katie a. cychoszand matthias thommes -...

Katie A. Cychosz and Matthias Thommes*

Quantachrome InstrumentsBoynton Beach, Florida, USA

Surface Area Pore Size/Volume Distribution Pore Geometry, Structure of Pore Network Surface Properties

IUPAC (1985)

Micropores: < 2 nm

Mesopores: 2‐ 50 nm

Macropores: > 50 nm

MicroporeHeterogeneous Planar Surface

Heterogeneous Planar Surface

Mesopore

“Ideal” Planar Surface

New IUPAC Project – revision of recommendation from 1985: started in March 2010 (http://www.iupac.org/web/ins/2010-009-1-100)

This isotherm classification is valid for adsorption of subcritical adsorptives on rigid solids.

Mesopore and Micropore

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Pore size/volume characterization of nanoporous carbons

Combination of carbon dioxide (273 K) with nitrogen (77 K) or argon (87 K)

Pore size/volume characterization of microporous materials with polar surfaces (e.g. MOFs, zeolites)

Argon (87 K)

Analysis of materials with ultra‐low surface area

Krypton (77 K) adsorption for surface area onlyKrypton (87 K) for pore size analysis of thin films

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Problem: Below 100 mTorr (P/P0 = 10‐5) is regime of extremely slow kinetics. The selection of proper equilibrium parameters is essential for obtaining accurate adsorption isotherm data.

5 10-7 5 10-6 5 10-5 5 10-4 5 10-3 5 10-2 5 10-1 5 100

P/P0

0

70

140

210

280

350

Vol

ume

[cm

3 g-1

] STP

Ar (87 K) - Faujasite ZeoliteAr (87 K) - Faujasite ZeoliteN2 (77K) - Faujasite ZeoliteN2 (77K) - Faujasite Zeolite

10-7 5 10-6 5 10-5 5 10-4 5 10-3 5 10-2 5 10-1 5 100

Relative Pressure [P/P0]

0

100

200

300

400

500

600

700

800

Vol

ume

[cm

3 g-1

]

CMC2-Carbon (Argon, 87.3K)CMC2-Carbon (Argon, 87.3K)CMC2-Carbon (Nitrogen, 77.3 K)CMC2-Carbon (Nitrogen, 77.3 K)

Ar and N2 adsorption on Faujasite zeolite

Ar and N2 adsorption on activated carbon

N2 (77 K)

Ar (87 K)Ar (87 K)

N2 (77 K)

Zeolites: N2 – quadrupole interactions important

Many Carbons: N2 – quadrupoleinteractions not important

Thommes, M. Textural Characterization of Zeolites and Ordered Mesoporous Materials by Physical Adsorption in: Introduction to Zeolite Science and Practice, 2007, p. 495‐523

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Effective pore width ~ 5 Å

structural change

Lässig, D.; Lincke, J.; Moellmer, J.; Reichenbach, C.; Moeller, A. Gläser, R.; Kalies, G.; Cychosz, K.A.; Thommes, M.; Staudt, R.; Krautscheid, H. Angew. Chemie. Int. Ed. 2011, 50, 10344‐10348

pore filling

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N2, 77 K

Ar, 87 K

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Zhang, X.; Liu, D.; Xu, D.; Asahina, S.; Cychosz, K.A.; Agrawal, K.V.; Al Wahedi, Y.; Bhan, A.; Al Hashimi, S.; Terasaki, O.; Thommes, M.; Tsapatsis, M. Science 2012, 336, 1684‐1687

High resolution TEM image (A) of self‐pillared zeolite nanosheet

NLDFT model fits the experimental argon data

Cumulative pore volumes (C) were plotted for zeolites with varying Si/Al ratios

NLDFT pore size distributions (D) clearly show the micro‐and mesoporosity

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

4 6 8 10 12 14 16 18 20Pore Size Å

Pore

Vol

ume,

cc/

g

CON

2

2

At elevated temperatures and higher absolute pressure (P0 = 26200 torr) CO2 can access micropores which are not accessible for nitrogen and argon at 77 K, 87 K

Fast analysis: due to higher diffusion rate, equilibrium is achieved faster as compared to nitrogen adsorption at 77 K dramatic decrease in analysis time, i.e. 3‐5 h for CO2 versus 30‐50 h N2

No need for high vacuum system No need for a low‐pressure transducer

1000 torr transducer is sufficientAnalysis Time:

CO2 = 5 hN2 = 40 hGarrido, J., et al. Langmuir, 1987, 3, 76‐81

Cazorla‐Amorós, D., et al. Langmuir, 2996, 12, 2820‐2824

NLDFT Analysis: slit/cylinder model

Zhu, Y.; Murali, S.; Stoller, M.D.; Ganesh, K.J.; Cai, W.; Ferreira, P.J.; Pirkle, A.; Wallace, R.M.; Cychosz, K.A.; Thommes, M.; Su, D.; Stach, E.A.; Ruoff, R.S. Science 2011, 332, 1537‐1541

Macroscopic, thermodynamic methodsMicropores (< 2 nm): e.g. Dubinin‐Radushkevitch, Horvath‐Kawazoe (HK), Saito‐Foley (SF), comparison plot methods (t‐method, alpha‐s method)

Meso‐ and Macropores (> 2 nm): e.g. Kelvin equation based methods such as Barrett, Joyner, Halenda (BJH) or Broeckhoff‐de Boer (BDB)

Modern, microscopic methods based on statistical mechanics describe configuration of adsorbed molecules on a molecular level Both Micro‐ and Mesopore size range: e.g. Density Functional Theory (DFT), Molecular Simulation

An accurate pore size analysis over the complete pore size range can be performed by a single method.

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DFT (NLDFT, QSDFT) is widely used for micro‐ and mesopore analysis.

A comprehensive library of DFT methods for various adsorptive/adsorbent pairs is available.

Since 2007: NLDFT methods for pore size analysis are featured/recommended in standards of the International Standard Organization (ISO, i.e. ISO‐15901‐3).Facilitates the application and use of DFT methods for pore size analysis in industry.

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DFT Review: Landers, J.; Gor, G.; Neimark, A.V. Colloids Surfaces A 2013, 437, 3‐32.

0 0.2 0.4 0.6 0.8 1Relative Pressure P/P0

0

100

200

300

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500

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700

800

900

Vol

ume

[cm

3 g-1

] STP

N2 (77.4 K) - AdsN2 (77.4 K) - AdsN2 (77.4 K) - DesN2 (77.4 K) - DesAr (87.3 K) - AdsAr (87.3 K) - AdsAr (87.3 K) - DesAr (87.3 K) - Des

Data from: Zukal, A.; Thommes, M.; Cejka, J. Microporous and Mesoporous Materials 2007, 104, 52‐58

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Ordered mesoporous material Pore size verified using independent methods BJH (and other Kelvin equation based approaches) underestimates the pore size (up to 25%)

Molecular Simulation Tremendous progress in modeling realistic 3D structures (Gubbins, Monson, and others) of porous solids.

Non‐Local Density Functional Theory Various efforts to account for heterogeneity in NLDFT/DFT (Olivier, 1997; Ravikovitch, Jagiello, Neimark, 1999; Bhatia, 2002; Ustinov, Do, 2004‐06; Jagiello, Olivier, 2010).

Quenched Solid Density Functional Theory Solid enters the model as a quenched component with a fixed density distribution rather than a source of an external potential (Neimark, Ravikovitch: QSDFT for silica in 2006; QSDFT for carbons in 2007).

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QSDFT provides a much more realistic approach for the pore size analysis of heterogeneous activated carbon!

5 10-6 5 10-5 5 10-4 5 10-3 5 10-2 5 10-1 5 100

P/P0

0

100

200

300

400

500

600

Vol

ume

[cm

3 g-1

]

NLDFT FitNLDFT Fit QSDFT Fit QSDFT Fit

Experimental data, N2 (77 K)/ACF 15Experimental data, N2 (77 K)/ACF 15

5 10 50 100 500 1000Pore Diameter [Å]

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

Dv(

d) [c

m3 /Å

/g]

QSDFTQSDFTNLDFTNLDFT

Neimark, A.V.; Ravikovitch, P.I.; Lin, Y.; Thommes, M. Carbon 2009, 47, 1617

Activated Carbon Fiber ACF‐15

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QSDFT method for carbons has been originally developed assuming slit‐shaped pores which are typically found in activated microporous carbons.

Emergence of novel materials with pre‐designed pore morphology (obtained by synthesis routes which make use of structure directing agents or hard templates) requires the development of new methods.

We extend the QSDFT method to micro‐ and mesoporous carbons with cage‐like and channel‐like pore geometries.

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Gor, G.; Thommes, M.; Cychosz, K.A.; Neimark, A.V. Carbon 2012, 50, 1583‐1590

The obtained QSDFT pore size agrees well with the pore size derived from XRD (49.97 Å) by using the geometrical model of hexagonally arranged carbon rods described in the paper by Joo, Ryoo, Kruk, and Jaroniec (J. Phys. Chem.2002, 106, 4640‐ 4646)

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BJH underestimates true pore size up to 25%

BJH (3.5 nm)

NLDFT (5.1 nm)

Cylindrical Pores

Cylindrical &Spherical Pores

Disordered, lamellar pore structures, slit & wedge shape pores

Micro‐ and mesoporous adsorbents

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Cylindrical/Slit‐like pores Delayed condensation due to metastable pore

fluid Desorption branch reflects equilibrium transition H1 Hysteresis

Pore Networks and Ink‐Bottle Pores Delay in condensation due to metastable pore

fluid Delay in evaporation potentially due to pore

blocking, cavitation, and percolation phenomena H2, H3, H4 Hysteresis

Disordered Porous Materials with Non‐Uniform Pore Network Structures Combination of kinetic and thermodynamic effects

spanning the complete disordered pore system H2, H3, H4 Hysteresis

Equilibrium

Delayed condensation

Neimark, A.V.; Ravikovitch, P.I Microporous and Mesoporous Materials 2001, 697, 44‐56

Desorption Branch: Equilibrium liquid‐gas phase transition (evaporation)NLDFT Kernel of Equilibrium Isotherms

Adsorption Branch: NLDFT‐spinodal‐gas‐liquid phase transition (condensation)NLDFT Kernel of (Metastable) Adsorption Isotherms

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0 0.2 0.4 0.6 0.8 1Relative Pressure P/P0

0

100

200

300

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Vol

ume

STP

[cc/

g]

25 45 65 85 105 125Pore Diameter [Å]

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

Dv(

d) [c

c/Å

/g]

Ads (NLDFT-spinodal condensation)Ads (NLDFT-spinodal condensation)Des (NLDFT- equilibrium transition)Des (NLDFT- equilibrium transition)

M. Thommes, In Nanoporous Materials‐ Science and Engineering” (edited by Max Lu and G. Zhao), Imperial College Press, Chapter 11 p. 317 ‐ 364 (2004)

H1 Hysteresis

Delayed condensation

Equilibrium Transition

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PSD from adsorption calculated using NLDFT metastable adsorption branch method.

PSD from desorption calculated using NLDFT equilibrium transition kernel.

Wc = critical “neck” diameter 5‐6 nm for N2 (77 K)

From: Thommes, M.; Smarsly, B.; Groenewolt, M.; Ravikovitch, P.I.; Neimark, A.V. Langmuir 2006, 22, 756

Pore/cavity Size analysis from adsorption by DFT method which takes into account delayed condensation in spherical or cylindrical pores

Cavitation depends on the thermophysical properties of the adsorptive PSD determined from

desorption branch DOES depend on adsorptive or temperature

Pore blocking controlled desorption depends on the neck size, but not on the adsorptive PSD determined from

desorption branch DOES NOT depend on choice of adsorptive or temperature

24Sarkisov, L.D.; Monson, P.A. Langmuir 2001, 17, 7600

30 40 50 60 70 80 90 100 110 120 130Pore Diameter [Å]

0

0.08

0.16

0.24

0.32

0.4

0.48

D(v

)[cc/

Å/g

]

Argon 87 K Argon 87 K Nitrogen 77 K Nitrogen 77 K

NLDFT PSD from Desorption

30 42 54 66 78 90 102 114 126 138 150Pore Diameter [Å]

0

0.005

0.01

0.015

0.02

0.025

[cm

3 /Å/g

]

Argon (87 K), AdsArgon (87 K), AdsNitrogen (77K),AdsNitrogen (77K),Ads

NLDFT-PSD (from Adsorption Branch)

SE3030(PSD) | 17.2.2003

NLDFT pore size from adsorption

0 0.2 0.4 0.6 0.8 1P/P0

0

100

200

300

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Vol

ume

[cc/

g] [S

TP]

Nitrogen 77 KNitrogen 77 KArgon 87 KArgon 87 K

No quantitative pore size info from desorption!

Thommes, M.; Smarsly, B.; Groenewolt, M.; Ravikovitch, P.I.; Neimark, A.V. Langmuir 2006, 22, 756‐764

Disagreement between Ar and N2“pseudo” desorption PSDs due to cavitation transition

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CavitationQSDFT equilibrium kernel

QSDFT metastable adsorption branch kernel

PSD artifact due to cavitation

Thommes, M.; Cychosz, K.A.; Neimark, A.V. In: Novel Carbon Adsorbents, Ed. J.M.D. Tascon, 2012, Elsevier, p. 107‐145

Template: 3D colloidal crystals formed from lysine‐silica nanoparticles

High degree of control over nanoparticle size

Pore size of 3DOm carbon verified using SEM, TEM, SAXS

Fan, W.; Snyder, M.A.; Kumar, S.; Lee, P‐S.; Yoo, W.C.; McCormick, A.V.; Penn, R.L.; Stein, A.; Tsapatsis, M. Nature Materials 2008, 7, 984‐991

N2 at 77 K

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H1 Hysteresis

Pore size analysis from adsorption branch with novel QSDFT method assuming spherical pore geometry for mesopores which takes correctly into account delay in condensation due to metastable pore fluid.

QSDFT pore sizes in good agreement with SEM

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Comparison of N2 (77K) and Ar (87K) pore size distributions for 10 nm and 20 nm 3DOm carbons from desorption branch

Good agreement of N2 (77K) and Ar (87K) PSD curves indicates the absence of cavitation!! Desorption PSD reflects the distribution of window sizes

10 nm Carbon 20 nm Carbon

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Cychosz, K.A.; Guo, X.; Fan, W.; Cimino, R.; Gor, G.Y.; Tsapatsis, M.; Neimark, A.V.; Thommes, M. Langmuir 2012, 28, 12647‐12654

Narrow distribution of spherical pore sizes Narrow distribution of window sizes

10 nm Carbon 40 nm Carbon

H1 Hysteresis

pore size

pore sizewindowsize window

size

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Type H1 Hysteresis: Pores evaporate independently from one another (e.g. SBA‐15 silica)

Type H2 Hysteresis: Evaporation of certain pores depends on the state of neighboring pores Network effects/percolation

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Pioneered by Everett ‐ 1967, De Boer ‐ 1958

Pore Network ‐ Type H2 hysteresis

Quantitative analysis of scanning curves allows one to obtain information about

pore connectivity.

Cimino, R.; Cychosz, K.A.; Thommes, M.; Neimark, A.V. Colloids Surfaces A 2013, 437, 76‐89

Ar (87K) hysteresis desorption scanning curves Scanning hysteresis analysis clearly suggests the existence of two independent pore networks, a and b, in this 3DOm carbon sample

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345

a

b

a

b

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Pore size/volume characterization of nanoporous carbonsCombination of carbon dioxide (273 K) with nitrogen (77 K) or argon (87 K)

Pore size/volume characterization of microporous materials with polar surfaces (e.g. MOFs, zeolites)Argon (87 K)

Analysis of materials with ultra‐low surface areaKrypton (77 K) adsorption for surface area onlyKrypton (87 K) for pore size analysis of thin films

Pore structure and surface chemistry analysisWater adsorption at room temperature Favorable kinetics, small kinetic diameter of water permits entry into pores that are not accessible to carbon dioxide or nitrogen

Water adsorption is affected by both pore structure and surface chemistry

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0 0.2 0.4 0.6 0.8 1P/P0

0

100

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Vol

ume

[cm

3 g-1

] STP

Water (298.4 K) TE80 (CME2) Water (298.4 K) TE80 (CME2) Nitrogen (77.4K) TE80 (CME2)Nitrogen (77.4K) TE80 (CME2)

H2O/298 K (partial wetting fluid)

N2/77 K (wetting fluid)

Type I isotherm

Type V isotherm

Hysteresis in water adsorption isotherm is not regular capillary condensation

Clustering mechanism of adsorption

Thommes, M.; Morlay, C.; Ahmad, R.; Joly, J.P. Adsorption 2011, 17, 633

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Two CMK‐3 materials with identical micropore size and slightly different mesopore size (4 nm vs. 5 nm)

Identical surface chemistry Differences in water adsorption isotherms

– water is sensitive to small changes in pore size

Thommes, M.; Morell, J.; Cychosz, K.A.; Froeba, M. Langmuir 2013, DOI: 10.1021/la402832b

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

100

200

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1000

1100

1200

1300

Vol

ume

@ S

TP

Relative Pressure

CMK-3 (318) CMK-3 (348)

0 1 2 3 4 5 6 7 8 9 10 11 120.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

dV(d

) (cm

3 /nm

/g)

Pore Width (nm)

CMK-3 (318) CMK-3 (348)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

100

200

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800

900

Vol

ume

Ads

orbe

d (c

m3 /g

)

P/P0

CMK-3 (318) CMK-3 (348)

N2 (77 K)QSDFT pore size distributions

H2O (298 K)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

100

200

300

400

500

600

700

Vol

ume

Adso

rbed

(cm

3 /g)

P/P0

Benzene PMO Divinylbenzene PMO

2 3 4 5 6 7 80.0

0.1

0.2

0.3

0.4

0.5

0.6

dV(d

) (cm

3 /nm

/g)

Pore Width (nm)


0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

100

200

300

400

500

600

Vol

ume

Ads

orbe

d (c

m3 /g

)

P/P0


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Two PMO materials with identical pore size Different organic molecules lead to

different surface chemistry for the two PMOs

Differences in water adsorption isotherms due to differences in surface chemistry

Thommes, M.; Morell, J.; Cychosz, K.A.; Froeba, M. Langmuir 2013, DOI: 10.1021/la402832b

Ar (87 K)NLDFT pore size distributions

H2O (298 K)

Physical adsorption is a powerful method for surface and pore size/volume characterization.

Microscopic methods (NLDFT, QSDFT) allow one to obtain an accurate and comprehensive pore size analysis of micro‐mesoporous materials.

Water adsorption detects small difference in surface chemistry and micro‐mesoporous structure.

Chemisorption is a useful tool for characterization of active sites (acidic, basic) in catalysts and other materials.

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katie a. cychoszand matthias thommes -...

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