Chemistry. Physical Organic Inorganic. Chemistry. Crystallography. X-ray. Bioinorganic Solid State. Theory. Group. Polymers.

Transcription

1 Chemistry Physical Organic Inorganic Organometallics, Metal Complexes Clusters, Cages Bioinorganic Solid State Chemistry Group Theory X-ray Crystallography Polymers

2 What is Solid State Chemistry? What is Solid State Chemistry? Chemical aspects of solids Chemical and physical properties of infinite, nonmolecular solids Synthesis-structure-property-function relationships Materials with properties (or combinations of properties) tuned for specific applications Non-comprehensive, non-mathematical overview

3 Why Study Solid State Chemistry? Why Study Solid State Chemistry? Materials with properties (or combinations of properties) tuned for specific applications Electronics: Diodes, transistors, photodetectors, solar, cells Optical: Fiber optics, CDs, LEDs, lasers, NLO, photon gap, displays Magnetics: Switches, data storage, read-write heads, NMR Ionics: Batteries, fuel cells, sensors, displays, smart windows Energy: Catalysts, chemicals, fuels Mechanical: Construction, ceramics, composites, alloys, space vehicles, tools Evnironmental: Pollution prevention and removal, heavy metals, organics, NO x Separations: Molecular sieves, membranes, selective catalysis Biomaterials: Artificial bone, skin, organ replacement, repair, drug delivery

4 Porous Materials Porous Materials Name Pore Size Domain Microporous 5 to 20Å Mesoporous 20 to 500Å Macroporous > 500Å Crystalline or non-crystalline Metastable, require soft chemistry methods: crystallization from gels most common Applications: size/shape discrimination for catalysis, ionexchange, separation, sensing, host-guest inclusion chemistry, optical materials, magnetic materials Microporous, crystalline: molecular sieves Zeolites = (alumino)silicate molecular sieves

5 Zeolites Open framework silicates or aluminosilicates with ion-exchange properties M n+ x/n [(AlO 2 ) x (SiO 2 ) y ]x mh 2 O [x/(x+y)] of Si sites substituted for Al Corner-sharing TO 4 tetrahedra, T = Al or Si No adjacent Al tetrahedra 0 to 1 limit of Al : Si Structures drawn with polyhedra or lines connecting metal centers, ignoring doublybridging oxygens β-cage SBU Zeolite Y: α-cage, connected by 12-ring windows = See Crystal Structure Viewer

6 Prof. Sir J. M. Thomas: On the right, a projected structure of the zeolite we have been studying On the left, a pattern made on the wall of a mosque in Azerbaijan in 1086 AD There is nothing new under the sun. Prof. S. Oliver: I worked on interlocking stone on a summer job once.

7 Synthesis of Zeolites Synthesis of Zeolites Naturally occurring minerals: boiling stones Naturally occurring as well as new, synthetic zeolite structures Synthetic zeolites: 1930 s, Barrer; 1950 s, Union Carbide, characterized by PXRD Reactive, soluble form of silica and alumina Formation of a gel precursor: homogeneous, amorphous, alkaline Condensation polymerization: Si OH + HO Si Si O Si + H 2 O Si OH + HO Al Si O Al + H 2 O Hydrothermal synthesis: controlled ph, time, temperature

8 Hydrothermal Synthesis of Zeolites Hydrothermal Synthesis of Zeolites NaAl(OH) 4 (aq) + Na 2 SiO 3 (aq) + NaOH(aq) 25 C, Condensation polymerization Na a (AlO 2 ) b (SiO 2 ) c H 2 O, Gel 25 to 250 C, Gel ordering, Nucleation site formation and growth, autogenous P Na x (AlO 2 ) x (SiO 2 ) y zh 2 O crystals

9 What s s in a ame: a (AlO x ) (SiO 2 x ) 2 y zh O 2 Extraframework cations Al III O 4, T d Si IV O 4, T d Occluded water Charge balancing, void-filling (up to 50%), structurestabilizing, ion-exchangeable Equal ratio to Al Each oxygen shared with another metal center (AlO 2 ), introduces negative charge Each oxygen shared with another metal center (SiO 2 ), neutral Easily removed by heating under vacuum, 25 to 500 C Open inorganic framework One-, two- or three-dimensional networks of interconnected channels Channels connect through windows to define interior cavities Window size determines maximum size of molecule that can enter zeolite

10 Applications of Zeolites Applications of Zeolites Dehydrating agent Ion-Exchange Zeolite A: water softener in detergents, exchanges Na + for Ca 2+ Environmental remediation: 137 Cs, 90 Sr Adsorbents for purification or separation Zeolite A: removal of n-octane from gas Zeolite A: 196 C, O 2 (346pm) adsorbed but N 2 (364pm) excluded Size/Shape Selective Catalysts High internal surface area Acid sites due to [AlO 4 ]

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12 Post-Synthetic Treatment of Zeolites Super Brønsted Acid Catalyst Microporous material H x (AlO 2 ) x (SiO 2 ) y (NH 4 ) x (AlO 2 ) x (SiO 2 ) y (NH 4 ) + (aq) Metal fluoride (aq), (s) M = B 3+, Be 2+, Fe 3+, Ti 4+, Sn 2+, Cr 3+, Al 3+, Si 4+ Metal-substituted zeolites 450 C, vacuum 300 to 400 C Quantum-confined Semiconductors (MS) x/q H x (AlO 2 ) x (SiO 2 ) y H 2 S (g) M x/q (AlO 2 ) x (SiO 2 ) y Ion Exchange (M) q+ (aq) H 2(g) Na x (AlO 2 ) x (SiO 2 ) y Na x-n(alo 2 ) x-n(sio 2 ) y+n Isomorphic Framework Substitution n SiCl 4 (g) (500 C) (M) x/q H x (AlO 2 ) x ligand (SiO 2 ) y Encapsulated Metal Catalyst Encapsulated ML n (AlO 2 ) x (SiO 2 ) y Transition Metal Complexes (0 n x) Dealumination, formation of high-silica zeolites

13 Size/Shape Selective Catalysis Size/Shape Selective Catalysis Reaction occurs only for molecules that can enter zeolite channels Only molecules that can exit are present in product Reaction occurs only for specific transition state

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15 Zeolites are Metastable Molecular sieves are metastable, kinetic phases; thermodynamically unstable with respect to dense oxide phases Zeolite synthesis obeys Ostwald s law of successive reactions: initial metastable phase successively converts to more thermodynamically stable phase, finally to most stable phase e.g.: Zeolite A Sodalite Condensed SiO 2 + Al 2 O 3

16 Mesoporous Materials Microporous: 5 to 20Å; Mesoporous: 20 to 500Å; Macroporous: > 500Å 1992, Mobil Mesoporous (alumino)silicates, Å tunable pore size, high surface area (> 1000 m 2 g 1 ) Inorganic walls are amorphous and lack long-range order MCM-41, hexagonally packed, uniform cylindrical mesopores Structure-directing agent is self-assembled aggregate of amphiphiles

17 Mesophases of C 12 H 25 Me 3 Cl/H 2 O

18 Synthesis of Mesoporous Silica Silica source (Na 2 SiO 3, tetraethylothrosilicate (TEOS) or colloidal silica) Surfactant Alkyltrimethylammonium halide, C 16 H 33 (CH 3 ) 3 N + Cl Base (NaOH or TMAOH) Solvent H 2 O 80 C, 1 to 6 days Mesoporous aluminosilicate prepared by adding Al 2 O 3 to mixture Calcination at 500 yields mesoporous material Hexagonally packed cylindrical mesopores Hexagonal phase

19 Mode of Formation of Mesoporous Silica Self-assembly of amphiphiles into a mesophase (micellar rod hexagonal phase, lamellar phase or cubic phase) Coating by silica: cooperative interaction by ion-pair formation of surfactant and inorganic species

20 Tunable Pore Size C n H 2n+1 (CH 3 ) 3 N + n = 12 30Å pore size n = 14 34Å pore size n = 16 38Å pore size n < 8 no micellar rod formation Swollen micellar rods: C 16 H 33 (CH 3 ) 3 N + + auxiliary hydrocarbon (e.g.: 1,3,5-trimethylbenzene) pore sizes up to 100Å Aging sample prepared at low temperature (70 C) in mother liquor at higher temperature (150 C) Post-synthesis silylation, SiH 4(g)

21 Covalent Grafting of Guests into Covalent Grafting of Guests into Mesoporous Materials Silanization to form methylterminated, hydrophobic channels Introduction of functionality: reaction with tris(methoxy) mercaptopropylsilane, (CH 3 O) 3 Si(C 3 H 6 )SH Formation of terminal thiol groups, pore size from 36Å to 27Å Highly efficient removal of Hg from waste streams Renewable by HCl wash to remove Hg Adv. Mater. 2000, 12, 1403

22 Macroporous Materials: Aerogels 3D metal oxides with pore size > 500Å Aerogels: a material prepared by the replacement of the pore liquid of a gel with air Gel dried supercritically to avoid collapse of 3D framework Avoidance of liquid-gas interfaces (liquid cannot exist above supercritical point) Also, freeze drying: pore liquid is frozen and then sublimed Extremely low density materials: ~ 95% volume is air Lowest thermal conductivity of all solids, optically transparent Angew. Chem. Int. Ed. Engl. 1998, 37, 22

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24 Photonic Bandgap Materials Condensation of colloidal silica spheres to fcc lattice: colloidal crystal Tunable sphere diameter, 200 to 700nm lattice parameter Also, monodisperse latex spheres 3D periodic array with repeat distance on the same order as visible wavelengths Bragg diffraction due to presence of two media with different refractive indices Adv. Mater. 1998, 10, 480 Opal: close-packed amorphous silica spheres

25 Photonic Bandgap Tuning of a Colloidal Crystal Particle size dependence of optical diffraction Annealing temperature dependence of optical diffraction

26 Inverse Opal Inverse Opal Introduce Inorganic Remove Support Inverse Opal Opal 1 µm MO 2 growth from EtOH CVD of M Ozin & coworkers, Nature 2000, 405, 437