Comparison of Langmuir and Harkins-Jura Adsorption Isotherms for the Determination of Surface Area of Solids

Batch experiments were carried out for the adsorption of aniline on activated charcoal and titanium dioxide from toluene at 35, 40, 45, 50 and 55 degrees C. The adsorption of aniline on charcoal from toluene (ACT) was of L3 type and aniline on titanium dioxide from toluene (ATT) was of L2 type as per Giles classification. The experimental data were analyzed with Langmuir and Harkins-Jura adsorption isotherms. The Harkins-Jura equation was obeyed by all systems for the entire concentration range studied, where the Langmuir equation fails. All Harkins-Jura plots contained two intersecting straight lines. The point of intersection of the two lines relate to completion of a monolayer. From these monolayer values the specific surface areas of adsorbents were calculated. By Harkins-Jura relative method the surface areas of the adsorbents were also obtained by comparison of the slopes of the straight lines, without resorting to the ambiguous parameters like molecular area and unreliable monolayer values.