材料研究方法01-n2sorption

1、1材料研究方法與實(shí)驗(yàn)-N2吸附-脫附分析(N2 sorption/adsorption and desorption)李永生2014-11-112多孔材料分類Micropores20Mesopores 20 500Macropores500IUPAC: International Union of Pure and Applied Chemistry 國際純粹與應(yīng)用化學(xué)聯(lián)合會micropore=微孔?多孔材料微孔材料介孔材料大孔材料C60: 1.018 nm足球: 25.4 cm地球: 12756.3 km多孔材料的特點(diǎn)最大特點(diǎn)具有“孔” 通常使用宏觀參數(shù)來描述多孔固體，如固體材料的表面積、外

2、表面積、（微、介）孔容、孔徑分布、吸附-脫附等溫線、吸附特性、孔幾何學(xué)及孔道的連通性。34Surface area & porosity measurements-A few of most commonly used applications 5Analysis of Adsorption IsothermsSpecific Surface Area 沸石:500-800 m2/g, 介孔材料1000 m2/g，介孔碳 1000-2000 m2/gPore Size 微孔50nmPore Volume 0.3,0.5.2.0 ml/gPore Size DistributionFractal

3、 Dimension-分形維數(shù)-粗糙度Texture of Porous Material6N2 吸附-脫附分析 許多有關(guān)孔的性質(zhì)都是通過物理吸附來測定 吸附是物質(zhì)在兩相界面上濃集的現(xiàn)象；通常采用氮?dú)?、氬氣或氧氣為吸附質(zhì)進(jìn)行多孔物質(zhì)的比表面積、孔體積、孔徑的大小和分布的測定，也可通過完整的吸附-脫附曲線計(jì)算出介孔和微孔部分的體積和表面積等。N2 吸附-脫附分析儀7QuantachromeI N S T R U M E N T S Langmuir吸附假設(shè)固體表面是均勻的被吸附分子間沒有相互作用吸附是單分子層吸附在一定條件下吸附和脫附之間可建立動態(tài)平衡 表面積公式： Vm:單分子層體積；Vs：氣

4、體摩爾體積（22414） Na:阿伏伽德羅常數(shù)；：每個(gè)吸附質(zhì)分子所覆蓋面積（N2:0.162nm2）89基本吸附理論介紹10基本吸附理論介紹1112基本吸附理論介紹13基本吸附理論介紹14基本吸附理論介紹15吸附-脫附分析N2 吸附-脫附分析Planar Surface Mesopores (2-50 nm) Micropore (2 nm)Adsorption potential16IUPAC Classification of Sorption isothermsmicroporous materialsmacroporous materialsmesoporous materialssu

5、per-microporous materials吸附平衡等溫線17Hysteresis-遲滯現(xiàn)象N2 吸附-脫附分析圓柱形孔均一分布瓶裝孔狹縫狀孔形狀、尺寸不均勻狹縫狀孔均勻18hysteresisNetwork of Mesopores wneck wpore Neck Poree.g, porous Vycor glass Pore BlockingDelayed condensation Network of Micro/Mesopores. wneck 5 nm時(shí)通常低估20%；吸附與脫附分支不能重復(fù)；脫附曲線計(jì)算會出現(xiàn)4 nm左右的假峰；BdB考慮了不同孔徑孔道的表面吸附層厚度的不

6、同，特別是孔徑5 nm時(shí)，與實(shí)際孔道大小更接近；HK基于相對壓力只與孔徑有關(guān)的假設(shè)，主要用于活性炭和分子篩的狹縫狀孔道的計(jì)算；26孔徑的計(jì)算NLDFT(非定域密度泛函理論)從分子水平上描述受限于孔內(nèi)的吸附質(zhì)非均勻流體的行為，可用于微孔與介孔的全范圍孔徑分布的表征。27不同方法計(jì)算的MCM-41的孔徑分布28孔徑的計(jì)算SBA-15吸附等溫線和孔徑分布一般吸附分支計(jì)算大孔材料分析壓汞法 汞不會浸潤被它壓入的大多數(shù)材料（潤濕角90o），因此只有在外力作用下，汞才能壓入多孔材料的孔穴中。 r=-2cos/p r: 孔半徑 p: 外壓 ：汞的表面張力 ：汞對固體的潤濕角，一般2cos近似取值-750（M

7、Panm）29常見測量孔的技術(shù)方法與應(yīng)用范圍30Commonly used Adsorptives for Surface- and Pore size Analysis31Nitrogen: at 77.35 K (liquid nitrogen temperature, T/Tc = 0.61) pore size analysis of micro, meso and macropores surface area analysis Argon: at 77.35 K (T Tr = - 6.5 K; Tr : bulk triple point temperature; T/Tc =

8、0.50) at 87.27 K (liquid argon temperature, T/Tc = 0.57 ) pore size analysis of micro- , meso- and macropores surface area analysis CO2 : at 195 K (T/Tc = 0.63) at 273 K (T/Tc = 0.89) pore size analysis of micropores of widths 1.5 nm (particularly for microporous carbons)Krypton : at 77.35 K (T Tr =

9、 - 38.5 K) measurement of very low surface areas at 87.27 K (T Tr = - 28.5 K) pore size analysis of thin micro/mesoporous films (M. Thommes et al, 2004)32Example for Volumetric Adsorption Apparatus applicable for accurate Micro/Mesopore Size Analysis33Pore Size Analysis by Gas AdsorptionMacroscopic,

10、 thermodynamic methodsMicropores ( pore W243Effect of Pore size and Temperature on Pore Condensation and Hysteresis 3.3nm 3.6 nm4.2 nm Argon 77K/ MCM-41Argon/ MCM-48 (dp= 4.01nm) 87 K 77 KM. Thommes, R. Koehn and M. Froeba et al. J. Phys. Chem B 104, (2000), 7933In : S. Lowell, J. Shields, M. Thomas

11、, M. Thommes, Characterization of porous solids and Powders: Surface Area, Pore Size and Density, Kluwer Academic Publ, 2004, 44Application of argon adsorption for mesopore analysis Argon adsorption at 87.27 K is very well suited for a combined micro/mesopore analysisIn contrast, Argon adsorption at

12、 77.35 K (i.e. ca. 6.5 K below the triple point temperature) is more problematic, also because mesopore size analysis is limited (in case of silica materials the pore volume and pore size distribution of materials having diameters ca. 16 nm cannot be determined anymore). 45Effect of confinement on s

13、orption and phase behaviorPore size and temperature are complimentary variables with regard to the occurrence of hysteresisThe shape of sorption isotherms is affected by both, the texture of the material but also by the difference in thermodynamik states of pore and bulk fluid phases In contrast to

14、classical, macroscopic approaches modern microcopic theories based on statistical mechanics (e.g Density-Functional Theory and Molecular Simulation) take these phenomena into account46Pore Size Analysis byMicroscopic Methods based on Statistical Mechanics (a)Density Functional Theory : e.g.- Evans a

15、nd Tarazona (1985/86) - Seaton (1989), - Lastoskie and Gubbins (1993) - Sombathley and Olivier (1994) - Neimark and Ravikovitch (1995 )b)Monte Carlo (MC) and Moleculardyn. (MD), e.g. - Gubbins et. al. (1986. ) - Walton and Quirke (1989) - Gelb (1999- .) - Neimark and Ravikovitch (1995.) 47Theoretica

16、l predictions of the pore size dependence of the relative pressure of the equilibrium condensation/evaporation transition. Neimark AV, Ravikovitch P.I., Grn M., Schth F., Unger K.K, (1998) J. Coll. Interface Sci. 207,15948Calculation of Pore Size Distribution by NLDFTGeneralized Adsorption Integral

17、Equation (GAI): N(P/P0) = Experimental adsorption isotherm data N(P/P0,W) = Isotherm in a single pore of width W f(W) = Pore size distribution function49Nitrogen sorption (77 K) in MCM-41 and Pore Size Analysis by BJH and NLDFT BJH NLDFT50Argon adsorption at 87 K on a 50:50 mixture of ZSM-5 +MCM-41:

18、 Combined micro/mesopore analysis by NLDFT ZSM-5 MCM-4151Gas Adsorption Characterization: Argon and Nitrogen adsorption at 77.4 K in CMK-1 mesoporous carbonBJH : 1.7 nmNLDFT: 2.6 nmNLDFT methods: N2/77K slit-pore carbon model and Ar/77K slit-pore carbon modelTEM: ca. 2.7 nmAr N252Nitrogen Adsorption

19、 and Pore Size Analysis in CMK 3 Mesoporous Carbon NLDFT (5.1 nm) BJH (3.5 nm)53NLDFT vs. Classical Methods for Pore Size Analysis Non-Local-Density Functional Theory (NLDFT) or computers simulation methods (e.g., Grand Canonical Monte Carlo Simulation, GCMC) allow to obtain an accurate pore size an

20、alysis over a wide pore size (i.e., a combined micro/mesopore analysis). In contrast, classical methods, based on macroscopic thermodynamic assumptions (e.g.,BJH, DR) are only applicable over a specific pore size range and under- estimate the pore size significantly (at least up to 25 % for pore sizes 10 nm), if not properly corrected or calibrated. 54Mesopore Analysis Significa