Engineering performance of asphalt pavement highly depends on the properties of bitumen, the bonding material to glue aggregates and fillers together. During the service period, bitumen is exposed to sunlight, oxygen and vehicle loading which in turn leads to aging and degradation. A comprehensive understanding of the aging mechanism of bitumen is of critical importance to enhance the durability of asphalt pavement. This study aims to determine the relations between micro-mechanics, chemical composition, and macro-mechanical behavior of aged bitumen. To this end, the effect of aging on micro-mechanics, chemical functional groups, and rheological properties of bitumen were evaluated by atomic force microscope, Fourier transform infrared spectroscopy and dynamic shear rheometer tests, respectively. Results indicated that aging obviously increased the micro-surface roughness of bitumen. A more discrete distribution of micromechanics on bitumen micro-surface was noticed and its elastic behavior became more significant. Aging also resulted in raised content of carbonyl, sulfoxide, and aromatic ring functional groups. In terms of rheological behavior, the storage modulus of bitumen apparently increased after aging due to the transformation of viscous fractions to elastic fractions, making it stiffer and less viscous. By correlation analysis, it is noted that the bitumen rheological behavior was closely related to its micro-mechanics.
Highly
dispersed black SnO2–TiO2 nanocomposites
were successfully synthesized by the sol–gel method using a
Sn–POBC–Ti single-source precursor (POBC = p-carboxybenzaldehydeoxime), which adjusted the nanocomposite structure
at the molecular level. SnO2 and TiO2 in the
composites were highly dispersed due to the linkage of a single-source
precursor; no TiO2 crystalline phase showed up when Sn:Ti
≥ 1:1, and black SnO2–TiO2 nanocomposites
can be achieved when Sn:Ti ≤ 1:1, which was probably caused
by the transformation from Sn2+–Ti4+ to
Sn4+–Ti3+. The black nanocomposite with
Sn:Ti = 1:2 showed the best performance in methyl orange degradation,
phenol degradation, as well as photovoltaic conversion in the photoanode
form. This can be attributed to the high surface area and the nano-heterojunction
of SnO2 −TiO2 caused by the highly dispersed
elements of the single source precursor.
A heterogeneous catalyst CuO–CeO2 with
a hollow
structure was successfully synthesized by assembling CuO on the outer
surface of CeO2 hollow spheres through a layer-by-layer
deposition strategy. Further reduction under a H2 atmosphere
was carried out to modify its surface state, resulting in sample r-CuO–CeO2. The catalysts were characterized by X-ray diffraction, scanning
electron microscopy (SEM), transmission electron microscopy (TEM),
X-ray photoelectron spectroscopy (XPS), and Fourier transform-infrared
spectroscopy (FT-IR). SEM and TEM showed that the synthesized catalysts
had a hollow sphere structure, which can expose more active sites
and promote mass transfer. The results of XPS revealed that the content
of Cu0&Cu+ increased from 13.6 to 19.0%
after H2 reduction, which was conducive to the activation
of terminal alkyne to promote the annulation/A3-coupling
reaction. The conversion of this cascade reaction with the r-CuO–CeO2 catalyst can reach more than 95%, while the value was only
55% by using CuO–CeO2 as a catalyst. Moreover, the
r-CuO–CeO2 catalyst showed a good recycle property
and group compatibility in the general applicability of the cascade
annulation/A3-coupling reaction, providing a series of
propargylamine derivatives in good chemoselectivity.
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