EFFECT OF MODIFICATION OF ALUMINA SURFACES BY OZONE ON ADSORPTION BEHAVIOR OF BOVINE SERUM-ALBUMIN AT ALUMINA-WATER INTERFACES

The relationship between the surface properties of aluminum oxide (Al2 O3) after ozone exposure and the adsorption behavior of bovine serum a lbumin (BSA) at Al2O3-water interfaces was studied at the isoelectric point (IEP) of BSA. Al2O3 particles were exposed to ozone generated fr om oxygen or dry air at various concentrations of 50 to 1,000 ppm. Iso therms for BSA adsorption onto ozonized oxygen-and ozonized air-expose d Al2O3, which showed good fits to the Langmuir equation, had gentler initial slopes and lower saturation values (Gamma(s)) than the isother m for adsorption onto native Al2O3. The desorption rate of preadsorbed BSA during alkali cleaning was highest for ozonized air-exposed Al2O3 followed by ozonized oxygen-exposed and native Al2O3. X-ray photoelec tron spectroscopic analysis showed no significant differences in the s tates of aluminum-oxygen chemical bonds at the outermost surfaces of A l2O3 before and after ozone exposure. The adsorption affinity of water vapor for Al2O3 surfaces decreased slightly as a result of their expo sure to ozonized oxygen, but increased when the surfaces were exposed to ozonized air. The IEP of Al2O3 was shifted to the acidic side by ex posure to both the ozonized gases. The extent of the decrease in the a ffinity of BSA adsorption and of the shift in the IEP increased with i ncreasing ozone concentration, and were much greater for ozonized air- exposed Al2O3. The difference in the effects of ozone exposure was int erpreted as arising from the formation of nitrate groups on the ozoniz ed air-exposed Al2O3 surfaces, derived from nitrogen oxides in ozonize d air. The value of Gamma(s) was found to be correlated with the surfa ce charge densities of Al2O3 after ozone exposure. It was concluded th at the lower adsorption affinity of BSA for Al2O3 surfaces was attribu ted to the decrease in the density of hydroxyl groups by the oxidative action of ozone, and to the formation of nitrate groups on Al2O3 surf aces induced by the synergistic actions of ozone and nitrogen oxides.