Metal

Marketing

Quantum mechanics

Anisotropy

Adsorption

Pulsed field gradient

Engineering

Chemical physics

Metallurgy

Materials science

Molecular diffusion

Gaseous diffusion

Economics

Molecule

Inorganic chemistry

Chemical engineering

Business

Porosity

Physical chemistry

Thermodynamics

Physics

Nanotechnology

Organic chemistry

Diffusion

Optics

Metal-organic framework

Operations management

Porous medium

Self-diffusion

Analytical Chemistry (journal)

Chemistry

Electrode

Metric (unit)

Self-service

Carbon dioxide

Chemistry of Materials

The rapid diffusion of molecules in porous materials is critical for numerous applications including separations, energy storage, sensing, and catalysis. A common strategy for tuning guest diffusion rates is to vary the material pore size, although detailed studies that isolate the effect of changing this particular variable are lacking. Here, we begin to address this challenge by measuring the diffusion of carbon dioxide in two isoreticular metal–organic frameworks featuring channels with different diameters, Zn2(dobdc) (dobdc4– = 2,5-dioxidobenzene-1,4-dicarboxylate) and Zn2(dobpdc) (dobpdc4– = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate), using pulsed field gradient NMR spectroscopy. An increase in the pore diameter from 15 Å in Zn2(dobdc) to 22 Å in Zn2(dobpdc) is accompanied by an increase in the self-diffusion of CO2 by a factor of 4 to 6, depending on the gas pressure. Analysis of the diffusion anisotropy in Zn2(dobdc) reveals that the self-diffusion coefficient for motion of CO2 along the framework channels is at least 10000 times greater than for motion between the framework channels. Our findings should aid the design of improved porous materials for a range of applications where diffusion plays a critical role in determining performance.

Influence of Pore Size on Carbon Dioxide Diffusion in Two Isoreticular Metal–Organic Frameworks