RESUMO
To the limit: Electrolyte flow accelerates the mass-transfer process in a droplet cell (see picture). The limiting current in the cell is expressed as a sum of hydrodynamic and stagnant terms. The current derived from the latter term indicates that convective mass transfer in the cell would be changed dramatically at a significantly small volumetric flow rate. Convective mass transfer in a flowing-electrolyte-type droplet cell (f-DC) is investigated for quantitative analysis of an electrode process and precise electrofabrication of microstructures using this device. The limiting current in the f-DC was expressed theoretically and its practical equation is investigated experimentally by cyclic voltammetry in solutions containing a redox mediator. The limiting-current equation in the f-DC derived experimentally could be expressed as a sum of hydrodynamic and stagnant terms. The current derived from the latter term of the f-DC is ten times larger than that in a conventional stagnant cell, thus indicating that the convective mass transfer in the cell would be changed dramatically at a small volumetric flow rate.
RESUMO
A manganese-oxidizing fungus was isolated from a hot spring in Japan. The fungus was increasingly effective at oxidizing Mn(II) ions as the concentration of organic carbon sources in the growth medium was decreased. The fungus oxidized 50 ppm of Mn(II) ions within 160 h in a pH 7.3 medium at 25 degrees C. The presence of carbon fiber shortened the time to 80 h, and promoted steady oxidation. The oxidation products were identified by XPS and XRD to be poorly crystallized and amorphous MnO(2), both with and without the fiber. These results suggest that the fiber participates in kinetically limited oxidation. The fungus was entangled with and clung to the fibers, and the oxidized Mn species accumulated on the fungus. Similarly shaped polyethylene telephthalate fiber did not enhance the oxidation, nor was adhesion of the fungus observed. Although the mechanism is still unknown, the present work shows that removal of Mn from solution through the precipitation and accumulation of Mn-oxides on the fungus in the presence of carbon fiber is a promising improvement for water treatment.
