Riaan Schmuhl

Nanostructured ion-selective MCM-48 membranes

Templated MCM-48 silica was prepared using CTAB as surfactant. The MCM-48 powders and thin films were characterized by different techniques. MCM-48 layers were deposited on macroporous α-alumina supports and silicon nitride microsieves. The water permeability of MCM-48 was compared with the permeability of conventional mesoporous γ-alumina membranes. The applicability of MCM-48 as ion-selective electric field-driven switchable interconnect for microfluidic devices was demonstrated.

Synthesis and characterisation of dual-phase Y-TZP and RuO2 nanopowders: dense electrode precursors

The synthesis and characterisation of nanopowders in the dual-phase system tetragonal-Y2O3-doped ZrO2 (Y-TZP) and RuO2 are described. Five powders were prepared from a co-precipitation (CP) method with stoichiometric variation in the RuO2 content (5–46 mol%) and two powders were prepared from solid-phase mechanical mixing of the above oxides prepared separately. In the CP method, an aqueous chlorometal solution containing appropriate precursor ions was co-precipitated in a concentrated aqueous ammonia (pH y14) solution. Following filtration, washing and drying (100 uC), the CP synthesis route yielded black coloured amorphous powders. Crystalline dual-phase powders were obtained after calcination in stagnant air at 600 uC for 2 h. The average Y-TZP and RuO2 crystallite sizes were, respectively, 10 and 20 nm, i.e. a nano/nano powder. The powders were characterised by X-ray diffraction (XRD), transmission electron microscopy (TEM), backscatter Raman spectroscopy (ZrO2 phase determination) and quantitative X-ray fluorescence (XRF). Time-dependent calcination experiments for samples of similar composition revealed that under the synthesis conditions employed, a composite was formed where a fraction of the crystalline RuO2 phase was initially dissolved in the ZrO2 phase and which gradually transforms to a more stable, distinctly dual-phase system upon prolonged (¢20 h) calcination at 600 uC.

Tuneable ion-selective inorganic membranes

A new type of ion-selective ceramic membrane with electrically tuneable selectivity is reported. The membrane consists of a conventional supported γ-alumina membrane with porous gold electrodes sputtered on both sides. An electrical potential difference can be applied over the electrodes. The transport of Cu2+ ions was investigated as a function of the applied field strength over the membrane and the copper concentration in the feed solution. It is shown that the transport rate can be tuned efficiently by the magnitude and direction of the field. This technology may find application in micro-fluidic devices such as micro total analysis systems.

Tailor-Made Nanostructured Ion Selective MCM-48 Membranes

Mesoporous templated MCM-48 silica was prepared using a C16 surfactant as template. The MCM-48 powders and thin films were characterized by different techniques. Two types of porous supports were used, namely macroporous ?-alumina and silicon microsieves. The supported MCM-48 layers were applied as liquid permeable membranes in pressure-driven nanofiltration and electric field-mediated ion transport experiments.

The synthesis and composition of dual-phase 3Y-TZP/RuO2 electrode powders

This research was performed to learn more about the electron conducting yttria doped zirconia/ruthenia dual-phase system. The study indicated that for all starting powder precipitates (by either co-precipitation or sequential precipitation) strong separation between the Ru and Zr-species upon heating occurred already at the unexpected low temperature of 100–200°C. The solubility of RuO2 in 3Y-TZP (zirconia stabilised into a tetragonal phase by a 3 mol% Y2O3 addition) after calcination at 600°C was estimated at 3 mol%, independently of the used synthesis technique.

Electric Field Mediated Ion Transport Through Charged Mesoporous Membranes

The transport of ions from aqueous solutions through a stacked Au/alpha-alumina/gamma-alumina/Au membrane under the influence of a dc potential difference is reported. The membrane shows high cation permselectivity at ionic strengths of ~1 mM at pH 4.3-6.5, which is associated with a combination of anion adsorption and double-layer overlap inside the pores of the gamma-alumina layer. The cation flux can be controlled by ionic strength, dc potential difference and pH.