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Self-Healing Material Can Build Itself From Carbon In the Air (mit.edu)
MIT chemical engineers have reportedly designed a material that can react with carbon dioxide from the air, "to grow, strengthen, and even repair itself." According to MIT News, "The polymer, which might someday be used as construction or repair material or for protective coatings, continuously converts the greenhouse gas into a carbon-based material that reinforces itself." From the report: The current version of the new material is a synthetic gel-like substance that performs a chemical process similar to the way plants incorporate carbon dioxide from the air into their growing tissues. The material might, for example, be made into panels of a lightweight matrix that could be shipped to a construction site, where they would harden and solidify just from exposure to air and sunlight, thereby saving on the energy and cost of transportation. The material the team used in these initial proof-of-concept experiments did make use of one biological component -- chloroplasts, the light-harnessing components within plant cells, which the researchers obtained from spinach leaves. The chloroplasts are not alive but catalyze the reaction of carbon dioxide to glucose. Isolated chloroplasts are quite unstable, meaning that they tend to stop functioning after a few hours when removed from the plant. In their paper, [the researchers] demonstrate methods to significantly increase the catalytic lifetime of extracted chloroplasts. In ongoing and future work, the chloroplast is being replaced by catalysts that are nonbiological in origin.
The material the researchers used, a gel matrix composed of a polymer made from aminopropyl methacrylamide (APMA) and glucose, an enzyme called glucose oxidase, and the chloroplasts, becomes stronger as it incorporates the carbon. It is not yet strong enough to be used as a building material, though it might function as a crack filling or coating material, the researchers say. The team has worked out methods to produce materials of this type by the ton, and is now focusing on optimizing the material's properties. Commercial applications such as self-healing coatings and crack filling are realizable in the near term, they say, whereas additional advances in backbone chemistry and materials science are needed before construction materials and composites can be developed.
The material the researchers used, a gel matrix composed of a polymer made from aminopropyl methacrylamide (APMA) and glucose, an enzyme called glucose oxidase, and the chloroplasts, becomes stronger as it incorporates the carbon. It is not yet strong enough to be used as a building material, though it might function as a crack filling or coating material, the researchers say. The team has worked out methods to produce materials of this type by the ton, and is now focusing on optimizing the material's properties. Commercial applications such as self-healing coatings and crack filling are realizable in the near term, they say, whereas additional advances in backbone chemistry and materials science are needed before construction materials and composites can be developed.
H2 sits at a high energy state (elemental forms are defined as zero, most other molecules have negative Gibbs free energy, indicating a lower energy state). Generating molecules with high Gibbs free energy usually requires putting energy into the system. Since the mortar reaction drives itself (the mortar sets), more likely it forms H2O, which sits at a very low energy state (which is why water is the end product of a lot of combustion reactions).
CO2 is also a very low energy state (why it's also the end product of combustion of respiration), so converting it into nearly anything else requires putting energy in to drive the reaction up the energy gradient. Plants convert CO2 (and H2O) into glucose by using energy from sunlight (photosynthesis) to drive the reaction. Presumably this material does the same.
Also, the idea isn't completely new. Self-healing fiber reinforced polymers (like fiberglass or carbon fiber) have been made by encapsulating small amounts of the two components of epoxy (resin and hardener) separately inside the FRP. When the FRP develops a crack, some of these capsules are also broken open. The liquid resin and hardener ooze out, mix, and harden into epoxy to seal the crack. The material in TFA is a bit different in that it pulls the required materials out of the air.
Or like concrete. The concrete itself actually becomes stronger, denser and less permeable with age by absorbing carbon dioxide and converting to limestone.
The main reason why this is considered a bad thing is because modern concrete uses steel rebar reinforcement, and carbonation reduces the concrete's pH. High pH in concrete is required to protect the steel. Once the pH drops enough to prevent the passivation of the rebar, it begins rusting, expands by nearly an order of magnitude, and the concrete spalls out.
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