Sunlight could be the key to an economically viable form of carbon capture and storage (CCS), thanks to the discovery of a material which can absorb large quantities of the gas but releases it when exposed to the sun.
Developed by researchers in Australia, the material could reduce the amount of energy needed to move CO2 captured from fossil fuel burning into a storage facility.
The material, synthesised by research leader Matthew Hill of the Australian research agency CSIRO and colleagues at Monash University in Melbourne, is a metal-organic framework or MOF, a class of highly porous materials already well-known for their ability to store gases. Made by joining together clusters of metal atoms with organic bridging molecules known as ligands, MOFs can have internal surface areas as high as 10,000m2 — larger than the pitch at Wembley Stadium — per gramme.
This particular MOF is the first to be made photosensitive.
‘The MOFs are impregnated with light-responsive azobenzene molecules which react to UV light and trigger the release of CO2,’ explained researcher Richelle Lyndon. ‘It is this reaction, and the material’s ability to bend and flex, which makes the material we have created so unique.’
Current CCS techniques tend to use ammonia-based liquids to absorb CO2 from flue gas streams, which must then be heated to release the CO2 into storage and regenerate the absorbent. This can consume up to 30 per cent of the production capacity of a power plant, and is a major contributor to the difficulty of making CCS cost-effective.
In a paper published in the journal Angewandte Chemie, Lyndon and team claim that the azobenzene-containing MOF releases up to 64 per cent of the CO2 it has absorbed instantaneously when exposed to concentrated UV frequencies found in sunlight.
This could drastically reduce the cost of CCS, eliminating the loss of energy to regenerating absorbents.
The MOF created at Monash has a particular affinity to CO2, Lyndon said in a statement, but the ligh-responsive azobenzene ligands could be incorporated into different MOFs to make a material that can absorb different gases. Other MOFs have been investigated as hydrogen or methane storage materials for vehicles.