Role of Polymer Architecture in CO2 Capture from Air Using Supported Poly(alkylenimine)s - Linear vs Branched Polymers

Sep 21, 2026

Direct air capture of CO2 coupled with geologic storage is a promising climate mitigation approach, and supported solid amines act as CO2 sorbents. Branched poly(ethylenimine) is a common benchmark but shows limited oxidative stability, while poly(propylenimine) offers improved resistance. A side-by-side comparison of linear and branched PEI and PPI supported on SBA-15 evaluates CO2 adsorption under dry DAC-relevant conditions (400 ppm CO2, 30 °C), revealing architecture-dependent efficiency and binding strength.

LanguageEnglish

CategoryResearch & Report

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Pages11

Reading Time28 min

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Abstract

Introduction

This article is licensed under CC-BY 4.0 [pubs.acs.org/acsapm](pubs.acs.org/acsapm) Article Role of Polymer Architecture in CO2 Capture from Air Using Supported Poly(alkylenimine)s: Linear vs Branched Polymers Jacob Hoffman, Laura Proãno, and Christopher W. Jones * Cite This: ACS Appl. Polym. Mater. 2025, 7, 15671−15681 Read Online ACCESS Metrics & More Article Recommendations *sı Supporting Information Downloaded via 195.252.220.37 on January 10, 2026 at 02:56:02 (UTC) . See [https://pubs.acs.org/sharingguidelines](https://pubs.acs.org/sharingguidelines) for options on how to legitimately share published articles. ABSTRACT: Direct air capture (DAC) of CO2 coupled with geologic storage is a promising climate change mitigation strategy, with some applications employing amines supported on porous solids as CO2 sorbents. While branched poly(ethylenimine) (PEI) is the standard benchmark amine material, it suffers from limited oxidative stability. Poly(propylenimine) (PPI), as an alternative, has previously demonstrated improved resistance to degradation under harsh oxidative conditions. Linear and branched PEI are commercially available, though at different molecular weights, while PPI is not commercially available. For this reason, a comparative study of all four polymers (linear PEI, branched PEI, linear PPI, branched PPI) has not been reported for DAC. this study, we synthesize and compare low-molecular-weight ( 800 g/mol) linear (L) and branched (B) PEI and PPI supported on a model support, SBA-15 silica. These materials are evaluated for CO2 adsorption under dry, DAC-relevant conditions (400 ppm of CO2, 30 °C). LPPI exhibited the highest amine efficiency at all loadings, reaching a maximum of 0.14 mmol CO2/mmol N, outperforming BPEI, while LPEI consistently showed the lowest uptake capacity. Temperature-programmed desorption reveals that the structure of the amine polymer impacts the CO2 binding strength, with branched polymers displaying higher desorption energies of 102−111 kJ/mol. In situ infrared spectroscopy experiments show that all sorbents preferentially capture CO2 as ammonium carbamate. Isobaric CO2 uptake studies further underscore the influence of polymer mobility and support pore crowding on performance, while demonstrating the sorbents’ performance at elevated temperatures and CO2 concentrations. All materials demonstrated good stability over 25 adsorption−desorption cycles using thermal regeneration in an inert gas purge, with only BPPI displaying a 10−11% decrease in capacity/amine efficiency during cycling, possibly due to the loss of low molecular weight, oligomeric amines. This is the first side-by-side comparison of the CO2 sorption properties of linear and branched PEI and PPI with similar molecular weights. These findings highlight the significant role of polymer architecture in CO2 capture efficiency and inform future designs of durable, high-performance DAC sorbents. KEYWORDS: direct air capture, adsorbents, stability, amine efficiency, cyclic capacity, desorption energy ■ INTRODUCTION The increasing concentration of carbon dioxide (CO2) in the atmosphere since rapid industrialization and the initial usage of fossil fuels in the 19th century is widely regarded as the primary cause of climate change.1 The speedy and widespread rollout of carbon-neutral energy sources, combined with the retirement of carbon-intensive ones, is and will continue to bethe most significant measure to combat rising greenhouse gas levels.2 However, atmospheric carbon removal technologies are gaining traction as the largest countries fall behind their emissions targets. Among these, the removal of carbon dioxide from the atmosphere by chemical means, also referred to as direct air capture (DAC) of CO2, is one of the most scalable.3−5 When combined with geologic sequestration on a large scale, DAC can provide a way to reduce the atmospheric CO2 concentration.6 The most well-studied mode o

FAQs

Why compare linear and branched PEI and PPI for CO2 direct air capture?

Branched PEI is a standard benchmark but has limited oxidative stability. PPI can be more resistant to degradation, yet a comparable study across linear and branched forms with similar molecular weights had not been reported for DAC.

What support and conditions are used to evaluate the polymers?

The polymers are supported on model SBA-15 silica and tested for CO2 adsorption under dry, DAC-relevant conditions of 400 ppm CO2 at 30 °C.

How does polymer architecture affect CO2 binding and performance?

Temperature-programmed desorption indicates that polymer structure changes CO2 binding strength, with branched polymers showing higher desorption energies (102–111 kJ/mol). In situ infrared spectroscopy shows CO2 is captured preferentially as ammonium carbamate, and cyclic studies show good stability with architecture-dependent capacity retention.

Sep 21, 2026

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