Uneven Hydrophilic-Hydrophobic Nanoflowers Enhancing Solar Interface Evaporation: Se-Doped Carbon Loaded with Gradient Distribution of CoSe/Co.

Solar interface evaporation is a promising technology for sustainable freshwater acquisition. Regulating the hydrophilicity/hydrophobicity of the evaporator can optimize the water transport, heat transfer, and evaporation enthalpy during the evaporation process, thereby significantly improving the evaporation performance. The CoSe/Co-SeC nanoflower was prepared by high-temperature selenization of ZIF-67. Each petal of the nanoflower is loaded with a density-gradient distribution CoSe/Co, forming an uneven hydrophilic and hydrophobic surface that transitions from bottom hydrophilicity to top hydrophobicity. During the evaporation process, the hydrophilic bottom of the petals promotes rapid water supply, while the hydrophobic top of the petals protrudes from the water surface to form a large number of solid-liquid-gas three-phase interfaces. Therefore, water clusters activated by the strong hydrophilic sites at the bottom of the petals can reach the gas-liquid interface after a very short transmission distance and achieve water cluster evaporation. In addition, the nanoflower optimized the heat transfer at the solid-liquid interface and further promoted the increase in evaporation rate through micro-meniscus evaporation (MME). As a result, the evaporation rate and energy efficiency of the CoSe/Co-SeC evaporator are as high as 2.44 kg m h and 95.5%. This work passes controllable preparation of the gradient CoSe/Co-SeC and shows the enormous potential of micro-hydrophobic and hydrophilic regulation for improving solar interface evaporation performance.