Monolithic porous nanostructures of CaO−MgO composites were synthesized by a rapid self-sustained combustion reaction of molded pellets made of a mixture of nitrate salts of calcium and magnesium, urea, and starch. Urea is the fuel, and starch acts as a binder and a removable in situ template leading to porous monoliths. The synthesis is rapid, single-step, and solvent-free. In addition, the products retained a small quantity (1−2%) of carbon formed from starch. Porous monoliths were probed for high-temperature (650 °C) CO 2 capture at atmospheric pressure in a 20% CO 2 gas stream. While the pristine CaO porous nanostructure captured 76.8 mass % of CO 2 initially, it retained only a capture of 22 mass %, equivalent to 28% carbonation efficiency, after 100 carbonation−decarbonation cycles. The CaO−MgO porous nanostructures with varied amounts of MgO (10−40 mol %) exhibit CO 2 capture capacities of 67−51 mass % of the sorbent. CaO 80 −MgO 20 porous nanostructures captured 61.6 mass % of CO 2 and retained 84.6% (52.1 mass % of CO 2 ) of its initial capacity after 100 carbonation−decarbonation cycles. Thus, the hetero-oxide porous nanostructures exhibit enhanced cycle stability in addition to high CO 2 capture capacity, repressing the sintering-induced limitation of porous CaO. The high carbonation efficiency and cycling stability of the porous nanostructures as CO 2 sorbents are attributed to the synergistic combination of large surface area, a porous network, and an inert MgO stabilizer.
In this work, a series of Bi2Te3/X mol% MoS2 (X = 0, 25, 50, 75) bulk nanocomposites were prepared by hydrothermal reaction followed by reactive spark plasma sintering (SPS). X-ray diffraction analysis (XRD) indicates that the native nanopowders, comprising of Bi2Te3/MoS2 heterostructure, are highly reactive during the electric field-assisted sintering by SPS. The nano-sized MoS2 particles react with the Bi2Te3 plates matrix forming a mixed-anion compound, Bi2Te2S, at the interface between the nanoplates. The transport properties characterizations revealed a significant influence of the nanocomposite structure formation on the native electrical conductivity, Seebeck coefficient, and thermal conductivity of the initial Bi2Te3 matrix. As a result, enhanced ZT values have been obtained in Bi2Te3/25 mol% MoS2 over the temperature range of 300–475 K induced mainly by a significant increase in the electrical conductivity.
Pristine and Co-doped MoS2 nanosheets, containing a dominant 1T phase, have been densified by spark plasma sintering (SPS) to produce a nanostructured arrangement. The structural analysis by X-ray powder diffraction revealed that the reactive sintering process transforms the 1T-MoS2 nanosheets into their stable 2H form despite a significantly reduced sintering temperature and time testifying to the fast kinetics of phase change. Together with the phase conversion, the SPS process promoted a strong texturing of the nanosheets, which drives additional scattering processes and alters the electronic and thermal transport properties. In the pristine sample, it produced one of the lowest thermal conductivities ever reported on MoS2 with a minimal value of 0.66 W/m·K at room temperature. The effect of Co substitution in the final sintered samples is not significant, compared to the pristine MoS2 sample, except for a non-negligible improvement of the electrical conductivity by a factor of 100 in the high-Co content (6% by mass) sample.
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