《学术论文写作》课程论文题目The preparation of TiO2 aerogel byambient pressure drying and its performance ofphotocatalytic degradation of oily wastewater学生姓名学号教学院系研究生学院专业年级2013级材料化学工程指导教师职称副教授单位辅导教师职称单位材料科学与工程学院完成日期2013 年12 月 1 日摘要以钛酸四丁酯(TBT)为原料, 利用溶胶–凝胶法、小孔干燥和老化液浸泡工艺在常压下制备出了完整、无开裂的TiO2 气凝胶块体. 研究了小孔干燥和老化液浸泡技术对常压制备TiO2 气凝胶的影响, 研究结果表明: 小孔干燥能够降低TiO2 醇凝胶干燥过程中所受的不均匀收缩应力, 而TBT 醇溶液和TEOS 醇溶液浸泡处理, 能够增强凝胶的骨架强度, 有助于减轻凝胶在干燥过程中的收缩和开裂, 制备出完整的高性能TiO2 气凝胶块体. 基于小孔干燥和TEOS 乙醇溶液浸泡老化处理, 制备得到的高性能完整TiO2 气凝胶块体, 其密度为0.184 g/cm3, 比表面积达389.5 m2/g. 用高温煅烧后的锐钛矿相TiO2 气凝胶催化降解渤海原油污水模拟溶液, 在TiO2 气凝胶加入量为 400 mg/L 的情况下, 90 min 内对渤海原油污水的去除率最高可达91%.关键词：TiO2 气凝胶; 常压; 小孔干燥; 老化液; 光催化; 原油降解AbstractThe monolithic TiO2 aerogel was sucessfully synthesized at ambient pressure throughtechnique with TBT as the raw material and its photocatalyst property forwas investigated .During the ambient drying process, aging liquor and pinhole drying technology were found to be critical to the properties of TiO2 aerogels.in the drying process and the TEOS-Ethanol or TBT-Ethanol solution as the liquor for TiO2 wet-gel could enhance the strength of TiO2 gel skeleton .these effects, and the high-performance TiO2 aerogel monolith was eventually achieved. The most integrated TiO2 aerogel block exhibited low density (0.184 g/cm3) and high specific surface area (389.5 m2/g). By calcinations at high temperature, the TiO2changed from amorphous to anatase structure. The photocatalytic properties of heat-treated TiO2 aerogels were investigated via aqueous emulsion of crude oil in the Bohai Sea. The results of experiments showed that the catalytic degradation rate was up to 91% withaddition of TiO2 aerogel of 400 mg/L.Key words: crude oil degradationContents摘要 (2)Abstract (3)1. Introduction (5)2. Literature review (6)3.Methodology (6)4. Result and Discussion (8)5. Conclusion (15)Reference (16)1.Introductionthe development of modern industry, society and economy,’the demand for energy is growing, the oil exploration, transportation and refining process generated a lot of oily wastewater, causing serious a serious impact on the environment .To make a effective treatment of oily wastewater has become an urgent need to solve the environmental problems.The traditional youngest segment ( ramp degreasing, plus flotation select and walnut shell filter oil ) and other physical treatment , although ,can remove a lot of oil in oily water , but the treated sewage is still a high oil content. What is more, the traditional processing techniques , stay a long time , large equipment volume , large dependence on the demulsifier ,is not suitable for the development of marginal oil fields as needed. Since 1972,Fujishima and Honda et al [1] found that TiO 2 surface water by radiation can continued oxidation-reduction reaction, The photocatalytic reaction based bandgap semiconductor materials has been more widely appreciated by people. Because of the high photocatalytic efficiency , non-toxic , non-polluting ,low price and other features,in recent years, the useing of nano-TiO2 to make a photocatalytic degradation of various organic and inorganic pollutants for environmental pollution, aroused great interest of researchers [4-5] . Since 2002 Ziolli et al [6 ] reported a nano TiO2 photocatalytic degradation of the performance of the Brazilian oil sewage , subsequently many scholars [7-8]studied experimentally,they found that nano-TiO2 has a very excellent photocatalytic degradation performance to the oily wastewater : speed degradation , high degradation rate , low energy consumption , mild reaction conditions , simple operation , wide application, no secondary pollution .But the nano- TiO2 is difficult to be recycled , difficult to promote practical application in industry.For this reason, in recent years many people carried out a load TiO 2 and aphotocatalytic TiO 2 films research [ 8-9 ] , These methods can solve the problem of recovery of the TiO 2, but reduces the effective surface area of TiO2, thereby reducing the photocatalytic efficiency.2.Literature reviewNano- TiO2 aerogel is a porous material ,not only has the independent features of nano TiO2 nanoparticles but also has ultra-high surface area ,and it can be prepared in a complete block structure, which can be solved the problem of difficult to recover when used as a catalyst [ 10 ] , but the traditional TiO2 aerogel were prepared by supercritical drying process , which is high production cost , poor security, and difficult industrial production .[ 11-12 ] .In recent years , solvent replacement ,surfacemodification, technology made a breakthrough [ 13-14 ] , so that researchersexplore the ambient pressure drying for preparing SiO2 aerogel [ 15-16 ] .the reason that the network skeleton of TiO2is weaker than the SiO2. In addition TiO2 aerogel Shrinked and cracked serious , it has been difficult to prepare complete at atmospheric pressure. This work treated TBT as titanium source , based on the sol -with a dry hole and the old of liquid immersion techniqueat atmospheric pressure drying complete no cracking of TiO2 put it to thecrude sewage, and achieved good results.3.1 Preparation of TiO2 aerogels5 mL of tetrabutyltitanate (TBT, AR, Beijing Chemical test Agent Factory) was dissolved in 15 mL of anhydrous ethanol (AR, West Long Chemical Reagent),Then added 0.5 mL of glacial acetic acid, magnetic stirring to form solution A. 2 mL of deionized water was added 10 mL of anhydrous ethanol, was stirred to form solution B . Then B solution was added dropwise to a state of stirring solution A. After A was formed sol, add 2 mL formamide (AR, of West Long Learn Reagent Factory) as a dry chemical control agents. After continue stirring for 3 min, injected into the sol in a cylindrical polypropylene molds, and the mold was sealed with plastic wrap. After the rest period of time at room temperature, then we can get the milky TiO2 alcohol gel.Place gel TiO2 alcohol at room temperature for 1 day, put it into the anhydrouswere then immersed in absolute ethanol, tetrabutyl titanate Ester (TBT) solution of alcohol (ethanol and the volume ratio of 10:1 TBT),tetraethoxysilane (TEOS)in an alcohol solution (by volume of ethanol and TEOS 10:1), and in an environment of 50 ℃soaking 3 d, more daily for once soaked solution gel wassoaked after treatment with anhydrous alcohol washed three times, each time to soak at least 24 h at 50 ℃ environment, soak the gel in a solution to the remaining clean. After washing TiO2alcohol gel placed in an open container or hole polypropylene (container c over open a φ1 ~ 2 mm hole) and then turn on the TiO2 alcogel room temperature, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃ under various drying 2 d, Then we can get dried TiO2 airgel blocks.3.2 Photocatalytic TiO2 airgel performance testSodium naphthenate as emulsifier, the Bohai oil (heavy oil) emulsion to 100 mg / L of oily wastewater simulation solution each time taking 0.16 g calcined after crystallization firing TiO2 airgel was added to a mixture of 400 mL water,and kept stirred using a stirrer while open excitation light source (a100 W high-pressure mercury lamp and three 8 W UV lamp (254 nm)).Every so often take a certain volume of the mixture, still in the dark put 2 h later, supernatant was extracted with an equal volume of chloroform its in oil, and then centrifuged at 2500 r / min speed of from Heart 15 min, supernatant using UV-2802PC UV - can see spectrophotometer test solution concentration of crude oil, and then according to the formula as follow can be calculated at any time illumination of the Bohai oil TiO2 aerogels The degradation rate.Ct/Co-1%100/Ct-Co%=⨯=Co）（ηIn the formula, η% said oil degradation rate at time t, C0 is mixed with water the concentration of a mixed solution of the initial time, Ct is adding TiO2 aerogels, open concentration at time t after the mixture of oil and water sources.4.Result and Discussion4.1 Effect of atmospheric holes dried preparation of TiO2 aerogelsFig.1 is a sample photograp of which were dried in an ordinary open container and container holes TiO2 gel. From Fig.1,in general open container the drying TiO2 gel broken into many small pieces, shrunk serious; in the small port container,the drying TiO2 gel looked more complete,only in the middle of the had cracks, and the Shrinkage was l ess than the former.Fig.1 Photographs of TiO2 aerogel dryed at ambient pressure (a) Open container; (b) Pinhole containerCompared with formerstudythe two kinds of TiO2 gel which achieved in diffierent conditions. From the data of the table , compared with an open container the aerogels obtained inholes drying method having a lower density and higher specific surface area (167.5 m2 / g). The results indicats that the holes drying method has a good effect to prevent the gel from Shrinkage and cracking. This is mainly due to the drying rate of the gel and the partial pressure of the ethanol vapor. In an open container , the partial pressure of the ethanol in the container was the same with the environment, which was much lower than ethanol saturated vapor pressure , so the evaporation rate of ethanol is quickly, and the skeleton structure of alcohol gel is exposed to the large instantaneous stress. If the skeleton structure was uneven, the gel would be subject to greater uneven stress and then crack; but in the hole container, for the ethanol molecules evaporated from alcogel cannot spread to the external environment soon, the ethanol steam partial pressure in the container gets closer and closer to the saturated vapor pressure along with the evaporation of fluid ethanol in the gel pores. Thus the evaporation speed of the ethanol and drying speed of alcogel were reduced, which decreased the gel contraction and lowered the possibility of cracking, because the instantaneous compressive stress of the gel network skeleton also has been reduced in the whole drying process of alcogel.4.2 The function of the aging soaking to the atmospheric drying TiO2 aerogelsThe Fig.2 are the TiO2 gels used ethanol, TBT / ethanol solution, TEOS / ethanol solution as aging conservation soaking respectively, and at hole pressure drying. In pure ethanol solution, the TiO2 is translucentthe; and after soaking dried in the TBT and TEOS alcohol, the TiO2 aerogel is pale yellow and completely opaque. What is more, the TiO2 aerogel soaking dried in TBT / ethanol solution cracked into two parts along the center of the sample, and the TiO2 which was soakingdried in theTEOS/ethanol had a perfect appearance and no cracks.Fig.2 Photographs of TiO2 aerogel aged in different liquors (a) Ethanol; (b) TBT-Ethanol solution;(c) TEOS-EthanolTable 2 lists the different aging immersion liquid was prepared TiO2 physical performance parameters of airgel, seen from the data in the table, after TBT after the ethanol solution and soaking TEOS ethanol solution, TiO2 alcohol condensate glue drying shrinkage than pure ethanol produced by soaking samples significantly reduced, airgel prepared by soaking only significantly lower than the density of pure ethanol after drying the airgel samples, the specific surface area is soaked in pure ethanol a substantial increase in the airgel sample, which shows that TBT ethanol solution and TEOS solution in ethanol solution as aging, can be significantly reduced wet TiO2 gel contraction in atmospheric drying process, effectively preventing alcohol gel cracking during the drying process, especially upon aging as TEOS conservation ethanol solution was prepared to give a complete, non-cracking of theprepared TiO2 the body, the density of only 0.184 g/cm3, a specific surface area of 389.5 m2 / g. Such as density and Kucheyev the airgel blocks [17] using CO2 super- TiO2 critical density complete the drying process of the preparation of airgel blocks similar (0.18 g/cm3), the specific surface area above the supercritical drying process technology the specific surface area of aerogels prepared (290 m2 / g).TEOS alcohol solution and TBT alcohol solution as a reason for aging solution TiO2 backbone can improve the strength of the gel , the gel is due to TiO2 porous network node consists of a tiny skeleton of TiO2 particles composed of isomers , between colloidal particles by Ti-O-Ti bonds, hydrogen bonds and van der wales bonded together , the pores in the gel with a small amount of residual water molecules on the surface of colloidal particles and pore walls , then there are a lot of the Ti-OH group when TiO2 gel was immersed in an alcohol solution of TBT TEOS or alcoholic solution , and the solution of TEOS molecules and TBT molecules will diffuse into the pores of the gel , the residual water molecules across hydrolysis reaction of formula (2) or ( 3 ) shown in hydrolysis reaction intermediate the product TiO (OH) 2 or SiO (OH) 2 addition to the self-condensation reaction product occurs a new SiO2 colloid or TiO2 particles filled in the pores of the gel or the network skeleton, skeleton structure of the gel network play support and enhance external effect, but also the surface of the colloidal particles may be Ti-OH group occurs ( 5) condensation reaction represented by the formula ( 4 ) and , between the gel particles generated in the new the Ti-O-Ti bond or Si-O-Ti bond , the TiO2 particles with gel Ti-O-Ti bond or Si-O-Ti bond together , because the Ti-O-Ti bond and Si-O-Ti bond has a strong binding force , but also on TiO2 gel network played a skeleton network enhancement .(2)(3)(4)(5)Figure 3 is a different aging after soaking liquid preparation obtained TiO2 FT-IR spectra of the airgel . Ethanol to pure alcohol and TBT aging the liquid immersion liquid was prepared as a sample , the two -phase IR spectrum recently, a strong absorption at 480 to 533 cm-1peak is near the Ti-O bond stretching vibration absorption, is characteristic absorption peak of TiO2 absorption at 1035 cm-1 Closing peak is C-OH stretching vibration absorption , 1407 cm-1 absorption at Mainly closed by bending carboxyl (-COOH) of the C-O stretching and -OH 1581 cm-1 (1545 cm-1) to absorb vibration caused mainly at the from N-H bending vibration absorption and C-N bond stretching vibration absorption stack plus , these N-H bond , C-N bond , carboxyl groups mainly from adsorbed on the pore walls of the airgel formamide , acetic acid, other organic stars promoter, the absorption peak at 2362 cm-1 was adsorbed TiO2 airgel C-O deformation vibration of the walls of a small amount of mesoporous CO2 molecules , 3165 ( 3185 ) ~ 3400 cm-1 broad absorption peak at airgel table symmetric and antisymmetric adsorbed surface hydroxyl group or water molecules in the O-H bond stretch vibration absorbingreduction [ 18 ]. Immersion aging alcohol solution was prepared as in TBT Samples in 2926 and 2957 cm-1 and two peaks , the major from the C-H bond in the residual organic molecules -CH2- groups of stretching vibration absorption and -CH3 stretching groups in the C-H bond absorption.Fig. 3 FT-IR spectra of TiO2 aerogel aged in different liquors (a) Pure Ethanol; (b) TBT-Ethanol;(c) TEOS-Ethanol4.3 Thermal stability of the atmospheric drying TiO2 aerogelsThe ethanol solution , TBT alcohol solution , TEOS solution immersion of the alcohol TiO2 aerogels discharge processing in a muffle furnace ,respectively, at 480℃, under calcined at 600 ℃ 4 h, after calcination , all three airgel samples remain block Figure 4 is an XRD pattern of the three samples before and after calcination For TBT pure ethanol alcohol solution and soaked samples after 480 ℃ calcined after burning, the sample is completely transformed into the anatase phase , after calcination at 600℃ , a clear diffraction peak of the rutile phase in the XRD pattern shows someTo change rutile TiO2 . TEOS alcohol solution soak for at reasonable sample after 480℃ calcination , will remain the same for the amorphous phase ,appear in the XRD pattern of anatase samples calcined at 600 ℃diffraction peaks , but not rutile production. Thus , TEOS dissolved prepared by soaking liquid phase transition temperature of TiO2 aerogels TBT than pure ethanol alcohol solution and soakingplace to soak aging preparation of sample processing phase transition temperature is high, which is due to the TEOS solution as the aging process of soaking TiO2 gel , forming a large number of Si-O-Ti bond, TiO2 phase change can be suppressed to improve the gas TiO2 Gel thermal stability [ 15 ] .Fig. 4 XRD patterns of TiO2 aerogel calcined at different temperatures TiO2 aerogel aged in (a) ethanol; (b) TBT-ethanol; (c) TEOS-ethanol4.4 The photocatalytic properties of different aging soaking liquid preparation ofTiO2 aerogesTreat the calcined anatase phase TiO2 aerogels as a photocatalyst , test its photocatalytic degradation of performance of the Bohai Sea crude sewage. Figure 5 isthe photocatalytic degradation curves for bohai oil products by TiO2 aerogels prepared in different aging soaking ( The relative concentration of crude oil (C/C0)% -. illumination time curve ). As can be seen from figure , when the gel as a photocatalyst to decompose Bohai oil sewage, at the beginning of the bright lights, the concentration of crude oil in the mixture solution declined quickly, then gradually slows. Compared the three different degradation curves of the TiO2 aerogels, the degradation ability and the rate is increaing from alcohol solution to TEOS alcohol/solution. The main reason for this phenomenon is the difference of the surface area. As we know, the process of organic degradation contained the adsorption of the organic and the oxidation of the organic by the electron - hole pairs producted UV excitation. So the larger the surface area of the TiO2 aerogels the stronger adsorption capacity for organic molecules, as a result, the higher catalytic efficiency and the faster degradation rate. The table 3 lists the different surface area and catalytic degradation rate at 90min which was prepared by different aging soaking liquid and calcined in a high temperature. Among them, the sample which was prepared by the Traditional wordTEOS solution and calcined into anatase still had a high surfacethe area up to 210.4m 2/g, while the sample prepared by TBT and ethanol only had 49.8m 2/g and 15.8m 2/g respectively. The corresponding degradation rate of 90 min was 91 %, 87 %, 79 % respectively. This shows that the gegradation efficiency of the Bohai Oil has a certain relationship to the surface area.Fig. 5 Photocatalytic degradation curve of oily wastewater5. Conclusion 1 ) Firstly , a small hole drying method can reduce the sample suffers a uneven shrinkage stress, shrinkage and cracking of the TiO2 aerogel. The process helps to achieve perfect aerogel blocks.2 ) In addition,t he using of TBT and TEOS solution as a aging solution can enhance the skeleton strength of the TiO 2 glue , reduce the shrinkage and cracking of the TiO2 aerogel during the drying process. As a result,we can achieve a Complete block with high surface area, especially the TEOS.PresenttenseTransitionalwords3 ) Moreover, using TEOS alcohol solution as a aging solution, because of theforming of the Si-O-Ti bond, it can prevent the phase transition and improve thethermal stability of TiO2 aerogels.4 ) Finally, the TiO2 aerogels after calcination into anatase phase by high temperature has a good photocatalytic degradation. The degradation rate and the degradation speed have a great reletionship to the surface area.AcknowledgementThe authors are grateful to National Natural Science Foundation of China for nancial support .Reference[1] Fujishima A, Honda K. Electrochemical photolysis of water at a semiconductorelectrode. Nature, 1972, 238: 37–38.[2] Chuangchote S, Jitputti J, Sagawa T, et al. Photocatalytic Activity for HydrogenEvolution of Electrospun TiO2 Nanofibers. Applied Materials andInterfaces,2009, 1(5): 1140–1143.[3] Guo Peng, Liu Chun-Yan, Gao Min, et al. Effect of ZSM-5 crystal size onproperties of supported TiO2 photocatalyst. Chinese Journal of Catalysis, 2010, 31(5): 573–578.[4] Kim M I, Park D W, Park S W, et al. Selective oxidation of hydrogen sulfidecontaining excess water and ammonia over vanadia–titania aerogel catalysts.Catalysis Today, 2006, 111(3/4): 212–216.[5] Jing Wen-Heng, Wang Wei-Gang, Xing Wei-Hong. Preparation and photocatalyticactivity of macro-mesoporous N-doped TiO2. Chinese Journal of Catalysis, 2009, 30(5): 426–432.[6] Ziolli R L, Jardim W F. Photocatalytic decompsition of seawater-soluble crude oilfractions using high surface areacolloid nanoparticles of TiO2. Journal of Photochemistry and Photobiology a-Chemistry, 2002, 147(3): 205–212.[7] Hsu Y Y, Hsiung T L, Wang H P, et al. Photocatalytic degradation of spill oils onTiO2 nanotube thin films. Marine Pollution Bulletin, 2008, 57(6-12): 873–876.[8] Liao Zhen-Hua, Chen Jian-Jun, Yao Ke-Fu, et al. Preparation and characterizationof nanometer-sized magnetic photocatalyst TiO2/SiO2/Fe3O4. Journal of Inorganic Materials, 2004, 19(4): 749–754.[9] Addamo M, Augugliaro V, Paola A D, et al. Photocatalytic thin films of TiO2formed by a Sol–Gel process using titanium tetraisopropoxide as the precursor.Thin Solid Films, 2008, 516(12):3802–3807.[10] Akpan U G, Hameed B H. The advancements in Sol–Gel method of doped-TiO2photocatalysts. Applied Catalysis A: General., 2010, 375(1): 1–11.[11] Chen Long-Wu, Gab Li-Hua, Xu Zi-Jie. Preparation and characterization ofmonolithic TiO2 aerogels. Chemical Journal of ChineseUniversites,2001,22(11): 1916–1918.[12] Stengl V, Bakardjieva S, Subr J, et al. Titania aerogel prepared by lowtemperature supercritical drying. Microporous and Mesoporous Materials, 2006, 91(1/2/3): 1–6.[13] Hwang S W, Kim T Y, Hyun S H. Effect of surface modification conditions onthe synthesis of mesoporous crack-free silica aerogel monoliths from waterglass via ambient-drying. Microporous and Mesoporous Materials, 2010, 130(1/2/3): 295–302.[14] Hwang S W, Kim T Y, Hyun S H. Optimization of instantaneous solventexchange/surface modification process for ambient synthesis of monolithic silica aerogels. Journal of Colloid and Interface Science, 2008, 322(1): 224–230.[15] LIU Zhao-Hui, SU Xun-Jia, HOU Gen-Liang. Effects of silicon content onmicrostructure and photocatalytic activity of TiO2/SiO2 composite aerogels.Journal of Inorganic Materials, 2010, 25(9):911–915.[16] Hu Jie-Gang, Chen Qi-Yuan, Li Jie, et al. Preparation of TiO2 aerogels byambient pressure drying. Journal of Inorganic Materials,2009, 24(4): 685–689.[17] Kucheyev S O, Baumann T F, Wang Y M, et al. Synthesis and electronicstructure of low-density monoliths of nanoporous nanocrystalline anatase TiO2.Journal of Electron Spectroscopy and Related Phenomena., 2005, (144–147): 609–612.[18] Cao S L, Yao N, Yeung K L. Synthesis of freestanding silica and titania-silicaaerogels with ordered and disordered mesopores. J. Sol-Gel Sci. Technol., 2008, 46(3): 323–333.[19] Armaroli T, Milella F, Notari B. A spectroscopic study of amorphous andcrystalline, Ti-containing silica and their surface acidity. Chemistry and Materials Science., 2001, 15(1): 63–71.。