Utilizing modified weathered basalt as a novel approach in the preparation of Fe3O4 nanoparticles: Experimental and theoretical studies for crystal violet adsorption

Abstract Weathered basalt activated at 950 ⁰C for 3h was used, for the first time, as a source of Fe(III) to prepare magnetic Fe3O4 nanoparticles (MNPs). The synthesized Fe3O4 MNPs were characterized by XRD, FTIR, FESEM, and TEM and utilized as a cost effective adsorbent for the removal of crystal violet (CV) dye at pH 7.0 and 25, 40, and 50 °C. The experimental data were fitted to the Langmuir model with maximum adsorption capacities that ranged from 269.7 to 282.5 mg/g, and increased with the solution temperature. Three theoretical advanced models from statistical physics theory were used to interpret the corresponding adsorption mechanism. It was concluded that the single layer model, with one active site, was the best adsorption model for this system. The number of adsorbed CV molecules per the adsorption site (n) was 1.2 – 1.6 suggesting the existence of multi–interactions mechanism. The density of Fe3O4 active sites (DM) was the main steric factor governing the removal process, and this parameter improved from 134.7 to 218.33 mg/g consistent with the increase of the adsorption temperature. The adsorption energy was below 40 kJ/mol and, hence, the removal of CV molecules was directed mainly by physical forces. The low cost, regeneration performance, and chemical stability of these Fe3O4 MNPs suggest their application as a very promising approach for wastewater treatment. The results present a new approach in the fabrication of magnetic nanoparticles using Fe-rich natural materials, as alternative sources for iron compounds, to be employed in water and wastewater remediation.