Ionic liquids (ILs) provide a promising solution for
CO2 capture and storage to mitigate global warming. However,
identifying
and designing the high-capacity IL from the giant chemical space require
expensive and exhaustive simulations and experiments. Machine learning
(ML) can accelerate the process of searching for desirable ionic molecules
through accurate and efficient property predictions in a data-driven
manner. However, existing descriptors and ML models for the ionic
molecule suffer from the inefficient adaptation of molecular graph
structure. Besides, few works have investigated the explainability
of ML models to help understand the learned features that can guide
the design of efficient ionic molecules. In this work, we develop
both fingerprint-based ML models and graph neural networks (GNNs)
to predict the CO2 absorption in ILs. Fingerprint works
on graph structure at the feature extraction stage, while GNNs directly
handle molecule structure in both the feature extraction and model
prediction stage. We show that our method outperforms previous ML
models by reaching a high accuracy (MAE of 0.0137, R
2 of 0.9884). Furthermore, we take the advantage of GNN
representation and develop a substructure-based explanation method
that provides insight into how each chemical fragment within IL molecules
contributes to the CO2 absorption prediction of ML models.
We also show that our result agrees with some ground truth on functional
group importance from the theoretical understanding of CO2 absorption in ILs, which can advise on the design of novel and efficient
functional ILs in the future.