Poly O-toluidine-coated acetic acid modified eggshell-chitosan with ZnFe2O4 nanoparticles as a new and promising sorbent nanocomposite for rapid removal of toxic dyes such as Brilliant Green and Acid Red from the aquatic environment

The conversion of organic waste into valuable commodities is essential for safeguarding the environment and promoting the sustainable development of the economy. This investigation centres on the production of Zinc ferrite nanoparticles (ZnF NPs), modified eggshells (MES) impregnated with chitosan (CS) and coated with poly ortho-toluidine P(OT) nanocomposites (NCs). This synthesis involves a quaternary composition denoted as P(OT)/MES/CS/ZnF NCs, achieved through chemical polymerization techniques. The resulting NCs were characterized and applied for the removal of Brilliant Green (B.GR) and Acid Red (A.RE). Four distinct compositions, namely pure P(OT), binary P(OT)/MES, ternary P(OT)/MES/CS, and quaternary P(OT)/MES/CS/ZnF NCs, were synthesized. The outcomes revealed that the quaternary P(OT)/MES/CS/ZnF NCs exhibited the highest adsorption capacities for B.GR and A.RE at)27.03 and 142.8 mg⁻¹(, respectively. The findings revealed that the most favorable parameters for the removal of A.RE were attained at a pH of 2, using 15 mg of P(OT)/MES/CS/ZnF NCs at a concentration of 25 mg/L for a duration of 120 min. On the other hand, when it comes to removing B.GR, the best results were shown while using 15 mg of P(OT)/MES/CS/ZnF NCs at a concentration of 5 mg/L for 120 min, specifically at a pH of 6. The greatest real wastewater removal efficiencies for A.RE dye and B.GR dye, respectively, were found to be 99.5% and 97.6% under these operating circumstances. These optimal quaternary NCs demonstrated the ability to be regenerated four times without significantly compromising their adsorption properties and exhibited a remarkable capacity to remove 96–98% of dyes from real polluted water. Through the use of regression data and a pseudo-second-order model, the adsorption kinetics were explained, with R² values of 0.994 for A.RE and 0.993 for B.GR, respectively. Thermodynamic parameters of dye adsorption by the NCs affirmed the fact that adsorption occurs spontaneous and have endothermic nature. This study underscores an effective synthesis approach applicable for large-scale production of new adsorbents for water treatment purposes.