Organic and inorganic acids-functionalized CNTs for the adsorption of Cu2+ and Ni2+ ions from aqueous solution

Heavy metals like copper and nickel are highly toxic due to their non-biodegradable and carcinogenic nature. In this study, adsorption technique was used to remove these undesired heavy metals from aqueous solutions. Carbon nanotubes (CNTs) due to fascinating member in carbon family are selected as an adsorbent which was further functionalized by citric acid and sulfuric acid. The morphological and structural properties of CNTs before and after functionalization were studied by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray (EDX) spectroscopy. Batch adsorption method was applied to investigate the adsorption of Cu 2+ and Ni 2+ ions on bare and acid-functionalized CNTs. The equilibrium concentration of Cu 2+ and Ni 2+ ions was determined by atomic absorbance spectroscopy. The respective maximum adsorption capacity for Cu 2+ ions by CNTs, SA-CNTs and CA-CNTs was 13.19, 25 and 65.35 mg/g, whereas for Ni 2+ ions these were 14, 33 and 40 mg/g. The thermodynamic parameters like Δ H , Δ S and Δ G were also calculated by using van’t Hoff equation. The adsorption data was compared with the previous findings, and the results showed that acid-functionalized CNTs are more effective than bare CNTs for the adsorption of Cu 2+ and Ni 2+ . Finally, the adsorbent recovery was ensured by desorption study of metal ions by using pre-sorbed Cu 2+ and Ni 2+ ions.