Optical microscope image of a drop of porous liquid producing crystals of calcium carbonate over a period of time (inset) at 30 degrees. Credit: Bhattacharjee, A. et al.
Researchers have designed a porous liquid to capture and store carbon dioxide emissions from human and industrial activities, and then convert it into calcium carbonate – an industrially valuable chemical1.
The liquid, which has a honey-like viscosity, is simple to manufacture and easy to integrate with continuous flow industrial processes, say a team at the Indian Institute of Technology Bombay led by Professor Kamendra P Sharma.
In 2019, his group showed that a porous liquid made by combining hollow silica nanorods and a polymer (wetting agent) could capture carbon dioxide at room temperature.
In the current study, the group created a liquid composite by combining the porous liquid and an enzyme called bio-conjugated carbonic anhydrase (bCA) and adding calcium chloride. When carbon dioxide passes over the porous liquid, it is trapped by the hollow cavities of silica nanorods and slowly combines with bCA to form bicarbonate ions at room temperature. These ions react with calcium ions from the calcium chloride to form micrometre-sized calcium carbonate crystals, which are separated by heating the solution to release the crystals sediment.
“Calcium carbonate is used in making building materials, ceramic tiles, chalk and health supplements,” the researchers say. “The novelty of our process lies in combining porosity, and catalytic activity within a liquid to convert carbon dioxide into calcium carbonate which can be removed from the porous liquid, for the latter to be reused.”
There is more work to do before the porous liquid can be used on an industrial scale.
“Since the enzyme is the costliest component, the cost of porous liquid is too high for it to be commercially viable,” the researchers say. They are exploring ways to find either a cheaper method to make it or an inexpensive alternative.
