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Passive daytime radiative cooling (PDRC) is a promising energy-saving cooling method to cool objects without energy consumption. Although numerous PDRC materials and structures have been proposed to achieve sub-ambient temperatures, the technique faces unprecedented challenges brought on by complicated and expensive fabrication. Herein, inspired by traditional Chinese oil-paper umbrellas, we develop a self-cleaning and self-cooling oil-foam composite (OFC) made of recycled polystyrene foam and tung oil to simultaneously achieve efficient passive radiative cooling and enhanced thermal dissipation of objects. The OFCs show high solar reflectance (0.90) and high mid-infrared thermal emittance (0.89) during the atmospheric transparent window, contributing to a sub-ambient temperature drop of ∼5.4 °C and cooling power of 86 W m −2 under direct solar irradiance. Additionally, the worldwide market of recycled packaging plastics can provide low-cost raw materials, further eliminating the release of plastics into the environment. The OFC offers an energy-efficient, cost-effective and environmentally friendly candidate for building cooling applications and provides a value-added path for plastic recycling. 

Thermophotovoltaics is a promising technology for heat recovery and has garnered tremendous attention in the past decades. In a thermophotovoltaic system, a selective emitter is required to convert the incoming light in order to emit appropriate photons matched with the bandgap of the PV cell, both avoiding low-energy useless photons and thermalization loss caused by high-energy photons. This work aims to design a metal-based photonic narrowband emitter, and it is composed of tungsten, a refractory material which can withstand the high working temperature of the thermophotovoltaic system. Besides, the advantage of an all-metal emitter is that there is no concern of thermal expansion mismatch. Hexagon and square patterned arrays are numerically analyzed and a parametric study is conducted for different feature sizes, gaps, and pattern heights, leading to an emission peak shift and bandwidth change. Besides, a photonic metal-based emitter is fabricated using a photolithography method, optically characterized and compared with the calculated emissivity spectra. This work sheds light on the research of high-temperature thermal management, energy harvesting and power generation. 

Configured with a rapid evaporation rate and a high photothermal conversion efficiency, solar-driven interfacial evaporation displays considerable promise for seawater desalination. Inspired by the versatility and deployability of origami-based structures, we demonstrate a portable waterbomb origami pattern-based tower-like structure, named an “origami tower”, as a convertible photothermal evaporator floating on water for efficient solar-driven interfacial desalination. The origami tower has predictable deformability, featuring reversible radial expansion and contraction radially accompanied by small changes in the axial direction. The reversible adjustability of the origami tower offers convenience for transportation and storage, while the quick expansion into its tower shape provides rapid deployment capabilities. Benefiting from an enlarged evaporation surface, excellent light trapping ability, and heat localization, the origami-tower photothermal evaporator yields an evaporation rate of 2.67 kg m −2 h −1 under one sun illumination. This reversible 3D origami-based photothermal evaporator opens a new avenue for building a portable and efficient solar thermal desalination system. 

Water evaporation systems with solar energy as the primary driving energy have received extensive attention in recent years. This work studies the preparation method and performance of hydrogel evaporators using chitosan and polyvinyl alcohol (PVA) as a framework and carbon nanoparticles (CNPs) as the photothermal material. The evaporation rate of CPC (chitosan/PVA and CNPs) hydrogel obtained reaches 2.28 kg m⁻² h⁻¹. Simultaneously, a three-dimensional structure is designed based on the two-dimensional double-layer evaporation system in this study. An evaporator with a tiny-pool structure and a hydrogel with a dome-arrayed structure is designed. These two structures achieve highly efficient evaporation rates of 2.28 kg m⁻² h⁻¹and 3.80 kg m⁻² h⁻¹, respectively. These optimized designs improve the evaporation rate of the overall system by ~ 66.7%. The developed evaporation devices provide a promising pathway for developing the double-layer evaporators, which promote the new development of water purification with a solar-driven evaporation system.

 

Over the past decade, tremendous efforts have been devoted to the design of metamaterials with ultrahigh absorption. These perfect absorbers can realize the annihilation of incident electromagnetic waves by eliminating reflection and transmission of microwaves, infrared, visible, and ultraviolet. However, the optical properties are usually unchanged due to a rigid structure. In this work, we propose a mechanically stretchable metamaterial composed of polydimethylsiloxane and gold with tunable optical properties in the mid-infrared region. A large variation of absorptances with different gold filling ratios is demonstrated as well as the corresponding electric field distributions. Under moderate uniaxial and biaxial tensions, the proposed two-dimensional grating structure has achieved a dynamic tuning of infrared thermal properties, including a sharp reflectance-absorptance switch. This mechanically stretchable metamaterial can serve different optical and sensing functions due to its facile tunability.

 

Water scarcity and waste mismanagement are global crises that threaten the health of populations worldwide and a sustainable future. In order to help mitigate both these issues, a solar desalination device composed entirely of fallen leaves and guar – both natural materials – has been developed and demonstrated herein. This sustainable desalinator realizes an evaporation rate of 2.53 kg m −2 h −1 under 1 sun irradiance, and achieves consistent performance over an extended exposure period. Furthermore, it functions efficiently under a variety of solar intensities and in high salinity environments, and can produce water at salinities well within the acceptable levels for human consumption. Such strong performance in a large variety of environmental conditions is made possible by its excellent solar absorption, superb and rapid water absorption, low thermal conductivity, and considerable salt rejection abilities. Composed primarily of biowaste material and boasting a simple fabrication process, this leaf-guar desalinator provides a low-cost and sustainable avenue for alleviating water scarcity and supporting a green path forward.