• <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 ?

    4,5-二氨基-2-硫脲嘧啶膜氯化鈉溶液中對(duì)銅緩蝕性能的研究

    2019-06-10 02:57劉澤群范娟娟姜月月周洋應(yīng)葉郭小玉楊海峰
    關(guān)鍵詞:極化曲線

    劉澤群 范娟娟 姜月月 周洋 應(yīng)葉 郭小玉 楊海峰

    摘 要: 通過(guò)自組裝方法將4,5-二氨基-2-硫脲嘧啶(MPD)分子吸附在銅(Cu)表面,應(yīng)用電化學(xué)極化、電化學(xué)阻抗譜(EIS)和拉曼光譜方法,研究其在質(zhì)量分?jǐn)?shù)為3.5%的氯化鈉(NaCl)溶液中的緩蝕能力.在最佳裝配條件下,MPD膜的最大緩蝕效率達(dá)到98.1%.拉曼光譜研究表明:MPD分子通過(guò)N9-H10和S7-H8吸附在Cu表面上.

    關(guān)鍵詞: 銅; 緩蝕; 電化學(xué)阻抗譜(EIS); 極化曲線; 拉曼光譜

    1 Introduction

    As one of the most usual metals,copper and its alloys are being widely used in electronic manufacturers,marine industries,power stations,and heat exchangers due to their good corrosion resistance,high electrical and thermal conductivity,and strong malleability[1-3].Copper offers relevant corrosion resistance in the atmosphere and in neutral or alkalescent solutions due to the formation of a passive oxide film or nonconductive layer of corrosion products on its surface[4-5].However,pitting corrosion could occur on the surface when copper is exposed to oxygen or other oxidants,which would therefore cause serious economic loss and casualties[6-7].Hence,using organic and inorganic corrosion inhibitors,one of the most practical and effective methods among different corrosion protection methods,has been widely studied[8-9].The heteroatoms (such as N,O and S) in the organic compounds which acted as the adsorption sites could be adsorbed on the metal surface via π-π and Van der Waals interactions [10-11].

    Unfortunately,most of the corrosion inhibitors,such as triazines[8],imidazoles[12],and benzotriazole[13] are toxic,which hinder their applications in the sea environment[14].Therefore,numerous studies are now focused on eco-friendly drug compounds to reduce the pollution problems[15-16].

    Thiouracil and its derivatives,potent and safe pharmaceutical intermediates for anti-thyroid drugs and melanoma detection agents,have been widely used in medical and chemical fields.As corrosion inhibitors,they have been proved to have high corrosion inhibition efficiency.For instance,the marine paint formulations based on soluble resin which contain 6-amino-2-thiouracil and their derivatives can protect unprimed steel panels from sea water corrosion for more than two months[17].ISSA et al.[18] calculated the corrosion inhibition efficiency for dithiouracil,thiouracil,uracil and dihydrouracil against the copper corrosion.AL-ANDIS et al.[19] examined thiouracil derivatives on protecting carbon steel corrosion in sulfuric acid using gasometry and potentiometry,whilst HEAKAL et al.[20] measured their impedance data combing with density functional theory (DFT) calculations.

    In this work,the corrosion inhibition efficiency of one eco-friendly corrosion inhibitor,4,5-diamino-6-hydroxy-2-mercapto-pyrimidine (MPD),against copper corrosion in 3.5% (mass fraction) NaCl solution is carefully studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques and its molecular structure is shown in Figure 1.Besides,Raman spectroscopy was used to verify the adsorption site of MPD on the copper surface.

    2 Experimental

    2.1 Materials

    MPD (85% mass fraction) was purchased from Sigma-Aldrich Corporation.Sulfuric acid,sodium chloride,and ethanol were obtained from Sinopharm Chemical Reagent,Shanghai,China.All chemicals were of analytical grade reagents,and were used without further purification.All solutions were prepared with Milli-Q water (18 MΩ·cm).

    2.2 Pretreatment of the copper electrode

    Teflon sheathed copper rod (99.999% mass fraction,0.031 4 cm2 geometric area) was firstly rubbed with 500- and 1 000-grit papers,then polished by 0.3 μm alumina powder until a shiny mirror-like surface with less oxides and pits was visible.After that,such electrode was rinsed with Milli-Q water,pure ethanol and again with Milli-Q water to entirely remove the alumina particles and loose copper rust.

    2.3 Assembling MPD layer

    The pretreated copper electrodes were immersed immediately into the MPD aqueous solutions with different molar concentrations (i.e.5×10-5,1×10-4,5×10-4,1×10-3 mol·L-1),with different assembly times (1,3,5,8,12 h),respectively.Each MPD solution was firstly deoxygenated via purging nitrogen for 20 min before being used.After then,the MPD modified electrodes were taken out,rinsed with Milli-Q water,and dried under flowing nitrogen gas.

    2.4 Electrochemical experiments

    CHI750C electrochemistry workstation (CH Instruments,Inc.) was used to determine the electrochemical behavior of a traditional three-electrode cell (a saturated calomel electrode (SCE),a platinum foil electrode,and a copper electrode were used as reference,counter,and working electrode,respectively) in 3.5% (mass fraction),NaCl aqueous solution.Prior to every test,the copper electrodes with and without MPD modification were immersed in 3.5% NaCl aqueous solution for 3 000 s until a stable open circuit potential(OCP) (OCP vs.SCE) was achieved.EIS results were acquired under OCP with a 5 mV amplitude perturbing signal in the frequency range from 100 kHz to 10 mHz.The EIS data were then analyzed using Zsimpwin software.The electrochemical polarization curves were recorded with a voltage range from -0.4 to -0.05 V vs.SCE,a scan rate of 1 mV·s-1,and a sensitivity of 10-3.

    2.5 Surface characterization

    2.5.1 Scanning electron microscopy (SEM) test

    SEM images were taken by scanning electron microscopy (SEM,Hitachi S-4800 scanning electron microscope).For SEM test,the copper surfaces with or without MPD modification were examined before and after immersed in 3.5% NaCl aqueous solution for 5 h (corrosion time).

    2.5.2 Raman spectroscopy

    The pretreated copper electrode was roughened by the oxidation-reduction cycle (ORC) method[21] to obtain the surface enhance Raman scatting (SERS) active surface.Generally,the electrode was cycled in 2 mol·L-1 H2SO4 solution from -0.55 to +0.45 V vs.SCE (initial from -0.55 V) at 20 mV·s-1 for 10 scans,then washed thoroughly with Milli-Q water.

    The Raman equipment was a confocal micro-Raman spectrometer (Super LabRam II system,Dilor,F(xiàn)rance).A multichannel air cooled 1024 pixel ×800 pixel charge-coupled device was employed as a detector.The objective was with 50× long-working-length,and the laser power for 632.8 nm He-Ne laser was 5 mW.The pinhole and slit were 1000 μm and 100 μm,respectively.Each spectrum was average of 3 scans,and each scan time was 8 s.All spectra were calibrated with silicon at 519 cm-1.

    3 Results and discussion

    3.1 EIS measurements

    EIS,as an effective and nondestructive testing technique,was used to investigate the inhibition efficiency of MPD at the copper surface without destroying the protection layer.Figure 2 and Figure 3 are the Nyquist,Bode and phase angle plots of the copper electrodes modified with different MPD of molar concentrations and with different assembly time after corroded in 3.5% NaCl aqueous solution,respectively.In Fig.2(b),a straight line at low frequency range in the Nyquist plot of bare copper indicated the Warburg impedance and was due to either the soluble copper species (CuCl-2,CuCl-4) or the copper oxides diffused from the copper surface to the bulk solution or the dissolved oxygen transported to the copper surface[22].A small semicircle at high frequencies was owing to the surface inhomogeneity.Compared with bare copper,MPD covered copper electrodes [Fig.2(a)] showed much larger semicircles in the Nyquist plots.With the increasing MPD molar concentration,the diameter of the capacitance loops increased sharply at the beginning and reached its maximum value when the MPD molar concentration was 5×10-4 mol·L-1.However,as the molar concentration of MPD was higher than 5×10-4 mol·L-1,the semicircle of impedance value became smaller.The results suggested that the corrosion inhibition performance of MPD layer on the copper surface was molar concentration-dependent.Increasing its molar concentration could cause more MPD molecules to be adsorbed on the copper surface.When the molar concentration reached 5×10-4 mol·L-1,MPD molecules adsorbed on the copper surface were dense and compact,preventing the corrosion media to attack the copper interface and thus providing good corrosion inhibition efficiency.Nevertheless,further raising the MPD molar concentration would result in the accumulation of MPD molecules on the copper surface,leading to rough surfaces or shedding of the protection,hence causing intensified corrosion.

    concentrations in 3.5% mass fraction of NaCl aqueous solution,(b) is the magnification Nyquist plot of bare copper

    EIS measurements of 5×10-4 mol·L-1 MPD modified copper with different assembly times were then conducted.In Fig.3(a),diameters of the semicircles in the Nyquist plots gave similar trend:increased and then decreased with the increasing assembly time.The optimized assembly time was 8 h.It indicated that MPD molecules adsorbed on the copper surface were not dense enough if the assembly time was less than 8 h,while if the assembly time was more than 8 h,the accumulation of MPD would occur on the copper surface,leading to defects which hindered the corrosion inhibition effect.

    According to the Bode plots [shown in Fig.2(c) and Fig.3(b)],the same trend could also be found:the logZ values rose and then fell with the increasing MPD molar concentration and assembly time.The peak value was obtained with a MPD molar concentration of 5×10-4 mol·L-1 and an assembly time of 8 h.

    In addition,as shown in Fig.2(d) and Fig.3(c),the phase angle values were up and then down with the increasing MPD molar concentration and assembly time,and the maximum phase angle was ca.80° referring to the optimal assembly condition.

    The EIS data were then fitted by Zsimpwin software for a more detailed analysis.The main criterion for best fitting model selection is least error and chi-square value (χ2).As shown in Fig.4,R(Q(RW)) is the equivalent circuit mode for the Nyquist plots of bare copper,while for MPD modified copper electrode,R(Q(RW))(QR) was more suitable.In which,Rs,Rf,and Rct represent the solution resistance,the resistance of MPD film formed on the copper surface,and the charge transfer resistance,respectively.W is the Warburg impedance.Q is the constant phase elements (CPE),where Qf,Qdl are the film capacitance and double layer capacitance,respectively [23].

    The corresponding impedance parameters for R(Q(RW)) and R(Q(RW))(QR) are listed in Table 1 and Table 2,respectively.And Q can be described as below[24]:

    Potentiodynamic polarization curves of the copper electrodes with and without MPD modifications recorded in 3.5% NaCl aqueous solution are shown in Fig.5 and Fig.6,respectively.And the related electrochemical parameters obtained from the extrapolation of the Tafel curves,such as cathodic and anodic Tafel slopes (βc and βa),corrosion potential (Ecorr),and corrosion current density (jcorr) are listed in Table 3 and Table 4,respectively.

    As presented in Table 3 and Table 4,both cathodic and anodic Tafel slopes shifted to much lower current density values after the MPD modifications,compared with bare electrode.Besides,cathodic potion shifted more,indicating that MPD layer acted as a cathode-dominated mixed inhibitor on the copper surface.Moreover,the jcorr value decreased and the Ecorr value increased with MPD assembly on the copper surface.Furthermore,the lowest jcorr value was obtained in optimized coating condition.

    3.3 SERS analysis

    SERS was used to investigate the molecular surface interaction due to its high sensitivity.Figure 7(a) and 7(b) displayed the normal Raman spectrum of MPD powder and SERS spectrum of MPD modified copper formed under optimized condition.For better understanding of the spectral information,the vibrational assignments which were calculated from density functional theory (DFT) calculations based on UB3LYP/LANL2DZ were summarized in Table 5.According to Figure 7(a) and Table 5,the strongest peak at 1639 cm-1 and 488 cm-1 belonged to C4-C5 rocking vibration and N12-H13 stretching vibration,respectively.Peak at 1101 cm-1 was assigned to C4-C5 in-plane bending,while band at 886 cm-1 was S7-H8 rocking vibration.Based on the surface selection rule[26],SERS signal would be enhanced when the vibration mode was perpendicular to or getting close to the metal surface.Otherwise,if the vibration was parallel or away from the surface,SERS signal would be weakened.Therefore,it could be concluded that the MPD molecule was physisorbed on the copper surface via N9-H10 and S7-H8.Besides,with high MPD molar concentration,the vertical adsorbed MPD molecules would form π-π interaction between heterocyclic rings in pyrimidine molecules.Such π-π interaction would ensure that the coating formed on the copper surface would be dense and compact,providing excellent corrosion inhibition ability.The suggested adsorption fashion for MPD on the copper surface was displayed in Figure 8.

    3.4 Adsorption isotherm

    To further verify the MPD adsorption fashion on the copper surface,adsorption isotherm plot along with the standard Gibbs free energy was determined.θ (the degree of surface coverage) at different MPD molar concentrations in 3.5% NaCl solutions was obtained from EIS measurement according to:

    Assuming that the adsorption of MPD molecule on the copper surface obeys Langmuir adsorption isothermal,then the correlation between θ and c can be? represented as:

    where c is MPD molar concentration,and Kads is the equilibrium constant [27].The plot of c/θ against c gave a straight line (y=1.025x+0.007) as shown in Figure 9.Both the linear correlation coefficient (R2=0.9993) and the slope (value is 1.025) are close to 1,indicating the adsorption of MPD molecules on the copper surface in NaCl solution obeys the Langmuir adsorption isotherm.

    Generally,if ΔG0ads value is above -20 kJ·mol-1,adsorption behavior is assumed to be physisorption,dominated via electrostatic interactions between inhibitor molecules and the charged metal surface,whilst if ΔG0ads value is lower than 40 kJ·mol-1,chemisorption controlled where coordination bond is formed based on charge sharing or transfer from organic molecules to the metal surface[29].The calculated ΔG0adsvalue was -22.25 kJ·mol-1,suggesting that the adsorption mechanism of MPD molecule on the copper surface is mainly physisorption.

    SEM images of copper electrodes without and with optimized MPD modifications were observed before and after 5 h (corrosion time) immersion in 3.5% NaCl solution.Figure 10(a) and 10(b) exhibited the surface morphologies of the bare copper before and after immersion in NaCl solution,respectively,while Fig.10(c) and 10(d) demonstrated the MPD modified copper surface before and after immersion in NaCl solution,respectively.Obviously,as shown in Fig.10(b),seriously corrosion occurred on the bare copper surface after immersion in NaCl solution for 5 h.In contrast,in the presence of MPD [Fig.10(d)],the copper surface corroded barely.

    4 Conclusion

    In this work,MPD was prepared for the corrosion inhibition of copper in 3.5% mass fraction of NaCl aqueous solution.Under optimal assembly condition,5×10-4 mol·L-1 MPD assembly for 8 h,the MPD modified copper surface exhibited the greatest inhibition efficiency,98.1%.SERS spectrum indicated that MPD molecule was adsorbed on copper surface with N9-H10 and S7-H8.

    Acknowledgement

    This work is supported by International Joint Laboratory on Resource Chemistry (IJLRC),Shanghai Key Laboratory of Rare Earth Functional Materials and Shanghai Municipal Education Committee Key Laboratory of Molecular Imaging Probes and Sensors.

    References:

    [1] FAN Y H,CHEN Z J,LIANG J,et al.Preparation of superhydrophobic films on copper substrate for corrosion protection [J].Surface and Coatings Technology,2014,244:1-8.

    [2] YANG Z,LIU X,TIAN Y.Fabrication of super-hydrophobic nickel film on copper substrate with improved corrosion inhibition by electrodeposition process [J].Colloids and Surfaces A,2019,560:205-212.

    [3] HERNNDEZ R DEL P B,AOKI I V,TRIBOLLET B,et al.Electrochemical impedance spectroscopy investigation of the electrochemical behaviour of copper coated with artificial patina layers and submitted to wet and dry cycles [J].Electrochimica Acta,2011,56(7):2801-2814.

    [4] PAREEK S,JAIN D,HUSSAIN S,et al.A new insight into corrosion inhibition mechanism of copper in aerated 3.5 wt.% NaCl solution by eco-friendly imidazopyrimidine dye:experimental and theoretical approach [J].Chemical Engineering Journal,2019,358:725-742.

    [5] ADELOJU S,HUGHES H.The corrosion of copper pipes in high chloride-low carbonate mains water [J].Corrosion Science,1986,26(10):851-870.

    [6] FATEH A,ALIOFKHAZRAEI M,REZVANIAN A R.Review of corrosive environments for copper and its corrosion inhibitors [J/OL].Arabian Journal of Chemistry,2017 [2019-01-01].http://dx.doi.org/10.1016/j.arabjc.2017.05.021.

    [7] ATTIA A A,ELMELEGY E M,EL-BATOUTI M,et al.Anodic corrosion inhibition in presence of protic solvents [J].Asian Journal of Chemistry,2016,28(2):267-272.

    [8] CHEN W,HONG S,LUO H Q,et al.Inhibition effect of 2,4,6-trimercapto-1,3,5-triazine self-assembled monolayers on copper corrosion in NaCl solution [J].Journal of Materials Engineering and Performance,2014,23 (2):527-537.

    [9] ZHOU Y,XU S,GUO L,et al.Evaluating two new Schiff bases synthesized on the inhibition of corrosion of copper in NaCl solutions [J].RSC Advances,2015,5:14804-14813.

    [10] YADAV M,BEHERA D,KUMAR S,et al.Experimental and quantum chemical studies on the corrosion inhibition performance ofbenzimidazole derivatives for mild steel in HCl [J].Industrial & Engineering Chemistry Research,2013,52(19):6318-6328.

    [11] WEI N,JIANG Y,LIU Z,et al.4-Phenylpyrimidine monolayer protection of a copper surface from salt corrosion [J].RSC Advances,2018,8:7340-7349.

    [12] WANG Z L,ZHANG J,WANG Z M,et al.Emulsification reducing the corrosion risk of mild steel in oil-brine mixtures [J].Corrosion Science,2014,86:310-317.

    [13] KHAN P F,SHANTHI V,BABU R K,et al.Effect of benzotriazole on corrosion inhibition of copper under flow conditions [J].Journal of Environmental Chemical Engineering,2015,3 (1):10-19.

    [14] FOUDA A S,WAHED H A A.Corrosion inhibition of copper in HNO3 solution using thiophene and its derivatives [J].Arabian Journal of Chemistry,2016,9(Suppl.1):S91-S99.

    [15] ABDALLAH M,ZAAFARANY I,AL-KARANEE S O,et al.Antihypertensive drugs as an inhibitors for corrosion of aluminum and aluminum silicon alloys in aqueous solutions [J].Arabian Journal of Chemistry,2012,5:225-234.

    [16] ALDANA-GONZALEZ J,ESPINOZA-VAZQUEZ A,ROMERO-ROMO M,et al.Electrochemical evaluation of cephalothin as corrosion inhibitor for API 5L X52 steel immersed in an acid medium [J/OL].Arabian Journal of Chemistry,2015[2019-01-01].https://doi.org/10.1016/j.arabjc.2015.08.033.

    [17] TADROS A B,ABD EL NABEY B A.Marine anti-corrosion paints based on thiouracil compounds [J].Anti-Corrosion Methods and Materials,2000,47(4):211-214.

    [18] ISSA R M,AWAD M K,ATLAM F M.Quantum chemical studies on the inhibition of corrosion of copper surface by substituted uracils [J].Applied Surface Science,2008,255:2433-2441.

    [19] AL-ANDIS N,KHAMIS E,AL-MAYOUF A.Kinetics of steel dissolution in the presence of some thiouracil derivatives [J].Corrosion Prevention and Control,1995,42:13-20.

    [20] EL-TAIB HEAKAL F,F(xiàn)OUDA A S,ZAHRAN S S.Environmentally safe protection of carbon steel corrosion in sulfuric acid by thiouracil compounds [J].International Journal of Electrochemical Science,2015,10(2):1595-1615.

    [21] PAN Y C,WEN Y,XUE L Y,et al.Adsorption behavior of methimazole monolayers on a copper surface and its corrosion inhibition [J].The Journal of Physical Chemistry C,2012,116(5):3532-3538.

    [22] AMIN M A,KHALED K F.Copper corrosion inhibition in O2-saturated H2SO4 solutions [J].Corrosion Science,2010,52:1194-1204.

    [23] WINIARSKI J,CIES'LIKOWSKA B,TYLUS W,et al.Corrosion of nanocrystalline nickel coatings electrodeposited from choline chloride:ethylene glycol deep eutectic solvent exposed in 0.05 M NaCl solution [J].Applied Surface Science,2019,470:331-339.

    [24] LI X,DENG S,LIN T,et al.Inhibition action of triazolyl blue tetrazolium bromide on cold rolled steel corrosion in three chlorinated acetic acids [J].Journal of Molecular Liquids,2019,274:77-89.

    [25] MOURYA P,BANERJEE S,SINGH M M.Corrosion inhibition of mild steel in acidic solution by Tageteserecta (Marigold flower) extract as a green inhibitor [J].Corrosion Science,2014,85:352-363.

    [26] MCFARLAND A D,YOUNG M A,DIERINGER J A,et al.Wavelength-scanned surface-enhanced Raman excitation spectroscopy [J].The Journal of Physical Chemistry B,2005,109(22):11279-11285.

    [27] KRISHNEGOWDA P M,VENKATESHA V T,KRISHNEGOWDA P K M,et al.Acalyphatorta leaf extract as green corrosion inhibitor for mild steel in hydrochloric acid solution [J].Industrial & Engineering Chemistry Research,2013,52:722-728.

    [28] BAHRAMI M J,HOSSEINI S M A,PILVAR P.Experimental and theoretical investigation of organic compounds as inhibitors for mild steel corrosion in sulfuric acid medium [J].Corrosion Science,2013,52:2793-2803.

    [29] HEGAZY M A,BADAWI A M,ABD EL REHIM S S,et al.Corrosion inhibition of carbon steel using novel N-(2-(2-mercaptoacetoxy)ethyl)-N,N-dimethyldodecan-1-aminium bromide during acid pickling [J].Corrosion Science,2013,69:110-122.

    (責(zé)任編輯:郁 慧)

    猜你喜歡
    極化曲線
    含氮不銹鋼在不同溫度下的電化學(xué)腐蝕行為研究
    路譜激勵(lì)對(duì)于燃料電池極化曲線特征參數(shù)影響研究
    物理化學(xué)中極化曲線的測(cè)定實(shí)驗(yàn)改革
    電化學(xué)實(shí)驗(yàn)教學(xué)中極化曲線的測(cè)量與應(yīng)用
    給水球墨鑄鐵管腐蝕特性及腐蝕對(duì)水質(zhì)的影響
    油酸咪唑啉季銨鹽的合成及緩蝕性能的研究
    電化學(xué)合成聚苯胺涂層防護(hù)性能的研究
    鎂水泥混凝土中鋼筋的電化學(xué)腐蝕研究
    光亮劑對(duì)酸性中磷化學(xué)鍍鎳層性能的影響
    緩蝕劑在鎂合金化學(xué)機(jī)械拋光過(guò)程中的作用
    国产视频内射| 久久久国产一区二区| www.色视频.com| 亚洲综合色惰| 国产黄色免费在线视频| 日韩中字成人| 国国产精品蜜臀av免费| 日本欧美国产在线视频| 青春草国产在线视频| 国产 一区 欧美 日韩| 久久国产精品男人的天堂亚洲 | 黄片无遮挡物在线观看| 狂野欧美白嫩少妇大欣赏| 色视频在线一区二区三区| 国产精品人妻久久久影院| 91久久精品电影网| 国产av一区二区精品久久 | 大片电影免费在线观看免费| 只有这里有精品99| av播播在线观看一区| 成年美女黄网站色视频大全免费 | 亚洲精品,欧美精品| 亚洲无线观看免费| 久久久久性生活片| 免费观看的影片在线观看| 日本猛色少妇xxxxx猛交久久| 精华霜和精华液先用哪个| 在线天堂最新版资源| 日本-黄色视频高清免费观看| 伊人久久精品亚洲午夜| 久热这里只有精品99| 99久久人妻综合| 中文字幕人妻熟人妻熟丝袜美| 性色av一级| 熟女人妻精品中文字幕| av在线播放精品| 一级毛片电影观看| 97精品久久久久久久久久精品| 老女人水多毛片| 日韩一区二区视频免费看| 国产成人精品福利久久| 国产男女超爽视频在线观看| 成年免费大片在线观看| 亚洲国产日韩一区二区| av线在线观看网站| 亚洲国产色片| 国产高清有码在线观看视频| 一二三四中文在线观看免费高清| 亚洲精品国产色婷婷电影| 一本—道久久a久久精品蜜桃钙片| 久久国产乱子免费精品| 亚洲精品aⅴ在线观看| 亚洲久久久国产精品| 日韩,欧美,国产一区二区三区| 中文字幕久久专区| 尤物成人国产欧美一区二区三区| 久热久热在线精品观看| 中文字幕亚洲精品专区| 免费看光身美女| 精品熟女少妇av免费看| 亚洲精品久久久久久婷婷小说| 国产国拍精品亚洲av在线观看| 青青草视频在线视频观看| 七月丁香在线播放| a级毛片免费高清观看在线播放| 99久久精品国产国产毛片| 99热6这里只有精品| 中文字幕制服av| 在线精品无人区一区二区三 | 在线观看三级黄色| 日本爱情动作片www.在线观看| 久久午夜福利片| 亚洲欧美一区二区三区国产| 亚洲人成网站在线播| 一个人看视频在线观看www免费| 熟女电影av网| 街头女战士在线观看网站| 激情五月婷婷亚洲| 亚洲国产最新在线播放| 涩涩av久久男人的天堂| 久久鲁丝午夜福利片| 国产午夜精品久久久久久一区二区三区| 色婷婷av一区二区三区视频| 天天躁日日操中文字幕| 一级av片app| 中文资源天堂在线| 亚洲精品乱码久久久久久按摩| 国国产精品蜜臀av免费| 欧美成人一区二区免费高清观看| 日韩视频在线欧美| 五月开心婷婷网| 美女主播在线视频| 天堂8中文在线网| 亚洲欧美一区二区三区国产| 亚洲三级黄色毛片| 午夜福利在线在线| 亚洲欧洲国产日韩| 国产精品嫩草影院av在线观看| 国产乱人偷精品视频| 国产精品不卡视频一区二区| 午夜福利在线在线| 男女国产视频网站| 天堂俺去俺来也www色官网| av黄色大香蕉| 国产成人精品久久久久久| 在线观看免费日韩欧美大片 | 国产又色又爽无遮挡免| 亚洲av二区三区四区| 国产高清不卡午夜福利| 我的女老师完整版在线观看| 国产免费一区二区三区四区乱码| 亚洲精品第二区| 亚洲国产精品999| 精品国产露脸久久av麻豆| 国产精品秋霞免费鲁丝片| 免费大片18禁| 亚洲av免费高清在线观看| 国产精品麻豆人妻色哟哟久久| 久久久久久久久久成人| 欧美三级亚洲精品| 国产男女内射视频| 最近手机中文字幕大全| 久久久精品免费免费高清| 欧美区成人在线视频| 亚洲在久久综合| 女性生殖器流出的白浆| 亚洲美女黄色视频免费看| 成人18禁高潮啪啪吃奶动态图 | 久久久午夜欧美精品| 成人国产av品久久久| 中国三级夫妇交换| 高清不卡的av网站| 成人美女网站在线观看视频| 黑丝袜美女国产一区| 91久久精品电影网| 国产精品女同一区二区软件| 色视频www国产| 国产精品99久久久久久久久| 国产精品偷伦视频观看了| 国产精品一及| 男男h啪啪无遮挡| 99热6这里只有精品| 麻豆成人av视频| 亚洲av日韩在线播放| 欧美国产精品一级二级三级 | 国内精品宾馆在线| 秋霞伦理黄片| 女人久久www免费人成看片| 久久精品人妻少妇| 欧美区成人在线视频| 国产精品99久久久久久久久| 成人一区二区视频在线观看| 熟妇人妻不卡中文字幕| 国产色爽女视频免费观看| 国产一区有黄有色的免费视频| 在线观看人妻少妇| 大又大粗又爽又黄少妇毛片口| 熟女av电影| 亚洲国产精品999| 伦精品一区二区三区| 人人妻人人爽人人添夜夜欢视频 | 大香蕉久久网| 婷婷色综合大香蕉| 国产免费一区二区三区四区乱码| 久久久欧美国产精品| 91在线精品国自产拍蜜月| 亚洲精品456在线播放app| 少妇高潮的动态图| av又黄又爽大尺度在线免费看| 欧美zozozo另类| 久久久色成人| av又黄又爽大尺度在线免费看| 黄色一级大片看看| 国产 一区 欧美 日韩| 亚洲欧美中文字幕日韩二区| 少妇人妻精品综合一区二区| 九九爱精品视频在线观看| 久久久久久人妻| 国产精品国产三级国产专区5o| 国产精品嫩草影院av在线观看| 秋霞在线观看毛片| 国产精品伦人一区二区| 蜜桃久久精品国产亚洲av| 又大又黄又爽视频免费| 精品国产一区二区三区久久久樱花 | 久久久久视频综合| 自拍欧美九色日韩亚洲蝌蚪91 | 久久久久久九九精品二区国产| 高清黄色对白视频在线免费看 | 最近最新中文字幕大全电影3| 国产成人freesex在线| 三级经典国产精品| 精品熟女少妇av免费看| 亚洲av成人精品一二三区| 久久 成人 亚洲| 国产无遮挡羞羞视频在线观看| 亚洲色图av天堂| 亚洲天堂av无毛| 色哟哟·www| 青春草国产在线视频| 国产精品一区二区三区四区免费观看| 国产免费一级a男人的天堂| av免费观看日本| 一二三四中文在线观看免费高清| 亚洲成人一二三区av| 另类亚洲欧美激情| 国产在线免费精品| videossex国产| 九色成人免费人妻av| 亚洲精品国产色婷婷电影| 激情 狠狠 欧美| 嫩草影院新地址| 精品少妇久久久久久888优播| 久久久久久久精品精品| 久久久久网色| 国产中年淑女户外野战色| 妹子高潮喷水视频| 亚洲人成网站在线播| 精品少妇黑人巨大在线播放| 久久久久久久久久人人人人人人| 交换朋友夫妻互换小说| freevideosex欧美| 大片电影免费在线观看免费| 91在线精品国自产拍蜜月| 如何舔出高潮| av在线蜜桃| xxx大片免费视频| 婷婷色av中文字幕| 少妇高潮的动态图| 久久久久人妻精品一区果冻| 国产精品蜜桃在线观看| 欧美精品一区二区大全| 一级二级三级毛片免费看| 极品少妇高潮喷水抽搐| 亚洲精品aⅴ在线观看| 欧美少妇被猛烈插入视频| 久久人人爽人人片av| av福利片在线观看| 国产欧美另类精品又又久久亚洲欧美| 晚上一个人看的免费电影| 九草在线视频观看| 国产精品三级大全| 免费看日本二区| 夜夜看夜夜爽夜夜摸| 爱豆传媒免费全集在线观看| 国产视频内射| 国产黄片美女视频| 成人特级av手机在线观看| 韩国av在线不卡| 欧美+日韩+精品| 久久人妻熟女aⅴ| 中文字幕人妻熟人妻熟丝袜美| 亚洲精品国产av成人精品| 亚洲国产最新在线播放| 亚洲aⅴ乱码一区二区在线播放| 欧美xxxx性猛交bbbb| 成人二区视频| 免费黄频网站在线观看国产| 日韩一区二区视频免费看| 国产一区二区三区综合在线观看 | av一本久久久久| 久久久色成人| 国产一级毛片在线| 成人午夜精彩视频在线观看| 制服丝袜香蕉在线| 少妇人妻一区二区三区视频| 一区二区av电影网| 我的女老师完整版在线观看| 久久精品久久精品一区二区三区| 亚洲真实伦在线观看| 少妇被粗大猛烈的视频| 亚洲美女视频黄频| xxx大片免费视频| 久久久久网色| 日本欧美视频一区| 亚洲精品aⅴ在线观看| 久久久成人免费电影| 久久精品久久精品一区二区三区| 国产大屁股一区二区在线视频| 内射极品少妇av片p| 久久精品人妻少妇| 日本wwww免费看| 国产高清国产精品国产三级 | 99热全是精品| 国产亚洲一区二区精品| 又爽又黄a免费视频| 乱码一卡2卡4卡精品| 激情五月婷婷亚洲| 噜噜噜噜噜久久久久久91| 久久久精品94久久精品| 亚洲人与动物交配视频| 天堂俺去俺来也www色官网| 人人妻人人看人人澡| 午夜福利在线在线| 男女国产视频网站| 一级毛片我不卡| 男人和女人高潮做爰伦理| 女性被躁到高潮视频| 人妻少妇偷人精品九色| 亚洲国产成人一精品久久久| 亚洲av不卡在线观看| 欧美3d第一页| 国产淫语在线视频| 国产黄色免费在线视频| 99热网站在线观看| 国产精品女同一区二区软件| 女的被弄到高潮叫床怎么办| 国产又色又爽无遮挡免| 在线看a的网站| 久久99蜜桃精品久久| 自拍欧美九色日韩亚洲蝌蚪91 | 我的女老师完整版在线观看| 麻豆国产97在线/欧美| 99久国产av精品国产电影| 国产精品蜜桃在线观看| kizo精华| 中文字幕人妻熟人妻熟丝袜美| 18+在线观看网站| 1000部很黄的大片| 一本色道久久久久久精品综合| 久久精品夜色国产| 午夜视频国产福利| 汤姆久久久久久久影院中文字幕| 黑人猛操日本美女一级片| 国产亚洲精品久久久com| 下体分泌物呈黄色| 伊人久久精品亚洲午夜| 国产精品一区二区在线观看99| 色综合色国产| 欧美日韩精品成人综合77777| 成人国产av品久久久| 天堂8中文在线网| 午夜激情福利司机影院| 成人午夜精彩视频在线观看| 日韩欧美 国产精品| 18禁裸乳无遮挡动漫免费视频| 国产男人的电影天堂91| 欧美成人精品欧美一级黄| 少妇的逼水好多| 成人免费观看视频高清| 九色成人免费人妻av| 国产老妇伦熟女老妇高清| 少妇的逼水好多| 色婷婷av一区二区三区视频| 国产免费一区二区三区四区乱码| 乱码一卡2卡4卡精品| 亚洲激情五月婷婷啪啪| 日韩强制内射视频| 久久久久精品性色| 看免费成人av毛片| 日韩av在线免费看完整版不卡| 国产男女内射视频| 我要看黄色一级片免费的| 国产精品人妻久久久久久| 大话2 男鬼变身卡| av免费观看日本| 18禁在线播放成人免费| 亚洲人与动物交配视频| 日韩在线高清观看一区二区三区| 在线观看av片永久免费下载| 免费av中文字幕在线| 亚洲四区av| tube8黄色片| 亚洲成人av在线免费| 久久久精品94久久精品| av不卡在线播放| 高清在线视频一区二区三区| 亚洲av二区三区四区| 有码 亚洲区| 国产淫片久久久久久久久| 一级爰片在线观看| 亚洲精品乱码久久久久久按摩| 一级毛片 在线播放| 大片免费播放器 马上看| 一级爰片在线观看| 国产av码专区亚洲av| 亚洲怡红院男人天堂| 丰满乱子伦码专区| 超碰97精品在线观看| 亚洲人成网站在线观看播放| 精品国产露脸久久av麻豆| 国产亚洲午夜精品一区二区久久| 五月天丁香电影| 美女中出高潮动态图| 国产一区二区三区av在线| 亚洲一级一片aⅴ在线观看| 国产av国产精品国产| 午夜精品国产一区二区电影| 99久久精品一区二区三区| 欧美精品一区二区大全| 麻豆国产97在线/欧美| 久久精品国产鲁丝片午夜精品| 身体一侧抽搐| 日韩成人av中文字幕在线观看| 亚洲人与动物交配视频| 久久久久久久久久久丰满| av福利片在线观看| 免费大片18禁| 免费黄色在线免费观看| 欧美成人午夜免费资源| 亚洲av国产av综合av卡| 日韩三级伦理在线观看| 少妇猛男粗大的猛烈进出视频| 九九爱精品视频在线观看| 亚洲激情五月婷婷啪啪| 亚洲av福利一区| 久久久色成人| 色5月婷婷丁香| 黄片无遮挡物在线观看| 欧美xxxx黑人xx丫x性爽| av视频免费观看在线观看| 久久久久久九九精品二区国产| 久久青草综合色| 国产淫语在线视频| 日韩人妻高清精品专区| 丰满少妇做爰视频| a级一级毛片免费在线观看| 中文字幕av成人在线电影| 免费观看无遮挡的男女| 老熟女久久久| 一区二区三区精品91| 亚洲欧美日韩卡通动漫| 国产成人精品一,二区| 全区人妻精品视频| 久久人人爽人人爽人人片va| 国产片特级美女逼逼视频| 秋霞伦理黄片| 久久精品久久久久久噜噜老黄| 久久国产乱子免费精品| 国产午夜精品久久久久久一区二区三区| 亚洲精品久久午夜乱码| 亚洲国产成人一精品久久久| av网站免费在线观看视频| 九色成人免费人妻av| 99热全是精品| 亚洲av成人精品一区久久| 在线观看av片永久免费下载| 欧美少妇被猛烈插入视频| 青春草国产在线视频| 国产男女超爽视频在线观看| 日本vs欧美在线观看视频 | 亚洲av欧美aⅴ国产| 一边亲一边摸免费视频| 日韩 亚洲 欧美在线| 亚洲无线观看免费| 国产一区二区在线观看日韩| 亚洲色图综合在线观看| 亚洲三级黄色毛片| 99视频精品全部免费 在线| 一本色道久久久久久精品综合| 亚洲精品日本国产第一区| 观看免费一级毛片| 成人毛片a级毛片在线播放| 久久久久久久精品精品| 国产成人午夜福利电影在线观看| 少妇人妻一区二区三区视频| 欧美精品亚洲一区二区| 日日摸夜夜添夜夜添av毛片| 日韩一区二区视频免费看| 国产精品久久久久久久电影| 黑人猛操日本美女一级片| 中文在线观看免费www的网站| 久久热精品热| 啦啦啦中文免费视频观看日本| 国产精品不卡视频一区二区| 男女下面进入的视频免费午夜| 一区二区三区免费毛片| 亚洲久久久国产精品| 久久久久久伊人网av| 在线免费十八禁| 免费看日本二区| 亚洲欧美日韩东京热| 精品国产三级普通话版| 在现免费观看毛片| 极品少妇高潮喷水抽搐| 人体艺术视频欧美日本| 噜噜噜噜噜久久久久久91| 乱系列少妇在线播放| 美女中出高潮动态图| 婷婷色麻豆天堂久久| 99久久精品国产国产毛片| 亚洲精品一区蜜桃| 十八禁网站网址无遮挡 | 亚洲精品日韩av片在线观看| 一本—道久久a久久精品蜜桃钙片| 日韩制服骚丝袜av| 久久ye,这里只有精品| 国模一区二区三区四区视频| 干丝袜人妻中文字幕| 黄色欧美视频在线观看| 女性生殖器流出的白浆| 我的女老师完整版在线观看| 最近中文字幕高清免费大全6| 在线免费十八禁| 黄色欧美视频在线观看| 亚洲中文av在线| 精华霜和精华液先用哪个| 在线观看美女被高潮喷水网站| 亚洲综合精品二区| 精品99又大又爽又粗少妇毛片| 亚洲国产高清在线一区二区三| 美女xxoo啪啪120秒动态图| 99热这里只有精品一区| 黄色一级大片看看| 99热网站在线观看| 99热这里只有精品一区| 久久女婷五月综合色啪小说| 黑人高潮一二区| 亚洲人成网站在线播| 日韩人妻高清精品专区| 天天躁日日操中文字幕| 成人免费观看视频高清| 中文精品一卡2卡3卡4更新| 建设人人有责人人尽责人人享有的 | 成人毛片a级毛片在线播放| 日本爱情动作片www.在线观看| 蜜桃久久精品国产亚洲av| 男女啪啪激烈高潮av片| 亚洲国产色片| 99re6热这里在线精品视频| 一本—道久久a久久精品蜜桃钙片| 欧美成人午夜免费资源| 久久精品人妻少妇| 日韩欧美精品免费久久| 国产男女超爽视频在线观看| 国产精品爽爽va在线观看网站| 亚洲人与动物交配视频| av网站免费在线观看视频| 天天躁日日操中文字幕| 国产在线男女| 国产精品欧美亚洲77777| 久久久久久久国产电影| 欧美精品一区二区大全| 男人爽女人下面视频在线观看| 国产在线视频一区二区| 亚洲精品国产成人久久av| 国产成人精品福利久久| 嫩草影院入口| av网站免费在线观看视频| 国产美女午夜福利| 亚洲欧美日韩无卡精品| 欧美成人精品欧美一级黄| 日韩中文字幕视频在线看片 | 亚洲电影在线观看av| 日韩一区二区三区影片| 日韩一本色道免费dvd| 狂野欧美激情性bbbbbb| 久久99精品国语久久久| a级毛色黄片| 日日啪夜夜撸| 国产成人a∨麻豆精品| 国产免费福利视频在线观看| 六月丁香七月| 插逼视频在线观看| 中文字幕精品免费在线观看视频 | 九色成人免费人妻av| 中文字幕久久专区| 精品国产乱码久久久久久小说| 日韩 亚洲 欧美在线| 欧美精品一区二区大全| 午夜免费鲁丝| 免费黄频网站在线观看国产| av网站免费在线观看视频| 水蜜桃什么品种好| 久久久久国产网址| 亚洲av福利一区| 伊人久久国产一区二区| 高清午夜精品一区二区三区| 在线观看国产h片| 九九爱精品视频在线观看| 国产女主播在线喷水免费视频网站| 精品少妇久久久久久888优播| 美女视频免费永久观看网站| 我的老师免费观看完整版| 丰满乱子伦码专区| 特大巨黑吊av在线直播| 国产精品一区二区三区四区免费观看| 青春草亚洲视频在线观看| 啦啦啦啦在线视频资源| 免费高清在线观看视频在线观看| 欧美成人一区二区免费高清观看| 久久久久久久久久人人人人人人| 日本av手机在线免费观看| 十八禁网站网址无遮挡 | 国产伦精品一区二区三区四那| 免费播放大片免费观看视频在线观看| 日韩一区二区三区影片| 亚洲真实伦在线观看| 久久久久精品性色| 男人添女人高潮全过程视频| 一级a做视频免费观看| 日日啪夜夜爽| 深夜a级毛片| 久久久久久人妻| 一区二区三区精品91| 春色校园在线视频观看| 欧美人与善性xxx| 久久久精品94久久精品| 欧美变态另类bdsm刘玥| 亚洲怡红院男人天堂| 干丝袜人妻中文字幕| 欧美bdsm另类| a级毛色黄片| 日本免费在线观看一区| 99久国产av精品国产电影| 看免费成人av毛片| 免费大片18禁| 看免费成人av毛片| 噜噜噜噜噜久久久久久91| 国产精品麻豆人妻色哟哟久久| 2018国产大陆天天弄谢| 新久久久久国产一级毛片| 精华霜和精华液先用哪个| 亚洲人与动物交配视频| 国产女主播在线喷水免费视频网站|