Adsorption performance and mechanisms of Co2+ onto carboxyl-functionalized carbon nanotubes

Abstract

In this study, carboxyl-functionalized carbon nanotubes (cCNTs) were used as adsorbents for nuclide Co2+, and their adsorption characteristics and mechanisms were investigated. The cCNTs presented a characteristic tubular morphology, a moderately ordered crystal structure, and good thermal stability. Their specific surface area and isoelectric point were 405.6 m2/g and 2.4, respectively. The adsorption of Co2+ onto the cCNTs exhibited rapid kinetics, with a maximum adsorption capacity of 25.1 mg/g at 303 K. This adsorption process is pH-sensitive, with higher pH resulting in better adsorption capacity. Moreover, the order of selective adsorption onto the cCNTs was Co > Sr > Cs, and the presence of coexisting cations in the simulated seawater was found to influence Co adsorption. The adsorption mechanisms of Co on cCNTs involved physical and chemical adsorption, driven by electrostatic interactions and coordination with the active sites. Density functional theory (DFT) calculation revealed that the adsorption energy of Co2+ onto cCNTs was −197.6 kcal/mol, and O atoms on the surface of cCNTs played a vital role in coordination. This study was beneficial for comprehending the adsorption performance and mechanism, particularly concerning the competitive adsorption performance of nuclides onto carbon nanotubes (cCNTs).