Scalable and Flexible Electrospun Film for Daytime Subambient Radiative Cooling.

Daytime radiative cooling materials reflect solar light and dissipate heat directly to outer space without any energy consumption, and thus, have attracted much attention due to the potential applications in many fields. Recently, elaborately designed photonic crystal and metamaterials have been reported for daytime subambient radiative cooling. However, such materials and structures have the drawbacks of complex shapes, inflexibility, high cost, and limitation in scaling up. It is also extremely difficult to apply such materials to buildings, vehicles, and other objects having complex surfaces. Here, a scalable and flexible hybrid film for daytime subambient radiative cooling was fabricated by a facile electrospinning method. The hybrid film consists of poly(vinylidene fluoride)/alumina (PVDF/Al2O3) fibers with diameters of 0.5-2.5 µm. Owing to the efficient scattering by fibers and Al2O3 nanoparticles, the hybrid film exhibits an extremely high average solar reflectance of 0.97. A high average atmospheric window emittance of 0.95 is simultaneously achieved due to the molecular vibrations of PVDF and the phonon polariton resonance of Al2O3 nanoparticles. The composite film delivers an average net radiative cooling power of 82.7 W/m2, and a temperature drop of up to 4.0 °C under direct sunlight. The hybrid film exhibits remarkable radiative cooling performance under different weather conditions including sunny, cloudy, overcast, and rainy. It can be used not only for cooling buildings and vehicles but also for delaying the melting of glaciers. This work demonstrates a promising method for scale-up production of the radiative cooling film with high performance.

Magnetic resonance imaging and photothermal conversion properties of Gd-C nanocomposites for interstitial lymphography.

Dual-functional agents for magnetic resonance imaging (MRI) guided photothermal therapy (PTT) of lymph cancer are highly desired. Signal enhancement, selectivity between lymphatic nodes/vessels and blood vessels, and photothermal conversion property are the criteria for such dual-functional agent. In the current work, we demonstrated the potential of Gd-C nanocomposites as dual-functional agents for the MRI and PTT of lymph node cancer. Gd-C nanocomposites were synthesized via a hydrothermal carbonization approach with gadolinium chloride as Gd source and citric acid (CA) as C source. The particle size of the nanocomposites ranges from 40 to 100 nm which is smaller than the intercellular space of lymphatic vessels but much larger than that of the blood vessels. The nanocomposites were successfully applied to the MRI of cervical lymph nodes of rabbits. The signal enhancement of the lymph nodes reached the maximum value of 434% at 10 min after injection, without displaying any blood vessel. The Gd-C nanocomposites also exhibited strong photothermal conversion effect. Under the illumination of an 808 nm laser, the aqueous suspension containing 1.0 wt % Gd-C nanocomposites gave a maximum temperature rise of 28.2 °C and a light utilization efficiency of 30.4%. The results indicate that Gd-C nanocomposites have significant potential in MRI guided PTT of lymph cancer.

Broadband absorption and enhanced photothermal conversion property of octopod-like Ag@Ag2S core@shell structures with gradually varying shell thickness.

Photothermal conversion materials have promising applications in many fields and therefore they have attracted tremendous attention. However, the multi-functionalization of a single nanostructure to meet the requirements of multiple photothermal applications is still a challenge. The difficulty is that most nanostructures have specific absoprtion band and are not flexible to different demands. In the current work, we reported the synthesis and multi-band photothermal conversion of Ag@Ag2S core@shell structures with gradually varying shell thickness. We synthesized the core@shell structures through the sulfidation of Ag nanocubes by taking the advantage of their spatially different reactivity. The resulting core@shell structures show an octopod-like mopgorlogy with a Ag2S bulge sitting at each corner of the Ag nanocubes. The thickness of the Ag2S shell gradually increases from the central surface towards the corners of the structure. The synthesized core@shell structures show a broad band absorption spectrum from 300 to 1100 nm. Enhanced photothermal conversion effect is observed under the illuminations of 635, 808, and 1064 nm lasers. The results indicate that the octopod-like Ag@Ag2S core@shell structures have characteristics of multi-band photothermal conversion. The current work might provide a guidance for the design and synthesis of multifunctional photothermal conversion materials.

Optical Absorption and Photo-Thermal Conversion Properties of CuO/H2O Nanofluids.

Stable CuO/H2O nanofluids were synthesized in a wet chemical method. Optical absorption property of CuO/H2O nanofluids was investigated with hemispheric transmission spectrum in the wavelength range from 200 nm to 2500 nm. Photo-thermal conversion property of the CuO/H2O nanofluids was studied with an evaluation system equipped with an AUT-FSL semiconductor/solid state laser. The results indicate that CuO/H2O nanofluids have strong absorption in visible light region where water has little absorption. Under the irradiation of laser beam with a wavelength of 635 nm and a power of 0.015 W, the temperature of CuO/H2O nanofluids with 1.0% mass fraction increased by 5.6 °C within 40 seconds. Furthermore, the temperature elevation of CuO/H2O nanofluids was proved to increase with increasing mass fractions. On the contrast, water showed little temperature elevation under the identical conditions. The present work shows that the CuO/H2O nanofluids have high potential in the application as working fluids for solar utilization purpose.

Photo-Thermal Conversion of Copper Sulfide Hollow Structures with Different Shape and Thickness.

In the current paper, we report the synthesis of spherical and cubic copper sulfide hollow structures, as well as the influence of shape and thickness on the photo-thermal conversion of the as-synthesized products. Copper sulfide hollow structures of different thickness were synthesized base on a sacrificial template strategy using spherical and cubic Cu2O precursors as templates. Optical absorption of the as-synthesized products was investigated with UV-Vis spectrometer. Photo-thermal conversion property was studied with a lab-made evaluation system equipped with an AUT-FSL semiconductor/solid state laser. The results indicate that the as-prepared products exhibited significant absorption in visible light regions. Under the irradiation of laser beam with a wavelength at 635 nm and a power of 0.015 W, the temperature elevations of the aqueous suspensions containing 0.24% mass fraction of spherical and cubic copper sulfide hollow structures were measured to be 5 °C and 6 °C within 60 seconds, respectively. On the contrast, water showed little temperature elevation under the same conditions.

Thermal properties of carbon black aqueous nanofluids for solar absorption.

In this article, carbon black nanofluids were prepared by dispersing the pretreated carbon black powder into distilled water. The size and morphology of the nanoparticles were explored. The photothermal properties, optical properties, rheological behaviors, and thermal conductivities of the nanofluids were also investigated. The results showed that the nanofluids of high-volume fraction had better photothermal properties. Both carbon black powder and nanofluids had good absorption in the whole wavelength ranging from 200 to 2,500 nm. The nanofluids exhibited a shear thinning behavior. The shear viscosity increased with the increasing volume fraction and decreased with the increasing temperature at the same shear rate. The thermal conductivity of carbon black nanofluids increased with the increase of volume fraction and temperature. Carbon black nanofluids had good absorption ability of solar energy and can effectively enhance the solar absorption efficiency.

Preparation and thermal conductivity of CuO nanofluid via a wet chemical method.

In this article, a wet chemical method was developed to prepare stable CuO nanofluids. The influences of synthesis parameters, such as kinds and amounts of copper salts, reaction time, were studied. The thermal conductivities of CuO nanofluids were also investigated. The results showed that different copper salts resulted in different particle morphology. The concentration of copper acetate and reaction time affected the size and shape of clusters of primary nanoparticles. Nanofluids with different microstructures could be obtained by changing the synthesis parameters. The thermal conductivities of CuO nanofluids increased with the increase of particle loading.

Evaluation of electrospun polyvinyl chloride/polystyrene fibers as sorbent materials for oil spill cleanup.

A novel, high-capacity oil sorbent consisting of polyvinyl chloride (PVC)/polystyrene (PS) fiber was prepared by an electrospinning process. The sorption capacity, oil/water selectivity, and sorption mechanism of the PVC/PS sorbent were studied. The results showed that the sorption capacities of the PVC/PS sorbent for motor oil, peanut oil, diesel, and ethylene glycol were 146, 119, 38, and 81 g/g, respectively. It was about 5-9 times that of a commercial polypropylene (PP) sorbent. The PVC/PS sorbent also had excellent oil/water selectivity (about 1000 times) and high buoyancy in the cleanup of oil over water. The SEM analysis indicated that voids among fibers were the key for the high capacity. The electrospun PVC/PS sorbent is a better alternative to the widely used PP sorbent for oil spill cleanup.

Novel synthesis of bismuth tungstate hollow nanospheres in water-ethanol mixed solvent.

Bi(2)WO(6) hollow nanospheres were prepared in a sacrificial templates approach by converting the reaction medium from aqueous solution to a mixed solvent of water and ethanol.