Scientists from the National University of Singapore have developed a new material for direct carbon dioxide capture from the atmosphere. This solid sorbent in the form of millimeter-size cubes absorbs CO₂ three times more efficiently than its current counterparts.
The biggest problem with today’s direct CO₂ capture systems is bulkiness. Most sorbents are available in powder form, which is poorly suited for industrial use. Powder creates high resistance to air flow and quickly degrades. Attempts to turn these materials into granules or blocks via binders usually result in a loss of efficiency: the additives partially block the pores, adversely affecting gas penetration.
The Singaporean researchers have found an elegant solution to this problem at the structural level. They used a special nanoporous amorphous carbon produced by spark plasma sintering. This allowed them to create a strong framework with a system of interconnected pores. The material was then impregnated with polyethyleneimine, a compound that chemically binds CO₂.
A key role in the process was played by a three-dimensional network of pores permeating the entire material. Unlike cylindrical conduits in conventional materials, this network has no dead ends and enables gas to move freely even after the pores get filled with the active substance.
In order to give the material a convenient shape, the scientists mixed it with water, a small amount of clay and a binder, i.e., carboxymethyl cellulose. The resulting paste was cast into cubes 2–5 millimeters in size and dried without additional pressing. However, the binder molecules proved too large to penetrate the pores: they secured the structure from the outside without interfering with the function of the inner surface. As a result, the material retained high porosity and simultaneously acquired sufficient mechanical strength.
Tests conducted under realistic conditions (humidity of about 75% and a CO₂ concentration of some 500 ppm) showed that these cubes can absorb up to 1.6 millimoles of CO₂ per cubic centimeter of volume. This is more than three times higher than the indicators demonstrated by the best industrial sorbents. Moreover, the material continues to be stable: its efficiency remains virtually unchanged during repeated absorption and regeneration cycles.
These high performance indicators can be attributed to the optimal pore architecture. The size of the pores (about 4 nanometers) makes it possible to allocate polymer molecules efficiently without blocking gas access. The active substance layer is roughly 7 nanometers thick, which is sufficient to bind CO₂, but not enough to block the channels. As a point of comparison, conventional materials often have the polymer accumulating on the surface in a thicker layer and effectively sealing the pores, which reduces efficiency.
The new material combines high density (0.8 g/cm³), strength (4.5 MPa in compression) and excellent gas diffusion. The researchers believe that these sorbents will form the basis for direct capture systems the size of a standard container instead of huge hangars, making the technology accessible for use on a mass scale in the fight against climate change.
