Microwave-assisted synthesis of multi-walled carbon nanotubes for enhanced removal of Zn(II) from wastewater

Abstract

Removal of toxic metals is one of the biggest challenges in ensuring safe water for all as well as protecting the environment. Novel multi-walled carbon nanotubes (MCNTs) have been successfully synthesised by microwave techniques and improved to be an outstanding adsorbent for the removal of Zn(II) from wastewater. The adsorption of Zn(II) was studied and optimized as a function of pH, initial Zn(II) concentration, MCNT dosage, agitation speed, and adsorption time. In order to investigate the dynamic behavior of MCNTs as an adsorbent, the kinetic data were modeled using pseudo-first-order and second-order kinetic models. Different thermodynamic parameters, viz., ∆H°, ∆S° and ∆G° have also been evaluated and it has been found that the adsorption was feasible, spontaneous and endothermic in nature. Statistical analysis reveals that the optimum conditions for the highest removal (99.9 %) of Zn(II) are at pH 10, a MCNT dosage 0.05 g, an agitation speed and time of 160 rpm and 60 min, respectively, with an initial concentration of 10 mg/L. On the basis of the Langmuir model, qm was calculated to be 90.9 mg/g for microwave-synthesized MCNTs. Our results proved that MCNTs can be used as an effective Zn(II) adsorbent due to their high adsorption capacity as well as the short adsorption time needed to achieve equilibrium. Hence, MCNTs serve an important role in the removal of heavy metals from wastewater.