# Comparison of Gas Adsorption Properties in Methylated and Non-Methylated Imine-Linked Nanoporous Covalent Organic Frameworks

## TL;DR

This study compares how methyl groups in COFs affect their ability to adsorb gases, finding that non-methylated COFs have stronger interactions with certain compounds.

## Contribution

The study introduces a systematic comparison of methylated and non-methylated COFs for gas adsorption, revealing how structural modifications influence interaction strength.

## Key findings

- Non-methylated TFB-BD COF showed stronger interactions with toluene and heptane than methylated Me3TFB-BD.
- TFB-BD had higher adsorption capacity for toluene and heptane due to stronger interactions and smaller pores.
- COFs with lower methyl content showed reduced interaction strength with probes.

## Abstract

Gas-material interactions are crucial in various industrial
processes,
including microchip fabrication, fuel production, and exhaust gas
treatment. Covalent organic frameworks (COFs) are a class of porous,
crystalline nanomaterials composed of organic building blocks linked
by strong covalent bonds. Their highly tunable surface properties
make them promising candidates for gas adsorption. In this study,
we explored how the presence of methyl groups influences the gas adsorption
properties of volatile organic compounds, i.e., probes, in stable,
imine-linked COFs. Enthalpy measurements revealed that Me3TFB-BD, a methylated COF, exhibited weaker interactions with toluene
(−41.3 kJ/mol) and heptane (−45.6 kJ/mol) compared to
its nonmethylated derivative TFB-BD (−50.5 kJ/mol and −54.0
kJ/mol, respectively). Partition coefficient (K)
data also indicated that TFB-BD has stronger interactions with a broader
set of specific probes than Me3TFB-BD, likely due to a
higher imine bond accessibility. Both COFs also showed strong interactions
with polar alcohol probes, which can be attributed to their high polarizability.
Analysis of Me3TFB-PA, a COF with a lower methyl to carbon
ratio, led to further reduction in the COF-probe interaction strength.
All three COFs demonstrated moderate adsorption capacities, though
TFB-BD showed the highest uptake for toluene (0.1 μmol/m2) and heptane (∼0.07 μmol/m2), due
to its stronger interactions and smaller pore size. Additionally,
selectivity analysis revealed that TFB-BD exhibited the strongest
affinity for a broad range of probes. Overall, this study highlights
the potential of COFs as tunable and promising materials for targeted
gas sensing, gas separation, and related applications.