Enrichment of benzene from benzene–water mixture by adsorption in silylated mesoporous silica

Silylated MCM-41 (hexagonal mesoporous silica) was shown to preferentially adsorb only benzene from benzene–water mixtures (containing benzene in the range of 85–1580 ppm), thereby rejecting water. This results in enrichment of benzene in the mesopores (of about 4 nm diameter based on TEM and XRD) of MCM-41. Compared to 125 mg/gm of benzene adsorbed in unsilylated MCM-41, a much higher benzene content of 185 mg/gm of silylated MCM-41 powder was achieved by adsorption. This is much more than the adsorption capacities reported in literature, showing the benefit of functionalization [silylation of MCM-41 by trimethyl chlorosilane (TMCS)] in obtaining selective enrichment of benzene. Nitrogen adsorption data and FTIR spectroscopy together confirm that the trimethyl silyl (TMS) group is chemically bonded to the internal surface of the mesopores, desirable for better adsorption by MCM-41. Finally, about 95% of the adsorbed benzene could be removed by thermal desorption, for at least up to five successive cycles of adsorption and regeneration, showing the suitability of silylated MCM-41 as a reusable adsorbent for enrichment of organics from water.

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► Enrichment of benzene from a benzene–water mixture within the pores of mesoporous silica (MCM-41) has been made possible by silylation of mesoporous silica, whereby the pores have been made hydrophobic, thereby allowing only non-polar benzene molecules to diffuse and bond with silica inside the pores, and rejecting the polar water molecules.
► Measured higher adsorbed benzene content (185 mg/gm) on our silylated MCM-41 powder is much more than the reported adsorption capacities in literature (about 125 mg/gm) for unsilylated MCM-41 powder, showing the benefit of functionalization in selective enrichment of benzene in preference to water.
► Benzene adsorbed could be recovered almost completely and the porous adsorbent thereby regenerated and used, for up to at least 5 cycles, without any loss in activity.