Scientists have created a new class of material that uses sunlight to absorb and fix carbon dioxide from the atmosphere. It uses the carbon dioxide to grow and repair itself. In a cascade of reactions, the prototype material uses embedded chloroplasts from spinach to capture carbon. It stores the carbon in sugars produced by photosynthesis (glucose). Ultimately, the material transforms these sugars into a polymer matrix that is continuously regenerating and expanding. In this way, the material can repair itself.
Carbon dioxide is ubiquitous in the environment. Plants create materials and repair themselves through photosynthesis. Converting carbon dioxide (CO2) into organic materials is a critical part of this process. Despite the potential benefits, scientists have not been able to replicate this process in a human-made material until now. A material that could use atmospheric CO2 to form and augment chemical bonds would create new opportunities. This function could reduce the energy needed to produce materials and enable materials to repair themselves. These materials are a first step towards self-healing coatings, lightweight construction materials, and robust fabrics.
Researchers have developed a class of materials capable of forming and augmenting internal carbon backbones using ambient CO2 using a process like the one used by plants. A hydrogel matrix that contains the polymer precursor aminopropyl methacrylamide (APMA), the enzyme glucose oxidase, graphene flakes, and cerium oxide nanoparticles (nanoceria) with stabilized chloroplasts (extracted from spinach) can grow, densify and self-repair using carbon fixation. Chloroplasts in plant cells control the use of sunlight during photosynthesis to transform water and CO2 into sugars such as glucose. The plant then converts the sugars into organic materials needed to maintain the plant’s function as needed. In the human-made hydrogel material, the enzyme glucose oxidase converts the glucose produced by the chloroplasts into a molecule called gluconolactone, a common food additive. Then, the gluconolactone reacts with the APMA to form a continuously expanding and densifying polymer. The antioxidant nanoceria extends the chloroplast lifetime, normally only a few hours outside of the cell, by reacting with and thereby reducing the amount of oxygen produced during photosynthesis. The addition of graphene oxide flakes accelerates polymer crosslinking, resulting in a 17% increase in mechanical strength. In the experiments, after 18 hours the hydrogel extended to a thickness of more than 20 micrometers (about 25% the diameter of a human hair). Following cleavage of the material, exposure to light regenerated the damaged material and completely restored their mechanical strength. This self-healing process mimics the natural damage response. It also enables the hydrogel to exceed its local material balance through conversion CO2 in the surrounding atmosphere.
Prof. Michael Strano
Massachusetts Institute of Technology
This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.
S. Kwak, J. P. Giraldo, T. T. S. Lew, M. H. Wong, P. L., Y. J. Yang, V. B. Koman, M. K. McGee, B. D. Olsen, M. S. Strano, “Polymethacrylamide and Carbon Composites that Grow, Strengthen, and Self-Repair using Ambient Carbon Dioxide Fixation.” Advanced Materials, 2018, 30, 1804037. [DOI: 10.1002/adma.201804037]