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23-11-2021. Welcome!. Application of porous material in the field of environment.

Group members. Abhishek Das Bimalangshu Das Neha Sengupta Prantik Banerjee Pratik Pandey Siddhartha Ghosh Soumya Subhra Kundu Sriman Asutosh Nayak.

23-11-2021. CONTETNT. Definition Porosity Pore size Metallic foams and porous metals Micro porous Materials Activated Carbons Zeolites Metal organic frameworks (MFOs) Connector and Linkers Synthesis.

23-11-2021. DEFINITION. Classically porous materials are organic materials, polymeric foams… A large number of inorganic porous materials have been developed, e.g. for insulation, cushioning, impact protection, catalysis, membranes, construction materials. Materials with different pore sizes (from nanometer to millimeter) Ordered or irregular arrangement of pores Various chemical compositions (metal, oxides…) Different preparative approaches..

23-11-2021. POROSITY. Porous: Contain pores (cavities, channels, interstices) which are deeper than they are wide. Either describe the pores, or describe the cell/pore walls Accessibility: a: closed pores b,c,d,e,f: open pores b, f: blind pores (dead-end or saccate) e: through pores Shape: c:Cylindrical open f:Cylindrical blind b: ink-bottle-shaped d: funnel shaped g: roughness.

23-11-2021. PORE SIZE. Pore size is important for applications. IUPAC, three pore size regimes, associated with transport mechanisms: •Micro porous, smaller than 2 nm •Mesoporous, between 2 and 50 nm •Macro porous, larger than 50 nm Macropores: larger than typical mean free path length of typical fluid. Bulk diffusion and viscous flow. Mesopores: same order or smaller than the mean free path length. Knudsen diffusion and surface diffusion. Multilayer adsorption and capillary condensation ay contribute. Micropores: pore size comparable to the molecules. Activated transport dominates..

23-11-2021. METALLIC FOAMS AND POROUS METALS. May be seen as composite materials consisting of a solid and a gaseous phase. Porous metals: high bulk density, independent, distributed voids Metallic foams: Low bulk density, interconnected voids. Porosity: 30-98 vol% (pore volume/apparent volume, VP/V) Impact energy adsorption, air and water permeability, acoustical properties, low thermal conductivity. Energy absorbing systems, porous electrodes, sound absorbers, filters, insulating materials, heat exchangers, construction materials, electromagnetic shielding, membrane and membrane support..

23-11-2021. MICROPOROUS MATERIALS. A micro porous material is a material containing pores with diameters less than 2 nm Activated Carbons Zeolites Metal-organic frameworks Covalent organic frameworks Micro porous polymer.

23-11-2021. – Micropores are part of their crystal structure: • Most are synthetic • Alumino-silicates • Silicalite = no aluminum • Cation can be H+ , Na+ , Ca2+, NH4 + , etc. • Pore shape needs to be incorporated into pore size calculation for accurate results • Some adsorbates are better than others.

23-11-2021. APPLICATIONS. Micro porous 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/cm3 • 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/cm3 • Metal organic frameworks – Their huge surface area and pore volume makes them potentially useful for gas sequestration/storage. ρ< 0.5g/cm3.

23-11-2021. ACTIVATED CARBONS. Made from variety of materials.

ZEOLITES. Characteristics of zeolites: 1) Tectosilicates, i.e. three dimensional structure built from tetrahedra. Some silicon atoms have been replaced by aluminium, i.e. the (Si+Al)/O = ½. (Tetrahedra usually denoted T-atoms. 2) Open framework structure built from TO4-tetrahedra, containing pores and voids. The structure and porosity is periodic (i.e. crystalline materials). The pores have molecular dimensions. 3) Counter ions (cations) are present in order to compensate for the negative framework charge created by aluminum substitution. The counter ions are situated in the pores and voids, and are usually mobile..

ZEOLITES. 4) In the voids and pores are also water molecules (zeolitic water). One measure of the porosity is the amount of adsorbed water. The water molecules are also present in the pores and voids, and may (in many cases) be removed by heating and reabsorbed at lower temperatures. 5) Loewenstern's rule imposes a limit to the amount of aluminum which may be substituted into the framework: No Al-O-Al may be present in tectosilicates. This means that only half of the silicon atoms may be substituted by aluminum. For the general composition: Mn x/nSi1-xAlxO2 · yH2O This means that the Si/Al ratio is larger than 1 and that x is smaller than 0.5 This rule is not always obeyed! (High aluminum e.g. Si/Al = 0.5) High silica and pure silica zeolites have been synthesized.

23-11-2021. Zeolite (zeotype) structure. • The basic (primary) building blocks are tetrahedra •All tetrahedra share corners •The arrangement of the building blocks is periodic (crystalline) Building units: •Primary or basic building units (BBU): Tetrahedron •Secondary or composite building units (CBU): polymeric structures (rings, prisms etc.) •Tertiary building units: Larger cages The flexibility of the T-O-T bond angle (120-180˚) allows a large number of CBUs to exist, and results in a wealth of different structures to be constructed.

23-11-2021. CBUs. Zeolite structures may be seen as built from CBUs. For instance the ZSM-5 framework may be built from 5-1 units. It is important not to assume that the synthesis of zeotype materials occur via assembly of CBUs floating around in the synthesis mixture..

23-11-2021. METAL ORGANIC FRAMEWORKS (MFOs). Inorganic-Organic Hybrid, ordered structure – 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 (MFOs). Zn4O tetrahedra (blue) are joined by organic linkers (O, red, C, black), giving an extended 3D cubic framework with interconnected pores of 11.2 Å aperture width and 18.5Å pore (yellow sphere) diameter.

Connectors and linkers. The connectors are mostly transition metal or lanthanoid ions. Coordination number varies. May also be polynuclear clusters. • The linkers are organic (or inorganic) or multidentate. • The interaction between connectors and linkers are coordinative or ionic (not covalent as in zeolites) Popular linkers may contain nitrogen or oxygen donor atoms, e.g. 4,4’-bipyridine, benzene-1,4- dicarboxylate (terephthalate)..

Synthesis. The variety of different connectors and linkers makes it possible to construct a variety of 1-, 2- and 3-dimensional structures. The design of linkers is especially efficient in attempting to form new structure types. Standard coordination chemistry methods are used, where metal ions are reacted with an organic ligand. The conditions are low temperature and hydrothermal/solvothermal synthesis. This may be seen as “self-assembly” of basic building units. The products are usually not kinetically but thermodynamically determined. The flexibility/rigidity of the linker is important for the properties, e.g. the possibility of forming porous materials. Most used linker are fairly rigid. Also during formation the rigidity of the linkers are important; a very flexible linker may enable several possible conformations, resulting in poorly crystalline materials..

THANK YOU. 23-11-2021.