Bamboo-derived carbon nanospheres/polyvinyl alcohol composite coatings for sustainable dual-functional protection of paper-based cultural relics against UV radiation and acidification‑induced degradation

Paper-based cultural relics face degradation from ultraviolet radiation and oxidative free radicals, causing cellulose chain breakage, yellowing, acidification, and mechanical property decline. This study develops a green protection strategy using bamboo-derived carbon nanospheres (B-CNSs), prepared via one-step carbonization in deep eutectic solvent, combined with polyvinyl alcohol (PVA) as a composite coating. TEM reveals spherical B-CNSs with ~150 nm diameter. XRD confirms transformation from crystalline cellulose to amorphous carbon. XPS shows surface O (31.90%) and N (4.41%) with C-O (33.76%) and O=C-OH (18.98%) functional groups. DPPH assay gives IC₅₀ of 2.9 μg/mL. The coating effectively inhibits glycosidic bond cleavage and carbonyl formation, preserves fiber hydrogen bonding, and suppresses UV‑induced pH decline. Treated papers show significantly enhanced tensile strength, reduced yellowing, and superior UV shielding after accelerated aging. This work offers a sustainable pathway for bamboo valorization and dual-functional conservation of paper-based cultural relics.