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In the present study, defluoridation study of liquid phase with the help of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) were well investigated and elucidated. The impact of different experimental conditions such as solution pH, initial fluoride concentration, adsorbent dose, and contact time was well studied and optimized for the maximum fluoride removal from water. The experimental data were fitted by the Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherm models and the related equilibrium constants were calculated. The results of the isotherm studies showed that fluoride removal by both adsorbents followed the Freundlich isotherm model. Kinetic studies were conducted and the results demonstrated that the experimental data were fitted well with the pseudo-second order kinetic model. Furthermore, two multiple regression-based equations were also derived to model the removal of fluoride from aqueous solutions by the carbon nanotubes. This study demonstrated that the polynomial equations satisfactorily described the behavior of the present defluoridation process for both MWCNTs ( R 2 = 0.913) and SWCNTs ( R 2 = 0.941). [ABSTRACT FROM AUTHOR]

The adsorption capacity of two efficient adsorbents namely MWCNTs and SWCNTs for the rapid removal of noxious Cr (VI) ion from the polluted aqueous source was well studied and investigated. The impact of several influential parameters such as contact time, initial pH, initial Cr (VI) ion concentrations and the adsorption capacity of the adsorbent in the presence of competing anion was well elucidated and optimized. It was observed that the removal of efficiency of Cr (VI) ion depends on the pH of solution and the maximum efficiency was noticed at pH 2.5. Furthermore, the uptake of Cr (VI) ion was hindered in the presence of the competing anion, SO 4 2− . Experimental equilibrium data were fitted to four different isotherm models by linear regression method, however, the adsorption equilibrium data were well interpreted by the Langmuir model. The maximum adsorption capacity of Cr (VI) ion by MWCNTs and SWCNTs was 1.26 and 2.35 mg/g respectively, which is calculated by the Langmuir isotherm model. Kinetic studies are well suited and found in good agreement with pseudo-second order. The results evidently indicated that MWCNTs and SWCNTs would be suitable adsorbents for Cr (VI) ion in wastewater under specific conditions. [ABSTRACT FROM AUTHOR]