mesoporousmaterials-130320045656-phpapp02

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What are Porous materials

The history of porous materials began with the zeolites having

aluminoisilicates frameworkwhich was synthesized by the use single

template molecule with small pore.

Most generalized definition of porous materials is continuousand

solid network material filled through voids.

A material can be recognized as porous if its

internal voids can be filled with gases.


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Classification of porous materials

Depending on pore size Depending on building

framework

Micropoorus Mesoporous Macroporous

50nm

Purely inorganic Organic Inorganic

hybrid

Purely

organic

ZSM-5 MCM-41 Sponge

Silica MOF organicporous polymers


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Mesoporus Materials

Meso a Greek prefix in between - micro and macro

porous systemMesoporous materials may be ordered or disordered.

They possess high

Surface area -400 -1000 m2/g

Large pore volume

High stability -500 -600 C

They are usually synthesized by the use of Soft template

method.

Ex: MCM-41,SBA-15,FDU-11,IITM-56 etc.


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Difference between the zeolites and mesoporous materials

Zeolites Mesoporous MaterialsHighly crystalline Periodic arrangement with amorphous in

nature

TO4networks TO4,TO5and TO6networks

Si and Al are four connected by covalent

bond, less surface hydroxyl groupsHydrophobic surface area

Si and Al are 2 or three connected ,more

surface hydroxyl groupsHydrophilic surface area

High hydrothermal stability Less hydrothermal stability

Crystalline walls and are thick Amorphous walls and are thin

Synthesis temp is high (80300 C)Long crystallization time

Synthesis temp is low (-10 to 120C)Formation rates are fast

Aqueous media is required for

crystallization

Nonaqueous solvents and non polar

solvents can be used

Synthesis of zeolite is carried out in

neutral /weakly acid media

Synthesis pH rang is from 0 to 12


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Synthesis of mesoporous materials

Soft template (endo template)

Uses soft templates like organic

molecules .

Good shape , Size and morphology.simple

SBA-15 ,MCM-41 etc

Hard template (exo template, nano casting)

Uses inorganic materials like silica, carbon

etc

Tedious work up, hard to get good

morphology and costly

CMK-1

Meso-silica

CMK-1


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Synthesis of mesoporous materials using soft

template strategy

1. Surfactants.

2. Formation of Micelles.

3. Inorganic precursor .4. Interaction of Micelles with inorganic precursor.

5. Hydrothermal treatment followed by separation and drying

6. Removal of template.

7. Proposed mechanism

8. Characterization of material.


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1. Surfactant/ Template/Structure directing agent.

Large organic molecules(High molecular weight) with both

hydrophilic and hydrophobic groups.

Depending upon charge they can be

classified as

Cationic Anionic Non ionic/neutralExcellent solubility

High critical Micelle con.

acidic and basic mediatoxic and expensive

Excellent solubility

repulsion between the

anionic surfactant is more.

Excellent solubility

High critical micelle temp.

Acidic / basic medianon-toxic and cheap


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2. Formation of micelle

At a Low surfactant concentration will favor

arrangement on the surface.

As the concentration increases surface being more

crowded as result molecule arrange in to micelles.

At certain concentration the surface is completelyloaded and any further addition leads to the

Micelle arrengment.This conc. is known as CMC.

Beyond the CMC self assembly of micelle occurs tofrom 3D and 2D rod like arrays.

Different template have the different CMC.

To get ordered materials0 to20 mg/L


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Different type of surfactant arrangement


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What Makes them to show different type of arrangements ?

1. Critical micelle concentration

Low micelle conc. are good to get ordered materials.

2. Packing parameter (g)

g = V / ao l

V=Total volume of surfactant hydrophobic chains+ co-solvnet.

ao= Effective hydrophilic head group area at the aq. micelle surface.

l = kinetic surfactant tail length.

g


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3.Inorganic precursor and pH

Inorganic Precursor silica depends upon pH

Basic synthesis (pH =9.5 to 12.5)

-Polymerization and cross Linkage of silicate species are reversibleSilica gel, colloidal sol, Water glass , TEOS etc.

Acidic synthesis(pH= 1 to 2 )

-Irreversible.

-

Slow hydrolysis TEOS is preferred.


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4. Interaction of Micelles with inorganic precursor.

Direct interaction of Surfactant with inorganic precursor

Basic -Medium Acidic-Medium


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Interaction of Surfactant with inorganic precursor through

intermediate ions

Basic -MediumAcidic-Medium


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Interaction of non ionic Surfactant with inorganic precursor

through intermediate ions.

Hydrogen bonds favors most of times


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5. Hydrothermal treatment followed by separation and

drying.

Method to improve mesoscopic regularity's of products.

Reorganization, growth and crystallization

80 -150 C is temperature is usually used.

High temperature will lead to the disorder and decomposition of

surfactants.

Separationfiltration or centrifugation.

Washingalcohol or water. Basic media needs through washing.

Drying at room temperature is good.


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6. Removal of template.

Removal of template will give rise to mesoporosity

Different ways by which template can be

removed

CalcinationSlow heating rate.

N2-1 hr

O2- 4-6 hr2 C/min

O2-1 C/min

No surfactant recover

low Surface silanol groupsNot good for low thermal

stable materials

P-123 -550 C

CTAB -350 C

Solvent ExtractionSolvent ethanol /THF

small HCl is added

Surfactant can be reused

MicrowaveUltraviolet rays

O3and O

Light irradiation


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p6mmIa3d,

Pm3n

Im3m

Fd3m

Fm3m.

MCM-48

FDU-2SBA-16

KIT-5

SBA-1 and 6

SBA-15


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Proposed mechanisms for synthesis mesoporous materials

1. Silicate rod assembly

2 or 3 monolayer's of silicates species first deposits on isolated surfactant

miceller rods


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2. Cooperative self assembly

Low concentration Surfactant


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3. True liquid crystal templating route

High concentration Surfactant


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Complete synthesis summary

Ch i i f i l


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7. Characterization of mesoporous materials

1. Low angel XRD

0.5 -5 -2theta

- orederness / disorder.

2. N2 sorption measurementsBJH

method

Surface area/pore diameter /pore

volume

3. TEM imagesOrder ,Morphohology ,

Wall thickness

Applications


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Applications

l h l l


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Application Chemical Catalysis

1. Mesoporous Materials as catalyst

Al-MCM-41 ,B-MCM-41, Sn-SBA-15 - AcidicK- AlMCM-41 , Cs-AlMCM-41 -basic

TiMCM-41 ,V-MCM-41 -Redox


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2.Mesoporous Materials as catalyst support

Noble metal supported catalyst supports

Au-McM-41 , Pt- CMK-3

Metal oxide supported catalysisFe2O3- MCM-41 ,RuO2-SBA-15

Metal complex supported catalysts

Mn-SalenSBA-15

3 Application in environmental catalysis


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3. Application in environmental catalysis

Immobilization of enzyme on Mesoporous Materials as

catalysts

Enzymes are excellent biocatalysts with high selectivity and efficiencin environment field, chemical and pharmaceutical industries

are limited by their poor stability and chemical sensitivity

4 G d d b


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4. Good adsorbents


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5.Applications in Biomedical field

1) Sustained Drug Release System


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1) Sustained Drug Release System

M. Vallet-Regi, et al. A New Property of MCM-41: Drug Delivery System, Chem. Mater. 2001, 13, 308-311.

Virtually any drug within a size range compatible with the size of the meso-

channels has potential to be encapsulated and further deliver intracellularly.


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2. Mesoporous Materials for Bone Tissue Engineering

M Bi i ff ld


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Mesoporous Bioactive scaffoldsScaffolds are needed that can act as temporary templates for bone regeneration

and actively stimulate vascularized bone growth so that bone grafting is no

longer necessary.

Bioactive glass is an ideal material because it rapidly bonds to bone and

degrades over time, releasing soluble silica and calcium ions that are thought to

stimulate osteoprogenitor cells.


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1 Day

3 Day

7 Day

6 Mesoporous Polymers


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6.Mesoporous Polymers

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