Chemical modification of dimethylpolysiloxane for enhancement of CO₂ binding enthalpy

The intermittent increase in CO₂ concentration in the atmosphere is a serious problem that contributes to climate change; the combustion of fossil fuels produces the majority of CO₂, and technology is needed to capture it efficiently. Various CO₂ capture materials have been developed so far. Membrane separation, in particular, has an advantage over other capture technologies due to its ease of use. Poly(dimethylsiloxane) (PDMS) has been widely used as a membrane material for CO₂ capture because of its high gas permeability. However, despite their high CO₂ permeance, PDMS membranes are still in their infancy, especially regarding CO₂ selectivity due to the weak interaction between CO₂ and PDMS. Here we evaluated the CO₂ interaction with the PDMS chain at the atomic scale and attempted to improve the CO₂ affinity of the PDMS chain using density functional theory (DFT). Specifically, we substituted elements in the Si-O framework with other elements and substituted the methyl groups with other chemical groups, and incorporated metallic elements such as Mg and Ti. All the chemical modifications by main group elements resulted in physisorption, but chemisorption of CO₂ was observed in PDMS incorporating metallic elements. Since several modes of CO₂ binding were observed in PDMS with incorporated metal elements, the binding enthalpy and binding mode were analyzed. As a result of various chemical modifications, it was found that introducing earth metal elements into PDMS was the most effective way to enhance the interaction between PDMS and CO₂.