Thermodynamics of the Adsorption of 4-Nitrophenol from Aqueous Solutions at Activated Charcoal

O. K. Krasil’nikova, T. A. Kul’kova, and A. V. Larin

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, eninskii pr. 31, Moscow, 119991 Russia

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Received June 26, 2007

Abstract — The adsorption of 4-nitrophenol from aqueous solutions at activated FAS-1 charcoal was studied at

293, 308, 318, and 328 K. The experimental data obey the Dubinin–Astakhov–Stoeckli equation (a special case of the Dubinin–Radushkevich equation) for different exponents n. For experimental adsorption isotherms, the characteristic curve of the micropore volume filling theory was not temperature-invariant. However, these adsorption isotherms were described by the Dubinin–Radushkevich equation with n = 8 over a wide concentration range. This satisfacry description and the nonlinearity of the adsorption isotherms in the Dubinin–Asta-khov–Stoeckli coordinates (for different n values) for low filling values are probably associated with competitive adsorption of water and 4-nitrophenol molecules in small micropores of the adsorbent. The calculated isos-teric heats of adsorption increase with the adsorbed amount, which is also the case that the characteristic curve is not temperature-invariant.

PACS numbers: 68.43.-h