Solar-thermal desalination by interfacial evaporation that leverages abundant solar energy to convert saline water into clean freshwater has promised an exciting alternative to meet the grand challenges of water scarcity. Among a host of novel materials developed for efficient solar-thermal desalination, carbon-based materials are arguably the most competitive candidates for practical applications due to their superior biocompatibility. However, conventional carbon-based materials have the limitation of an unsatisfactory vapor generation performance under 1 sun illumination. Here, we report a hierarchical carbon nanostructure that is based on rational design of artificial hollow frameworks on natural cotton to achieve very favorable evaporation properties. Hierarchical water pathways of the evaporator rapidly replenish water as it evaporates. Water evaporation is facilitated by a thin-film effect in the hollow frameworks. The hollow carbonized cotton microfibers (HCMFs) evaporated water with an extremely high rate of 3.2 kg m⁻² h⁻¹ under 1 sun illumination, and exhibited outstanding solar desalination performance with excellent stability and durability. This new material design provides a novel approach to solar vapor generation for a broad range of practical applications.

Paraffin-based nanofluids have higher thermal conductivities compared to the paraffins, which makes them potential useful in thermal energy storage. However, few studies have been conducted on the solidification structure of paraffin-based nanofluids which directly decides whether or not they can be reused for energy storage. This paper investigated the effects of surfactant and ultrasound on the solidification behaviors of Al/Paraffin nanofluid. Sodium dodecyl sulfonate (SDS), polyvinyl pyrrolidone (PVP) and cetyl trimethyl ammonium bromide (CTAB) were used as surfactants to prepare Al/Paraffin nanofluids. Al/SDS/Paraffin, Al/PVP/Paraffin and Al/CTAB/Paraffin nanofluids as well as Al/Paraffin nanofluid without surfactant were cooled down with and without ultrasonic vibration. An environmental scanning electron microscope was used to measure the solidification structures of paraffin-based nanofluids. The Al/Paraffin nanofluid was found to solidify in the form of annulus icing. The advancing solidification front pushed the Al nanoparticles to the middle of container, resulting in the aggregation of Al nanoparticles there. The Al micro-aggregates settled down quickly during the subsequent melting process, bring out the failure problem of Al/Paraffin nanofluid. Surfactants CTAB, PVP and SDS couldn’t solve this failure problem of Al/Paraffin nanofluid fundamentally, but ultrasonic vibration could. The SEM images of solidified paraffin-based nanofluids with ultrasonic vibration showed that the Al nano-aggregates distributed evenly in the paraffin. It was found that solidification of each paraffin-based nanofluid assisted by ultrasonic vibration almost took place simultaneously throughout the container. We therefore obtained that ultrasonic vibration could promote the heterogeneous nucleation on Al nanoparticles mainly by reducing the temperature inhomogeneity in paraffin-based nanofluids.