Enhanced adsorption of As(V) and Mn(VII) from industrial wastewater using multi-walled carbon nanotubes and carboxylated multi-walled carbon nanotubes

The presence of As(V) and Mn(VII) in water beyond the permissible concentration allowed by World Health Organization (WHO) standard affects human beings, animals and the environment adversely. Hence, there is need for an efficient material to remove these potentially toxic elements from wastewater prior to discharge into water bodies. This research focused on the application of response surface method (RSM) assisted optimization of Fe-Ni/Activated carbon (AC) catalyst for the synthesis of MWCNTs. Also, the MWCNTs was carboxylated and the adsorption behaviors of both nano-adsorbents in the removal of As(V) and Mn(VII) from industrial wastewater was investigated through experimental and computational techniques. The prepared Fe-Ni/AC, MWCNTs and MWCNTs-OCH2CO2H were characterized using BET, TGA, FTIR, HRSEM, HRTEM, XRD and XPS. The result showed the BET surface area of Fe-Ni/AC, MWCNTs and MWCNTs-OCH2CO2H were obtained as 1100, 1250 and 1172 m2/g, respectively. Due to the enhanced impact of carboxylation, the adsorption capacity of As(V) and Mn(VII) removal increased from 200 to 192 mg/g for MWCNTs to 250 and 298 mg/g for MWCNTs-OCH2CO2H. The isotherm and kinetic models were best fitted by Langmuir and pseudo-second order kinetics, while the thermodynamic investigation found that the adsorption process was endothermic, spontaneous and chemisorptions controlled. The regeneration potential of MWCNTs and MWCNTs-OCH2CO2H after six repeated applications revealed good stability of adsorption efficiency. The study demonstrated optimization importance of Fe-Ni/AC catalyst design for MWCNTs adsorbents and the potentials of utilizing both MWCNTs and MWCNTs-OCH2CO2H in the removal of selected heavy metals from water and soil.