The effects of microwave regeneration on adsorptive performance of functionalized carbon nanotubes

In this study, the microwave regeneration method was applied to investigate the properties and adsorptive performance of functionalized carbon nanotubes (f-CNTs) in different cycles of regeneration/reuse. For this purpose, an organic and hazardous dye (Reactive Blue 19) was chosen as a widely used pollutant. N-2 adsorption/desorption isotherms, scanning electron microscopy and Fourier transform infrared spectroscopy were used to characterize f-CNTs during the regeneration/reuse procedure. The morphology, specific surface area and pore volume of f-CNT samples were not significantly altered. However, the functional groups present on the f-CNTs' surface were gradually removed after successive cycles of regeneration/reuse. A sudden decrease of adsorption capacity (about 20%) after the first cycle of regeneration/reuse was attributed to the elimination of functional groups interacting with the dye molecules because of the molecular-level heating. Relatively high regeneration efficiencies (73.30 to 80.16%) proved that the microwave regeneration method was successful. Very high step stripping efficiencies (80.16 to 98.02%) in four cycles of regeneration/reuse demonstrated that the microwave regeneration method could be utilized in consecutive cycles. After four cycles of regeneration/reuse, the CNTs could not be considered as functionalized.