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Volumetric solar steam generation has attracted substantial interest due to its low cost, minimum carbon footprint and wide application in many areas including clean water production, desalination, and wastewater treatment. However, the efficiency of volumetric solar evaporation is still low and there is an urgent need to investigate the fundamental of the limitation of low efficiency and find a new strategy to improve the solar evaporation efficiency. In the current work, antimony doped tin oxide@carbon (ATO@C) nanofluids were prepared by a hydrothermal approach. The ATO@C nanofluids exhibit broad-band and high absorption in the solar spectrum due to the complementary effect of C (in visible region) and ATO (in the near infrared region). ATO@C nanofluids of 0.3 wt% could harvest 99.9% of the incident solar energy within 1 cm penetration distance. The photothermal conversion efficiency is 97.8%. The coupling relationship between the solar harvesting and the energy distribution was revealed. Increasing mass fraction and reducing thickness can localize the heat in the surface layer of nanofluids and thus minimize the energy consumption in heating water (internal energy) and therefore improve the solar evaporation efficiency. A high evaporation efficiency of 88.6% was achieved in this way.

Broad-band absorbers are very important for solar thermal utilization. However, seeking ideal solar absorbers whose absorption spectra match well with the solar spectrum is still a great challenge. In this work, zirconium carbide (ZrC) nanofluids with broad-band absorption characteristic were prepared by milling and dispersing ZrC nanoparticles in water. The ZrC nanoparticles show strong optical absorption in the range from 300 to 2000 nm. At a penetration distance of 1 cm, the ZrC nanofluids of 0.02 wt% can absorb almost 100% of the solar irradiation in the full spectrum and the solar weighted absorption coefficient (Am) is 0.99. The results indicate that the ZrC nanofluids of 0.02 wt% are very close to the ideal solar irradiation absorbers. The photo-thermal conversion efficiency of the ZrC nanofluids was evaluated by a direct method focusing on the nanofluids themselves instead of indirectly represented by the efficiency of the solar thermal collector as presented in the previous reports. By recording and analyzing the temperature rise of the nanofluids under the illumination of a solar simulator, the photo-thermal conversion efficiency for the ZrC nanofluids of 0.02 wt% was determined to be 92%. The high efficiency is attributed to the broad-band absorption of the ZrC nanoparticles.

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.

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.

The efficiency and effectiveness of solar energy capture and storage are to a large extent functions of the heat transfer and storage capacity of the medium used. This paper investigates the potential of using carbon nanotube (CNT)-glycol nanosuspension as such a medium, prepared by freeze drying-ultrasonic dispersing after oxidation treatment with HNO3. The influences of the mass fraction of CNTs glycol nanofluids and temperatures on photo-thermal properties, thermal conductivities and rheological behavior were investigated. The results show that CNTs with oxidation treatment exhibited good dispersing performance. Strong optical absorption of the CNTs glycol nanofluids was detected in the range of 200–2500 nm. At room temperature, 18% enhancement was found in the photo-thermal conversion efficiency of the 0.5% mass fraction CNTs glycol nanofluids in comparison to the basic fluids, without significant increase in viscosity. At 55 °C, CNTs glycol nanofluids with 4.0% mass fraction exhibited much lower viscosity and 25.4% higher thermal conductivity in comparison to that of pure glycol at room temperature.

Nanofluid is a new class of heat transfer fluids containing nano-sized particles, fibers, or tubes that are stably suspended in a carrier liquid. In this article, carbon black nanofluids were prepared by dispersing the pre-treated carbon black powder into ethylene glycol. The thermal conductivities, rheological behaviors and photo-thermal properties of the nanofluids were investigated. The results showed that the thermal conductivities of carbon black nanofluids increased with particle loading and temperature. The nanofluids performed a shear thinning behavior. The shear viscosity increased with particle loading while decreased with temperature at the same shear rate. Carbon black nanofluids had good absorption ability of solar energy and could effectively enhance the solar absorption efficiency.

Nanofluid is a new class of heat transfer fluids containing nano-sized particles, fibers, or tubes that are stably suspended in a carrier liquid. In this article, carbon black nanofluids were prepared by dispersing the pre-treated carbon black powder into ethylene glycol. The thermal conductivities, rheological behaviors and photo-thermal properties of the nanofluids were investigated. The results showed that the thermal conductivities of carbon black nanofluids increased with particle loading and temperature. The nanofluids performed a shear thinning behavior. The shear viscosity increased with particle loading while decreased with temperature at the same shear rate. Carbon black nanofluids had good absorption ability of solar energy and could effectively enhance the solar absorption efficiency. © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of MRS-Taiwan

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.

Manganese ferrite (MnFe2O4) hollow microspheres were synthesized through a sacrificial template approach using manganese carbonate (MnCO3) microspheres as sacrificial templates. Different from the literatures, the synthesis of MnFe2O4 hollow spheres was achieved through a one-pot hydrothermal process without subsequent calcination process. The temperature and reaction time of the hydrothermal process were set to be 180 °C and 8 h. The formation mechanism of the MnFe2O4 hollow microspheres was also investigated. Results indicate that the average diameter of the as-synthesized MnFe2O4 hollow microspheres is 1.2 μm. The shells of the hollow microspheres are composed of nanoparticles. During hydrothermal process, Mn2+ ions diffused outward and resulted in shell materials of MnFe2O4, thus MnCO3 templates were consumed and MnFe2O4 hollow microspheres were obtained.

A hydrogen arc plasma method for preparing nano-particles was introduced. A method which possesses higher production rate, lower energy consumption and is suitable for preparation of nano-particles of metals with high melting point. The microstructures and properties of the nano-particles prepared by this method were reported.

Nanoscale copper and silver were synthesized by the H2+Ar arc plasma method. During the synthesis, hydrogen molecules were dissociated into hydrogen atoms and stored in the particles. At the same time, nanometer copper and silver particles were prepared by the inert gas condensation method whose power is about identical with the hydrogen arc plasma method. Various specimens were annealed respectively at low temperature. The particle size was measured by a transmission electron microscopy. A proper temperature was chosen to prepare the standard specimen.

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.

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.