Synthesis of carboxyl-modified multi-walled carbon nanotubes for efficient adsorption of furfurylamine

Background: Furfurylamines are important components for the synthesis of many pharmacologically active compounds and polymers, but there is still a gap in the field of furfurylamine isolation.Method: In this study, we designed and synthesised a series of carboxy-modified multi-walled carbon nanotubes (MWCNTs) with four modification strategies (acidification, grafting, acidification and grafting, grafting and acidification). Grafting refers to the efficient radical polymerisation using the abundant double bonds on MWCNTs; acidification refers to the conversion of defective five-or seven-membered rings to carboxyl groups. In addition, the adsorption behaviors (static adsorption, thermodynamics, kinetics) of the new materials has been systematically investigated. Significant findings: Overall, grafting and acidification were the best strategies, with the MWCNTs-AA (MWCNTs grafted by acrylic acid) exhibiting an adsorption capacity (Qe) for furfurylamine of 133.16 mg/g. Subsequently, the acidified material MWCNTs-AA-COOH (Acidification of MWCNTs-AA)(Qe=176.29 mg/g) was obtained by response surface optimisation on a grafting basis. Qe of MWCNTs-AA-COOH was 59.3% higher than that of commercial materials. Thermodynamic data suggested that Langmuir equation could better describe the adsorption behaviors of MWCNTs-AA-COOH, indicating that the adsorption process was endothermic and chemisorbed (Qm=280.71 mg/g). Meanwhile, the kinetic adsorption could be better modeled by Pseudo-second-order equation, demonstrating the adsorption rate of MWCNTs-AA-COOH was faster. Overall, it was proved that we have successfully designed an efficient modification strategy for MWCNTs had been established, which could realize effective adsorption of furfuramine by ion exchange.