Mesoporous Materials

Presented by Mannu KaurM.Tech NST 1st year (2nd sem)

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Outline What are Porous materials?

Classification of Porous materials

What is Mesoporous material?

Synthesis of Mesoporous material

Applications

Magnetic Nanoparticles with Mesoporous Structures

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Zeolites• Zeolites are porous, hydrated aluminosilicates. They may be natural minerals or synthetic

materials.

• The general chemical composition of a zeolite is: Mx/nSi1-xAlxO2 · yH2O Where M = e.g. Na+, K+, Li+, Ag+, NH4

+, H+, Ca2+, Ba2+

• These are three dimensional structure built from tetrahedra. Some silicon atoms have been replaced by aluminium.

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Background• The synthesis of porous material started in late 1940’s with synthesis of

synthetic Zeolites by Barrer, Breck, Milton and Co-workers.

• Coming years witnessed the formation various zeolites with different compositions and topologies.

• In 1982 Flenigen reported the formation of non-silicate microporous materials- formation of Aluminophosphate sieves.

• In 1992 Mobil scientists synthesized porous material, M41S, that had pore size in meso range.

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What are Porous materials It can be defined as, continuous, solid material filled with voids

Porous materials are characterized by its ‘Porosity’.

There are a variety of porous materials differing in chemical composition, pore geometry and size.

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PorosityPorous material contain pores (cavities, channels) which are deeper

than they are wide. Either describe the pores, or describe the cell/pore walls

Accessibility:a: closed poresb,c,d,e,f: open poresb, f: blind pores (dead-end )e: through poresShape:c:Cylindrical openf:Cylindrical blindb: ink-bottle-shapedd: funnel shapedg: roughness

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Pore sizePore size is important for applications. IUPAC, three pore size regimes.•Microporous, smaller than 2 nm•Mesoporous, between 2 and 50 nm•Macroporous, larger than 50 nm

Different pore size material show characteristic physical

adsorption isotherm.

Microporous: these material show type-I isotherm

Mesoporous: type-IV isotherm is seen in this material

Associated with capillary condensation

Macroporous: this material shows type-II adsorption isotherm

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Classification of Porous material

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Mesoporous materials Mesoporous materials are the materials which have their pore size in

between Micro- and Macroporous materials.

They can be used in variety of applications mainly because of its high - surface area - pore volume - stability

The most common method of synthesis of mesoporous material is, Soft template method.

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Synthesis of Mesoporous materials

Soft template Hard template • Uses soft template like

organic molecules.• Good shape, size and

morphology• SBA-15, MCM-41 etc.

• Uses inorganic material like silica.

• Difficult work up, hard to get good morphology

• CMK-1

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Hard templateSynthesis of mesoporous carbons with well-defined mesoporous structure is usually done by hard template method a) Preparation of silica gel with controlled pore structure.b) Impregnation/infiltration of the silica template with monomer or

polymer precursors.c) Cross-linking and carbonization of the organic precursors.d) Dissolution of the silica template.

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Preparation of silica gel• Pluronic P123 (block co-polymer), dissolved in distilled water, in

presence of acid. • After complete dissolution, n-butanol is added and continued to stir

for 1h. Followed by addition of tetraethyl orthosilicate (TEOS).• The mixture was further kept for stirring and subsequently

hydrothermally heated.• Removal of surfactant by extraction with water followed by

calcination.

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Soft template method for synthesis

1. Surfactants.2. Formation of Micelles.3. Inorganic precursor .4. Interaction of Micelles with inorganic precursor.5. Hydrothermal treatment followed by separation and drying6. Removal of template.7. Proposed mechanism

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1. Surfactant/ Template Large organic molecules(High molecular weight) with both hydrophilic and hydrophobic groups.

Depending upon charge they can be classified as

Cationic Anionic Non ionic/neutral•Excellent solubility•High critical Micelle con.•toxic and expensive

•Excellent solubility• repulsion between the anionic surfactant is more.

•Excellent solubility•High critical micelle temp.•non-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 completely loaded and any further addition leads to the Micelle arrengment.This conc. is known as CMC.

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

Different template have the different CMC.

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3.Inorganic precursor and pHInorganic Precursor silica depends upon pHBasic synthesis (pH =9.5 to 12.5)-Anion species is obtainedAcidic synthesis(pH= 1 to 2 )-Cationic species is obtained

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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 non ionic Surfactant with inorganic precursor through intermediate ions.

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5. Hydrothermal treatment followed by separation and drying.

80 -150 °C is temperature is usually used.

High temperature will lead to the decomposition of surfactants.

Separation – filtration or centrifugation.

Washing –alcohol 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

Calcination•Slow heating rate.•No surfactant recover•Not good for low thermal stable materials•CTAB -350 °C

Solvent Extraction• Solvent ethanol /THF• small HCl is added• Surfactant can be reused

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Effect of surfactant 1. Critical micelle concentration Low micelle conc. are good to get ordered materials.2. Packing parameter (g) g = V / ao

V=Total volume of surfactant hydrophobic chains

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

g <1/3 = cubic and 3 D hexagonal,1/3<g>1/2 = 2D hexagonal1/2<g>2/3 = cubicg=1 = Lamellar

3.The hydrophilic and hydrophobic Volume ratio (VH /VL)

Different type of surfactant arrangement

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Complete synthesis summary

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Functionalization of Mesoporous material

• Mesoporous silicates have very high surface area and their surfaces are covered by silanol groups, which makes the functionalization of the pore surface of the mesoporous materials adjustable. • The surface functionalization of mesoporous silicates could change the

chemical and physical properties of these materials dramatically.• There are two major ways to functionalize the surface of mesoporous

silicates by organic functional groups, named as post-synthesis grafting and co-condensation.

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Grafting method• It is a post-synthesis method to modify a pre-fabricated inorganic

mesoporous material surface, by attachment of functional groups to the surface of material, usually after surfactant removal.• In the process of grafting mesoporous silicates, the surface silanol

groups (Si-OH), which can be present in high concentration, act as convenient anchoring points for organic functionalization.

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Co-condensation MethodCo-condensation method is another strategy to functionalize mesoporous silicate’s, surface by sol-gel chemistry between tetraalkoxysilane and one or more organoalkoxysilanes with Si-C bonds.

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Characterization of Mesoporous material

Powder XRD pattern for ordered mesoporous silica templates and ordered mesoporous carbon

TEM image of CMK-1

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Template synthesis of nanowires in O/I hybrid Mesoporous material

• The “ship-in-bottle” synthesis is one of the promising methods for template synthesis of metal complexes and nanocomposites mesoporous materials.

• Organic-inorganic hybrid HMM and other hybrid materials have mesopores to accommodate bulky metal complexes or nanocomposites, which are accessible to large substrates in catalytic reactions.

• HMM-1 dried under vacuum. The dry HMM-1 was impregnated with an aqueous solution of H2PtCl6 .6H2O and RhCl3.3H2O.

• Then the sample was irradiated with a high-pressure mercury lamp. The resulting pale gray powder, designated Pt-Rh/HMM-1. Pt-Pd/HMM-1 (Pt/Pd ) the same method with H2PtCl6 .6H2O and H2PdCl4 as precursors.

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Drug Delivery• The functionalization of MCM-41 and SBA-15, respectively, with amino groups as an effective method to control IBU release.• The ionic interaction between the

carboxy groups in IBU and the amino groups on the matrix surface allows the release rate of IBU from amino functionalized SMMs to be

effectively controlled (SMM=silica mesoporous material).

• NMR analysis revealed that IBU molecules are tightly linked at the surface because the drug–surface ionic interactions are stronger

than the IBU dimer hydrogen bonds

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Magnetic nanocomposites with Mesoporous structures

Magnetic nanoparticles have potential applications in magnetic fluids, catalysis, biomedicine, magnetic resonance imaging, data storage and environmental remediation.

There are many problems that are associated with Magnetic nanoparticles, such as instability over long periods due to their tendency to aggregate.

As a solution, these magnetic nanoparticles can be coated with suitable mesoporous material, in order to exploit their properties and keep them stable.

Mesoporous materials with their attractive properties makes them suitable to be used as drug delivery carriers, imaging agents, water treatment adsorbents and as catalysts.

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Types of magnetic mesoporous materials

Magnetic mseoporous nanocomposites with different morphologies, structures and particle size can be broadly classified into:

A. Monodisperse magnetic np embedded in mesoporous nanospheres

B. Microspheres encapsulating magnetic cores into perpendicularly aligned mesoporous shells

C. Ordered mesoporous materials Loaded with magnetic np inside porous channels

D. Rattle type magnetic nanocomposites.

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Synthesis of magnetic nanoparticles

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Magnetic NPs inside the porous channels

• Selecting monodisperse mesoporous silica as hosts, ferrocenecarbaldehyde as the iron precursor and furfuryl alcohol as a solvent, a large amount of γ –Fe2O3 NPs can be incorporated into the silica host. • Magnetic iron metal/silica and magnetic/silica nanocomposites have

been prepared via temperature-programmed reduction of an iron oxide on SBA-15.• The resulting Fe3O4 /SBA-15 and Fe/SBA-15 exhibit

superparamagnetic properties.

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Biomedical and biotechnological applications

These materials are attractive magnetic probes for biological imaging and therapeutic applications.

Core diameter near about 20nm and overall particle diameter near about 50nm, the size is much smaller than size of the cell and is comparable to size of nuclei.

When these are coupled with target agent, they serve as nanovectors and interact specifically with biomolecules.

Drug carriers with magnetic NPs can respond to an external magnetic field, which makes them good magnetic targeting agents for drug delivery.

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Wastewater treatmentRemoval of toxic heavy metal ions from wastewater is a challenge.Various organo-functionalized mesoporous materials such as thiols,

thioether and amino groups have been reported for metal ion removal and dye adsorption.

These functionalized materials can be easily separated from aqueous systems by an external magnetic field and lower operational costs in adsorbent separation.

Shi and coworkers synthesized thioether functionalized mesoporous aluminosilicate hollow spheres with magnetic cores.

These materials exhibited highly selective adsorption of Hg+2 .

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Catalysis Magnetic separation provides a easy method for removing and

recycling magnetized species.This approach could be used to prevent the agglomeration of catalyst

particles during recovery.Various types of reactions are catalyzed using magnetic mesoporous

nanocomposites, such as olefin epoxidation, hydrogenation, Knoevenagel reaction.

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References A Review: Fundamental Aspects of Silicate Mesoporous Materials Zeid A. ALOthman

Magnetic Nanocomposites with Mesoporous Structures: Synthesis and Applications, Jian Liu, Shi Zhang Qiao, Qiu Hong Hu and Gao Qing Lu

Soft templating strategies for the synthesis of mesoporous materials: Inorganic, organic–inorganic hybrid and purely organic solids

On the Controllable Soft-Templating Approach to Mesoporous Silicates,Ying Wan and Dongyuan Zhao, chemical reviews, Volume 107, Number 7

Ordered porous materials for emerging applications Mark E. Davis

Porous Materials Metal-Organic Frameworks 2012 Nanocamp NCMN, UNL Dr. Jian Zhang & Jacob Johnson Department of Chemistry

Soft templating Davos Marine, Quibus Laurent, Pecher Romain, Schrobiltgen Jordan.

Porous Inorganic Materials Xiqing Wang, Xianhui Bu & Pingyun Feng California State University, Long Beach, CA, USA, University of California Riverside, Riverside, CA, USA

Mesoporous Materials for Drug Delivery Mara Vallet-Reg,Francisco Balas, and Daniel Arcos

A Review: Fundamental Aspects of Silicate Mesoporous Materials Zeid A. AL Othman

Synthesis, Characterization, and Catalytic Properties of a Microporous/Mesoporous Material, MMM-1 Raja H. P. R. Poladi and Christopher C. Landry

Syntheses of High-Quality Mesoporous Materials Directed by Blends of Nonionic Amphiphiles under Nonaqueous Conditions Bozhi Tian, Xiaoying Liu, Zhendong Zhang, Bo Tu, and Dongyuan Zhao

Porous Inorganic Materials Xiqing Wang, Xianhui Bu & Pingyun Feng

Functionalization of mesoporous silica nanoparticles and their applications in organo-, metallic and organometallic catalysis Yulin Huang