One-Step Enhances the Photothermal Performance of Lignin: Experimentation, Mechanism and Application

Solar-driven photothermal conversion technologies have gotten much attention for addressing the global freshwater crisis and energy shortage. However, several challenges remain regarding the applied materials with their single function, complex manufacturing process, and high raw material cost. Herein, the photothermal performance of the low-cost lignin was improved by the one-step hydroxymethyl modification with up to 52.16% of the maximum photothermal conversion efficiency of the modified lignin (Lg1-OH). The enhancement mechanism of the Lg1-OH was proposed by the structural analysis and simulation calculations. First, a larger hydrogen bond network strengthens the π-π stacking between the benzene rings and thus enhances the photothermal performance of lignin. Second, the conjugation effect of hydroxymethyl groups increases the electron cloud density of the benzene ring, ensuring more heat can be obtained by exciting more electrons under the same solar power. Subsequently, a photothermal gel (PG) was successfully prepared using Lg1-OH for solar-driven thermoelectric production and water purification. The thermoelectric device (TED) obtained the maximum power density of 20.85 W/m² under 0.5 W/cm² sun irradiation, and the evaporator reached a superior evaporation rate of 4.72 kg/(m² h) under 0.3 W/cm² sun irradiation. Additionally, no salt accumulation was found on the surface of the evaporator in a long period operation of 24 h. Besides, an outdoor solar-driven evaporation device achieved 8.58 kg/m² of cumulative aquatic production in 9 h. This study offers a promising way for the commercial application of lignin in solar-driven electricity generation and water purification.