Removal of congo red from water using quercetin modified α-Fe₂O₃ nanoparticles as effective nanoadsorbent

In the present investigation, Quercetin modified α-Fe₂O₃ nanoadsorbent (Qur-Fe₂O₃) is synthesized by a simple chemical impregnation method, followed by characterization and evaluated for the removal of congo red dye (CR) from the aqueous solution. The adsorption of CR onto the novel Qur-Fe₂O₃ is investigated with variable parameters such as contact time, initial concentration of CR, adsorbent dosage and pH of solution using batch adsorption technique. It is found that the adsorption of CR on Qur-Fe₂O₃ is rapid during the initial stages and reached a steady-state condition with an uptake of approximately 95.4% after 140 min. Langmuir and the Freundlich adsorption isotherms are used to observe and quantify the interaction of CR and Qur-Fe₂O₃. Dye adsorption equilibrium data are well-fit with Langmuir isotherm rather than Freundlich isotherm. The maximum monolayer dye adsorption capacity at the optimum pH 5.4 by applying the Langmuir equation is 427.35 mg g⁻¹ at 25 °C for Qur-Fe₂O_3. Thermodynamic examination demonstrated that CR adsorption on the Qur-Fe₂O₃ nanoadsorbent was reasonably spontaneous and endothermic. A comparison of kinetic models showed that the overall adsorption process is described in well manner by pseudo-second-order kinetic model. The intraparticle diffusion model described that the rate-limiting step is not the diffusion of intraparticle alone. Moreover, the adsorption capacity is about 81.64% of the initial saturation adsorption capacity after being used four times. Thus, Qur-Fe₂O₃ nanoparticles are good candidate for efficient CR removal process from wastewater and for the deep-purification of polluted water.