Preparation and characteristics of a magnetic carbon nanotube adsorbent: Its efficient adsorption and recoverable performances

Abstract

The challenges encountered in solid–liquid separation hinder the wide applications of carbon nanotube adsorbents. To overcome this problem, MnFe2O4/multiwalled carbon nanotubes (MMWCNTs) that combined the satisfactory adsorption properties of multiwalled carbon nanotubes (MWCNTs) with the magnetic separation of nanoparticles (MnFe2O4) was developed. MMWCNTs with a size of 10–50 nm exhibited remarkable magnetic separability (10.8 emu/g) and high adsorption capacity (qm = 494.91 mg/g, 308 K). Batch experiments to study the effect of pH on tetracycline (TC) adsorption showed that when the TC concentration was less than 80 mg L−1, the MMWCNTs could effectively adsorb TC in the pH range of 2–10, with a removal efficiency greater than 80%. The well fitted pseudo-second-order dynamic adsorption model and Langmuir isotherm indicated that the TC adsorption onto MMWCNTs mainly involved chemical and monolayer adsorption. Since the TC adsorption process was endothermic, increasing temperature could favor TC removal. Besides, after six cycles of regeneration with the NaOH solution, the removal efficiency could be maintained at 70% of the original, which indicated that the MMWCNTs had an excellent regeneration performance. At the same time, the results of our research showed that MMCWNT could not only be used as a good adsorbent for TC treatment, but also could be applied to other types of wastewater treatment.