Metal@semiconductor core−shell nanoparticles (NPs) are widely used in photocatalysts, sensors, and optical applications owing to their unique metal−semiconductor interface and the integration of the properties from both core and shell materials. Although many efforts have been made toward the precise synthesis of Au@Cu 2 O core−shell structures, the chemical stability of Au@Cu 2 O aqueous suspensions, which is of great significance in many related applications, is not mentioned in any published research. Herein we report the synthesis of Au@Cu 2 O core−shell NPs with small shell thickness from 2 to 40 nm through a wet-chemistry method. The UV−vis absorption properties are found to be tunable with Cu 2 O thickness in the range of 2−40 nm. Furthermore, the chemical stability of Au@Cu 2 O core−shell nanoparticle suspensions in water/ethanol mixed solvents is investigated. It is found that water/ethanol mixed solvents with a larger amount of water are more likely to deteriorate the stability of Au@Cu 2 O NPs by oxidizing Cu 2 O to CuO. The results from this work may provide useful information for the preparation of metal@Cu 2 O water-based suspensions that are expected to be used for SERS, photocatalyst, or photothermal applications.

The most commonly used phase change materials (PCMs), like organic compounds and inorganic salts, were limited in application by their low thermal conductivity. Herein, for the first time, alumina-encapsulated metallic Snbased PCMs, named Sn@Al 2 O 3 , were successfully fabricated with tunable size (60−2000 nm) by a facile process from lowcost chemicals. The robust fabrication process consists of a surfactant-free solvothermal synthesis of SnO 2 spheres, boehmite treatment on SnO 2 spheres, calcination in the air, and the final hydrogen reduction to transform SnO 2 to metallic Sn, endowing the PCMs with high potential for mass production. The as-obtained Sn@Al 2 O 3 showed a core−shell structure, in which a main metallic Sn core located in the center covered with an Al 2 O 3 shell with small Sn nanoparticles distributed inside. The boehmite treatment, in which the penetration of aluminum species into SnO 2 spheres played an important role, was found to be responsible for the unique structure formation of final Sn@Al 2 O 3 . The understanding of structure formation mechanism gives the possibilities of a new facile way for the synthesis of metal nanoparticles and particle-distributed nanostructures. The obtained Sn@Al 2 O 3 particles not only have high PCM content (92.37 wt %) but also show a stable thermal behavior and morphology during 100 melt−freeze cycles in the air atmosphere. Furthermore, the low melting temperature of the PCM core, combined with high thermal conductivity of both core material (Sn, 66.8 W m −1 K −1 ) and shell material (Al 2 O 3 , 35 W m −1 K −1 ), makes Sn@Al 2 O 3 potentially suitable for rapid thermal energy storage in the range 100−300 °C.

Black TiO2 nanoparticles (b-TiO2) with superior solar–thermal water evaporation performance are prepared using a one-step solution plasma process (SPP) in ambient conditions. It is found that radicals that are generated during SPP play a critical role in b-TiO2 formation by comparing several water–alcohol electrolyte environments for the SPP synthesis. Our results show that the radical-induced formation of a black TiO2–x layer on the Ti electrode is necessary for b-TiO2 formation, which was ignored in previous studies. A two-step mechanism for b-TiO2 formation in SPP synthesis is proposed: (I) preoxidation of a Ti electrode surface; and (II) quenching and aggregation of sputtered molten TiO x clusters to form b-TiO2 particles. The b-TiO2-loaded hydrophobic mesh exhibited high water evaporation rates in the solar–thermal water evaporation experiments, which were 1.2, 1.4, and 2.3 times higher than that of the control group without using mesh at 1000, 2000, and 5000 W·m–2, respectively. The understanding in this study may inspire strategies for the facile synthesis of self-structured modified metal-oxide materials for more efficient solar energy harvesting in solar–thermal conversion applications.

We report a facile method for preparing a silica (SiO 2 )-based material containing Sn nanoparticles (NPs) distributed inside for enhancing the thermal cyclic stability of the inserted Sn NPs. Absorption of a Sn precursor (i.e., an aqueous SnCl 2 solution) into a mesoporous SiO 2 matrix resulted in confinement of the Sn precursor in a mesoporous SiO 2 matrix. Hydrogen thermal reduction of the above composite yielded Sn nanoparticles with a diameter of ca. 30 nm uniformly distributed inside porous SiO 2 (p-SiO 2 ) spheres: Sn NPs@p-SiO 2 . Our investigation of the transformation of the porous SiO 2 structure to hold Sn NPs revealed that the process was closely related to the transformation of the amorphous hydrolyzed Sn precursor into Sn oxides followed by, probably, the rearrangement of the SiO 2 matrix via its interaction with the melting Sn. This led to the formation of stable Sn NPs@p-SiO 2 . The SiO 2 matrix effectively prevented the coalescence of the Sn NPs, and the obtained product exhibited negligible changes in melting behavior during the second to 100th cycle of a freeze− melt cycle test.

A new class of phase change materials based on encapsulated metal and alloy micro- and nano-particles with advanced thermophysical properties for cyclable and stable thermal energy storage/release is highlighted.