Decontamination of selenate from aqueous solution by oxidized multi-walled carbon nanotubes

•Removal of selenate — a hazardous pollutant using MWCNTs was investigated.•Results show that MWCNT was highly efficient material for the removal of selenate.•Adsorption equilibrium follows pseudo-second-order model.•Equilibrium data were well described by the typical Langmuir adsorption isotherm.•Thermodynamic studies revealed that the adsorption reaction was spontaneous.

Selenium (Se) is emerging as a contaminant that must be dealt with in many areas of the world. In this study, we evaluated the effectiveness of oxidized multiwalled carbon nanotubes (MWCNT) as an adsorbent to remove selenate [Se (VI)] from aqueous solutions. A systematic study of the adsorption process was performed by varying pH, ionic strength, and temperature. The experimental results showed that MWCNT is an excellent selenate adsorbent with an adsorption capacity of up to 1.865 mg g− 1 at an initial selenate concentration of 2.0 mg/L and temperature of 303 K. The adsorption kinetics was modeled by first- and second-order rate, Elovich and Weber and Morris intra-particle diffusion models. The results indicate that second order kinetics model was well suitable to model the kinetic adsorption of selenate. The adsorption isotherms were modeled by Langmuir, Freundlich and D–R isotherm models. Equilibrium data were well described by the typical Langmuir adsorption isotherm. Thermodynamics studies were carried out and the calculated values of enthalpy change (∆H) and entropy change (∆S) are 19.474 kJ/mol and 69.9058 J/mol K respectively. Further, these studies revealed that the adsorption reaction was spontaneous and endothermic process and the calculated activation energy is 19.474 kJ/mol.

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