1 Layered Compounds Graphite and Graphene Clay Minerals, Mica Layered Double Hydroxides (LDHs) Layered Zirconium Phosphates and Phosphonates Layered Metal Oxides Layered Metal Chalcogenides - TiS2, MoS2, WS2, MPS3 (M = Ti, V, Mo, W, Mn, Fe, Co, Ni, Zn) Alkali Silicates and Crystalline Silicic Acids 2D = Two-dimensional layers 2 Layered Compounds Intralayer bonding - strong (covalent, ionic) Interlayer bonding - weak (H-bonding, vdWaals) 3 Host-Guest Structures Host dimensionality 3D 2D 1D 0D TOPOTACTIC SOLID-STATE REACTIONS = modifying existing solid state structures while maintaining the integrity of the overall structure 4 Intercalation Intercalation Insertion of molecules between layers 5 Intercalation 6 Intercalation Exfoliation Host + Guest Staging Intercalate APB = advancing phase boundary Hendricks-Teller 7 Exfoliation Decrease attractive forces between layers Separate layers H-bonding Tandem Molecular Intercalation 8 Nat. Commun. 2015,6, 5763, Jan. 9, 2015 Transition-Metal Chalcogenides Lewis base short initiator first intercalates to open up the interlayer gap, and the long molecules then bring the gap to full width and overcome the interlayer attractive force resulting in spontaneous exfoliation APB = Advancing Phase Boundary 9 APB = advancing phase boundary 10 Staging Hendricks-Teller Effect 11 HT = galleries are filled randomly Intercalation 12 Dependence of the basal spacing of the intercalates of the alkylamines (circles) and alkanols (crosses) on the number of carbon atoms nC in SrC6H5PO3ꞏ2H2O 13 Graphite Stacking of layers ABABAB Graphite sp2 sigma-bonding in-plane p-p-bonding out of plane Hexagonal graphite = two-layer ABAB stacking sequence SALCAOs of the p-p-type create the valence and conduction bands of graphite, very small band gap, metallic conductivity properties in-plane, 104 times that of out-of plane conductivity 14 Graphite GRAPHITE INTERCALATION G (s) + K (melt or vapour)  C8K (bronze) C8K (vacuum, heat)  C24K  C36K  C48K  C60K C8K potassium graphite ordered structure Ordered K guests between the sheets, K to G charge transfer AAAA stacking sequence reduction of graphite sheets, electrons enter CB K+ nesting between parallel eclipsed hexagonal planar carbon six-rings 15 Graphite Intercalates Intercalation in Li-ion Cells 16 C6Li Intercalation in Li-ion Cells 17 Anode discharge C6Lix → 6 C + x Li+ + x e- Cathode discharge Li1-xCoIII/IVO2 + x Li+ + x e- → LiCoIIIO2 Graphene Family 18 Graphene Graphene oxide h-BN BCN Fluorographene C3N4 Graphene • 1962 H.-P. Boehm monolayer flakes of reduced graphene oxide • 2004 Andre Geim and Konstantin Novoselov - Graphene produced and identified • Exotic properties: – Firm structure – Inert material – Hydrofobic character – Electric and thermal conductivity – High mobility of electrons – Specific surface area (theoretically): 2630 m2g-1 K. Novoselov A. Geim 19 2010 Nobel Prize in Physics 20 Graphene High electric conductivity (metallic, ~20,000 S/cm) High mobility at low temperature (2 105 cm2 V1 s1, Si ~800 cm2 V1 s1 at r.t.) Optically transparent (~97.7%) – 1 layer absorbs 2.3% of photons Low reflectiveness (<0.1%) High mechanical strength (E ~ 1 TPa) High thermal conductivity (K ~ 5 103 W m1 K1 ) Low anisotropic thermal expansion coefficient High stability in air atmosphere up to 400 C HRTEM 21 Graphene LCAO-band structure of graphene Synthesis of Graphene Top down Mechanical exfoliation Chemical exfoliation (oxidation/reduction) Dry and/or liquid-phase exfoliation Unzipping of nanotubes Bottom up CVD, epitaxial growth, (on SiC and on metals) Precipitation Molecular beam epitaxy 22 Synthesis of Graphene 23 http://www.nanowerk.com/what_is_graphene.php 24 Graphene Preparation: • Scotch tape – layer peeling, flaking • SiC pyrolysis – epitaxial graphene layer on a SiC crystal • Exfoliation of graphite (chemical, sonochemical) • CVD from CH4, CH2CH2, or CH3CH3 on Ni (111), Cu, Pt surfaces 25 Scotch Tape – Layer Peeling Mechanical exfoliation 26 Scotch Tape – Layer Peeling 27 SiC Pyrolysis • Annealing of the SiC crystal in a vacuum furnace (UHV 10-10 Torr) • Sublimation of Si from the surface at 1250 - 1450 °C • The formation of graphene layers by the remaining carbon atoms 28 Exfoliation Chemical exfoliation (surfactant) Sonochemical exfoliation 29 CVD from CH4 / H2 on Metal Surfaces (A) SEM - graphene on a copper foil (B) High-resolution SEM - Cu grain boundary and steps, two- and three-layer graphene flakes, and graphene wrinkles. Inset (B) TEM images of folded graphene edges. 1L, one layer; 2L, two layers. Graphene transferred onto (C) a SiO2/Si substrate (D) a glass plate 30 CVD from Hydrocarbons on Metal Surfaces The first graphene synthesis by CVD 2006 Somani - camphor and nickel substrate Carbon cannot diffuse into Cu = monolayer graphene Carbon diffuses into Ni = formation of multi-layered graphene 31 Graphene on SiO2 32 Pseudo-Magnetism Graphene on platinum grown from ethylene at high temperatures Cooled to low temperature to measure STM to a few degrees above absolute zero Both the graphene and the platinum contracted – but Pt shrank more, excess graphene pushed up into bubbles, size 4-10 nm x 2-3 nm The stress causes electrons to behave as if they were subject to huge magnetic fields around 300 T (record high in a lab, max 85 T for a few ms) Magic-Angle Twisted Bilayer Graphene 33 Twisted Bilayer Graphene 34 Graphene Oxide • More reactive than graphene • Presence of oxygen groups: -OH, -COOH, =O, -O• Hydrophilic character • Electric insulator, sheet resistance Rs ~1012 Ω/sq • Specific SA (theoretical): ~890 m2g-1 (1700-1800 m2g-1) • Photoluminescence properties • Bandgap from 1.7 to 2.1 eV 35 Graphene Oxide 36 Graphene Oxide 37 Graphene Oxide 38 Hummers Method 39 Graphene Oxide Characterization UV-vis: ~227-231 nm (arom. C=C, ππ) ~300 nm (C=O, nπ) 40 Well oxidized GO: C/O = 2.1 - 2.9 C 1s XPS spectrum (eV) C–C/C=C 284.6 C–O 286.6 C=O 287.8 O–C=O 289.0 Graphene Oxide Characterization Zeta potential: 44 mV aqueous dispersions 0.05 mg/ml 41 Raman, cm1 G-band 1590 D-band 1350 FTIR ATR spectra, cm1 C-O-C 1000, C-O 1230, C=C 1590-1620, C=O 1740–1720, O-H stretching 3600– 3300 Graphene Oxide Characterization Solid-state 13C NMR, ppm Ketone carbonyls 190 Ester and lactol carbonyls 164 Graphitic sp2 carbons 131 Lactols O-C(sp3)-O 101 Alcohols 70 Epoxides 61 The measure of oxidation The ratio between the alcohol/epoxide signal and graphitic sp2 carbon signal 42 Graphane – Hydrogenated Graphene • 2009 (graphene + cold hydrogen plasma) • Two conformations: chair x boat • Calculated binding energy = most stable compound with stoichiometric formula CH • Chair type graphane insulating nanotubes 43 Fluorographene • Monolayer of graphite fluoride • Chair type x boat type-strong repulsion • Sythesis: – Graphene + XeF2/CF4 (room temperature) – Mechanical or chemical exfoliation of graphite fluoride – By heating graphene in XeF2 gas at 250 °C • Graphene + XeF2 at 70 °C – high-quality insulator, stable up to 400 °C (resemblence with teflon) 44 Graphyn, Graphydiyn • Predicted • ‘‘Non-derivatives‘‘ of graphene • Semiconductors • Movement of electrons as in graphene but only in one direction 45 Graphydiyn Synthesis 46 Graphitic Carbon Nitride 47 Temperature- induced condensation dicyandiamide NH2C(=NH)NHCN In a LiCl/KCl melt 1834 Berzelius, Liebig Graphitic Carbon Nitride 48 (a) triazine and (b) tri-s-triazine (heptazine) Graphitic Carbon Nitride 49 (‘‘g-C3N4’’) Band gap 1.6 - 2.0 eV Small band gap semiconductors Si (1.11 eV), GaAs (1.43 eV), and GaP (2.26 eV) Porphene 50 Fully conjugated Antiaromatic Semiconductor Rectangular unit cell P2mm Family of 2-dimensional polymers Changing metal, up to two substituents Surface-constrained oxidative coupling of metalloporphyrins (zinc porphyrin) at the air/water interface A bilayer is formed Phosphorene 51 Semiconductor - direct band gap bulk BP 0.3 eV monolayer phosphorene 1.5 eV N -methyl-2-pyrrolidone Black phosphorus Orthorhombic a = 3.31 Å, b = 4.38 Å, c = 10.50 Å = 90 Space group Bmab Exfoliation Phosphorene 52 Height-mode AFM images single-layer phosphorene ca. 0.9 nm Phosphorene 53 Black phosphorus 12 lattice vibrational modes 6 Raman active modes 3 vibrational modes A1 g , B2g , and A2 g can be detected when the incident laser is perpendicular to the layered phosphorene plane: 361 cm1, 438 cm1, 465 cm1 As the number of phosphorene layers increases, the three Raman peaks red-shift 54 Zirconium Phosphates (a) α-zirconium phosphate = Zr(HPO4)2.H2O interlayer spacing 7.6 Å (b) γ-zirconium phosphate = Zr(PO4)(H2PO4)2H2O interlayer spacing 12.2 Å 55 Zirconium Phosphates α-zirconium phosphate Zr(HPO4)2.H2O interlayer spacing 7.6 Å 56 Zirconium Phosphates (a) α-zirconium phosphate = Zr(HPO4)2.H2O interlayer spacing 7.6 Å (b) γ-zirconium phosphate = Zr(PO4)(H2PO4)2H2O interlayer spacing 12.2 Å Brucite - Mg(OH)2 57 trioctahedral CdI2 hexagonal Bayerite and Gibbsite - Al(OH)3 58 dioctahedral Bayerite and Gibbsite - Al(OH)3 59 Opposite faces of a single layer Al(OH)3 (A and B sides, respectively) Bayerite and Gibbsite - Al(OH)3 60 Gibbsite is stacked by AB-BA sequence CCP of oxides Bayerite and Gibbsite phases have an identical single layer as the building block Bayerite is stacked by AB-AB sequence HCP of oxides 61 Clay Minerals 2:1 1:1 kaolinitemontmorillonite [Mg6O12]12- trioctahedral sheet of octahedral units [Al4O12]12- dioctahedral sheet [Si4O10]4- tetrahedral sheet 62 Montmorillonite (Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2ꞏ10H2O Phyllosilicate Minerals 63 Phyllosilicate Minerals 64 65 Clay Minerals N2 sorption isotherms (a) TMA- and Ca- montmorillonite (b) An Italian sepiolite (c) Natural SHCa-1 Na-hectorite (d) synthetic laponite and Li-(silane)-hectorites Closed symbols = adsorption Open symbols = desorption H3 H4 H4 H2 66 Surface Area nonpolar guest molecules N2 do not penetrate the interlayer regions Na+ forms of smectites and vermiculites – no penetration larger ions (Cs+ and NH4 + keep the basal planes far enough) - limited penetration The most important parameters of clays with respect to catalytic applications Layered Double Hydroxides 67 LDH = layered double hydroxides HT = hydrotalcites 68 Layered Double Hydroxides LDH = layered double hydroxides HT = hydrotalcites Natural mineral hydrotalcite Mg6Al2(OH)16CO3.4H2O Brucite layers, Mg2+ substituted partially by Al3+ Layers have positive charge Interlayer spacing d(003) = 0.760 nm Hydrotalcite Mg6Al2(OH)16CO3.4H2O the brucite-like layer = 0.480 nm gallery height = 0.280 nm 69 Hydrotalcites Brucite layers, Mg2+ substituted partially by Al3+ Layers have positive charge (a) [Ca2Al(OH)6]2SO4.6H2O (b) [LiAl2(OH)6]Cl (c) [Mg2.25Al0.75( OH)6]OH 70 Hydrotalcite The layered structure of LDH is closely related to brucite Mg(OH)2 a brucite layer, Mg2+ ions octahedrally surrounded by six OHthe octahedra share edges and form an infinite two-dimensional layer the brucite-like layers stack on top of one another either rhombohedral (3R) or hexagonal (2H) sequence Hydrotalcite Mg6Al2(OH)16CO3.4H2O - 3R stacking [MII 1-xMIII x (OH)2]x+(Am-)x/m]ꞏnH2O x = 0.25 Mg6Al2(OH)16CO3 x = 0 Mg(OH)2 71 Hydrotalcite The interlayer spacing c′ is equal to d003, 2d006, 3d009, etc.; c′ = (d003 + 2d006 + … + nd00(3n)) / n The cell parameter c is a multiple of the interlayer spacing c′ c = 3c′ for rhombohedral (3R) c = 2c′ for hexagonal (2H) sequences 72 Hydrotalcite Hydrotalcite Mg6Al2(OH)16CO3.4H2O - 3R stacking unit cell parameters a = 0.305 nm c = 3d(003) = 2.281 nm the interlayer spacing: d(003) = 0.760 nm the spacing occupied by the anion (gallery height) = 0.280 nm a thickness of the brucite-like layer = 0.480 nm the average M—O bond = 0.203 nm the distance between two nearest OH- ions in the two opposite side layers = 0.267 nm shorter than a (0.305 nm) and indicative of some contraction along the c-axis 73 XRD Patterns of LDH XRD patterns of layered double hydroxides synthesized by coprecipitation method with various cations composition: A – Mg/Al; B- Mg/Co/Al; C- Mg/Ni/Al * = Reflections from Si crystal used as a reference 74 XRD Patterns of LDH rhombohedral structure the cell parameters c and a The lattice parameter a = 2d(110) corresponds to an average cationcation distance The c parameter corresponds to three times the thickness of d003 c = 3/2 [d003+2d006] 75 Intercalation to LDH The intercalation of methylphosphonic acid into Li/Al LDH (a) [LiAl2(OH)6]Cl.H2O (b) second-stage intermediate, alternate layers occupied by Cl and MPA anions (c) first-stage product with all interlayer regions occupied by MPA 76 Intercalation to LDH LDH = layered double hydroxides hydrotalcites mineral Mg6Al2(OH)16CO3.4H2O Brucite layers, Mg2+ substituted partially by Al3+ Layers have positive charge Intercalate anions [Cr(C2O4)3]3- 77 The Anionic Exchange Capacity (AEC) 78 LDH Composite Structures Li Intercalation Compounds 79 80 Li Intercalation x Li + TiS2  LixTiS2 1T 81 Li Intercalation Li/C  e + Li+ + C Li+ + e + FePO4  LiFePO4 Molybdenum Disulfide (MoS2) 82 Mineral molybdenite Hydrodesulfurization catalyst (at edges) Lubricant Polymorphs of MoS2 83 semiconductors metallic MoO6 octahedralMoO6 trigonal prismatic 2H phase - thermodynamically stable 1T and 3R polymorphs - metastable Polymorphs of MoS2 84 semiconductors metallic 1T - MoO6 octahedral2H - MoO6 trigonal prismatic Li intercalation (2H to 1T), annealing (1T to 2H) Polymorphs of MoS2 85 Digit = number of monolayers in the unit cell the letters T = trigonal, H = hexagonal, R = rhombohedral 1T - MoO6 octahedral2H, 3R - MoO6 trigonal prismatic Molybdenum Disulfide (MoS2) 86 (b,c) infraredand (d−f) Raman-active Frequency of A1g band is increasing while that of E1 2g is decreasing with increase in number of layers Molybdenum Disulfide (MoS2) 87 Fermi level An indirect band gap 1.29 eV A direct band gap 1.9 eV (2H) Conduction band Valence band photoluminescence Molybdenum Disulfide (MoS2) 88 Nature Reviews Materials volume 2, Article number: 17033 (2017) Molybdenum Disulfide (MoS2) 89 MoS2 nanosheets - all sulfur atoms exposed on surfaces S = a soft Lewis base - a high affinity for heavy metal ions (e.g., Hg2+ and Ag+) = soft Lewis acids MoS2 nanosheets • high adsorption capacity - abundant sulfur adsorption sites • fast kinetics - easy access to adsorption sites 90 3D Intercalation Compounds Cu3N and Mn3N crystallize in the (anti-) ReO3-type structure the large cuboctahedral void in the structure can be filled By Pd to yield (anti-) perovskite-type PdCu3N By M = Ga, Ag, Cu leading to MMn3N 91 3D Intercalation Compounds Tungsten trioxide structure = WO6 octahedra joined at their corners = the perovskite structure of CaTiO3 with all the calcium sites vacant The color and conductivity changes are due to the intercalation of protons into the cavities in the WO3 structure, and the donation of their electrons to the conduction band of the WO3 matrix The material behaves like a metal, with both its conductivity and color being derived from free electron behavior The coloration reaction used in electrochromic displays for sun glasses, rear view mirrors in cars Zn + 2 HCl  2 H + ZnCl2 WO3 + x H  HxWO3 92 0D Intercalation Compounds C60 = FCC K3 C60 Octahedral voids (N) Tetrahedral voids (2N) K