Aminated nanoporous activated carbon fibers: Adsorption materials for the recovery of Cu2+ and Cd2+ ions

In this article, we report on and compare the texture, thermal properties, and adsorption capacity of aminated nanoporous activated carbon fibers (NACFs), which were prepared using the bromination followed by the amination with ethylenediamine, diethylamine, monoethanolamine, and sulfolanylethylenediamine. FTIR ATR confirmed the grafting of the amino groups. Surface morphology and microstructure of NACFs were assessed based on the results of SEM and nitrogen adsorption. Simulation of nitrogen adsorption with 2D-NLDFT models showed a highly porous structure with nanopore diameters between 0.5 and 0.8 nm and from 1.1 to 2.1 nm. The aminated NACFs with up to 0.95 mmol of amino groups per gram have moderate thermal stability. Thermal decomposition and detachment of amino groups were registered by TPD MS and TGA between 200 degrees C and 400 degrees C. Effective adsorption of 80-98% of Cd2+ and Cu2+ ions from very dilute water solutions were achieved with the aminated NACFs. The equilibrium adsorption isotherms for Cd2+ and Cu2+ were well fitted with the Langmuir and Dubinin-Radushkevich (DR) models. These results suggest sufficient energy homogeneity of the carbon surfaces and adsorption in the nanopores. As compared with the unmodified NACFs, the adsorption of Cd2+ and Cu2+ ions on the aminated surface of the NACFs is characterized by up to three times higher values of the maximum adsorption capacity and from two to five times higher values of the constants describing the adsorption equilibrium for each model.