structural characterization of nano-porous...

Structural Characterizationof

Nano-porous Materials

奈米孔洞材料的結構鑑定

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, EDXSurface area & Pore size

- N2 adsorption-desorption isotherm- Mercury Intrusion Porosimetry

Morphology- SEMPore structure- TEM

奈米孔洞材料鑑定技術Techniques for characterization of nano-porous materials

•Long distance ordered-arrangement of atoms- Single crystal & Powder X-ray diffraction (XRD)

Electron crystallography

•Long distance ordered-arrangement of pores- XRDXRD, 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

Structural Determination

The Electromagnetic Spectrum

X-Ray Source

Monochromatic light source

Bragg’s Law

X-Ray Diffraction Image & Pattern

Single crystal Powder

Faujasite

Mordenite

As-synthesized

ZSM-5

calcined

(010) (100)

Discovery of M41S FamilyC.T. Kresge et al., Nature, 1992, 357, 710.

SBA-15D. Zhao et al. Science, 1998, 279, 548.

Cubic Hexagonal

Structures and Low-Angle XRD patterns of Nano-porous Silica

In-situ phase transformation studies

Ming-Chang Liu, and Soofin Cheng *aDepartment of Chemistry, National Taiwan University

SBA-15

MCM-48 SBA-1

Overlapping of peaks ?

Difficulties in solving the crystal structure from X-ray powder diffraction patterns

•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 180o 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 relationλ = h / mv

Electron diffraction crystallography

(100)

(110)

(111)

Particle Size Determination from XRD peaks

XRD Pattern of Meso-Porous ZrO2

-500

0

500

1000

1500

2000

2500

3000

3500

4000

0 10 20 30 40 50 60 70

2 Theda

Inte

nsit

y/(A

. U)

As-made

Calcined (673 K)

Scherrer Equation

Kλd =β1/2 (cosθ)

β1/2 = √(B2 – b2)(calibrated peak widthat half maximum)

B = peak width at half maximum

b = instrumental peak width

(~0.16 for NaCl(s))

6.74 nm



Elemental analysis- ICP-AES, XPSSurface area & Pore size



Techniques for characterization of nano-porous materials

Survey on Pore Size Determination Methods

N2 or Ar Adsorption-Desorption Isotherm

Non-porous

Micro-porous

b. N2 adsorption -

Capillary condensationapplicable to mesopore only

Non-porous

20 Å < d < 500 Å

hysteresis

Explanation for hysteresis

(1) Changes in Contact Angles upon Ads. & Des.

On adsorption,

According to Kelvin eq.

krRT?Vs

a

k

a ePP

RTrV

PP

cos 2

00

?coss 2

ln−

=−=

radius of empty pore

surface tension of liquid

molar volume of liquid

On desorption, θ=0, cosθ=1

krRTV

d

k

d ePP

RTrV

PP

s2

00

s2

ln−

=−=

00

1?cosPP

PP da >⇒≤

θ

r

Since

(2) Ink-bottle pores

n

b

RTrVs

d

RTrVs

a

ePP

ePP

2

0

2

0

−

−

=

=

00

PP

PP da >⇒

rn < rb

uniform narrow-distributed pores

Pores between laminated plates

Small neck, large body (~100nm) Pores

Capillary condensation occurs conical, wedge-pore close at one end

(reversible)

BET (Brunauer-Emmett-Teller) Surface Area Measurement

(3-1)

(3-2)

(3-3)

(3-4)

q1 = heat of adsorption of the first layerqL = heat of liquefication of the gas adsorbatVm = amount of gas adsorbed upon monolayer coverage

Physical Adsorption of Gas AdsorbateBET equation:

s = surface areaσ = mean area per molecule of the gas adsorbate

Effective BET plot is usually in the range of

P/P0 = 0.05~ 0.3

Porous Structure Determinationα - Plot

α = Va/ Va(P/P0 = 0.4000)

t - Plot

0

0

BJH Pore Size Distribution

Kelvin Equation

P* = the critical condensation pressureγ = the liquid surface tensionν = molar volume of the condensed adsorbateθ = contact anglerm = mean radius of the curvature of the liquid meniscus

θrm

r = rk + t

ln(P*/P0) = - (2 γν)/ RTrm

tr = rk + t = rm cosθ + tr = pore radius t =thickness of adsorbate on the wall

rm = (r - t)/ cosθ

ln(P/P0) = - (2 γνcosθ)/ RT(r - t)

cylindrical pore

On desorption, θ~0, cosθ~1

ln(P/P0) = - (2 γνcosθ)/ RT(r – t)

r = - (2 γν)/ RT ln(P/P0) + t

Ryoung Ryoo et al., Adv. Mater. 13(9), 677(2001)

Mercury Intrusion Porosimetry (MIP)

P = applied pressureD = pore diameterγ= surface tension of Hgθ = contact angle

Resistance force due to surface tension = Force due to applied pressure

(Washburn equation)

For slit-like pores

W = width between the plates Pr

7500~

(nm) (atm)

P P ↑↑ ⇒⇒ r r ↓↓

4P p

cos? ? p2D

D =−

A: sample of relatively coarse grainsB: a single piece of material with a wide distribution of

pore sizesC: fine powders without pores

Pores inside the grain

Void space among the grains



Elemental analysis- ICP-AES, XPSSurface area & Pore size




TEM photograph of Hexagonal Mesoporous Material

Synthesis and characterization of chiral mesoporous silica

Nature (2004), 429 (6989), 281-284

Continuous

Spectrum

Line Spectrum

Emission Spectrum

Energy Levels and Spectral Lines for Hydrogen

K

L

MNO

shell

Orbital Energy Diagrams

Atomic Emission Spectra of Some Elements

Inductively Coupled Plasma (ICP)

- Excitation of the Sample for Elemental Analysis

The Photoelectric EffectAlbert Einstein considered electromagnetic energy to be bundled in to little packets called photons.

Energy of photon = E = hvPhotons of light hit surface electrons and transfer their energy

hv = B.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 escapedUPS – UV as the light source, valence electrons escaped

hve- (K.E.)

Ek = hν – Eb – ϕϕ = work function

Ek(KL1L2) = [Eb(K) – Eb(L1)] – Eb(L2) – ϕ

X-ray

Pt metal

Pt(0)

Pt(II)

Pt(IV)

4f 5/24f 7/2

structural characterization of nano-porous...

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