High-performance
broadband microwave absorbers are greatly required
to cope with the increasingly serious microwave radiation pollution.
Integration of dielectric and magnetic components is a promising strategy
to achieve desirable microwave absorption performance. Herein, we
demonstrated a facile and efficient approach to fabricate two-dimensional
cobalt@carbon (Co@C) hybrids by solvothermal synthesis of cobalt–metal–organic
framework (Co-MOF) nanosheets and subsequent thermal pyrolysis for
efficient microwave absorption application. The resultant nanolayered
Co@C hybrids inherit the two-dimensional architecture of the Co-MOF
nanosheets. During the thermal pyrolysis of Co-MOF, its organic component
is carbonized to amorphous carbon while its cobalt ions are carbothermally
reduced to cobalt nanoparticles, thus in situ integrating the magnetic
metal nanocrystal with the dielectric carbon. Consequently, a wide
effective absorption bandwidth of 5.44 GHz at a small thickness of
1.76 mm and a minimum reflection loss value of −49.76 dB are
achieved for the wax composite with 30 wt % of Co@C hybrid pyrolyzed
at 800 °C. The outstanding microwave absorption performances
are attributed to the synergistic effects of the Co@C hybrid nanosheets
and their large shape anisotropy, which facilitates the strong dielectric
loss and good impedance matching, thus promising the nanolayered Co@C
hybrid as a lightweight and high-performance microwave absorber.
Polylactide
[PLA, two enantiomers: poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA)] has been widely applied as biomaterials because
of its biocompatibility, biodegradability, and good mechanical capacity.
However, the chirality of PLA materials has not been intensively explored
yet. In the present study, chiral porous poly(high internal-phase
emulsion)s (polyHIPEs) derived from enantiopure PLAs were successfully
prepared via a HIPE template method. The resulting polyHIPEs show
optical activity. More interestingly, the polyHIPEs demonstrate enantioselective
release capacity, using cinchona alkaloid and naproxen as the model
chiral drugs. Notably, PLLA-based polyHIPE shows enantioselectivity
in both the drug-loading step and drug-releasing step, while PDLA-based
polyHIPE fails. The interesting finding is essentially different from
other chiral polymer materials reported earlier. The cytotoxicity
test demonstrates that all the three types of polyHIPEs, PLLA-, PDLA-,
and PDLLA-based polyHIPE show biocompatibility; however, their different
chirality exerts varying effects on cell growth. Accordingly, special
attention should be devoted to the chirality of PLA when used as biomaterials.
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