Surface Area, Pore Size and More: Theory and Application of Porous Materials Characterization Methods

• Gas Adsorption Measurements with particular focus on Microporous Materials • Liquid Intrusion Porosimetry with particular focus on Meso- and Macroporous Materials • Other Methods of Pore Size measurement Capillary Flow Porometry and Electroacoustics • Catalyst Characterization using Chemisorption and Temperature Programmed Analyses • Dynamic Water Vapor Sorption - Adsorption, Absorption, Hydrophobicity, Hydrophilicity

Inert Gas Adsorption

– What can be measured using this technique?

– Who would be interested in such results?

– A

brief

overview of measurement fundamentals.

– Microporous materials • Carbons • Zeolites • Metal organic frameworks – Instrument selection for these materials – Specific features of benefit to analyzing microporous materials – Mesoporous/nonporous materials • Carbon black • Ceramics • Pigments • Alumina • Silica • Metal powders • Pharmaceuticals – Instrument selection for these materials – Specific features of benefit to analyzing meso-/nonporous materials

Inert Gas Adsorption

– What can be measured using this technique?

• Specific Surface Area – How low?

» Depends on instrument sensitivity and amount of sample (more later!) – How high?

» No limit • Pore Size Distribution – Min, max?

» As small as the smallest gas molecule that can be adsorbed – Pore Volume » No limit • Heats of Adsorption » More later

Inert Gas Adsorption

– Who would be interested in such results?

– Everyone who needs to understand how pore structure affects material performance.

• Surface Area – affects dissolution rates.

– affects electron/ion current density at electrode interface with electrolyte.

– affects adsorption capacity.

– represents surface free energy available for bonding in tabletting and sintering.

Inert Gas Adsorption

– Who would be interested in such results?

– Everyone who needs to understand how pore structure affects material performance.

• Pore Size Distribution – affects diffusion rates.

– affects molecular sieving properties.

– affects surface area per unit volume.

Measurement Overview

• Two techniques available • Dynamic flow (uses different concentrations of the adsorbing gas, i.e. gas mixtures)… this will only be covered in discussion session • Vacuum-volumetric, better to say “Manometric” (uses different pressures of the adsorbing gas)… our main focus

What is a Gas Sorption Analyzer?

• Does it actually measure surface area and pore size?

• NO!! It simply records various pressures of gas in the sample cell due to adsorption and desorption.

The instrument then calculates the amount (as STP volume) of gas adsorbed/desorbed. Surface area, pore size are calculated by PC software (iQWin, NovaWin, Quadrawin).

• Pressure measurements are critical!

Adsorption/Desorption

• Adsorption is the sticking of gas molecules onto the surface of a solid… all available surfaces including that surface inside open pores.

• Increasing the pressure of gas over a solid causes increasing adsorption.

• Temperature dependent

Adsorption/Desorption

• Desorption is the removal of gas molecules from the surface of a solid… all available surfaces including that surface inside open pores.

• Decreasing the pressure of gas over a solid causes increasing desorption.

• Done at same temperature as adsorption.

Movie time!

So, How Does It Work?

• Basic Construction – Removable sample cell – Dosing manifold – Pressure transducers – Vacuum system – Analysis gas – Valves to move gas in and out of manifold and sample cell – Sample thermostat (dewar, furnace, cryostat)

So, How Does It Work?

• Basic Construction – Removable sample cell • A long stemmed piece of glassware that holds the sample during degassing (preparation) and analysis.

• Available in different stem diameters and bulb sizes.

So, How Does It Work?

• Basic Construction – Dosing manifold • A chamber of known (i.e. calibrated) physical volume from which gas is added to and removed from the sample cell during adsorption and desorption respectively (think burette).

So, How Does It Work?

• Basic Construction – Pressure transducers • Used to both quantitatively determine the amount of gas adsorbed/desorbed and the pressures at which the sorption is measured.

So, How Does It Work?

• Basic Construction – Vacuum system • Vacuum pump(s) generate sub-atmospheric pressure conditions.

• Rotary oil pumps for low vacuum applications.

• Turbo pump backed by oil-free diaphragm pump for high vacuum applications.

So, How Does It Work?

• Basic Construction – Analysis gas • Nitrogen is used most often.

• Argon is recommended for micropore size measurements.

• Krypton is used for very low surface area and thin film applications.

• Multiple gases can be connected at one time, though only one is actively used.

So, How Does It Work?

• Basic Construction – Valves to move gas in and out of manifold and of sample cell • Automatically operated to fill the dosing manifold to a pressure sufficient to yield a datum point at a specified target pressure (or at target sorbed amount) • Magnetic latching valves… no heat generated during pressure equilibration

So, How Does It Work?

• Basic Construction – Sample thermostat (dewar, furnace, cryostat) • Dewar holds cryogenic liquids (liquefied gases) like liquid nitrogen (LN 2 ) and liquid argon (LAr) • Furnace: used for chemisorption measurements at temperatures above ambient • Cryostat: for advanced research applications, overcomes limitations of restricted choice of temperatures available with liquefied gases in a dewar.

Analysis gas

Basic Construction

Pressure transducer(s) to vacuum Manifold Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold Manifold, transducer and sample cell are evacuated.

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold Manifold, transducer and sample cell are evacuated… and cell is cooled.

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold Intermediate valve status.

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold Analysis gas is admitted to build some pressure in the manifold.

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold A steady pressure in the manifold is recorded, P1.

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold Gas expands from manifold into sample cell; pressure drops in the manifold, rises in sample cell.

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold Gas is adsorbed by the sample, pressure drops further in both volumes.

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold Eventually the pressure equilbrates. Final pressure, P2, is recorded.

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold Process is repeated at higher and higher pressures.

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold Adsorption measurements are complete... Getting ready to desorb!

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold In desorption, some gas is removed from the manifold while the sample cell remains isolated.

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold Manifold is isolated and desorption P1 is measured.

Sample cell

Analysis gas

Basic Operation

Pressure transducer(s) to vacuum Manifold Gas is expanded from sample cell into manifold, pressure drops in the sample cell, rises in the manifold… P2 (desorption) Sample cell

A More Realistic Representation

Sample Temperature Control

• As the coolant evaporates, the level sensor signals the dewar drive to compensate for the change in level, thereby maintaining a constant and zone.

small

cold cabinet level sensor sample cell 90 hr dewar drive shaft dewar support arm

What’s Really Measured

• The

pressure

of gas

not

the sample, just filling the currently adsorbed by

void volume

.

• To know

quantitatively

what

is

adsorbed, the instrument calculates: – The dose amounts, i.e. amount of gas moved into (adsorption) or out of (desorption) the cell by the end of an equilibration period.

– The amount of gas remaining unadsorbed (in the void volume) at that time.

–

The difference is what is adsorbed.

What’s Measured

• To calculate the gas amounts dosed (in/out) the instrument must know: – P1 – P2 – Volume of the manifold – Temperature of the manifold

What’s Measured

• To know the volume of the manifold: – it is calibrated using a special cell and glass cyclinder (rod).

– All instrument manifolds are factory calibrated.

• To know the temperature of the manifold: – it is constantly monitored by a solid state sensor.

What’s Measured

• To calculate the gas amounts

not

adsorbed the instrument must know: – Volume of the void volume (sample cell) – Temperature of the void volume (sample cell)

What’s Measured

• To know the volume of the sample cell the instrument can: – Measure it by expanding helium from the manifold (as part of initializing the analysis) – Use a previously measured value – Use a stored value based on expanding nitrogen into an empty cell, correcting for sample volume (the so-called NOVA method)

What’s Measured

• To know the temperature of the sample cell (in coolant) the instrument: – is told it as an analysis parameter.

• To ensure that the volume of cell in coolant remains constant: – a coolant level sensor and dewar elevator mechanism combine to maintain level of coolant around the sample cell.

Small Cold Zone = Sensitivity

Coolant level controlled here creates a small cold zone.

Quantachrome’s instruments

Working Equation

PV = nRT n

ads

= n

dosed

- n

void

n

ads

= (



PV/RT)

man.

- (PV/RT)

cell

Refinements

• Corrections for “non-ideality” of gas, especially at cryogenic temperatures.

• Compensation for the slight change in temperature of that part of the sample cell not in coolant (“TempComp”).

• Determination of “saturation vapor pressure” of the coolant, known as

Po

.

What Is The Result?

It’s called an “isotherm” Equilibrium pressure

What Is The Result?

The values on the y-axis are calculated

from

pressure

measurements (and temperature values) The values on the x-axis

are

pressure

measurements.

Equilibrium pressure

What Is The Result?

Desorption curve may overlay on, or appear to left of, the adsorption curve The values on the x-axis are in fact expressed as relative pressure, P/Po Relative pressure

Very Low Pressure Behavior (micropore filling)

Relative Pressure (P/Po)

Low Pressure Behavior (monolayer)

The “knee” Relative Pressure (P/Po)

Medium Pressure Behavior (multilayer)

Relative Pressure (P/Po)

High Pressure Behavior (capillary condensation)

Relative Pressure (P/Po)

Instrument Features

• Multiple transducers – 1000 torr • Used for usual BET (surface area) range and mesopore analyses – 10 torr • Used for krypton BET areas and shifted BET range (e.g. zeolites) • Used to cover intermediate pressure range between 1 torr and 1000 torr • Always associated with turbo pump – 1 torr • Used for krypton BET areas and micropore measurements • Always associated with turbo pump – 0.1 torr

(in place of 1 torr, iQ-XR only)

• Extended range micropore

Instrument Features

• Degassing – Is done on the

degassing

ports – Is

not

for grossly wet samples – Is done

without

a filler rod* – Should include a “test” – Dirty filters can reduce effectiveness – Should be done using LN 2 in cold trap – *When using a Cell-Seal a filler rod is added first, so degassing is done with the rod.

Applications I

– Microporous materials • Carbons • Zeolites • Metal organic frameworks – Instrument selection for these materials – Specific features of benefit to analyzing microporous materials

Applications I

– Microporous materials •

Activated carbons

– The small size of their pores gives them great surface area… they can adsorb a large amount of gas directly on to their surface. Popular support for some catalyst metals (especially palladium and platinum).

ρ ~

2g/cm 3 •

Zeolites

– The narrow size distribution of their pores makes them very useful for gas separation. Also used as catalysts because of acid sites in the pores.

ρ ~

4g/cm 3 •

Metal organic frameworks

– Their huge surface area and pore volume makes them potentially useful for gas sequestration/storage.

ρ <

0.5g/cm 3

Activated Carbons

– Made from a variety of materials: • • • •

Rice husk Coconut fiber Nut shells Waste biomass

–

plant

–

animal

Activated Carbons

– Activation is done chemically and thermally.

– It creates spaces between layers of carbon (graphene) of non-uniform micropore size .

– It usually produces a chemically heterogeneous surface.

• Presents a problem for accurate pore size calculations.

N 2 , Ar (at 77.35 K)

vs

. CO 2 (273.15 K) Adsorption on Activated Carbon Fiber (ACF-10) and NLDFT-PSD Histograms 400 300 N2 (77 K) Ar (77 K) CO2 (273 K)

N 2 /77.35 K

200 N 2 100 Ar

CO 2 /273.15 K

0 1E-06 1E-05 0.0001 0.001

0.01

CO 2 , 0.1

1 0.07

0.06

0.05

0.04

0.03

0.02

0.01

0 4

Relative Pressure

6

Analysis Time:

8

Quantachrome’s Powder Technote 35

CO 2 N 2 = 3 h = 40 h

10 12

Pore Size Å

14 CO 2 N 2 16 18 20

Microporous Carbons: the Standard way

700 600 500 400 300 200 100 0 0 Nitrogen, 77.35 K 2 .

10 -1 4 .

10 -1 P/P 0 6 .

10 -1 8 .

10 -1 10 0 Nitrogen (77.35 K and Water Sorption (298.4K) in Activated Carbon Fibers (ACF), (M. Thommes, et al., FOA 8, 2004)

600

Featureless Isotherms

Nitrogen, 77.35 K 480 360 240 120 0 5 10 -6 5 10 -5 5 10 -4 5 10 -3 P/P 0 5 10 -2 5 10 -1 5 10 0 Nitrogen (77.35 K and Water Sorption (298.4K) in Activated Carbon Fibers (ACF), (M. Thommes, et al., FOA 8, 2004

0.8

State of the Art Cryogenic Differentiation

NLDFT A 15 0.64

0.48

0.32

A 10 A 5 0.16

0 6 8 10 20 Pore Diameter [Å] 40 60 80 100 Nitrogen (77.35 K and Water Sorption (298.4K) in Activated Carbon Fibers (ACF), (M. Thommes, et al., FOA 8, 2004

The Special Behavior of Water

800 700 600 500 400 300 200 100 0 0 Water, 25 C 0.2

A5 25C A10 25C A15 25C 0.4

0.6

0.8

A15 A10 A5 1 Nitrogen (77.35 K and Water Sorption (298.4K) in Activated Carbon Fibers (ACF), (M. Thommes, et al., FOA 8, 2004

Zeolites

– Micropores are part of their crystal structure: • • • • •

Most are synthetic Alumino-silicates Silicalite = no aluminum Cation can be H + , Na + , Ca 2+ , NH 4 + , etc Pore shape needs to be incorporated into pore size calculation for accurate results

•

Some adsorbates are better than others

Adsorption of Nitrogen (77.35 K) and Argon (87.27 K) on a Zeolite

350 280 210 140 70 Faujasite: Ar and N 2 Adsorption

.

N 2 /77.35 K Ar/87.27 K

0 10 -6

ZEOLITE | 10.5.2001

5 10 -5 5 10 -4 5 10 -3

P/P 0

5 10 -2 5 10 -1 5 10 0

Different Sized Pores Fill at Different P/Po

Pore Shape is Important for Accurate Pore Size Analysis of Zeolites

(M.Thommes et al., presented at the International Zeolite Conference, Cape Town, 2004) 300

0.7

240 180 120 60 0 10 -6 5 10 -5 5 10 -4 5 10 -3 P/P 0 5 10 -2 5 10 -1 5 10 0

X-Zeolite structure (spherical pores) Mordenite structure (cylindrical pores)

0.56

0.42

0.28

0.14

180 120 60

0

4 12 20 28 Pore Diameter Å 300 240 Zeolite X- type DFT-Fitting : cylindrical pore model 36 44 0 10 -5 5 10 -4 5 10 -3 P/P 0 5 10 -2 5 10 -1 5 10 0

Metal Organic Frameworks MOFs

– Synthetic materials – Also called coordination polymers – Similar materials without metals are called COFs… covalent coordination polymers – Still a very active research area

Metal Organic Frameworks MOFs

ZnO4 tetrahedra (blue) are joined by organic linkers (O, red, C, black), giving an extended 3D cubic framework with inter-connected pores of 11.2 Â aperture width and 18.5Â pore (yellow sphere) diameter

Microporous Materials

– Instrument selection for these materials • • A micropore size distribution requires an isotherm to be measured at low enough pressures to see the micropore filling, and accurately enough to yield an accurate pore size analysis.

– Why?:

Best high vacuum performance = lowest starting pressure.

• •

Best (i.e. lowest) leak rate = data quality.

Lowest pressure measurement possible (0.1 torr xducer) = greatest confidence at smallest pore filling pressure.

•

Largest dewar = Longest unattended analysis time = even the slowest measurements are possible.

•

Optional second station = no sharing transducers = significantly increased throughput (almost double!).

Microporous Materials

– Instrument selection for these materials •

No high vacuum available? = no micropore size distribution except when using CO on carbons.

2 at 0degC

•

Can still measure total BET surface area including contribution from micropores.

•

Can determine micropore area and micropore volume using t-plot method.

The Autosorb-iQ

• Basic specs – Transducers: (optional 0.1 torr), 1 torr, 10 torr, 1000 torr – Vacuum system: turbo pump

(dry pump is standard)

– Multiple gas inputs – Large dewar

(90 hour)

– Two degas ports each with own mantle – Programmable degassing – Po port – Dosing algorithms

etc

The Autosorb-iQ

• Advanced specs – Metal seals and very low leak rate allow us to measure very low pressure isotherms even when using helium void volume mode.

No need to disconnect helium and all other gases from the unit when measuring micropore isotherm!

– Two stations data quality are the same as one station (see next slide).

No transducer or dosing manifold sharing.

– Dedicated Po transducer.

Sample station(s) NOT interrupted to re-measure.

This plot actually shows THREE isotherms. One generated using just one station, and a pair generated simultaneously using both stations of the iQ2.

Accurate pore size calculations

• Accurate pore size calculations – QSDFT for activated carbons…accounts for surface heterogeneity.

– Argon NLDFT models for different pore shapes (zeolites and MOFs) • Full and proper equilibration

incorrect correct

Applications II

– Mesoporous/nonporous materials • Carbon black • Ceramics Pigments • Alumina • Silica • Metal powders • Pharmaceuticals – Instrument selection for these materials – Specific features of benefit to analyzing meso /nonporous materials

Applications II

– Mesoporous/nonporous materials •

Carbon black

– Essential for tires and other rubber applications. BET (NSA) and t-plot (STSA) are important.

•

Ceramics

– Particle size affects surface area, surface area remains after particle size is history. Pore size affects wicking of liquids.

•

Pigments

– Surface area and porosity “immobilize” liquids and alter rheology.

•

Alumina

– Surface area and pore size are the dominant quality control parameter. Often used as a catalyst support.

•

Silica

– Surface area and pore size are the dominant quality control parameter.

•

Metal powders

– Surface area supports particle size data especially fines.

•

Pharmaceuticals

– Surface area is lost during tabletting (however pore size affects wicking of liquids) but after ingestion (and dissolution of excipient) s.s.a. of active controls release rate.

Carbon Black

Aluminas

Aluminas

Mesoporous Templated Carbons

Mesoporous Templated Carbons

Mesoporous Oxides

Mesoporous Oxides (Calcination Temperature)

Applications II

– Mesoporous/nonporous materials •

Materials Research

–

Templated silicas

» MCM41 is the most famous example. Pore size by gas adsorption is an essential part of characterization.

–

Templated carbons

–

Thin films

» For low-k (dielectric) applications. Difficulty is associated with very small amount of porous material.

Mesopore Analysis

Significant progress in the pore size analysis of porous materials made in the last few years, mainly because of the following reasons :

•

(i) The discovery of novel ordered mesoporous

molecular sieves

which were used as

model adsorbents

to test theories of gas adsorption •

(ii) The development of microscopic methods

, such as Non-Local-Density Functional Theory (

NLDFT

) and Quenched Solid Density Functional Theory (

QSDFT

) •

(iii) Carefully performed adsorption

experiments…

something at which

Quantachrome

excels

.

What Does a Model Adsorbent Look Like?

TEM of MCM-41 Silica

Sorption, Pore Condensation and Hysteresis Behavior of a Fluid in a Single Cylindrical Mesopore From: M Thommes, “ Physical adsorption characterization of ordered and amorphous mesoporous materials”, Nanoporous Materials Science and Engineering” (edited by Max Lu, X.S Zhao), Imperial College Press, Chapter 11, 317-364 (2004)

Pore Size Can Also be Controlled by Granulation

SEM- of Mesoporous TiO 2

Different Sized Pores Fill at Different P/Po

150 120

Nitrogen Sorption at 77 K into Mesoporous TiO 2 6 nm 10 nm

90 60

30 nm

30 0 0 0.2

0.4

0.6

P/P 0

H. Kueppers, B. Hirthe, M.Thommes,

G.I.T

,

3

(2001) 110 0.8

100 nm

1

Different Sized Pores Fill at Different P/Po

600

3.6 nm

500 400

3.3nm

4.2 nm

Argon 77K/ MCM-41 300 200 100 0.0

ads des

MCM-41A MCM-41B MCM-41C

3.3nm

3.6 nm 4.2 nm

0.2

0.4

0.6

0.8

RELATIVE PRESSURE p/p 0

1.0

In : S. Lowell, J. Shields, M. Thomas, M. Thommes, Characterization of porous solids and Powders: Surface Area, Pore Size and Density, Kluwer Academic Publ, 2004,

Different Temperatures Cause Same Sized Pores to Fill at Different P/Po

70 60 50 40 30 20 10 0 0.0

77 K

0.2

Ar / 77 K and 87 K 87 K

ads des 77 K 87 K

Argon/ MCM-48 (d = 4.01nm)

0.4

0.6

relative pressure p/p 0 0.8

1.0

M. Thommes,, R. Koehn and M. Froeba et al. J. Phys. Chem B 104, (2000), 7933

Some History of Pore Size Analysis of Mesoporous Materials

(a) Methods based on (modified) Kelvin Equation

• e.g., - Barrett-Joyner-Halenda (BJH) (1951) - Dollimore-Heal (DH) (1964) - Broeckhoff de Boer (BdB) (1967/68) - Kruk-Jaroniec-Sayari (KJS)) (1997) - Bhatia

et al

(mod. BdB) (1998/2004) - D.D.Do & Ustinov (mod. BdB) (2004/2005)

(b) Density Functional Theory (DFT / NLDFT):

e.g.- Evans and Tarazona (1985/86) - Seaton (1989), - Lastoskie and Gubbins (1993) - Sombathley and Olivier (1994) Neimark and Ravikovitch (1995 ……)

(c) Quenched Solid DFT (QSDFT):

Neimark and Ravikovitch (1995 ……)

(d) Monte Carlo (MC) and Molecular dynamics (MD),

e.g. Gubbins et. al. (1986…. ) Walton and Quirke (1989…) - Gelb (1999 ….) Neimark and Ravikovitch (1995….)

Theoretical Predictions of Pore Filling P/Po as Function of Pore Size N 2 / 77K in cylindrical silica pores

X X  . Neimark AV, Ravikovitch P.I., Grün M., Schüth F., Unger K.K, (1998) J. Coll. Interface Sci. 207,159

BJH and NLDFT Compared

560 490

N 2 (77 K): ads N 2 2 (77 K): des

420 350 280 210 140 0 0.2

0.4

0.6

RELATIVE PRESSURE p/p 0

0.8

1 0.3

0.25

0.2

0.15

0.1

0.05

0 15 23

BJH

X

NLDFT

31 39 Pore Diameter [Å]

NLDFT method: N2/77K cylindrical-silica pore model

 47 55

Combined Micro/Mesopore Analysis by NLDFT (can’t be done by BJH)

Argon adsorption at 87 K on a 50:50 mixture of ZSM-5 + MCM-41: 25 20 0.1

0.09

0.08

0.6

0.5

0.07

0.4

15 0.06

MCM-41

0.05

0.3

10 MCM-41 ZSM-5 50-50 0.04

0.03

ZSM-5

histogram integral 0.2

5 0.02

0.1

0.01

0 0.000001

0.00001

0.0001

0.001

P/Po 0.01

0.1

1 0 1 10 100 1000

D, [Å]

S. Lowell, J.E. Shields, M.A. Thomas and M. Thommes, Characterization of porous solids and powders: Surface Area, Pore Size and Density, Kluwer Academic Publisher, 2004 0

Studying Pore Geometry, Connectivity and Disorder Nitrogen Sorption at 77 K into various Mesoporous Silica Materials

700 600 500 400 300 200 100 0

0 0.2

0.4

0.6

RELATIVE PRESSURE P/P 0

0.8

1

IUPAC Classification of Hysteresis

Due to intrinsic fluid property

Cylindrical Pores Cylindrical & Spherical Pores Disordered; lamellar pore structures, slit & wedge, shape pores Micro/Mesoporous adsorbents

Due to pore blocking / cavitation (wide bodies, narrow necks)

0.05

Why Does Type H1 Exist?

equilibrium transition spinodal evaporation 0.04

0.03

Adsorption, mmol/m

2

0.02

spinodal condensation 0.01

Experimental (des) Experimental (ads) NLDFT in 4.8nm pore 0 0 0.2

0.4

0.6

Relative pressure, P/P 0 0.8

1

It can be clearly seen that the experimental desorption branch is associated with the equilibrium gas-liquid phase transition,

whereas the condensation step corresponds to the spinodal spontaneous transition (i.e. delayed until nucleation occurs). (a)Neimark A.V., Ravikovitch P.I. and Vishnyakov A. (2000) Phys. Rev. E 62, Microporous and Mesoporous Materials 44-56, 697.

R1493; (b)Neimark A.V. and Ravikovitch P.I. (2001)

Pore Size from H1 Can be Calculated from Ads and/or Des using NLDFT (but not BJH)

200 100 0

0

700 600 500 400 300

Nitrogen adsorption/desorption at 77.35 K in SBA-15 and pore size distributions

0.22

0.2

0.18

0.16

0.14

0.2

0.4

0.6

Relative Pressure P/P 0 0.8

1

0.12

0.1

0.08

0.06

0.04

0.02

0 25 45 65 85 Pore Diameter [Å] 105 M. Thommes, in Nanoporous Materials Science and Engineering” (edited by Max Lu), Imperial College Press, Chapter 11 p. 317 - 364 (2004) 125

Pore Size from H1 Can be Calculated from Ads and/or Des using NLDFT (but not BJH)

420 350 280 210 140 70 0

0 Nitrogen sorption at 77 K in CPG (Controlled Pore Glass)

0.026

0.013

0.2

0.4

0.6

Relative Pressure P/P 0 0.8

1

0

40 90 140

Pore Diameter [Å]

190 240

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

Why Does Type H2 Exist?

Type H2 Hysteresis Two Problems for Pore Size Analysis : Adsorption Branch : metastable pore fluid



delayed pore condensation Desorption Branch : pore blocking,percolation



delayed evaporation How to Solve:



Application of novel NLDFT approaches

Body Pore Size from H2 Calculated from Ads and Neck Size from Des using NLDFT (but not BJH) Nitrogen sorption at 77 K in porous Vycor Glass and pore size distributions from adsorption- (NLDFT spinodal condensation kernel) and desorption (NLDFT equilibrium transition kernel)

60 30 0 0 150 120 90 0.2

0.4

0.6

Relative Pressure p/p 0

0.8

0.04

0.032

0.024

0.016

0.008

1 0

25

VYCOR(PSD) | 12.11.2002

50 75 100 Pore Diameter [Å] 125 150

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

H3 Hysteresis

240 210 180 150 120 90 60 30

0

N2/77K sorption on disordered alumina catalyst 1

0.2

0.4

0.6

Relative Pressure P/P 0 0.8

0.8

0.6

0.4

1

0.2

0

10 BJH-PSD

Artifact

50 100 Pore Diameter [Å] 500 1000

M. Thommes, In Nanoporous Materials Science and Engineering, (Max Lu and X Zhao, eds.), World Scientific, in press (2004)

H4 Hysteresis

500 400 300 200 100 0 0

Nitrogen adsorption at 77.4 K in activated carbon

0.2

0.4

P/P 0

0.6

0.8

1

Neck size H2 versus “H2”/H3/H4 NO size information Pore body size Pore body size NO size information; Cavitation is a property of the liquid

M. Thommes, B. Smarsly, P.I. Ravokovitch, A.V. Neimark et al.. Langmuir, 22, 765 (2006)

Product Selection

• Mesopore analysis needs: – Regular vacuum – 1000 torr pressure range – 24 hour dewar – Po station (usually) – A simple BET does not need a long life dewar and Po is less critical

Product Selector 1

ONE SAMPLE Quantachrome Model Stations Nova1 1 iQ 1 Nova2 1+1 Po ports Full ads 0 y 1 y (1) y Full des y y y Degas stn Xducer (s) specification 2 (vac / flow) 0.11% f.s.

2 (vacuum) 0.11% f.s.

2 (vac / flow) 0.11% f.s.

Product Selector 2-3

TWO-THREE SAMPLES Model Quantachrome Nova2 Quad 2 iQ2 Quantachrome Nova 3 Quad 3 Nova 4 Stations Po ports Full ads Full des Degas stn Xducer (s) specification 1+1 (1) y y 2 (vac / flow) 0.11% f.s.

2 2 y 2 1 y 2+1 (1) y y y y 0.11% f.s.

2 (vacuum) 0.11% f.s.

4 (vac / flow) 0.11% f.s.

3 3 y 3+1 (1) y y 0.11% f.s.

y (vac / 4 flow) 0.11% f.s.

Product Selector 4+

Q’chrome FOUR or MORE SAMPLES Model Stations Po ports Full ads Full des Degas stn Xducer (s) specification Quantachrome N4 Quad 3+1 (1) y y 4 (vac/flow) 0.11% f.s.

4 4 y y 0.11% f.s.

AS6B y 6 6 y 0.11% f..s.

Workshop topics

• Selecting sample cells • Degassing conditions • BET points • Mesopore points • Micropore points