Adsorption of anionic dyes from aqueous solutions by a novel CTAB/MXene/carbon nanotube composite: Characterization, experiments, and theoretical analysis

Abstract

A novel three-dimensional composite was prepared by the self-assembly of MXene nanosheets and carbon nanotubes (CNTs) with the assistance of cetyltrimethylammonium bromide (CTAB), which was named as CMC composite. Adsorption of three anionic dyes, including Acid orange (AO7), Methyl orange (MO) and Congo red (CR), from aqueous solutions on the composite and the mechanisms were investigated in this study. Compared with MXene and CNTs, the CMC composite exhibited superior adsorption performance for AO7, MO and CR with maximum adsorption capacities of 367.9, 294.2, and 628.5 mg/g, respectively. The adsorption capacities of AO7 and MO on the CMC composite decreased, while that of CR increased with increasing temperatures. Quantum chemical calculations indicated that electrostatic interactions, π-π electron-donor-acceptor interactions and hydrogen bonding played important roles on the adsorption. The approximate site energy distribution analysis demonstrated that more adsorption active sites existed on the CMC composite than on MXene and CNTs, which endowed the CMC composite with higher adsorption capacities for these anionic dyes. The differences of adsorption behaviors for three anionic dyes could be ascribed to the number of available adsorption sites and the change of the site heterogeneity on the CMC surface.