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.

Graphical abstractWe herein used Fe3O4 nanoparticles (NPs), coated and uncoated, as an adsorption interface for concurrent removal of ubiquitous air pollutants — benzene, toluene, ethylbenzene and xylene (BTEX) and another gaseous co-pollutant such as sulfur dioxide (SO2), at different relative humidities (RH). For uncoated and coated Fe3O4 NPs, high toluene removal efficiency was detected under dry conditions up to 95 ± 2%. Under our experimental conditions, we still observed 40 ± 4% toluene removal at supersaturation for Fe3O4 NPs, and from 83 ± 4% to 59 ± 6% for OA-Fe3O4 NPs. In presence of SO2, toluene uptake was reduced under dry conditions to 89 ± 2% and 75 ± 1% for the uncoated and coated NPs, respectively. At higher RH, competitive adsorption reduced removal efficiency to 27 ± 1% for uncoated NPs whereas the coated OA-Fe3O4 NPs exhibited moderate efficiency loss of 55 ± 2% at supersaturation.Figure optionsDownload full-size imageDownload as PowerPoint slide