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Cooling in buildings is vital to human well-being but inevitability consumes significant energy, adding pressure on achieving carbon neutrality. Thermally superinsulating aerogels are promising to isolate the heat for more energy-efficient cooling. However, most aerogels tend to absorb the sunlight for unwanted solar heat gain, and it is challenging to scale up the aerogel fabrication while maintaining consistent properties. Herein, we develop a thermally insulating, solar-reflective anisotropic cooling aerogel panel containing in-plane aligned pores with engineered pore walls using boron nitride nanosheets by an additive freeze-casting technique. The additive freeze-casting offers highly controllable and cumulative freezing dynamics for fabricating decimeter-scale aerogel panels with consistent in-plane pore alignments. The unique anisotropic thermo-optical properties of the nanosheets combined with in-plane pore channels enable the anisotropic cooling aerogel to deliver an ultralow out-of-plane thermal conductivity of 16.9 mW m −1 K −1 and a high solar reflectance of 97%. The excellent dual functionalities allow the anisotropic cooling aerogel to minimize both parasitic and solar heat gains when used as cooling panels under direct sunlight, achieving an up to 7 °C lower interior temperature than commercial silica aerogels. This work offers a new paradigm for the bottom-up fabrication of scalable anisotropic aerogels towards practical energy-efficient cooling applications. Scaling up anisotropic freeze-casting processes can be challenging due to the temperature gradient farther from the cold source. Here, authors report an additive freeze-casting technique able to produce large-scale aerogel panels and demonstrate it towards practical passive cooling applications.

HighlightsHighly porous aerogel with longitudinally aligned channels and whisker-like ligaments is constructed by solvent-assisted unidirectional freezing.The thermal insulation and solar reflection capabilities of the composite aerogel reach a state-of-the-art level.The composite aerogel capable of infrared stealth and temperature preservation presents great potential for application in energy-saving buildings.With the mandate of worldwide carbon neutralization, pursuing comfortable living environment while consuming less energy is an enticing and unavoidable choice. Novel composite aerogels with super thermal insulation and high sunlight reflection are developed for energy-efficient buildings. A solvent-assisted freeze-casting strategy is used to produce boron nitride nanosheet/polyvinyl alcohol (BNNS/PVA) composite aerogels with a tailored alignment channel structure. The effects of acetone and BNNS fillers on microstructures and multifunctional properties of aerogels are investigated. The acetone in the PVA suspension enlarges the cell walls to suppress the shrinkage, giving rise to a lower density and a higher porosity, accompanied with much diminished heat conduction throughout the whole product. The addition of BNNS fillers creates whiskers in place of disconnected transverse ligaments between adjacent cell walls, further ameliorating the thermal insulation transverse to the cell wall direction. The resultant BNNS/PVA aerogel delivers an ultralow thermal conductivity of 23.5 mW m−1 K−1 in the transverse direction. The superinsulating aerogel presents both an infrared stealthy capability and a high solar reflectance of 93.8% over the whole sunlight wavelength, far outperforming commercial expanded polystyrene foams with reflective coatings. The anisotropic BNNS/PVA composite aerogel presents great potential for application in energy-saving buildings.

Spider-capture-silk (SCS) can directionally capture and transport water from humid air relying on the unique geometrical structure. Although there have been adequate reports on the fabrication of artificial SCSs from petroleum-based materials, it remains a big challenge to innovate bio-based SCS mimicking fibers with high-performance fog collection ability and efficiency simultaneously. Herein, we report an eco-friendly and economical fiber system for water collection by coating gelatin on degummed silk. Compared to the previously reported fibers with the best fog collection ability (~ 13.10 μL), Gelatin on silk fiber 10 (GSF10) can collect larger water droplet (~ 16.70 μL in 330 s) with ~ 98% less mass. Meanwhile, the water collection efficiency of GSF10 demonstrates ~ 72% and ~ 48% enhancement to the existing best water collection polymer coated SCS fibers and spidroin eMaSp2 coated degummed silk respectively in terms of volume-to-TCL (vapor–liquid-solid three-phase contact line) index. The simultaneous function of superhydrophilicity, surface energy gradient, and ~ 65% water-induced volume swelling of the gelatin knots are the key factors in advancing the water collection performance. Abundant availability of feedstocks and ~ 75% improved space utilization guarantee the scalability and practical application of such bio-based fiber.Graphic Abstract

Background The psychological well-being of university students is an important factor in successfully coping with the demands of academic life. This study aimed to assess the impact of a peer-led intervention of mental health promotion combined with coping-strategy-based group workshops on mental health awareness and help-seeking behavior among university students in Hong Kong. Method A mixed-method concurrent design was used for this study. Quantitative data, based on one-group pretest-posttest design, were collected using Mental Health Knowledge Schedule Questionnaire to assess mental health awareness, and Attitude Towards Seeking Professional Help Questionnaire-Short Form to examine help-seeking behavior of university students from The Hong Kong Polytechnic University. Qualitative data were collected from written post-activity reflections and focus group discussions which were thematically analyzed. Results A total of 62 university students (mean age: 23.2 ± 5.1 years) were included in this study. Mental health awareness was significantly improved ( p  = 0.015, 95% Confidence Interval of − 2.670, − 0.297) after program implementation. Help-seeking behavior mean score increased from pretest to posttest, however, no significant difference was observed ( p  = 0.188, 95% CI = − 1.775, 0.355). Qualitative analysis revealed that the program helped participants learn about coping strategies to help themselves and others with mental health challenges. Conclusions The peer-led intervention provided a positive impact through increased mental health awareness and knowledge of coping strategies on self-help and helping others among university students. Further study could focus on the impact of the program when applied regularly throughout the entire academic year.

Tubuliform silk is one of the seven different types of spider silks, which is well known for its unique tensile behaviour with Flat Tensile Stress–Strain (FTSS) curve. It is found that anisotropic microstructure of β-sheets is responsible for this property. In recent years, bioinspired approaches to engineer fibres supported by modern manufacturing systems have been attracting considerable interest. The present paper aims to investigate a strategy to biomimic the FTSS behaviour of tubuliform silk in synthetic polymer composite fibres by blending polyurethane (PU) and regenerated silk fibroin (RSF) at different ratios. Wet spinning of composite fibres results in the reconstruction of β-sheets in the synthetic fibre matrix. PU/RSF composite fibre at a ratio of 75/25 produce a tensile curve with FTSS characteristics. Secondary structural changes in RSF and interchain directions of β-sheets within the fibre are studied using Fourier Transform Infra-red (FTIR) spectroscopy and Transmission Electron Microscopy (TEM), respectively. Interestingly, results of TEM patterns confirm transverse anisotropic properties of RSF β-sheets. The composite fibres also display tuneable mechanical properties with respect to RSF contents.

An antibacterial agent (MgO 2 ) was synthesised using 0.2 and 0.4 M concentrations of MgCl 2 ·6H 2 O and H 2 O 2 , which was subsequently applied to cotton fabric using a conventional pad-dry-cure method in order to achieve antibacterial properties against S. aureus and E. Coli microorganisms. The antibacterial effect against these microorganisms was investigated using a zone of inhibition test and the percent reduction method. The outcomes of these measurements showed that when the cotton fabric was treated with the reaction product of MgCl 2 ·6H 2 O and H 2 O 2 , it retained 90–93% antibacterial activity against S. aureus and 89–91% against E. coli bacteria. This antibacterial effect against these microorganisms was attributed to the presence of reactive oxygen species and Mg ions on the treated cotton fabric. Long term antibacterial effects against S. aureus and E. coli microorganisms were recorded for up to 70 laundering cycles, and the amounts of retained bound peroxide and Mg ions on the finished specimens were measured using iodimetric titration and MP-AES measurements. Additionally, the properties of synthesised MgO 2 crystalline powder and treated cotton fabric were studied using UV–Vis, EDX, FTIR spectroscopy, and SEM measurements. The influence of the MgO 2 application on mechanical properties such as tensile strength, tear strength, whiteness index, and crease recovery angle of the treated cotton fabric was also analysed. The results obtained clearly confirmed that the treated cotton fabric possessed antibacterial effects for up to 70 laundering cycles. This is likely due to the presence of the required amount of oxidative species and Mg ions on the treated cotton fabrics. The FTIR and EDX results showed that the presence of these key elements (oxygen containing groups) was responsible for the antibacterial property of the finished fabrics. The whiteness index and tensile strength were improved after treatment with MgO 2 , although tear strength and flexibility of treated specimens were decreased after treatment.