“We were able to demonstrate how much carbon can be sequestered from agricultural waste products like corn husks while producing a valuable, green material typically produced from fossil fuels.”Suzanne Thomas
A team of researchers from the Salk Institute in California have shown how to transform atmospheric carbon into materials with numerous industrial uses. They managed to quantify an innovative process to permanently store plant-captured CO2 as silicon carbide (SiC), an ultra-hard material used in semiconductors, light-emitting diodes, ceramics, automobile manufacture, astronomical mirrors and even sandpaper.
While the ability of plants to capture CO2 from the air so crucial, this has be balanced by the fact that the natural carbon cycle of the planet has not sequestered enough excess atmospheric CO2 from human activities to combat global climate change. However, this study, which was published in the journal RSC Advances [Thomas et al. RSC Adv. (2021) DOI: 10.1039/D1RA00954K], shows a more permanent way to store this captured carbon by turning plants into an industrial material.
An approach to changing tobacco and corn husks into SiC was demonstrated, before the process was quantified in great detail. They used a previously reported way to transform plant material into SiC, also known as carborundum, in a three-step process by counting carbons at each stage. First, tobacco with a short growing season was grown from seed, before the harvested plants were frozen and then ground into a powder and treated with chemicals such as a silicon-containing compound. In a final step, the powdered plants were petrified to produce SiC in a process that involved heating the material up to 1,6000C.
Analysis of these plant powders showed a 50,000-fold increase in sequestered carbon from seed to lab-grown plant, proving the efficiency of the process in reducing atmospheric carbon. Although when heated to such a high temperature for the petrification stage, the material does lose some of its carbon in decomposition, it does retain about 14% of the plant-captured carbon. It was calculated that the process to make 1.8 g of SiC required about 177 kW/h of energy, with about 70% of the energy being used for the heating.
Existing manufacturing processes for SiC have similar energy costs, and therefore the production energy required means that the plant-to-SiC process is not carbon neutral, new technologies being developed could help reduce energy costs.
The team will now look to investigate their process further using different types of plant, such as horsetail and bamboo, as they naturally contain large amounts of silicon. As first author Suzanne Thomas said, “We were able to demonstrate how much carbon can be sequestered from agricultural waste products like corn husks while producing a valuable, green material typically produced from fossil fuels”.