A new living material actively removes carbon dioxide (CO2) from the atmosphere. Photosynthetic cyanobacteria grow in the material. This creates biomass and solid minerals, and the material binds CO2 to itself in two different ways.
The material was developed by an interdisciplinary research team led by Mark Tibbitt, Professor of Macromolecular Engineering at ETH Zurich. Within their project, the researchers combine conventional materials with bacteria, algae and fungi.
The aim here is to create living materials that acquire useful properties thanks to the metabolism of micro-organisms. Removing CO2 from the air through photosynthesis is an example.
Cyanobacteria incorporated into a hydrogel
The material includes cyanobacteria, bacteria capable of photosynthesis. These bacteria are incorporated into a gel. The material lives, grows and can actively remove CO2 from the air. The researchers manufacture the material using a 3D printer. Then, only sunlight and artificial seawater with readily available nutrients are needed, combined with CO2.
A striking feature of the material is that it binds CO2 to itself in two ways. Not only does the material absorb CO2 through organic growth, but it can also store it in the form of minerals. "As a building material, it could help in the future to store CO2 directly in buildings," Tibbitt explains.
'One of the oldest life forms in the world'
Yifan Cui, one of the two lead authors of the study, adds: "Cyanobacteria are among the oldest life forms in the world. They are highly efficient in photosynthesis and can use even the dimmest light to produce biomass from CO2 and water."
At the same time, the bacteria change their chemical environment outside the cell thanks to photosynthesis, precipitating solid carbonates. These minerals thus provide additional CO2 storage.
26 milligrams of CO2 per gram of material
Laboratory tests show that the material binds CO2 continuously over a period of 400 days. In the process, most of the material is stored in mineral form: about 26 milligrams of CO2 per gram of material. This is significantly more than many biological approaches and comparable to the chemical mineralisation of recycled concrete, the researchers report.
The material is integrated into a hydrogel, which is made of coupled polymers with a high water content. The network of polymers is capable of transporting light, CO2, water as well as nutrients. It also ensures that cells disperse evenly within the gel.
Optimised geometry
To ensure that the cyanobacteria live as long as possible and remain efficient, the researchers optimised the geometry of the structures. They used 3D printing processes for this purpose. This increases the surface area, increases light penetration and promotes nutrient flow.
The researchers see their living material as a low-energy and environmentally friendly approach that can bind CO2 from the atmosphere and complement existing chemical processes for carbon sequestration. "In the future, we want to investigate how the material can be used as a coating for building facades to bind CO2 throughout the life cycle of a building," Tibbitt states.
