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

Abstract

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 (n1 and n2), density of first and second receptor site (Nm1 and Nm2), concentration at half saturation relative to the first and second receptor site (W1 and W2) 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.