Compared
with CsPbBr3 nanocrystals (NCs), the study
of the structure and physical properties of Cs4PbBr6 and CsPb2Br5 NCs is not sufficient.
In this paper, CsPbBr3, CsPb2Br5,
and Cs4PbBr6 NCs were prepared by a hot-injection
method using oleylamine (OAm) and oleic acid (OA) without adding other
ligands. The evolution of phase composition, morphology, and photoluminescence
(PL) property was investigated. It is found that rhombohedral Cs4PbBr6 was created at low temperature with low Pb/Cs
ratios and short reaction time. The CsPbBr3 phase was then
obtained with increasing Pb/Cs ratios at high temperature through
the reaction of Cs4PbBr6 and PbBr2. The evolution of phase composition occurred with time to create
CsPbBr3, CsPb2Br5, and Cs4PbBr6 NCs. For a Pb/Cs molar ratio of 3, CsPbBr3 was first obtained at 180 °C. However, the resulting sample
is the CsPb2Br5 phase after 120 min. The excess
PbBr2 is a key for such phase change because no similar
phenomenon was observed in the case of molar ratio of Pb/Cs of 2.
At low temperature (e.g., 140 and 160 °C), the rhombohedral Cs4PbBr6 phase was obtained and then reacted with
PbBr2 to fabricate cubic CsPbBr3 nanosheets
with sizes of several hundred nanometers. With changing phase composition,
cubic, rod, and rhombohedral morphologies were created. The PL properties
of the NCs depended strongly on the phase composition. As a result,
CsPbBr3 NCs reveal highly bright PL with narrow and symmetrical
PL spectra (PL peak at 520 nm). In contrast, no PL was observed for
Cs4PbBr6 and CsPb2Br5 phases.
The results provide a possibility to well control the growth for the
application of cesium lead halide NCs.
Zeolite-confined metal nanoparticles (NPs) have attracted much attention owing to their superior sintering resistance and broad applications for thermal and environmental catalytic reactions. However, the pore size of the conventional zeolites is usually below 2 nm, and reactants are easily blocked to access the active sites. Herein, a facile in situ mesoporogen-free strategy is developed to design and synthesize palladium (Pd) NPs enveloped in a single-crystalline zeolite (silicalite-1, S-1) with intra-mesopores (termed Pd@IM-S-1). Pd@IM-S-1 exhibited remarkable light alkanes deep oxidation performances, and it should be attributed to the confinement and guarding effect of the zeolite shell and the improvement in mass-transfer efficiency and active metal sites accessibility. The Pd−PdO interfaces as a new active site can provide active oxygen species to the first C−H cleavage of light alkanes. This work exemplifies a promising strategy to design other high-performance intra-crystalline mesoporous zeolite-confined metal/metal oxide catalysts for high-temperature industrial thermal catalysis.
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