Dead plants may work as well as living plants in mopping up carbon dioxide from admissions, a duo of Spanish scientists has found.

Reporting for the Royal Society of Chemistry on Mar 18, Yaundi Li writes that sawdust is showing promise as a porous solid, able to absorb carbon dioxide in its pores. Other solids, such as zeolites, are already used in this way, but most are hard to fabricate and can absorb only about 3 mmol of carbon dioxide per gram (3mmol CO₂/g).

A research group at Spain’s National Institute of Carbon in Oviedo have been able to convert sawdust into a lower cost material that absorbs up to 50% more of the greenhouse gas per volume—potentially the largest ever carbon uptake at room temperature, in fact.

I’ll leave it to Yi to describes the process:

The two step synthesis involves hydrothermal carbonisation of the sawdust, creating a hydrochar, which is then activated using potassium hydroxide. The KOH treatment creates pores in the sawdust structure by oxidation of carbon and carbon gasification from K₂CO₃ decomposition. These pores are responsible for the material’s uptake capabilities, bestowing it with a capacity as high as 4.8mmol CO₂/g. In addition, [the] material has good selectivity for CO₂ over N₂, fast adsorption rates and can be easily regenerated.

More work must be done in advance of commercialization. But the find is promising given that raw material is plentiful and the fabrication process is “not complex” according to Antonio Fuertes, the lead researcher, as quoted in the article.

Caption: Magnified image of sawdust before (left) and after
(right) being heated and activated showing the pores, via RSC.org.

For the serious carbon scientists I know we have here in the GCCSI community, I waited until the end for the serious technical stuff, so as not to scare off too many layfolk. Here’s the abstract for Sevilla and Fuertes’ study. For more, click here to go to the full journal citation at Energy & Environmental Science.

Sustainable porous carbons have been prepared by chemical activation of hydrothermally carbonized polysaccharides (starch and cellulose) and biomass (sawdust). These materials were investigated as sorbents for CO₂ capture. The activation process was carried out under severe (KOH/precursor = 4) or mild (KOH/precursor = 2) activation conditions at different temperatures in the 600–800 °C range. Textural characterization of the porous carbons showed that the samples obtained under mild activating conditions exhibit smaller surface areas and pore sizes than those prepared by employing a greater amount of KOH. However, the mildly activated carbons exhibit a good capacity to store CO₂, which is mainly due to the presence of a large number of narrow micropores (<1 nm). A very high CO₂ uptake of 4.8 mmol·g^-1 (212 mg CO₂·g^-1) was registered at room temperature (25 °C) for a carbon activated at 600 °C using KOH/precursor = 2. To the best of our knowledge, this result constitutes the largest-ever recorded CO₂ uptake at room temperature for any activated carbon. Furthermore, we observedthat these porous carbons have fast CO₂ adsorption rates, a good selectivity for CO₂–N₂ separation and they can be easily regenerated.