along a curve and jumps high sharply at the same points(6% to 7%)under tensile strain,then increases slightly and linearly.

    Figs.S1a-d(Supporting information)present four typical points in order to further understand the band structure.The band gap of the BTO without strain is 3.41 eV(Fig.S1a)with an indirect band gap,while the conduction band minimum(CBM)and the valence band maximum(VBM)are respectively located atΓand A points.The HSE calculation result agrees well with the experimental band gap 3.2 eV[34].At the compression ratio of 8%,the band gap decreases to 3.19 eV,mimicking the trend ofdTi-O.Compared to the system without strain,the band gap decreases due to the overall downward shift of the conduction band electron energy level under the compressive strain.Similar to the compression trend,slight band gap decrease is observed prior to the 6% tensile ratio.This contrasts with the slight increase trend ofdTi-O.Figs S1c and d indicate an abrupt increase in the band gap for the enhanced conduction band energy,attributed to the center site charge transfer induced by polarization under tensile strain.The band structure results suggest the ability of the piezoelectric process to slightly adjust the band gap.

    To better understand the piezo-photocatalysis mechanism and the contribution of different elements of BTO in the photocatalysis,we investigated the partial density of states(PDOS)of the tension catastrophe point(6%?7%)(Figs.S2a and b in Supporting information).The BTO valence band generally consists of O 2p states as well as a small contribution from the Ti 3d states,while the dominant influences of CBM are the Ti 3d states with a marginal contribution of the O 2p states,consistent with previous research[40].A strong interaction is present between the O 2p and Ti 3d states,indicating that the Ti?O bonding is covalent.The electronic transition near the Fermi surface determines the optical properties of the material.Therefore,octahedral oxygen is likely to be the decisive origin of the BTO electron transitions as the VBM is largely influenced by oxygen.The increase in the band gap with tensive strain from 6% to 7% is attributed to the localization of the 3d orbit,while the CBM shifts to the right energy level.Figs.S2c and d(Supporting information)show the PDOS of BaTiO3without strain and 8% compressive strain.In contrast to Fig.S2c,the electrons located at the O 2p orbital near the VBM in Fig.S2d are partially transferred,while the Ti 3d orbital near CBM becomes more delocalized.This results in a wider band and a smaller band gap.The density states of the Ti 3d orbital are much higher than that of O 2p,and thus the electrons in the O atom are transferred from the valence band(VB)to the conduction band(CB)by hybridization with the Ti 3d orbital.

    In addition,as discussed in Fig.1c,the distance of the central Ti atom shifts away from the center along the polarization direction as the strain ratio varies.It is known that the shift is lager the polarization is more significant[41].As shown in Fig.1d,the offset distance is ignorable under compressive strain and tensile strain below 6%.Then it suddenly jumps to 0.30 ?A at the tensile strain ratio of 6%?7%,then it continues to increase gradually and linearly.In other words,polarization is ignorable under compressive strain and tensile strain below 6%,and the polarization is present only at the tensile strain above 7%.It is known that polarization would form a stronger internal electric field and thus inducing charge separation and accumulation under the tensile strain.Therefore,the internal electric field would alert the photo generated electrons-hole separation and recombination,thus tuning the photocatalytic performance.

    The piezoelectric potential of piezoelectric materials is enhanced by applied stress,which changes the charge distribution[42].The adsorption performance of the catalyst material has strong influence on the photocatalytic properties,and thus plays a significant role in the photocatalytic degradation of VOCs.Various types of VOCs exist in the environment,including acetone,ethanol,methanol,formaldehyde,toluene,etc.The most common and toxic VOCs(formaldehyde and acetone)and involved reactive oxygen species(oxygen and hydroxyl)were examined in our work.As the piezoelectric polarization direction of BTO is generally along the(001)direction,the BTO(001)surface was employed as the adsorption surface.The(001)surface has two different types terminated surfaces:BaO- and TiO2-terminated surfaces,both of which were considered.The BaO-terminated surface was more stable based on the surface energy stability calculations.Three adsorption sites on the BaO-terminated surface of BTO were considered and their adsorption energies were compared.Fig.S3(Supporting information)depicts the three adsorption sites,the O atom(O1)located at the center of the square,the Ba atom located at the top site of the square,and the O atom(O2)located at the right vertex of the triangle,labeled 1,2,and 3 respectively.The geometry and energetics of the adsorption systems on the BTO surfaces were calculated and analyzed,particularly focus on the trend in adsorption variations under different strain ratio.Note that new O-Ba bonds may be formed in the adsorption system due to the electronegativity of the oxygen atoms and the surface Ba atoms.

    Fig.2.Most stable adsorption conformations of formaldehyde on BaTiO3 surfaces,(a)without strain and(b)12% tensile strain.Oxygen adsorption on BaTiO3 surfaces,(c)without strain and(d)12% tensile strain.(e)Adsorption energy of formaldehyde on BaTiO3(001)as a function of the applied strain(with a step size of 1%);(f)oxygen,acetone and hydroxyl adsorption energies on the BTO surface with different strains.

    In order to clarify the effect of piezoelectricity on the adsorption energy,we first investigated the adsorption changes of formaldehyde at different strains(Fig.2a).For the compressive strain,the adsorption energy of the formaldehyde molecules did not change much(?0.60 eV to ?0.57 eV),which is consistent with the Ti?Otopbond length change(Fig.1c).For the tensile strain process,the adsorption energy remains unchanged prior to the mutation point of 6% tensive strain,and exhibits sharp rise between 6%(?0.57 eV)and 7%(?1.26 eV).This agrees with theEganddTi-Otrends.The similarities in trends suggests that there may exist a correlation between the bond length,band gap and adsorption energy.The adsorption energy subsequently increases with the tensile strength and the most favorable tensile strain ratio range for adsorption improvement is identified as 7%?12%,with a maximum adsorption energy of ?1.56 eV at 12% tension strain.Thus,the formaldehyde adsorption energy is sensitive to the structure strain of BTO within a certain range(after 7%).

    In order to further explore the relationships between adsorption energy and structure strain,we identified the most stable formaldehyde structures adsorbed on the BTO(001)surface at 0% and 12% tensions(Figs.2b and c).The distance between the formaldehyde O atom and the Ba1/Ba2of the surface is 3.08 ?A/4.18 ?A(Fig.2b).The Ba1,Ba2and Ba3sites are marked in the top view.The formaldehyde O atom is observed to be more inclined to interact with the Ba1atom on the surface,with an interaction intensity of ?0.57 eV.At the tension of 12%,the formaldehyde O atom is centered between the two Ba atoms while the distances of O?Ba1and O?Ba2are reduced to 2.67 ?A and 2.69 ?A,respectively(Fig.2c),compared with the 0% tension.The adsorption performance of formaldehyde under tensile strain exhibits a marked improvement to ?1.56 eV compared to the unstrained performance.The enhanced adsorption can be attributed to the builtin electric field formed by the piezoelectric effect,which greatly enhances the directional separation charge during photocatalysis.The directional separation of charges makes it aggregate on the surface,while the enhanced surface piezoelectric potential facilitates the adsorption of the molecules on the surface,thus increasing the adsorption energy.

    Typical strain ratios(?8%,?4%,6%,7% and 12%)were selected based on the formaldehyde adsorption trend to investigate the adsorption of O2,C3H6O and?OH on the BTO surface.Figs.2d and e depict the most stable structures of O2adsorption on the BTO(001)surface.The O(OA)atom of O2is located at the Ba1-Ba3atom bridge from the side view and the distances of OA?Ba1and OA?Ba3are determined as 3.25 ?A and 3.27 ?A,respectively(Fig.2d).The O2is parallel to the BTO surface,while the OAof O2is typically adsorbed between the Ba1and Ba3surface,with an adsorption energy of ?0.60 eV.Compared with the adsorption structure on the unstrained surfaces,the O2under the tensile strain(12%ratio)is closer to the surface,with the distances of OA?Ba1and OA?Ba3reduced to 2.53 ?A and 2.51 ?A,respectively(Fig.2e).The top view of Fig.2e indicates that the O2rotates clockwise approx.45°,while the oxygen OAremains at the center of the two Ba atoms with an adsorption energy of ?3.17 eV.Thus,the adsorption performance of oxygen is significantly improved under tensile strain.Fig.2f depicts the adsorption energy of hydroxyl and acetone at different strain ratios,demonstrating similar energy trends to those of oxygen and formaldehyde.The adsorption energy values of hydroxyl and acetone on the unstrained BTO system are determined as ?2.23 eV and ?1.08 eV,respectively.The adsorption energy of these molecules on the BTO remains almost unchanged prior to the tension of 6%.However,when the tensile strain ratio reaches 7%,the adsorption of all these molecules is enhanced,while the adsorption energy mutation points remain unchanged.Table S1 and Fig.S4(Supporting information)present the corresponding adsorption energies and configurations,respectively.The results demonstrate the improvements in the adsorption of the HCHO,O2,C3H6O and?OH molecules on the BTO surface can be improved within a certain strain range,which provides a perfect prerequisite for the subsequent photocatalytic systems.

    To further illustrate the mechanisms underlying the piezoelectricity-induced photocatalytic electron-hole pair separation and the variations in the VOCs adsorption caused by the applied strain,we calculated the charge density differences of the BTO substrate along the(001)axis under strain(Figs.3a-f).The isosurface of electron density differences in the BTO is also shown.Blue indicates electron lost while red indicates electrons captured.The charge distribution around the Ti and Ba sites generally indicate covalent and ionic Ti-O and Ba-O bonds.By considering the crystal symmetry of the BTO with tetragonal(P4mm)structures,Fig.3c marks the corresponding atoms on the electron charge density contour map.No significant changes in the charge density difference are observed during the compression process.At the tensile strain ratio of 6%,the charge density remains unchanged.Unexpectedly,an obvious charge transfer occurs when the tensile ratio increases to 7%(Fig.3e).The surface O(central Ti)atom gains(losses)more electrons,which is consistent with the polarization direction and adsorption trend.This proves that the built-in electric field formed by the piezoelectric effect greatly enhances the charge directional separation during the photocatalysis process.When the tensile strain is increased to 12%,a greater amount of charge is accumulated on the surface.Therefore,tensile strain values from 7% to 12% significantly influences the electron distribution,enhancing the separation of the electron hole pairs and the adsorption of VOCs in the photocatalytic process.

    Fig.3.Isosurface of BaTiO3 electron density differences under(a)8% compressive strain,(b)4% compressive strain,(c)without strain,(d)6% tensile strain,(e)7%tensile strain and(f)12% tensile strain.Electron accumulation and depletion areas are shown in red and blue,respectively.(g)The BaTiO3 spontaneous polarization intensity under different strain ratios.

    Fig.4.Photo-piezoelectric synergistic degradation mechanism of the VOCs on tensile strained BaTiO3.

    To quantitatively shed light on the relationship between the polarization intensity and adsorption energy in the photopiezoelectric process,the Born effective charge tensors(BECs)of BTO in its P4mm phase were determinedviathe DFT method to estimate polarizationPs.No obvious changes in spontaneous polarization are observed under compressive strain(Fig.3f).Under the tensile strain condition,the spontaneous polarization increases from the 6%(0.08 C/m2)to 7%(0.44 C/m2)strain.This is consistent with the changes in bond length,band gap and adsorption energy,and further confirmed the enhancement of the built-in electric field.Thus,there is an obvious polarization enhancement during the tension process from the 7% to 12% strain,hence enhancing the built-in electric field to promote the charge separation during photocatalysis.

    Fig.4 depicts the photo-piezoelectric synergistic mechanism based on the above results.With tensile strain,the center Ti atom shifts upward,and the dipole moment of the positive and negative center charges increases.This consequently enhances the piezoelectric polarization of BTO and forms a stronger built-in electric field to promote more electrons and holes to move in the opposite direction.This forms a large number of charges on the BTO surface,facilitating the adsorption of the molecules on the surface,thus improving the photocatalytic efficiency.

    In this work,a series of strain ratios of BTO were applied to simulate the piezoelectric process through DFT calculations.The atomic and electronic structure changes were initially investigated during the piezoelectric process.The change trend ofdTi-Oand the band gap was consistent in the compression condition and opposing under tension.A turning point was observed between 6% and 7%.Adsorption is a precondition for the photocatalytic degradation of pollutants,and therefore the adsorption process of the VOCs on the BTO(001)surface was evaluated with different applied strains.The results indicated the optimum strain ratio of the piezophotocatalysis for formaldehyde adsorption to be 7%?12%.Oxygen,acetone and hydroxyl adsorption exhibited the same optimal strain range.In addition,the charge density differences and BECs,and the charge transfer and spontaneous polarization changes in the piezoelectric strain process were also analyzed.The mechanism underlying the charge separation induced by the enhancement of the built-in electric field formed by polarization in the piezoelectric photocatalysis was revealed.In addition,the relationship between strain intensity,the electronic structure and adsorption energy was further constructed to determine the strain intensity range for the optimal catalytic effect.Our work can provide theoretical guidance for the design of the piezo-photocatalytic degradation of pollutants.

    Declaration of competing interest

    The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

    Acknowledgments

    This work was supported by the National Natural Science Foundation of China(Nos.21777033 and 22006023),Natural Science Foundation of Guangdong Province(No.2019A1515010428),Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program(No.2017BT01Z032),and the Innovation Team Project of Guangdong Provincial Department of Education(No.2017KCXTD012).

    Supplementary materials

    Supplementary material associated with this article can be found,in the online version,at doi:10.1016/j.cclet.2021.06.059.

    最黄视频免费看| 黄片播放在线免费| 精品熟女少妇八av免费久了| 国产成人精品久久二区二区91| 欧美精品av麻豆av| 国产欧美日韩综合在线一区二区| 另类亚洲欧美激情| 国产精品久久久av美女十八| 日本五十路高清| 午夜视频精品福利| 在线观看www视频免费| 水蜜桃什么品种好| 又黄又粗又硬又大视频| 黄色a级毛片大全视频| 男女国产视频网站| 18禁裸乳无遮挡动漫免费视频| 日本午夜av视频| 国产色视频综合| 国产黄频视频在线观看| 美女大奶头黄色视频| 国产成人精品久久二区二区91| 波野结衣二区三区在线| 亚洲人成77777在线视频| 日韩av不卡免费在线播放| 久久av网站| 国产精品二区激情视频| 免费在线观看完整版高清| 国产不卡av网站在线观看| 两个人免费观看高清视频| 丝瓜视频免费看黄片| 99久久99久久久精品蜜桃| 热re99久久国产66热| 国产1区2区3区精品| 啦啦啦中文免费视频观看日本| 丰满人妻熟妇乱又伦精品不卡| 欧美日韩福利视频一区二区| 汤姆久久久久久久影院中文字幕| 大陆偷拍与自拍| 美女高潮到喷水免费观看| 国产欧美日韩精品亚洲av| 午夜福利在线免费观看网站| 亚洲av电影在线进入| 午夜福利在线免费观看网站| 肉色欧美久久久久久久蜜桃| 老鸭窝网址在线观看| 高清黄色对白视频在线免费看| 国产一区二区激情短视频 | av国产精品久久久久影院| 中文字幕最新亚洲高清| 欧美大码av| 精品一区在线观看国产| 久久久国产一区二区| 日韩一卡2卡3卡4卡2021年| 最新在线观看一区二区三区 | 我的亚洲天堂| 天堂8中文在线网| 国产高清国产精品国产三级| 亚洲av电影在线观看一区二区三区| 中文精品一卡2卡3卡4更新| 久久这里只有精品19| 成人国产av品久久久| 午夜福利影视在线免费观看| 热re99久久国产66热| 高清欧美精品videossex| 精品久久久精品久久久| 精品高清国产在线一区| 真人做人爱边吃奶动态| 日韩免费高清中文字幕av| a 毛片基地| 啦啦啦啦在线视频资源| 中文字幕制服av| 日韩一区二区三区影片| 老司机在亚洲福利影院| 亚洲午夜精品一区,二区,三区| 丝袜脚勾引网站| 婷婷色av中文字幕| 女人被躁到高潮嗷嗷叫费观| 亚洲中文字幕日韩| 欧美日韩黄片免| 亚洲av成人不卡在线观看播放网 | 热re99久久精品国产66热6| 欧美 日韩 精品 国产| 天天躁夜夜躁狠狠躁躁| videos熟女内射| 在线观看一区二区三区激情| 久久精品熟女亚洲av麻豆精品| 亚洲国产成人一精品久久久| 狠狠精品人妻久久久久久综合| 免费在线观看影片大全网站 | 国产精品麻豆人妻色哟哟久久| 人人妻,人人澡人人爽秒播 | 啦啦啦 在线观看视频| 国产在线视频一区二区| 久久国产精品大桥未久av| 大话2 男鬼变身卡| 男女免费视频国产| 伊人亚洲综合成人网| 免费看十八禁软件| 欧美人与性动交α欧美精品济南到| 亚洲精品久久久久久婷婷小说| 18在线观看网站| 视频在线观看一区二区三区| 国产精品国产三级专区第一集| 亚洲熟女精品中文字幕| 免费高清在线观看视频在线观看| 国产精品偷伦视频观看了| 午夜老司机福利片| 最新在线观看一区二区三区 | 99久久99久久久精品蜜桃| 老司机深夜福利视频在线观看 | 中文字幕高清在线视频| 色婷婷久久久亚洲欧美| 久久久久国产精品人妻一区二区| 亚洲av片天天在线观看| 国产成人精品久久二区二区免费| 色婷婷久久久亚洲欧美| 蜜桃国产av成人99| 嫩草影视91久久| 亚洲视频免费观看视频| 国产精品九九99| 满18在线观看网站| 亚洲天堂av无毛| 极品人妻少妇av视频| 国产精品三级大全| 美女福利国产在线| 一级黄色大片毛片| 亚洲国产精品国产精品| 一区福利在线观看| 看十八女毛片水多多多| 亚洲精品自拍成人| 欧美日韩福利视频一区二区| 人人妻人人添人人爽欧美一区卜| av国产久精品久网站免费入址| 99久久人妻综合| 欧美日韩综合久久久久久| 少妇的丰满在线观看| 国产精品熟女久久久久浪| 男人添女人高潮全过程视频| 只有这里有精品99| 精品一区二区三区av网在线观看 | 成人18禁高潮啪啪吃奶动态图| 午夜两性在线视频| 欧美日韩综合久久久久久| 一本色道久久久久久精品综合| 欧美 亚洲 国产 日韩一| 国产主播在线观看一区二区 | 欧美成人精品欧美一级黄| 亚洲国产日韩一区二区| av网站在线播放免费| 亚洲熟女毛片儿| 久久鲁丝午夜福利片| 视频区图区小说| 老司机影院成人| 精品人妻在线不人妻| 欧美成狂野欧美在线观看| 中文字幕高清在线视频| 国产又色又爽无遮挡免| 人人妻人人澡人人看| 国产老妇伦熟女老妇高清| 91麻豆精品激情在线观看国产 | 亚洲欧美日韩高清在线视频 | 欧美日韩精品网址| 老汉色av国产亚洲站长工具| 99久久精品国产亚洲精品| 成年人午夜在线观看视频| a级片在线免费高清观看视频| 亚洲美女黄色视频免费看| 亚洲中文日韩欧美视频| 午夜福利一区二区在线看| 欧美日韩视频精品一区| 丝袜脚勾引网站| 一二三四社区在线视频社区8| 精品国产一区二区久久| 在现免费观看毛片| 国产一区二区三区综合在线观看| 黄色片一级片一级黄色片| 在线 av 中文字幕| 一本一本久久a久久精品综合妖精| 亚洲一卡2卡3卡4卡5卡精品中文| av国产久精品久网站免费入址| 欧美在线黄色| 亚洲美女黄色视频免费看| av电影中文网址| 久久精品aⅴ一区二区三区四区| 超色免费av| 热re99久久国产66热| 午夜福利乱码中文字幕| 美女主播在线视频| 午夜激情av网站| 九草在线视频观看| 黑人猛操日本美女一级片| 亚洲 国产 在线| 亚洲av欧美aⅴ国产| 国产av国产精品国产| 欧美+亚洲+日韩+国产| 男女下面插进去视频免费观看| 精品第一国产精品| 日本欧美视频一区| 精品国产一区二区久久| 妹子高潮喷水视频| 交换朋友夫妻互换小说| 99久久99久久久精品蜜桃| 久久久欧美国产精品| 亚洲av日韩在线播放| 亚洲色图 男人天堂 中文字幕| 亚洲中文日韩欧美视频| 男女床上黄色一级片免费看| 久久久久视频综合| 久久精品久久久久久久性| 午夜福利在线免费观看网站| 黑人猛操日本美女一级片| 国产深夜福利视频在线观看| 这个男人来自地球电影免费观看| 久久国产亚洲av麻豆专区| 午夜免费观看性视频| 国产精品一国产av| 最近手机中文字幕大全| 国产精品久久久人人做人人爽| 波多野结衣一区麻豆| 国产老妇伦熟女老妇高清| 99re6热这里在线精品视频| 日韩制服骚丝袜av| 亚洲熟女毛片儿| 肉色欧美久久久久久久蜜桃| 久久青草综合色| 国产xxxxx性猛交| 精品熟女少妇八av免费久了| 一二三四在线观看免费中文在| 亚洲中文av在线| 免费av中文字幕在线| 成人国产一区最新在线观看 | 欧美 日韩 精品 国产| 欧美xxⅹ黑人| 少妇猛男粗大的猛烈进出视频| 日本91视频免费播放| 香蕉国产在线看| 2021少妇久久久久久久久久久| 1024香蕉在线观看| 亚洲综合色网址| 成年av动漫网址| 电影成人av| 午夜91福利影院| 高清视频免费观看一区二区| 中文精品一卡2卡3卡4更新| 欧美亚洲日本最大视频资源| 最近最新中文字幕大全免费视频 | 老司机影院毛片| 国产视频首页在线观看| 丝袜喷水一区| 久9热在线精品视频| 下体分泌物呈黄色| 久久中文字幕一级| av又黄又爽大尺度在线免费看| 国产精品一二三区在线看| 视频区欧美日本亚洲| 久久久精品94久久精品| 天天躁夜夜躁狠狠躁躁| 波多野结衣一区麻豆| 97人妻天天添夜夜摸| 黑丝袜美女国产一区| 欧美大码av| 成人国产一区最新在线观看 | 亚洲精品国产区一区二| 欧美精品人与动牲交sv欧美| 美国免费a级毛片| 欧美日本中文国产一区发布| 亚洲精品国产色婷婷电影| 亚洲欧美色中文字幕在线| 18禁黄网站禁片午夜丰满| 97精品久久久久久久久久精品| 黄色视频不卡| 在线观看国产h片| av在线app专区| av福利片在线| 免费在线观看影片大全网站 | 欧美日韩国产mv在线观看视频| 午夜福利一区二区在线看| 一本—道久久a久久精品蜜桃钙片| 建设人人有责人人尽责人人享有的| 丝袜美腿诱惑在线| 丝袜美足系列| 黄色视频不卡| 91老司机精品| 91麻豆精品激情在线观看国产 | 亚洲国产最新在线播放| 九草在线视频观看| 国产精品一区二区在线不卡| 国产亚洲av片在线观看秒播厂| 亚洲五月婷婷丁香| 亚洲熟女毛片儿| 国产精品久久久久久人妻精品电影 | 国产欧美日韩精品亚洲av| svipshipincom国产片| 国产野战对白在线观看| 国产精品秋霞免费鲁丝片| 国产亚洲一区二区精品| 欧美精品一区二区大全| 国产在视频线精品| 美女高潮到喷水免费观看| 青青草视频在线视频观看| 巨乳人妻的诱惑在线观看| 少妇人妻 视频| 国产成人欧美| 欧美精品一区二区免费开放| 曰老女人黄片| av网站免费在线观看视频| 超碰成人久久| 久久精品国产亚洲av高清一级| 国产成人免费无遮挡视频| 国产精品国产av在线观看| av又黄又爽大尺度在线免费看| 伊人久久大香线蕉亚洲五| 欧美成狂野欧美在线观看| 亚洲五月色婷婷综合| 国产精品久久久久久人妻精品电影 | 中文欧美无线码| 亚洲午夜精品一区,二区,三区| 国产精品一区二区在线观看99| 中文字幕最新亚洲高清| 熟女av电影| 激情五月婷婷亚洲| 午夜福利乱码中文字幕| 免费av中文字幕在线| 日韩电影二区| 极品人妻少妇av视频| 18禁观看日本| 久久精品久久久久久噜噜老黄| 一级黄片播放器| 国产免费现黄频在线看| 男女边吃奶边做爰视频| 午夜影院在线不卡| 亚洲精品乱久久久久久| 亚洲成人免费电影在线观看 | 777久久人妻少妇嫩草av网站| 久久中文字幕一级| 2021少妇久久久久久久久久久| 国产免费现黄频在线看| 99九九在线精品视频| 午夜福利免费观看在线| 中文字幕高清在线视频| 午夜福利免费观看在线| 丰满少妇做爰视频| 国产免费现黄频在线看| 99九九在线精品视频| 国产成人精品在线电影| 大片免费播放器 马上看| 久久久久精品人妻al黑| 欧美日韩视频高清一区二区三区二| 在线观看一区二区三区激情| 成年女人毛片免费观看观看9 | 免费观看av网站的网址| 男男h啪啪无遮挡| 久久鲁丝午夜福利片| 国产高清国产精品国产三级| 久久久欧美国产精品| 免费久久久久久久精品成人欧美视频| 国产一区有黄有色的免费视频| 又大又黄又爽视频免费| 少妇粗大呻吟视频| 欧美日韩一级在线毛片| 自线自在国产av| 女警被强在线播放| 亚洲av成人不卡在线观看播放网 | 国产免费视频播放在线视频| www.av在线官网国产| 制服人妻中文乱码| 免费在线观看完整版高清| 国产一区二区 视频在线| 国产欧美日韩一区二区三 | 久久久久久久久免费视频了| 欧美激情 高清一区二区三区| 一本色道久久久久久精品综合| 久久精品国产a三级三级三级| 欧美日韩一级在线毛片| 精品亚洲乱码少妇综合久久| 亚洲国产av影院在线观看| 成人国产一区最新在线观看 | 国产真人三级小视频在线观看| 桃花免费在线播放| 精品国产一区二区三区四区第35| 亚洲综合色网址| 久久精品熟女亚洲av麻豆精品| 亚洲国产欧美在线一区| 国产精品麻豆人妻色哟哟久久| 亚洲免费av在线视频| av在线app专区| 在线av久久热| 国产精品麻豆人妻色哟哟久久| 人人妻人人澡人人看| 亚洲图色成人| 精品国产乱码久久久久久小说| 亚洲欧美精品综合一区二区三区| 交换朋友夫妻互换小说| 亚洲欧美激情在线| 国产黄色免费在线视频| 精品少妇一区二区三区视频日本电影| 这个男人来自地球电影免费观看| 国产视频一区二区在线看| 日韩大码丰满熟妇| 亚洲精品在线美女| 视频区图区小说| 日本五十路高清| 各种免费的搞黄视频| 天天躁狠狠躁夜夜躁狠狠躁| 国产男女内射视频| 蜜桃在线观看..| 制服人妻中文乱码| www.av在线官网国产| 啦啦啦在线免费观看视频4| www.av在线官网国产| 亚洲,一卡二卡三卡| 国产免费现黄频在线看| 免费在线观看视频国产中文字幕亚洲 | 男女免费视频国产| 亚洲欧美日韩另类电影网站| 久久精品亚洲av国产电影网| 老司机靠b影院| 欧美日韩福利视频一区二区| 涩涩av久久男人的天堂| 国产精品免费大片| 国产不卡av网站在线观看| 久久人妻福利社区极品人妻图片 | 1024视频免费在线观看| 亚洲三区欧美一区| 亚洲一卡2卡3卡4卡5卡精品中文| 91字幕亚洲| 极品人妻少妇av视频| 国产成人系列免费观看| 男女边吃奶边做爰视频| 中文字幕人妻丝袜一区二区| 免费一级毛片在线播放高清视频 | 欧美在线黄色| 欧美大码av| 日韩,欧美,国产一区二区三区| 校园人妻丝袜中文字幕| 精品少妇黑人巨大在线播放| 脱女人内裤的视频| 亚洲九九香蕉| 9热在线视频观看99| 欧美亚洲 丝袜 人妻 在线| 国产无遮挡羞羞视频在线观看| 一区二区三区精品91| 婷婷色av中文字幕| 人人妻人人澡人人看| 97在线人人人人妻| 亚洲欧洲日产国产| 精品人妻在线不人妻| 9色porny在线观看| 免费高清在线观看日韩| 欧美日韩av久久| 久久精品亚洲av国产电影网| 国产深夜福利视频在线观看| 久久久国产一区二区| 国产av一区二区精品久久| 中国国产av一级| 久久久精品免费免费高清| 国产人伦9x9x在线观看| 国产男女超爽视频在线观看| 王馨瑶露胸无遮挡在线观看| 成年美女黄网站色视频大全免费| 国产片特级美女逼逼视频| 日韩一本色道免费dvd| 韩国高清视频一区二区三区| 欧美人与性动交α欧美精品济南到| 18禁观看日本| 色综合欧美亚洲国产小说| 少妇被粗大的猛进出69影院| 日日爽夜夜爽网站| 久久精品国产亚洲av高清一级| 精品福利观看| 婷婷色综合大香蕉| 搡老岳熟女国产| 久久午夜综合久久蜜桃| 欧美激情极品国产一区二区三区| 亚洲国产欧美网| 99国产精品一区二区蜜桃av | 男人操女人黄网站| 午夜福利视频在线观看免费| 黑人猛操日本美女一级片| 国产一区二区三区综合在线观看| 99九九在线精品视频| 美女大奶头黄色视频| 老汉色∧v一级毛片| 国产一区二区在线观看av| 国产又爽黄色视频| 青春草亚洲视频在线观看| 尾随美女入室| 人妻人人澡人人爽人人| 最新的欧美精品一区二区| 国产高清视频在线播放一区 | 男男h啪啪无遮挡| 最近最新中文字幕大全免费视频 | 日本午夜av视频| 91字幕亚洲| 久久久国产一区二区| 少妇被粗大的猛进出69影院| 真人做人爱边吃奶动态| 欧美在线一区亚洲| 久久久久久人人人人人| 久久久国产一区二区| 另类亚洲欧美激情| 99久久综合免费| 电影成人av| 久久久久久久国产电影| 国产精品人妻久久久影院| 亚洲,欧美精品.| 亚洲中文日韩欧美视频| a级毛片在线看网站| 久久久久久久国产电影| 国产精品人妻久久久影院| 亚洲av美国av| 中文字幕精品免费在线观看视频| 1024视频免费在线观看| 亚洲av成人不卡在线观看播放网 | 两个人看的免费小视频| 99国产精品免费福利视频| 午夜91福利影院| 黄色一级大片看看| 一级片'在线观看视频| 91成人精品电影| 18禁裸乳无遮挡动漫免费视频| 少妇精品久久久久久久| 黑人欧美特级aaaaaa片| 色网站视频免费| 97人妻天天添夜夜摸| 99热国产这里只有精品6| 美女中出高潮动态图| av国产精品久久久久影院| 男女免费视频国产| 少妇粗大呻吟视频| 免费久久久久久久精品成人欧美视频| 久久精品国产亚洲av涩爱| 欧美乱码精品一区二区三区| 免费人妻精品一区二区三区视频| 亚洲av在线观看美女高潮| 两人在一起打扑克的视频| 欧美老熟妇乱子伦牲交| 日韩免费高清中文字幕av| 国产精品偷伦视频观看了| 免费黄频网站在线观看国产| 中国国产av一级| 波野结衣二区三区在线| 久久人人爽人人片av| 美女主播在线视频| 欧美在线黄色| 久久 成人 亚洲| 精品福利永久在线观看| 自线自在国产av| www.熟女人妻精品国产| 大香蕉久久网| 老司机影院成人| 国产精品一国产av| 国产精品久久久av美女十八| av在线播放精品| 亚洲av日韩在线播放| 欧美日韩黄片免| 啦啦啦在线观看免费高清www| 国产精品二区激情视频| 中文乱码字字幕精品一区二区三区| 亚洲美女黄色视频免费看| 搡老岳熟女国产| 日日夜夜操网爽| 天天躁夜夜躁狠狠久久av| 老司机靠b影院| 免费久久久久久久精品成人欧美视频| 在线精品无人区一区二区三| 成年人午夜在线观看视频| 黄色片一级片一级黄色片| 久久久欧美国产精品| 好男人视频免费观看在线| 日韩一本色道免费dvd| 日本五十路高清| 国产成人av激情在线播放| 大型av网站在线播放| 国产欧美日韩一区二区三区在线| 国产亚洲欧美精品永久| 国产精品九九99| 一级黄色大片毛片| 国产精品亚洲av一区麻豆| 亚洲精品美女久久av网站| 男人爽女人下面视频在线观看| 最黄视频免费看| 欧美黑人精品巨大| 一区二区三区乱码不卡18| 亚洲五月婷婷丁香| 欧美97在线视频| 日日爽夜夜爽网站| 最新的欧美精品一区二区| 国产一区有黄有色的免费视频| 黄色a级毛片大全视频| 欧美在线一区亚洲| av天堂在线播放| 人人妻人人添人人爽欧美一区卜| 日本a在线网址| 中文字幕亚洲精品专区| av网站在线播放免费| 90打野战视频偷拍视频| 性色av一级| 狂野欧美激情性xxxx| 宅男免费午夜| 日韩免费高清中文字幕av| 国产黄频视频在线观看| av天堂在线播放| 欧美大码av| 欧美日韩亚洲综合一区二区三区_| 午夜两性在线视频| 最新在线观看一区二区三区 | 成人黄色视频免费在线看| 天天影视国产精品| av国产精品久久久久影院| 纵有疾风起免费观看全集完整版| 999精品在线视频| 午夜激情久久久久久久| 久久精品国产亚洲av涩爱| 日韩免费高清中文字幕av|