Browsing by Author "Mdoe, James"
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Item The Activity of Invertase Immobilized on Cashew Nut Shell Liquid-Templated Large Pore Silica Hybrids(2011) Mubofu, Egid B.; Mdoe, James; Kinunda, GraceThe characterization and activity of invertase enzymes immobilized on large pore micelle templated silica (LP-MTS) hybrid materials is reported. The LP-MTS hybrid materials were prepared by a co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltrimethoxysilane (AMPTS) in a cashew nut shell liquid (CNSL) template. A commercially available dodecylamine template was also used to afford similar materials, hereinafter abbreviated as DDA-MTS, for comparison purposes. The prepared materials were characterized by different techniques to determine their physicochemical properties. The maximum loading for the amine groups in LP-MTS and DDA-MTS were 3.3 and 2.8 mmol g�1, respectively. Modification of the materials for immobilization of the invertase enzyme was done by reacting them with glutaraldehyde resulting in Glu-LP-MTS or Glu-DDA-MTS. The as-prepared hybrid materials have surface areas ranging from 100 to 214 m2 g�1 with pore diameters ranging from 3.1 to 25 nm. Scanning electron microscopy (SEM) images show that LP-MTS and DDA-MTS materials comprise of roughly spherical particles whereas enzyme and glutaraldehyde supported micelle templated silicas show a rupture of the spherical particles to a fine powder. The activities of free and immobilized invertases have been determined by measuring the amount of reducing sugar produced upon hydrolysis of sucrose at different temperatures, pH and substrate concentrations. Both free and immobilized invertase enzymes showed a maximum activity at a particular optimum temperature, pH and substrate concentration. The maximum activity for the free invertase was 15 229 U at pH 5.0 and at 40 1C whereas those of the LP-MTS immobilized invertases were 14 833 U and 14 625 U for covalent and cross-linked invertases, respectively, at pH 4.0 and 40 1C. The maximum activity for DDA-MTS covalently immobilized invertase was 4750 U, at pH 4.0 and 40 1C.Item Catalysis of the Knoevenagel reaction by γ-aminopropylsilica(1997-12) Macquarrie, Duncan J.; Clark, James H.; Lambert, Arnold; Mdoe, James; Priest, AndrewThe Knoevenagel reaction can be catalysed by γ-aminopropylsilica. Reactions are rapid and essentially quantitative with small amounts of catalyst. A range of aldehydes and ketones can be reacted successfully, the only exceptions being very bulky ketones. The reaction is very dependent on the efficient removal of water, which leads to faster reaction rates and to much higher conversions. The choice of solvent is also extremely important, with nonpolar solvents such as cyclohexane being optimal. Less polar, higher boiling solvents are significantly less effective, even at much higher reaction temperatures. Catalyst poisoning is slow and appears to be due to amide formation on the surface.Item Functionalized Mesoporous Organo-Silica Nanosorbents for Removal of Chromium (III) Ions from Tanneries Wastewater(Springer Link, 2016) Gervas, Charles; Mubofu, Egid B.; Mdoe, James; Revaprasadu, NeerishOrgano-silica mesoporous materials with cyano functional groups were prepared by a one pot co-condensation of 2-cyanoethyltriethoxysilane (CETS) and tetraethoxysilane (TEOS) at ratios of 1:4 and 1:9 using either sunflower oil or n-dodecylamine as templating agents. The tethered cyano groups were used as adsorption sites or hydrolysed to carboxylic surface functional groups. The prepared materials were characterized by diffuse reflectance infrared Fourier transform spectroscopy, atomic force microscopy (AFM), Brunauer, Emmettt and Teller, thermogravimetric analysis, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Results indicated that materials with cyano and carboxylic surface groups were successfully prepared. AFM results indicated that primary particles with irregular shapes and grain size ranging from 0.28 ± 0.03 to 0.46 ± 0.08 µm were obtained depending on the CETS to TEOS ratio used and the structure directing template. SEM and TEM micrographs depict spherical like morphology of the same size as portrayed by AFM results. Sunflower cyano functionalized micelle template silica (MTS-S-CN) at a ratio of 1:9 had surface area of 760.5 m2/g and average pore diameters of 3.5 nm while MTS-S-CN at a ratio 1:4 had pore diameter of 10.1 nm with surface area of 734.1 m2/g. On the other hand, the MTS-S-COOH (1:9) had surface area of 975.9 m2/g with pore diameter of 4.6 nm whereas MTS-S-COOH (1:4) had surface area of 740.1 m2/g with pore diameter of 6.3 nm. The materials were used in adsorption studies of Cr(III) ions from tannery wastewater. Cr(III) ions removal ranged from 48 to 83 % depending on the adsorbent functional group and the organosilyl groups to silica ratio. This study has indicated that materials prepared were good adsorbents with an adsorption maximum of 19.7 mg Cr(III) ions per g of adsorbent.Item Michael Additions Catalyzed by N,N-Dimethyl-3-aminopropyl — Derivatized Amorphous Silica and Hexagonal Mesoporous Silica (HMS)(1998-06) Mdoe, James; Clark, James H.; Macquarrie, Duncan J.Solid bases prepared by derivatisation of amorphous silica and hexagonal mesoporous silica with dimethylaminopropyl groups are good catalysts for Michael addition reactions. Of the prepared catalysts, those based on hexagonal mesoporous silica show particularly high activities. The sol-gel method used in preparing the catalysts based on hexagonal mesoporous silica enables loading to be increased to more than twice that of those based on amorphous silica which are prepared by the post-modification method.Item Organomodified hexagonal mesoporous silicates(1999-01) Macquarrie, Duncan J.; Jackson, Dominic B.; Mdoe, James; Clark, James H.A neutral templating route to organically modified silicates with tightly controlled porosity is described. The materials prepared are characterised and compared to the corresponding organofunctionalised silica