Rice University scientists have figured out a way to engineer wood to trap carbon dioxide through a potentially scalable, energy-efficient process that also makes the material stronger for use in construction. 

Structural materials like steel or cement come at a high cost both in money terms and carbon dioxide emissions; building construction and use accounts for an estimated 40% of emissions. Developing sustainable alternatives to existing materials could help mitigate climate change and reduce carbon dioxide emissions.

Working to address both issues at once, 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.

Sustainable, renewable structural material

"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."

To achieve the feat, the network of cellulose fibres that gives wood its strength is first cleared out through a process known as delignification.

"Wood is made up of three essential components: cellulose, hemicellulose and lignin," said Rahman. "Lignin is what gives wood its colour, so when you take lignin out, the wood becomes colourless. Removing the lignin is a fairly simple process that involves a two-step chemical treatment using environmentally benign substances. After removing the lignin, we use bleach or hydrogen peroxide to remove the hemicellulose."

Next, the delignified wood is soaked in a solution containing microparticles of a metal-organic framework, or MOF, known as Calgary framework 20 (CALF-20). MOFs are high-surface-area sorbent materials used for their ability to adsorb carbon dioxide molecules into their pores.

"The MOF particles easily fit into the cellulose channels and get attached to them through favourable surface interactions," said Soumyabrata Roy, a Rice research scientist and lead author on the study.

MOFs are among several nascent carbon capture technologies developed to address anthropogenic climate change. "Right now, there is no biodegradable, sustainable substrate for deploying carbon dioxide-sorbent materials," said Rahman. "Our MOF-enhanced wood is an adaptable support platform for deploying sorbent in different carbon dioxide applications."

Varying environmental conditions

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

CALF-20, however, developed by University of Calgary Professor George Shimizu and collaborators, stands out in terms of both performance level and versatility under a variety of environmental conditions, said Roy.

"The manufacturing of structural materials such as metals or cement represents a significant source of industrial carbon emissions," said Rahman. "Our process is simpler and 'greener' in terms of both substances used and processing byproducts.

"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," he added.