title: Protection of open-metal V(III) sites and their associated CO₂/CH₄/N₂/O₂/H₂O adsorption properties in mesoporous V-MOFs.
abstract: Metal-organic frameworks with open metal site are potential sorbents for the separation of gas mixtures; however, low valence metal will bind to oxygen in the open air causing a decrease in adsorption ability. We now report open-metal sites V(III) on both MIL-100V(III/IV) and MIL-101V(III/IV) that can be protected with water molecules, and which associated CO2/CH4/N2/O2 adsorption properties on these two mesoporous V-MOFs were investigated. The protective properties of water were investigated and evaluated using density functional theory simulations. The binding energy of single O2 on open-metal V(III) site was 93.278 kJ/mol, which decreased to 26.5 kJ/mol when H2O occupies the site. When the water coating is removed, the X-ray photoelectron spectroscopy pattern of V2p showed that the V-MOF changes to MIL-100V(IV) and MIL-101V(IV) at 298 K because of the action of O2. Under these conditions, O2 binds strongly on the open V site significantly reducing the BET (Brunauer-Emmett-Teller) surface and CH4 adsorption volume of the V-MOFs. From the ideal adsorbed solution theory calculated, the adsorption selectivity of CH4/N2 is higher before than after binding of O2 (with V(III) site). In contrast, the adsorption selectivity of CO2/CH4 is higher after than before O2 binding (with no more V(III) sites).
authors.affiliation: Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan 030024, Shanxi, PR China.
authors.forename: Jiangfeng
authors.initials: J
authors.lastname: Yang
authors.affiliation: Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan 030024, Shanxi, PR China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan 030024, Shanxi, PR China.
authors.forename: Libo
authors.initials: L
authors.lastname: Li
authors.affiliation: Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan 030024, Shanxi, PR China.
authors.forename: Zhuoming
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan 030024, Shanxi, PR China. Electronic address: jpli211@hotmail.com.
authors.forename: Jinping
authors.initials: J
authors.lastname: Li
keywords: Adsorption; Adsorption selectivity; Metal–organic frameworks; O(2) binding; Open-metal site