Preparation of L-cysteine modified MnFe2O4 nanoparticles based on high-gravity technology and application for the removal of lead

Abstract

MnFe2O4 nanoparticles, usually applied as a magnetic adsorbent for removing heavy metals in wastewater, have attracted widespread attention for the characteristics of excellent magnetic properties and chemical stability. This study firstly used high-gravity technology coupled with surface modification by L-cysteine to prepare novel L-cysteine modified MnFe2O4 nanocomposite (MnFe2O4-Cys) with small size (< 10 nm), narrow size distribution range and good dispersion in water, and serves as the efficient adsorbent for Pb(II) removal from water. The different preparation conditions were optimized and the obtained products were charactered through a series of characterization methods. As compared to a traditional stirred reactor, the MnFe2O4-Cys prepared via high-gravity technology using impinging stream-rotating packed bed (IS-RPB) reactor (MnFe2O4-Cys-R) has higher crystallinity and saturation magnetization (57.16 emu·g-1). As seen from TEM images and DLS results, the MnFe2O4-Cys-R exhibits a small average size of 7.25 nm and good dispersion in water. Besides, the BET specific surface area of MnFe2O4-Cys-R (169.63 m2·g-1) is 31.2% higher than that of unmodified MnFe2O4 (129.26 m2·g-1) prepared by IS-RPB reactor (MnFe2O4-R). The adsorption behavior of Pb(II) on MnFe2O4-Cys-R is best described by pseudo-second-order kinetic and Temkin isotherm models, respectively, whereas Elovich kinetic and Freundlich isotherm models are best for describing the adsorption of Pb(II) on MnFe2O4-R. The realized experimental maximum adsorption capacity of MnFe2O4-Cys-R is 137.45 mg·g-1, which is 1.98 times that of MnFe2O4-R (69.50 mg·g-1). This study provides a new route for production of small uniform MnFe2O4 nanoparticles with excellent magnetic and adsorption performance for wastewater treatment.