From the Journal of the American Chemical Society:
After calibration, the initial CO2 concentration in air was determined and was generally between 410 and 420 ppm; somewhat higher than the average global atmospheric CO2 concentration of 390 to 395 ppm. The air flow (335 mL/min) was then opened on the adsorbent bed. Almost immediately the CO2 concentration in the gas outlet fell to 0 ppm, signaling complete CO2 adsorption from the air.
Sure, it's a lab experiment. The airflow was tiny, as was the amount of adsorbent, just 3 grams.
But still. Wow.
The adsorbing* molecule is polyethylenimine, or PEI. It's been known for about 10 years that PEI can absorb CO2, but PEI is a fragile molecule and needs some structure behind it to avoid breaking. Previous supports have been either stronger plastics, or a silica nanostructure called MCM-41.
In the latest breakthrough, UCLA chemists Alain Goeppert, G. K. Surya Prakash, chemistry Nobel Laureate George A. Olah and their colleagues tried a different supporting structure: fumed silica. Cheaply made from plain sand, fumed silica is noted for having a very large surface area for its weight, due to its highly-branched structure. By coating fumed silica with PEI, the plastic inherits the large surface area of its support. The results for CO2 adsorption turned out to be quite remarkable:
some of the highest carbon dioxide removal capacity ever reported for real-world conditions where the air contains moisture
Once the material is full of CO2, you can reverse the process: heat the material in air to 85° C, and you get high-concentrated air (2 to 5% CO2); or, heat the material in a vacuum to the same temperature, and you get pure CO2. The PEI adsorber can then be reused, over and over again.
Implications
Carbon capture and storage (CCS) is one way to mitigate climate change. This new substance makes the carbon capture part of that equation easier and cheaper, and that's important. But unfortunately, it's the storage part of CCS that seems to be the major sticking point. We just don't know what to do with the stuff to take it out of the carbon cycle for the long haul. Cavern storage has been tried, but that has proven to be leaky.
In a diary a couple of years ago, I suggested using captured CO2 from the air, plus renewable electricity, to make methane, using methanogenic bacteria in electrobiochemical cells. That would allow you to have a totally non-fossil source of methane, which could be used everywhere natural gas is used now.
This process would very likely be more expensive that just drilling a hole in the ground to get gas, unless of course fossil fuels were taxed in a way appropriate to their external costs. But it is theoretically possible.
*Adsorb, with a d, is when the target substance sticks to the surface of the adsorber. The more common word absorb (with a b) is when the target substance is absorbed throughout the entire volume of the absorber, like water inside a sponge. At the molecular level where chemists work, things are adsorbers. I used "absorb" in the title because most people understand it better.