Adsorption of methylene blue and Congo red from aqueous solution on 3D MXene/carbon foam hybrid aerogels: A study by experimental and statistical physics modeling

Abstract

In this paper, a new type of adsorbent MXene/carbon foam hybrid aerogel (MCF) was synthesized from Ti3C2TX-MXene and melamine foam (MF), and its removal properties of both cationic and anionic dyes were studied. The physicochemical properties of MCF were analyzed by a variety of characterization techniques, while its dye adsorption mechanism was further elucidated by the statistical physics models. The results show that MCF exhibited excellent adsorptive efficiency towards the two hazardous dyes methylene blue (MB) and Congo red (CR), and their adsorption capacity were 356.97 mg/g and 647.75 mg/g, respectively, which were fitted better for the Langmuir equation and quasi-second-order kinetic model. Moreover, the mechanism of MCF-MB and MCF-CR adsorption systems was discussed through the saturated multilayer model at the molecular level. The numerical simulation results show that the MB molecules were adsorbed by MCF in the form of dimer, which was a process of multi-anchoring (303 K and 318 K), single connection (333 K) and mixed adsorption orientation. On the contrary, CR molecules were adsorbed as monomers, which was a process of multi-anchored and pure non-parallel adsorption directions (303 K and 318 K) and mixed adsorption orientation (333 K). From the statistical physical and thermodynamic analysis, the adsorption mechanism of MB and CR onto MCF was mainly determined by the receptor density (Dm), which was a reversible endothermic adsorption process driven by the physical interaction, and high temperature was beneficial to the occurrence of high adsorption capacity.