Interaction Influence of Contact Time and pH on Cobalt Retention by Carbon Nanotubes Bearing Various Loads of TiO2 and Fe3O4

Background: Nanomaterials have facilitated remarkable advances in the remediation of many environmental problems. A few studies have tackled the removal of Co (II) from aqueous solutions using nanomaterials. Herein, we studied the retention kinetics of cobalt species on carbon nanotubes (CNTs) bearing different amounts of TiO2 and Fe3O4/TiO2 nanomaterials individually. Methods: CNTs and their TiO2/Fe3O4/TiO2-modified nanomaterials were well characterized. Cobalt retention by these adsorbents was investigated considering different influencing factors such as Co (II) content, solution pH, and time. The kinetic data were fitted with pseudo-first-order, pseudosecond- order rate models, and intra-particle diffusion models for better elucidation of the mechanism of Co retention. Results: XRD evidenced the formation of TiO2 and Fe3O4/TiO2. High loads of both oxides were needed for higher and faster Co retention by CNTs. Co retention capacity increased with increasing the solution pH. The pseudo-second-order model presented the kinetics of Co retention at 30°C, and 48% of available capacity was attained within the first hour of interaction by CNT-TiO2 and with a moderate S/L ratio of 0.5 g/L. Co retention was increased with the amount of oxide to reach a maximum value of 16. 40 mg/g (90.2% TiO2) and 13.60 mg/g (48.2% Fe3O4/TiO2). The JovanoviĦ#135; equilibrium model predicted the maximum retention values as the nearest to the experimental ones. Conclusion: The potential of CNT-Fe3O4/TiO2 nanomaterials has been successfully demonstrated for the removal of cobalt, which makes them highly attractive and cost-effective adsorbents for wastewater treatment. The reported retention and removal rate values were relatively better than those seen in the literature. Loading different active oxides by CNTs is an interesting research area as selective adsorbents can be fabricated with affordable experimental costs.