New V(IV)-based metal-organic framework having framework flexibility and high CO2 adsorption capacity

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) are advanced porous materials with tunable structures.
• Vanadium-based MOFs are of interest for gas storage and separation applications.
• The MIL-47 structure type is known for its potential flexibility.

Purpose of the Study:

• To synthesize and characterize a vanadium-based MOF with an expanded MIL-47 structure.
• To investigate the gas sorption properties, particularly for CO2 and CH4.
• To understand the structural transitions and the influence of mixed oxidation states on framework flexibility.

Main Methods:

• Solvothermal and microwave synthesis methods.
• In situ synchrotron X-ray powder diffraction for structural analysis.
• Molecular simulations to determine free energy profiles.
• Gas/vapor sorption isotherms (CO2, CH4, N2) at various temperatures.
• Spectroscopic techniques to analyze oxidation states.

Main Results:

• Successful synthesis of VO(BPDC) with an expanded MIL-47 structure.
• Observation of a distinct breathing effect in response to adsorptives.
• Differential sorption behavior for CO2 and CH4 at specific temperatures.
• Experimental and computational evidence for narrow pore, large pore, and overstretched narrow pore forms.
• V(III)/V(IV) mixed oxidation states hinder framework flexibility compared to pure V(IV).

Conclusions:

• The synthesized vanadium MOF exhibits tunable porosity and a significant breathing effect.
• Framework flexibility and gas sorption are strongly dependent on pore size and the presence of mixed vanadium oxidation states.
• This MOF shows potential for selective gas adsorption applications, with its flexibility being a key characteristic.