Cadmium ion sorption from aqueous solutions by high surface area ethylenediaminetetraacetic acid- and diethylene triamine pentaacetic acid-treated carbon nanotubes

Abstract

A novel and rapid microwave-assisted approach along with Friedel–Crafts acylation has been successfully introduced for functionalization of carbon nanotubes (CNT) via aliphatic and aromatic carboxylic acids. This green and efficient route may play an essential role for realizing miscellaneous functionalizations of CNT, which were successfully functionalized via ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). Qualitative (FT-IR) and quantitative (TGA, Raman, XPS) characterization has been employed to investigate the degree of functionalization. The N₂ adsorption isotherm shows significant increases of 270% and 262% in specific surface area in the low partial pressure region after functionalization of CNT with EDTA and DTPA, respectively, which resulted from eliminating the tube ends or caps. By looking at the potential of EDTA and DTPA for sequestering metal ions, EDTA- & DTPA-treated CNT were used to evaluate the aqueous cadmium(II) adsorption efficiency. Then, the effects of solution temperature, pH and contact time on the adsorption of Cd²⁺ ions onto the treated samples and pristine CNT were investigated. The adsorption performance of Cd²⁺ ions by functionalized samples showed dramatic growth when compared with the pristine sample, which was effectively pH dependent. The pseudo second-order model precisely captured the kinetic analyses of adsorption. This study suggested that the functionalization method not only enhanced the effective surface area including active adsorption sites on the CNT structure, but also decreased the functionalization time and cost significantly and proposed a promising material for capacitive deionization.