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Passive climate regulation with transpiring wood for buildings with increased energy efficiency

Buildings are significant end-users of global energy. About 20% of the energy consumption worldwide is used for maintaining a comfortable indoor climate. Therefore, passive systems for indoor temperature and humidity regulation that can respond to environmental changes are very promising to reduce buildings' energy consumption. We developed a process to improve the responsiveness of wood to humidity changes by laser-drilling microscopic holes and incorporating a hygroscopic salt (calcium chloride). The resulting "transpiring wood" displays superior water adsorption capacity and high moisture exchange rate, allowing regulation of humidity and temperature by the exchange of moisture with the surrounding air. We proved that the hygrothermal performance of transpiring wood can be used to regulate indoor climate, with associated energy savings, for various climate types, thus favoring its application in the building sector. The reduction of temperature fluctuations, thanks to the buffering of temperature peaks, can lead to an indirect energy saving of about 10% for cooling and between 4-27% for heating depending on the climate. Furthermore, our transpiring wood meets different sustainability criteria, from raw materials to the fabrication process, resulting in a product with a low overall environmental impact and that is easy to recycle.

Open Access
Graphene-interfaced flexible and stretchable micro–nano electrodes: from fabrication to sweat glucose detection

Flexible and stretchable wearable electronic devices have received tremendous attention for their non-invasive and personal health monitoring applications. These devices have been fabricated by integrating flexible substrates and graphene nanostructures for non-invasive detection of physiological risk biomarkers from human bodily fluids, such as sweat, and monitoring of human physical motion tracking parameters. The extraordinary properties of graphene nanostructures in fully integrated wearable devices have enabled improved sensitivity, electronic readouts, signal conditioning and communication, energy harvesting from power sources through electrode design and patterning, and graphene surface modification or treatment. This review explores advances made toward the fabrication of graphene-interfaced wearable sensors, flexible and stretchable conductive graphene electrodes, as well as their potential applications in electrochemical sensors and field-effect-transistors (FETs) with special emphasis on monitoring sweat biomarkers, mainly in glucose-sensing applications. The review emphasizes flexible wearable sweat sensors and provides various approaches thus far employed for the fabrication of graphene-enabled conductive and stretchable micro-nano electrodes, such as photolithography, electron-beam evaporation, laser-induced graphene designing, ink printing, chemical-synthesis and graphene surface modification. It further explores existing graphene-interfaced flexible wearable electronic devices utilized for sweat glucose sensing, and their technological potential for non-invasive health monitoring applications.

Fabricating defogging metasurfaces via a water-based colloidal route.

Metamaterials possess exotic properties that do not occur in nature and have attracted significant attention in research and engineering. Two decades ago, the field of metamaterials emerged from linear electromagnetism, and today it encompasses a wide range of aspects related to solid matter, including electromagnetic and optical, mechanical and acoustic, as well as unusual thermal or mass transport phenomena. Combining different material properties can lead to emergent synergistic functions applicable in everyday life. Nevertheless, making such metamaterials in a robust, facile, and scalable manner is still challenging. This paper presents an effective protocol allowing for metasurfaces offering a synergy between optical and thermal properties. It utilizes liquid crystalline suspensions of nanosheets comprising two transparent silicate monolayers in a double stack, where gold nanoparticles are sandwiched between the two silicate monolayers. The colloidally stable suspension of nanosheets was applied in nanometre-thick coatings onto various substrates. The transparent coatings serve as absorbers in the infrared spectrum allowing for the efficient conversion of sunlight into heat. The peculiar metasurface couples plasmon-enhanced adsorption with anisotropic heat conduction in the plane of the coating, both at the nanoscale. Processing of the coating is based on scalable and affordable wet colloidal processing instead of having to apply physical deposition in high vacuum or lithographic techniques. Upon solar irradiation, the colloidal metasurface is quickly (60% of the time taken for the non-coated glass) heated to the level where complete defogging is assured without sacrificing transparency in the visible range. The protocol is generally applicable allowing for intercalation of any nanoparticles covering a range of physical properties that are then inherited to colloidal nanosheets. Because of their large aspect ratio, the nanosheets will inevitably orient parallel to any surface. This will allow for a toolbox capable of mimicking metamaterial properties while assuring facile processing via dip coating or spray coating.