抄録
Dead-end ultrafiltration of the mixtures of titanium dioxide (TiO2) of the rutile form and bovine serum albumin (BSA) was performed under various conditions of the salt concentration and TiO2/BSA mixing ratio at pH 4.2 where both TiO2 and BSA were charged positively. For salt-free suspensions, the average specific filtration resistance αav of the filter cake increased with an increase of the mixing ratio of BSA because αav of BSA was significantly larger than that of TiO2. However, when the salt was added, αav in the range of quite small BSA fractions tended to become smaller than αav of cake composed of TiO2 alone. These unique variations of αav can be explained based on the zeta potential of colloids and the mean particle size. Thus, the variation of the stability of particles plays a vital role in determining the filterability of fine particle/macromolecule mixtures.
Next, dead-end microfiltration of the mixtures of aluminum oxide (Al2O3) and BSA was conducted at pH 6.0 where Al2O3 and BSA were charged oppositely, and the filtration rate and the rejection of BSA were measured for various Al2O3/BSA mixing ratios. The filtration rate increased remarkably by a small addition of BSA to Al2O3 suspension, which was caused by a marked decrease in the zeta potential of the particles. On the other hand, the BSA rejection of about 0.1 to 0.3 was observed although a BSA molecule was considerably smaller than the pore size. The adsorption test revealed that the retention of BSA in filtration experiments was attributed mainly to the adsorption of BSA onto the surface of Al2O3.
