Characterization and application of Fe1−xCoxFe2O4 nanoparticles in Direct Red 79 adsorption

Abstract

Water pollution remains a significant global challenge, with dye contamination from industrial activities being particularly problematic. Adsorption is widely recognized as an efficient, rapid, and cost-effective method for pollutant removal. To enhance adsorption efficiency, researchers have increasingly focused on the development of reusable adsorbent materials. Magnetic materials, in particular, have garnered attention due to their ability to be easily recovered through the application of an external magnetic field. In this study, ferrite spinel adsorbents were synthesized by substituting Co(ii) into the FeFe2O4 spinel structure using a coprecipitation method. The random distribution of a Co cation into host FeFe2O4 compounds, Fe1–x CoxFe2O4 (x = 0–1), strongly influenced optical and magnetic properties. Nanoparticle sizes varying within 10–17 nm were obtained in Fe1−x CoxFe2O4 compounds. X-ray diffraction and Fourier transform infrared spectroscopy analyses revealed a single-crystal phase that was well fabricated. The optical bandgap energy decreased from 2.27 to 1.89 eV, together with a reduction of magnetic moment from 93.5 to 43.1 emu/g. The Fe1−x CoxFe2O4 materials demonstrated significant adsorption performance for Direct Red 79 (DR79), particularly at low pH levels, with optimal results observed at x = 0.5 (FC3). The adsorption behavior was effectively described by the Langmuir and Redlich–Peterson models. Kinetic analysis revealed that the pseudo-second-order and intragranular diffusion models provided the best fit. Thermodynamic analysis indicated an endothermic process (ΔH = 74.947 kJ/mol), suggesting that the adsorption mechanism is primarily physical. This study underscores the potential of Fe1−x CoxFe2O4 materials for the effective removal of Direct Red 79 (DR79), offering valuable insights into their synthesis, characterization, and application for environmental remediation. After four cycles of recovery and reuse, the FC3 magnetic nanomaterial was able to remove 42% of the DR79 pollutant while maintaining good chemical stability. The adsorption efficiency of the material for the actual textile wastewater sample reached 57% for color removal and 54.5% for chemical oxygen demand reduction.

Keywords

• magnetism
• cobalt
• spinel
• ferrite
• co-precipitation