• <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 ?

    多壁碳納米管-二氧化硅吸附劑對甲苯的吸附性能

    2021-07-29 05:00:16張紹鵬建偉偉馬丹竹
    燃料化學(xué)學(xué)報(bào) 2021年6期
    關(guān)鍵詞:撫順二氧化硅甲苯

    劉 微 ,李 壯 ,張紹鵬 ,建偉偉 ,馬丹竹

    (遼寧石油化工大學(xué),遼寧 撫順 113001,中國)

    Volatile organic compounds (VOCs) are ubiquitous air pollutants, which are precursors of fine particulate matter and ground level ozone[1,2].Photochemical smog, which is a mixture of pollutants(ozone, nitric acid, aldehydes, peroxyacyl nitrates(PANs), and other secondary pollutants)[3]formed when nitrogen oxides interact with VOCs, creating a brownish-gray haze above urban areas. VOCs may lead to eye, nose, and throat irritation and respiratory diseases, and some of them are highly toxic[4,5]. Because of their adverse effects on the human health and the environment[6], control and reduction of VOC concentrations have become a popular research topic in the field of environmental science and engineering.Volatile organic compounds are emitted from a variety of sources including automobile coating; 1 kg of coating releases 0.02-0.09 kg VOCs, and more household products coated with paint also generate large amounts of VOCs[7]. Volatile organic compounds include nonmethane hydrocarbons such as alkanes, olefins, and aromatic hydrocarbons, and oxygen-containing organic compounds such as aldehydes, ketones, alcohols, and ethers[8,9], halogenated hydrocarbons, nitrogenous compounds, and sulfur-containing compounds. Toluene is a widely used solvent in various applications, and thus was used as the research object in this study[5,10].

    Widely used VOC emission reduction technologies include incineration, catalytic combustion,biodegradation, plasma, photocatalysis[8], adsorption,condensation, and membrane separation[11-13]. Parmar et al[14]showed that the incineration method and the catalytic combustion method consume high energy and the products can cause secondary pollution,and the biodegradation method is time-consuming. Ulrich et al[15]use a nanoporous, hydrophobic membrane to separate VOCs from a stream of water-saturated air.Their experiments have proved that although membrane separation method is safe and pollution-free,its mass transfer rate drops very fast and requires regular cleaning, which is not suitable for the treatment of high concentration VOCs. The adsorption method is popular because of its low cost and large benefits[16-19];traditional activated carbon is widely used as an adsorbent because of its high recovery efficiency and low cost[20-23]. Han et al[24]doped silicon on activated carbon to prepare an adsorbent. The newly prepared AC-Si composite had a mesoporous structure with a specific surface area of 729 m2/g. Silicon doping improved the adsorption performance; the maximum adsorption capacity ofp-xylene was 292 mg/g, and the adsorption material was renewable. Dou et al[25]showed that the adsorption capacity of a carbon silicon composite at 25, 35, and 45 °C to remove benzene was increased by 7.5%, 9.7%, and 15.7% compared to activated carbon (AC). Mohammadi et al[26]also showed that the adsorption capacity of carbon silicon composite to remove ethylbenzene and benzene was 1.3 and 1.8 times that of AC under the same conditions,respectively.

    Compared with activated carbon, multi-walled carbon nanotubes (MWCNTs) have a highly porous and hollow structure, larger specific surface area,lighter mass density, and higher thermal and chemical stability[27]. Owing to their unique properties and potential application prospects, they have attracted widespread attention[28-33]and can be modified to improve the adsorption performance[29,31]. Su et al[34]oxidized MWCNTs in a NaOCl solution to increase their carbon purity, surface carboxyl groups, and negative charge and demonstrated that MWCNTs showed a good adsorption capacity for benzene,toluene, ethylbenzene, andp-xylene (BTEX) in aqueous solutions[30,35,36]. Ganguponu et al[37]studied the treatment of single-walled CNTs with acid oxidation to enhance the adsorption potential of their surfactants and generate more internal adsorption sites[38], and their specific surface area increased from 1136 to 1347 m2/g.The ability to absorb toluene was 1.6 times that of granular activated carbon (GAC).

    To date, only a few studies have focused on modifying MWCNTs with silicon as an effective adsorbent for VOCs. The aim of this study is to investigate the adsorption properties of silicon-doped MWCNTs for toluene. The sol-gel method was used to modify MWCNTs by loading SiO2to synthesize adsorbents CS2, CS4, and CS6 with different MWCNT molar contents. A temperature-variable fixed-bed device was established, and a dynamic VOC adsorption technique was used to comprehensively evaluate the adsorption performance of CS2, CS4, and CS6 for toluene. Based on this system, the influence of various factors (MWCNT molar content, temperature, water vapor concentration, and cycle regeneration times) on the adsorption capacity was explored, and the operating parameters were obtained when the adsorption capacity was optimal. Then, the kinetic models were fitted with experimental data, and the best adsorption kinetic model was selected.

    1 Experiments

    1.1 Material synthesis

    l g MWCNTs was placed in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid for 2 h, then the MWCNTs were separated with a centrifuge, rinsed repeatedly with deionized water to make them neutral, and finally placed in a drying oven(80 °C) for 16 h .

    MWCNTs with 2%, 4%, and 6% ethanol mass fraction were added to an adequate amount of ethanol(10 mL) and stirred for 30 min. Then, 20% of tetraethyl silicate/water solution was added followed by concentrated hydrochloric acid until the pH dropped to 2.0-3.0, and reacted for 30 min. The temperature of the solution was then raised to 40 °C, and a 10% ammonia/ethanol solution was added dropwise to form a gel.

    The surface of the gel was covered with ethanol for 24 h to prevent the reverse reaction of surface modification[39]. Then, an appropriate amount of nhexane (10 mL) was added to replace water and ethanol in the gel to reduce the surface tension of the gel. Later, a 10% trimethylchlorosilane/n-hexane solution was added dropwise to complete the surface modification. The modified MWCNTs-SiO2was dried at 50 °C, 80 °C for 2 h and at 120 °C, 150 °C for 1 h.Finally, adsorbents MWCNTs-SiO2-2, MWCNTs-SiO2-4, MWCNTs-SiO2-6 (CS2, CS4, and CS6) were obtained by reduction in nitrogen at 500 °C for 2 h.

    1.2 Parameter setting measurements

    A gas chromatograph equipped with a flame ionization detector was used to detect toluene. The carrier gas was high-purity nitrogen, and the chromatographic column was an ATOV-225 capillary column (50 m × 0.32 mm × 1 μm). The parameters were set as follows: column box temperature 80 °C,detector 230 °C, and capillary column temperature 80 °C. A standard gas with 300 mg/L toluene was passed into the pipeline and operated at a flow rate of 100 mL/min for 10 min, and 1 mL of gas was extracted with a gas injector from the injection port 15 cm away from the exhaust port. The peak of toluene was determined via gas chromatography. This operation was repeated until the peak time and peak area of toluene were stable and set as the standard curve of toluene. Similarly, inject 1 mL of the gas to be detected into the gas chromatograph, and the peak curve was compared with the toluene standard curve to determine the toluene concentration.

    1.3 Characterization methods

    The main adsorbent characterization methods used in the experiment were JEM-2100F transmission electron microscopy (TEM)[0.20 nm (accelerating voltage 200 kV)] and SU8010 scanning electron microscope (SEM)[1.0 nm (accelerating voltage 15 kV,WD = 4 mm), 1.3 nm (accelerating voltage 1 kV, WD =1.5 mm)]. The automatic physical static analysis[Brunauer-Emmett-Teller (BET) adsorption] using Autosorb-IQ2-MP calculates the total volume of pores using the data under maximum pressure[24]. Fourier transform infrared (FTIR) spectrometer of Nicolet iS50 has a spectral range of 7000-350 cm-1(host type of KBr) and 5100-600 cm-1(host type of ZnSe), resolution >2 cm-1, wavenumber accuracy of 0.05 cm-1, and wavenumber reproducibility of 0.005 cm-1.

    1.4 Dynamic adsorption process

    The experimental system (Figure 1) consists of a gas supply device, a fixed-bed equipment, and an analysis system[40]. In the experiment, N2was used as the gas source and divided through two pipes. One channel of N2produced toluene through a gas bubbler containing liquid toluene, and the other produced steam through a constant temperature water bath. The water vapor content is controlled by the N2flow rate and the temperature of the water. Quartz wool with a certain thickness is placed in the slot inside the adsorption tube to support the adsorbent. The quartz tube can be placed in a heating furnace with a programmed temperature control function to achieve accurate temperature control. The experiment was carried out on an adsorption reactor. Gas chromatograph GC-9600 (China Inesa Analytical Instrument Co., Ltd.) was used for measurement at the end of the gas supply device, and then the adsorption results were fed back through the N2000 GC data workstation (Zhejiang University,China). The experimental conditions for adsorption were as follows: VOC concentration of 700 mg/L, flow rate of 40 mL/min, and 1 g adsorbent.

    Figure 1 Experimental system

    2 Results and discussion

    2.1 Characterization

    2.1.1 TEM

    Figure 2(a) shows that the MWCNTs without any treatment are long and easy to aggregate, the surface of the MWCNTs is relatively smooth. A small amount of impurities and amorphous carbon can be observed on the surface. Figure 2(b) shows the MWCNTs after oxidation treatment in the mixed acid solution, the length of a single MWCNT became shorter than before, and the external surface of the oxidized MWCNTs was no longer smooth and the surface area was increased compared with that before oxidation treatment. In addition, a large number of oxidation openings appeared on MWCNTs, which increased the number of adsorption sites and was conducive to the adsorption of VOCs.

    Figure 2 TEM images: (a) MWCNTs, (b) purified MWCNTs

    2.1.2 SEM

    Figure 3 shows the SEM morphology of the MWCNTs-SiO2-6 adsorbent. The resolutions are 30 μm,2 μm, 1 μm, and 500 nm, respectively. Figure 3(a)displays the presence of SiO2particles, which indicates that the surface modification reaction in the MWCNTs-SiO2adsorbent has been fully completed, as also observed in the FT-IR analysis. Figure 3(b) demonstrates that the structure of the MWCNTs-SiO2adsorbent contains spherical solid clusters and shows a porous network structure. The MWCNTs loaded with SiO2were wrapped and exposed to the outside of SiO2, and hundreds of nano-sized holes were observed. Figure 3(c)depicts that SiO2and MWCNTs are combined by van der Waals forces. Figure 3(d) reveals the image of the sampling part of the Energy Dispersive Spectrometer(EDS) analysis. The EDS analysis results are: the content of Cu element accounts for about 60%, and the element C and Si each account for about 20%.

    Figure 3 SEM: (a) 30 μm, (b) 2 μm, (c) 1 μm and (d) 500 nm

    2.1.3 FT-IR

    The FT-IR characterization results of CS2, CS4,and CS6 are shown in Figure 4. FT-IR analysis indicated the completion of the surface modification of the MWCNTs. The band around at 568 cm-1belongs to the curved O-Si-O vibration. The peak vibrations around at 800 cm-1are attributed to the three modes of asymmetry, symmetry, and bending in SiO2[41]. The peaks near 845 cm-1is caused by the bending vibration of the Si-O-H hydroxyl group. The vibration band around 1095 cm-1is due to the tensile vibration of the C-O bond or the Si-O bond. The absorption peak corresponding to the CH3functional group at 1400 cm-1is very strong. Vibration of the peak near 1400 cm-1was also observed in the FT-IR spectrum, which was attributed to the C-H bond.

    Figure 4 FT-IR spectra of pattern for CS2, CS4, CS6

    The peak at 1600 cm-1in the FT-IR spectrum can be attributed to the OH group. The intensity of the OH peak in CS6 (1600 cm-1) was less than that in CS2(1600 cm-1), which indicates that CS6 is more hydrophobic. Subsequent adsorption experiments also verified this result, which is caused by the surface modification effect of trimethylchlorosilane on the aerogel of SiO2. The vibrational peaks corresponding to the Si-H bond at 2120 cm-1and 2190 cm-1were not observed in FT-IR characterization. Therefore, according to reaction formula (1), the Si-H bond of siloxane may react with acidic groups on the CNT surface. The discovery of the C-O bond or Si-O bond peak confirms this result.

    The analysis showed that the surface modification reaction in the samples containing SiO2was fully completed, and the hydrophobicity of the MWCNTs-SiO2adsorbent increased with the increasing MWCNT content. The OH peak intensity was small and hydrophobicity was strong.

    2.1.4 BET

    The pore size, specific surface area, and pore volume of CS2, CS4, CS6, and AC were compared by using the Barrett-Joyner-Halenda (BJH) model. As shown in Table 1, microporosity of the MWCNTs-SiO2adsorbent increased as the MWCNT content increased,while the total pore volume decreased. The FTIR analysis results also confirmed that the amount of supported Si(CH3)3increased with the increase in the molar content of the MWCNT, which increased the average pore diameter[26]. In general, the adsorption process relies on microporous adsorption, and microporous adsorption is controlled by the micropore surface area, which is consistent with the BET detection results (Figure 5). Therefore, the increase in hydrophobicity and the decrease in adsorption performance can be attributed to the decrease in BET surface area and micropore structure[42].

    Table 1 Textural properties of MWCNTs-SiO2 composites

    Figure 5 Nitrogen adsorption and desorption isotherms

    2.2 Adsorption performance of MWCNTs-SiO2 adsorbent

    2.2.1 Influence of temperature

    Temperature has a significant impact on the removal of VOCs by the MWCNTs-SiO2adsorption.Breakthrough measurements are typically used to analyze the adsorption performance of MWCNTs-SiO2adsorbents for VOCs. Figure 6 shows the relationship between the outlet concentration and adsorption time of toluene when AC, CS2, CS4, and CS6 are adsorbed at 30, 40, 50, and 60 °C. Figure 7 shows the relationship between adsorption time, equilibrium adsorption capacity, and adsorption rate of CS2, CS4, and CS6 at 30, 40, 50, and 60 °C. Other experimental variables were kept constant during the experiment.

    Figure 6 Influence of temperature on outlet concentration

    Figure 7 Adsorption performance of MWCNTs-SiO2 adsorbent at different temperatures

    During the entire adsorption process at the same temperature, the amount of toluene adsorbed on the MWCNTs-SiO2adsorbent was directly proportional to the MWCNT content (CS6 > CS4 > CS2 > AC), which is consistent with the micropore size of the MWCNTs-SiO2adsorbent[43]. The adsorption of MWCNTs-SiO2for toluene mainly depends on micropores, and the adsorption by micropores is controlled by the surface area of the micropores, which is in accordance with the BET detection results. As the adsorption temperature increased from 30 to 60 °C, the mass transfer rate of toluene in the MWCNTs-SiO2adsorbent decreased. For every 10 °C increase in temperature, the adsorption time of CS2 and CS6 decreased by 30 and 20 min,respectively. The adsorption capacity decreased by approximately 16 and 4 mg/g, respectively, because the structure of the MWCNTs-SiO2adsorbent is mainly microporous, and the microporous structure is conducive to the physical adsorption of toluene by MWCNTs-SiO2.

    The adsorption capacities of CS2, CS4, and CS6 for toluene are proportional to the breakthrough time.For adsorption temperatures at 30, 40, and 50 °C, the capacities of CS2, CS4, and CS6 increased by 8.08,2.87, and 2.00 mg/g, respectively, for every 10 min increase in the breakthrough time. When the adsorption temperature increases, the impact of breakthrough time on the adsorption capacity also decreases because the increase in temperature reduces the time for fully saturated adsorption[44]. Therefore, the adsorption temperature is in the range of 30-60 °C. The relatively low adsorption temperature can increase the adsorption capacity of the MWCNTs-SiO2adsorbent and prolong the breakthrough time, and the influence of temperature on adsorption capacity decreases with the increase of temperature.

    2.2.2 Influence of water vapor concentration

    In this experiment, the range of water vapor volume concentration was 1%-5%. As shown in Figure 8, AC is a hydrophilic material, and the adsorption capacity of AC decreased to 34% of the original adsorption amount when the volume concentration of water vapor was 5%. When the volume concentration of water vapor was 1%, the amount of toluene adsorbed on MWCNTs-SiO2was almost unchanged. The adsorption capacity of CS2, CS4, and CS6 for toluene decreased with increasing water vapor concentration. When the water vapor concentration was 3%, the adsorption capacities of CS2, CS4 and CS6 were 38.8, 46.28, and 47.1 mg/g, which were 92%, 93.1%, and 93.8% of those under dry conditions. When the water vapor concentration was 5%, the adsorption capacities of CS2, CS4, and CS6 were 35.8, 42.6, and 43.6 mg/g,which were 84.9%, 85.7%, and 86.9% of those under dry conditions. When the water vapor volume concentration increased by 1%, the adsorption capacity of MWCNTs-SiO2for toluene decreased by 3.5%, and the reduction of CS6 adsorption was less than that of CS2. The FTIR spectrum shows the content of OH groups; the OH peak intensity in CS6 (1600 cm-1) is less than that in CS2, indicating that the hydrophobicity of CS6 is stronger, which is consistent with the conclusion drawn from the experimental data.

    Figure 8 Influence of water vapor content on outlet concentration

    2.2.3 Analysis of adsorption kinetics

    Experimental data of toluene on the CS2, CS4,and CS6 adsorbents were fitted using the quasi first-order kinetic model[45-48], quasi second-order kinetic model[47-49], intraparticle diffusion model[50,51], and Elovich kinetic model[47,48]. The relevant parameters of model fitting are shown in Table 2.

    Table 2 Fitting related parameters of each sample model

    The results of the pseudo-first-order adsorption kinetic equation for toluene adsorption on CS2, CS4,and CS6 were fitted (Figure 9(a)). The quasi-first-order kinetic equation fitting curve of CS6 did not show a linear correlation (R2= 0.839), whileR2of CS4 was 0.900, which was higher thanR2of CS2 and CS6. The fitting of the quasi-first-order equation in the entire process has a strong linear correlation only at 50-75 min, indicating that the absorption rate in the entire process of toluene removal is not completely controlled by the absorption performance of the outer surface layer.

    Figure 9 Adsorption kinetic model fitting

    The dynamic adsorption process of toluene on CS2, CS4, and CS6 was fitted by using a quasi-secondorder equation (Figure 9(b)). Multiple fittings of the pseudo-second-order equation of CS2, CS4, and CS6 showed that CS2, CS4, and CS6 had strong linear relationships at 170-270 min, 180-260 min, and 180-260 min, withR2values of 0.997, 0.995, and 0.992, respectively. However, the deviation from the straight line in other time periods was larger, which indicates that the removal rate of toluene during the entire adsorption process is not completely dominated by the surface absorption performance. In the adsorption process, 170-270 min and 180-260 min were the stages where toluene had the fastest mass transfer rate in the sample. The fitting line of the Quasi-secondary kinetic model passed almost all data points, indicating that the dynamic process of toluene adsorption on CS2, CS4, and CS6 could be described accurately by the pseudo second-order kinetic model.

    Figure 9(c) shows the relationship betweenqtandt0.5of samples CS2, CS4, and CS6. The linear correlation between CS2, CS4, and CS6 is strong in the initial stage of absorption during the entire process, but it becomes weaker as the adsorption progresses to the later stage of the experiment. During the adsorption of toluene on CS2, CS4, and CS6, toluene diffused into the adsorbent after the active sites on the surface were completely covered, and the intraparticle diffusion played a major role in this stage. Therefore, adsorption was more relevant in the initial stage of the experiment.When the adsorption experiment progressed to the later stage, the intraparticle diffusion no longer played a major role, and the linear correlation became weaker.Table 3 shows thatR2of each sample is close to 1,indicating that the adsorption of toluene by CS2, CS4,and CS6 conforms to the intraparticle diffusion equation. Furthermore, the intraparticle diffusion rate constantkpiincreased with an increase in the MWCNT content of the adsorbent. This result can be explained by the increase in the MWCNT content of the adsorbent, which is beneficial to the adsorption of toluene.

    The fitting diagram of the Elovich kinetic equation for the dynamic adsorption of toluene on CS2,CS4, and CS6 is shown in Figure 9(d). As the molar content of MWCNTs increased,R2gradually decreased;R2of CS2, CS4, and CS6 were 0.94, 0.92,and 0.91, respectively. The desorption rate constantsβof toluene on the surface of CS2, CS4, and CS6 were 0.065, 0.059, and 0.054, respectively; the lower the MWCNT content of the MWCNTs-SiO2adsorbent, the easier the desorption. The adsorption rate constants α of toluene on the surface of CS2, CS4, and CS6 were 0.968, 0.827, and 1.003, respectively; the higher the MWCNT content, the easier the adsorption of toluene on the surface.

    2.2.4 Recycling performance

    The inability of an adsorbent to be recycled and reused has always been an important factor that restricts its industrialization. In this study, the solvent extraction-heat treatment method was used to regenerate the MWCNTs-SiO2adsorbent. The specific operation scheme is as follows: first, the saturated MWCNTs-SiO2adsorbent was immersed in ethanol for 1 h. Then, the liquid on the surface of the MWCNTs-SiO2adsorbent was evacuated with a syringe, and the MWCNTs-SiO2adsorbent soaked in ethanol was placed in a drying oven at 80 °C until the absolute ethanol and toluene in the micropores of the adsorbent were completely removed.

    The adsorption-regeneration cycle was repeated seven times (Figure 10), and the adsorption experiment of toluene was carried out using CS6 at 30 °C. The regenerated CS6 was analyzed using FT-IR. Figure 11 shows the change in the adsorption capacity of CS6 after regeneration. The adsorption capacity of CS6 for toluene was 50.28 mg/g, which was reduced to 44 mg/g after the first regeneration and no less than 87% of that before regeneration. After seven regenerations, the adsorption capacity of CS6 for toluene was not less than 73% of the original capacity. Therefore, the pore structure of CS6 showed no obvious changes after regeneration, which suggests that MWCNTs-SiO2adsorbs toluene mainly by physical adsorption. Figure 12 shows the FT-IR detection results of CS6 after solvent extraction and heat treatment. The FT-IR analysis of the regenerated MWCNTs-SiO2adsorbent did not change significantly. The structure of MWCNTs-SiO2was not changed by this method, the width of the C-O or Si-O bond widened, and the strength of the O-Si-O and CH3functional groups decreased significantly.Hence, the decrease in the number of O-Si-O and CH3functional groups is the likely reason for the decrease in the adsorption capacity. In addition to micropores,the MWCNTs-SiO2adsorbent also uses O-Si-O and CH3functional groups on the surface to adsorb toluene.The OH group peak at 1600 cm-1confirms that the MWCNTs-SiO2adsorbent remains hydrophobic after regeneration.

    Figure 10 Regeneration performance of CS6

    Figure 11 Adsorption capacity of CS6 after regeneration

    Figure 12 FT-IR spectra of pattern for CS6

    3 Conclusions

    Three types of MWCNTs-SiO2adsorbents were prepared by using the sol-gel method and analyzed by TEM, SEM, BET, and FT-IR. The adsorption performance of adsorbents AC, CS2, CS4, and CS6 for toluene were studied in a fixed-bed device. The effects of temperature and water vapor concentration on the adsorption process were explored, and the cyclic regeneration performance was investigated. The results can be summarized as follows:

    High temperature and water vapor inhibit the adsorption of toluene onto the MWCNTs-SiO2adsorbent. Within 30-60 °C, the toluene adsorption capacity of the adsorbent was AC < CS2 < CS4 < CS6.Under optimal conditions (7 × 10-4toluene, 0 H2O, 30°C, and 100 mL/min), the adsorption capacity of CS6 was 50.28 mg/g. The breakthrough time decreased by 10-20 min when the temperature increased by 10 °C,and the adsorption content decreased by 3.5% when the water vapor concentration increased by 1%.

    The rate of adsorption of toluene on the MWCNTs-SiO2adsorbent was not completely controlled by the adsorption reaction of the outer surface layer. When toluene diffused into the adsorbent,intraparticle diffusion played a major role in the adsorption process.

    The MWCNTs-SiO2adsorbent showed satisfactory recycling performance. FTIR characterization indicated that the surface chemical functional groups of the regenerated MWCNTs-SiO2adsorbent remained unchanged. After seven cycles of regeneration, the adsorption capacity was still no less than 73% of the original adsorption capacity.

    The results of this study suggest that the MWCNTs-SiO2adsorbent has a great potential to control VOC emissions.

    猜你喜歡
    撫順二氧化硅甲苯
    撫順平頂山慘案紀(jì)念館
    高效液相色譜法測定降糖藥甲苯磺丁脲片中甲苯磺丁脲的含量
    1-(對甲苯基)-2-(三對甲苯基-5-亞磷?;?乙醛的汞(Ⅱ)配合物的X射線晶體學(xué)、光譜表征和理論計(jì)算研究
    圖說撫順琥珀(六)
    中國寶玉石(2018年3期)2018-07-09 03:14:02
    姜黃提取物二氧化硅固體分散體的制備與表征
    中成藥(2018年2期)2018-05-09 07:19:43
    氨基官能化介孔二氧化硅的制備和表征
    齒科用二氧化硅纖維的制備與表征
    介孔二氧化硅制備自修復(fù)的疏水棉織物
    甲苯-4-磺酸催化高效合成尼泊金正丁酯防腐劑
    萃取精餾分離甲苯-正庚烷混合物的模擬研究
    少妇高潮的动态图| 这个男人来自地球电影免费观看 | 午夜影院在线不卡| 亚洲无线观看免费| 国产精品一区二区在线观看99| 亚洲av二区三区四区| 亚洲国产欧美日韩在线播放 | 秋霞伦理黄片| 亚洲欧美一区二区三区国产| 18禁在线播放成人免费| 亚洲美女黄色视频免费看| 日韩熟女老妇一区二区性免费视频| 国产成人精品一,二区| 在线观看免费高清a一片| 久久综合国产亚洲精品| 九色成人免费人妻av| 菩萨蛮人人尽说江南好唐韦庄| 在线观看免费日韩欧美大片 | 亚洲精品乱码久久久久久按摩| 99久久精品热视频| 六月丁香七月| 蜜桃久久精品国产亚洲av| a级片在线免费高清观看视频| 夜夜看夜夜爽夜夜摸| 成人黄色视频免费在线看| 大片电影免费在线观看免费| 亚洲va在线va天堂va国产| 亚洲精品中文字幕在线视频 | 精品久久久久久电影网| 亚洲高清免费不卡视频| 久久久久久久大尺度免费视频| 欧美一级a爱片免费观看看| av福利片在线观看| 久久久久久久久大av| 成人漫画全彩无遮挡| 五月天丁香电影| 国产日韩欧美亚洲二区| 美女脱内裤让男人舔精品视频| 久久久久精品久久久久真实原创| 国产成人免费无遮挡视频| 日本黄色片子视频| 伦精品一区二区三区| 久久热精品热| 国产高清国产精品国产三级| 久久人人爽人人片av| h视频一区二区三区| 精品国产露脸久久av麻豆| 欧美日韩在线观看h| 国产成人91sexporn| 国产男女内射视频| 亚洲婷婷狠狠爱综合网| 国产黄色视频一区二区在线观看| 另类亚洲欧美激情| 日产精品乱码卡一卡2卡三| 有码 亚洲区| 精品一区二区三区视频在线| 中文字幕久久专区| 伊人亚洲综合成人网| 爱豆传媒免费全集在线观看| 热99国产精品久久久久久7| 国产亚洲av片在线观看秒播厂| h日本视频在线播放| 精品国产乱码久久久久久小说| 久久精品久久精品一区二区三区| 黑人巨大精品欧美一区二区蜜桃 | 免费看不卡的av| 男的添女的下面高潮视频| 五月玫瑰六月丁香| 男人爽女人下面视频在线观看| 国产成人精品一,二区| 欧美三级亚洲精品| 一级毛片电影观看| 婷婷色av中文字幕| 一个人看视频在线观看www免费| 国产精品偷伦视频观看了| 搡老乐熟女国产| 国产中年淑女户外野战色| 日韩一区二区视频免费看| 我的老师免费观看完整版| 亚洲国产欧美在线一区| 精品人妻熟女av久视频| 色5月婷婷丁香| 在线观看免费日韩欧美大片 | 韩国av在线不卡| 97超碰精品成人国产| 久久热精品热| 99九九线精品视频在线观看视频| 视频区图区小说| 99九九线精品视频在线观看视频| 特大巨黑吊av在线直播| av福利片在线观看| 午夜激情久久久久久久| 丰满饥渴人妻一区二区三| 国产伦理片在线播放av一区| 久久久久精品久久久久真实原创| 男男h啪啪无遮挡| 国产欧美日韩一区二区三区在线 | 一区二区三区精品91| 最近最新中文字幕免费大全7| 国产亚洲最大av| 久久午夜福利片| 一级黄片播放器| 免费黄网站久久成人精品| 麻豆成人av视频| 久久人妻熟女aⅴ| av福利片在线| 偷拍熟女少妇极品色| 国产成人免费无遮挡视频| 男人狂女人下面高潮的视频| 亚洲丝袜综合中文字幕| 亚洲第一区二区三区不卡| 久久久久久伊人网av| 青春草亚洲视频在线观看| 女性被躁到高潮视频| 精品99又大又爽又粗少妇毛片| 成年女人在线观看亚洲视频| 黄色一级大片看看| 寂寞人妻少妇视频99o| 亚洲精品日韩在线中文字幕| 亚洲天堂av无毛| 亚洲av.av天堂| 狂野欧美激情性xxxx在线观看| 狂野欧美激情性xxxx在线观看| 校园人妻丝袜中文字幕| 人妻人人澡人人爽人人| 51国产日韩欧美| 人妻系列 视频| 免费看日本二区| 一级毛片aaaaaa免费看小| 国产成人精品久久久久久| 一级毛片电影观看| 在线亚洲精品国产二区图片欧美 | 久久精品国产自在天天线| 少妇猛男粗大的猛烈进出视频| 内地一区二区视频在线| 两个人的视频大全免费| 久久精品久久精品一区二区三区| 亚洲第一av免费看| 久久99蜜桃精品久久| 久久青草综合色| 熟妇人妻不卡中文字幕| 你懂的网址亚洲精品在线观看| 爱豆传媒免费全集在线观看| 久久久久国产精品人妻一区二区| 不卡视频在线观看欧美| 免费不卡的大黄色大毛片视频在线观看| 亚洲欧美中文字幕日韩二区| 高清视频免费观看一区二区| 桃花免费在线播放| 丝袜脚勾引网站| 日韩欧美一区视频在线观看 | 老司机影院成人| 国产伦精品一区二区三区四那| 国产极品天堂在线| 热re99久久国产66热| 高清毛片免费看| 在线天堂最新版资源| 99久久中文字幕三级久久日本| 日韩欧美精品免费久久| 日韩精品免费视频一区二区三区 | 国产午夜精品一二区理论片| 国内揄拍国产精品人妻在线| 精品人妻熟女av久视频| 成人免费观看视频高清| 久久人人爽人人爽人人片va| 国产69精品久久久久777片| 十八禁网站网址无遮挡 | 亚洲av在线观看美女高潮| 九九在线视频观看精品| 777米奇影视久久| 黄色视频在线播放观看不卡| 欧美+日韩+精品| 日韩中字成人| 2021少妇久久久久久久久久久| 国产欧美日韩精品一区二区| 国产极品粉嫩免费观看在线 | 男男h啪啪无遮挡| 在线观看一区二区三区激情| 欧美亚洲 丝袜 人妻 在线| 午夜免费鲁丝| 午夜影院在线不卡| 91aial.com中文字幕在线观看| 啦啦啦视频在线资源免费观看| 麻豆精品久久久久久蜜桃| kizo精华| 亚洲av日韩在线播放| 久久精品久久久久久噜噜老黄| 校园人妻丝袜中文字幕| 国产免费一区二区三区四区乱码| 国产亚洲一区二区精品| 99热这里只有精品一区| 久热这里只有精品99| 亚洲,欧美,日韩| 高清黄色对白视频在线免费看 | 国产中年淑女户外野战色| 亚洲精品色激情综合| 国产av精品麻豆| 五月伊人婷婷丁香| 国产黄片视频在线免费观看| 久久人人爽av亚洲精品天堂| 亚洲高清免费不卡视频| 18禁动态无遮挡网站| 日韩电影二区| 色94色欧美一区二区| 精品国产一区二区久久| 国产综合精华液| 亚洲精品456在线播放app| 人妻制服诱惑在线中文字幕| 日韩精品有码人妻一区| 久久97久久精品| 三级国产精品片| 男女无遮挡免费网站观看| 精品酒店卫生间| 日日啪夜夜撸| 精品久久久久久久久av| 少妇 在线观看| 看免费成人av毛片| 亚洲av成人精品一二三区| 能在线免费看毛片的网站| tube8黄色片| 亚洲第一区二区三区不卡| 又粗又硬又长又爽又黄的视频| 婷婷色综合www| 久久久久久久大尺度免费视频| 欧美激情国产日韩精品一区| 日本av免费视频播放| 日韩中文字幕视频在线看片| 男女边吃奶边做爰视频| 欧美 亚洲 国产 日韩一| 国产在线一区二区三区精| 日韩在线高清观看一区二区三区| 久久久久久久久久成人| 日本与韩国留学比较| 久久久久久伊人网av| 18禁在线无遮挡免费观看视频| 内地一区二区视频在线| 亚洲成色77777| 日韩av在线免费看完整版不卡| 精华霜和精华液先用哪个| 一级二级三级毛片免费看| 九九爱精品视频在线观看| 色网站视频免费| 精品国产乱码久久久久久小说| av一本久久久久| 男人爽女人下面视频在线观看| 一区二区三区乱码不卡18| 亚洲美女搞黄在线观看| 国产成人午夜福利电影在线观看| 久久久久久久久久人人人人人人| 少妇人妻 视频| 久久6这里有精品| 成人二区视频| 色5月婷婷丁香| 色网站视频免费| 亚洲国产精品专区欧美| 人人澡人人妻人| 亚洲四区av| 老女人水多毛片| 成人免费观看视频高清| 国内揄拍国产精品人妻在线| 在线观看美女被高潮喷水网站| 国产精品久久久久久精品电影小说| 日韩欧美一区视频在线观看 | 美女视频免费永久观看网站| 男人舔奶头视频| 亚洲欧美清纯卡通| 亚洲经典国产精华液单| 久久99热这里只频精品6学生| 大又大粗又爽又黄少妇毛片口| 久久精品久久久久久噜噜老黄| 在线免费观看不下载黄p国产| 国产成人freesex在线| 大片电影免费在线观看免费| 少妇精品久久久久久久| 亚洲美女视频黄频| 青春草国产在线视频| 国产精品久久久久久久电影| 午夜老司机福利剧场| 日日摸夜夜添夜夜添av毛片| 国产精品三级大全| 中文字幕久久专区| 国产亚洲91精品色在线| 国产91av在线免费观看| 亚洲精品视频女| 国产在视频线精品| 国产av码专区亚洲av| 免费大片18禁| 久久久欧美国产精品| 欧美精品国产亚洲| 久久久久久久亚洲中文字幕| 国产成人91sexporn| 亚洲精品中文字幕在线视频 | 欧美 亚洲 国产 日韩一| 国产欧美亚洲国产| 黄色怎么调成土黄色| 少妇被粗大的猛进出69影院 | 亚洲成人av在线免费| 亚洲国产精品一区三区| 国产又色又爽无遮挡免| 有码 亚洲区| 国产精品麻豆人妻色哟哟久久| 国产精品无大码| 亚洲欧美中文字幕日韩二区| 亚洲av日韩在线播放| 精品久久久精品久久久| 国产精品一区二区三区四区免费观看| 观看美女的网站| 97超碰精品成人国产| 免费不卡的大黄色大毛片视频在线观看| 三上悠亚av全集在线观看 | 国产无遮挡羞羞视频在线观看| 色网站视频免费| 亚州av有码| 建设人人有责人人尽责人人享有的| 日本-黄色视频高清免费观看| 中文字幕av电影在线播放| 国产色婷婷99| 亚洲天堂av无毛| 王馨瑶露胸无遮挡在线观看| 日本黄色日本黄色录像| xxx大片免费视频| a 毛片基地| 国产有黄有色有爽视频| 成人无遮挡网站| 欧美日本中文国产一区发布| 亚洲情色 制服丝袜| 久久久欧美国产精品| 日韩中文字幕视频在线看片| 丝袜喷水一区| 我的女老师完整版在线观看| 又爽又黄a免费视频| 久久久久精品久久久久真实原创| 在线亚洲精品国产二区图片欧美 | 偷拍熟女少妇极品色| 99久久精品一区二区三区| 亚洲av.av天堂| 自线自在国产av| 国产真实伦视频高清在线观看| 亚洲欧美一区二区三区国产| 久久久亚洲精品成人影院| 国产精品熟女久久久久浪| 九九在线视频观看精品| av卡一久久| 精品人妻熟女毛片av久久网站| 成人特级av手机在线观看| 在线观看一区二区三区激情| 又粗又硬又长又爽又黄的视频| 老女人水多毛片| 精品久久久久久电影网| 亚洲av在线观看美女高潮| 人人妻人人澡人人看| 国产精品久久久久久久久免| 日本午夜av视频| 男人狂女人下面高潮的视频| 欧美日韩av久久| 国产成人精品无人区| 大香蕉97超碰在线| 国产免费福利视频在线观看| 亚洲国产色片| 男的添女的下面高潮视频| 国产精品熟女久久久久浪| 亚洲第一区二区三区不卡| 最后的刺客免费高清国语| 人人妻人人澡人人爽人人夜夜| 久久 成人 亚洲| 国产探花极品一区二区| 校园人妻丝袜中文字幕| 日韩,欧美,国产一区二区三区| 亚洲av电影在线观看一区二区三区| h视频一区二区三区| 国产亚洲91精品色在线| 久久久精品免费免费高清| 一级a做视频免费观看| 欧美97在线视频| 中国三级夫妇交换| 久久久国产欧美日韩av| 高清av免费在线| 男人添女人高潮全过程视频| 一级片'在线观看视频| 久久国产精品男人的天堂亚洲 | av福利片在线| 纯流量卡能插随身wifi吗| 欧美日韩精品成人综合77777| 99热6这里只有精品| 国产永久视频网站| 亚洲人与动物交配视频| av播播在线观看一区| 久久人人爽人人片av| 男女边摸边吃奶| 少妇人妻精品综合一区二区| 国产极品天堂在线| 国产无遮挡羞羞视频在线观看| 午夜av观看不卡| 丰满饥渴人妻一区二区三| 只有这里有精品99| 丝袜在线中文字幕| 成人国产麻豆网| 伊人久久国产一区二区| 各种免费的搞黄视频| 国产色爽女视频免费观看| xxx大片免费视频| 黄色欧美视频在线观看| 一级a做视频免费观看| 久久精品熟女亚洲av麻豆精品| 国产精品免费大片| 国产又色又爽无遮挡免| 欧美日韩视频高清一区二区三区二| 午夜福利,免费看| 久久综合国产亚洲精品| 黄色配什么色好看| 毛片一级片免费看久久久久| 精品熟女少妇av免费看| 人妻少妇偷人精品九色| 亚洲精品日韩在线中文字幕| 青春草国产在线视频| 亚洲精品日韩av片在线观看| 精品99又大又爽又粗少妇毛片| 精品久久久久久电影网| av在线老鸭窝| 日韩av免费高清视频| a级一级毛片免费在线观看| 亚洲精品国产成人久久av| 国产精品不卡视频一区二区| 校园人妻丝袜中文字幕| 亚洲av二区三区四区| 国语对白做爰xxxⅹ性视频网站| 日本免费在线观看一区| 老司机影院成人| 91久久精品电影网| 亚洲欧美日韩另类电影网站| 婷婷色综合大香蕉| 亚洲精品乱码久久久v下载方式| www.色视频.com| 亚洲国产毛片av蜜桃av| 国国产精品蜜臀av免费| 伊人久久精品亚洲午夜| 精品卡一卡二卡四卡免费| 国产av精品麻豆| 亚洲av免费高清在线观看| 久久久亚洲精品成人影院| 日韩一区二区三区影片| 最黄视频免费看| 久久久久久人妻| 我的女老师完整版在线观看| 一级毛片aaaaaa免费看小| 亚洲精品国产成人久久av| 中文资源天堂在线| 精品少妇久久久久久888优播| 少妇高潮的动态图| 亚洲av免费高清在线观看| 美女大奶头黄色视频| 99热6这里只有精品| av免费观看日本| 蜜桃久久精品国产亚洲av| 国产成人免费观看mmmm| 男人添女人高潮全过程视频| 成人亚洲欧美一区二区av| 一级毛片电影观看| 十八禁网站网址无遮挡 | 日本免费在线观看一区| 水蜜桃什么品种好| 欧美日韩在线观看h| 丝瓜视频免费看黄片| 我的女老师完整版在线观看| 免费人成在线观看视频色| 成人漫画全彩无遮挡| 九草在线视频观看| 婷婷色综合www| 91午夜精品亚洲一区二区三区| 99热这里只有是精品在线观看| 精品久久久久久久久亚洲| 婷婷色av中文字幕| 最新中文字幕久久久久| 亚洲国产毛片av蜜桃av| 国产视频首页在线观看| 性高湖久久久久久久久免费观看| 99久国产av精品国产电影| 伊人亚洲综合成人网| a级毛色黄片| 亚洲欧美成人综合另类久久久| 久久久国产欧美日韩av| 男女国产视频网站| 国产在线免费精品| 日韩免费高清中文字幕av| 亚洲激情五月婷婷啪啪| 中文字幕亚洲精品专区| 日韩三级伦理在线观看| 大又大粗又爽又黄少妇毛片口| 偷拍熟女少妇极品色| 少妇高潮的动态图| 麻豆成人午夜福利视频| 观看av在线不卡| 久久久a久久爽久久v久久| 伦理电影免费视频| 人人妻人人澡人人爽人人夜夜| 国产淫片久久久久久久久| 国产精品久久久久成人av| 高清黄色对白视频在线免费看 | 久久久久精品久久久久真实原创| 99热这里只有是精品50| 国产精品一区二区在线不卡| 国产白丝娇喘喷水9色精品| 春色校园在线视频观看| 国产精品偷伦视频观看了| 国产精品蜜桃在线观看| 十分钟在线观看高清视频www | 自拍欧美九色日韩亚洲蝌蚪91 | 人人澡人人妻人| 色94色欧美一区二区| 五月天丁香电影| 国产精品福利在线免费观看| av线在线观看网站| 亚洲av福利一区| 中文资源天堂在线| 99九九在线精品视频 | 免费看日本二区| 美女国产视频在线观看| 亚洲丝袜综合中文字幕| 91精品国产国语对白视频| 免费观看在线日韩| 建设人人有责人人尽责人人享有的| 亚洲欧美成人综合另类久久久| 亚洲丝袜综合中文字幕| 国产综合精华液| 久久国产精品大桥未久av | 日本午夜av视频| 国产高清三级在线| 9色porny在线观看| 国产有黄有色有爽视频| 人妻系列 视频| 七月丁香在线播放| 欧美97在线视频| 午夜免费鲁丝| 永久网站在线| 特大巨黑吊av在线直播| 国产男人的电影天堂91| 精品少妇黑人巨大在线播放| 国产精品久久久久成人av| 建设人人有责人人尽责人人享有的| 婷婷色综合大香蕉| 久久国产精品男人的天堂亚洲 | 亚洲av福利一区| 欧美变态另类bdsm刘玥| 午夜福利视频精品| 欧美精品人与动牲交sv欧美| 欧美日韩亚洲高清精品| 国产精品三级大全| 成人免费观看视频高清| 国产 精品1| 婷婷色综合大香蕉| 青春草视频在线免费观看| 搡老乐熟女国产| 国产精品一区二区在线观看99| 亚洲欧美日韩另类电影网站| 菩萨蛮人人尽说江南好唐韦庄| 成人午夜精彩视频在线观看| 中文字幕av电影在线播放| 永久免费av网站大全| 国产爽快片一区二区三区| 久久久国产一区二区| 国产欧美亚洲国产| 丝袜脚勾引网站| 日本wwww免费看| 午夜免费男女啪啪视频观看| av国产久精品久网站免费入址| 91午夜精品亚洲一区二区三区| 久久久久久久久久久丰满| a级毛片免费高清观看在线播放| 伊人久久精品亚洲午夜| 国产老妇伦熟女老妇高清| 又大又黄又爽视频免费| 欧美变态另类bdsm刘玥| 国产免费一区二区三区四区乱码| freevideosex欧美| 欧美精品高潮呻吟av久久| 欧美日韩视频高清一区二区三区二| 大话2 男鬼变身卡| 国产美女午夜福利| 亚洲av.av天堂| 午夜福利,免费看| 在线 av 中文字幕| 久久精品久久久久久噜噜老黄| 人妻 亚洲 视频| 国语对白做爰xxxⅹ性视频网站| av在线观看视频网站免费| 一个人免费看片子| 91在线精品国自产拍蜜月| 永久免费av网站大全| 熟妇人妻不卡中文字幕| 我要看日韩黄色一级片| 精品熟女少妇av免费看| 极品教师在线视频| 国产精品三级大全| 国产av码专区亚洲av| 妹子高潮喷水视频| av又黄又爽大尺度在线免费看| 免费看光身美女| 日韩 亚洲 欧美在线| 国产成人91sexporn| 麻豆成人av视频| 中文乱码字字幕精品一区二区三区| 亚洲美女视频黄频| 国产精品不卡视频一区二区| 国产精品久久久久成人av| av免费观看日本| 久久毛片免费看一区二区三区| 国语对白做爰xxxⅹ性视频网站| 国产一区二区三区av在线| 午夜免费观看性视频| 精品卡一卡二卡四卡免费| 有码 亚洲区| 女性生殖器流出的白浆| 色视频在线一区二区三区| 免费观看av网站的网址| 精品99又大又爽又粗少妇毛片|