Thermoresponsive studies of porous and non-porous borophosphates.

In this work we present the synthesis and structure-property investigation of anhydrous low porosity borophsophates [1] BPO4 and porous (NH4)0.5M1.25(H2O)2)(BP2O8)(H2O)0.5 M = Co (II), Mn (II) and NH4Fe[BP2O8(OH)] phases. Cristobalite-type BPO4 crystallizes in the tetragonal lattice, space group I-4 (No. 82) [2]. Variable-Temperature Powder X-ray diffraction (VT-PXRD) patterns for these material were analysed by the sequential and parametric Rietveld refinement [3] protocols. Both methods were used to determine the temperature dependency of the lattice parameters and linear thermal expansion coefficient. Whereas the lattice parameters were refined freely in the sequential method, the individual cell parameters were described using an empirically derived function in the parametric method. Both refinement protocols reveal significant anisotropy along the a- and c- axis as a function of temperature, with thermal expansion coefficients of 10.6 x10-6 /⁰C and 2.83 x10-6 /⁰C, respectively. Structural changes accompanying this thermoresponsive behaviour will be discussed, including the variation of the interatomic distances and P-O-B (inter-polyhedral angle, figure 1) with temperature. The open framework (NH4)0.5M1.25(H2O)2)(BP2O8)(H2O)0.5 M = Co(II) (1a), Mn(II) (1b) and NH4Fe[BP2O8(OH)] (2) phases were synthesized under mild hydrothermal methods at 180⁰C. The crystal structure of the isostructural (1a) and (1b) phases were refined in the hexagonal lattice, space group P65 (no. 170) and compound (2) in the monoclinic lattice, space group P21/c (no.14). Both (1a) and (1b) phases consists of NH4+ and H2O molecules located within the helical channels running along the [001] direction with compound (2) consisting exclusively of NH4+ molecules located within the helical channels running along the [100] direction. Thermoresponsive investigation conducted by TGA analysis reveal a five, four and three step mass loss process for compounds (1a), (1b) and (2) respectively, with the final step observed at 500-700⁰C range. Preliminary VT-PXRD results of these compounds will also be presented.

In situ PXRD studies of heterogeneous catalysts and pre-catalysts

During the course of the last couple of years, my collaborators and I have studied a number of catalytic systems using a lab based PXRD facility at our disposal. Of particular interest to us has been the supported catalysts used in Fischer Tropsch catalysis as well as those used in the synthesis of multiwalled carbon nano tubes. These studies have all proven invaluable to the understanding of the often complex phase evolution that is an intricate and inherent part of the heterogeneous processes of interest to us. Selected results will be presented to illustrate the usefulness and value of these studies. For example below is the intensity profile of the diffraction patterns collected during the heat-treatment of the pre-catalyst: A - anatase, R - rutile, S - silicon, H - hematite and P - pseudobrookite

Stimulating the development of Crystallography in Africa, a southern perspective

During the last two to three decades the author has been aware of a number of initiatives aimed at stimulating and/or assisting the development of crystallography in various parts of Africa. This includes the CCDC initiatives of the 90's that let to them making the database available to African researchers. As well as a number of attempts to get basic diffraction equipment up and running in a number of locations. During the same time period I have been directly involved in the installation and commissioning of at least seven systems at Wits University. Also during this same period I organised at least three international meetings, in which African delegates were encouraged to attend via the provision of targeted financial assistance. This I believe has provided me with a rather unique perspective on the challenges faced by initiatives to stimulate the development of crystallography in Africa. In this presentation I hope to present an overview of some of the successes to date as well as some of the unique challenges we have encountered.