2 research outputs found
Microwave-Assisted Synthesis and Luminescence of Mesoporous RE-Doped YPO<sub>4</sub> (RE = Eu, Ce, Tb, and Ce + Tb) Nanophosphors with Lenticular Shape
Mesoporous tetragonal RE:YPO<sub>4</sub> nanophosphors
(RE = Eu,
Ce, Tb, and Ce + Tb) with a lenticular morphology, narrow size distribution,
and high surface area have been prepared by an homogeneous precipitation
procedure consisting of aging, at low temperature (80–120 °C)
in a microwave oven, ethylene glycol solutions containing only yttrium
acetylacetonate and phosphoric acid. This synthesis method involves
important advantages such as its simplicity, rapidness (reaction time
= 7 min), and high reaction yields. The mechanism of nanoparticle
growth has been also addressed finding that the lenticular nanoparticles
are formed through an ordered aggregation of smaller entities, which
explains their porosity. In all cases, the doping levels were systematically
varied in order to optimize the nanophosphors luminescence. All optimum
nanophosphors presented a high luminescence quantum yield (QY). In
particular, for the Eu and Tb doped systems, the obtained QY values
(60% for Eu and 80% for Tb) were the highest so far reported for this
kind of nanomaterial. The morphological, microstructural, and luminescent
properties of these nanophosphors and their dispersibility in water
make them suitable for biomedical applications
High-Temperature Stable Gold Nanoparticle Catalysts for Application under Severe Conditions: The Role of TiO<sub>2</sub> Nanodomains in Structure and Activity
Metal nanoparticles with precisely
controlled size are highly attractive
for heterogeneous catalysis. However, their poor thermal stability
remains a major concern in their application at realistic operating
conditions. This paper demonstrates the possibility of synthesizing
gold nanoparticles with exceptional thermal stability. This has been
achieved by using a simple conventional deposition–precipitation
technique. The material employed as catalyst consists of gold supported
on a TiO<sub>2</sub>-impregnated SiO<sub>2</sub> bimodal mesoporous
support. The resulting material shows gold nanoparticles with a narrow
size distribution around 3.0 nm, homogeneously dispersed over the
TiO<sub>2</sub>/SiO<sub>2</sub> material. Most interestingly, the
gold nanoparticles show exceptional thermal stability; calcination
temperatures as high as 800 °C have been employed, and negligible
changes in the gold particle size distribution are apparent. Additionally,
the presence of an amorphous titanium silicate phase is partially
preserved, and these factors lead to remarkable activity to catalyze
a range of oxidation reactions