There is a growing need to advance CO2 capture materials and technology to mitigate the impact of climate change especially due to the escalating levels of CO2 that is strongly tied to the rapid pace of urbanization. Cities are reportedly responsible for more than 80% of global greenhouse gases (GHG) and CO2 is the most prominent component of anthropogenic GHG emissions. The elevated CO2 levels leads to higher absorption and thermal trapping which contributes partly to the urban heat island effect. This has led to increased research efforts to remove CO2 directly from the atmosphere using technical means such as direct air capture, to keep up with the pace of urbanization. Since the efficiency of CO2 capture is proportional to the purity of the gas stream, key challenges of direct air capture are the relatively low atmospheric CO2 concentration and low air circulation in most dense urban environments. Amongst the existing forms of carbon capture materials (CCMs), such as liquid sorbents or bulky ceramic-based honeycomb structures, mixed matrix polymeric composites are attractive material system that allow us to tailor the carbon capture performance and yet remain in a form that is versatile and be easily adapted for eventual implementation. The separation performance and properties of the mixed matrix composites depends on intrinsic properties of filler and matrix, filler loading and filler-matrix interaction.
In this work, we will discuss the effects of surface modification and processing strategies on the carbon capture performance of polyethylenimine (PEI)-modified porous silica sorbents (PEI-SiO2) that were dispersed in an elastomeric Pebax® matrix. PEI functionalization of high surface area silica is required for CO2 capture by harnessing the high interaction affinity between the amine groups of PEI with CO2. In this work, we will discuss how the PEI molecular weight and solvents used during the modification affect the PEI-SiO2 interfacial interactions and its impact on the CO2 capture capacity. By controlling the PEI-SiO2 interfacial interactions, we have optimized our PEI-SiO2 sorbent chemistry to achieve a CO2 capture capacity of 167 mg of CO2/g material (75°C), which is comparable to existing reported benchmarks of 132 to 141 mg of CO2/g material (75°C). These PEI-SiO2 sorbents were next dispersed within Pebax® to form free-standing films to facilitate eventual wide implementation of these CCMs. The composite formulation and filler dispersion was subsequently tailored to control the capture capacity, CO2 permeability and CO2/N2 selectivity of mixed matrix composite. Our preliminary studies that show successful ambient CO2 capture in a simulated indoor environment. The captured CO2 was subsequently recovered through desorption by purging the system using an inert gas such as N2. The recovered CO2 could be used as an alternative feed source for other carbonation chemistries.