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The aim of this study was to investigate the applicability of the adsorption process for the removal of organophosphorus pesticide malathion 57% from water by using multi-walled carbon nanotubes (MWCNTs). The impact of various experimental conditions such as pH, quantity of adsorbent, concentration of pesticides, contact time and temperature was studied and optimized for the maximum removal of malathion. Unlike conventional optimization, a limited number of experiments (26 steps) were performed in a cost-effective manner for different independent variables such as MWCNTs concentration (0.1–0.5 g/L), the malathion (57%) concentration (6 mg/L and 10 mg/L), contact time (2–30 min) and pH (neutral range). Based on the experimental data obtained in a lab-scale batch study, a three-factor response surface modeling (RSM) approach was implemented in order to optimize the conditions for maximum removal of malathion, and compare experimental results with standardized malathion samples. The optimized conditions to achieve the maximum removal of malathion (100%) were determined to be a malathion concentration of 6 mg/L, an initial MWCNTs concentration of 0.5 g/L, and a contact time of 30 min. Findings of this study clearly indicated that 100% of the malathion could be cost-effectively removed by MWCNTs in conditions predicted by the proposed optimization methodology. [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]