Background and purpose: The aim of this study was to investigate the efficiency of Fe₃O₄ nanoparticles synthesized by the chemical co-precipitation method for removal of black acid 1 from aquatic solutions.

Materials and methods: In an experimental study, the Fe₃O₄ nanoparticle was synthesized by the chemical co-precipitation method using Fe⁺² and Fe⁺³ solution in the presence of N₂. The effect of different parameters including initial pH, adsorbent dose, contact time, initial dye concentration, temperature, and EC and also intervening variables such as nitrate, sulfate, fluoride, chloride and hardness were investigated. In addition, equilibrium data was fitted into Langmuir and Freundlich isotherm model, and pseudo-second order and pseudo-first order kinetic models.

Results: We found that the adsorption capacities of nanoparticle increased when pH and adsorbent dose decreased. But the removal efficiency decreased by increase in temperature and dye concentration. Also intervening variables (nitrate, sulfate, fluoride, chloride, and hardness) were found to have low effect on decreasing the color absorption capacity by Fe3O4 nanoparticles. The removal of dye using Fe₃O₄ nanoparticle complies with Freundlich isotherm model (R²= 0.991). Also, the equilibrium adsorption data fitted with pseudo-second order kinetic (R²= 0.992).

Conclusion: This study showed that the Fe3O4 nanoparticle is highly capable of removing black acid 1 dye from aqueous solutions in low contact time. Therefore, the Fe3O4 nanoparticle can be considered as an effective adsorbent in dye removal.