Study of adsorption of differently charged dyes by carbon adsorbents

The article investigates the adsorption of basic (Methylene blue) and acidic (Congo red) dyes by three types of industrial activated carbon synthesized from natural raw materials. Using the method of isothermal adsorption/desorption of nitrogen, the porous structure of all types of carbon was studied, and the effect of the size of the adsorbent particles on the adsorption capacity was shown. It was established that the adsorption isotherms of both dyes can be described using the Langmuir model. It is assumed that dye molecules are weakly bound to the surface of the carbon material due to van der Waals and hydrophobic interactions. It is shown that the adsorption of Methylene blue is significantly greater than the adsorption of Congo red. This is due to the peculiarities of the dissociation of the functional groups of dye molecules, as well as the almost twice the length of Congo red molecules compared to Methylene blue molecules. It is shown that the boundary amount of adsorbed Methylene blue allows us to estimate the specific surface area of microporous activated carbon with high accuracy if the hydrophilicity of the surface of this carbon is taken into account.