1 Zeolites and Zeolitic Materials Molecular sieves = highly organized matrices of tunable pore shape, size, and polarity for separation, recognition, and organization of molecules with precision of about 1 Å. IUPAC classification of porous materials Macroporous > 50 nm Mesoporous 250 nm Microporous  2 nm Ultramicroporous  0.7 nm detergent builders, adsorbents, size-shape selective catalysts, supramolecular chemistry, nanotechnology Pores and Channels 2 ACO AFI SSY UFI STI 3 Zeolite Types >60 naturally occurring zeolites - large deposits of analcime, chabazite, clinoptilolite, erionite, mordenite and phillipsite >232 zeolite framework types (IZA - 2017) many hundreds of zeolite compounds Nomenclature http://www.iza-structure.org/ Structure types - three capital letter codes Most well known zeolite archetypes: SOD, LTA, FAU, MOR, MFI Aluminium Cobalt Phosphate - 1 (One) = ACO •Four-connected frameworks •Interrupted frameworks (denoted by a hyphen: –CLO, cloverite) Structure types do not depend on: chemical composition, element distribution, cell dimensions, symmetry Several zeolite compounds can belong to the same structure type: FAU – faujasite, Linde X, Y, Beryllophosphate-X, SAPO-37, Zincophosphate-X 4 Zeolite Names Names of zeolite materials: •trivial names – Alpha, Beta, Rho •chemical names – Gallogermanate-A •mineral names – Chabazite, Mordenite, Stilbite, Sodalite •codes – AlPO4-5, 8, 11, ..., 54, ZSM-4, 18, 57, ... •brand names – Linde A, D, F, L, N, Q , R, T, W, X, Y •university names VPI-5 (Virginia Polytechnical Institute) ULM (University Le Mans) MU-n (Mulhouse, Université de Haute Alsace) 5 Zeolites Building Units Isoelectronic relationship (SiO2)2 [AlSiO4 ]- AlPO4 Primary building units: Al(III)O4, P(V)O4 and Si(IV)O4 tetrahedra 6 Secondary (Structural) Building Units (SBU) Framework Type ACO 7 Polyhedral composite building units 8 Chain composite building units (a) zig-zag unbranched single chain, periodicity of two (b) sawtooth unbranched single chain, periodicity of three (c) crankshaft unbranched single chain, periodicity of four (d) natrolite branched single chain (e) double crankshaft chain, an unbranched double chain (f) narsarsukite chain, a branched double chain (g) a pentasil chain 9 Sodalite Unit Truncated octahedron 10 Sodalite Unit Packing of the sodalite units: SOD – bcc, sharing of 4-rings LTA – sc, 4-rings connected through O bridges FAU (faujasite) – cubic diamond, 6-rings connected through O bridges EMT – hexagonal diamond, 6-rings connected through O bridges 11 Zeolite LTA 12 (a) [TO4] tetrahedra as BBU (b) four-membered single rings (c) lB fuenfer chains (d) cubes [46] (e) truncated octahedra [4668] (sodalite- or -cages) (f) truncated cubeoctahedra [4126886] (-cavities) Zeolite A 13 Pores in Zeolite A (LTA) (a) the sodalite cage [4668] (b) the -cavity [4126886] (c) the 3-dimensional channel system (d) the 8-ring defining the 0.41 nm effective channel width 14 AFM growth studies of LTA S. Sugiyama et. al. Microporous and Mesoporous Materials 28 (1999) 1–7 D4R 15 D4R 16 Zeolite A crystal in an amorphous gel particle after a synthesis time of 3 days at room temperature 17 Zeolite FAU (X and Y) and EMT 18 Zeolite FAU (X and Y) and EMT Cubic diamond (sfalerite) Hexagonal diamond (wurzite) 19 Molecular Sieves Zeolite Cation Code Pore diameter Zeolite A: Na 4A 0.42 nm Ca 5A 0.48 nm Na, K 3A 0.38 nm Zeolite X: Na 13X 0.8-1.0 nm Ca 10X 0.7 nm Zeolite Y contains more Si 20 Framework Density Framework density (FD) Defined as the number of tetrahedral atoms (T-atoms) per cubic nanometer (1000 A3) FD is related to the void volume of the crystal: as the FD value decreases, the void volume and capacity for adsorption increases FD < 20 are characteristic of microporous structures the minimum known FD is 12.5 with the void occupying just over half of the crystal volume quartz 21 Pores Various sizes (4 - 13 Å), shapes (circular, elliptical, cloverleaf-like), and connectivity (1-3D) The size of the rings formed by the TO4 tetrahedra ranges from 4 to 18 of the T-atoms and determines the pore aperture Extraframework charge-balancing cations Ion-exchangeable, size, charge, positions, distribution, ordering, coordination number Si-to-Al ratio Influences cation content, hydro-phobicity/-philicity, acidity Löwenstein rule: absence of the Al-O-Al moieties, in aluminosilicates Si/Al > 1 Linde A (LTA) Si/Al = 1 ZK-4 (LTA) Si/Al = 2.5 ZSM-5 Si/Al = 20 -  Pure SiO2 Si/Al =  Pentasils ZSM-5 Pores 22 2 nm 23 Zeolite Synthesis 24 Zeolite Synthesis Structure of the zeolite product depends on: - Composition - Concentrations and reactant ratios - Order of mixing - Temperature - Ageing time (hours to weeks) - Crystallization time (days to weeks, kinetics of the structure-directing process is slow) - pH - Stirring/no stirring - Pressure - Seeding - Reactor material (PTFE, glass, steel) - Templates Templates: Organic cationic quaternary alkylammonium salts, alkylamines, aminoalcohols, crownethers, structure-directing, space-filling, charge-balancing Vary the template - discover new structures ! 25 Zeolite Synthesis 26 Templates 27 Templates The ratio TO2/(C + N + O) is a measure of space-filling of the framework by the guest molecules, characteristic for a specific guest and structure. Existence of primary and secondary units in a synthesis mixture 4R, 6R, 8R, D4R, D6R, 5-1, cubooctahedron 28 Zeolite Synthesis Mechanisms (b) “in situ” rearrangement of the gel (a) gel dissolution and solution mediated crystallization (SBU in solution) 29 Zeolite Synthesis Mechanisms 30 Zeolite Synthesis Mechanisms Structure directing agents 31 Crystallization Mechanism crystallization mechanism of FAU-type zeolite under ambient conditions 32 Zeolites and zeolitic materials Wide range of solid state characterization methods for zeolites: diffraction, microscopy, spectroscopy, thermal, adsorption and so forth Zeolite post modification for controlling properties of zeolites Tailoring channel, cage, window dimensions: Cation choice (Ca2+ exchanged for Na+) Larger Si/Al decreases unit cell parametrs, window size decreases number of cations, free space increases hydrophobicity Reaction temperature, higher T, larger pores 33 Stability Rules Lőwenstein rule: never Al-O-Al Dempsey rule: Al-O-Si-O-Si-O-Al is more stable than Al-O-Si-O-Al NNN-principle 34 Production 1.6 million tons p.a. (about half that of natural zeolites) Detergent - water softening by ion exchange (82%) - zeolites A and X Catalysis (8%) - zeolite Y (faujasite, 96 wt.%), mordenite, ZSM-5, zeolite Beta Desiccants/absorption (5%) - zeolites A, X, Y and mordenite Host-guest inclusion, atoms, ions, molecules, radicals, organometallics, coordination compounds, clusters, polymers (conducting, insulating) Nanoreaction chambers Advanced zeolite devices, electronic, optical, magnetic applications, nanoscale materials, size tunable properties, QSEs Mineral zeolites - odor control, antidiarrheal Synthetic Zeolite Applications Natural Mineral Zeolite Applications 35 Aquaculture Ammonia filtration in fish hatcheries Biofilter media Agriculture Odor control Confined animal environmental control Livestock feed additives Horticulture Nurseries, Greenhouses Floriculture Vegetables/herbs Foliage Tree and shrub transplanting Turf grass soil amendment Reclamation, revegetation, landscaping Silviculture (forestry, tree plantations) Medium for hydroponic growing Household Products Household odor control Pet odor control Industrial Products Absorbents for oil and spills Gas separations Radioactive Waste Site remediation/decontamination Water Treatment Water filtration Heavy metal removal Swimming pools Wastewater Treatment Ammonia removal in municipal sludge/wastewater Heavy metal removal Septic leach fields 36 Brønsted Acidity FAU 3648 cm−1 site 1 (pointing to the supercage) 3625 cm−1 site 1‘ or 4 (pointing to the supercage) 3571 cm−1 site 2 (pointing to the sodalite cage) 3526 cm−1 site 3 (pointing to the hexagonal prism) 3744 cm−1 free terminal OH at the external surface 37 Solid acid catalysts for the hydrocarbon cracking Introducing Bronsted acidity into zeolites: (1) direct H+-exchange of the charge-compensating metal cations (2) NH4 + -exchange of the compensating metal cations followed by calcination to decompose the ammonium cation leaving a proton on the surface (3) exchange with polyvalent cations that can generate H+ via partial hydrolysis of H2O molecules (4) exchange by metal cations that can be reduced by H2 to a lower valence state, generating protons on the surface Brønsted Acidity 38 Tuning Brønsted acidity: • Ion exchange for NH4 + • Pyrolysis to expel NH3 • Calcination to expel H2O Solid acid for the hydrocarbon cracking The larger the Si/Al ratio of a zeolite, the more Brønsted acidic is the OH, but the number of these sites decreases Brønsted Acidity 450 °C 39 Strong Brønsted Acidity Protonation of benzene -complex Transition state for H/D exchange Low T High T Not present in zeolites 40 41 Size-shape selective catalysis, separations, sensing Selectivity at: •Reactants •Products •Transition state Size-Shape Selectivity 42 Separation of xylene isomers by pervaporation through a MFI membrane 43 HRTEM 44 Isoelectronic relationship of AlPO4 to (SiO2)2 Ionic radius of Si4+ (0.26 Å) is very close to the average of the ionic radii of Al3+ (0.39 Å) and P5+ (0.17 Å) Many similarities between aluminosilicate and AlPO4 molecular sieves Dense AlPO4 phases are isomorphic with the structural forms of SiO2: quartz, tridymite, and cristobalite Aluminosilicate framework charge balanced by extraframework cations Aluminophosphate frameworks neutral (AlO2 -)(PO2 +) = AlPO4 Aluminophosphates 45 Aluminophosphates Some AlPO4 structures are analogous to zeolites while other are novel and unique to this class of molecular sieves. Only even-number rings = the strict alternation of Al and P atoms Incorporation of elements such as Si, Mg, Fe, Ti, Co, Zn, Mn, Ga, Ge, Be, Li, As, and B into the tetrahedral sites of AlPO4 gives a vast number of element-substituted molecular sieves (MeAPO, MeAPSO, SAPO) important heterogeneous catalysts M1+, M2+, and M3+ incorporate into the Al sites M5+ elements incorporate into the P sites This substitution introduces a negative charge on these frameworks. Si4+, Ti4+, and Ge4+ can either replace P and introduce a negative charge or a pair of these atoms can replace an Al/P pair and retain the charge neutrality. 46 Aluminophosphates 47 Aluminophosphate Synthesis Aluminophosphates prepared by the hydrothermal synthesis Source of Al: pseudoboehmite, Al(O)(OH), Al(Oi-Pr)3 Mixing with aqueous H3PO4 in the equimolar ratio – low pH ! Forms an AlPO4 gel, left to age One equivalent of a guest compound = template Crystallization in a reactor Separated by filtration, washed with water Calcination Other zeolite materials Oxide and non-oxide frameworks, sulfides, selenides Coordination frameworks, supramolecular zeolites The quest for larger and larger pore sizes 48 Cobalto-Aluminophosphate ACP-1 (Co/Al 8.0) bcc arrangement of the double 4-ring units (D4R) Ethylenediamine molecules are located inside 8-ring channels At the centre of each D4R, there is a water molecule, 2.31 Å away from four metal sites Al(O-iPr)3, CoCO3.H2O, 85% H3PO4, ethylene glycol, ethylenediamine, pH 8.4 Heated in a Teflon-coated steel autoclave at 180 °C for 4 d 49 Synthesis of Double 4-ring Units (D4R) 50 Metallo-Organic Framework (MOF) Structures 4000 structures known (2008), 1000 new per year Porous coordination polymers (PCP) Metal centers • Coordinative bonds • Coordination numbers 3-6 • Bond angles Polytopic Ligands • Organic spacers • Flexible – rigid • Variable length Reticular Chemistry 51 A building-block approach to the synthesis of nanostructured materials Materials formed by a bottom-up self-assembly of building blocks (reticuli) with predetermined symmetry Targeted, predictable, and straightforward design and synthesis Chemistry of the self-assembly and the design should not interact Building blocks: Discrete symmetry: C∞, C2, C3, C4, Td, … Rigid, inert Functional groups for linking Suitable linking reaction Discrete bonding direction 52 Polytopic Organic Linkers 53 Polytopic N-bound Organic Linkers Cationic framework structures Evacuation of guests within the pores usually results in collapse of the host framework 54 55 Metallo-Organic Framework Structures 56 Polytopic carboxylate linkers 57 Polytopic Carboxylate Linkers Aggregation of metal ions into M-O-C clusters form more rigid frameworks frameworks are neutral no need for counterions MOF Crystallization 58 Entropy-driven errors in self-assembly Mechanism for error correction required The reaction should be reversible to allow for thermodynamic control No side-reactions should exist (loss of reagents, contamination) The building block rigidity, symmetry and discrete bonding direction decrease the incidence of errors Solvothermal methods – control over p, T, μ to establish equilibrium Low energy difference (ΔH < –TΔS) 59 Zn4O(BDC)3.(DMF)8(C6H5Cl) MOF-5 a primitive cubic lattice Cavity diam. 18.5 Å Nature, 1999, 402, 276 •Zn(NO3)2 + H2BDC in DMF/PhCl •Addition of TEA: deprotonation of H2BDC •Addition of Zn2+ • Addition of H2O2: formation of O2- in the cluster center Zn4O 60 MOF-5 Stable even after desolvation at 300 °C in air gas sorption isotherms for MOF-5 MOF-5 61 Interpenetration MOF-9 62 Interpenetration 63 Metallo-Organic Framework Structures 64 Basic Nets 65 Inorganic and Metallo-Organic Quartz 66 MIL-100 and MIL-101 MIL-101 Record Surface area 5 900 m2/g 67 COF - Covalent Organic Frameworks Linking reactions produce covalent bonds Covalent Organic Frameworks 68 Linking reactions 69 Covalent Organic Frameworks COF-1 Solvents - reactants are poorly soluble (to slow down the reversible condensation) mesitylene-dioxane (1:1) Sealed pyrex tubes, 110 °C, 72 h, minimize defects by self- healing COF-1 = microcrystalline, high yield, high structural order by XRD Solvent molecules are enclosed inside the pores, can be removed at 200 ºC without collapse of the crystalline structure Surface area of 711 m2 g-1, pore size 0.7 nm Interlayer spacing: 0.333 nm Covalent Organic Frameworks 70 + 23 COF-5 Surface area 1590 m2/g Pore size: 2.7 nm Interlayer spacing: 0.346 nm Covalent Organic Frameworks 71 Covalent Organic Frameworks 72 Layer stackings: AA, AB, serrated and inclined 73 Covalent Organic Frameworks 3D frameworks COF-102, COF-103, COF-105, and COF-108 COF-108 - bor structure two different types of pores diameters of 15.2 and 29.6 Å. density 0.17 g cm-3 surface area, m2 g-1 COF 102 3472 COF 103 4210 74 Borazine COFs 75 BET: 1178 m2/g Pore size: 0.64 nm Jackson K., Reich T., Chem. Commun., 2012, 48, 8823–8825