Highly efficient as-synthesized and oxidized multi-walled carbon nanotubes for copper(II) and zinc(II) ion adsorption in a batch and fixed-bed process

In this work, the optimization of temperature, argon gas flow rate, acetylene gas flow rate and time effect on the yield of as-synthesized multi-wall carbon nanotubes (AS-MWCNTs) using a novel iron-nickel/biochar catalyst was investigated. Subsequently, the AS-MWCNTs were functionalized to obtain oxidized multi-wall carbon nanotubes (OX-MWCNTs). The nanoadsorbents were applied for Cu(II) and Zn(II) ions adsorption from wastewater in a batch and fixed-bed process. Remarkably, the results revealed optimum AS-MWCNTs yield (280%) at the following experimental conditions; temperature (725 degrees C), argon gas flow rate (250 mL/min), acetylene gas flow rate (180 mL/min) and time (75 min). OX-MWCNTs demonstrated higher surface area of 1210 m(2)/g compared to AS-MWCNTs (1140 m(2)/g). The optimum removal of Cu(II) and Zn(II) ions were obtained at pH (6), contact time (30 min), adsorbent dosage (20 mg/L), initial metal concentration (Cu(II) (75 mg/L) and Zn(II) (80 mg/L)) and temperature (45 degrees C). Maximum adsorption capacities for Cu(II) and Zn(II) ions removal by AS-MWCNTs were obtained as 364.66 and 347.01 mg/g, while OX-MWCNTs produced higher maximum adsorption capacities of 416.47 and 411.88 mg/g. The experimental data were better fitted by Langmuir isotherm and pseudo-second order kinetics, while thermodynamic investigation revealed a favorable and spontaneous chemisorption controlled adsorption of metal ions. Furthermore, the breakthrough curves of Cu(II) and Zn(II) ions was suitably modelled by Thomas kinetic model. Accordingly, AS-MWCNTs and OX-MWCNTs indicate a promising choice to eliminate Cu(II) and Zn(II) ions in wastewater due to its stability, high efficiency, environmental friendliness and excellent recyclability capacity. (C) 2021 Published by Elsevier B.V.

Automated summary

This study focused on optimizing the synthesis of multi-wall carbon nanotubes and their functionalization for efficient removal of Cu(II) and Zn(II) ions from wastewater. The experimental conditions led to high yield of AS-MWCNTs and OX-MWCNTs with promising adsorption capacities for metal ions removal, indicating their potential as effective and environmentally friendly adsorbents.