Purpose UV light (200-400 nm) converts wood lignin and extractives into quinone chromophores, causing irreversible discoloration and strength loss that limit high-end applications. Existing coatings either hide the grain or lack transparency and long-term UV protection. Here, we report a transparent poly(vinyl alcohol) (PVA) film armed with triazine-functionalized wood-derived carbon dots (CDs) that blocks UV while keeping the natural texture visible.

Method Fast-growing, terpene-rich and decay-resistant Cunninghamia lanceolata sawdust was used as the carbon source. After pre-extraction at 150 ℃ to enrich carbohydrates, nitrogen-rich triaminotriazine (THT) was added as a surface modifier and the mixture was subjected to high-temperature hydrothermal carbonization to yield THT-CDs. The dots were then blended with PVA and cast into PVA@THT-CDs composite films. TEM, FTIR, XPS, XRD, fluorescence and UV-Vis spectroscopy were combined to image the morphology, chemistry and optical response of THT-CDs, and to quantify the UV-shielding efficiency of the composite film, using inorganic ZnO and organic UV-384 coatings as comparison. The film was laid over veneer and aged under high-power UV light. CIE Lab* values were recorded at intervals to rate color suppression. A fiber-optic spectrometer collected the transmission spectra of the film under 370 nm monochromatic light and simulated solar irradiation; comparison of the two spectra revealed the light-transport behavior at the wood surface and the mechanism of UV-induced yellowing.

Results THT-CDs exhibit a graphitic spherical morphology with an average diameter of 5.53 nm and excellent dispersibility in water. Upon excitation at 372 nm, they emit bright blue light at 445 nm with a photoluminescence quantum yield of 21.4%, indicating highly efficient light emission. When incorporated at only 2 wt%, the PVA@THT-CDs composite film blocks over 90.3% of UV radiation; transmittance drops to 0.3% at 380 nm and 9.7% at 400 nm, while 82.4% of visible light at 800 nm is still transmitted. This UV-vis selective separation efficiency is markedly superior to that of ZnO and UV-384 reference coatings. CIE color trajectory analysis further confirms that the composite film effectively suppresses color change of the underlying wood during accelerated UV ageing, demonstrating outstanding optical stability.

Conclusion Triazine-functionalized, wood-derived carbon dots were used to overcome the weak UV absorption, low shielding efficiency, and poor transparency of conventional additives. The broad-spectrum UV-vis conversion of THT-CDs delivers high UV blocking without sacrificing transparency. A clear, durable, grain-preserving anti-aging film was formed on wood. The approach bypasses the poor clarity of conventional UV blockers and upgrades fast-grown fir into a high-value material, offering a green route for furniture, displays and outdoor timber.