Hexamethyldisiloxane Removal from Biogas Using a Fe₃O₄-Urea-Modified Three-Dimensional Graphene Aerogel

Volatile methyl siloxanes (VMS), which are considered to be the most troublesome impurities in current biogas-cleaning technologies, need to be removed. In this study, we fabricated a series of Fe₃O₄-urea-modified reduced graphene-oxide aerogels (Fe₃O₄-urea-rGOAs) by using industrial-grade graphene oxide as the raw material. A fixed-bed dynamic adsorption setup was built, and the adsorption properties of the Fe₃O₄-urea-rGOAs for hexamethyldisiloxane (L2, as a VMS model pollutant) were studied. The properties of the as-prepared samples were investigated by employing various characterization techniques (SEM, TEM, FTIR, XRD, Raman spectroscopy, and N₂ adsorption/desorption techniques). The results showed that the Fe₃O₄-urea-rGOA-0.4 had a high specific surface area (188 m² g^-1), large porous texture (0.77 cm³ g^-1), and the theoretical maximum adsorption capacity for L2 (146.5 mg g^-1). The adsorption capacity considerably increased with a decrease in the bed temperature of the adsorbents, as well as with an increase in the inlet concentration of L2. More importantly, the spent Fe₃O₄-urea-rGOA adsorbent could be readily regenerated and showed an excellent adsorption performance. Thus, the proposed Fe₃O₄-urea-rGOAs are promising adsorbents for removing the VMS in biogas.