Adsorption of Congo red dye on Fe_xCo_3-xO₄ nanoparticles

The advanced treatment of industrial wastewater often calls upon the use of highly-efficient treatment methods to remove hazardous pollutants prior to the effluent discharge. Adsorption can be used towards removing micro-pollutants. Congo Red dye is widely used in the paper and textile industry, and residual quantities are present in the process effluents. Adsorbing metal oxide nanoparticles have abundant pores of appropriate size, a large specific surface area, and can efficiently remove organic pollutants from waste water. Fe_xCo_3-xO₄ nanoparticle adsorbents were synthesized. Their magnetic properties facilitate their recovery. Experiments were conducted for different Congo Red concentrations and Fe_xCo_3-xO₄ nanoparticles dosage. The maximum Congo Red adsorption capacity of Fe_xCo_3-xO₄ nanoparticles at equilibrium was 128.6 mg/g. The adsorption yield of Congo Red decreased from 86.12% to 79.53% when the initial concentration of Congo Red increased from 10 mg/L to 30 mg/L, Adsorption results were modeled to define essential parameters such as the adsorption mechanisms and kinetics. A pseudo-first-order kinetic model fitted the results. The equilibrium adsorption data were moreover fitted by isotherm models, with both the Langmuir and Freundlich equations shown appropriate. The re-use of the nanoparticle adsorbent was moreover investigated for 5 successive adsorption cycles, without loss of adsorption capacity. A case study for the adsorption of Congo Red on the Fe_xCo_3-xO₄ nanoparticles demonstrates that the required mass of adsorbent can be calculated for any amount of Congo Red to be removed. It was demonstrated that the fairly cheap and environmentally friendly Fe_xCo_3-xO₄ nanoparticles have a strong adsorption and removal ability for dyes and are easy to recycle.