Porous materials - PDF document

1 Porous materials 2 A large number of inorganic porous maten, catalysis, membranes,construction •Materials with different pore si•Ordered or irregular arrangement of pores•Various chemical compositions (metal, oxides…)•Different preparative approaches. s) which are deeperthan they are wide. c:Cylindricalopenf:Cylindricalblind 4 Some definitions 7Metallic foams and porous metals r permeability, acousticalproperties, low 8Metallic foam production 11Porous gold 12 Casting metal around densely packed granular material (template)Interconnected sponge-like materials are obtained, porosity ca. 70%The template materials should be soluble, but heat resistant. E.g. sodium chloride, Hollow spheresAlternatively: stirring of granular materials into the melt. 13 1.Charging the melt with hydrogen 2.Solidification of the melt, whereby thm –10 mm Gasars. (abbreviation of the Russian term for gas-reinforced.) 14 Cu and Mg gasars V. Shapovolovand L. Boyko,Adv. Eng. Mater. 2004, 407 CVD, electrochemical, PVD methods may be used.Electrochemically deposited on porous 18 Pores in the mesoporousrange, 2-50 nm.ca spheres forming a three dimensional network. Bulk densities 0.004 –0.5 g/cm 23 Templatingapproach to ordered porous so SynthesisTemplate removal Microporouszeolite-like materialsAluminophosphates, AlPO’sIII-V analogues of SiOE.g. Berlionitestructurally similar to Microporousaluminophosphates(Flannigan, Union Carbide)More than 40 aluminophosphatebased structuresSubstitution of atoms with different valencDivalent cationswhich can adoptMAPO: divalent cationssubstitutes only for Al, i.e. H Adsorption in zeolitesis significantly differentbution of pore sizes,and where the size of In zeolitesthe porosity is dearrngedin a regular fashion with only one (opores have molecular dimensions. zeolitesas adsorbantsand molecular low equilibrium water vapourpressure)Gas (hydrogen?) storage materialsstructure and cationsize and position. Atlas of ZeoliteFramework Types ZON WEI VET TON -RON RHO OSO OFF OBW MON MFS MAZ MAR LOV LOS -LIT IHW HEU GON GME FER EUO EON DOH CZP -CHI AEL ZON WEI VET TON -RON RHO OSO OFF OBW MON MFS MAZ MAR LOV LOS -LIT IHW HEU GON GME FER EUO EON DOH CZP -CHI AEL http://www.iza-structure.org/databases/ Zeolitesynthesisliteis attributed to Deville, who in 1862 synthesized levyne(levynite) Ca(levynite) Ca18Si36O108] .50 H2O by heating potassium silicate and sodium aluminatein a glass ampoule. liteswas seen after 1940 when X-ray Usually synthesized from a basic medium (sol or gel) under mild to medium Contains: Water, silica source, aluminhttp://www.iza-online.org/synthesis/default.htm 37 Cations(and hydrated cations) acts as counterions, but also have a templatingAdded templates, e.g. aminesGoal: targeted synthesis of microporousstructures by template control.Structure directing or templatingagent 38 increased the number of zeolitetype hitherto unknown zeolitesand other microporousmaterials.synthesize zeoliteswith various Si/Al ratios, e.g. zeoliteLTA with a Si/Al not possible to predict which zeolite 39Combinatorial approach (SINTEF) in hydrothermal synthesis of microporousmaterials. Zeolite(zeotype) structure •All tetrahedrashare cornersRepresentation of a six memberedring(Contains 6 Siand 6 O)•Secondary or composite building units (CBU): polymeric structures (rings, prisms etc.))allows a large number of CBUsto exist, and results in a wealth of different 42 Zeolitestructures may be seen of CBUsfloating around in the synthesis mixture. 43Rings and pore size Pore openings or rings in zeolites.8-, 10-, and 12-rings shown as connecting spheres.The openings may have various shapes, influencing the kinetic diameter. Analcime8-ringEdingtonite8-ring Cages and channels ZeoliteLTA. May be seen as built from the CBUs: 8, 4-4, 6-2, 6, 1-4-1, 4May be seen as built from interconnected sodalitecages ( 47 A new class of ordered microporousmaterials are the metalorganicframework materials. 48 •The connectors are mostly transition metal or lanthanoidions. Coordination number varies. May also be polynuclear•The linkers are organic (or inorganic) bi-or multidentate.•The interaction between connectors and nitrogen or oxygen donor atoms, variety of 1-, 2-and 3-dimensional sthydrothermal/solvothermalsynthesis.e linkers are important;a very flexible conformations, resulting in poorly 50 3-D MOF materials are among those with 51O(terephthalate) (Yaghi) Very low density: (0.59g/cm)Framework stable up to 300Very high surface area. •1st generation: The framework is only maintaineswith the guest molecules •2nd generation: The framework is stable•3rd generation: the framework is fl2nd and 3rd generation materials may be •In principle the dimensions and shape of the channels are easilytunable by •Functionality may be built into the linkers.•The materials are light weight, making Mesoporoussolids with ordered porosity.ordered mesoporousmaterials were made by using supramolecularspecies cationsor organic molecules.Amphiphilicsurfactant molecules (lyotropicliquid crystals) were used.Monomodalnarrow distribution of ofpore sizes. 54 host structures for nanometer sized guest compounds.MCM-48: Cubic three-dimensional Water, an amphophilicmolecule, a solubl Formation of supramoleculararrangement of molecules, Supramoleculararrangements e.g. CTAB: cetyltrimethylamoniumbromide, CHLow concentration: individual molecules•Small spherical micelles above the micelle concentration (cmc)•Micelles coalesce into elongatedecylindrical micelles•Bicontinouscubic arrangement•Lamellar arrangement supramoleculararrays, e.g. micelles. 57 Phase diagrams Two mechanisms were proposed:1)Liquid crystal initiated pathway: Organization of the surfactantmolecules n). Followed by formation of the 2)Silicate anion-initiated pathway: The organizes into a supramoleculararray. 59 Synthesis by electrostatic templatingpro 63 Macroporoussolids with ordered porosityrials. (as described with metal foams)1)Colloidal crystal formed by closed packed monodispersespheres (e.g. latex 2)The interstitial space is f3)The precursor solidifies4)The template is removed 64 Opals and inverse opals