A lignin-enrichment approach for processing natural wood into highly NIR-selective optical filters

Transparent wood engineering enables the transformation of natural wood into various optical materials. However, typical top-down strategies rely on lignin removal, which significantly reduces the near-infrared (NIR) selectivity of the resulting materials, making it challenging to develop wood-based NIR optical filters. Herein, we present a lignin-enrichment approach to fabricate highly NIR-selective optical filters directly from natural wood. By enriching the lignin content from 19.81% to 35.19%, we amplify its dual functionality in ultraviolet-visible (UV-Vis) light absorption and binding ability, increasing the NIR selectivity of wood after densification. The resulting wooden filters completely block light below 600 nm while achieving an NIR transmittance exceeding 80%, enabling them to harness 77.90% of solar NIR for phototherapy. This lignin-enrichment approach not only establishes a transformative strategy for designing NIR optical filters but also promotes the efficient utilization of natural wood and solar NIR energy. Conventional transparent wood preparation methods remove lignin and result in poor near-infrared selectivity. Here, the authors develop a lignin-enrichment approach, increasing the wood’s lignin content and achieving highly NIR-selective wood-based optical filters.