The fabrication of photonic wood

(Nanowerk News) What is photonic wood you ask? Inspired by the unique UV light absorption and photo-excitation of lignin, a team of researchers from the University of Maryland in situ chemically modified native lignin within wood via a simple, rapid, and scalable UV-assisted photocatalytic oxidation method to fabricate what they call 'photonic wood', which retains a high lignin content of >80%.
Reporting in Advanced Materials ("In Situ Lignin Modification toward Photonic Wood"), the team developed a new strategy for modifying lignin – which serves as a binder that forms strong matrices of the cell walls of wood – that involves the photocatalytic oxidation of native lignin in wood by H2O2 and UV light.
The resulting photonic wood retains ∼80% of its original lignin content, which continues to serve as a strong binder and water-proofing agent. As a result, photonic wood features a much higher mechanical strength in a wet environment (20 times higher tensile strength and 12 times greater compression resistance), significant scalability (∼2 m long sample), and largely reduced processing times (1–6.5 hours vs 4–14 hours) compared with delignification methods.
Additionally, this in situ lignin-modified wood structure is easily patterned through a photocatalytic oxidation process.
Design of photonic wood with great optical properties and tunable pattern
Design of photonic wood with great optical properties and tunable pattern. The schematic illustration of the preparation of photonic wood. Lignin is present in wood as a binder and contains chromophore groups that give wood its natural color. The porous channel of wood serves as a route for UV transmission. When light passes through the wood channels, the chromophore groups of lignin are photocatalyzed to free radicals, which are further oxidized by H2O2, resulting in the production of photonic wood. (Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
Wood, as a renewable and earth-abundant resource, has played a major role in the development of sustainable functional biocomposites due to its attractive hierarchical porous structure and unique chemical components, including cellulose, hemicellulose, and lignin.
For structural applications in particular, lignin serves as a necessary binder to form strong wood matrices that contribute to the material’s mechanical properties. That makes in situ lignin engineering an attractive route for expanding the functionalities of wood.
Unfortunately, chromophore groups in lignin make natural wood a monotonic brownish color, with strong light absorption, making it undesirable for optical management. In addition, the intrinsic optical instability of the chromophore groups can make wood susceptible to degradation over time, limiting its application in optical devices as well as energy-efficient buildings.
This photocatalytic production of photonic wood, though, paves the way for the large-scale manufacturing of sustainable biosourced functional materials for a range of applications, including energy-efficient building
The authors point out that, compared with delignified wood, their lignin-modified photonic wood has more advantages as a structural material, including a higher wet mechanical strength, excellent water stability, and superior scalability, along with patterning capabilities.
"Given its eco-friendly, efficient, scalable manufacturing potential, and good mechanical robustness even under wet conditions, the demonstrated photonic wood may open new opportunities for developing bio-based sustainable functional materials using this photocatalytic oxidation method," they conclude.
By Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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