3 research outputs found
Efficient and Lightweight Electromagnetic Wave Absorber Derived from Metal Organic Framework-Encapsulated Cobalt Nanoparticles
Porous-carbon-based
nanocomposites are gaining tremendous interest because of good compatibility,
lightweight, and strong electromagnetic wave absorption. However,
it is still a great challenge to design and synthesize porous-carbon-based
composites with strong absorption capability and broad frequency bandwidth.
Herein, a facile and effective method was developed to synthesize
Co magnetic nanoparticles/metal organic framework (MOF) (Co NPs/ZIF-67)
nanocomposites. Co NPs/porous C composites were subsequently obtained
by annealing Co NPs/ZIF-67 nanocomposites at different temperatures
under an inert atmosphere. The carbonized nanocomposites showed highly
efficient electromagnetic wave absorption capability. Specifically,
the optimal composite (i.e., Co/C-700) possessed a maximum reflection
loss (RL) value of −30.31 dB at 11.03 GHz with an effective
absorption bandwidth (RL ≤ −10 dB) of 4.93 GHz. The
electromagnetic parameters and the absorption performance of the composites
are readily tunable by adjusting the carbonization temperature and
the concentration of Co NPs in the composites. Because of the combination
of good impedance matching, dual-loss mechanism, and the synergistic
effect between Co NPs and porous carbon composites, these Co NPs/MOF-derived
composites are attractive candidates for electromagnetic wave absorbers
Ferromagnetism and Microwave Electromagnetism of Iron-Doped Titanium Nitride Nanocrystals
Titanium nitride (TiN) nanocrystals doped with different
dosages
of iron were prepared by calcinating nanotubular titanic acid precursor
in flowing ammonia. The structure of as-prepared Fe-doped TiN nanocrystals
was characterized, and their ferromagnetism and microwave electromagnetism
were investigated. It has been found that as-prepared Fe-doped TiN
nanocrystals exhibit distinct room temperature ferromagnetic properties
and improved microwave electromagnetic loss behavior when compared
with the undoped counterpart. Considering the crystal structure and
chemical feature of as-synthesized products, we suppose that structural
defects are responsible for the observed ferromagnetism and microwave
electromagnetism of as-synthesized Fe-doped TiN, and it may be feasible
to tune the magnetic and electromagnetic properties by manipulating
the generation of the structural defects. Hopefully, the present research
is to shed light on Fe-doped TiN nanocrystal as a promising microwave
absorption material and to help acquiring insights into the origin
of ferromagnetism and microwave electromagnetism in a broad range
of nanostructures, thereby broadening the scope of dilute magnetic
and electromagnetic wave absorbing materials
Preparation of Graphene Sheets by Electrochemical Exfoliation of Graphite in Confined Space and Their Application in Transparent Conductive Films
A novel
electrochemical exfoliation mode was established to prepare
graphene sheets efficiently with potential applications in transparent
conductive films. The graphite electrode was coated with paraffin
to keep the electrochemical exfoliation in confined space in the presence
of concentrated sodium hydroxide as the electrolyte, yielding ∼100%
low-defect (the D band to G band intensity ratio, <i>I</i><sub>D</sub>/<i>I</i><sub>G</sub> = 0.26) graphene sheets.
Furthermore, ozone was first detected with ozone test strips, and
the effect of ozone on the exfoliation of graphite foil and the microstructure
of the as-prepared graphene sheets was investigated. Findings indicate
that upon applying a low voltage (3 V) on the graphite foil partially
coated with paraffin wax that the coating can prevent the insufficiently
intercalated graphite sheets from prematurely peeling off from the
graphite electrode thereby affording few-layer (<5 layers) holey
graphene sheets in a yield of as much as 60%. Besides, the ozone generated
during the electrochemical exfoliation process plays a crucial role
in the exfoliation of graphite, and the amount of defect in the as-prepared
graphene sheets is dependent on electrolytic potential and electrode
distance. Moreover, the graphene-based transparent conductive films
prepared by simple modified vacuum filtration exhibit an excellent
transparency and a low sheet resistance after being treated with NH<sub>4</sub>NO<sub>3</sub> and annealing (∼1.21 kΩ/□
at ∼72.4% transmittance)