Abstract
The isotherm of histidine adsorption from an aqueous solution by carbon nanotubes MKN-SWCNT-S1 is constructed. The isotherm has the shape of a sigmoid. The alanine adsorption isotherm by these carbon nanotubes was constructed in previous work and has the shape of two-plateau isotherm. The model is considered describing the adsorption of molecules from the solution with the formation of clusters of i molecules (i = 1,2, … n) on the sorbent surface for which analytical expressions of the isotherm are obtained. This model makes it possible to clarify the sorbate structure on the sorbent surface using the experimental isotherm of adsorption.It is shown that the obtained experimental isotherm of histidine adsorption reflects the cooperative amino acid sorption, consisting in the formation on the sorbent's surface the monomers and clusters of 4 and 8 layers of histidine zwitterion ions. Experimental isotherm of alanine adsorption reflects the cooperative amino acid sorption, consisting in the formation of monomers and seven-dimensional clusters on the sorbent surface. The experimental adsorption isotherms and the proposed model were used to determine the monolayer capacities of the CNT to the investigated amino acids and to estimate specific surface area of nanotubes.
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