Co-adsorption of gaseous benzene, toluene, ethylbenzene, m-xylene (BTEX) and SO2 on recyclable Fe3O4 nanoparticles at 0-101% relative humidities

We herein used Fe₃O₄ nanoparticles (NPs) as an adsorption interface for the concurrent removal of gaseous benzene, toluene, ethylbenzene and m-xylene (BTEX) and sulfur dioxide (SO₂), at different relative humidities (RH). X-ray diffraction, Brunauer-Emmett-Teller, and transmission electron microscopy were deployed for nanoparticle surface characterization. Mono-dispersed Fe₃O₄ (Fe₂O₃·FeO) NPs synthesized with oleic acid (OA) as surfactant, and uncoated poly-dispersed Fe₃O₄ NPs demonstrated comparable removal efficiencies. Adsorption experiments of BTEX on NPs were measured using gas chromatography equipped with flame ionization detection, which indicated high removal efficiencies (up to (95 ± 2)%) under dry conditions. The humidity effect and competitive adsorption were investigated using toluene as a model compound. It was observed that the removal efficiencies decreased as a function of the increase in RH, yet, under our experimental conditions, we observed (40 ± 4)% toluene removal at supersaturation for Fe₃O₄ NPs, and toluene removal of (83 ± 4)% to (59 ± 6)%, for OA-Fe₃O₄ NPs. In the presence of SO₂, the toluene uptake was reduced under dry conditions to (89 ± 2)% and (75 ± 1)% for the uncoated and coated NPs, respectively, depicting competitive adsorption. At RH >100%, competitive adsorption reduced the removal efficiency to (27 ± 1)% for uncoated NPs whereas OA-Fe₃O₄ NPs exhibited moderate efficiency loss of (55 ± 2)% at supersaturation. Results point to heterogeneous water coverage on the NP surface. The magnetic property of magnetite facilitated the recovery of both types of NPs, without the loss in efficiency when recycled and reused.