New insights about reactive red 141 adsorption onto multi–walled carbon nanotubes using statistical physics coupled with Van der Waals equation.

• New insights about RR 141 adsorption were presented considering non ideality. • The intermolecular interactions between the RR 141 molecules cannot be neglected; • OH and COOH groups were more important than aromatic rings for dye adsorption. • The attraction energy between adsorbed molecules cannot be neglected; • The Van der Waals parameter, b , ranged from 0.00001 to 0.00302 L mg−1. In this communication, statistical physics models (sta–phy) coupled with the Van der Waals (VDW) state equation were employed to demonstrate insights regarding the reactive red 141 (RR 141) adsorption onto multi–walled carbon nanotubes (MWCNTs). Experimental isotherms were constructed for two types of carbon nanotubes (MWCNTs–OH and MWCNTs–COOH) at four different temperatures (298, 308, 318 and 328 K). These curves were predicted by sta–phy models coupled or not with the VDW state equation. It was demonstrated that the sta–phy coupled with VDW equation was able to predict the experimental isotherms more accurately than the other used models. Based in this approach, insights about RR 141 adsorption on the MWCNTs were presented considering the following parameters: number of molecules adsorbed at first and second site (n 1 and n 2), density of first and second receptor site (N m 1 and N m 2), concentration at half saturation relative to the first and second receptor site (W 1 and W 2) and VDW interaction parameters (a and b). The Van der Waals parameter related with the co–volume of the adsorbate molecule (b) was significant and ranged from 0.00001 to 0.00302 L mg−1. [ABSTRACT FROM AUTHOR]