Self-floating monodisperse microparticles with a nano-engineered surface composition and structure for highly efficient solar-driven water evaporation

Solar-driven water evaporation is a promising approach to capture solar energy for pure water production. Optimization of the composition and structure of photothermal materials is decisive for performance upgradation. Herein, we demonstrate the exploration of self-floating monodisperse microparticles with a nano-engineered surface composition and structure for highly efficient solar water evaporation. The monodisperse microparticles integrating multifunctional entities are assembled by a fast and scalable aerosol-assisted evaporation-induced self-assembly approach. The ultrafast drying process drives the formation of novel surface compositional and structural features. The microparticles possess micro-wrinkled and water-proof surfaces and large hollow cavities, and can thus stably self-float on water. In the microparticles, the surface-enriched Cu nanoparticles within the carbon decorated oxygen-vacancy-rich TiO2 matrix can absorb broadband solar light with high solar thermal conversion. The SiO2 component as a thermal insulator reduces heat loss. The wrinkled surfaces and inter-particle voids provide large interfacial areas and unique micro-channels for water heating and evaporation. Under the illumination of one sun, a self-floating monolayer of these microparticles delivers an excellent and stable water evaporation rate of 1.5 kg m(-2) h(-1), a record high mass specific evaporation rate of 30.0 kg m(-2) h(-1) g(-1) and a high energy efficiency of 92.2%. Several parameters having an influence on performance are elucidated, confirming that microparticles with well-designed structures and compositions are attractive for solar-driven water evaporation.