Mesoporous materials

Just basics of mesoporous materials!!The Break through came around 1992 by both Japanese and Mobil scientist on the soft template based synthesis of mesoporous materials

1. Mesoporous Materials – Synthesis and Applications Vijaykumar S.Marakatti, PPISR, Bangalore.

2. Outline of the talk Introduction to porous materials Classification of porous materials Synthesis mechanism of mesoporous materials Applications of mesoporous materials

3. Introduction “the overwhelming tendency for solids to minimize void space within their structure” is inherent , porous materials are difficult to make naturally. But Einstein say “ in the middle of difficulty lies opportunity ” The above statement was made true by the Mobil scientist in the year of 1992 by successfully synthesizing the Mesoporous materials (MCM-41 and MCM-48) by using soft template strategy. This opened a new area of materials called Mesoporous materials , and still lot of work are fascinating in this field.

4. What are Porous materials The history of porous materials began with the zeolites having aluminoisilicates framework which was synthesized by the use single template molecule with small pore. Most generalized definition of porous materials is continuous and solid network material filled through voids . A material can be recognized as porous if its internal voids can be filled with gases.

5. Classification of porous materials Depending on pore size Depending on building framework Micropoorus Mesoporous Macroporous <2nm 2-50 nm >50nm Purely inorganic Organic Inorganic hybrid Purely organic ZSM-5 MCM-41 Sponge Silica MOF organic porous polymers

6. Mesoporus Materials Meso a Greek prefix – “ in between ” - micro and macro porous system Mesoporous materials may be ordered or disordered. They possess high Surface area -400 -1000 m 2 /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.

7. Difference between the zeolites and mesoporous materials Zeolites Mesoporous Materials Highly crystalline Periodic arrangement with amorphous in nature TO 4 networks TO 4, TO 5 and TO 6 networks Si and Al are four connected by covalent bond, less surface hydroxyl groups Hydrophobic surface area Si and Al are 2 or three connected ,more surface hydroxyl groups Hydrophilic surface area High hydrothermal stability Less hydrothermal stability Crystalline walls and are thick Amorphous walls and are thin Synthesis temp is high (80 – 300 °C) Long crystallization time Synthesis temp is low (-10 to 120°C) Formation rates are fast Aqueous media is required for crystallization Non –aqueous 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

8. 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

9. Synthesis of mesoporous materials using soft template strategy Surfactants. Formation of Micelles. Inorganic precursor . Interaction of Micelles with inorganic precursor. Hydrothermal treatment followed by separation and drying Removal of template. Proposed mechanism Characterization of material.

10. 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/neutral Excellent solubility High critical Micelle con. acidic and basic media toxic and expensive Excellent solubility repulsion between the anionic surfactant is more. Excellent solubility High critical micelle temp. Acidic / basic media non-toxic and cheap

11. 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. To get ordered materials – 0 to20 mg/L

12. Different type of surfactant arrangement

13. What Makes them to show different type of arrangements ? Critical micelle concentration Low micelle conc. are good to get ordered materials. 2. Packing parameter (g) g = V / a o l V=Total volume of surfactant hydrophobic chains+ co- solvnet . a o = Effective hydrophilic head group area at the aq. micelle surface. l = kinetic surfactant tail length. g <1/3 = cubic and 3 D hexagonal, 1/3<g>1/2 = 2D hexagonal 1/2<g>2/3 = cubic g=1 = Lamellar 3. The hydrophilic and hydrophobic Volume ratio (VH/VL)

14. 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 reversible Silica gel, colloidal sol, Water glass , TEOS etc. Acidic synthesis(pH= 1 to 2 ) Irreversible. Slow hydrolysis TEOS is preferred.

15. 4. Interaction of Micelles with inorganic precursor. Direct interaction of Surfactant with inorganic precursor Basic -Medium Acidic-Medium

16. Interaction of Surfactant with inorganic precursor through intermediate ions Basic -Medium Acidic-Medium

17. Interaction of non ionic Surfactant with inorganic precursor through intermediate ions. Hydrogen bonds favors most of times

18. 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. Separation – filtration or centrifugation. Washing –alcohol or water. Basic media needs through washing. Drying at room temperature is good.

19. 6. Removal of template. Removal of template will give rise to mesoporosity Different ways by which template can be removed Calcination Slow heating rate. N 2 -1 hr O 2 - 4-6 hr – 2 °C/min O 2 -1 °C/min No surfactant recover low Surface silanol groups Not good for low thermal stable materials P-123 -550 °C CTAB -350 °C Solvent Extraction Solvent ethanol /THF small HCl is added Surfactant can be reused Microwave Ultraviolet rays O 3 and O Light irradiation

20. p6mm Ia3d , Pm3n Im3m Fd3m Fm3m . MCM-48 FDU-2 SBA-16 KIT-5 SBA-1 and 6 SBA-15

21. 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

22. 2. Cooperative self assembly Low concentration Surfactant

23. 3. True liquid crystal templating route High concentration Surfactant

24. Complete synthesis summary

25. 7. Characterization of mesoporous materials Low angel XRD 0.5 -5 -2theta - orederness / disorder . N 2 sorption measurements –BJH method Surface area/pore diameter /pore volume 3. TEM images Order ,Morphohology , Wall thickness

26. Applications

27. Application Chemical Catalysis 1. Mesoporous Materials as catalyst Al-MCM-41 ,B-MCM-41, Sn-SBA-15 - Acidic K- AlMCM-41 , Cs-AlMCM-41 -basic TiMCM-41 ,V-MCM-41 - Redox

28. 2.Mesoporous Materials as catalyst support Noble metal supported catalyst supports Au-McM-41 , Pt- CMK-3 Metal oxide supported catalysis Fe 2 O 3 - MCM-41 ,RuO 2- SBA-15 Metal complex supported catalysts Mn-Salen –SBA-15

29. 3. Application in environmental catalysis Immobilization of enzyme on Mesoporous Materials as catalysts Enzymes are excellent biocatalysts with high selectivity and efficiency in environment field, chemical and pharmaceutical industries are limited by their poor stability and chemical sensitivity

30. 4. Good adsorbents

31. 5.Applications in Biomedical field

32. 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 .

33. 2. Mesoporous Materials for Bone Tissue Engineering

34. Mesoporous Bioactive scaffolds Scaffolds 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.

35. 1 Day 3 Day 7 Day

36. 6.Mesoporous Polymers

37. Pioneers in Mesoporous Materials Galen Stucky SBA-15 Ryong Ryoo KIT -6 Hard template CMK materials Fudan university FDU-11 P.Selvum IITM-56, NCCR-56

38. Thank you References: “On the Controllable Soft- Templating Approach to Mesoporous Silicates” Ying Wan and Dongyuan Zhao , chemical reviews, Volume 107, Number 7 . “Soft templating strategies for the synthesis of mesoporous materials: Inorganic, organic–inorganic hybrid and purely organic solids” Nabanita Pal, Asim Bhaumik , Advances in Colloid and Interface Science 189–190 (2013) 21–41