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 °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 oC). 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.