Lignin simultaneously acts as CuS growth carrier and polyol substitute to synthesize polyurethane films with doubly enhanced photothermal conversion capacity

The π-π conjugation structure in lignin could endow its derived polyurethanes with photothermal conversion property to some extent, but is undesirable with those reported carbon or metal materials. Herein, lignin-based polyurethane films loaded with copper sulfide nanoparticles (CuS-OLPUs) were rationally designed by simultaneously utilizing lignin as a growth carrier for CuS nanoparticles and as a bio-based polyol substitute in polyurethane synthesis. Benefiting from the synergistic photothermal contributions of lignin and CuS, the CuS-OLPUs exhibited markedly enhanced light absorption across the ultraviolet and visible regions, and thus exhibited great application potential in the field of UV shielding. Under simulated sunlight irradiation at 0.5 W cm −2 , the surface temperature in the optimized CuS-OLPU rapidly increased and stabilized at 106 °C, demonstrating efficient photothermal conversion performance. Furthermore, a lignin-based phenolic foam with interconnected porosity and low thermal conductivity was fabricated and integrated with the optimized CuS-OLPU to construct a solar-driven evaporator. The water evaporation rate under the action of the evaporator increased by eight times in comparison with pure water without the evaporator, highlighting its effectiveness in solar-driven water evaporation. Overall, this work demonstrates a synergistic lignin-based material design strategy that bridges metal photothermal agents and polyurethane matrices, offering a promising route for enhancing the photothermal performance of polyurethanes and boosting lignin valorization.