The synthesis of CoNi@SiO2 @TiO2 core-shell and CoNi@Air@TiO2 yolk-shell microspheres is reported for the first time. Owing to the magnetic-dielectric synergistic effect, the obtained CoNi@SiO2 @TiO2 microspheres exhibit outstanding microwave absorption performance with a maximum reflection loss of -58.2 dB and wide bandwidth of 8.1 GHz (8.0-16.1 GHz, < -10 dB).
Oriented
self-assembly between inorganic nanocrystals and surfactants is emerging
as a route for obtaining new mesocrystalline semiconductors. However,
the actual synthesis of mesoporous semiconductor mesocrystals with
abundant surface sites is extremely difficult, and the corresponding
new physical and chemical properties arising from such an intrinsic
porous mesocrystalline nature, which is of fundamental importance
for designing high-efficiency nanostructured devices, have been rarely
explored and poorly understood. Herein, we report a simple evaporation-driven
oriented assembly method to grow unprecedented olive-shaped mesoporous
TiO2 mesocrystals (FDU-19) self-organized by ultrathin
flake-like anatase nanocrystals (∼8 nm in thickness). The mesoporous
mesocrystals FDU-19 exhibit an ultrahigh surface area (∼189
m2/g), large internal pore volume (0.56 cm3/g),
and abundant defects (oxygen vacancies or unsaturated Ti3+ sites), inducing remarkable crystallite-interface reactivity. It
is found that the mesocrystals FDU-19 can be easily fused in situ
into mesoporous anatase single crystals (SC-FDU-19) by annealing in
air. More significantly, by annealing in a vacuum (∼4.0 ×
10–5 Pa), the mesocrystals experience an abrupt
three-dimensional to two-dimensional structural transformation to
form ultrathin anatase single-crystal nanosheets (NS-FDU-19, ∼8
nm in thickness) dominated by nearly 90% exposed reactive (001) facets.
The balance between attraction and electrostatic repulsion is proposed
to determine the resulting geometry and dimensionality. Dye-sensitized
solar cells based on FDU-19 and SC-FDU-19 samples show ultrahigh photoconversion
efficiencies of up to 11.6% and 11.3%, respectively, which are largely
attributed to their intrinsic single-crystal nature as well as high
porosity. This work gives new understanding of physical and chemical
properties of mesoporous semiconductor mesocrystals and opens up a
new pathway for designing various single-crystal semiconductors with
desired mesostructures for applications in catalysis, sensors, drug
delivery, optical devices, etc.
Preparation of reliable, stable, and highly responsive gassensing devices for the detection of acetone has been considered to be a key issue for the development of accurate disease diagnosis systems via exhaled breath. In this paper, novel CeO 2 nanodot-decorated WO 3 nanowires are successfully synthesized through a sequential hydrothermal and thermolysis process. Such CeO 2 nanodot-decorated WO 3 nanowires exhibited a remarkable enhancement in acetone-sensing performance based on a miniaturized micro-electromechanical system device, which affords high response (S = 1.30−500 ppb, 1.62−2.5 ppm), low detection limit (500 ppb), and superior selectivity toward acetone. The improved performance of the acetone sensor is likely to be originated from the fast carrier transportation of WO 3 nanowires, the formation of WO 3 −CeO 2 heterojunctions, and the existence of large amounts of oxygen vacancies in CeO 2 . The improved reaction thermodynamics and sensing mechanisms have also been revealed by the specific band alignment and X-ray photoelectron spectroscopy analysis.
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