cis,cis-1,2,3,4-Tetraphenylbutadiene (TPBD) exhibits aggregation-induced emission (AIE) in the UV-blue band: the photoluminescence (PL) quantum yield of TPBD aggregates can differ from that of molecularly dissolved species by 2 orders of magnitude (>200). When the isolated molecules in solutions are cooled to extremely low temperature, they also emit intense light comparable to that in the solid state. TPBD thin layer shows on-off fluorescence switching behavior that can be utilized for the sensing of organic vapors. The phenyl substituents in TPBD are twisted in the solid state, and excimer formation is greatly prohibited. The cooling-enhanced emission of the TPBD solution and the fluorescence switching behavior suggest that the aggregation-induced emission is caused by restricted intramolecular rotation of the phenyl groups. The intramolecular phenyl rotations of TPBD can be regarded as rotational relaxations around their equilibrium positions, from which mean relaxation time is defined based on an Arrhenius equation. All the PL behaviors of TPBD can be well explained qualitatively by the magnitude of the relaxation time.
Food safety is a major concern for the Chinese public. This study collected 465 published papers on heavy metal pollution rates (the ratio of the samples exceeding the Grade II limits for Chinese soils, the Soil Environmental Quality Standard-1995) in farmland soil throughout China. The results showed that Cd had the highest pollution rate of 7.75%, followed by Hg, Cu, Ni and Zn, Pb and Cr had the lowest pollution rates at lower than 1%. The total pollution rate in Chinese farmland soil was 10.18%, mainly from Cd, Hg, Cu, and Ni. The human activities of mining and smelting, industry, irrigation by sewage, urban development, and fertilizer application released certain amounts of heavy metals into soil, which resulted in the farmland soil being polluted. Considering the spatial variations of grain production, about 13.86% of grain production was affected due to the heavy metal pollution in farmland soil. These results many provide valuable information for agricultural soil management and protection in China.
The synthesis of the first delaminated
borosilicate layered zeolite
precursor is described, along with its aluminosilicate analogue, which
consists of Al-containing UCB-3 and B-containing UCB-4 from as-made
SSZ-70. In addition, the delamination of PREFER (which is the precursor
to ferrierite zeolite) under similar conditions yields delaminated
layered zeolite precursors consisting of Al-containing UCB-5 and Ti-containing
UCB-6. Multinuclear solid-state NMR spectroscopy (11B and 27Al), diffuse-reflectance UV-vis spectroscopy, and heteroatom/Si
ratios measured via elemental analysis are consistent with a lack
of heteroatom leaching from the framework following delamination.
Such mild delamination conditions are achieved by swelling the zeolite
precursor in a fluoride/chloride surfactant mixture in DMF solvent,
followed by sonication. Powder X-ray diffraction, argon gas physisorption,
and chemisorption of bulky base probes strongly suggest delamination,
and demonstrate a 1.5-fold increase in the number density of external
acid sites and surface area of calcined UCB-3, relative to calcined
Al-SSZ-70. The synthesis of microporous pockets in materials UCB-3–UCB-5
suggests the possibility of interlayer porosity in SSZ-70, which is
a layered zeolite precursor material whose structure remains currently
unknown. The mildness of the delamination method presented here, as
well as the lack of need for acidification in the synthesis procedure,
enables the delamination of heteroatom-containing zeolites while preserving
the framework integrity of labile heteroatoms, which could otherwise
be leached under harsher conditions.
This manuscript represents a comparative
study of Lewis acid catalysis
using heteroatom-substituted delaminated zeolites, which are synthesized
using an approach that obviates the need for surfactants and sonication
during exfoliation. The comparison involves heteroatom substitution
into silanol nests of delaminated zeolites consisting of DZ-1 and
deboronated UCB-4. Diffuse reflectance ultraviolet (DR-UV) spectroscopy
demonstrates framework heteroatom sites, and the Lewis acidity of
these sites is confirmed using infrared spectroscopy of adsorbed pyridine.
The enhanced catalytic accessibility of these Lewis acid sites is
confirmed when performing Baeyer–Villiger oxidation of substituted
2-adamantanones with hydrogen peroxide as the oxidant. Comparison
of delaminated Sn-DZ-1 with three-dimensional Sn-Beta for this reaction
shows that the delaminated zeolite is more active for bulkier ketone
substrates. The role of the two-dimensional crystalline framework
of the delaminated zeolite on catalysis is highlighted by comparing
delaminated zeolites Sn-DZ-1 with Sn-UCB-4. The former exhibits a
significantly higher activity for Baeyer–Villiger oxidation,
yet when comparing Ti-DZ-1 with Ti-UCB-4, it is the latter that exhibits
a significantly higher activity for olefin epoxidation with organic
hydrogen peroxide, whereas both delaminated zeolites are more robust
and selective in epoxidation catalysis compared with amorphous Ti/SiO2.
To address the debates on whether superhydrophobic coatings can reduce fluid drag for underwater motions, we have achieved an underwater drag-reducing effect of large superhydrophobic submarine models with a feature size of 3.5 cm × 3.7 cm × 33.0 cm through sailing experiments of submarine models, modified with and without superhydrophobic surface under similar power supply and experimental conditions. The drag reduction rate reached as high as 15%. The fabrication of superhydrophobic coatings on a large area of submarine model surfaces was realized by immobilizing hydrophobic copper particles onto a precross-linked polydimethylsiloxane (PDMS) surface. The pre-cross-linking time was optimized at 20 min to obtain good superhydrophobicity for the underwater drag reduction effect by investigating the effect of pre-cross-linking on surface wettability and water adhesive property. We do believe that superhydrophobic coatings may provide a promising application in the field of drag-reducing of vehicle motions on or under the water surface.
Carbon nanotube-incorporated double-walled phase-change microcapsules with excellent thermal and mechanical properties were realized via a facile layer-by-layer self-assembly technique.
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