Structural Characterization of Nano-porous Materials
Techniques for characterization of nano-porous materials Crystalline structure - Single crystal & Powder X-ray diffraction (XRD) - Electron crystallography Oxidation state & Coordination - X-ray absorption spectra - X-ray photoelectron spectra (XPS & Auger) - Solid state NMR ( mainly coordination) - IR & Raman ( mainly coordination) - UV-Vis spectra Elemental analysis- ICP-AES, XPS, EDX Surface area & Pore size - N 2 adsorption-desorption isotherm - Mercury Intrusion Porosimetry Morphology- SEM Pore structure- TEM
Structural Determination Long distance ordered-arrangement of atoms - Single crystal & Powder X-ray diffraction (XRD) Electron crystallography Long distance ordered-arrangement of pores - XRD, Electron crystallography Local arrangement of atoms (coordination environment) - X-ray absorption spectra (XAS) - Solid state NMR - IR & Raman Oxidation state - X-ray photoelectron spectra (XPS), XAS - UV-Vis spectra
The Electromagnetic Spectrum
X-Ray Source Monochromatic light source
Bragg s Law
X-Ray Diffraction Image & Pattern Single crystal Powder
Faujasite
Mordenite
ZSM-5 As-synthesized (010) (100) calcined
Discovery of M41S Family C.T. Kresge et al., Nature, 1992, 357, 710
SBA-15 D. Zhao et al. Science, 1998, 279, 548.
Structures and Low-Angle XRD patterns of Nano-porous Silica Cubic Hexagonal In-situ phase transformation studies Ming-Chang Liu, and Soofin Cheng * a Department of Chemistry, National Taiwan University
MCM-48 SBA-1 SBA-15
Overlapping of peaks? Difficulties in solving the crystal structure from X- ray powder diffraction patterns
Structural Determination Long distance ordered-arrangement of atoms - Single crystal & Powder X-ray diffraction (XRD), Electron crystallography Long distance ordered-arrangement of pores - XRD, Electron crystallography Local arrangement of atoms (coordination environment) - X-ray absorption spectra - Solid state NMR - IR & Raman Oxidation state - X-ray photoelectron spectra (XPS) - UV-Vis spectra
Two HRTEM (high-resolution TEM) images. The left image reveals a buried hexagonal phase in cubic CdTe. The right image shows the atomic structure of planar defects in thin-film silicon: a twin defect (in which the upper layers are rotated 180 o from the lower layers), an intrinsic stacking fault (ISF in which adjacent layers are shifted slightly), and an extrinsic stacking fault (ESF in which there is an intervening layer between two layers slightly shifted from each other). [National Renewable Energy Lab, USA]
de Broglie relation l = h / mv Electron diffraction crystallography
(100) (110) (111)
Particle Size Determination from XRD peaks
XRD Pattern of Meso-Porous ZrO 2 Intensity/(A. U) 4000 3500 3000 2500 2000 1500 1000 500 0-500 6.74 nm As-made Calcined (673 K) 0 10 20 30 40 50 60 70 2 Theda Scherrer Equation d = K 1/2 (cos ) 1/2 = (B 2 b 2 ) (calibrated peak width at half maximum) B = peak width at half maximum b = instrumental peak width (~0.16 for NaCl (s) )
Techniques for characterization of nanoporous materials Crystalline structure - Single crystal & Powder X-ray diffraction (XRD) - Electron crystallography Oxidation state & Coordination - X-ray absorption spectra - X-ray photoelectron spectra (XPS & Auger) - Solid state NMR ( mainly coordination) - IR & Raman ( mainly coordination) - UV-Vis spectra Elemental analysis- ICP-AES, XPS Surface area & Pore size - N 2 adsorption-desorption isotherm - Mercury Intrusion Porosimetry Morphology- SEM Pore structure- TEM
Survey on Pore Size Determination Methods
N 2 or Ar Adsorption-Desorption Isotherm
Non-porous Micro-porous
b. N 2 adsorption - Non-porous hysteresis Capillary condensation applicable to mesopore only 20 Å < d < 500 Å
Explanation for hysteresis (1) Changes in Contact Angles upon Ads. & Des. r On adsorption, According to Kelvin eq. ln P P a 0 surface tension of liquid molar volume of liquid 2s V cos? = RTr k P P a 0 = e 2s V cos? RT r k q radius of empty pore On desorption, =0, cos =1 ln P P d 0 = 2s V RTr k P P d 0 = e 2s V RT r k Since cos? 1 P P a > 0 P P d 0
(2) Ink-bottle pores r n < r b P P a P 0 d P 0 = e = e 2sV 2sV RTr b RTr n P P a > P d 0 P 0
uniform narrowdistributed pores
Pores between laminated plates Small neck, large body (~100nm) Pores
(reversible) Capillary condensation occurs conical, wedge-pore close at one end
BET (Brunauer-Emmett-Teller) Surface Area Measurement Physical Adsorption of Gas Adsorbate BET equation: (3-1) q 1 = heat of adsorption of the first layer q L = heat of liquefication of the gas adsorbat V m = amount of gas adsorbed upon monolayer coverage (3-2) (3-3) s = surface area = mean area per molecule of the gas adsorbate (3-4)
Effective BET plot is usually in the range of P/P 0 = 0.05~ 0.3
Porous Structure Determination - Plot = V a / V a (P/P 0 = 0.4000
0
t - Plot 0 0
BJH Pore Size Distribution Kelvin Equation ln(p*/p 0 ) = - (2 )/ RTr m P* = the critical condensation pressure = the liquid surface tension = molar volume of the condensed adsorbate = contact angle r m = mean radius of the curvature of the liquid meniscus r = r k + t = r m cos + t r = pore radius t =thickness of adsorbate on the wall r m = (r - t)/ cos ln(p/p 0 ) = - (2 cos )/ RT(r - t) t r = r k + t r m cylindrical pore
On desorption, ~0, cos ~1 ln(p/p 0 ) = - (2 cos )/ RT(r t) r = - (2 )/ RT ln(p/p 0 ) + t
Ryoung Ryoo et al., Adv. Mater. 13(9), 677(2001)
Mercury Intrusion Porosimetry (MIP) Resistance force due to surface tension = Force due to applied pressure p p D? cos? = D 4 P = applied pressure D = pore diameter = surface tension of Hg = contact angle 2 P (Washburn equation) For slit-like pores W = width between the plates r ~ (nm) 7500 P (atm) P r fl
Pores inside the grain Void space among the grains A: sample of relatively coarse grains B: a single piece of material with a wide distribution of pore sizes C: fine powders without pores
Structural Determination Crystalline structure - Single crystal & Powder X-ray diffraction (XRD) - Electron crystallography Oxidation state & Coordination - X-ray absorption spectra - X-ray photoelectron spectra (XPS & Auger) - Solid state NMR ( mainly coordination) - IR & Raman ( mainly coordination) - UV-Vis spectra Elemental analysis- ICP-AES, XPS Surface area & Pore size - N 2 adsorption-desorption isotherm - Mercury Intrusion Porosimetry Morphology- SEM Pore structure- TEM
TEM photograph of Hexagonal Mesoporous Material
Synthesis and characterization of chiral mesoporous silica Nature (2004), 429 (6989), 281-284
Techniques for characterization of nanoporous materials Crystalline structure - Single crystal & Powder X-ray diffraction (XRD) - Electron crystallography Oxidation state & Coordination - X-ray absorption spectra - X-ray photoelectron spectra (XPS & Auger) - Solid state NMR ( mainly coordination) - IR & Raman ( mainly coordination) - UV-Vis spectra Elemental analysis- ICP-AES, XPS, EDX Surface area & Pore size - N 2 adsorption-desorption isotherm - Mercury Intrusion Porosimetry Morphology- SEM Pore structure- TEM
Emission Spectrum Continuous Spectrum Line Spectrum
O N M Energy Levels and Spectral shell Lines for Hydrogen L K
Orbital Energy Diagrams
Atomic Emission Spectra of Some Elements
Inductively Coupled Plasma (ICP) - Excitation of the Sample for Elemental Analysis
Techniques for characterization of nanoporous materials Crystalline structure - Single crystal & Powder X-ray diffraction (XRD) - Electron crystallography Oxidation state & Coordination - X-ray absorption spectra - X-ray photoelectron spectra (XPS & Auger) - Solid state NMR ( mainly coordination) - IR & Raman ( mainly coordination) - UV-Vis spectra Elemental analysis- ICP-AES, XPS, EDX Surface area & Pore size - N 2 adsorption-desorption isotherm - Mercury Intrusion Porosimetry Morphology- SEM Pore structure- TEM
The Photoelectric Effect Albert Einstein considered electromagnetic energy to be bundled in to little packets called photons. Energy of photon = E = hv Photons of light hit surface electrons and transfer their energy hv = B.E. + K.E. hv e - (K.E.) The energized electrons overcome their attraction and escape from the surface Photoelectron spectroscopy detects the kinetic energy of the electron escaped from the surface. XPS X-ray as the light source, core electrons escaped UPS UV as the light source, valence electrons escaped
X-ray E k = hν E b ϕ ϕ = work function E k (KL 1 L 2 ) = [E b (K) E b (L 1 )] E b (L 2 ) ϕ
4f 5/2 4f 7/2 Pt(0) Pt metal Pt(II) Pt(IV)