• <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 ?

    Characterization of the adsorption behavior ofaqueous cadmium on nanozero-valent iron based on orthogonalexperiment and surface complexation modeling☆

    2016-05-30 01:54:54DongmeiLiuHuanTangYingZhaoFuyiCuiJingLu

    DongmeiLiu,Huan Tang,Ying Zhao*,FuyiCui*,Jing Lu

    1 State Key Laboratory ofUrban Water Resource and Environment,Harbin Institute ofTechnology,Harbin 150090,China

    2 Schoolof Municipaland EnvironmentalEngineering,Harbin Institute ofTechnology,Harbin 150090,China

    1.Introduction

    Cadmium(Cd)is a major environmental contaminant which is known to accumulate in rice plants[1].Cd can be introduced into the environment through a combination of natural processes(volcanic eruptions and forest fires)as well as anthropogenic activities(nonferrous metals production,electroplating,manufacturing of Ni–Cd batteries and pigments,application ofphosphatic fertilizers,and burning of fossilfuels)[2,3].The naturaloccurrence of Cd in groundwater is ofgreatconcern due to the toxicity ofCd and the potentialfor chronic exposure[4].To address this problem,the World Health Organization(WHO)had set a maximum guideline concentration of0.003 mg·L-1for Cd in drinking water[5].On this occasion many public watersystems have to adopt cadmium removal processes in their water treatment systems in order to meet the stringent drinking water standards.

    Various technologies are currently available to remove cadmium from water,such as chemicalmethods[6–8],membrane separation technique[9],ion exchange technique[10]and adsorption technique[11–13].Adsorption is a common practice for Cd removalfrom drinking water due to technologicaland cost advantages.

    Nano zero-valentiron(nZVI)has been developed as an ef ficientabsorbent material to treat various heavy metals from contaminated water[14].The speci fic removalmechanisms involved depend on the standard redox potential(E0)of the target metal.The E0of Fe0is-0.44 V.Metals with E0s that are more negative or similar to-0.44 V willbe removed by adsorption,others with E0s that are more positive than-0.44 will be removed by reduction and precipitation.Metals with slightly more positive E0than Fe0willbe removed by reduction,adsorption,oxidation or co-precipitation which depend upon the prevailing geochemicalconditions[15,16].

    As shown by several studies,factors such as aqueous phase pH,concentrations of contaminants and the presence of competitive ions have a signi ficant effect on nZVI's reactivity with metals[17–21].Although researches had investigated the factors that may have effect on the ef ficiency of nZVI,comparatively little research had studied which factor is the most signi ficant one.Figuring out this factor will mean a lot on the application ofnZVI.

    Among allthe nZVIsynthesis methods,chemicalreduction is widely used due to its simplicity and chemicalhomogeneity[22].During the nZVIpreparation,mechanicalagitation needs to be employed to insure the size of ZVI at nanoscale[23].Aggregation of nanoparticles was reported to be caused by the large surface area and magnetic dipole–dipole interactions of the individual particles[24].If the solution is stirred vigorously,the aggregation would be weakened to some extent.However,this mechanical stir method brings some questions(1)the waste ofelectricity,(2)some of the nanoparticles may stick to the agitator which are hard to clean.

    The main objective ofthis study is to find outthe mostsigni ficantfactor that affects the ef ficiency ofnZVI.First,nZVIwillbe prepared by an improved liquid-phase reduction and characterized to verify this new method.Then an orthogonalexperiment and simulation willbe performed underthe same conditions to find outthe mostsigni ficantfactor.

    2.Materials and Methods

    2.1.Synthesis ofnZVIparticles

    The nanoparticles were synthesized via the classical reaction as follows:

    Allthe aqueous solutions were prepared with deionized deoxygenated water.Before the reaction begins,the FeCl3·6H2O(1 mol·L-1)was mixed with PVP(1 g·L-1).Then the NaBH4(1.6 mol·L-1)solution was added to the mixture mentioned above.The nitrogen was sparged into the solution during the whole process to maintain an anaerobic atmosphere.

    2.2.Characterization ofnZVI

    Morphologicalanalysis of the samples was performed by transmission electron microscopy(TEM)using a FEITecnai G2 F30 operated at 300 kV.Samples for TEMobservation were suspended in ethanoland then supported on a double carbon membrane.

    The speci fic surface area(SBET)ofnZVIwas calculated by Brunauer–Emmett–Teller(BET)N2method,and the pore size was measured by the BJH(Barrett,Joyner,and Halenda)N2adsorption/desorption isotherm method at 77 K using the automatic analyzer(ASAP 2020,Micromeritics,USA).

    2.3.Orthogonalexperiment

    The experiments were based on an orthogonalarray experiment design and the following three variables were analyzed:initialpH of the solution,dosage ofnZVIand the initialconcentration ofcadmium.These three factors were identi fied to have signi ficant impact on the ef ficiency ofnZVI[25].

    Other factors such as temperature and existence ofother metalions maybe as importantas the parameters picked.But the effectoftemperature had been studied by Boparai et al.completely so we didn't take this factor into account[26].As for other metalions,such as Pb(II)and As(III),although they may have signi ficant effect on the adsorption of Cd2+by nZVI,it is not appropriate to consider this factor in orthogonal experiment.Therefore,the effects ofmetalions were excluded in our orthogonal experiment.Li et al.had studied the effect of pH in the range of 4–9[27],and Zhang et al.had studied the effect of pH in the range of3–8.6[28].Butin actualproject,the pHofef fluents from chemicalfactory may beyond this range,so itis necessary to study the pHin a larger range.On this occasion,the range ofpH used in our experiment was 2–10.Based on the waste water ofmetallurgicalindustry,the concentration of Cd(II)used in our experiment was 10,20 and 40 mg·L-1.And the dose ofnZVIwas based on ourearlierexperiments.Above all,an L9(33)matrix,which is an orthogonalarray of three factors and three levels,was employed to assign the considered factors and levels as listed in Table 1.

    Data analysis would be carried out through the range analysis to re flect the magnitudes of the three factors.

    Table 1 Levels and factors in orthogonalexperiment design

    Allthe experiments were performed at ambient temperature and pressure using a 250.0 mlserum bottle.The pH values of the solutions were controlled and adjusted with the 0.02 Mbuffer as Boparai et al.had used[29].

    The contents were mixed on a thermostatic oscillator operated at 200 r·min-1.After 1 h an aliquot of supernatant was sampled and filtered using a 0.22μm filter(Millipore),the samples were then transferred into clean falcon tubes and diluted using nitric acid(5%).The remaining concentration of cadmium in the filtrate was determined by means of inductively coupled plasma-optical emission spectroscopy(ICP-OES,AA 200,Agilent Technologies).Blank experiments with and without nZVIand without filtering were also performed to obtain the initialcadmium concentration prior to adsorption,as well as to rule out filtration as a reason forthe decrease on the concentration ofcadmium in the supernatant.

    2.4.Surface complexation modeling

    In aqueous solution,transition metals are known to assume different chemicalforms that the formations depend on the pH of the solution.The speciation analysis ofaqueous Cd2+ions was performed at various initialconcentration,temperature,pH,and ionic strength values using visualMINTEQ software.

    In actualwater,bare nZVIparticles willreactwith water and oxygen to form outer iron(hydr)oxide layer[30].On this occasion,the essence of the adsorption is the interaction between Cd and the outer layer.Based on this,a surface complexation modeling was carried out by VisualMINTEQ 3.0.

    The iron oxide/hydroxide–water interface was represented by,for example,≡FeOH and ≡FeO,where the“≡Fe”represents the solid–surface interface.Adsorbed materials are written as complexes of these surface oxides,for example,≡FeOCd+.And the possible reactions are as follows:

    Modeling was performed using the Diffuse Layer Model(DLM).This surface precipitation modelcan simulate the distribution of ions between adsorbed and dissolved phases based on the reactions as is mentioned above.Since the DLM model has been successfully used to describe metalion adsorption on pure mineralmaterials[31],it is unnecessary to go into details about the theory.Parameters used in the modeling were based on experiment data and/or previous reports[29].

    3.Result and Discussion

    3.1.Characterization ofnZVI

    The microimages of the synthesized nZVIare shown in Fig.1.As shown(Fig.1(a)and(b)),the aggregates can reach to severalmicrometers in length but less than 100 nm in diameter(Fig.1(c))

    The resultdemonstrated thatwe can use N2bubbling and PVP to replace mechanicalstirring in the preparation ofnZVI.PVP,which is a kind ofsurfactantthathas been widely used in the field ofsynthesizing nanosilver,can modify the surface properties of the particles[32].The added PVP can effectively preventthe aggregation ofZVIparticlesby(1)reducing the speci fic surface energy ofnZVIparticles and(2)increasing the steric hindrance between nZVIparticles.

    Fig.1.TEMimage of the nZVI.

    The morphologies of nZVIs showed in Fig.1(a)and(c)were fresh and those in Fig.1(b)and(d)were placed for two months after preparation.As is shown in Fig.1(b)and(d),there is a layer ofsemi-transparent film less than 10 nmthick around the black particle.Itwas reported thatthe exposure ofnZVIto oxygen can lead the formation ofiron oxide layer which contains Fe2O3,Fe3O4and FeOOH[33].The iron nanoparticles possessed a core–shellstructure.The shellrepresented the oxidized part that surrounded the Fe0core and it can prevent the nZVIagainst further oxidation[34].The addition ofnZVIto aqueous systems usually generates OH-by the reduction ofwater,resulting in the immobilization ofmetals by precipitation as hydroxides[35].

    BET analysis indicated a speci fic surface area of 20.3159 m2·g-1.This data was used in the simulation later.Fig.2 is the adsorption isotherm line,the trend of the plot indicated that nZVIis a typicalmaterial without holes or with macroporous.

    The TEMand BET results showed that nZVIprepared with this new approach possessed excellent surface characters.With the presence of PVP,the size ofZVIcan be insured to be in nanosize withoutmechanical stirring.

    Compared to traditionalmethods(Fig.3),this improved method has severaladvantages as follows.

    ·Compared with the three-necked flask,the serum bottle used as reactor is easier to clean and the solid–liquid separation is easier to achieve.

    Fig.2.BJH adsorption/desorption isotherm.

    Fig.3.Diagrammatic sketch ofcomparison between traditionalmethod and new method in the synthesis ofnZVI.

    ·In conventional approaches,negative pressure would be formed induced by rapid stirring,air will be introduced into the reaction mixture and the nZVIwould be oxidized more easily.

    3.2.Orthogonalexperiment

    An L9(33)orthogonalexperimentwas performed and the results are listed in Table 2.All the experiments were aimed at increasing the removalrate ofcadmium by nZVI.

    Table 2 Results of the orthogonalexperiment

    In order to figure out which factor is the most important,a range analysis is necessary.There are two parameters in a range analysis:Kjiand Rj.Kjiis de fined as the sum of the evaluation indexes of alllevels(i,i=1,2,3)in each factor(j,j=A,B,C)andis the mean value of Kji.Rjis de fined as the range between the maximumand minimumvalue ofand is used for evaluating the importance of the factors,i.e.Larger Rjvalue means a greater importance of the factor[36].The calculation is displayed below(for the factor of A):

    where KAiis the K value of the i levelof the factor A;and Yiis the value of the result of the trial number.Other K values of the factors can be determined by the same calculation steps.The mean values of Kfor different factors at different levels in the range analysis were listed in Table 3.

    Table 3 Range analysis data of the removalrate

    As is mentioned above,Rjindicates the signi ficance ofa factor and a larger Rjmeans that this factor has a more signi ficant impacton the removalrate.Based on the comparation of Rj,the prominence order of the factors was:initialpHof the solution(96.453)>initialconcentration of cadmium(3.294)>amount of nZVI(1.747).RCis the largest,which means a smallchange in the initialpH willhave a signi ficant effect on the removalrate ofcadmium.

    The mean value ofeach factor was displayed in Fig.4.Based on the changes in the mean value ofeach factor,it can be speculated that the removalrate sharply increased from 1.98%to 98.267%with the initial pH increased from 4 to 10.When the amount ofnZVIincreased from 1 g·L-1to 4 g·L-1,the removalrate increased steadily from 65.987%to 67.213%,which suggested that the amount ofnZVIhad a little effect on the removal ef ficiency of nZVI.Similarly,it can be speculated that the effect of the cadmium concentration ion is very small.

    Fig.4.Relationship between mean value ofeach factor and the removalrate.

    Based on the orthogonalexperimentand the range analysis,itcan be speculated that the initial pH of the solution is the most signi ficant factor that affects the adsorption performance of Cd2+onto nZVI.

    3.3.Surface precipitation modeling

    In order to con firm that initialpH is the most signi ficant factor,a simulation was performed.Parameters used in the modeling are as follows.The speci fic surface area of the iron(hydr)oxide shell was 20.3159 m2·g-1which was obtained from the BET analysis.The site density oftype 1 sites(weak sorption sites)was 2.26 sites nm-2,and of type 2 sites(strong sites)was 0.056 sites nm-2as recommended.The electrolyte was 0.01 mol·L-1NaNO3.After the adsorption equilibrium achieved,the result of the distribution of ions between adsorbed and dissolved phases is shown in Fig.5.The tendency of the curve showed that in acidic condition most of the cadmium was dissolved and Cd2+was found to be the dominant species.If the solution pH was higher,more cadmium would be adsorbed onto the nZVI and(≡FeO)2Cd was found to be the dominant form.

    Fig.5.Distribution ofions between adsorbed and dissolved phases in different pH.

    Simulations were performed under the same condition and the range ofeach factor is illustrated in Fig.6.The result showed that the range of factor C(99.99)is much larger than that of factor A(7.15)and factor B(7.16).The result is consistent with the conclusion we drew upon the orthogonalexperiment:the initialpH is the most signi ficant factor.

    Fig.6.Range ofeach factor calculated based on simulation.

    Both the experiments and the simulations showed that pH has the most signi ficant effect on the adsorption ef ficiency of the nZVI.In the range of4–10,the higher the pH,the more cadmium is adsorbed.This conclusion is important to maximize the adsorption rates and adsorption capacity ofnZVIfor cadmium.

    As the E0of cadmium is-0.40 V,which is close to that of Fe0(-0.44 V),Cd will be removed by sorption and/or precipitation.The dominant adsorption mechanism and the existing form of cadmium in aqueous solutions are both related to the solution pH.At lower pH,Cd2+is found to be the dominant species(Fig.7).Since the isoelectric point(IEP)ofnZVIwas around 8.1–8.2[37].At pH values below the IEP,the surface is expected to possess a positive potential,this willdecrease the adsorption ofmetalanions due to electrostatic repulsion.At higher pH,the abundant hydroxylwillresult in the immobilization ofmetals in the form ofhydroxides and precipitation is the dominantremovalmechanism.Fig.7 is the species distribution ofcadmium overa pHrange of1 to 14.Itcan be seen thatatpH 10,Cd2+existsdominantas Cd(OH)2,and the percentage of Cd(OH)2is about 85%,this means that the Cd2+willbe removed from water by precipitation without nZVI.But in the presence of nZVI,the removalrate of Cd2+at pH 12 is 97.1–99.2 in our experiment,which means that nZVIcan promote the removalofcadmium.In acidic conditions,the lowerthe pH,the strongerthe repulsion.In alkaline conditions,the higher the pH,the easier the precipitation is to form.

    Fig.7.The speciation of cadmium over a pH range of1 to 14.

    4.Conclusions

    In this study,traditionalliquid-phase reduction for preparing nZVI was improved by the introduction of PVP.TEMand BET analyses indicated that the improve method was better for nZVI preparation.An L9(33)orthogonalexperiment was employed to find out the dominant factor that affects the removalrate of cadmium by nZVI.Three factors were examined:initialpH of the solution,concentration of cadmium and the dosage of nZVI,and initial pH was found to be the most signi ficant factor.Surface precipitation modeling showed in different conditions,the Ca2+was removed by nZVIin different mechanisms.

    [1]S.Ishikawa,N.Ae,M.Sugiyama,M.Murakami,T.Arao,Genotypic variation in shoot cadmium concentration in rice and soybean in soils with different levels of cadmium contamination,Soil Sci.Plant Nutr.51(2005)101–108.

    [2]M.D.L.Dinis,A.Fiúza,Exposure assessment to heavy metals in the environment:Measures to eliminate or reduce the exposure to criticalreceptors,environmental heavy metal pollution and effects on child mental development,Springer,Netherlands,2011 27–50.

    [3]T.Kikuchi,M.Okazaki,K.Toyota,T.Motobayashi,M.Kato,The input–outputbalance of cadmium in a paddy field of Tokyo,Chemosphere 67(2007)920–927.

    [4]G.F.Nordberg,Historical perspectives on cadmium toxicology,Toxicol.Appl.Pharmacol.238(2009)192–200.

    [5]WHO,Guidelines for drinking water quality,second ed.,Recommendations,Vol.1,WHO,Geneva,1993.

    [6]O.Tunay,T.Ozkok,T.O.Hanci,I.Kabdasli,Applicability of phosphonic acid complexes as a means of cadmium removal from aqueous solutions,J.Selcuk Univ.Nat.Appl.Sci.(2013)70–77.

    [7]L.Charerntanyarak,Heavy metals removal by chemicalcoagulation and precipitation,Water Sci.Technol.39(1999)135–138.

    [8]S.A.Bayar,E.Yilmaz,R.Boncukcuo?lu,B.A.Fìla,M.M.Kocakerìm,Effects of operationalparameters on cadmium removalfrom aqueous solutions by electrochemical coagulation,Desalin.Water Treat.51(2013)2635–2643.

    [9]B.Pospiech,W.Kujawski,Ionic liquids as selective extractants and ion carriers of heavy metal ions from aqueous solutions utilized in extraction and membrane separation,Rev.Chem.Eng.31(2015)179–191.

    [10]A.Akcil,C.Erust,S.Ozdemiroglu,A review of approaches and techniques used in aquatic contaminated sediments:Metalremovaland stabilization by chemicaland biotechnological processes,J.Clean.Prod.86(2015)24–36.

    [11]J.A.Arcibar-Orozco,J.R.Rangel-Mendez,P.E.Diaz-Flores,Simultaneous adsorption of Pb(II)–Cd(II),Pb(II)–phenol,and Cd(II)–phenolby activated carbon cloth in aqueous solution,Water Air Soil Pollut.226(2015)1–10.

    [12]R.Liu,F.Liu,C.Hu,Simultaneous removalofCd(II)and Sb(V)by Fe–Mn binary oxide:Positive effects of Cd(II)on Sb(V)adsorption,J.Hazard.Mater.300(2015)847–854.

    [13]L.Yan,Y.Huang,J.Cui,Simultaneous As(III)and Cd removalfrom copper smelting wastewater using granular TiO2columns,Water Res.68(2015)572–579.

    [14]S.M.Ponder,J.G.Darab,T.E.Mallouk,Remediation of Cr(VI)and Pb(II)aqueous solutions using supported,nanoscale zero-valent iron,Environ.Sci.Technol.34(2000)2564–2569.

    [15]X.Q.Li,W.X.Zhang,Sequestration ofmetalcations with zero valentiron nanoparticles—A study with high resolution X-ray photoelectron spectroscopy,J.Phys.Chem.C 111(2007)6939–6946.

    [16]D.O'Carroll,B.Sleep,M.Krol,H.Boparai,C.Kocur,Nanoscale zero valent iron and bimetallic particles for contaminated site remediation,Adv.Water Resour.51(2013)104–122.

    [17]T.Tosco,M.P.Rapini,C.C.Viggi,R.Sethi,Nanoscale zerovalent iron particles for groundwater remediation:A review,J.Clean.Prod.44(2014)10–21.

    [18]M.Rivero-Huguet,W.D.Marshall,Reduction ofhexavalent chromium mediated by micro-and nano-sized mixed metallic particles,J.Hazard Mater.169(2009)1081–1087.

    [19]T.Phenrat,Y.Liu,R.D.Tilton,G.V.Lowry,Adsorbed polyelectrolyte coatings decrease Fe0nanoparticle reactivity with TCE in water:Conceptualmodeland mechanisms,Environ.Sci.Technol.43(2009)150–154.

    [20]Y.Liu,S.A.Majetich,R.D.Tilton,D.S.Sholl,G.V.Lowry,TCE dechlorination rates,pathways,and ef ficiency of nanoscale iron particles with different properties,Environ.Sci.Technol.39(2005)1338–1345.

    [21]F.He,D.Zhao,C.Paul,Field assessment of carboxymethyl cellulose stabilized iron nanoparticles for in situ destruction of chlorinated solvents in source zones,Water Res.44(2010)2360–2370.

    [22]W.Zhang,Nanoscale iron particles for environmental remediation:An overview,J.Nanopart.Res.5(2003)323–332.

    [23]Y.H.Hwang,D.G.Kim,H.S.Shin,Effects ofsynthesis conditions on the characteristics and reactivity of nano scale zero valent iron,Appl.Catal.B Environ.105(2011)144–150.

    [24]T.Phenrat,N.Saleh,K.Sirk,R.D.Tilton,G.V.Lowry,Aggregation and sedimentation of aqueous nanoscale zerovalent iron dispersions,Environ.Sci.Technol.41(2007)284–290.

    [25]N.Efecan,T.Shahwan,A.E.Eroglu,Characterization of the adsorption behavior of aqueous Cd(II)and Ni(II)ions on nanoparticles of zero-valent ironM.S.Thesis ?zmir Institute of Technology,2008.

    [26]H.K.Boparai,M.Joseph,D.M.O'Carroll,Kinetics and thermodynamics of cadmium ion removal by adsorption onto nano zerovalent iron particles,J.Hazard.Mater.186(2011)458–465.

    [27]Y.Li,H.Ma,B.Ren,T.Li,Simultaneous adsorption and degradation of Cr(VI)and Cd(II)ions from aqueous solution by silica-coated Fe0nanoparticles,J.Anal.Methods Chem.2013(2013).

    [28]Y.Zhang,Y.Li,C.Dai,H.Zhou,W.Zhang,Sequestration of Cd(II)with nanoscale zero-valent iron(nZVI):Characterization and test in a two-stage system,Chem.Eng.J.244(2014)218–226.

    [29]H.K.Boparai,M.Joseph,D.M.O'Carroll,Cadmium(Cd2+)removal by nano zerovalent iron:Surface analysis,effects ofsolution chemistry and surface complexation modeling,Environ.Sci.Pollut.Res.20(2013)6210–6221.

    [30]Y.P.Sun,X.Q.Li,J.S.Cao,W.X.Zhang,H.P.Wang,Characterization ofzero-valent iron nanoparticles,Adv.Colloid Interf.120(2006)47–56.

    [31]X.Wen,Q.Du,H.Tang,Surface complexation modelfor the heavy metaladsorption on naturalsediment,Environ.Sci.Technol.32(1998)870–875.

    [32]K.A.K.Huynh,L.Chen,Aggregation kinetics of citrate and polyvinylpyrrolidone coated silver nanoparticles in monovalent and divalent electrolyte solutions,Environ.Sci.Technol.45(2011)5564–5571.

    [33]J.T.Nurmi,P.G.Tratnyek,V.Sarathy,D.R.Baer,J.E.Amonette,K.Pecher,C.Wang,J.C.Linehan,D.W.Matson,R.L.Penn,M.D.Driessen,Characterization and properties of metallic iron nanoparticles:Spectroscopy,electrochemistry,and kinetics,Environ.Sci.Technol.39(2005)122–130.

    [34]X.Li,W.Zhang,Sequestration ofmetalcations with zerovalent iron nanoparticles—A study with high resolution X-ray photoelectron spectroscopy(HR-XPS),J.Phys.Chem.C 111(2007)6939–6946.

    [35]W.Yan,A.A.Herzing,C.J.Kiely,W.Zhang,Nanoscale zero-valent iron(nZVI):Aspects of the core–shellstructure and reactions with inorganic species in water,J.Contam.Hydrol.118(2010)96–104.

    [36]X.Wu,D.Y.C.Leung,Optimization of biodiesel production from camelina oil using orthogonalexperiment,Appl.Energy 88(2011)3615–3624.

    [37] ?.üzüm,T.Shahwan,A.E.Ero?lu,I.Lieberwirth,T.B.Scott,K.R.Hallam,Application of zero-valent iron nanoparticles for the removal of aqueous Co2+ions under various experimentalconditions,Chem.Eng.J.144(2008)213–220.

    小说图片视频综合网站| 亚洲人成网站在线播放欧美日韩| 90打野战视频偷拍视频| 国产伦在线观看视频一区| 在线观看日韩欧美| 最近视频中文字幕2019在线8| 少妇的逼水好多| 最近在线观看免费完整版| 午夜福利免费观看在线| 亚洲人成网站在线播放欧美日韩| 日韩欧美在线二视频| 我要搜黄色片| 久久欧美精品欧美久久欧美| 中文字幕高清在线视频| 国产亚洲欧美98| 女生性感内裤真人,穿戴方法视频| 成年版毛片免费区| 蜜桃久久精品国产亚洲av| 天美传媒精品一区二区| 91av网一区二区| 亚洲va日本ⅴa欧美va伊人久久| 久久精品91无色码中文字幕| 男人舔奶头视频| av专区在线播放| 欧美乱妇无乱码| 波多野结衣高清作品| 黄色成人免费大全| 午夜福利成人在线免费观看| 欧美色视频一区免费| 国产一区二区亚洲精品在线观看| 国产伦在线观看视频一区| 又黄又粗又硬又大视频| 岛国在线观看网站| 久久精品91蜜桃| 免费在线观看影片大全网站| 久久久久久九九精品二区国产| 中文字幕av成人在线电影| 五月伊人婷婷丁香| 日本精品一区二区三区蜜桃| 香蕉丝袜av| 嫁个100分男人电影在线观看| 51国产日韩欧美| 亚洲男人的天堂狠狠| 精品国内亚洲2022精品成人| 国产亚洲精品综合一区在线观看| 国产精品国产高清国产av| 欧美日韩黄片免| 97人妻精品一区二区三区麻豆| 中文字幕人妻丝袜一区二区| 在线视频色国产色| 黄色女人牲交| 淫秽高清视频在线观看| 亚洲五月天丁香| 在线免费观看不下载黄p国产 | 国产精品国产高清国产av| 不卡一级毛片| 亚洲精品日韩av片在线观看 | 一进一出抽搐动态| 美女高潮的动态| 两个人看的免费小视频| 欧美日韩国产亚洲二区| 日本成人三级电影网站| 97碰自拍视频| 精品国产三级普通话版| 欧美一区二区国产精品久久精品| 男女视频在线观看网站免费| 可以在线观看的亚洲视频| 欧美中文综合在线视频| 欧美高清成人免费视频www| 美女被艹到高潮喷水动态| 国产色婷婷99| 日本在线视频免费播放| 丝袜美腿在线中文| 国产精品女同一区二区软件 | 国产av不卡久久| 又粗又爽又猛毛片免费看| 国产伦精品一区二区三区四那| 亚洲欧美激情综合另类| 色播亚洲综合网| 真人一进一出gif抽搐免费| 校园春色视频在线观看| 精品国内亚洲2022精品成人| 变态另类成人亚洲欧美熟女| 精品电影一区二区在线| 在线观看一区二区三区| 伊人久久大香线蕉亚洲五| 午夜免费男女啪啪视频观看 | 99精品欧美一区二区三区四区| 中文字幕av成人在线电影| 欧美日韩精品网址| 校园春色视频在线观看| 午夜福利视频1000在线观看| 黄色视频,在线免费观看| 2021天堂中文幕一二区在线观| 特级一级黄色大片| 国产精品 欧美亚洲| 欧美日韩一级在线毛片| 亚洲狠狠婷婷综合久久图片| 男人舔女人下体高潮全视频| 每晚都被弄得嗷嗷叫到高潮| 人妻丰满熟妇av一区二区三区| 欧美成狂野欧美在线观看| 一个人免费在线观看电影| 搡女人真爽免费视频火全软件 | 久99久视频精品免费| 色播亚洲综合网| 五月玫瑰六月丁香| 悠悠久久av| 久久精品国产亚洲av涩爱 | 久久久久久人人人人人| 亚洲成av人片在线播放无| 午夜福利成人在线免费观看| 嫁个100分男人电影在线观看| 色综合站精品国产| x7x7x7水蜜桃| 欧美成人免费av一区二区三区| 一区二区三区激情视频| 一区福利在线观看| 99国产综合亚洲精品| bbb黄色大片| a级一级毛片免费在线观看| 精品久久久久久久久久久久久| 亚洲人成网站高清观看| 日本成人三级电影网站| 一进一出好大好爽视频| 欧美乱妇无乱码| 亚洲人成网站高清观看| 大型黄色视频在线免费观看| 俄罗斯特黄特色一大片| 欧美日韩亚洲国产一区二区在线观看| 国产在线精品亚洲第一网站| 91久久精品电影网| 综合色av麻豆| 欧美成人免费av一区二区三区| 国产精品国产高清国产av| 国产一区二区在线观看日韩 | 亚洲av中文字字幕乱码综合| 神马国产精品三级电影在线观看| 午夜a级毛片| 丁香欧美五月| 成人国产一区最新在线观看| 在线视频色国产色| 69av精品久久久久久| 欧美一级毛片孕妇| 亚洲精品在线美女| av在线天堂中文字幕| 亚洲精品456在线播放app | 91av网一区二区| 3wmmmm亚洲av在线观看| 搡女人真爽免费视频火全软件 | 99久久精品一区二区三区| 91九色精品人成在线观看| 99国产精品一区二区三区| 国产乱人伦免费视频| 午夜两性在线视频| 国产爱豆传媒在线观看| 亚洲国产精品sss在线观看| 丰满的人妻完整版| 国产成人福利小说| 一个人免费在线观看电影| 日韩av在线大香蕉| 久久久国产成人免费| 99久久综合精品五月天人人| 丁香六月欧美| 老熟妇乱子伦视频在线观看| 久久久久久人人人人人| 亚洲av一区综合| 亚洲国产中文字幕在线视频| 国产精品综合久久久久久久免费| 天美传媒精品一区二区| 淫妇啪啪啪对白视频| 好男人电影高清在线观看| 超碰av人人做人人爽久久 | 国产真实伦视频高清在线观看 | 乱人视频在线观看| 国内久久婷婷六月综合欲色啪| 成年女人看的毛片在线观看| 超碰av人人做人人爽久久 | 日韩成人在线观看一区二区三区| 18禁裸乳无遮挡免费网站照片| 国产激情欧美一区二区| av欧美777| 亚洲最大成人手机在线| 久久精品国产亚洲av涩爱 | 成人无遮挡网站| 脱女人内裤的视频| 美女大奶头视频| 最后的刺客免费高清国语| 99精品在免费线老司机午夜| av欧美777| 1024手机看黄色片| 国产精品国产高清国产av| 岛国视频午夜一区免费看| 午夜激情福利司机影院| av天堂中文字幕网| 深爱激情五月婷婷| xxx96com| 啦啦啦免费观看视频1| 嫁个100分男人电影在线观看| 成人精品一区二区免费| 欧美午夜高清在线| 精品一区二区三区人妻视频| 精品免费久久久久久久清纯| 丁香六月欧美| 高清日韩中文字幕在线| 又爽又黄无遮挡网站| 麻豆成人av在线观看| 久久香蕉国产精品| 精品久久久久久久久久久久久| 日韩免费av在线播放| 男女之事视频高清在线观看| 美女被艹到高潮喷水动态| 国产成人系列免费观看| 在线观看日韩欧美| 又紧又爽又黄一区二区| 叶爱在线成人免费视频播放| 亚洲在线观看片| 久久人人精品亚洲av| 国产精品久久视频播放| 国产精品亚洲美女久久久| 免费av毛片视频| 热99re8久久精品国产| 激情在线观看视频在线高清| 噜噜噜噜噜久久久久久91| 法律面前人人平等表现在哪些方面| 每晚都被弄得嗷嗷叫到高潮| 亚洲精华国产精华精| 亚洲av中文字字幕乱码综合| 久久中文看片网| 欧美色欧美亚洲另类二区| 级片在线观看| 淫妇啪啪啪对白视频| 最新在线观看一区二区三区| 国产成人av教育| 欧美成人免费av一区二区三区| 国产高清三级在线| 国产激情偷乱视频一区二区| 亚洲av成人精品一区久久| 欧美乱色亚洲激情| 久久久久久人人人人人| 九九久久精品国产亚洲av麻豆| 国产欧美日韩精品亚洲av| 亚洲七黄色美女视频| 91久久精品国产一区二区成人 | 国内精品久久久久久久电影| 免费一级毛片在线播放高清视频| 午夜免费男女啪啪视频观看 | 久久久久免费精品人妻一区二区| 精品久久久久久久人妻蜜臀av| 国产午夜精品论理片| 不卡一级毛片| 亚洲美女视频黄频| 欧美一区二区亚洲| 99精品久久久久人妻精品| 午夜精品久久久久久毛片777| 成人性生交大片免费视频hd| 日韩欧美免费精品| 久久午夜亚洲精品久久| 成人亚洲精品av一区二区| 久久精品国产综合久久久| 人妻夜夜爽99麻豆av| 国产免费av片在线观看野外av| 黄色视频,在线免费观看| 亚洲成av人片免费观看| 国产av一区在线观看免费| 国产精品国产高清国产av| 免费看a级黄色片| 成年女人永久免费观看视频| 国产亚洲av嫩草精品影院| 亚洲不卡免费看| www日本在线高清视频| 亚洲专区中文字幕在线| 亚洲,欧美精品.| 有码 亚洲区| 少妇人妻一区二区三区视频| 亚洲av成人av| 女警被强在线播放| 韩国av一区二区三区四区| 在线观看av片永久免费下载| 97超视频在线观看视频| 久久6这里有精品| 老司机午夜福利在线观看视频| 亚洲欧美日韩东京热| 日本与韩国留学比较| 舔av片在线| 99在线视频只有这里精品首页| 免费观看精品视频网站| 成人特级黄色片久久久久久久| 人妻夜夜爽99麻豆av| 色综合亚洲欧美另类图片| 欧美性猛交╳xxx乱大交人| 美女cb高潮喷水在线观看| 内地一区二区视频在线| 757午夜福利合集在线观看| 在线视频色国产色| 18禁美女被吸乳视频| 成年免费大片在线观看| 亚洲午夜理论影院| 午夜福利在线在线| 极品教师在线免费播放| 美女 人体艺术 gogo| 精品久久久久久久人妻蜜臀av| 此物有八面人人有两片| 丰满乱子伦码专区| 精品熟女少妇八av免费久了| 欧美三级亚洲精品| 午夜老司机福利剧场| 天天一区二区日本电影三级| 国产伦人伦偷精品视频| 香蕉久久夜色| 国产一区二区三区在线臀色熟女| 美女被艹到高潮喷水动态| 在线免费观看的www视频| 国产精品久久电影中文字幕| 国产一区在线观看成人免费| www国产在线视频色| 久久精品人妻少妇| 可以在线观看的亚洲视频| 国产99白浆流出| 久久天躁狠狠躁夜夜2o2o| 日本熟妇午夜| 性色av乱码一区二区三区2| 少妇的逼水好多| 免费高清视频大片| 淫妇啪啪啪对白视频| 一进一出好大好爽视频| av黄色大香蕉| 他把我摸到了高潮在线观看| 黄色丝袜av网址大全| 欧美在线黄色| 日本撒尿小便嘘嘘汇集6| 国产高潮美女av| 青草久久国产| 亚洲成人免费电影在线观看| 国产成人影院久久av| 一个人看的www免费观看视频| 午夜亚洲福利在线播放| 欧美乱色亚洲激情| 搡老妇女老女人老熟妇| 久久精品国产亚洲av涩爱 | 一区二区三区免费毛片| 国产精品1区2区在线观看.| 精品免费久久久久久久清纯| 在线十欧美十亚洲十日本专区| 国产一区二区三区在线臀色熟女| 亚洲成av人片在线播放无| 亚洲内射少妇av| 日本一本二区三区精品| 亚洲国产欧洲综合997久久,| 高潮久久久久久久久久久不卡| 久久精品国产清高在天天线| 亚洲天堂国产精品一区在线| 18禁国产床啪视频网站| 久久国产精品人妻蜜桃| 97超视频在线观看视频| 午夜精品一区二区三区免费看| 久久中文看片网| 国产高清videossex| 国产主播在线观看一区二区| 丰满人妻熟妇乱又伦精品不卡| 久久精品夜夜夜夜夜久久蜜豆| 久久精品国产99精品国产亚洲性色| 国产av在哪里看| 热99re8久久精品国产| 日本免费一区二区三区高清不卡| 成人性生交大片免费视频hd| 伊人久久大香线蕉亚洲五| 日韩有码中文字幕| 成人国产一区最新在线观看| xxxwww97欧美| 亚洲精品日韩av片在线观看 | 日韩欧美 国产精品| 国产亚洲av嫩草精品影院| 成人特级黄色片久久久久久久| 99riav亚洲国产免费| av天堂中文字幕网| 嫁个100分男人电影在线观看| 国产亚洲精品久久久久久毛片| 日本 欧美在线| 老熟妇乱子伦视频在线观看| 中国美女看黄片| 欧美最新免费一区二区三区 | 操出白浆在线播放| 成人国产一区最新在线观看| 夜夜夜夜夜久久久久| 亚洲真实伦在线观看| 亚洲欧美激情综合另类| 国产三级在线视频| 色综合欧美亚洲国产小说| 少妇人妻一区二区三区视频| 99热这里只有精品一区| 亚洲欧美日韩无卡精品| 狂野欧美激情性xxxx| 美女大奶头视频| 91麻豆av在线| 久久久成人免费电影| 亚洲第一电影网av| 黄片小视频在线播放| 国产 一区 欧美 日韩| 香蕉av资源在线| 制服人妻中文乱码| 99精品欧美一区二区三区四区| 精品一区二区三区av网在线观看| 少妇的逼好多水| 99精品在免费线老司机午夜| 噜噜噜噜噜久久久久久91| 搡老熟女国产l中国老女人| 少妇裸体淫交视频免费看高清| 国产精品99久久久久久久久| 欧美在线一区亚洲| 在线观看免费视频日本深夜| 午夜精品在线福利| 大型黄色视频在线免费观看| 欧美3d第一页| 最新中文字幕久久久久| 天堂影院成人在线观看| 亚洲av成人av| 欧美日本视频| 久久久久久久久大av| 一本久久中文字幕| 日日夜夜操网爽| 一区二区三区高清视频在线| 精品乱码久久久久久99久播| 老司机午夜福利在线观看视频| 亚洲成人中文字幕在线播放| 久久久久精品国产欧美久久久| 免费电影在线观看免费观看| 免费人成在线观看视频色| 久久久久久久午夜电影| 欧美日韩国产亚洲二区| 欧美zozozo另类| 欧美最新免费一区二区三区 | 中国美女看黄片| 亚洲黑人精品在线| 窝窝影院91人妻| 亚洲精品成人久久久久久| 亚洲国产色片| 在线天堂最新版资源| 69av精品久久久久久| 免费av观看视频| 国产成年人精品一区二区| 亚洲久久久久久中文字幕| 女人高潮潮喷娇喘18禁视频| 国产精品久久视频播放| 熟妇人妻久久中文字幕3abv| 亚洲内射少妇av| 国产 一区 欧美 日韩| 男人舔女人下体高潮全视频| 夜夜夜夜夜久久久久| 日韩欧美 国产精品| 啪啪无遮挡十八禁网站| 成人永久免费在线观看视频| 久久久久久国产a免费观看| 久久国产精品人妻蜜桃| 久久这里只有精品中国| 又爽又黄无遮挡网站| 国产男靠女视频免费网站| 成人性生交大片免费视频hd| 亚洲精品在线美女| 中国美女看黄片| 亚洲精品一卡2卡三卡4卡5卡| 高清毛片免费观看视频网站| 日韩人妻高清精品专区| 国产精品久久久久久久久免 | 午夜福利欧美成人| 亚洲天堂国产精品一区在线| 亚洲av日韩精品久久久久久密| 老司机深夜福利视频在线观看| 国产精品久久视频播放| 日本免费一区二区三区高清不卡| 亚洲欧美精品综合久久99| 国产精品久久久久久精品电影| 久久久精品大字幕| 90打野战视频偷拍视频| 欧美不卡视频在线免费观看| 久久久色成人| 日本与韩国留学比较| 国内久久婷婷六月综合欲色啪| 国产国拍精品亚洲av在线观看 | 久久久久久国产a免费观看| 欧美乱色亚洲激情| 俺也久久电影网| 精品人妻偷拍中文字幕| 蜜桃亚洲精品一区二区三区| 国产精品免费一区二区三区在线| 中文字幕av在线有码专区| 久久6这里有精品| 亚洲精品在线美女| 美女高潮的动态| 精品国产美女av久久久久小说| 国产激情欧美一区二区| 精品免费久久久久久久清纯| 久久精品91蜜桃| 国产日本99.免费观看| 久久这里只有精品中国| 国产伦精品一区二区三区四那| 狠狠狠狠99中文字幕| 精品国产超薄肉色丝袜足j| xxxwww97欧美| 国产精品一及| 成人精品一区二区免费| 国产黄色小视频在线观看| 亚洲中文字幕日韩| 午夜激情福利司机影院| 2021天堂中文幕一二区在线观| 免费在线观看成人毛片| 精华霜和精华液先用哪个| 国产又黄又爽又无遮挡在线| 岛国视频午夜一区免费看| 国产成人av激情在线播放| 19禁男女啪啪无遮挡网站| 亚洲欧美日韩东京热| 亚洲最大成人手机在线| 国产真实伦视频高清在线观看 | 日韩欧美在线二视频| 国产av不卡久久| 又黄又粗又硬又大视频| 69人妻影院| 色老头精品视频在线观看| 狠狠狠狠99中文字幕| 亚洲成av人片在线播放无| 中文字幕av成人在线电影| 18禁黄网站禁片午夜丰满| 国产极品精品免费视频能看的| 亚洲成av人片免费观看| 一区二区三区高清视频在线| 国产亚洲精品久久久com| 成年女人看的毛片在线观看| 真人一进一出gif抽搐免费| 国产爱豆传媒在线观看| 国产97色在线日韩免费| 久久亚洲精品不卡| 真实男女啪啪啪动态图| 99久久精品热视频| 欧美一级毛片孕妇| av欧美777| 国产又黄又爽又无遮挡在线| 国产三级黄色录像| 欧美绝顶高潮抽搐喷水| 午夜日本视频在线| 一级黄片播放器| 日本色播在线视频| 高清在线视频一区二区三区| 国产男人的电影天堂91| 波多野结衣巨乳人妻| 天美传媒精品一区二区| 免费av不卡在线播放| 性色avwww在线观看| 国产老妇女一区| 国内精品宾馆在线| 身体一侧抽搐| 人妻少妇偷人精品九色| 国产精品国产三级专区第一集| 欧美xxxx性猛交bbbb| 国产黄频视频在线观看| 亚洲成人一二三区av| 亚洲精品日韩av片在线观看| 免费黄网站久久成人精品| 九九久久精品国产亚洲av麻豆| 国产大屁股一区二区在线视频| 777米奇影视久久| 赤兔流量卡办理| 亚洲av一区综合| 成人亚洲精品一区在线观看 | 国产日韩欧美在线精品| 色哟哟·www| 久久久久免费精品人妻一区二区| 最近中文字幕高清免费大全6| 人人妻人人澡人人爽人人夜夜 | 大又大粗又爽又黄少妇毛片口| 久久久国产一区二区| 少妇的逼水好多| 亚洲精品久久午夜乱码| 白带黄色成豆腐渣| 亚洲综合精品二区| 成人毛片a级毛片在线播放| 一级黄片播放器| 美女大奶头视频| 亚洲国产精品国产精品| 精品午夜福利在线看| 人妻制服诱惑在线中文字幕| 51国产日韩欧美| 色吧在线观看| 日韩,欧美,国产一区二区三区| 日韩 亚洲 欧美在线| 一级毛片 在线播放| 不卡视频在线观看欧美| 国产成人aa在线观看| 亚洲综合色惰| 久久久久免费精品人妻一区二区| 六月丁香七月| 91久久精品电影网| 成人鲁丝片一二三区免费| 国产一区二区三区av在线| 深爱激情五月婷婷| 九草在线视频观看| 少妇丰满av| 久久久久久久亚洲中文字幕| 乱人视频在线观看| 久久久久久久久久人人人人人人| 国产成人aa在线观看| 少妇被粗大猛烈的视频| 精品久久久噜噜| 国产精品女同一区二区软件| 国产精品.久久久| 午夜精品在线福利| 亚洲真实伦在线观看| 99久久人妻综合| 一级片'在线观看视频| 熟妇人妻久久中文字幕3abv| 美女cb高潮喷水在线观看| 亚洲成人精品中文字幕电影| 国产综合懂色| 久久综合国产亚洲精品| 欧美三级亚洲精品|