Trapped CO2 ‘hardens’ engineered wood

Schematic of the step-by-step fabrication process of the Wd-CALF-20 composite for CO2 capture and storage (A). Optical images of 1×1×1 cm3 wood pieces (B) at different stages of modification. Optical images of the wood pieces (C) showing the volume shrinkage on drying in the case of the d-Wd versus the Wd-CALF-20 composite because of the filler effect of the MOF.

Scientists at US-based Rice University have figured out a way to engineer wood to trap carbon dioxide (CO2) through a potentially scalable, energy-efficient process that also makes the material stronger.

Materials scientist Muhammad Rahman and collaborators found a way to incorporate molecules of a carbon dioxide-trapping crystalline porous material into wood, according to a study published in Cell Reports Physical Science.

“Wood is a sustainable, renewable structural material that we already use extensively,” said Rahman. “Our engineered wood did exhibit greater strength than normal, untreated wood.”

The network of cellulose fibres that gives wood its strength is first cleared out through a process known as de-lignification.

Wood is made up of three essential components: cellulose, hemicellulose and lignin. Lignin is what gives wood its colour.

“Removing the lignin is a fairly simple process that involves a two-step chemical treatment using environmentally benign substances,” says Rahman. “After removing the lignin, we use bleach or hydrogen peroxide to remove the hemicellulose.”

The de-lignified wood is soaked in a solution containing micro-particles of a metal-organic framework (MOF), known as Calgary framework 20 (CALF-20). MOFs are high-surface-area sorbent materials used for their ability to adsorb CO2 molecules into their pores.

“The MOF particles easily fit into the cellulose channels and get attached to them through favourable surface interactions,” wrote Soumyabrate Roy, a Rice research scientist and lead author of the study.

MOFs are among several nascent carbon capture technologies developed to address anthropogenic climate change.

“Right now, there is no bio-degradable, sustainable substrate for deploying CO2-absorbent materials,” Rahman said. “Our MOF-enhanced wood is an adaptable support platform for deploying sorbent in different CO2 applications.”

“Many of the existing MOFs are not very stable in varying environmental conditions,” Roy said. “Some are very susceptible to moisture, and you don’t want that in a structural material.”

The manufacturing of structural materials, such as metals or cement, represents a significant source of industrial carbon emissions. “Our process is simpler and ‘greener’ in terms of both substances used and processing by-products,” says Rahman.

The next step would be to determine sequestration processes, as well as a detailed economic analysis to understand the scalability and commercial viability of this material. For details, visit www.cell.com.

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