• <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 ?

    Graphene Based Electrochemical Sensor for the Detection of Volatile Organic Compounds

    2015-06-02 23:38:32YixinZhangKimKTL
    學(xué)周刊·下旬刊 2014年12期
    關(guān)鍵詞:彩霞責(zé)編

    Yixin+Zhang+Kim+KT+Lau

    Abstract:Many household consumables contain volatile organic compounds (VOCs) as the active ingredient. Long term exposure to VOCs could cause various health problems, especially to the respiratory system. Graphene has attracted a lot of attention recently for its potential to be used as sensing material for VOCs. In this project we have constructed graphene/PVA composite based gas sensors for VOC detection. It was perceived that the polymer could introduce better selectivity to the sensor. Results suggest that the proposed sensor is highly sensitive to low molecular weight VOCs and that the manner in which the sensor respond to the vapour depends on the polarity or hydrophobicity of the vapour.

    Keywords:gas sensor; volatile organic compounds (VOCs); grapheme; electrochemical sensors

    Ⅰ.Introduction

    1. Background of VOC

    Volatile organic compounds (VOCs) are low boiling organic solvents and solids with high vapor pressure at room temperature. They are major component in household consumables such as cleaners, paints, glues, building material etc. (Figure 1) and hence exposure to VOCs is unavoidable. Acute exposure to high concentration and chronic exposure to low concentrations of VOCs pose different health risks. Acute poisoning causes severe headache, vomiting, coughing, irritation and damage to respiratory system and cornea of the eyes. In serious cases, it can result in fatality. Chronic exposure to low concentration of VOCs could cause asthma, skin disease, migraine, drowsiness, general fatigue, and in some cases, cancer.Typical examples of VOCs are ethanol, propanol, formaldehyde and chloroform. Air pollutants in home environment constitute mainly these organic solvents, especially in China, the strong economic drives building industries to flourish; thousands of new estates are built every year with millions of people now living in environment with slow release of toxic VOCs. One commonly encountered is formaldehyde. The elderly and the young are the most affected populations because of their weakened or under developed immune system. To protect such population and the healthy alike, gas sensors that are simple, small, inexpensive and easy to use are in high demand. This project is to explore a new carbon material, graphene, as a potential sensing material in the development of sensor that fits the above criteria.

    2. Graphene as a Sensing Material

    Graphene is a form of carbon that can be easily synthesized. The physical and chemical properties of this new material are totally different from graphite. All the atoms in graphene are strictly arranged into a two-dimensional (2D) honeycomb lattice, hence graphene is highly flexible and is an excellent conductor. Super electron mobility and transport properties boost graphene as a sensing material. It has very good mechanical strength, very large surface area, and is chemically and physically stable (Figure 2).

    3. Principle of Gas Sensing

    Absorption of VOC molecules causes the graphene film to undergo a volume change to results in a change in resistance (ΔR), where ΔR = Rfinal – Rinitial.

    The simplified sensing mechanisms can be illustrated in Figure 3:

    When the graphene film is exposed to a gas or vapour, the gas molecule will diffuse into and out of the film, and at equilibrium, the number of gas molecules absorb into the film is equal to the gas molecule leaving the film[14]. The film resistance also changes from an initial value Rinitial to a final value Rfinal which is related to the amount of gas molecules absorbed.

    The equilibrium constant K for the gas-solid interactions can be defined as:

    K = Cg/Cs

    where Cg is the gas concentration in gas phase and CS the gas concentration in the solid film.

    Since K is specific to a gas-sorbent combination, the sensitivity and selectivity of a given sorbent material can be established.

    4. Objective

    Graphene is an excellent absorbent for many vapours, hence a sensor based on graphene alone may offer good sensitivity but the selectivity will generally be poor[15]. It is anticipated that the addition of polymer materials with different chemical functionalities would improve the selectivity performance of graphene based sensor. In this short summer student project, we explore the use of Graphene/PVA composite sensor for measuring VOCs. The aims of this project is to investigate how the Graphene/PVA based sensor would response to VOC standards and to evaluate the optimal ratio of Graphene/PVA to give fast, sensitive, stable and repeatable sensor response.

    Ⅱ. Experimental Procedure

    1. Sensor Construction

    Graphene Oxide/polyvinyl alcohol (GO/PVA) composite film was first formed on the electrode from casting a solution of GO/PVA mixture of a certain ratio on the electrode, followed by drying in the oven. Then excess hydrazine hydrate was added onto the surface of the film for GO reduction. The reaction was allowed to proceed at 90°C for 1 hour to afford a solid thin film of PVA/graphene composite. (Figure 4) The procedure was repeated to form multiple layers of GO/PVA composite film.

    2. Sensor Calibration

    Test VOC sample 2 mL was put into a 20 mL glass vial with a screw cap. The sensor was fixed on the modified cap and then sealed into the sample vial containing the test VOC sample. Laboratory air was used as the reference and sensor resistances in air and inside the sample vial were recorded in real time by an HP Multimeter using a Microsoft ExcelTM compatible HP software. The list of sample tested includes methanol, ethanol, 1-propanol and isopropanol.

    Ⅲ. Results and Discussions

    1. Sensor performance

    Here we present the performance of an optimized sensor fabricated from 10% (w/w) Graphene Oxide in PVA. The sensor was fabricated with 2 layers of the composite film and had an initial sensor resistance of 88.2 k.

    The choice of PVA as the polymer matrix for the fabrication of the gas sensor is to introduce selectivity to organic vapours that are able to form hydrogen bonding with the hydroxyl groups of the polymer. Alcohols therefore would be the expected targets for this investigation. Hence a group of alcohols methanol, ethanol, propanol and isopropanol were used to calibrate the proposed sensor.

    In order to meaningfully compare their responses, all sensor response are normalized with the actual vapour concentration in the sample vial, and also with baseline corrected.

    The actual vapor concentration for each sample VOC was calculated according to the ideal gas equation: P V = n R T (1) and

    Antoine equation: log P = A - B / (t +C) (2)

    (where P is vapor pressure, V is volume, n is the number of mole, T is temperature , R is the gas constant; A, B, C are constants).

    A typical real time sensor response profile is shown in Figure 5 to demonstrate the sensor behavior on exposure to methanol vapour. On exposure to methanol, the sensor resistance increased rapidly and reached equilibrium in approximately 20 s. A normalized resistance change of ca.19 K?.m3/g was recorded which corresponded to ca. 10% change in resistance. However, a baseline drift was observed due to a ‘memory effect which is quite typical of polymer based sensors.

    Shown in Figure 6 are the sensor response profiles of the four alcohol vapours, methanol, ethanol, propanol and isopropanol. Interestingly, very different response characteristics were observed depending on the size and structure of the vapour molecules. Methanol and ethanol caused the sensor resistance to increase as expected, due to the swelling of the sensor film as a result of strong H-bonding interactions between the hydroxyl groups of the vapour molecules and those of the PVA polymer. However, unexpectedly, both propanol and isopropanol caused the sensor resistance to decrease, meaning that electron conduction had been made more efficient with the absorption of the molecules. A speculation is that the hydrophobic interactions between the polymer backbone, the vapor molecules and the graphene create alternative conduction pathways to allow better electron hopping. At present, there is not enough evident to explain the observation, and this will be an interesting subject of future investigation.

    2. Repeatability of sensor

    This graphene/PVA composite based sensor responded to vapours with good repeatability. Figure 7 shows a typical example of the sensor being repeated exposed to methanol vapour. Although there was obviously a basline drift after each exposure, the actual sensitivity i.e. resistance change (?R) measured were quite consistence, with standard deviation of ca. 5% (n =3). The repeatability of responses for other alcohol vapours were within the same range, indicating that the effect of baseline drift did not have significant effect to the sensitivity of the sensor. Overall, this proposed Graphene/PVA composite based gas sensor gave satisfactory response characteristics. It is believed that further optimisation of sensor fabrication technique and polymer:graphene ratio would improve further the sensor performance. This work to evaluate the feasibility of this composite approach of sensor fabrication has been encouraging, and results suggest that polymers with different chemical signatures could improve the selectivity of the sensor. However, much research effort are needed in the future to fully explore the possibility.

    Ⅳ. Conclusion

    Wehave successfully constructed graphene/PVA composite based gas sensor for measuring alcohol vapours. The sensor has exhibited good sensitivity, fast response time with also good repeatability. An unexpected behavior towards the two propanols was observed that required further investigation.

    Acknowledgement

    The authors would like to thank XJTLU SURF programme 2014 for financial support.

    Reference:

    [1]D. S Hafner, et al. Emission of Volatile Organic Compounds from Silage: Compounds, Sources, and Implications. Atmospheric Environment , 2013 (77): 827–839.

    [2]S Cakmak, et al. Residential Exposure to Volatile Organic Compounds and Lung Function: Results from a Population-Based Cross-Sectional Survey. Environmental Pollution, 2014 (194): 145-151.

    [3]P. A Jones. Indoor Air Quality and Health. Atmospheric Environment, 1999 (33.28): 4535–4564.

    [4]M. J Mendell. Indoor Residential Chemical Emissions as Risk Factors for Respiratory and Allergic Effects in Children:A Review. Indoor Air, 2007: 259-277.

    [5]E. M Adler. A Volatile Response to Injury. Science, 2007: 112.

    [6]R Dales. Quality of Indoor Residential Air and Health. Canadian Medical Association Journal , 2008: 147-152.

    [7]P Wolkoff, et al. Organic Compounds in Office Environments-Sensory Irritation, Odor, Measurements and the Role of Reactive Chemistry. Indoor Air, 2006: 7-19.

    [8]Mallya et al. Conducting Polymer–Carbon Black Nanocomposite Sensor for Volatile Organic Compounds and Correlating Sensor Response by Molecular Dynamics. Sensors and Actuators B: Chemical, 2014 (201): 308–320.

    [9]C Lee, et al. Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene. Science, 2008 (321.5887): 385-388.

    [10]A. A Balandin. et al. Superior Thermal Conductivity of Single-Layer Graphene. Nano Letters, 2008 (8.3): 902-907.

    [11]A Geim. & K Novoselov. The Rise of Graphene. Nature Materials , 2007 (6.3): 183-191.

    [12]K. I. Bolotin, et al. Ultrahigh Electron Mobility in Suspended Graphene. Science, 2008 (146.9-10): 351-355.

    [13]S. V. Morozov, et al. Giant Intrinsic Carrier Mobilities in Graphene and Its Bilayer. Physical Review Letters , 2008: 100.

    [14]W Zhang. Exploring Graphite Oxide and Its Derivatives as Materials for Building Chemical Sensors. Laboratory of Advanced Materials and Smart Sensors. Suzhou, 2014.

    [15]Y Dan, et al. Intrinsic Response of Graphene Vapor Sensors. Philadelphia: National Center of Biotechnology Information, 2009.

    [16]C.L. Yaws & H.C. Yang. To Estimate Vapor Pressure Easily. Hydrocarbon Processing, 1989: 65.

    (責(zé)編 田彩霞)

    猜你喜歡
    彩霞責(zé)編
    沒有愛不能到達的地方
    做人與處世(2022年4期)2022-05-26 21:50:38
    Time-Consistent Investment and Reinsurance Problems for Mean-Variance Insurers with Default Risk Under Variance Premium Principle
    清而不俗 妍而不媚 馮彩霞制蓮子壺
    Optimization and application of protein C-terminal labeling by carboxypeptidase Y
    Use scientific methods to learn the vocabulary well
    Frequency-SPeed Control Model Identification of Ultrasonic Motor Using SteP ResPonse
    一顰一笑
    巧匠
    一顰一笑
    漫畫閱讀(一)
    亚洲国产精品成人久久小说| 亚洲国产精品专区欧美| 亚洲经典国产精华液单| 天天影视国产精品| 妹子高潮喷水视频| 人妻人人澡人人爽人人| 国产亚洲午夜精品一区二区久久| 精品国产乱码久久久久久小说| 亚洲av欧美aⅴ国产| 精品人妻熟女毛片av久久网站| 又黄又爽又刺激的免费视频.| 999精品在线视频| 一本久久精品| 啦啦啦中文免费视频观看日本| 一边亲一边摸免费视频| 一区二区av电影网| 精品福利永久在线观看| 成人亚洲精品一区在线观看| 宅男免费午夜| 亚洲伊人色综图| 成人二区视频| 51国产日韩欧美| 久久 成人 亚洲| 日本猛色少妇xxxxx猛交久久| 大香蕉久久成人网| 国产有黄有色有爽视频| 精品人妻在线不人妻| 丝袜喷水一区| 成人午夜精彩视频在线观看| 久热这里只有精品99| 考比视频在线观看| 秋霞伦理黄片| 亚洲国产成人一精品久久久| 丝袜脚勾引网站| 久久97久久精品| 女人精品久久久久毛片| 精品人妻在线不人妻| 女人被躁到高潮嗷嗷叫费观| 高清欧美精品videossex| 成人18禁高潮啪啪吃奶动态图| 亚洲伊人久久精品综合| 丝袜人妻中文字幕| 亚洲成人av在线免费| 男人舔女人的私密视频| 亚洲av免费高清在线观看| 免费av中文字幕在线| 又大又黄又爽视频免费| 91午夜精品亚洲一区二区三区| 国产成人精品福利久久| 午夜福利乱码中文字幕| 18禁动态无遮挡网站| 亚洲欧美一区二区三区国产| 丝袜美足系列| 国产日韩一区二区三区精品不卡| 日韩大片免费观看网站| 80岁老熟妇乱子伦牲交| 久久人人97超碰香蕉20202| av黄色大香蕉| 久久久国产欧美日韩av| 免费看av在线观看网站| 亚洲精品日本国产第一区| 美女福利国产在线| 青青草视频在线视频观看| 黑人高潮一二区| 欧美bdsm另类| 国产精品国产三级专区第一集| 国产av精品麻豆| 熟女av电影| 精品一区二区三卡| 国产深夜福利视频在线观看| 少妇人妻精品综合一区二区| 人妻人人澡人人爽人人| 久久 成人 亚洲| 综合色丁香网| 2018国产大陆天天弄谢| 菩萨蛮人人尽说江南好唐韦庄| 黄片无遮挡物在线观看| 精品福利永久在线观看| 哪个播放器可以免费观看大片| 国产成人免费无遮挡视频| 亚洲精品自拍成人| 日韩一区二区视频免费看| 久久99热6这里只有精品| 美女xxoo啪啪120秒动态图| 日韩伦理黄色片| 在线看a的网站| 国产xxxxx性猛交| 性色av一级| 人妻少妇偷人精品九色| 色视频在线一区二区三区| 精品一区二区三区四区五区乱码 | 亚洲国产日韩一区二区| 亚洲欧美色中文字幕在线| 亚洲人与动物交配视频| 亚洲成人手机| 国产亚洲欧美精品永久| 亚洲色图 男人天堂 中文字幕 | 成人毛片a级毛片在线播放| 国产精品不卡视频一区二区| 精品亚洲成国产av| 久久久精品区二区三区| 国产免费一区二区三区四区乱码| 成人影院久久| 国产激情久久老熟女| 在线观看免费日韩欧美大片| 交换朋友夫妻互换小说| 色网站视频免费| 欧美+日韩+精品| 亚洲国产看品久久| 又黄又爽又刺激的免费视频.| 国产乱来视频区| 又黄又粗又硬又大视频| 久久99热这里只频精品6学生| 国产男女内射视频| 久久久久久伊人网av| 99香蕉大伊视频| 伊人亚洲综合成人网| 日本黄色日本黄色录像| 亚洲精品一二三| 国产在线一区二区三区精| 99热这里只有是精品在线观看| 王馨瑶露胸无遮挡在线观看| 少妇的逼好多水| 香蕉国产在线看| 国产精品久久久久久久电影| 两个人免费观看高清视频| 自线自在国产av| 久久精品国产鲁丝片午夜精品| 亚洲精品第二区| 美女福利国产在线| 97在线视频观看| 中文字幕人妻熟女乱码| 伊人亚洲综合成人网| 夫妻性生交免费视频一级片| 亚洲久久久国产精品| 18+在线观看网站| 国产日韩欧美亚洲二区| 狂野欧美激情性bbbbbb| 欧美 亚洲 国产 日韩一| 大片免费播放器 马上看| 黄色怎么调成土黄色| 亚洲av福利一区| 菩萨蛮人人尽说江南好唐韦庄| 最新中文字幕久久久久| 91国产中文字幕| 欧美xxⅹ黑人| 女性生殖器流出的白浆| 黄色配什么色好看| 国产成人精品福利久久| 国产av一区二区精品久久| 欧美97在线视频| 国产一区有黄有色的免费视频| 老熟女久久久| 内地一区二区视频在线| 黄网站色视频无遮挡免费观看| 韩国av在线不卡| 国产精品三级大全| 免费高清在线观看视频在线观看| 国产高清不卡午夜福利| 亚洲中文av在线| 伦精品一区二区三区| 国产精品不卡视频一区二区| 18+在线观看网站| 在线观看免费视频网站a站| 国产淫语在线视频| 亚洲精品一区蜜桃| 欧美3d第一页| 国产亚洲精品第一综合不卡 | 五月开心婷婷网| 一本一本久久a久久精品综合妖精 国产伦在线观看视频一区 | 一级,二级,三级黄色视频| 亚洲中文av在线| 久久婷婷青草| 国产精品久久久av美女十八| 欧美日韩亚洲高清精品| 99热这里只有是精品在线观看| 日韩 亚洲 欧美在线| 久久久久网色| av国产久精品久网站免费入址| 日韩成人av中文字幕在线观看| 少妇的逼好多水| 亚洲精品乱久久久久久| 一区二区三区精品91| 91午夜精品亚洲一区二区三区| 亚洲第一区二区三区不卡| 亚洲成色77777| 精品人妻熟女毛片av久久网站| av在线老鸭窝| 香蕉精品网在线| 亚洲精品国产av蜜桃| 久久99热6这里只有精品| 久久久久久久大尺度免费视频| 在线观看www视频免费| 黄网站色视频无遮挡免费观看| 9热在线视频观看99| 一级毛片我不卡| 日日摸夜夜添夜夜爱| 国产视频首页在线观看| 黄色怎么调成土黄色| 最近的中文字幕免费完整| 久久久a久久爽久久v久久| 国产成人一区二区在线| 欧美日韩综合久久久久久| 国产精品无大码| 高清av免费在线| 人妻人人澡人人爽人人| 欧美日韩av久久| 久久精品国产鲁丝片午夜精品| 深夜精品福利| 22中文网久久字幕| 亚洲av男天堂| 久久综合国产亚洲精品| a级毛片黄视频| 男人舔女人的私密视频| 热99久久久久精品小说推荐| 中文字幕人妻丝袜制服| 日韩伦理黄色片| 两个人看的免费小视频| 欧美日韩av久久| tube8黄色片| 亚洲成色77777| 如日韩欧美国产精品一区二区三区| 精品久久国产蜜桃| 最后的刺客免费高清国语| 国产一级毛片在线| 蜜桃在线观看..| 在线天堂最新版资源| 免费播放大片免费观看视频在线观看| 男女边吃奶边做爰视频| 精品少妇内射三级| 国产成人欧美| 国产又色又爽无遮挡免| 最近最新中文字幕大全免费视频 | 亚洲精品乱久久久久久| 国产成人a∨麻豆精品| 国产精品久久久久久久久免| 熟女av电影| 国产黄频视频在线观看| 男女高潮啪啪啪动态图| 中文乱码字字幕精品一区二区三区| 国产爽快片一区二区三区| 精品少妇黑人巨大在线播放| 免费人妻精品一区二区三区视频| 九色成人免费人妻av| 女性被躁到高潮视频| 精品亚洲乱码少妇综合久久| 黄色一级大片看看| 伊人亚洲综合成人网| 久久久久视频综合| 亚洲 欧美一区二区三区| 少妇人妻精品综合一区二区| 精品国产一区二区三区四区第35| 欧美日韩综合久久久久久| 菩萨蛮人人尽说江南好唐韦庄| 国产综合精华液| www日本在线高清视频| 久久国产精品男人的天堂亚洲 | av国产久精品久网站免费入址| 女人被躁到高潮嗷嗷叫费观| 成年动漫av网址| 国产成人精品久久久久久| 国产一级毛片在线| 18禁国产床啪视频网站| 成年美女黄网站色视频大全免费| 日韩中文字幕视频在线看片| 丰满少妇做爰视频| 老熟女久久久| 九九在线视频观看精品| 26uuu在线亚洲综合色| 黄色怎么调成土黄色| 另类精品久久| 久久亚洲国产成人精品v| 欧美日韩成人在线一区二区| 狂野欧美激情性xxxx在线观看| 少妇人妻精品综合一区二区| 欧美老熟妇乱子伦牲交| 免费观看av网站的网址| 最黄视频免费看| 91精品国产国语对白视频| 国产成人欧美| 伦精品一区二区三区| 亚洲美女黄色视频免费看| 激情五月婷婷亚洲| 青春草国产在线视频| 免费看光身美女| av在线观看视频网站免费| av天堂久久9| 亚洲精品中文字幕在线视频| 97超碰精品成人国产| 蜜臀久久99精品久久宅男| 久久影院123| 麻豆精品久久久久久蜜桃| 久久av网站| 国产成人精品无人区| 有码 亚洲区| 黄网站色视频无遮挡免费观看| 久久av网站| 欧美人与性动交α欧美精品济南到 | 久久国产亚洲av麻豆专区| 狠狠精品人妻久久久久久综合| 国产在线视频一区二区| 成人国产麻豆网| 一本大道久久a久久精品| 成人综合一区亚洲| 永久免费av网站大全| 搡老乐熟女国产| 另类精品久久| 国产精品一区二区在线观看99| 最近最新中文字幕免费大全7| 国产亚洲精品久久久com| 国产成人精品一,二区| 狠狠婷婷综合久久久久久88av| 精品国产乱码久久久久久小说| 自拍欧美九色日韩亚洲蝌蚪91| 五月天丁香电影| 韩国精品一区二区三区 | 男女高潮啪啪啪动态图| 97精品久久久久久久久久精品| 深夜精品福利| 精品国产一区二区久久| 亚洲四区av| 欧美变态另类bdsm刘玥| 亚洲一区二区三区欧美精品| 国产精品女同一区二区软件| 婷婷成人精品国产| 亚洲av电影在线进入| 国产一区亚洲一区在线观看| 免费黄色在线免费观看| 人妻一区二区av| 欧美人与性动交α欧美精品济南到 | 久久精品国产亚洲av涩爱| 精品国产一区二区久久| 在现免费观看毛片| 久久精品aⅴ一区二区三区四区 | 亚洲性久久影院| www.色视频.com| 在线免费观看不下载黄p国产| 亚洲成av片中文字幕在线观看 | 日韩视频在线欧美| 夜夜爽夜夜爽视频| 午夜福利视频在线观看免费| 亚洲欧美中文字幕日韩二区| 啦啦啦在线观看免费高清www| 亚洲精品乱码久久久久久按摩| 成人亚洲欧美一区二区av| 免费高清在线观看视频在线观看| 色视频在线一区二区三区| 免费黄网站久久成人精品| 高清黄色对白视频在线免费看| 中国国产av一级| 日日啪夜夜爽| 精品人妻偷拍中文字幕| 人人澡人人妻人| 亚洲伊人色综图| 最近最新中文字幕大全免费视频 | 高清欧美精品videossex| 国产不卡av网站在线观看| 久久久久精品久久久久真实原创| 国产精品久久久久成人av| 国产精品国产av在线观看| 日韩中字成人| 国产精品熟女久久久久浪| 免费看不卡的av| 99热国产这里只有精品6| 久久国内精品自在自线图片| 国产av一区二区精品久久| 又大又黄又爽视频免费| 国产亚洲精品久久久com| 日韩在线高清观看一区二区三区| 免费播放大片免费观看视频在线观看| 在现免费观看毛片| 人妻一区二区av| 中国三级夫妇交换| 国产精品久久久久久精品古装| 久久国产精品大桥未久av| 免费av中文字幕在线| 九九爱精品视频在线观看| 免费女性裸体啪啪无遮挡网站| 9色porny在线观看| 亚洲伊人色综图| 这个男人来自地球电影免费观看 | 99国产精品免费福利视频| 亚洲成国产人片在线观看| 少妇 在线观看| 飞空精品影院首页| 午夜福利网站1000一区二区三区| 两个人看的免费小视频| 精品亚洲成a人片在线观看| 免费高清在线观看视频在线观看| 久久精品久久精品一区二区三区| 男女午夜视频在线观看 | 熟女人妻精品中文字幕| 五月开心婷婷网| 免费久久久久久久精品成人欧美视频 | 最近2019中文字幕mv第一页| 日韩熟女老妇一区二区性免费视频| 精品午夜福利在线看| 亚洲精品456在线播放app| 亚洲第一区二区三区不卡| xxxhd国产人妻xxx| 午夜免费观看性视频| 国产极品粉嫩免费观看在线| 国产老妇伦熟女老妇高清| 久久精品国产亚洲av涩爱| 五月玫瑰六月丁香| 99热这里只有是精品在线观看| 熟女电影av网| 久久ye,这里只有精品| 乱码一卡2卡4卡精品| 91国产中文字幕| 99久久精品国产国产毛片| 日本黄色日本黄色录像| av天堂久久9| 赤兔流量卡办理| 国产国拍精品亚洲av在线观看| 亚洲av在线观看美女高潮| 黄片无遮挡物在线观看| 好男人视频免费观看在线| 少妇的逼水好多| 最近最新中文字幕免费大全7| 国产亚洲一区二区精品| 中文字幕人妻丝袜制服| 成人18禁高潮啪啪吃奶动态图| 国产高清三级在线| 国产熟女午夜一区二区三区| 中文乱码字字幕精品一区二区三区| 亚洲精品美女久久久久99蜜臀 | 少妇的逼好多水| 亚洲美女搞黄在线观看| 18在线观看网站| 国内精品宾馆在线| www.av在线官网国产| 亚洲精品国产色婷婷电影| 精品99又大又爽又粗少妇毛片| 中文天堂在线官网| 欧美精品av麻豆av| videos熟女内射| 国产一区二区三区av在线| 我要看黄色一级片免费的| 国产午夜精品一二区理论片| 国产成人免费观看mmmm| 国产精品久久久久久久久免| 亚洲av国产av综合av卡| 亚洲欧美清纯卡通| 亚洲在久久综合| 夫妻午夜视频| 日韩制服丝袜自拍偷拍| 精品人妻偷拍中文字幕| 日韩免费高清中文字幕av| 国产在线免费精品| 国产精品女同一区二区软件| 精品一区二区三卡| 欧美bdsm另类| 99热6这里只有精品| 最近最新中文字幕大全免费视频 | 狂野欧美激情性bbbbbb| 大陆偷拍与自拍| xxxhd国产人妻xxx| 午夜免费观看性视频| 中国三级夫妇交换| 高清毛片免费看| 丝袜人妻中文字幕| 在现免费观看毛片| 色94色欧美一区二区| 青春草亚洲视频在线观看| 啦啦啦在线观看免费高清www| 菩萨蛮人人尽说江南好唐韦庄| 日韩一区二区三区影片| 男女下面插进去视频免费观看 | 成人亚洲精品一区在线观看| 男女高潮啪啪啪动态图| 午夜影院在线不卡| 精品久久久久久电影网| 黄色 视频免费看| 91午夜精品亚洲一区二区三区| 国产亚洲精品久久久com| 夫妻性生交免费视频一级片| 黄色怎么调成土黄色| 久久久精品免费免费高清| 国产成人免费观看mmmm| 国产爽快片一区二区三区| 两性夫妻黄色片 | 日韩视频在线欧美| 日本wwww免费看| 欧美日韩亚洲高清精品| 丝袜人妻中文字幕| 午夜激情av网站| 国产精品久久久久久久电影| 啦啦啦视频在线资源免费观看| 久久av网站| 一级毛片电影观看| 亚洲欧美色中文字幕在线| 一级毛片 在线播放| 狠狠精品人妻久久久久久综合| 一区二区三区精品91| 一级黄片播放器| 一级片免费观看大全| av不卡在线播放| 美女脱内裤让男人舔精品视频| 卡戴珊不雅视频在线播放| 日韩在线高清观看一区二区三区| 午夜久久久在线观看| 欧美97在线视频| 五月玫瑰六月丁香| 久久久国产欧美日韩av| 国产一区二区在线观看日韩| 美女视频免费永久观看网站| 亚洲色图 男人天堂 中文字幕 | 99国产精品免费福利视频| 搡老乐熟女国产| 国产午夜精品一二区理论片| 日韩av免费高清视频| 午夜福利视频在线观看免费| 亚洲国产精品专区欧美| 黑人巨大精品欧美一区二区蜜桃 | 如何舔出高潮| 哪个播放器可以免费观看大片| 欧美丝袜亚洲另类| 亚洲精品,欧美精品| 黄网站色视频无遮挡免费观看| 男女下面插进去视频免费观看 | 捣出白浆h1v1| 欧美性感艳星| 人妻一区二区av| 中国国产av一级| 尾随美女入室| 青春草亚洲视频在线观看| 少妇被粗大的猛进出69影院 | 侵犯人妻中文字幕一二三四区| 日本黄大片高清| 女性被躁到高潮视频| 国产免费一级a男人的天堂| 热99国产精品久久久久久7| 最近最新中文字幕大全免费视频 | 丝瓜视频免费看黄片| 国产一区二区在线观看av| 乱人伦中国视频| 久久这里只有精品19| 亚洲国产欧美日韩在线播放| 美女主播在线视频| 如何舔出高潮| 中文欧美无线码| 天堂俺去俺来也www色官网| freevideosex欧美| 亚洲欧美一区二区三区国产| 亚洲精品自拍成人| 国产亚洲精品久久久com| 日本-黄色视频高清免费观看| 最后的刺客免费高清国语| 免费高清在线观看日韩| 毛片一级片免费看久久久久| 波野结衣二区三区在线| av卡一久久| 国产av精品麻豆| 我要看黄色一级片免费的| 欧美日韩一区二区视频在线观看视频在线| 国语对白做爰xxxⅹ性视频网站| 国产熟女欧美一区二区| 99久国产av精品国产电影| 亚洲第一区二区三区不卡| 一级毛片我不卡| 插逼视频在线观看| av不卡在线播放| 成人毛片a级毛片在线播放| 老司机亚洲免费影院| 亚洲一码二码三码区别大吗| 丝袜脚勾引网站| 狠狠婷婷综合久久久久久88av| 国语对白做爰xxxⅹ性视频网站| 狠狠婷婷综合久久久久久88av| 老司机亚洲免费影院| 男的添女的下面高潮视频| 亚洲精品成人av观看孕妇| 亚洲美女黄色视频免费看| 欧美日韩亚洲高清精品| 视频区图区小说| av在线老鸭窝| 多毛熟女@视频| 欧美人与善性xxx| 热re99久久国产66热| 日本免费在线观看一区| a 毛片基地| 亚洲激情五月婷婷啪啪| 99热全是精品| 欧美日韩精品成人综合77777| 国产在线一区二区三区精| 亚洲精品乱久久久久久| 成年女人在线观看亚洲视频| 免费av中文字幕在线| 欧美老熟妇乱子伦牲交| 日韩成人av中文字幕在线观看| 国产白丝娇喘喷水9色精品| 一本大道久久a久久精品| 永久免费av网站大全| 黄网站色视频无遮挡免费观看| 免费观看a级毛片全部| 国产深夜福利视频在线观看| 日日撸夜夜添| 精品一品国产午夜福利视频| 成人18禁高潮啪啪吃奶动态图| 亚洲在久久综合| 午夜91福利影院| 成人毛片60女人毛片免费| 麻豆乱淫一区二区| 欧美日韩视频精品一区| 亚洲图色成人| 少妇的丰满在线观看| 日韩一区二区视频免费看| 精品第一国产精品| 岛国毛片在线播放| 性色avwww在线观看| 午夜福利网站1000一区二区三区| 三级国产精品片| 五月伊人婷婷丁香| 少妇精品久久久久久久|