Lignin derived bio-polyhydroxyurethane with enhanced and durable photothermal performance under sunlight irradiation

Sunlight-driven photothermal materials have received increasing attention as promising candidates for addressing energy and freshwater crises; however, achieving a balance among high photothermal conversion efficiency, long-term stability, and environmental sustainability remains a significant challenge. Herein, a bio-derived sustainable photothermal material, polyhydroxyurethane (PHU) containing hydroxycarbamate structures, was designed and synthesized using lignin and CO₂ as renewable feedstocks. In this strategy, phenolic lignin is incorporated into polyurethane molecular backbone to construct hydroxycarbamate structure and dense hydrogen-bonded network, which strengthening π-π stacking interactions, endowing lignin-derived polyhydroxyurethane (LPHU) with broad-spectrum light absorption (200-2500 nm) and high photothermal conversion capability of 85.90%. Under simulated sunlight irradiation, the surface temperature of LPHU can reach 119.8 °C within 120 s. Furthermore, a thermoelectric generator combined with LPHU produced an open-circuit voltage of 1.6 V under natural sunlight, sufficient to drive cooling fan. Additionally, the phenolic hydroxyl groups and conjugate structures in lignin endow LPHU with enhanced UV-shielding and antioxidant properties. Exposed to UV radiation and thermal aging at 60 °C for 14 d, LPHU maintained its structural integrity, and 92% of photothermal conversion efficiency in comparison to the initial value. Furthermore, DFT calculations and quantum chemical simulations were conducted to provide molecular-level insights into the contribution of π-π conjugation interactions and intramolecular charge transfer processes to photothermal conversion enhancement.