High-performance bilayer solar evaporators constructed by candle-derived carbon nanoparticle/wood hybrid

Abstract Solar steam generation is regarded as a promising technique to produce drinkable water using renewable solar energy. However, synthesizing low-cost solar evaporators with high evaporation rates and good scalability remains challenging. Herein, we fabricate novel bilayer solar evaporators by in-situ growth of carbon nanoparticles on the wood surface through incomplete combustion of paraffin candle flame. As the light absorption layer, the carbon nanoparticles with interconnected porous structures exhibit a broadband and high light absorption (ca. 93–97%) via multiple reflections and subsequently convert solar to thermal energy for heating the interfacial region of water/air. The vertically aligned tubular structures of wood substrate effectively transport water from bottom to the surface carbon nanoparticles via capillary force and guarantee sufficient water supply for evaporation. Meanwhile the abundant hydrophilic groups of wood form hydrogen bonds with water molecules, which weakens the hydrogen bonds among intermediate water molecules and reduces the water evaporation enthalpy by ca. 26%. The resultant bilayer solar evaporator displays a high evaporation rate of 2.06 kg/m2/h with the conversion efficiency of 90% under 1 kW/m2, long-term stability, self-cleaning capability, and good anti-acid/base abilities. Importantly, a large-scale solar desalination device is developed for outdoor experiments to produce freshwater. The daily freshwater production amount per unit area (3.1 kg) satisfies the consumption of one adult. This work develops a convenient method to convert wood into advanced solar evaporators to address the global freshwater shortage.