Next-generation water-saving strategies for greenhouses using a nexus approach with modern technologies

The escalating food and water crisis, propelled by population growth, urbanization, and climate change, demands a reimagining of agricultural practices. Traditional water-saving irrigation methods have reached their limits, necessitating the exploration of innovative approaches. This perspective explores the potential of utilizing excess light and water in greenhouse cultivation through advanced materials and engineering technologies. We investigate the potential of four key technologies-sorption-based atmosphere water harvesting (SAWH), superabsorbent polymer water holding materials (SPWH), radiative cooling (RC), and seawater desalination. The perspective proposes suitable application methods and future development directions for greenhouse water conservation, aiming to introduce novel water-saving strategies and smarter resource management.

Robust fluorinated cellulose composite aerogels incorporating radiative cooling and thermal insulation for regionally adaptable building thermal management

Passive radiative cooling (PRC) is an emerging sustainable technology that plays a key role for achieving the goal of carbon neutrality. However, several challenges remain for PRC materials in their practical application in building thermal management, including overcooling problems and unsatisfactory cooling efficiency caused by solar absorption and parasitic heat gains. In this work, fluorinated cellulose-based composite aerogels (FCCA) integrating thermal insulation and PRC were developed by a facile manufacturing strategy that combined phase separation and freeze-drying. P(VdF-HFP) was utilized to promote the formation of nano/micro porous architectures in FCCA, resulting in a decrease in the thermal conductivity of the aerogel to 0.034 W m-1 K-1 while simultaneously increasing its solar reflectance and infrared emissivity (8-13 μm) to 95.74 % and 97.15 %, respectively. The aerogel cooler achieved a sub-ambient cooling temperature of ∼9.68 °C during the daytime and maintained its cooling effectiveness even on cloudy days. The fluorinated aerogels demonstrated excellent hydrophobicity and chemical durability after outdoor exposure and heat aging tests. This work opens up a new pathway to design low-cost cellulose-based materials for efficient thermal management of energy-saving buildings around the world.

Sky cooling for LED streetlights

Thermal management is a critical challenge for semiconductor light-emitting diodes (LEDs), as inadequate heat dissipation reduces luminous efficiency and shortens the devices' lifespan. Thus, there is an urgent need for more effective cooling strategies to enhance the energy efficiency of LEDs. LED streetlights, which operate primarily at night and experience high chip temperatures, could benefit greatly from improved thermal management. In this study, we introduce a sky-facing radiative cooling strategy for outdoor LED streetlights, an innovative yet less explored approach for thermal management of optoelectronics. Our method employs a nanoporous polyethylene (nanoPE) material that possesses both infrared transparency and visible reflectivity. This approach enables the direct release of heat generated by the LED through a sky-facing radiative cooling channel, while also reflecting a significant portion of the light back for illumination. By incorporating nanoPE as a cover for sky-facing LED lights, we achieved a remarkable temperature reduction of 7.8 °C in controlled laboratory settings and 4.4 °C in outdoor environments. These reductions were accompanied by an efficiency improvement of approximately 5% and 4%, respectively. This enhanced efficiency translates into substantial annual energy savings, estimated at 1.9 terawatt-hours when considering the use of LED streetlights in the United States. Furthermore, this electricity saving corresponds to a reduction of approximately 1.3 million metric tons of CO2 emissions, equivalent to 0.03% of the total annual CO2 emissions by the United States in 2018.

A Transparent Polymer-Composite Film for Window Energy Conservation

As living standards improve, the energy consumption for regulating indoor temperature keeps increasing. Windows, in particular, enhance indoor brightness but also lead to increased energy loss, especially in sunny weather. Developing a product that can maintain indoor brightness while reducing energy consumption is a challenge. We developed a facile, spectrally selective transparent ultrahigh-molecular-weight polyethylene composite film to address this trade-off. It is based on a blend of antimony-doped tin oxide and then spin-coated hydrophobic fumed silica, achieving a high visible light transmittance (> 70%) and high shielding rates for ultraviolet (> 90%) and near-infrared (> 70%). When applied to the acrylic window of containers and placed outside, this film can cause a 10 °C temperature drop compared to a pure polymer film. Moreover, in building energy simulations, the annual energy savings could be between 14.1% ~ 31.9% per year. The development of energy-efficient and eco-friendly transparent films is crucial for reducing energy consumption and promoting sustainability in the window environment.

Fast-Developing Dynamic Radiative Thermal Management: Full-Scale Fundamentals, Switching Methods, Applications, and Challenges

Rapid population growth in recent decades has intensified both the global energy crisis and the challenges posed by climate change, including global warming. Currently, the increased frequency of extreme weather events and large fluctuations in ambient temperature disrupt thermal comfort and negatively impact health, driving a growing dependence on cooling and heating energy sources. Consequently, efficient thermal management has become a central focus of energy research. Traditional thermal management systems consume substantial energy, further contributing to greenhouse gas emissions. In contrast, emergent radiant thermal management technologies that rely on renewable energy have been proposed as sustainable alternatives. However, achieving year-round thermal management without additional energy input remains a formidable challenge. Recently, dynamic radiative thermal management technologies have emerged as the most promising solution, offering the potential for energy-efficient adaptation across seasonal variations. This review systematically presents recent advancements in dynamic radiative thermal management, covering fundamental principles, switching mechanisms, primary materials, and application areas. Additionally, the key challenges hindering the broader adoption of dynamic radiative thermal management technologies are discussed. By highlighting their transformative potential, this review provides insights into the design and industrial scalability of these innovations, with the ultimate aim of promoting renewable energy integration in thermal management applications.

Recent advances in atmospheric water harvesting technology and its development

Water scarcity is a pressing issue worldwide. Given the ample atmospheric water sources, water harvesting from the atmosphere presents a promising solution to this challenge. In recent years, the solar-driven atmospheric water harvesting technology utilizing an adsorption-desorption process has garnered considerable interest. This is attributed to the abundant availability of solar energy, advanced adsorbents, improved photothermal materials, sophisticated interface heating system designs, and efficient thermal management techniques, all of which collectively enhance conversion efficiency. This article provides an overview of the advancements in atmospheric water collection, specifically focusing on hygroscopic water harvesting driven by solar energy. The discussion also encompasses the roles of materials, surfaces, equipment, and systems in enhancing water collection efficiency. By outlining both the advantages and challenges of atmospheric water collection, this study aims to shed light on future research directions in this research field.

Accelerated photonic design of coolhouse film for photosynthesis via machine learning

Controlling the suitable light, temperature, and water is essential for plant photosynthesis. While greenhouses/warm-houses are effective in cold or dry climates by creating warm, humid environments, a cool-house that provides a cool local environment with minimal energy and water consumption is highly desirable but has yet to be realized in hot, water-scarce regions. Here, using a synergistic genetic algorithm and machine learning, we propose and demonstrate a coolhouse film that regulates temperature and water for photosynthesis without requiring additional energy or water. This scalable film, selected from hundreds of potential designs, selectively and precisely transmits sunlight needed for photosynthesis while reflecting excess heat, thereby reducing thermal load and evapotranspiration. Its optical properties also exhibit weak angle dependence. In demonstrations in subtropical and arid regions, the film reduces temperatures by 5-17 °C and cuts water loss by half, resulting in more than doubled biomass yield and survival rates. It also improves crop resistance to heat and drought in greenhouse cultivation. The integration of machine learning and photonics provides a powerful toolkit for designing photonic structures and devices aimed at sustainability.

Adaptive Phase Change Microcapsules for Efficient Sustainable Cooling

Passive radiative cooling has recently gained significant attention as a highly promising technology that offers a zero-energy and electricity-free solution to tackle the pressing issue of global warming. Nevertheless, research efforts have predominantly focused on enhancing daytime and hot-day radiative cooling efficacy, often neglecting the potential downsides associated with excessive cooling and the consequent increased heating expenses during cold nights and winter days. Herein, we demonstrate a micro-nanostructured engineered composite film that synergistically integrates room-temperature adaptive silica-shell/oil-core phase change microcapsules (S-PCMs) with commercially available cellulose fibers. The resultant composite film exhibits a solar reflectance of 0.92 and a mid-infrared emissivity of 0.96, achieving a remarkable average daytime subambient cooling of 7.5 °C under direct sunlight in hot conditions. Encouragingly, upon reaching the phase transition temperature, the heat previously absorbed and stored by S-PCMs is released, resulting in a temperature elevation of the composite film with an average temperature differential of merely 3.0 °C compared to surrounding air. The exceptional latent heat storage capability of our S-PCMs/cellulose composite film mitigates the radiative overcooling effect and substantially diminishes the heating demand, particularly across a diverse array of environmental conditions.

Enhancing Passive Radiative Cooling Films with Hollow Yttrium-Oxide Spheres Insights from FDTD Simulation

Passive daytime radiative cooling (PDRC) presents a promising avenue for efficient thermal management without relying on electrical power. In this study, the potential of integrating Hollow Yttrium-Oxide Spheres (HYSs) within a Polydimethylsiloxane (PDMS) matrix to enhance PDRC is investigated. Through a combination of experimental characterization and computational analysis, the optical properties and radiative cooling performance of PDMS films embedded with HYSs are evaluated. These results demonstrate that HYSs significantly improve both solar reflectivity and long-wave infrared (LWIR) emissivity of the PDMS matrix. Finite-Difference Time-Domain (FDTD) simulations confirm the scattering efficiency of HYSs across various wavelength ranges, highlighting their effectiveness as additives for enhancing the radiative properties of passive cooling materials. Experimental validation reveals enhanced reflectivity and emissivity of PDMS films with embedded HYSs, resulting in superior cooling performance compared to non-HYS counterparts. Overall, this study underscores the potential of HYS-infused PDMS films as a promising solution for passive radiative cooling, with broad applicability in diverse domains requiring efficient thermal management solutions. Additionally, these research insights pave the way for establishing an AI database for passive radiative cooling research, offering new avenues for further exploration and application in this field.

Turning Discarded Oyster Shells into Sustainable Passive Radiative Cooling Films

Inorganic materials used in passive radiative cooling have achieved a commendable level of performance through synthesis, yet they lack sustainability and environmental friendliness as they do not incorporate recycling. This study developed a novel passive radiative cooling (PRC) film utilizing calcium carbonate extracted from discarded oyster shells (D-CaCO3) and polyurethane (PU) as the matrix. This sustainable approach leverages the unique properties of CaCO3, such as high solar reflectance and strong infrared emissivity, to achieve significant cooling effects. The PU/D-CaCO3 film absorbs only 22% of total solar light and exhibits a high emissivity of 95% in the atmospheric window, achieving temperatures up to 7 °C lower than the surrounding environment under 650 W/m2 solar irradiance. Furthermore, field tests were conducted to verify the implementation of our optical strategy by analyzing the optical properties and FDTD simulations. Consequently, the PU/D-CaCO3 film outperformed conventional white paint and pure PU, demonstrating a maximum temperature difference of 7 °C. Additionally, the passive radiative cooling efficiency of the film was verified through theoretical calculations. The oyster-shell-derived CaCO3 utilizes waste and contributes to carbon sequestration, aligning with sustainable and eco-friendly goals. This research demonstrates the potential of using marine-derived materials in passive cooling technologies, offering a path to reduce energy consumption and greenhouse gas emissions in cooling applications. The findings highlight the commercial viability and environmental benefits of PU/D-CaCO3 films, marking significant progress in passive radiative cooling.

Fabrication and modulation of flexible electromagnetic metamaterials

Flexible electromagnetic metamaterials are a potential candidate for the ideal material for electromagnetic control due to their unique physical properties and structure. Flexible electromagnetic metamaterials can be designed to exhibit specific responses to electromagnetic waves within a particular frequency range. Research shows that flexible electromagnetic metamaterials exhibit significant electromagnetic control characteristics in microwave, terahertz, infrared and other frequency bands. It has a wide range of applications in the fields of electromagnetic wave absorption and stealth, antennas and microwave devices, communication information and other fields. In this review, the currently popular fabrication methods of flexible electromagnetic metamaterials are first summarized, highlighting the electromagnetic modulation capability in different frequency bands. Then, the applications of flexible electromagnetic metamaterials in four aspects, namely electromagnetic stealth, temperature modulation, electromagnetic shielding, and wearable sensors, are elaborated and summarized in detail. In addition, this review also discusses the shortcomings and limitations of flexible electromagnetic metamaterials for electromagnetic control. Finally, the conclusion and perspective of the electromagnetic properties of flexible electromagnetic metamaterials are presented.

Water-Resistant Poly(ethylene oxide) Electrospun Membranes Enabled by In Situ UV-Cross-Linking for Efficient Daytime Radiative Cooling

Daytime radiative cooling, based on selective infrared emissions through atmospheric transparency windows to outer space and the reflection of solar irradiance, is a zero-energy and environmentally friendly cooling technology. Poly(ethylene oxide) (PEO) electrospun membranes have both selective mid-infrared emissions and effective sunlight reflection, inducing excellent daytime radiative cooling performance. However, PEO is highly water soluble, which makes electrospun PEO membranes unable to cope with rainy conditions when used for outdoor daytime radiative cooling. Herein, we report an in situ UV-crosslinking strategy for preparing PEO electrospun membranes with water resistance for the application of daytime radiative cooling. Acrylate-terminated PEO was synthesized and mixed together with cross-linking agents and photoinitiators to prepare the electrospinning solution. During electrospinning, the nanofibers were irradiated with UV light to initiate the cross-linking. For a membrane with a thickness of 200 μm, the average solar reflectance was 89.6%, and the infrared emissivity (8-13 μm) was 96.3%. Although slight swelling happens to the cross-linked membrane once it comes into contact with water, the fibrous morphology shows no obvious change when prolonging the water soaking time, indicating excellent water resistance. The outdoor cooling performance test results showed that compared to the average temperature of the air in the test box, the average temperature drop in the membrane before and after water soaking was 13.8 °C and 11.5 °C, respectively. Crosslinked PEO-based electrospun membranes with both water resistance and radiative cooling performance may have real applications for outdoor daytime radiative cooling.

Enhanced ensemble learning-based uncertainty and sensitivity analysis of ventilation rate in a novel radiative cooling building

The rising global demand for air conditioning systems, driven by increasing temperatures and urbanization, has led to higher energy consumption and greenhouse gas emissions. HVAC systems, particularly AC, account for nearly half of building energy use, highlighting the need for efficient cooling solutions. Passive cooling, especially radiative cooling, offers potential to reduce cooling loads and improve energy efficiency. However, most studies focus on idealized conditions, neglecting the real-world variability of indoor and outdoor environments. This study proposes a novel machine learning-based ensemble stacking model to predict ventilation rates in passive cooling buildings, addressing the challenges of black-box modeling. The model's performance is improved across key metrics such as R2, RMSE, and MAE. For the first time, uncertainty and sensitivity analysis is applied to assess the impact of indoor and outdoor conditions on ventilation rates. Sensitivity analysis shows that the reference model's ventilation rate highly depends on inlet air temperature, internal temperatures at 0.1 and 0.2 m, and internal wall heat flux, with optimization of these parameters having a significant impact on building performance. In contrast, the test building relies on fewer parameters, with external temperature, outlet air temperature, and net roof radiation being notable factors; as ambient temperature increases, so does the ventilation rate. The analysis reveals that uncertainties have minimal impact in the reference building, while the test building demonstrates greater sensitivity during warmer months, emphasizing the importance of accounting for seasonal variations. This research underscores the significance of optimizing key features to enhance natural cooling and ventilation, contributing to sustainable climate control solutions and providing an interpretable, robust model for predicting ventilation rates in energy-efficient buildings.

Achieving a Porous PDMS Film for Passive Cooling through the Utilization of Ultrafine NaCl Sacrificial Templates

Passive radiative cooling technology serves as an energy-free alternative to traditional cooling systems. Porous polymer structures are frequently employed for radiative cooling by leveraging the refractive index mismatch between the polymer and the pores, enabling the scattering of incoming sunlight. Recently, water-soluble and readily available Sodium chloride (NaCl) particles have been utilized as sacrificial templates for sustainable pore creation. Nevertheless, optimizing NaCl particle size, and thus the polymer pore size to enhance scattering capabilities remains a challenge. Here, we report a simple, scalable, and sustainable approach to creating an optimized porous polydimethylsiloxane (PDMS) film. This approach utilizes ultrafine NaCl powders as sacrificial templates, which were synthesized via ultrasonic precipitation to ensure their small size. The ultrafine NaCl particles have a size distribution centered around 6-8 μm, and the as-fabricated porous PDMS film achieves a high thermal emissivity of 0.95 within the atmospheric window (8-13 μm) and exhibits a reflectivity of 0.95 within the visible range (0.4-0.78 μm). Due to the desired dual-spectrum properties, the porous PDMS film exhibits a superior subambient cooling capacity over that fabricated with typically larger NaCl particles under strong sunlight. This study offers a scalable and practical radiative cooling solution for sustainable thermal management.

UV-Cured Robust and Transparent Double-Layer Membrane on Windows for Water Harvesting and Room Cooling

The increasing demand for energy in cooling systems due to global warming presents a significant challenge. Conventional air-conditioning methods exacerbate climate change by contributing to heightened carbon emissions. Glass facades, renowned in modern architecture for their versatility and aesthetic appeal, inadvertently trap solar radiation, resulting in heat buildup and the greenhouse effect. To tackle these issues, we utilized roll-to-flat and light-curing technology to develop a hydrogel coating on a glass substrate with the assistance of ultraviolet (UV) adhesive. This water-contained hydrogel selectively absorbs ultraviolet and infrared light while allowing visible light transmission, thereby maintaining glass transparency. Leveraging the absorption of partial ultraviolet and infrared as active cooling and the liquid-to-gaseous phase change enthalpy of water as passive cooling, the hydrogel significantly reduces room temperatures by up to 8.1 °C under 0.75 sun irradiation, corresponding to a total room cooling power of about 192.6 W m-2. This study introduces a novel approach to transparent and energy-saving cooling in glass buildings, with the added potential for water resource recycling.

Mechanosensitive stacking structure with continuous solar controllability for real-time thermal management

Adaptive control of solar light based on an optical switching strategy is essential to tune thermal gain, while real-time solar regulation and hence on-demand thermal management coupled with dynamic conditions still faces a formidable challenge. Herein, we develop a stacking structure which is mechanosensitive and can be finely tuned depending on the dynamic cavitation effect. Specifically, the stacking structure transfers from a solid monolith state to porous layered state progressively under mechanical stretching, and the resulting porous layered state gradually goes back to the solid monolith state once the load is released. Such structure switching results in gradual reversible optical transition from highly transparent to highly reflective, giving rise to high solar regulation capability coupled with continuous solar controllability. Based on this, the stacking structure functions allow multiple thermal management, not only for solar heating and radiative cooling, but also multi-stage thermoregulation and real-time thermal management on demand via a simple mechanical method. Moreover, the mechanosensitive stacking structure demonstrates impressive optical stability against external mechanical forces and extreme environments, with the combination of stability, durability, scalability, applicability, and self-cleaning ability.

Materials in Radiative Cooling Technologies

Radiative cooling (RC) is a carbon-neutral cooling technology that utilizes thermal radiation to dissipate heat from the Earth's surface to the cold outer space. Research in the field of RC has garnered increasing interest from both academia and industry due to its potential to drive sustainable economic and environmental benefits to human society by reducing energy consumption and greenhouse gas emissions from conventional cooling systems. Materials innovation is the key to fully exploit the potential of RC. This review aims to elucidate the materials development with a focus on the design strategy including their intrinsic properties, structural formations, and performance improvement. The main types of RC materials, i.e., static-homogeneous, static-composite, dynamic, and multifunctional materials, are systematically overviewed. Future trends, possible challenges, and potential solutions are presented with perspectives in the concluding part, aiming to provide a roadmap for the future development of advanced RC materials.

Biomimetic Alumina Film for Passive Daytime Radiative Cooling

Passive daytime radiative cooling is receiving more and more attention as a cooling method that does not consume energy to cool objects. However, most radiative cooling materials require the mixing of multiple particles, which increases the manufacturing process requirements. Most radiative cooling materials are susceptible to outdoor abrasion, pollution, and UV exposure, which leads to decreased performance. In this paper, the biomimetic film with both radiative cooling and self-cleaning functions was prepared by a simple evaporation-induced self-assembly process and spraying process using Al2O3 as the main radiatively cooling raw material, poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] as the additive, and polydimethylsiloxane as the binder. Therefore, we can get a biomimetic-Al2O3-P(VDF-HFP)-PDMS film (BAPPF). The BAPPF was spectrally selective. Specifically, the reflectance of BAPPF in the solar spectrum (0.45-0.89 μm) exceeded 100%, and the average reflectance in the main thermal effect of the solar spectrum (0.78-1.10 μm) was 99.92%. In addition, the BAPPF had 96.97% reflectance in the solar spectrum (0.3-2.5 μm) and 90.55% mid-infrared emissivity in the atmospheric window (8-13 μm). The combined performance enabled BAPPF to reduce temperature by up to 8.4 °C over air temperature in outdoor tests. What's more, BAPPF had excellent superhydrophobic properties, with a water contact angle of up to 159°. The self-cleaning of the BAPPF prevented contamination and maintained cooling even when working outdoors for long periods of time. Furthermore, the BAPPF maintained high performance after mechanical friction, chemical corrosion, UV aging, and water impact, which has broad reference value and application prospects.

Can Thermal Nonreciprocity Help Radiative Cooling?

Radiative cooling has witnessed substantial progress while its performance is constrained by the thermal reciprocal Kirchhoff's law. Violating Kirchhoff's law to pursue nonreciprocal radiative cooling seems promising; however, the energy conservation requirement and radiant flux integrated over the entire hemisphere make the nonreciprocal benefit insignificant. This commentary discusses the practical limits of nonreciprocal radiative cooling and points toward the future direction of directional radiative cooling.

Radiative cooling technology with artificial intelligence

As sustainable thermal management becomes a global priority, the development of radiative cooling (RC) technology has recently emerged as a promising solution. Simultaneously, recent advent of artificial intelligence (AI) offers the potential to revolutionize current research in sustainable cooling strategies. This article discusses the advancement of radiative cooling technology through the integration of AI, tackling the challenging issues arising from the conventional approach and offering strategic solutions to address global issues. AI, capable of mimicking or exceeding human capabilities through various algorithms, enables the efficient optimization of RC structures. Moreover, integrating AI with advanced RC technologies, which have the potential to surpass traditional RC configurations and applications but are still in the early stages, can further accelerate progress in the field of RC. Hence, AI-driven RC technologies will contribute to addressing the increasingly prevalent environmental challenges, further being a leading solution for next-generation sustainable thermal managements as these technologies continue to mature.

Cooling Performance of TiO2-Based Radiative Cooling Coating in Tropical Conditions

The cooling power of radiative cooling (RC) coatings depends not only on the radiative properties of the coating but also on environmental variables. In tropical environments, the cooling performance of RC coatings deteriorates due to high humidity and high solar radiation. Previous studies focused on developing high solar-reflective coatings to achieve subambient cooling in tropical environments. However, these coatings have not demonstrated the ability to be used at a large scale, mainly due to their high cost or less durability. Herein, we test an RC paint coating composed of TiO2 and polydimethylsiloxane (PDMS) in three different cities with high and moderate humidity levels. Though a significant reduction in the internal temperature of an RC paint-coated aluminum (Al) box is observed, compared to an uncoated Al box, in both high and moderate humidity environments, subambient cooling is not achieved. A comprehensive analysis is conducted to clarify the reasons behind the inability to attain subambient cooling.

Self-Adaptive Smart Thermochromic Film with Quick Response for All-Year Radiative Cooling and Solar Heating

The advancement of energy-saving buildings requires both high-performance passive radiative cooling (PRC) and solar absorption heating (SAH) materials. Although many materials with PRC or SAH functions have been developed, they cannot adapt to the large fluctuations of ambient temperature in different seasons. Herein, we report the design and fabrication of a new thermochromic porous film (TMRC) with combined temperature-adaptive SAH and PRC performance to achieve "warm in winter and cool in summer" for all-year radiative cooling and solar heating. The porous structure and embedding thermochromic particles endow the TMRC with an ultrawide modulation capability for solar reflectivity ranging from 86.1% to 13.3% and a reversible color change in response to temperature variation. When the ambient temperature exceeds the transition temperature (Tc = 22 °C), TMRC enters a radiative cooling mode. At temperatures below the Tc, TMRC heats up by 6.5 °C in cold winter due to its high solar absorptivity. TMRC exhibits a rapid response time of 40 s at near room temperature. Compared to traditional cement coatings, TMRC can reduce energy consumption up to 38.05 kWh/m2 (18%) in midlatitude regions according to energy consumption simulations. In addition, TMRC shows excellent self-cleaning and UV-aging resistance abilities. Therefore, this work provides a low-cost and scalable technique for reversible TMRC for all-year-efficient thermal management.

High-Performance Radiative Cooling Sunscreen

Radiative cooling is a zero-energy-consumption cooling technology that shows great potential for outdoor human thermal management. To keep human skin comfortable in hot days, we herein develop a radiative cooling (RC) sunscreen that exhibits a low ultraviolet (UV) transmissivity (4.86%), a high solar reflectivity (90.19%), and a high mid-infrared emissivity (92.09%) to effectively provide both UV protection and skin cooling. As a result, the RC sunscreen exhibits a high cooling performance for decreasing the human skin temperature by 2.3-6.1 °C more than commercial sunscreens and 4.2-6.0 °C more than bare skin in a variety of outdoor scenarios in summer (e.g., low-humidity sunny days, high-humidity sunny days, and high-humidity cloudy days). In addition, the RC sunscreen also shows a good UV stability (12 h, 125 W), a high water resistance (106°), a long working life (30 days), and a good biocompatibility, thereby exhibiting promising commercial potentials in the sunscreen market.

Anodization-Processed Colored Radiative Thermoregulatory Film

Colored radiative thermal management materials (RTMM) not only provide superior thermoregulatory performance but also satisfy aesthetic requirements. However, the complexity of the preparation procedures and constrained color selection have hindered their widespread adoption. Here, we presented a facile one-step anodizing strategy for fabricating colored dual-mode RTMM based on titanium film (Ti) and P(VDF-HFP) with mid-infrared (MIR) emissivities of 0.07 and 0.96, respectively, which allow for on-demand temperature modulation (rise of 28.2 K and drop of 9 K) without energy consumption. Furthermore, demonstrations of a colored radiative warming membrane also validate the effectiveness of anodizing treatment. The colored Ti/nano PE membrane with 10.8 μm thickness enables a temperature rise of 2.3 K on real human skin, which is much higher than that of commercial fabric with 120 μm thickness (0.7 K). This strategy provides insights for the scalable fabrication and application of colored low emissivity materials, contributing to the goal of a sustainable society.

Superhydrophobic PVDF/SiO2 composite films with a hierarchical structure for highly stabilized radiative cooling

PVDF/SiO2 composite films with a hierarchical structure were prepared by water bath solvent exchange and they realized the integration of self-cleaning and radiative cooling. The high scattering properties of SiO2 effectively enhanced the radiative cooling performance of the films, and the weathering stability of the composite films was evaluated by UV radiation treatment and friction resistance analysis.

Subambient daytime radiative cooling of vertical surfaces

Subambient daytime radiative cooling enables temperatures to passively reach below ambient temperature, even under direct sunlight, by emitting thermal radiation toward outer space. This technology holds promise for numerous exciting applications. However, previous demonstrations of subambient daytime radiative cooling require surfaces that directly face the sky, and these cannot be applied to vertical surfaces that are ubiquitous in real-world scenarios such as buildings and vehicles. Here, we demonstrate subambient daytime radiative cooling of vertical surfaces under peak sunlight using a hierarchically designed, angularly asymmetric, spectrally selective thermal emitter. Under peak sunlight of about 920 watts per square meter, our emitter reaches a temperature that is about 2.5°C below ambient temperature, corresponding to a temperature reduction of about 4.3° and 8.9°C compared with a silica-polymer hybrid radiative cooler and commercial white paint, respectively.

Multifunctional Smart Fabrics with Integration of Self-Cleaning, Energy Harvesting, and Thermal Management Properties

Due to their good wearability, smart fabrics have gradually developed into one of the important components of multifunctional flexible electronics. Nevertheless, function integration is typically accomplished through the intricate stacking of diverse modules, which inevitably compromises comfort and elevates processing complexities. The integration of these discrete functional modules into a unified design for smart fabrics represents a superior solution. Here, we put forward a rational approach to functional integration for the typical challenges of thermal management, energy supply, and surface contamination in smart fabrics. This sandwich-structured multilayer fabric (MLF) is obtained by continuous electrospinning of two layer P(VDF-HFP) fabric and one layer P(VDF-HFP) fabric functionalized with core-shell SiO2/ZnO/ZIF-8 (SZZ) nanoparticles. Specifically, MLFs achieve effective and stable energy harvesting in triboelectric nanogenerators (TENGs) with hydrophobicity and antibacterial properties. Meanwhile, MLFs also have high mid-infrared emissivity and sunlight reflectivity, successfully realizing radiative cooling under different climates, and have been applied in wearing clothing, roof shading, and car covers. This work may contribute to the design and manufacturing of next-generation thermal comfort smart fabrics and wearable electronics, particularly in terms of the rational design of multifunctional devices.

Transparent and Thermally Stable Rare-Earth-Doped Luminescent Gallate Glass toward Passive Daytime Radiative Cooling Applications

Currently, the implementation of passive daytime radiative cooling based on zero-energy cooling methodologies primarily focuses on polymers and composite materials, whereas the available literature on all-inorganic materials is relatively few. Here, we present a novel microcrystalline glass material CaGa0.5Al1.5O4 (CGAO), doped with rare-earth elements and prepared by the high-temperature melting method. This material exhibits long-term stability at 200 °C, coupled with an effective infrared radiation cooling function, demonstrating a 4.9 °C temperature reduction at solar noon. The energy transfer and luminescence mechanisms of Tb3+ and Sm3+ doped CGAO glass have been thoroughly investigated, along with thorough assessments of its thermal stability and hardness. The glass exhibits ultrahigh light transmission in the ultraviolet to near-infrared range, with the transmittance reaching 98% in specific spectral bands. Furthermore, it demonstrates superior luminescent thermal stability, retaining 85.6% and 71.2% of its initial luminescence intensity at 423 and 523 K, respectively. The high-temperature resistance and stability and long-term cooling properties render CGAO glass as an optimal candidate for integration into future energy-efficient and sustainable building designs.

Simple preparation of PVDF composite flexible film with transparent, self-cleaning and radiative cooling properties

Daytime radiative cooling is a technique that relies on reflecting sunlight and radiating heat through mid-infrared wavelengths to cool objects. However, most daytime radiative cooling materials are not transparent, cannot be used for vehicle windows or other objects that need to retain their original color, and are susceptible to rain, dust, and other contamination, resulting in reduced cooling performance. Here, we developed a transparent, self-cleaning, radiative cooling, highly flexible PVDF composite film (PPF film), which was prepared by solvent evaporation phase conversion method and scraping coating method. The preparation method is simple and the material is easy to obtain. The obtained PPF film can be crimped to different degrees, has high flexibility, a transmittance of 94% in the visible light range (380-760 nm), and a water contact angle of 105° and above, and has self-cleaning performance. In the range of 8-13 μm, the average emissivity of the film reached 94.42%. Outdoor experiments show that, on sunny days, the cavity temperature of the device coated with PPF film glass decreases by 5-6 °C compared with that of bare glass, indicating that the PPF film has excellent radiative cooling performance. In addition, it has relatively strong mechanical properties, ultraviolet aging resistance and acid and alkali resistance. The design of the PPF film enables the radiative cooling material to be transparent, self-cleaning and flexible, with broad application prospects in the outer surface of objects requiring light transmission and cooling, such as special-shaped curved surfaces, solar panels, and architectural glass.

Solar-Adaptive Cooling Blocks Composed of Recycled Fabric

Radiative cooling technologies have had a significant impact on advancing carbon neutrality efforts by significantly improving the passive cooling efficiency. The tandem of conduction and radiation enables solar-adaptive radiative cooling through the insulating effect of materials along with solar absorption, which affects the thermal state of materials and enhances radiative thermal transfer from the surface under solar irradiation. This enhancement is achieved by utilizing the porous polymeric structure of materials, which facilitates improved conduction pathways along with solar reflectance, while maintaining the effective emission of thermal radiation. In this particular scenario, blocks, which were made of recycled fibers, offer a great opportunity as solar-adaptive cooling materials, enabling their easy deployment for cooling applications. Herein, we have fabricated a porous block using fiber wastes that combines strong solar reflectance (92%) at the 1 μm region and high thermal infrared emittance (∼75%) at the 10 μm region. The combination of effective solar reflection and thermal infrared emission allows the fiber block to achieve a high cooling performance of approximately 68 W/m2 under solar irradiation. In addition, the fiber block works effectively for insulation during the night, thereby enhancing its heat retention capabilities. The economic and environmental advantages of the fiber block make it a cost-competitive and sustainable choice for near-market cooling technologies. This design is anticipated to expand the practical application range of passive cooling.

Scalable colored Janus fabric scheme for dynamic thermal management

The art of passive thermal management lies in effectively mitigating heat stress by manipulating the optical spectra of target objects. However, a significant obstacle remains in finding a structure that can seamlessly adapt to diverse thermal environments. In response to this challenge, we posit that Janus fabrics have unique advantages for multi-scene applications when carefully engineered. A Janus fabric with an upper side exhibiting a 92% solar reflectivity and a 94% emissivity, along with a lower side possessing an infrared emissivity below 30% could enable energy savings at a large scale. It outperforms commercial products in terms of energy-saving efficiency under different climate conditions. Furthermore, the scalable manufacturing compatibility and outstanding performance make the Janus structure a promising avenue for diverse passive thermal management scenarios.

Biomimetic Cooling: Functionalizing Biodegradable Chitosan Films with Saharan Silver Ant Microstructures

The increasing occurrence of hot summer days causes stress to both humans and animals, particularly in urban areas where temperatures can remain high, even at night. Living nature offers potential solutions that require minimal energy and material costs. For instance, the Saharan silver ant (Cataglyphis bombycina) can endure the desert heat by means of passive radiative cooling induced by its triangular hairs. The objective of this study is to transfer the passive radiative cooling properties of the micro- and nanostructured chitin hairs of the silver ant body to technically usable, biodegradable and bio-based materials. The potential large-scale transfer of radiative cooling properties, for example, onto building exteriors such as house facades, could decrease the need for conventional cooling and, therefore, lower the energy demand. Chitosan, a chemically altered form of chitin, has a range of medical uses but can also be processed into a paper-like film. The procedure consists of dissolving chitosan in diluted acetic acid and uniformly distributing it on a flat surface. A functional structure can then be imprinted onto this film while it is drying. This study reports the successful transfer of the microstructure-based structural colors of a compact disc (CD) onto the film. Similarly, a polyvinyl siloxane imprint of the silver ant body shall make it possible to transfer cooling functionality to technically relevant surfaces. FTIR spectroscopy measurements of the reflectance of flat and structured chitosan films allow for a qualitative assessment of the infrared emissivity. A minor decrease in reflectance in a relevant wavelength range gives an indication that it is feasible to increase the emissivity and, therefore, decrease the surface temperature purely through surface-induced functionalities.

Pushing Radiative Cooling Technology to Real Applications

Radiative cooling is achieved by controlling surface optical behavior toward solar and thermal radiation, offering promising solutions for mitigating global warming, promoting energy saving, and enhancing environmental protection. Despite significant efforts to develop optical surfaces in various forms, five primary challenges remain for practical applications: enhancing optical efficiency, maintaining appearance, managing overcooling, improving durability, and enabling scalable manufacturing. However, a comprehensive review bridging these gaps is currently lacking. This work begins by introducing the optical fundamentals of radiative cooling and its potential applications. It then explores the challenges and discusses advanced solutions through structural design, material selection, and fabrication processes. It aims to provide guidance for future research and industrial development of radiative cooling technology.

Experimental studies on the cooling and heating performance of a highly emissive coating

In this study, the cooling effect below ambient air temperature, heat dissipation properties and heating energy efficacy of a superomniphobic self-cleaning (SSC) highly emissive (HE) coating were systematically investigated. Except at midday, the SSC-HE coating with an extremely high solar reflectance of 0.985 showed a better cooling effect than a 10-cm-thick polyurethane insulation layer. The coating substantially reduced the interior air temperature of a well-insulated system by as much as 6.9 °C. The SSC-HE coating enabled the roof surface and room temperatures of the brick bungalow to be 3.4 and 10.2 °C below the ambient air temperature, respectively. Compared with the sunshade and spray water, the SSC-HE coating exhibited better cooling effect. The SSC topcoat allowed the battery cabinet of an HE-coated distributed telecommunication base station to remain its original sub-ambient cooling effect for a long time. Regardless of the location of the HE-coated metal facility, the ultrahigh emissivity of the coating enabled it to exhibit excellent heat dissipation performance during both day and night, even under adiabatic conditions. Additionally, under identical room temperature settings, the HE-coated electric oil heater not only showed faster heating but also had heating energy efficiency of 5.9 % and 4.4 % relative to heaters coated with aluminium- and black paints, respectively. Under identical heating power consumption levels, compared to black paint-coated heater, the HE-coated heater endowed the surrounding environment with a higher equilibrium air temperature, improving the thermal comfort of the indoor environment.

Particle-Solid Transition Architecture for Efficient Passive Building Cooling

Electricity consumption for building cooling accounts for a significant portion of global energy usage and carbon emissions. To address this challenge, passive daytime radiative cooling (PDRC) has emerged as a promising technique for cooling buildings without electricity input. However, existing radiative coolers face material mismatch issues, particularly on cementitious composites like concrete, limiting their practical application. Here, we propose a cementitious radiative cooling armor based on a particle-solid transition architecture (PSTA) to overcome these challenges. The PSTA design features an asymmetric yet monolithic morphology and an all-inorganic nature, decoupling radiative cooling from building compatibility while ensuring UV resistance. In the PSTA design, nanoparticles on the surface serve as sunlight scatterers and thermal emitters, while those embedded within a cementitious substrate provide build compatibility and cohesiveness. This configuration results in enhanced interfacial bonding strength, high solar reflectance, and strong mid-infrared emittance. Specifically, the PSTA delivers an enhanced interfacial shear strength (0.93 MPa), several-fold higher than that in control groups (metal, glass, plastic) along with a cooling performance (a subambient temperature drop of ∼6.6 °C and a cooling power of ∼92.8 W under a direct solar irradiance of ∼680 W/m2) that rivals or outperforms previous reports. Importantly, the design concept of the PSTA is applicable to various particles and solids, facilitating the practical application of PDRC technology in building scenarios.

Multifunctional Radiation Conditioning Emitter for Laser and Infrared with Adaptive Radiative Cooling

With the development of technology, multifunctional multiband emitters have been paid much attention due to their wide range of applications, such as LIDAR detection, spectroscopic sensing, and infrared thermal management. However, the development of such emitters is impeded by incompatible structural requirements of different electromagnetic wavebands. Here, we demonstrate coupled modulation between near-infrared (NIR) laser-wavelength and long-wavelength-infrared by constructing a multifunctional emitter (MFE) with a structure of Al/HfO2/VO2, utilizing the phase transition of VO2. The MFE displays excellent thermal modulation capability within the 8-14 μm range, achieving a thermal insulation effect (ε8-14 μm = 0.18) at low temperatures, and heat dissipation effect (ε8-14 μm = 0.64) at high temperatures. The MFE's radiation power regulation capability is 145.06 W m-2 between a temperature of 0 to 60 °C. Moreover, the MFE possesses a large reflectivity modulation value of 0.78 at NIR laser-wavelength (1.06 μm) with a short phase transition time of 1003 ms under 3 W cm-2 laser irradiation. This study provides a guideline for the coordinated control of electromagnetic waves and intelligent collaborative thermal management through simple structural design, thus, having broad implications in energy saving and thermal information processing.

A High-Performance Passive Radiative Cooling Metafabric with Janus Wettability and Thermal Conduction

With the development of industry and global warming, passive radiative cooling textiles have recently drawn great interest owing to saving energy consumption and preventing heat-related illnesses. Nevertheless, existing cooling textiles often lack efficient sweat management capacity and wearable comfort under many practical conditions. Herein, a hierarchical cooling metafabric that integrates passive radiation, thermal conduction, sweat evaporation, and excellent wearable comfort is reported through an electrospinning strategy. The metafabric presents excellent solar reflectivity (99.7%, 0.3-2.5 µm) and selective infrared radiation (92.4%, 8-13 µm), given that the unique optical nature of materials and wettability gradient/micro-nano hierarchical structure design. The strong moisture-wicking effect (water vapor transmission (WVT) of 2985 g m-2 d-1 and directional water transport index (R) of 1029.8%) and high heat-conduction capacity can synergistically enhance the radiative cooling efficiency of the metafabric. The outdoor experiment reveals that the metafabric can obtain cooling temperatures of 13.8 °C and 19.3 °C in the dry and sweating state, respectively. Meanwhile, the metafabric saves ≈19.3% of annual energy consumption compared with the buildings with HAVC systems in Shanghai. The metafabric also demonstrates desirable breathability, mechanical strength, and washability. The cost-effective and high-performance metafabric may offer a novel avenue for developing next-generation personal cooling textiles.

Stretchable and Self-Cleaning Daytime Radiative Coolers for Human Fabric and Building Applications

Advancements in radiative cooling technology have shown significant progress in recent years. However, the limited mechanical properties of most radiative coolers greatly hinder their practical applications, particularly in the context of human cooling fabrics. In this study, we present the fabrication of facile and stretchable radiative coolers with exceptional cooling performance by utilizing the design of porous radiative coolers as guidelines for developing promising elastomer coolers. Subsequently, we employ a simple electrospinning method to fabricate these coolers, resulting in impressive solar reflectivity (∼96.1%) and infrared emissivity (over 95%). During the summer, these coolers demonstrate a maximum temperature drop of ∼9.6 °C. Additionally, the developed coolers exhibit superior hydrophobicity and mechanical properties, with a high strain capacity exceeding 700% and a stress tolerance of over 30 MPa, highlighting their potential for application in automobile textiles and cooling fabrics. Furthermore, we evaluate the radiative cooling performance of stretchable coolers using global-scale modeling, revealing their significant cooling potential across various regions worldwide.

Hierarchically Micro- and Nanostructured Polymer via Crystallinity Alteration for Sustainable Environmental Cooling

Cooling environments are a pervasive need in our society, with conventional air conditioners being the most popular approach. However, air conditioners rely heavily on electricity and Freon, a chemical that depletes ozone and contributes to greenhouse gas effects. To address this issue, passive daytime radiative coolers (PDRCs) have been proposed to achieve cooling by simultaneously reflecting sunlight and allowing internal heat to escape without electricity. Despite their potential, most high-performance PDRCs are composed of thick polymer films, which increases material costs during PDRC preparation and limits thermal transport. In this work, we introduced an economical and scalable solvent evaporation-based method to prepare a relatively thin hierarchically micro- and nanostructured poly(vinylidene fluoride-trifluoroethylene) via crystallinity alteration. Particularly, we find that the key to generating nanosized pores is to remove the water residual within the film without sample annealing, which significantly enhances the scattering efficiency across the solar spectrum. With our design, we demonstrate effective cooling of the outdoor environment, achieving a cooling temperature of Δ2.5 °C, with a film thickness of only 215 μm. Furthermore, our model suggested that applying this material could lead to annual energy savings of up to ∼39% in warmer climates across the country and up to 715 GJ nationwide. Developing effective PDRCs with reduced material thickness, such as the one discussed here, is imperative for implementing sustainable cooling solutions and reducing our carbon footprint.

Reversible Solar Heating and Radiative Cooling Devices via Mechanically Guided Assembly of 3D Macro/Microstructures

Solar heating and radiative cooling are promising solutions for decreasing global energy consumption because these strategies use the Sun (≈5800 K) as a heating source and outer space (≈3 K) as a cooling source. Although high-performance thermal management can be achieved using these eco-friendly methods, they are limited by daily temperature fluctuations and seasonal changes because of single-mode actuation. Herein, reversible solar heating and radiative cooling devices formed via the mechanically guided assembly of 3D architectures are demonstrated. The fabricated devices exhibit the following properties: i) The devices reversibly change between solar heating and radiative cooling under uniaxial strain, called dual-mode actuation. ii) The 3D platforms in the devices can use rigid/soft materials for functional layers owing to the optimized designs. iii) The devices can be used for dual-mode thermal management on a macro/microscale. The devices use black paint-coated polyimide (PI) films as solar absorbers with multilayered films comprising thin layers of polydimethylsiloxane/silver/PI, achieving heating and cooling temperatures of 59.5 and -11.9 °C, respectively. Moreover, mode changes according to the angle of the 3D structures are demonstrated and the heating/cooling performance with skin, glass, steel, aluminum, copper, and PI substrates is investigated.

A smart mask for exhaled breath condensate harvesting and analysis

Recent respiratory outbreaks have garnered substantial attention, yet most respiratory monitoring remains confined to physical signals. Exhaled breath condensate (EBC) harbors rich molecular information that could unveil diverse insights into an individual's health. Unfortunately, challenges related to sample collection and the lack of on-site analytical tools impede the widespread adoption of EBC analysis. Here, we introduce EBCare, a mask-based device for real-time in situ monitoring of EBC biomarkers. Using a tandem cooling strategy, automated microfluidics, highly selective electrochemical biosensors, and a wireless reading circuit, EBCare enables continuous multimodal monitoring of EBC analytes across real-life indoor and outdoor activities. We validated EBCare's usability in assessing metabolic conditions and respiratory airway inflammation in healthy participants, patients with chronic obstructive pulmonary disease or asthma, and patients after COVID-19 infection.

Micro/nanofabrication of heat management materials for energy-efficient building facades

Advanced building facades, which include windows, walls, and roofs, hold great promise for reducing building energy consumption. In recent decades, the management of heat transfer via electromagnetic radiation between buildings and outdoor environments has emerged as a critical research field aimed at regulating solar irradiation and thermal emission properties. Rapid advancements have led to the widespread utilization of advanced micro/nanofabrication techniques. This review provides the first comprehensive summary of fabrication methods for heat management materials with potential applications in energy-efficient building facades, with a particular emphasis on recent developments in fabrication processing and material property design. These methods include coating, vapor deposition, nanolithography, printing, etching, and electrospinning. Furthermore, we present our perspectives regarding their advantages and disadvantages and our opinions on the opportunities and challenges in this field. This review is expected to expedite future research by providing information on the selection, design, improvement, and development of relevant fabrication techniques for advanced materials with energy-efficient heat management capabilities.

Study of Manipulative Pore Formation upon Polymeric Coating for the Endowment of the Switchable Property between Passive Daytime Radiative Cooling and Heating

Passive daytime radiative cooling (PDRC) emerges as a promising cooling strategy with an attractive feature of no energy and refrigerant consumption. In the current study, for the purpose of achieving cost-efficient fabrication of a PDRC polymeric material, a microporous polymeric coating is prepared by a novel "inverse emulsion"-"breath figure" (Ie-BF) method using water droplets as pore-formation template, and the porous morphologies of both the surface and bulk layer can be dynamically manipulated by tuning the emulsion composition as well as environmental conditions. Therefore, the solar reflectivity of the Ie-BF coating can be efficiently tuned within a rather wide range (21-91%) by facile modulation of porosity and thickness. The Ie-BF coating with a thickness of only 125 μm exhibits a high solar reflectance of 85.4% and a long-wave infrared emissivity of 96.3%, realizing a subambient radiative cooling of 6.7 °C and a cooling power of ∼76 W m-2 in the open air. Moreover, by employing the reversible feature of in situ pore formation and erasure combined with the additional attachment of a carbon black layer, the composite film could be easily switched between cooling and heating modes by solvent post-treatment. This research establishes a cost-efficient strategy with high flexibility in the structural manipulation concerning the construction of porous polymeric PDRC coating.

Metal-Organic Frameworks as a Thermal Emitter for High-Performance Passive Radiative Cooling

Passive radiative cooling represents a transformative approach to achieving sustainable cooling on Earth without relying on energy consumption. In this research, the optical characteristics of five readily accessible metal-organic frameworks (MOFs): ZIF-67(Co), MOF-74(Ni), HKUST-1(Cu), MOF-801(Zr), and UiO-66(Zr) are meticulously explored. The objective is to identify the pivotal factors that influence their ability to facilitate radiative cooling. Through an in-depth analysis encompassing spectroscopic features, surface texture, and porosity, it is found that the MOFs' cooling efficacy is largely influenced by their optical bandgaps and functional groups, although other factors like chemical composition and structural characteristics remain to be considered. Notably, UiO-66(Zr) emerged as the standout performer, boasting an impressive solar reflectance of 91% and a mid-infrared emissivity of 96.8%. Remarkably, a fabric treated with UiO-66(Zr) achieved a substantial sub-ambient cooling effect, lowering temperatures by up to 5 °C and delivering a cooling power of 26 W m-2 at 300 K. The findings underscore the vast potential of MOFs in offering new opportunities to advance passive radiative cooling technologies, paving the way for their extensive application in this field.

Bioinspired Superhydrophobic All-In-One Coating for Adaptive Thermoregulation

The development of scalable and passive coatings that can adapt to seasonal temperature changes while maintaining superhydrophobic self-cleaning functions is crucial for their practical applications. However, the incorporation of passive cooling and heating functions with conflicting optical properties in a superhydrophobic coating is still challenging. Herein, an all-in-one coating inspired by the hierarchical structure of a lotus leaf that combines surface wettability, optical structure, and temperature self-adaptation is obtained through a simple one-step phase separation process. This coating exhibits an asymmetrical gradient structure with surface-embedded hydrophobic SiO2 particles and subsurface thermochromic microcapsules within vertically distributed hierarchical porous structures. Moreover, the coating imparts superhydrophobicity, high infrared emission, and thermo-switchable sunlight reflectivity, enabling autonomous transitions between radiative cooling and solar warming. The all-in-one coating prevents contamination and over-cooling caused by traditional radiative cooling materials, opening up new prospects for the large-scale manufacturing of intelligent thermoregulatory coatings.

Superhydrophobic stereocomplex-type polylactide/ultra-fine glass fibers aerogel for passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) technology offers a green and sustainable strategy for cooling, eliminating the need for external energy sources through its exceptional efficiency in heat radiation and sunlight reflection. Despite its benefits, the widespread usage of non-biodegradable PDRC materials has unfortunately caused environmental pollution and resource wastage. Furthermore, the effectiveness of outdoor PDRC materials can be significantly diminished by rainfall. In this work, a superhydrophobic composite aerogel composed of stereocomplex-type polylactide and ultra-fine glass fiber has been successfully developed through simple physical blending and freeze-drying, which exhibits low thermal conductivity (36.26 mW m-1 K-1) and superhydrophobicity (water contact angle up to 150°). Additionally, its high solar reflectance (91.68 %) and strong infrared emissivity (93.95 %) enable it to effectively lower surface temperatures during daytime, resulting in a cooling effect of approximately 3.8 °C below the ambient temperature during the midday heat of summer, with a cooling power of 68 W/m2. This aerogel offers an environmentally friendly and sustainable approach for the utilization of radiative refrigeration materials, paving the way for environmental protection and sustainable development.

Radiative cooling assisted self-sustaining and highly efficient moisture energy harvesting

Harvesting electricity from ubiquitous water vapor represents a promising route to alleviate the energy crisis. However, existing studies rarely comprehensively consider the impact of natural environmental fluctuations on electrical output. Here, we demonstrate a bilayer polymer enabling self-sustaining and highly efficient moisture-electric generation from the hydrological cycle by establishing a stable internal directed water/ion flow through thermal exchange with the ambient environment. Specifically, the radiative cooling effect of the hydrophobic top layer prevents the excessive daytime evaporation from solar absorption while accelerating nighttime moisture sorption. The introduction of LiCl into the bottom hygroscopic ionic hydrogel enhances moisture sorption capacity and facilitates ion transport, thus ensuring efficient energy conversion. A single device unit (1 cm2) can continuously generate a voltage of ~0.88 V and a current of ~306 μA, delivering a maximum power density of ~51 μW cm-2 at 25 °C and 70% relative humidity (RH). The device has been demonstrated to operate steadily outdoors for continuous 6 days.

Switchable and Tunable Radiative Cooling: Mechanisms, Applications, and Perspectives

The cost of annual energy consumption in buildings in the United States exceeds 430 billion dollars ( Science 2019, 364 (6442), 760-763), of which about 48% is used for space thermal management (https://www.iea.org/reports/global-status-report-for-buildings-and-construction-2019), revealing the urgent need for efficient thermal management of buildings and dwellings. Radiative cooling technologies, combined with the booming photonic and microfabrication technologies ( Nature 2014, 515 (7528), 540-544), enable energy-free cooling by radiative heat transfer to outer space through the atmospheric transparent window ( Nat. Commun. 2024, 15 (1), 815). To pursue all-season energy savings in climates with large temperature variations, switchable and tunable radiative coolers (STRC) have emerged in recent years and quickly gained broad attention. This Perspective introduces the existing STRC technologies and analyzes their benefits and challenges in future large-scale applications, suggesting ways for the development of future STRCs.

A photoluminescent hydrogen-bonded biomass aerogel for sustainable radiative cooling

Passive radiant cooling is a potentially sustainable thermal management strategy amid escalating global climate change. However, petrochemical-derived cooling materials often face efficiency challenges owing to the absorption of sunlight. We present an intrinsic photoluminescent biomass aerogel, which has a visible light reflectance exceeding 100%, that yields a large cooling effect. We discovered that DNA and gelatin aggregation into an ordered layered aerogel achieves a solar-weighted reflectance of 104.0% in visible light regions through fluorescence and phosphorescence. The cooling effect can reduce ambient temperatures by 16.0°C under high solar irradiance. In addition, the aerogel, efficiently produced at scale through water-welding, displays high reparability, recyclability, and biodegradability, completing an environmentally conscious life cycle. This biomass photoluminescence material is another tool for designing next-generation sustainable cooling materials.

Highly Tunable Cellulosic Hydrogels with Dynamic Solar Modulation for Energy-Efficient Windows

Smart windows that can passively regulate incident solar radiation by dynamically modulating optical transmittance have attracted increasing scientific interest due to their potential economic and environmental savings. However, challenges remain in the global adoption of such systems, given the extreme variability in climatic and economic conditions across different geographical locations. Aiming these issues, a methylcellulose (MC) salt system is synthesized with high tunability for intrinsic optical transmittance (89.3%), which can be applied globally to various locations. Specifically, the MC window exhibits superior heat shielding potential below transition temperatures, becoming opaque at temperatures above the Lower Critical Solution Temperature and reducing the solar heat gain by 55%. This optical tunability is attributable to the particle size change triggered by the temperature-induced reversible coil-to-globular transition. This leads to effective refractive index and scattering modulation, making them prospective solutions for light management systems, an application ahead of intelligent fenestration systems. During the field tests, MC-based windows demonstrated a 9 °C temperature decrease compared to double-pane windows on sunny days and a 5 °C increase during winters, with simulations predicting an 11% energy savings. The ubiquitous availability of materials, low cost, and ease-of-manufacturing will provide technological equity and foster the ambition toward net-zero buildings.