Preparation and characterization of magnetic Fe^sub 3^O^sub 4^/CNT nanoparticles by RPO method to enhance the efficient removal of Cr(VI)

This work described a novel method for the synthesis of high-ferromagnetism nanoparticles (Fe^sub 3^O^sub 4^/CNTs) to efficiently remove Cr(VI) from aqueous solution. The Fe^sub 3^O^sub 4^/carbon nanotubes (CNT) were prepared by in situ reduction with post-oxidation method by using cheap and environmentally friendly precursor under mild condition. Magnetic hysteresis loops revealed that Fe^sub 3^O^sub 4^/CNTs had superior saturation magnetization (152 emu/g), enabling the highly efficient recovery of Fe^sub 3^O^sub 4^/CNTs from aqueous solution by magnetic separation at low magnetic field gradients. FTIR, Raman, XPS, and TEM observations were employed to characterize the physical-chemical properties of Fe^sub 3^O^sub 4^/CNTs, demonstrating that CNTs were successfully coated with iron oxide matrix. The adsorption equilibrium of Cr(VI) on Fe^sub 3^O^sub 4^/CNTs was reached within 30 min. Langmuir, Freundlich, and Dubinin-Radushkevich isotherm were chosen to analyze the equilibrium data. The results indicated that Langmuir model can well describe the equilibrium data with the maximum adsorption capacity of 47.98 mg/g at room temperature and 83.54 mg/g at 353 K. The adsorption capacity of Fe^sub 3^O^sub 4^/CNTs for Cr(VI) was greatly improved as compared to raw CNTs and other similar adsorbents reported. The pseudo-second-order kinetic model provided the best description of Cr(VI) adsorption on Fe^sub 3^O^sub 4^/CNTs. Most importantly, possible synthesis mechanism and Cr(VI) removal mechanism were explored. The results suggest that large amounts of Cr(VI) were adsorbed on Fe^sub 3^O^sub 4^/CNTs surface by substituting the surface position of -OH and then reducing it to Cr(OH)^sub 3^ and Cr^sub 2^O3.[PUBLICATION ABSTRACT]