• <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 ?

    Synthesis and characterization of colored layered double hydroxides for thermal stabilizer

    2015-03-01 09:24:11LiuXunjunZhangYuchaoWangJuanLeiLixu
    關(guān)鍵詞:除塵器噪音營(yíng)造

    Liu Xunjun  Zhang Yuchao  Wang Juan  Lei Lixu

    (School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China)

    ?

    Synthesis and characterization of colored layered double hydroxides for thermal stabilizer

    Liu Xunjun Zhang Yuchao Wang Juan Lei Lixu

    (School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China)

    Abstract:Colored layered double hydroxides (LDHs) can be synthesized by introducing colored cations such as Fe3+and Cr3+, which can be used as thermal stabilizers for polyvinyl chloride (PVC). The yellowish Mg/Fe and bluish Mg/Cr LDHs are prepared by the co-precipitation method. The results show that the Mg3Cr-CO3and Mg3Fe-CO3colored layered double hydroxides can stabilize PVC for more than 30 min under the thermal aging temperature of 180 ℃. The preparation can use cheap Mg(OH)2instead of MgCl2, which produces a much smaller amount of the by-product NH4Cl. It is known that NH4Cl is a cheap fertilizer that is difficult to sell; therefore, the preparation is much greener and more economic than the one using magnesium salt.

    Key words:colored layered double hydroxides; magnesium hydroxide; ferric chloride; chromic chloride; thermal stabilizer; polyvinyl chloride

    Received 2015-01-04.

    Biographies:Liu Xunjun (1988—), male, graduate; Lei Lixu (corresponding author), male, doctor, professor, lixu.lei@seu.edu.cn.

    Foundation items:The Fundamental Research Funds for the Central Universities, the Scientific Innovation Research of College Graduates in Jiangsu Province (No.CXLX12-0105), the Analysis and Test Fund of Southeast University (No.201226).

    Citation:Liu Xunjun, Zhang Yuchao, Wang Juan,et al.Synthesis and characterization of colored layered double hydroxides for thermal stabilizer[J].Journal of Southeast University (English Edition),2015,31(4):566-571.[doi:10.3969/j.issn.1003-7985.2015.04.023]

    In the previous studies, the most common precipitating agent was sodium hydroxide; however, a great amount of sodium salt will be produced as a by-product. As we know, sodium salts are cheap and difficult to sell, so we have to decrease the formation of the sodium salt. An attempt has been noted by us, which uses ammonia as the precipitant, and also, Mg(OH)2is used instead of MgCl2or Mg(NO3)2as the source of Mg2+[24]. By this method, the only by-product, agricultural fertilizer NH4Cl is formed with only 1/3 amount of previous route, which greatly alleviates the pressure from the by-product. This can be seen from the preparation of [Mg3Fe(OH)8]2CO3from Mg(OH)2:

    6Mg(OH)2+2FeCl3+4NH3·H2O+(NH4)2CO3=

    [Mg3Fe(OH)8]2CO3+6NH4Cl

    However, if it is prepared from MgCl2, the reaction is

    6MgCl2+2FeCl3+16NH3·H2O+(NH4)2CO3=

    [Mg3Fe(OH)8]2CO3+18 NH4Cl

    It can be seen that three times as much NH4Cl is formed and four times NH3·H2O is consumed if MgCl2is used as a starting material when the same amount of [Mg3Fe(OH)8]2CO3is formed.

    As we know, plastics can be degraded if they are exposed to sunlight for a long time. It is known that the UV light in the sunlight causes the degradation. Transition metals and their compounds such as Fe3+, Cr3+, Zn2+can absorb ultraviolet light well, thus they may protect plastics from ultraviolet radiation. Therefore, it is possible to make multifunctional additives if we introduce transition metals into the LDHs. This paper reports the syntheses of two colored layered double hydroxides, [Mg1-xFex(OH)2]2CO3(short as MgxFe-CO3) and [Mg1-xCrx(OH)2]2CO3(short as MgyCr-CO3), and their properties.

    1Materials and Experimental Methods

    1.1 Chemicals

    All the chemicals used were of analytical grade, which were produced by Sinopharm Chemical Reagent Co., Ltd.

    1.2 Mg/Fe and Mg/Cr layered double hydroxide samples preparation

    1.2.1Preparation of MgxFe-CO3

    Mg(OH)2and FeCl3·6H2O were mixed in 150 mL water, which is then added into 100 mL of ammonia water containing ammonium carbonate under stirring. To make Mg3Fe-CO3with the Mg/Fe molar ratio of 3, the molar ratio of Mg(OH)2, FeCl3·6H2O, NH3·H2O, (NH4)2CO3was 3∶1∶2∶0.5. The temperature of the reaction mixture was then raised to make the water reflux, and the pH of the suspension was maintained between 7 and 9, which was continuously stirred for 2 h. After that, the suspension was filtered. Solids were washed with deionized water, and then dried in an oven at 120 ℃ for 48 h.

    [MgFe(OH)8]2CO3and [Mg2Fe(OH)8]2CO3were synthesized similarly with the molar ratio of Mg and Fe being changed according to the chemical figure.

    1.2.2Preparation of MgyCr-CO3

    MgyCr-CO3was synthesized by the same method as above, but it was not quite successful. Therefore, MgCl2was used instead of Mg(OH)2; all others were the same except that the amount of ammonia water was increased according to the chemical equation. Therefore, the molar ratio of MgCl2, CrCl3·6H2O, NH3·H2O, and (NH4)2CO3was 3∶1∶8∶0.5 for the preparation of [Mg3Cr(OH)8]2CO3.

    [MgCr(OH)8]2CO3and [Mg2Cr(OH)8]2CO3were also synthesized by changing only the amount of MgCl2according to the chemical figure.

    1.3 Characterization

    2Results and Discussion

    2.1 The XRD patterns of the LDHs

    Fig.1 shows the X-ray diffraction patterns of samples prepared under the exploratory conditions (aged for 2 h at the refluxing temperature of water). For MgxFe-CO3, it is observed that the intensities of diffraction peaks increase with the increase of Fe3+content. When the molar ratio of Mg and Fe is 1, the diffraction peaks are almost unobservable (see Fig.1(a)). This was observed and believed that more Mg2+could have contributed to the formation of laminar structure before[25].

    However, it was not very successful when we attempted to synthesize MgyCr-CO3in the same method. Fig.1(b) shows the result of the attempt. It can be seen that there are the characteristic peaks of the proposed LDHs, but there are still impurity peaks from Mg(OH)2which appeared at around 18°[26]. Thus, the Cr3+cannot react with Mg(OH)2as smoothly as Fe3+. Perhaps this is ascribed to the insolubility of Mg(OH)2and the inertness in ligand substitution reactions of Cr3+.

    (a)

    (b)

    (c)Fig.1 Powder X-ray diffraction patterns of MgxFe-CO3 products and MgyCr-CO3(y=1, 2 and 3). (a) MgxFe-CO3 synthesized from Mg(OH)2; (b) Mg3Cr-CO3 synthesized from Mg(OH)2; (c) MgyCr-CO3 synthesized from MgCl2

    Therefore, we use MgCl2instead of Mg(OH)2to synthesize MgyCr-CO3, which is very successful. Fig.1(c) shows the related XRD patterns. Similarly, the MgxFe-CO3, MgyCr-CO3crystallized better with the increase of the Mg2+∶Cr3+molar ratio, but they are less well-crystallized than MgxFe-CO3. As we have discussed before, this may be also related to the inertness in ligand substitution reactions of Cr3+.

    2.2 The IR spectra of as-prepared LDHs

    Fig.2 shows the infrared spectrum of two typical samples. It is clear that both samples display similar characteristics, which is in accordance with the general knowledge on LDHs. The strong and broad band at around 3 442 cm-1is attributed to the hydroxyl groups stretching mode from both the layer hydroxyl groups and the interlayer water molecules[27]. The band observed at around 1 633 or 1 639 cm-1is ascribed to theδOHbending vibration[28]. The sharp absorption band observed at around 1 384 cm-1is attributed to the interlayer carbonate[29-30]. The lattice vibrations of metal-oxygen bonds vibrations likely result from the appearance of the strong bands at 588 cm-1.

    Fig.2 The FT-IR spectra of Mg3Fe-CO3 and Mg3Cr-CO3 samples

    2.3 UV-vis spectrum characterization

    The optical absorption behavior of the as-prepared Mg3Fe-CO3and Mg3Cr-CO3samples under the exploratory conditions are illustrated by the UV-vis absorption spectrum, as shown in Fig.3. Both materials show strong UV absorption at around 200 nm, which is assigned to the charge transfer of isolated Fe3+and Cr3+ions octahedrally coordinated in the brucite layered structure[31]. In the visible light region, the Mg3Fe-CO3shows absorption at above 400 nm, which is ascribed to the dd transition of Fe3+[32]. The Mg3Cr-CO3exhibits two bands at 419 and 588 nm which can be easily ascribed to spin-allowed, Laporte-forbidden transitions from the fundamental state4A2g(F)→4T1g(P) and4A2g(F)→4T2g(P), respectively, in its brucite layers[33-34].

    2.4 Thermogravimetric studies

    Fig.4 shows the TG-DTA curves of the samples. The Mg3Fe-CO3roughly undergoes two separate weight loss processes on heating, which is in agreement with studies

    (a)

    (b)Fig.3 The UV-vis spectrum. (a) Mg3Fe-CO3 sample;(b) Mg3Cr-CO3 sample

    reported on other LDHs[35]. There are two obvious endothermic peaks at 177.9 and 362.4 ℃. The first-step weight loss of 10.8% at about 177.9 ℃ can result from the loss of interlayer water. The second-step weight loss of 25.9% at about 362.4 ℃ is due to the dehydroxylation of the layers to form oxides[36]. If the chemical figure of LDHs is [Mg3Fe(OH)8]2CO3·4H2O, the loss of the 4 crystal waters will be 10.9% of their weight,

    森林中的樹木是天然的除塵器。隨著工業(yè)的不斷發(fā)展,一些噪音和污染開始出現(xiàn)影響人們的生活,而進(jìn)行營(yíng)造林建設(shè)具有降低噪音和凈化空氣的作用。

    (a)

    (b)Fig.4 TG-DTA curves. (a) Mg3Fe-CO3 sample; (b) Mg3Cr-CO3 sample

    and the loss of 8 crystal waters from dehydroxylation will be 21.8% of weight. The total loss of weight will be 39.4%, which is very close to the experimental value of 36.7% if the carbonate also decomposes during the thermal decomposition[37]. The thermal decomposition analysis shows that there is a great loss of the crystal waters which will bring a large amount of heat away and a great deal of loss of water and CO2which also brings a large amount of heat away and H2O and CO2will dilute the concentration of O2on the surface of be polymer materials. Thus, LDH material can also be used as a flame-retardant.

    The TG/DTA behavior of Mg3Cr-CO3is a slightly different from Mg3Fe-CO3. The weight loss is continuous but the rate is different. The endothermic peaks are not very clear (see Fig.4(b)), which reveals that there are different ways of decomposition. Perhaps it is related to its initial poor crystallization.

    2.5 Thermal stability testing of prepared PVC composites

    The PVC composite strips were prepared and made of 100 g PVC powder, 45 g DOP, 0.2 g Zn(st)2, 0.3 g Ca(st)2, Mg3Cr-CO3or Mg3Fe-CO3. The resulting PVC composite strips were placed in a thermal aging test box maintained at 180 ℃ to observe their color changes. The thermal stability of PVC is defined by the time when the strips become black. As shown in Fig.5, the strips

    Fig.5 Thermal stability of composites of polyvinyl chloride. (a) Mg3Cr-CO3;(b) Mg3Fe-CO3

    are colored by the LDHs. As the aging time is prolonged, the color of the strips changes. From Fig.5(a), it can be seen that the color of the blue PVC Mg3Cr-CO3composite becomes yellow when the time lasts 40 min, then deepens gradually, and finally turns red when the time lasts 90 min. The color of the pale red PVC-Mg3Cr-CO3composite becomes yellow when the time lasts 50 min, then deepens gradually, and finally turns brown when the time lasts 80 min. It was proposed by Lin et al.[38]that the stabilization of PVC by LDHs includes two steps. The first step is that HCl produced by the thermal dehydrochlorination of PVC reacts with the interlayer carbonate anions, and then more HCl reacts with the hydroxyl groups in the layers. Those processes remove the HCl which can catalyze the dehydrochlorination of PVC and thus stabilize the PVC material.

    3Conclusion

    [Mg3Fe(OH)8]2CO3has been successfully prepared from FeCl3·6H2O, Mg(OH)2, NH3·H2O, (NH4)2CO3in water under refluxing for 2 h. By using Mg(OH)2, the amount of by-product NH4Cl is reduced dramatically. Using Mg(OH)2to produce MgxCr-CO3is a little difficult, so it is better to use MgCl2as the starting material. The existence of Fe3+or Cr3+makes LDHs colored, and they also absorb UV lights. This may make plastics colored and UV-resistant. The decomposition of Mg3Fe-CO3leads to the weight loss due to the loss of water and CO2. Similarly, the decomposition of Mg3Cr-CO3leads to weight loss. This property can allow them to be used as a flame retardant as well as PVC thermal stabilizers.The as-prepared [Mg3Fe(OH)8]2CO3and [Mg3Cr(OH)8]2CO3were tested as the PVC thermal stabilizers, which show that the former can stabilize PVC for 50 min, and the latter for 30 min at 180 ℃.

    References

    [1]Wang L J, Xu X Y, Evans D G, et al. Synthesis of an N,N-Bis(phosphonomethyl)glycine anion-intercalated layered double hydroxide and its selective infrared absorption effect in low density polyethylene films for use in agriculture[J].IndEngChemRes, 2010, 49(11): 5339-5346.

    [2]Feng Y J, Tang P G, Xi J M, et al. Layered double hydroxides as flame retardant and thermal stabilizer for polymers[J].RecentPatentsonNanotechnology, 2012, 6(3): 231-237.

    [3]Ahamad A, Patil C B, Gite V V, et al. Evaluation of the synergistic effect of layered double hydroxides with micro-and nano-Ca2CO3on the thermal stability of polyvinyl chloride composites[J].JThermoplastComposMater, 2013, 26(9): 1249-1259.

    [4]Yi S, Yang Z H, Wang S W, et al. Effects of MgAlCe-CO3layered double hydroxides on the thermal stability of PVC resin[J].JApplPolymSci, 2011, 119(5): 2620-2626.

    [5]Wen R J, Yang Z H, Chen H Y, et al. Zn-Al-La hydrotalcite-like compounds as heating stabilizer in PVC resin[J].JRareEarths, 2012, 30(9): 895-902.

    [6]Xu S L, Zhang L X, Lin Y J, et al. Layered double hydroxides used as flame retardant for engineering plastic acrylonitrile-butadiene-styrene (ABS)[J].JPhysChemSolids, 2012, 73(12): 1514-1517.

    [7]Shi L, Li D Q, Wang J R, et al. Synthesis, flame-retardant and smoke-suppressant properties of a borate-intercalated layered double hydroxide[J].ClaysClayMiner, 2005, 53(3): 294-300.

    [8]Matusinovic Z, Wilkie C A, Fire retardancy and morphology of layered double hydroxide nanocomposites [J].JMaterChem, 2012, 22(36): 18701-18704.

    [9]Guo Y W, Zhu Z L, Qiu Y L, et al. Adsorption of arsenate on Cu/Mg/Fe/La layered double hydroxide from aqueous solutions[J].JHazardMater, 2012, 239: 279-288.

    [10]Mandal S, Mayadevi S. Adsorption of fluoride ions by Zn-Al layered double hydroxides[J].ApplClaySci, 2008, 40(1/2/3/4): 54-62.

    [11]Zhao J K, Xie Y F, Yuan W J, et al. A hierarchical Co-Fe LDH rope-like nanostructure: facile preparation from hexagonal lyotropic liquid crystals and intrinsic oxidase-like catalytic activity[J].JMaterChemB, 2013, 1(9): 1263-1269.

    [12]Dubey A. Synthesis and catalytic applications of CMK-LDH (layered double hydroxides) nanocomposite materials[J].GreenChem, 2007, 9(5): 424-426.

    [13]Zeng L, Zhao T S, Li Y S. Synthesis and characterization of crosslinked poly (vinyl alcohol)/layered double hydroxide composite polymer membranes for alkaline direct ethanol cells[J].IntJHydrogEnergy, 2012, 37(23): 18425-18432.

    [14]Yarger M S, Steinmiller E M P, Choi K S. Electrochemical synthesis of Zn-Al layered double hydroxide (LDH) films[J].InorgChem, 2008, 47(13): 5859-5865.

    [15]Lei L X, Hu M, Gao X R, et al. The effect of the interlayer anions on the electrochemical performance of layered double hydroxide electrode materials[J].ElectrochimActa, 2008, 54(2): 671-676.

    [16]Ghotbi M Y, Hussein M Z, Yahaya A H, et al. LDH-intercalated D-gluconate: generation of a new food additive-inorganic nanohybrid compound[J].JPhysChemSolids, 2009, 70(6): 948-954.

    [17]Mandel K, Drenkova-Tuhtan A, Hutter F, et al. Layered double hydroxide ion exchangers on superparamagnetic microparticles for recovery of phosphate from waste water[J].JMaterChemA, 2013, 1(5): 1840-1848.

    [18]Nyambo C, Songtipya P, Manias E, et al. Effect of MgAl-layered double hydroxide exchanged with linear alkyl carboxylates on fire-retardancy of PMMA and PS[J].JMaterChem,2008, 18(40): 4827-4838.

    [19]Millange F, Walton R I, O’Hare D, Time-resolved in situ X-ray diffraction study of the liquid-phase reconstruction of Mg-Al-carbonate hydrotalcite-like compounds[J].JMaterChem, 2000, 10(7): 1713-1720.

    [20]Costantino U, Coletti N, Nocchetti M, et al. Anion exchange of methyl orange into Zn-Al synthetic hydrotalcite and photophysical characterization of the intercalates obtained[J].Langmuir, 1999, 15(13): 4454-4460.

    [21]Sun G B, Sun L N, Wen H, et al. From layered double hydroxide to spinel nanostructures: Facile synthesis and characterization of nanoplatelets and nanorods[J].JPhysChemB, 2006,110(27):13375-13380.

    [22]Greenwell H C, Jones W, Rugen-Hankey S L, et al. Efficient synthesis of ordered organo-layered double hydroxides[J].GreenChem, 2010, 12(4): 688-695.

    [23]Guo Z, Feng J, Feng Y, et al. In situ synthesis of solid base catalysts for the regeneration of degradation products formed during the anthraquinone process for the manufacture of hydrogen peroxide[J].ApplCatalAGeneral, 2011, 401(1/2): 163-169.

    [24]Zhang L H, Zhu J, Jiang X R, et al. Influence of nature of precursors on the formation and structure of Cu-Ni-Cr mixed oxides from layered double hydroxides[J].JPhysChemSolids, 2006, 67(8):1678-1686.

    [25]Vulic T, Reitzmann A, Ranogajec J, et al. The influence of synthesis method and Mg-Al-Fe content on the thermal stability of layered double hydroxides[J].JThermAnalCalorim, 2012, 110(1):227-233.

    [26]Sierra-Fernandez A, Gomez-Villalba L S, Milosevic O, et al. Synthesis and morpho-structural characterization of nanostructured magnesium hydroxide obtained by a hydrothermal method[J].CeramicsInternational, 2014, 40(8): 12285-12292.

    [27]Kagunga W, Baddour-Hadjean R, Kooli F, et al. Vibrational modes in layered double hydroxides and their calcined derivatives[J].ChemPhys, 1998, 236(1/2/3): 225-234.

    [29]Du L C, Qu B L. Structural characterization and thermal oxidation properties of LLDPE/MgAl-LDH nanocomposites[J].JMaterChem, 2006,16(16): 1549-1554.

    [30]O’Leary S, O’Hare D, Seeley G. Delamination of layered double hydroxides in polar monomers: new LDH-acrylate nanocomposites[J].ChemCommun2002,(14): 1506-1507.

    [31]Heredia A I C, Oliva M I, Zandalazini C I, et al. Synthesis, characterization, and catalytic behavior of Mg-Al-Zn-Fe mixed oxides from precursors layered double hydroxide[J].IndEngChemRes, 2011, 50(11): 6695-6703.

    [32]Parida K, Satpathy M, Mohapatra L. Incorporation of Fe3+into Mg/Al layered double hydroxide framework: effects on textural properties and photocatalytic activity for H2generation[J].JMaterChem, 2012, 22(15): 7350-7357.

    [33]Liu J W, Chen G, Li Z H, et al. Electronic structure and visible light photocatalysis water splitting property of chromium-doped SrTiO3[J].JSolidStateChem, 2006, 179(12): 3704-3708.

    [34]Guo Y, Zhang H, Zhao L, et al. Synthesis and characterization of Cd-Cr and Zn-Cd-Cr layered double hydroxides intercalated with dodecyl sulfate[J].JSolidStateChem, 2005, 178(6): 1830-1836.

    [35]Spratt H J, Palmer S J, Frost R L, Thermal decomposition of synthesised layered double hydroxides based upon Mg/(Fe,Cr) and carbonate[J].ThermochimicaActa, 2008, 479(1/2): 1-6.

    [36]Wang Y L, Wu P X, Li B, et al. In-depth study on intercalating threonine into layered double hydroxides[J].ApplClaySci, 2011, 53(4):615-620.

    [37]Moscowitz H, Lando D, Cohen H, et al. Bishophite chlorination[J].IndEngChemProdResDev, 1978, 17(2): 156-160.

    [38]Lin Y J, Li D Q, Evans D G, et al. Modulating effect of Mg-Al-CO3layered double hydroxides on the thermal stability of PVC resin[J].PolymDegradStab, 2005, 88(2): 286-293.

    doi:10.3969/j.issn.1003-7985.2015.04.023

    猜你喜歡
    除塵器噪音營(yíng)造
    誠(chéng)心為“僑” 營(yíng)造“家”溫暖
    2021年山西將完成營(yíng)造林26.67萬公頃(400萬畝)
    噪音,總是有噪音!
    無法逃避的噪音
    脈沖袋式除塵器在高爐煉鐵中的應(yīng)用與維護(hù)
    山東冶金(2019年1期)2019-03-30 01:35:20
    提高除塵器運(yùn)行效率的技改措施
    噪音的小把戲
    擅長(zhǎng)營(yíng)造美好的音色 Marantz SA-10 S1/PM-10 S1
    白噪音的三種用法
    Coco薇(2017年9期)2017-09-07 22:09:28
    下進(jìn)風(fēng)袋式除塵器內(nèi)部流場(chǎng)的數(shù)值模擬
    久久综合国产亚洲精品| 大香蕉久久成人网| 男女边摸边吃奶| 日韩欧美免费精品| 夜夜夜夜夜久久久久| 黑人猛操日本美女一级片| 日韩大片免费观看网站| 日韩欧美一区二区三区在线观看 | 秋霞在线观看毛片| 欧美乱码精品一区二区三区| 午夜日韩欧美国产| 精品高清国产在线一区| 国产精品久久久久成人av| 亚洲午夜精品一区,二区,三区| 午夜激情av网站| 国产精品国产三级国产专区5o| 999久久久国产精品视频| 精品亚洲成国产av| 青春草视频在线免费观看| 1024香蕉在线观看| 国产亚洲欧美在线一区二区| 亚洲七黄色美女视频| 又大又爽又粗| 菩萨蛮人人尽说江南好唐韦庄| 久久久久国产一级毛片高清牌| 国产日韩一区二区三区精品不卡| 欧美激情久久久久久爽电影 | 国产精品免费视频内射| av电影中文网址| 国产av国产精品国产| 国产亚洲精品一区二区www | a在线观看视频网站| 如日韩欧美国产精品一区二区三区| 亚洲一卡2卡3卡4卡5卡精品中文| 在线av久久热| 国产高清国产精品国产三级| 国产av国产精品国产| 欧美精品啪啪一区二区三区 | 老汉色av国产亚洲站长工具| 欧美日韩亚洲综合一区二区三区_| 十八禁网站网址无遮挡| 久久国产精品大桥未久av| 69av精品久久久久久 | 男女免费视频国产| 嫁个100分男人电影在线观看| 欧美日韩亚洲国产一区二区在线观看 | 欧美亚洲日本最大视频资源| 亚洲精品美女久久av网站| 国产精品成人在线| 黄色毛片三级朝国网站| 久久人人97超碰香蕉20202| 国产伦理片在线播放av一区| 美女脱内裤让男人舔精品视频| bbb黄色大片| av天堂久久9| 91精品伊人久久大香线蕉| 亚洲精品国产av成人精品| 亚洲午夜精品一区,二区,三区| 欧美 日韩 精品 国产| 国产又爽黄色视频| 国产精品.久久久| 欧美亚洲 丝袜 人妻 在线| 国产精品亚洲av一区麻豆| 老司机福利观看| 久久久精品94久久精品| 丝袜美足系列| 又紧又爽又黄一区二区| 女人高潮潮喷娇喘18禁视频| av视频免费观看在线观看| 成人亚洲精品一区在线观看| 亚洲激情五月婷婷啪啪| 日本一区二区免费在线视频| www.精华液| 久久 成人 亚洲| 丝袜脚勾引网站| 在线亚洲精品国产二区图片欧美| 在线永久观看黄色视频| 久久人妻福利社区极品人妻图片| 亚洲五月婷婷丁香| 久久热在线av| 黑人巨大精品欧美一区二区蜜桃| 最近中文字幕2019免费版| 99久久国产精品久久久| 国产人伦9x9x在线观看| 精品卡一卡二卡四卡免费| 亚洲一区中文字幕在线| 亚洲全国av大片| 一区福利在线观看| 精品久久久久久久毛片微露脸 | 成人国产av品久久久| 亚洲精华国产精华精| 中文字幕人妻熟女乱码| 欧美另类亚洲清纯唯美| av国产精品久久久久影院| 无限看片的www在线观看| 成人av一区二区三区在线看 | 日本撒尿小便嘘嘘汇集6| 男女国产视频网站| 亚洲精品av麻豆狂野| 亚洲欧美清纯卡通| 久久人人爽av亚洲精品天堂| 国产精品一区二区免费欧美 | 天堂中文最新版在线下载| 波多野结衣一区麻豆| 午夜成年电影在线免费观看| 人妻人人澡人人爽人人| 婷婷色av中文字幕| 欧美变态另类bdsm刘玥| 久久人妻熟女aⅴ| 最黄视频免费看| 国产激情久久老熟女| 在线观看舔阴道视频| 国产日韩欧美视频二区| 男女无遮挡免费网站观看| 黄色视频,在线免费观看| a在线观看视频网站| 菩萨蛮人人尽说江南好唐韦庄| 久久久精品94久久精品| 无限看片的www在线观看| 国产精品免费视频内射| 男人舔女人的私密视频| 亚洲欧美清纯卡通| √禁漫天堂资源中文www| av国产精品久久久久影院| 亚洲av片天天在线观看| 亚洲成人手机| √禁漫天堂资源中文www| 色播在线永久视频| 热99国产精品久久久久久7| 一二三四在线观看免费中文在| 动漫黄色视频在线观看| 免费少妇av软件| 人人妻,人人澡人人爽秒播| 欧美日韩黄片免| 搡老岳熟女国产| 美女视频免费永久观看网站| avwww免费| 精品久久久精品久久久| 久久中文看片网| 视频区欧美日本亚洲| svipshipincom国产片| 亚洲熟女精品中文字幕| 国产熟女午夜一区二区三区| 汤姆久久久久久久影院中文字幕| 爱豆传媒免费全集在线观看| av一本久久久久| 老熟妇乱子伦视频在线观看 | 手机成人av网站| 老司机靠b影院| 乱人伦中国视频| 欧美久久黑人一区二区| 麻豆乱淫一区二区| 日本黄色日本黄色录像| 黑丝袜美女国产一区| 男人操女人黄网站| 桃花免费在线播放| 亚洲美女黄色视频免费看| 性色av乱码一区二区三区2| 1024视频免费在线观看| 三级毛片av免费| 成年美女黄网站色视频大全免费| 两性夫妻黄色片| 老司机亚洲免费影院| 免费久久久久久久精品成人欧美视频| 亚洲第一欧美日韩一区二区三区 | 一区二区日韩欧美中文字幕| 交换朋友夫妻互换小说| 一级毛片电影观看| 在线观看舔阴道视频| 老熟妇仑乱视频hdxx| 国产精品自产拍在线观看55亚洲 | 国产91精品成人一区二区三区 | 天堂中文最新版在线下载| 制服人妻中文乱码| 久久久久久久国产电影| 亚洲国产精品一区二区三区在线| 亚洲av国产av综合av卡| 99久久99久久久精品蜜桃| 欧美人与性动交α欧美软件| 国产野战对白在线观看| 国产三级黄色录像| 中国美女看黄片| 丰满人妻熟妇乱又伦精品不卡| 成人黄色视频免费在线看| 性少妇av在线| 99精国产麻豆久久婷婷| 每晚都被弄得嗷嗷叫到高潮| 99久久人妻综合| 十八禁网站免费在线| 亚洲av欧美aⅴ国产| 一进一出抽搐动态| 我的亚洲天堂| 欧美日韩精品网址| avwww免费| 精品免费久久久久久久清纯 | 国产欧美日韩一区二区三区在线| 精品国产一区二区三区四区第35| 五月开心婷婷网| 久9热在线精品视频| 久久影院123| 久久人人爽av亚洲精品天堂| 亚洲精品一卡2卡三卡4卡5卡 | 久久久久网色| 国产亚洲av片在线观看秒播厂| 国产91精品成人一区二区三区 | 日韩,欧美,国产一区二区三区| 亚洲性夜色夜夜综合| 超色免费av| 黄片大片在线免费观看| 国产成人啪精品午夜网站| 人妻人人澡人人爽人人| 久久久久久久大尺度免费视频| 国产欧美日韩精品亚洲av| 大香蕉久久成人网| 中文字幕最新亚洲高清| 精品福利观看| 国产亚洲av片在线观看秒播厂| 亚洲精品美女久久av网站| 亚洲黑人精品在线| 菩萨蛮人人尽说江南好唐韦庄| 法律面前人人平等表现在哪些方面 | 成人国语在线视频| 50天的宝宝边吃奶边哭怎么回事| av免费在线观看网站| 国产精品麻豆人妻色哟哟久久| 老司机影院毛片| 国产成人av教育| 美女福利国产在线| 午夜激情av网站| 婷婷色av中文字幕| 久久久水蜜桃国产精品网| 啪啪无遮挡十八禁网站| 黄片大片在线免费观看| 国产一区二区 视频在线| 亚洲中文字幕日韩| 久久久国产欧美日韩av| 蜜桃在线观看..| 国产成人精品久久二区二区91| 欧美日韩一级在线毛片| 中文字幕最新亚洲高清| 亚洲自偷自拍图片 自拍| 国产高清视频在线播放一区 | 国产又色又爽无遮挡免| 亚洲精华国产精华精| 精品国产一区二区久久| 一本—道久久a久久精品蜜桃钙片| 欧美日韩亚洲国产一区二区在线观看 | 成人三级做爰电影| 一级毛片精品| 丰满饥渴人妻一区二区三| kizo精华| 欧美日韩亚洲综合一区二区三区_| 国产国语露脸激情在线看| 黄色毛片三级朝国网站| 一区二区三区激情视频| 久久精品aⅴ一区二区三区四区| 91麻豆精品激情在线观看国产 | 国产精品 国内视频| 夫妻午夜视频| 欧美日韩黄片免| 日韩,欧美,国产一区二区三区| 免费看十八禁软件| 99热国产这里只有精品6| 国产精品成人在线| 日本av免费视频播放| 国产精品一区二区在线不卡| 黄片播放在线免费| 日韩一区二区三区影片| av欧美777| 十八禁网站网址无遮挡| 69精品国产乱码久久久| 制服人妻中文乱码| 黄片播放在线免费| 亚洲精品国产av成人精品| 91字幕亚洲| 亚洲成人免费av在线播放| 啦啦啦 在线观看视频| 日韩人妻精品一区2区三区| 菩萨蛮人人尽说江南好唐韦庄| 丰满人妻熟妇乱又伦精品不卡| 午夜激情av网站| 日韩 欧美 亚洲 中文字幕| 久久精品国产亚洲av香蕉五月 | 国产精品 国内视频| 久久久久久亚洲精品国产蜜桃av| 我要看黄色一级片免费的| 91精品伊人久久大香线蕉| 欧美大码av| 欧美日韩av久久| 久久中文看片网| 如日韩欧美国产精品一区二区三区| 热99re8久久精品国产| 久久ye,这里只有精品| 丰满迷人的少妇在线观看| 看免费av毛片| 午夜福利视频精品| 丰满饥渴人妻一区二区三| 精品国产一区二区三区四区第35| 叶爱在线成人免费视频播放| 国产精品成人在线| 精品一区二区三区av网在线观看 | 午夜激情久久久久久久| 亚洲一区中文字幕在线| 蜜桃在线观看..| 成人亚洲精品一区在线观看| 美女大奶头黄色视频| 久久久国产精品麻豆| 精品久久久久久电影网| 女性被躁到高潮视频| 欧美黑人欧美精品刺激| 亚洲性夜色夜夜综合| 日韩大码丰满熟妇| 久久久国产成人免费| av又黄又爽大尺度在线免费看| 高清在线国产一区| 我的亚洲天堂| 精品亚洲乱码少妇综合久久| 国产成人精品久久二区二区91| 成人影院久久| 青青草视频在线视频观看| 在线观看舔阴道视频| 在线观看人妻少妇| 欧美精品人与动牲交sv欧美| 国产精品亚洲av一区麻豆| 亚洲一区中文字幕在线| 午夜福利一区二区在线看| 黄色视频不卡| 国产一区二区三区av在线| 欧美日韩亚洲国产一区二区在线观看 | 美女主播在线视频| 丝袜美足系列| av欧美777| 亚洲av国产av综合av卡| 精品国内亚洲2022精品成人 | 久9热在线精品视频| 高潮久久久久久久久久久不卡| 999久久久国产精品视频| 成年美女黄网站色视频大全免费| 伦理电影免费视频| 久久久久久久大尺度免费视频| 狠狠狠狠99中文字幕| 久久午夜综合久久蜜桃| 女人被躁到高潮嗷嗷叫费观| 大陆偷拍与自拍| 国产欧美日韩一区二区精品| 99久久国产精品久久久| 91九色精品人成在线观看| 黄网站色视频无遮挡免费观看| 免费在线观看完整版高清| 一区二区三区精品91| 一本—道久久a久久精品蜜桃钙片| 一级毛片女人18水好多| av电影中文网址| 免费在线观看影片大全网站| 少妇被粗大的猛进出69影院| 大陆偷拍与自拍| 成人手机av| 欧美乱码精品一区二区三区| a级毛片黄视频| 久久亚洲精品不卡| 日本精品一区二区三区蜜桃| cao死你这个sao货| 麻豆国产av国片精品| 人妻久久中文字幕网| av一本久久久久| 在线观看免费高清a一片| av在线app专区| 欧美精品人与动牲交sv欧美| 日日爽夜夜爽网站| 少妇精品久久久久久久| 亚洲七黄色美女视频| 午夜激情久久久久久久| 久久人人97超碰香蕉20202| 亚洲人成电影观看| 无限看片的www在线观看| 丝袜喷水一区| 欧美激情高清一区二区三区| 最新在线观看一区二区三区| 亚洲精品久久午夜乱码| 老司机亚洲免费影院| 国产亚洲av高清不卡| 一个人免费看片子| 亚洲,欧美精品.| 在线看a的网站| 最新在线观看一区二区三区| 水蜜桃什么品种好| 亚洲av电影在线进入| 午夜激情久久久久久久| 又紧又爽又黄一区二区| 午夜福利在线免费观看网站| 欧美国产精品一级二级三级| 欧美日韩黄片免| 国产亚洲精品久久久久5区| 永久免费av网站大全| 午夜成年电影在线免费观看| 老汉色∧v一级毛片| 久久精品人人爽人人爽视色| 精品欧美一区二区三区在线| 激情视频va一区二区三区| 中文字幕人妻丝袜制服| 亚洲av电影在线观看一区二区三区| av天堂在线播放| 欧美日韩成人在线一区二区| 国产视频一区二区在线看| 久久午夜综合久久蜜桃| 搡老岳熟女国产| 亚洲国产欧美在线一区| 亚洲精品久久成人aⅴ小说| 欧美另类一区| 人妻一区二区av| 黄片播放在线免费| 亚洲精品粉嫩美女一区| 亚洲av成人一区二区三| 亚洲av电影在线进入| 黑人操中国人逼视频| 日韩,欧美,国产一区二区三区| www.精华液| av天堂在线播放| 青草久久国产| 婷婷色av中文字幕| 一进一出抽搐动态| av在线app专区| 18禁裸乳无遮挡动漫免费视频| 精品亚洲成国产av| av网站在线播放免费| 日韩欧美一区视频在线观看| 中文字幕最新亚洲高清| 久久久久精品人妻al黑| 欧美日韩国产mv在线观看视频| 狠狠婷婷综合久久久久久88av| 欧美性长视频在线观看| 男女边摸边吃奶| 在线观看www视频免费| 午夜精品久久久久久毛片777| 天天躁夜夜躁狠狠躁躁| 亚洲成国产人片在线观看| 精品一区二区三卡| 久久ye,这里只有精品| 一本一本久久a久久精品综合妖精| av在线播放精品| 午夜福利免费观看在线| av不卡在线播放| 欧美精品一区二区大全| 建设人人有责人人尽责人人享有的| 麻豆国产av国片精品| 好男人电影高清在线观看| 日本wwww免费看| 久久久国产欧美日韩av| 国产精品欧美亚洲77777| 王馨瑶露胸无遮挡在线观看| 一级毛片电影观看| 他把我摸到了高潮在线观看 | 中文字幕精品免费在线观看视频| 国产福利在线免费观看视频| 国产亚洲av高清不卡| 两性夫妻黄色片| 老熟妇仑乱视频hdxx| 精品一区二区三区四区五区乱码| 国产在线观看jvid| www.熟女人妻精品国产| 99re6热这里在线精品视频| 50天的宝宝边吃奶边哭怎么回事| 人人妻人人澡人人爽人人夜夜| 一本大道久久a久久精品| 69av精品久久久久久 | 黄片小视频在线播放| 精品少妇久久久久久888优播| 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 | 黄色 视频免费看| 日韩制服骚丝袜av| 国产精品麻豆人妻色哟哟久久| 欧美中文综合在线视频| 在线精品无人区一区二区三| 天天躁日日躁夜夜躁夜夜| 纵有疾风起免费观看全集完整版| 亚洲三区欧美一区| 一区二区av电影网| avwww免费| 人人澡人人妻人| 19禁男女啪啪无遮挡网站| 亚洲欧美清纯卡通| 免费看十八禁软件| 久久久久久久大尺度免费视频| 亚洲免费av在线视频| 午夜福利一区二区在线看| 我的亚洲天堂| 成人免费观看视频高清| 亚洲一区中文字幕在线| 久久性视频一级片| 日韩欧美国产一区二区入口| 免费久久久久久久精品成人欧美视频| 日本精品一区二区三区蜜桃| 亚洲av片天天在线观看| 欧美人与性动交α欧美精品济南到| 99国产极品粉嫩在线观看| 亚洲综合色网址| 精品乱码久久久久久99久播| 天天躁日日躁夜夜躁夜夜| 人成视频在线观看免费观看| 啦啦啦啦在线视频资源| 女人精品久久久久毛片| 蜜桃在线观看..| 91精品伊人久久大香线蕉| 国产成人精品无人区| 黄网站色视频无遮挡免费观看| 一区二区av电影网| 成年动漫av网址| 50天的宝宝边吃奶边哭怎么回事| 中文字幕人妻丝袜制服| 久久人人爽人人片av| 日韩有码中文字幕| avwww免费| 久久青草综合色| 国产精品av久久久久免费| 久久国产精品影院| 亚洲国产av新网站| 久久精品熟女亚洲av麻豆精品| 9色porny在线观看| 狠狠婷婷综合久久久久久88av| 亚洲精品第二区| 麻豆国产av国片精品| 国产一区有黄有色的免费视频| 国产精品一区二区在线不卡| 人人妻人人澡人人爽人人夜夜| 曰老女人黄片| 日韩有码中文字幕| 久久狼人影院| 精品国内亚洲2022精品成人 | 99热全是精品| 一区二区av电影网| 久久久欧美国产精品| 真人做人爱边吃奶动态| 在线看a的网站| 12—13女人毛片做爰片一| 亚洲第一欧美日韩一区二区三区 | 天天添夜夜摸| 国产视频一区二区在线看| 久久久精品国产亚洲av高清涩受| 80岁老熟妇乱子伦牲交| 亚洲av成人一区二区三| 久久免费观看电影| av线在线观看网站| 男女国产视频网站| 大香蕉久久网| 国产精品99久久99久久久不卡| 人人妻人人澡人人看| 精品人妻在线不人妻| 丁香六月欧美| av网站免费在线观看视频| 91字幕亚洲| 国产成人啪精品午夜网站| 国产亚洲欧美在线一区二区| a 毛片基地| 国产熟女午夜一区二区三区| 男女无遮挡免费网站观看| 黄色毛片三级朝国网站| 国产精品久久久久久人妻精品电影 | 日韩中文字幕欧美一区二区| 老司机午夜十八禁免费视频| 国产欧美日韩一区二区三 | 亚洲男人天堂网一区| 中文字幕高清在线视频| 亚洲精品日韩在线中文字幕| 亚洲成人免费av在线播放| 久久国产精品人妻蜜桃| 中文字幕另类日韩欧美亚洲嫩草| 欧美亚洲日本最大视频资源| 精品久久蜜臀av无| 亚洲精品美女久久av网站| 欧美日韩精品网址| 视频区图区小说| 考比视频在线观看| 在线观看舔阴道视频| 欧美精品人与动牲交sv欧美| 亚洲 国产 在线| 伦理电影免费视频| 欧美日韩亚洲综合一区二区三区_| 日韩中文字幕欧美一区二区| 爱豆传媒免费全集在线观看| 一二三四社区在线视频社区8| 热99国产精品久久久久久7| 99精品久久久久人妻精品| 80岁老熟妇乱子伦牲交| 精品亚洲成a人片在线观看| 久久影院123| 少妇裸体淫交视频免费看高清 | 老鸭窝网址在线观看| 成年av动漫网址| 男女国产视频网站| 欧美日韩亚洲综合一区二区三区_| 精品人妻1区二区| 亚洲情色 制服丝袜| 日韩欧美免费精品| 免费在线观看影片大全网站| 午夜成年电影在线免费观看| 免费高清在线观看日韩| 天堂俺去俺来也www色官网| 亚洲综合色网址| 美女高潮到喷水免费观看| 黑人巨大精品欧美一区二区mp4| 欧美黄色淫秽网站| 十八禁网站网址无遮挡| av免费在线观看网站| 国产区一区二久久| 亚洲精品美女久久久久99蜜臀| 在线 av 中文字幕| 国产一区二区在线观看av| 亚洲,欧美精品.| 国产精品熟女久久久久浪| 三级毛片av免费| 欧美老熟妇乱子伦牲交| 中文字幕精品免费在线观看视频| 免费在线观看黄色视频的| av视频免费观看在线观看|