Adsorption of hazardous dyes on functionalized multiwalled carbon nanotubes in single and binary systems: Experimental study and physicochemical interpretation of the adsorption mechanism

The crystal violet (CV) and rhodamine B (RhB) dyes were selected in this paper to study their adsorption on functionalized multiwalled carbon nanotubes (MCN). Adsorbent morphology and its corresponding physico-chemical properties were characterized by applying various experimental techniques namely SEM, XRD and FTIR. Results of phenomenological modeling and the experimental adsorption data showed that the adsorption capacities of both dyes in single solutions were similar. However, synergistic and antagonistic adsorption effects were observed in binary solutions. Results indicated that the CV dye molecule was practically adsorbed in a double amount in comparison to the RhB dye molecule at most of the adsorption temperatures. Saturation adsorption capacities ranged from 0.57 to 0.86 mmol/g and from 0.75 to 0.88 mmol/g for CV and RB dyes at 298-328 K, respectively. It has been concluded that the size of dye molecule played a negligible role during the adsorption. CV and RhB dye molecules can interact with the same functional groups of the adsorbent. A competitive statistical physics model was reliable to predict the multicomponent adsorption behavior of these dyes. The adsorption orientation of both dyes was discussed using the results of the physical modeling and a possible theoretical mechanism was proposed based on the estimated adsorption energies. Finally, the effect of temperature on the adsorbent performance for both single and binary dye solutions was analyzed providing a clear understanding of the observed trends in the experimental dye adsorption capacities.