Turning cracks into treasures: Clever use of crack structures to create highly efficient solar-powered water treatment systems

More than 3.6 billion people around the world face water shortage, and traditional desalination technology relies on high-energy processes. Although solar-driven interfacial evaporation (SDIE) is environmentally friendly, the core contradiction is that most of the existing photothermal materials waste energy in heating the excess water inside the material, which leads to the limitation of SDIE efficiency. The nanocoatings that improve water transport efficiency are extremely fragile and fall off when mechanical pressure is applied. How to balance efficient evaporation, pollutant degradation and coating stability has become an unsolved "impossible triangle" in the field.

The research team drew inspiration from the flexibility and compressive resistance of crocodile cracked skin and the efficient water transport of leaf veins. Through a multi-step impregnation process, they constructed an multifunctional cracked metal-phenolic networks (MC-MPNs) coating with a controllable crack structure on a commercial sponge substrate. The crack network of the coating enables the sponge skeleton to form a ultra-thin water layer during evaporation, achieving efficient "confinement capillarity", and heat concentration at the evaporation interface greatly reduces heat loss, with a high evaporation rate of 3.2 kg m^-2 h^-1. The metal ions (such as Fe³⁺) in the coating give the material excellent photocatalytic activity, which enables the efficient degradation of organic dyesand antibiotics, thus achieving simultaneous evaporation and purification. More importantly, the crack structure of the coating can act as a "buffer" to disperse stress and protect the integrity of the coating under mechanical compression. Experiments show that the evaporation performance and catalytic performance of the coating have almost no attenuation after 1000 compression cycles, which completely breaks through the bottleneck of mechanical stability faced by the confinement capillarity for a long time. The research team also successfully constructed an outdoor solar-driven water treatment device based on the coating, which was tested outdoors for up to 7 days using seawater from the South China Sea. The results showed that the plant not only achieved stable high evaporation rate (2.8-3.3 kg m^-2 h^-1) under natural light, but also effectively degraded pollutants in the saline dye wastewater (>99% removal rate) with clear water and ion concentration far below the WHO drinking water standard.

This research, through ingenious bionic design, has successfully broken through the bottleneck in photothermal evaporation technology where efficiency, stability and multi-functionality are difficult to achieve simultaneously. It has laid a solid foundation for the development of efficient, durable and integrated solar desalination and water restoration equipment, and has shown broad application prospects in the field of addressing the global water resource crisis.

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