The fractal dimension D values of the mesoporous silica gel and activated carbon have been determined by the method of adsorption from solutions. The results are as follows. (1) The adsorption isotherms of aliphatic alcohols, ketones, esters and oxy aromatic compounds from carbon tetrachloride or cyclohexane on silica gel, and those of aromatic compounds from water on activated carbon can be represented by the Langmuir equation. The fractal dimension D can be calculated by the limiting adsorbed amount, n_ms, and the apparent molecular across section, σ_a, based on log n_ms=-D/2logσ_a+constant. The n_ms and σ_a were calculated with the Langmuir equation and the specific surface area of adsorbents. (2) The fractal dimension D values of the mesoporous silica gel derived by the method of adsorption from solutions are the same as those from gases, which are ca. 2. As long as the radius of the surface curvature is larger than the size of adsorbed molecules, the surface of adsorbent may have low fractal dimension. (3) The obtained fractal dimension D value of the mesoporous activated carbon derived by the method of adsorption from solutions is also close to 2. A possible explanation is that progressive activation changes the microporous structure of the original charcoal gradually to a meso/macroporous structure. Then the mesoporous activated carbon can be also characterized by low fractal dimension.

Key words: fractal surface, fractal dimension, adsorption from solution, activated carbon, silica gel