Salt-blocking three-dimensional Janus evaporator with superwettability gradient for efficient and stable solar desalination.

Solar interfacial steam power generation is a prospective method for seawater desalination. In this work, a salt-blocking three-dimensional (3D) Janus evaporator with a superhydrophobic to superhydrophilic gradient was fabricated by spraying a composite dispersion of multi-walled carbon nanotubes/polydimethylsiloxane (CNTs/PDMS) onto the top side of a polyurethane (PU) foam and polyvinyl alcohol (PVA) solution onto the bottom side. The CNTs/PDMS composite dispersion with nanostructured CNTs and low surface energy PDMS combined with the porous structure of the PU foam rendered the top side superhydrophobic. Therefore, a layer suitable for photothermal conversion was obtained. The hydrophilic PVA combined with the porous structure of the foam rendered the bottom side superhydrophilic, facilitating water absorption and transportation. The asymmetric wettability gradient of the CNTs/PDMS-PU-PVA as a 3D evaporator caused the evaporation rate and transportation speed of water to reach a balance, and the salt was quickly dissolved at the superhydrophilic interface. This 3D salt-resistant Janus evaporator achieved an evaporation rate of 2.26 kg m-2 h-1 under 1 kW m-2 illumination.

Scalable and Mechanically Durable Superhydrophobic Coating of SiO2/Polydimethylsiloxane/Epoxy Nanocomposite.

The mechanical durability of superhydrophobic surfaces is of significance for their practical applications. However, few reports about superhydrophobic coating on certain substrates took into consideration both the mechanical stability of the superhydrophobic coating and adhesion stability between the coating and the substrate. Herein, we put forward a facile and efficient strategy to construct robust superhydrophobic coatings by simply spray-coating a composite suspension of SiO2 nanoparticles, polydimethylsiloxane (PDMS), and epoxy resin (EP) on substrates pretreated with an EP base-coating. The as-obtained coating exhibited excellent superhydrophobicity with water contact angle of 163° and sliding angle of 3.5°, which could endure UV irradiation of 180 h, immersion in acidic or basic solutions for 168 h, and outdoor exposure for over 30 days. Notably, the coating surface retained superhydrophobicity after being successively impacted with faucet water for 1 h, impinged with 360 g sand grains, and abraded with sandpaper of 120 grid under a load of 500 g for 5 m distance. The outstanding mechanical stability was mainly attributed to the cross-linking of EP and the elastic nature of PDMS which ensured strong cohesion inside the whole coating and to the substrate. Additionally, the coating showed self-healing capacity against O2 plasma etching. The method is simple with the materials commercially available and is expected to be widely applied in outdoor applications.

Superhydrophobic Porous Coating of Polymer Composite for Scalable and Durable Daytime Radiative Cooling.

Passive daytime radiative cooling (PDRC) technology provides an eco-friendly cooling strategy by reflecting sunlight reaching the surface and radiating heat underneath to the outer space through the atmospheric transparency window. However, PDRC materials face challenges in cooling performance degradation caused by outdoor contamination and requirements of easy fabrication approaches for scale-up and high cooling efficiency. Herein, a polymer composite coating of polystyrene, polydimethylsiloxane and poly(ethyl cyanoacrylate) (PS/PDMS/PECA) with superhydrophobicity and radiative cooling performance was fabricated and demonstrated to have sustained radiative cooling capability, utilizing the superhydrophobic self-cleaning property to maintain the optical properties of the coating surface. The prepared coating is hierarchically porous which exhibits an average solar reflectance of 96% with an average emissivity of 95% and superhydrophobicity with a contact angle of 160°. The coating realized a subambient radiative cooling of 12.9 °C in sealed air and 7.5 °C in open air. The self-cleaning property of the PS/PDMS/PECA coating helped sustain the cooling capacity for long-term outdoor applications. Moreover, the coating exhibited chemical resistance, UV resistance, and mechanical durability, which has promising applications in wider fields.

A Superhydrophobic Dual-Mode Film for Energy-Free Radiative Cooling and Solar Heating.

Traditional electric cooling in summer and coal heating in winter consume a huge amount of energy and lead to a greenhouse effect. Herein, we developed an energy-free dual-mode superhydrophobic film, which consists of a white side with porous coating of styrene-ethylene-butylene-styrene/SiO2 for radiative cooling and a black side with nanocomposite coating of carbon nanotubes/polydimethylsiloxane for solar heating. In the cooling mode with the white side, the film achieved a high sunlight reflection of 94% and a strong long-wave infrared emission of 92% in the range of 8-13 µm to contribute to a temperature drop of ∼11 °C. In the heating mode with the black side, the film achieved a high solar absorption of 98% to induce heating to raise the air temperature beneath by ΔT of ∼35.6 °C. Importantly, both sides of the film are superhydrophobic with a contact angle over 165° and a sliding angle near 0°, showing typical self-cleaning effects, which defend the surfaces from outdoor contamination, thus conducive to long-term cooling and heating. This dual-mode film shows great potential in outdoor applications as coverings for both cooling in hot summer and heating in winter without an energy input.