A sustainable solution: mitigating sulphur dioxide emissions through adsorption on chemically modified iron oxide nanoparticles

Air pollution caused by sulphur dioxide (SO₂) emissions is pervasive and has severe health and environmental consequences. In recent years, global SO₂ emissions have decreased dramatically due to the widespread adoption of cleaner technologies and stricter emission regulations. The availabilities of highly concentrated SO₂ separation prompted this study’s focus on reducing SO₂ emissions, particularly for low-concentrated SO₂ (100 ppm), employing ferric oxide nanoparticles. Upon thermal degradation of the adsorptive ferric oxide, both functional Fe–O and ferric oxide were observed. A 3:1 mixture of sodium hydroxide and ethanol was used to chemically activate the surface of the adsorbent, increasing both the pH and surface area from 6.5 to 10 and 183 to 531 m² g⁻¹, respectively. Maximum adsorption capacity (477.5 mg g⁻¹) and maximum adsorption percentage (97.89%) were highest for the lowest SO₂ concentration (56 mg m⁻³) compared to the other two SO₂ concentrations (65 and 73 mg m⁻³). The Freundlich isotherm outperforms the other four models with the highest correlation coefficient (R² = 0.9897). SO₂ adsorption was physisorption, as the thermodynamic values, change of enthalpy and free energy decreased from −902 to −2052 kJ mol⁻¹ and −243 to −562 kJ mol⁻¹ as the temperature of the adsorption process ascended from room temperature to 70 °C. The SO₂ was successfully removed from the adsorbent using temperature-programmed desorption analysis, with a maximal discharge of 1681 mg m⁻³ of SO₂ and enhanced ferric oxide. Effective SO₂ adsorption by the adsorbent for up to four cycles suggests that SO₂ capture costs could be decreased.