Abstract
Rice hull ash (RHA) was treated with 1.0 M HNO3 (RHA-A1) and another batch was treated with 14.0 M HNO3 (RHA-A14). RHA-A1 and RHA-A14 had a pH of 6.58 and 6.13, respectively. Adsorption of saturated fatty acids (C8, C10, C12, C14, C16, and C18) was carried out on RHA-A1 and RHA-A14 at 32±1°C. The adsorption data conformed to the Langmuir isotherm. The specific surface area of RHA-A1 was 183.84 m2 g−1 while that of RHA-A14 was 174.67 m2 g−1. The specific pore volume of RHA-A1 was 0.216 cm3 g−1 while that of RHA-A14 was 0.234 cm3 g−1. The acid-treated ash, RHA-A14 (q m =0.43±0.03 mmol g−1 where q m is the amount of adsorbate adsorbed to form a monolayer coverage on the ash particles) showed a twofold increase in the adsorption of fatty acid per gram ash compared to RHA-A1 (q m =0.25±0.03 mmol g−1). The free energy of adsorption, ΔG° ads, was determined to be −7.06±0.10 and −6.75±0.11 kcal mol−1 for RHA-A1 and RHA-A14, respectively. The reduced ΔG° ads values observed for RHA-A14 were attributed to the electrostatic repulsion of the hydrophobic chain of the fatty acid adsorbed on adjacent sites and brought into close proximity of each other. The ΔG° ads values showed that the process of adsorption took place through physisorption on both RHA.
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Farook, A., Ravendran, S. Saturated fatty acid adsorption by acidified rice hull ash. J Amer Oil Chem Soc 77, 437–440 (2000). https://doi.org/10.1007/s11746-000-0070-0
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DOI: https://doi.org/10.1007/s11746-000-0070-0