Introducing the Kabachnik–Fields multicomponent reaction for functionalization of multiwalled carbon nanotubes and their performance for removal of methylene blue

Abstract

Abstract The development of functionalized carbon nanotubes (CNTs) for environmental application is an area of research that holds great promise and intense interest. In this study, an organic-inorganic CNTs composite was synthesized via a novel “one-pot” route and was used as an adsorbent for removal of methylene blue (MB) from aqueous solution. At first, furfural as a diene was covalently anchored onto the surface of pristine CNTs through the Diels–Alder (DA) cycloaddition reaction. Then, the Kabachnik–Fields (KF) reaction, a nearly century-old multicomponent reaction, was rediscovered as an efficient “connector” which conveniently builds up polymer architectures on CNTs surfaces under rather mild conditions (including air atmosphere, aqueous solution, and catalyst-free). The surface morphology and chemical structure were analyzed by transmission electron microscopy, thermal gravimetric analysis, and X-ray photoelectron spectroscopy. Moreover, adsorption characteristics of MB on the as-prepared CNTs adsorbents were examined by varying experimental conditions such as contact time, solution pH, temperature and initial MB concentration. It was shown that the removal process was pH dependent. Kinetics indicated that the adsorption equilibrium can be achieved within 20 min and experimental data were best described by the pseudo-second-order model. The adsorption isotherms data were preferably fitted to the Langmuir model, yielding the maximum adsorption capacity of 346.88 mg/g. The thermodynamic study suggested that the adsorption process is endothermic and spontaneous in nature. It is concluded that the possible mechanisms of adsorption may be attributed to π–π stacking or electrostatic interaction. These results suggested that the modified CNTs based composite is expected to be a new candidate for dye removal. More importantly, we believe that the current work paves a facile and green way to fabricate new libraries of CNTs/polymer functional materials via the combination of DA reaction and KF reaction and might prompt the broader study of the KF reaction in interdisciplinary fields.