Techniques for characterization of nano- porous...
Transcript of Techniques for characterization of nano- porous...
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
Techniques for characterization of nano-porous materials
X-ray Absorption Spectroscopy
x
I(0, ω)I(x, ω)
Beer’s Law: I(x, ω)=I(0, ω) e -µ(ω) x
−µtx = ln (I(x, ω) / I(0, ω))
8800 9000 9200 9400 9600 9800 10000 10200-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
Abs
orpt
ion
Energy (eV)
XANES EXAFS
Cu
Cu
constructive
destructive
Absorption edge
S K-edge XANES spectra of (a) MPTMS,(b) dipropyl disulfide, (c) S16-SO3H (10%) 2M HCl, (d) S16-SO3H (20%) 0.5M HCl, (e) S16-SO3H (20%) 1.0M HCl, (f) S16-SO3H (20%) 2.0M HCl and (g) S16-SO3H (30%) 2.0M HCl
Si-OH
Si-OH
Si-OH
H3COSiH3CO
H3CO
SHO
O
OSi SH
H2O2
O
O
OSi
SOH
O
O
2455 2460 2465 2470 2475 2480 2485 2490 2495 2500 2505
(g)
(f)
(e)
(d)
(c)
(b)
(a)
Nor
mal
ized
Inte
nsity
Energy/eV
MPTMS
d
Neighbor AtomAbsorbing Atom
Unoccupied ValenceStates
k = kc = 2π /d
k < kc
k > kc
EXAFS
XANES
E
EC
ER
E0
Continuum States
hv
de Broglie eq.
( )edgek Ehh
mE
hm
−
=
== ν
ππλπ
κ 2
221
2
2 88
2
2
21
mvEhE bk =−= ν
)(2 bEhm
hmvh
−==
νλ
photoelectron wave vector
EXAFS function
[ ] )()()()( 00 EEEE µµµχ −=
μ:measured absorption coeff.μ0: no EXAFS
( )edgek Ehh
mE
hm
−
=
== υ
ππλπ
κ 2
221
2
2 88
2
m = mass of electron
When the unit of Ek is eV, κ = [0.2625(E-E0)]1/2
In EXAFS region
Kronig structure – reflected the local structure surrounding the atom under study
Usually taking the spectra 50 – 1000 eV above adsorption edge, then subtract the background, and obtain the spectrum of χ(k) vs. K
( )
)2
exp(
)2exp()(22sin)( 222
κ
κσκφδκκ
κχ
ji
jjjjj
j
j
RV
fRR
N
−⋅
−⋅⋅++⋅⋅
= ∑
E2 a κ photoelectron wave vector
δ: phase shift of emitting atomφj: phase shift of back scattering atom in jth shellfj(K): amplitude of the back scattering factorσj
2: Debye-Waller factorvi: inelastic scattering of photo-electron waveNj: coordination no. of jth shellRj: interatomic distance of jth shell
the mean square fluctuation ofthe interaction distance
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-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
expt bkg
Abs
orpt
ion
Energy (eV)
0 2 4 6 8 1 0 12 14 16 18 20-10
-8
-6
-4
-2
0
2
4
6
8
10
ok (A -1)
k3 χ
(k)
0 1 2 3 4 5 6 7 8 9 100
2
4
6
8
10
12
14
|χ(R)|data
|χ(R)|model
o
|FT[
k3 χ
(k)]
|=| χ
(R)|
R (A)
EXAFS
∑ −−+=
j
kR
jjj
jj j
j
eekkRkR
kFkSNk
2222
2
20 )](2sin[
)()()( σλδχ
原始實驗數據
去除不正常的數值點
扣除背景值及規一化
傅立葉轉換
r < 1 Å 之振幅
傅立葉濾波
在k空間進行曲線配適
在r空間進行曲線配適
EXAFS simulation provides informations on(i) Rj: accurcy ±0.01 ~ 0.05 Å for the 1st & 2nd shell(ii) Nj: ±20% for the 1st shell(iii) σj
2: as small as possible(iv) r: deviation factor (as small as possible)
Rh metal
Rh2O3
RhCl3
Coordination Number
Hydrogen Chemisorption and EXAFS Results of Rh, Ir and Pt Nano-Particles Supported on Alumina
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
Techniques for characterization of nano-porous materials
• Electron Paramagnetic Resonance Spectroscopy
molecules, ions or atoms possess electron with unpaired spins magnetic moment of e-
HSg ee
vvvv ⋅=Η−= µβµ - ,
zSHg ˆˆ β=Η
2.0023193g .e free afor value,-g :g
operatorspin :ˆ2
magnetonBohr :
- =
=
Z
e
S
Cmeh
β
g value for an unpaired e- in a gaseous ion or atom
)1(2)1()1()1(
1+
+−++++=
JJLLSSJJ
g
HamiltonianMagnetic field
Zeeman Splitting for e- is ~700 times larger than for 1H
e.g. H0=10,000 gauses,
MHz 58.42
MHz 026,28
1 =∆
=∆ −
H
e
E
E
Sensitivity of EPR > NMR (because of ΔE)EPR lines broader than NMR
H g β=∆E
ms = +1/2, E = +1/2 gβH0
ms = -1/2, E = -1/2 gβH0
For electron of spin S= ½ ,
lα>, lβ>
lα>
lβ>
In magnetic field, H0
Two common freq. for EPR experiment (fixed frequeacy)micro-wave range
“X-band” H0=3,400 Gauss, ν~9500 MHz
“Q-band” H0=12,500 Gauss, ν~35,000 MHz
sensitivity α ν2
(free e- resonance freq.)
Water, alcohols, high dielectric constant solvents absorb microwave power, ⇒ not suitable solvent
Samples can be gases, solutions, powders, single crystals or frozen solutions
in NMR
in EPR
INN mHgE ∆−−=∆ 0)1( σβ
0HgE β=∆change in shielding constant
change in g value
For 1H, I=1/2
I=1
Zeeman interaction⇒ 2I+1 states
mI = +1/2, E = -1/2 gNβNH0
mI = -1/2, E = +1/2 gNβNH0
0NN H g β=∆E
mI = +1, E = -gNβNH0
mI = -1, E = +gNβNH0
mI = 00NN H g β=∆E
For H0 ˜ 14,000 Gauss, ν=60 MHz (60,000,000 sec-1) ~ 2x10-3 cm-1
Boltzmann Distribution
999995.01)2
1(
)21(
=∆
−≈=+
− ∆−
kTE
eN
NkT
E ΔE ~ 10-3 cm-1
kT ~ 200 cm-1
resolution ~ 0.1 Hz
If use higher field, e.g. 300 MHz ⇒ better resolution
0.999995
1.0
mI = -1/2
mI = +1/2
For 1H
I = 1/2
• High resolution NMR spectra of solids
ψψ E=Η
SRQCSJDRFZ Η+Η+Η+Η+Η+Η+Η=Η
external Hamiltonian internal Hamiltonian
HZ: Zeeman interaction of the nuclear magnetic moment with the applied field B0
HRF: interaction between nuclear spin & the time-dependent radio freq. field B1(t)
HD: dipolar interaction between nuclear magnetic dipole momentsHJ: e— mediacted nuclear spin-spin interactionHCS: chemical shift associated with electronic screening of nucleiHSR: spin-rotation interaction; I and molecular angular momentumHQ: nuclear spin & quadruple moment
not importantin solid
importantfor I > 1/2
A general Hamiltonian for the interactions experienced by a nucleus of spin I
HamiltonianWave function
eigenvalue
A general Hamiltonian for the interactions experienced by a nucleus of spin I in the solid state may be written as in equation (1.2)
H = HZ + HD + HCS + H SC + HQ (1.2)
0 ~ 109Quadrupolar
0 ~ 104Scalar Coupling
0 ~ 105Chemical Shift
0 ~ 105Dipolar
106 ~ 108Zeeman
Table 1.1 Approximate ranges of the different spin interactions (in Hz)
Zeeman interaction
ZNNzZ
ZZ
IHgIHH
HHHH
00
000 cos
βγ
µθµµ
−=−=
−=−=⋅−=
h
vv
=
==
Cme
g
IgI
PN
NN
2h
h βγµ
magnetogyric ratio
nuclear g factorBohr magneton of the particular nucleus
Dipolar interaction HD
IDIr
HHij
IIID
vvh⋅⋅== ˆ
3
22γ
internuclear distance
dipolar coupling tensor
magnetogyric ratio
For single type of spin, I
Chemical shift interaction
0ˆ HIH ICS
vvh ⋅⋅= σγ Proportional linearly to the applied field
Range of common isotropic chemical shift (ppm)
necleus
20031P
10019F
25013C
8029Si
35015N
201H
Table. Typical values of chemical shift
Spin-spin coupling interaction
SJIH SC
vv⋅⋅= ˆ
field independent and is usually smaller than the other interaction
Quadrupolar interaction
IQIHQ
vv⋅⋅= ˆ
nuclear electric quadrupole moment eQ
only when I > ½field independent
ν
ν
ν1
ν2
Dipolar Interaction
HD = 0, if 3cos2θij – 1 = 0
Magic Angle Spinning
(MAS)
Q4
Q3
Q2
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
Techniques for characterization of nano-porous materials
△E = hνm
Vibrational Spectroscopy
IR Spectroscopy
IRstretching
bending
stretchingbending
stretchingbending
stretching
stretching
stretching
Faujasite
Ferrierite
ZSM-5
Raman Spectroscopy
Boltzman Distribution affects the intensity of Anti-Stocks
Anatase638
515 395
200400600800
Rutile445
608
200400600800
Fig. 3.2 FT-Raman spectra of TiO2 of anatase and rutile phases: (a) lab-made, and after calcination at (b) 400 ℃, (c) 700 ℃, in comparison to (d) ) commercially available.
(a)(a)
(b)(b)
(c) (c)
(d)
(d)
Conclusions
There are still a huge There are still a huge SPACESPACE in the research of in the research of nanonano--porous materials. porous materials.