Equilibrium, Kinetic and Isotherm Studies of Dye Adsorption from Aqueous Solution by Recyclable Amine-Functionalized Silica Coated Magnetic Nanoparticles

The evaluation of the adsorption capacity of amine-functionalized silica coated iron oxide magnetic particles (Fe₃O₄/SiO₂-NH₂) as a highly recyclable adsorbent for Congo Red (CR) and Eriochrome Black T (EBT) azo-dyes from water is reported. The Fe₃O₄/SiO₂-NH₂ were prepared by a simple co-precipitation method of iron oxide (Fe₃O₄) nanoparticles followed by silica coating on oleic acid coated Fe₃O₄. A series of investigation was performed to assess the various experimental parameters like contact time (0–360 min), pH (3–10), stirring speed (0–500 rpm), adsorbent dosages (0.02–0.12 g) and initial concentrations (0.02–0.15 mg mL⁻¹) of dyes. According to the Langmuir isotherm, the maximum adsorption capacities of CR and EBT on Fe₃O₄/SiO₂-NH₂ particles were found to be 211.86 mg g⁻¹ and 81.98 mg g⁻¹, respectively. In comparison, the pseudo-second order model provided adsorption capacities of 200.40 mg g⁻¹ for CR and 80.91 mg g⁻¹ for EBT. Additionally, the maximum adsorption amounts of CR and EBT on Fe₃O₄/SiO₂-NH₂ particles were 179.37 mg g⁻¹ and 75.43 mg g⁻¹, achieved within 300 min and 180 min at pH 3, respectively. The dye-loaded particles were recoverable for CR and EBT removal by simple regeneration with 0.1 molL⁻¹ NaOH solution to use the particles until more than five cycles.