Surface properties and adsorption breakthrough curves of plasma-treated silica gels

Plasma treatments are used widely in surface modification of thin films and membranes. A similar treatment method was used for granular silica gel by using both argon and oxygen plasma. The surface properties, such as contact angle of water, pore diameter, and BET surface area, and the adsorption breakthrough curves for water were obtained on the plasma-treated silica gel. The contact angle of water decreased rapidly and then remained approximately constant during the plasma treatment. This indicated that argon- or oxygen-plasma treatment made the silica gel surface more hydrophilic. The increase in BET surface area of the plasma-treated silica gels was 13 to 15%. The experimental breakthrough curves showed that modification not only increased the effective surface area and active sites but also reduced the mass transfer resistance. The time for breakthrough increased by about 4 minutes when either argon- or oxygen-plasma treated silica gels were compared to the untreated one. The amount of moisture adsorbed by the modified silica gel as calculated from the breakthrough curve was increased by 18% compared to the untreated sample.