Synthesis and Characterization of Humic Acid Coated Magnetite Nanoparticles for the Removal of methylene blue from Aqueous Solutions

Abstract

During the last few decades different methods were studied for the removal of dyes from industrial effluents as their disposal have toxic effects to humans, animals, plants and the aquatic organisms. Very recently magnetic nanoparticles (NPs) have been extensively used to remove this dye but to enhance its removal efficiency problem related to aggregation and oxidation of these nanoparticles in aqueous solution needs to be addressed .Therefore, the focus of this research was to address the problems by coating the NPs with polymeric materials like humic acid. Magnetite NPs were synthesized by coprecipitation method. Humic acid coated magnetite nanoparticles of labeled HAC-1(10:1ratio) and HAC-2 (20:1) were synthesized with the same method by varying the proportion of precursor magnetite and humic acid ratio (10:1 and 20:1).The chemical and physical characteristic of synthesized nanoparticles were characterized by Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction spectroscopy, Scanning electron microscopy-energy dispersive x-ray spectroscopy (SEMEDX) and UV-Vis DRS spectroscopy. The characterized nanoparticles were used for the removal of methylene blue from aqueous solution by adsorption mechanism. The effects of the contact time, dose of the adsorbent, pH, and initial dye concentration on the adsorption capacity were studied. The kinetics and adsorption isotherm were also studied. The crystal size of NPs calculated by Debye-Scherer equation were 9.17 nm, 12.65 nm and 11.5 nm for HAC-1, HAC-2and bare magnetite NPs, respectively. Both of the bare magnetite and the coated magnetite had cubic spinel structure and the spherical shaped morphology. The band gap energy of synthesize NPs were 3.24 eV, 3.2 eV and 3.18 Ev for Fe3O4 HAC1 and HAC-2 respectivly.The results showed that the adsorption capacity for the dye increased by increasing the contact time, adsorbent dose and initial pH of the solution until reach to equilibrium but slightly decrease after equilibrium. However, it decreased with increasing the adsorbate (methylene blue) concentration. The adsorption kinetics was in good agreement with pseudo 2ndorder kinetic equation and the adsorption isotherm showed good fitting to Langmuir equation and the maximum adsorption capacity was 62 mg/g, 40 mg/g and 34.48mg/g for HAC-1 , HAC-2 and bare magnetite NPs respectively. The MB removal efficiency of HAC-1, HAC-2 and bare magnetite from aqueous solution were 99.5%, 97.6% and 95.8% respectively. The result clearly indicated the MB removal efficiency of magnetite nanoparticles from aqueous solution can be improved by coating with humic acid.