日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

This article describes preparation method and gas separation characteristics of innovative graphene-wrapped zeolite (G-zeolite) membranes. The G-zeolite particles are prepared by heating of graphene oxide-wrapped zeolites at 623 K in Ar. The compression of the G-zeolite particles with 920 MPa provides the crack-free membrane of 5 mm in diameter. The interfacial nanochannels between graphene-sheets and zeolite crystal surfaces can induce quite high separation factors. The G-zeolite membrane has intergranular voids of 100 nm in size which lead to the unusually large permeability constant. The G-zeolite membrane shows excellent separation characteristics for hydrogen against methane that the ideal separation factor is 245 and the permeability constant is 5.8 × 10⁶ barrers (1.3 × 10⁻⁵ mol m⁻² s⁻¹ Pa⁻¹). This permeability is more than 100 times larger than those of previously published membranes. The Robeson plot for H₂ against CH₄ clearly shows the superiority of the G-zeolite membrane. The separation mechanism through interfacial nanochannels between the graphene-zeolite surfaces is supported by molecular dynamics study using a graphene-wrapped rod-like MFI zeolite crystal of (100) and (010) crystal faces. Here, the graphene-wrapping the zeolite rod has two nanowindows for entrance and exit for gas. The trajectory analysis from the entrance nanowindow to the exit one shows the marked separation function due to interfacial channels between the graphene and (100) MFI crystal surface. The G-zeolite membrane exhibits the best separation characteristics even for CO₂ against N₂ of the published data. Also the G-zeolite membrane has novel N₂ selective separation property against O₂ (N₂/O₂ : 3–4) with unusually large permeability constant being 100 times-larger than the membranes published.