Control & Determination of Nanoporous silica surface hydrophobicity by dye adsorption model

Surface hydrophobicity control using various silylation reagents was studied by UV-Vis spectrometry. Nanoporous LUS-1 sample was characterized using XRD, SEM, BET surface measurement, pore size distribution and FT-IR. The silylated samples were treated with malachite green in alkaline condition. Adsorption of malachite green oxalate, a cationic dye, from aqueous solution offers a spectroscopic approach to measure surface hydrophobicity. The UV-Vis results showed a logic trend with respect to the surface free silanolates. For an initial concentration 200 mg/l adsorbent, as-synthesized silica a still containing the templating surfactant exhibited the lowest percentage of dye adsorption (82%) and for acid washed sample, this value was the highest (96%). Between these two limits, full silylated sample adsorbed relatively small amount of dye molecules (85.6%) due to the nearly complete coverage of hydrophobic trimethylsilane and hexamethyldisiloxane groups on its surface. Semi-silylated sample with hexamethyldisiloxane and partially silylated one with hexamethyldisilazane had 91.5% and 95.5% adsorpsion amount, respectively. By this adsorption model we are able to control the surface hydrophobicity through easy silylation method.

Keywords:

Silica , Silylation , Nanoporous , Surface hydrophobisity , Dye adsorption