Green mechano-synthesis of high-efficiency and recyclable lignin-liquid metal photothermal composites for solar-driven desalination and power generation

Solar-powered photothermal conversion has great promise for mitigating pressures on the global water-energy nexus. Photothermal materials enabling efficient light-to-heat conversion have thus attracted considerable scientific and industrial interest. Despite considerable advancements in material design, a critical challenge remains in developing sustainable materials that achieve high-efficiency solar energy conversion through simple synthesis methods. Here, we develop a solvent-free and one-step mechanochemical strategy to synthesize lignin-liquid metal (LM) composite photothermal powder by exploiting the reactive wettability of LM. The resulting core-shell particles exhibit broad-spectrum light absorption and excellent photothermal performance. When incorporated into a wood-based evaporator, the composite achieves a high evaporation rate of 2.23 kg m⁻² h⁻¹ and a solar-thermal efficiency of 95.94 % under 1 sun. Moreover, when applied as a coating on a thermoelectric generator, it delivers a maximum output voltage of 179 mV, demonstrating concurrent photothermal-thermoelectric performance. The composite is fully recyclable, derived from renewable lignin and low-toxicity LM, offering a scalable solution with minimal environmental footprint. This work presents a multifunctional, low-cost material platform for integrated solar energy harvesting in water purification and electricity generation.