Enhanced adsorption of emerging contaminants by green carbon nanotubes in binary and ternary systems

Abstract

Carbon nanotubes (CNTs) functionalized by green synthesis were assessed in adsorptive multicomponent systems to remove the nonsteroidal anti-inflammatory drug (NSAID) diclofenac and the antibiotics ciprofloxacin and ofloxacin. Kinetic and equilibrium studies were performed in binary and ternary systems. The kinetic models of pseudo-first and pseudo-second order fitted the multicomponent data very well. The equilibrium study revealed a slight adsorption capacity increase with the temperature rise and that the multicomponent adsorptive process is synergistic. The Langmuir-Freundlich model was the one that best fitted the binary equilibrium data. For the ternary system, the diclofenac data were not well represented by the equilibrium models, and this may have occurred due to its much faster adsorption than for the other two drugs, and the complexity of the process. The characterization techniques indicated that the adsorption process occurred efficiently and did not significantly modify the structure of the material, indicating that the process occurred only on its surface. π-π and n-π interactions, hydrogen bonds and electrostatic interactions are some of the adsorption mechanisms present in the process. Diclofenac adsorption was favored in the presence of the other two contaminants, and the modified CNTs showed great promise as an adsorbent in multicomponent systems.