(237b) Materials Exhibiting Biomimetic Carbon Fixation and Self Repair

The United States alone generates 35.4 million tons of plastic, mostly petroleum-derived, with 26.8 million tons ending up in landfills. Along with this material waste, the energy consumed to produce these materials—accounting for up to 4% of total energy use in the United States—is thrown away. We envision plastics and materials designed to continuously absorb atmospheric carbon sources, such as carbon dioxide (CO₂) and methane (CH₄). These materials would also scavenge energy from the environment to renew and self-regenerate. The use of ambient carbon sources and solar irradiation models such materials after natural mechanisms operative in the trunk of a tree or the leaf of a plant. Traditional materials often fail due to the propagation of microcracks and the accumulation of relatively small defects over time. The amount of mass needed to prevent such failure and avoid landfills is small, meaning that growth rates of such carbon-fixing materials need only be commensurate with living plants to have drastically increased operational lifetimes.

As a proof of concept, we have utilized extracted plant chloroplasts as unique photocatalysts that react with atmospheric carbon dioxide using ambient solar energy to produce sugars such as glucose. In our material prototype, glucose oxidase converts glucose into reactive gluconolactone. This gluconolactone then reacts with a primary amine-functionalized acrylamide monomer, forming a continuously extending polymer matrix. The rheology and mechanical properties evolve over time, and the material grows measurably over a 24-hour period to produce a polymer matrix that can be augmented with nanoparticle inclusions such as graphene oxide to enhance its mechanical properties. This study establishes that carbon-fixing materials are possible and possess desirable materials science properties.

Furthermore, we have developed a reaction engineering framework. This framework is designed for analyzing carbon-fixing materials, with a focus on understanding the limitations of growth. These limitations may arise from CO₂ absorption, conversion selectivity, and polymer growth. By performing a Damköhler analysis, we derived criteria for the cross-over from the regime of kinetic limitations (CO₂ conversion or polymerization) to mass transfer limited growth (CO₂ absorption)—defining the upper limits on the growth rate of this new class of materials. This framework allows us to rapidly analyze any combination of absorbent, CO₂ reduction photocatalyst, and polymerization chemistry to understand optimal material growth rates as well as the inherent limitations within the potential carbon-fixing material system.

Lastly, we have developed methanotrophic systems operating under ambient conditions. Methane, a critical fuel, chemical precursor, and potent greenhouse gas, is the focus of this innovation. Its production, transportation, and use result in its emission to the atmosphere, where it induces ~30 times more warming than CO₂ on a per-mass basis. Currently, there remains minimal understanding of efficient chemical methods for the conversion and or valorization of methane streams—specifically under the conditions in which they are emitted i.e. low partial pressures and ambient temperatures. To address this, we have created a synthetic methanotrophic system which is capable of oxidizing methane at ambient temperatures and pressures into a growing polymer material. Finally, we also investigated the ability of commonly used transition metal-modified zeolite (ZSM-5) catalysts for the H₂O₂-mediated oxidation of methane in the liquid phase at ambient conditions—room temperature and one atmosphere of partial pressure.