Synthesis of novel magnetite nanoparticles with chitosan mesoporous silica coating for efficient removal of heavy metals from wastewater

Abstract

Contamination of natural water resources by heavy metal pollutants present in wastewater has become a worldwide concern. Removal of heavy metal ions by surface functionalized magnetic nanoparticles adsorption is an economical route due to its simplicity and easy operation. However, bare magnetite nanoparticles are not good adsorbents and are susceptible to oxidation and agglomeration. The challenge is to develop economically feasible magnetite nanoparticles with an appropriate surface functionalization that will simultaneously provide adsorption efficiency, hydrophilicity, and recyclability without compromising magnetic properties. The aim of this study was to develop magnetite nanoparticles with a combined coating of chitosan and mesoporous silica which would act as an efficient adsorbent of heavy metal ions i.e., Pb2+ Cd2+ and As3+ from water. The Fe3O4 nanoparticles were synthesized via thermal decomposition method of iron-oleate precursor. The synthesized particles were subjected to X-ray diffraction (XRD), Physical Property Measurement System (PPMS), and Transmission Electron Microscopy (TEM) to determine the crystalline phase, crystallitesize, magnetic properties, and morphology respectively. The coating of mesoporous silica was formed on the particles by reaction of phase transferring them with the help of Cetrimonium bromide (CTAB) and addition of Tetraethyl orthosilicate (TEOS). The chitosan coating over the mesoporous silica coated particles was put by subjecting the particles to 5% chitosan solution in acetic acid with pH 6.0. The successful formation of the coatings was confirmed by conducting Fourier-transform infrared spectroscopy (FTIR) analysis. The final substance to be used as the adsorbent exhibited a saturation magnetization of 28.84 emu/g. The coated particles were used as adsorbents for Pb2+, Cd2+ and As3+ present in water. During the adsorption experiments the contact time and initial concentration parameters were varied and the corresponding data was fitted to pseudo-first order and pseudo-second order kinetic model to determine the adsorption mechanism. The data was also fitted to the Langmuir and Freundlich adsorption isotherms. The data demonstrated a closer fitting to the Pseudo-2nd order kinetic model and the Langmuir Isotherm model. Based on these results the adsorption process is determined to be a monolayer chemisorption and the particles were concluded to be an efficient heavy metal adsorbent with adsorption capacity of 150.33 mg/g, 126.26 mg/g, and 3.021 mg/g for Pb2+, Cd2+ and As3+respectively.

Keywords: Adsorption, magnetite nanoparticles, mesoporous silica, chitosan, adsorption kinetic models, adsorption isotherm models, lead, cadmium, arsenic.