Timothy J. Bastow

A new method to position and functionalize metal-organic framework crystals

With controlled nanometre-sized pores and surface areas of thousands of square metres per gram, metal-organic frameworks (MOFs) may have an integral role in future catalysis, filtration and sensing applications. In general, for MOF-based device fabrication, well-organized or patterned MOF growth is required, and thus conventional synthetic routes are not suitable. Moreover, to expand their applicability, the introduction of additional functionality into MOFs is desirable. Here, we explore the use of nanostructured poly-hydrate zinc phosphate (α-hopeite) microparticles as nucleation seeds for MOFs that simultaneously address all these issues. Affording spatial control of nucleation and significantly accelerating MOF growth, these α-hopeite microparticles are found to act as nucleation agents both in solution and on solid surfaces. In addition, the introduction of functional nanoparticles (metallic, semiconducting, polymeric) into these nucleating seeds translates directly to the fabrication of functional MOFs suitable for molecular size-selective applications.

Ending Aging in Super Glassy Polymer Membranes

Aging in super glassy polymers such as poly(trimethylsilylpropyne) (PTMSP), poly(4-methyl-2-pentyne) (PMP), and polymers with intrinsic microporosity (PIM-1) reduces gas permeabilities and limits their application as gas-separation membranes. While super glassy polymers are initially very porous, and ultra-permeable, they quickly pack into a denser phase becoming less porous and permeable. This age-old problem has been solved by adding an ultraporous additive that maintains the low density, porous, initial stage of super glassy polymers through absorbing a portion of the polymer chains within its pores thereby holding the chains in their open position. This result is the first time that aging in super glassy polymers is inhibited whilst maintaining enhanced CO2 permeability for one year and improving CO2/N2 selectivity. This approach could allow super glassy polymers to be revisited for commercial application in gas separations.

Study of precipitation in aged binary Mg-Al and ternary Mg-Al-Zn alloys using 27Al NMR spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy of 27Al was used to study the development of precipitation in aged Mg–6 wt%Al, Mg–9 wt%Al and Mg–9 wt%Al–(x) wt%Zn alloys. The 27Al spectra for the aged alloys consist of two peaks; one from the aluminium in solid solution and the other from aluminium in the precipitate phase. The proportion of aluminium atoms in the matrix and precipitate phases was measured, as a function of time at temperature, using the relative intensities of peaks. The nucleation of the continuous precipitates was found to be highly dependent on the initial supersaturation and it is proposed that it is a homogeneous process. The Austin–Rickett relation successfully models the amount of continuous precipitation with aging time; the kinetics is consistent with one-dimensional and interface-controlled growth. Changes in composition of the matrix and precipitate phases were correlated with the 27Al Knight shift characterising these phases. The Knight shift data from a series of ternary Mg–9 wt%Al–(x)wt%Zn alloys indicates that the Zn segregates to the precipitate phase during precipitation.

Lithiated Porous Aromatic Frameworks with Exceptional Gas Storage Capacity

Kristina Konstas, James W. Taylor, Aaron W. Thornton, Cara M. Doherty, Wei Xian Lim, Timothy J. Bastow, Danielle F. Kennedy, Colin D. Wood, Barry J. Cox, James M. Hill, Anita J. Hill, Matthew R. Hill

Electric field gradients at the M-site in MCO3: M=Mg, Ca, Sr and Ba

Abstract The electric field gradient (Vzz) has been measured at the Mg, Sr and Ba sites in MgCO3 SrCO3 and BaCO3 by nuclear magnetic resonance. These measurements, along with the results of Dupree et al. for the Vzz at the Ca site in the calcite and aragonite forms of CaCO3, have been compared with ab initio electronic structure calculations using the density functional based code for crystalline solids, W ien 97. The agreement between the theoretical and experimental values of Vzz is found to be within 10%.

Structure evolution in dilute Al(Cu) alloys observed by 63Cu NMR

63Cu NMR has been used to observe the evolution of the precipitate structures in the solution treated and quenched dilute alloy Al-1.7 at%Cu following thermal aging. The distinguishable phases in this alloy form in the following sequence (i) fcc α-phase with Cu in random substitutional sites, (ii) Guinier-Preston zones, (iii) θ″-phase, (iv) θ′-phase and finally (v) θ-phase, where the last two phases are structural variants of CuAl2. The Cu site in all five of these phases has been detected as a resolved line in the 63Cu FT-NMR spectrum at room temperature, together with a line assigned to surface Cu sites on θ′-phase platelets. Two additional lines have been observed in spectra from specimens containing the θ-phase due to Cu substituting for Al in the CuAl2 structure, and Cu in the CuAl η2-phase. Density functional based ab initio electronic structure calculations have been used to reproduce accurately the observed electric field gradient (Vzz) at the Cu site in θ-phase CuAl2 and to explain the relatively narrow 63Cu lines observed for GP-zones, θ″-phase and θ′-phase.

91Zr NMR characterisation of phases in transformation toughened zirconia.

A detailed 91Zr NMR investigation is presented of the five component (cubic, monoclinic, tetragonal, orthorhombic and delta) phase mixture in the transformation toughened engineering ceramic, magnesia-partially-stabilised zirconia (MgPSZ). The phases are distinguished on the basis of the quadrupole interaction displayed in the powder pattern of the 91Zr(1/2, -1/2) transition. This paper reports: (i) the first characterisation of the magnesia-fully-stabilised cubic phase at the eutectic composition (13.5 mol% MgO); (ii) the observation of a poorly ordered tetragonal phase on fast cooling ZrO2 (9.3 mol% MgO) from the cubic phase field at 1720 degrees C, and the subsequent growth and ordering of the tetragonal phase precipitates due to further annealing; (iii) the observation of the (partial) transformation of the cubic phase to the ordered delta-phase (Mg2Zr5O12) on annealing MgPSZ at 1100 degrees C for 8 h; and (iv) the observation of the transformation of the tetragonal phase into the orthorhombic phase after cooling in liquid nitrogen, and the reverse transformation after heating to 600 degrees C.

Observation of precipitation in Mg-Al alloys by 25Mg and 27Al NMR

A combination of 25Mg and 27Al NMR has been shown to be an effective structural probe for the intermetallic phase Mg17Al12, able to detect precipitation of this phase in dilute alloys of aluminium in magnesium during age hardening, with well-resolved signals from the precipitate and the alloy. Knight shift and spin-lattice relaxation measurements for the intermetallic phase are examined for evidence of a quasigap at the Fermi surface, recently proposed as the origin for the stability of this phase.

An NMR study of 137Ba and 47,49Ti in ferroelectric BaTiO3

A complete NMR characterisation, for the isotopes 137Ba, 47Ti and 49Ti, has been made for a single crystal of BaTiO3 in the orthorhombic ferroelectric phase at room temperature. The nuclear quadrupole coupling constant and the axially anisotropic component of the chemical shift tensor have been determined for each isotope. In a variable-temperature study up to the Curie point, the nuclear quadrupole coupling constants were found to vary very nearly as the square of the spontaneous polarisation.

47,49Ti NMR: hyperfine interactions in oxides and metals

A 47,49Ti NMR characterisation is given of various polymorphs of TiO2 (anatase, rutile and brookite), Ti2O3, perovskites CaTiO3 and BaTiO3, FeTiO3, TiB2, titanium metal, the titanium aluminides Ti3Al, TiAl, TiAl2, TiAl3, and TiAg. Values of chemical or Knight shift, nuclear quadrupole coupling constant and asymmetry parameter were derived from the (1/2, -1/2) powder lineshapes. For TiB2, titanium metal, TiAl, and TiAl3, where +/- (1/2, 3/2), and higher satellite transitions were observed, a value for the axial component of the Knight shift was obtained.