Fully Lignocellulosic Biomass‐Based Double‐Layered Porous Hydrogel for Efficient Solar Steam Generation

Solar‐driven interfacial evaporation is an important approach for solving the issue of freshwater scarcity. However, the practical application of solar steam generation is hindered by high fabrication cost and environmental concerns regarding the petroleum‐based materials. Herein, lignocellulose (cellulose‐lignin composite) hydrogel (LCG) and lignin‐derived carbon (LC) are used as the substrate and photothermal material, respectively, to construct a fully lignocellulose‐based double‐layered hydrogel (LC@LCG) evaporator. Results indicate that LC has an ultrahigh specific surface area and full‐spectrum solar absorption of 98%. The presence of lignin can improve the hydrophilicity and maintain the capillary channels of the hydrogel, which tunes water into an intermediate state and reduces the vaporization enthalpy of water. Moreover, it ensures a high water transport rate in the hydrogel. Based on these advantages, the evaporation rate and photothermal conversion efficiency of hydrogel evaporator reach 1.84 kg m−2 h−1 under one sun and 86.5%, respectively. The lignocellulosic hydrogel evaporator could remove >99.95% of primary metal ions from seawater to generate fresh water, and shows outstanding salt resistance, durability, and long‐term stability for desalination. This study demonstrates an eco‐friendly and economic solution for continuous freshwater production from seawater using a fully lignocellulosic biomass‐based hydrogel evaporator. Hierarchical and porous lignocellulose‐based hydrogels are fabricated for high‐performance and salt‐resistant solar steam generation. The presence of lignin tunes the water into an intermediate state and reduces the evaporation enthalpy of the water in the hydrogels, which endows the evaporator with an evaporation rate of 1.84 kg m−2 h−1 and a photothermal conversion efficiency of 86.5% under 1 sun irradiation.