UC San Diego

The use of electrically conductive mesoporous ceramic powders is a new way for enzyme immobilization aiming for biocatalysts. In this study, mesoporous indium oxide, zinc oxide and titanium dioxide were synthesized by a hydrothermal reaction method. Soft-template and hard-template approaches were utilized to enable mesoporous materials with varying pore sizes. Pore sizes were evaluated by the Brunauer–Emmett–Teller (BET) method and were in the range of 7 to 10 nm. Additionally, indium oxide, zinc oxide and titanium dioxide were doped with tin, gallium, and silver/niobium, respectively, to obtain increased values of electrical conductivity. Afterwards, stable suspensions of mesoporous powders with varying powder volume fractions and pH values were produced through magnetic stirring and ultrasonication and further evaluated by dynamic light scattering (DLS).

Meanwhile, we describe an analytical model predictive of the electrical conductivity of stable ceramic suspensions. Specific model systems in this study include fluids containing mesoporous powders of TiO2 doped with silver or niobium, ZnO doped with gallium, and In2O3 doped with tin. The electrical conductivities for all four suspensions were found to be lower in acidic solutions (i.e., lower pH) compared to those in basic ones (i.e., higher pH). The behavior of these ceramic suspensions can be explained by considering surface charge and suspension stability. We have also determined that the particle size of the powders has a more pronounced effect on the electrical conductivity of the suspensions compared to powder volume fraction. Particularly, for the same material, larger particle sized suspensions were found to have smaller electrical conductivity due to smaller cumulative surface area of the particles. A theoretical model to describe the electrical conductivity of diluted powder suspensions by incorporating the effects of powder volume fraction, particle size and suspension stability was proposed. This new model predicts the final electrical conductivity of the ceramic suspension by incorporating the effects of powder volume fraction, particle size and suspension stability. The calculations from our model present excellent correlation with the experimental results.