Ligand functionalization boosts ammonia adsorption in MOFs and COFs, with −O₂Mg and −OLi exhibiting the strongest interaction with NH₃. Adsorption process is elucidated through isosteric heat of adsorption plots, providing insights for material fine-tuning in NH₃ adsorption. Additionally, a proof of concept machine learning analysis effectively predicts NH₃ binding energies, underscoring its potential in guiding the synthesis of advanced adsorbents.

Abstract

Our study aims to examine the impact of ligand functionalization on the ammonia adsorption properties of MOFs and COFs, by combining multi-scale calculations with machine learning techniques. Density Functional Theory calculations were performed to investigate the interactions between ammonia (NH₃) and a comprehensive set of 48 strategically chosen functional groups. In all of the cases, it is observed that functionalized rings exhibit a stronger interaction with ammonia molecule compared to unfunctionalized benzene, while −O₂Mg demonstrates the highest interaction energy with ammonia (15 times stronger than the bare benzene). The trend obtained from the thorough DFT screening is verified via Grand Canonical Monte-Carlo calculations by employing interatomic potentials derived from quantum chemical calculations. Isosteric heat of adsorption plots provide a comprehensive elucidation of the adsorption process, and important insights can be taken for studies in fine-tuning materials for ammonia adsorption. Furthermore, a proof of concept machine learning (ML) analysis is conducted, which demonstrates that ML can accurately predict NH₃ binding energies despite the limited amount of data. The findings derived from our multi-scale methodology indicate that the functionalization strategy can be utilized to guide synthesis towards MOFs, COFs, or other porous materials for enhanced NH₃ adsorption capacity.