https://doi.org/10.3390/nano12101677
” A polymer solution of 10 wt.% was prepared by dissolving 1 g of polyacrylonitrile with a molecular weight of 150,000 (PAN, Sigma-Aldrich, Saint Louis, MO, USA) in 9 g of N,N-dimethylformamide (DMF, Sigma-Aldrich, Saint Louis, MO, USA) under magnetic stirring for 2 h at 50 °C. A quantity of 0.5 g of calcium acetylacetonate (CaAA, Sigma-Aldrich, Saint Louis, MO, USA) was added into the fabricated solution and stirred at 50 °C until transparent solution was obtained.
The obtained composite solution was poured into a plastic syringe and then electrospun through a 23 G blunt-tip needle on a rectangular-frame collector made of copper wire. The collector was placed in a NANON-01A electrospinning apparatus (MECC, Fukuoka, Japan). The fibers were collected as non-woven mats. The following electrospinning parameters were used to fabricate smooth and bead-free composite fibers: distance between the needle tip and the collector of 12 cm, the accelerating voltage of 14 kV and a feeding rate of 0.8 mL/h.
To prepare the CaO nanofibers, the electrospun composite filaments were annealed in a muffle furnace at 800 °C for 1 h in air atmosphere. The heating rate was 1 °C/min to ensure the delicate removal of CaAA and PAN decomposition products. The annealing temperature value was chosen in accordance with the results of the thermogravimetric (TG) analysis. The TG analysis was performed on the thermal analyzer EXSTAR TG/DTA7200 (SII Nano Technology, Tokyo, Japan) in air atmosphere with a heating rate of 10 °C/min. “
“The grain structure of the prepared CaO fibers is confirmed by SEM microstructural analysis (Figure 3). The resulting filaments are nanofibers, which are characterized by the coarse surface and the average diameter of 130 ± 11 nm. Since nanofibers contain no binding polymer and no products of its thermal decomposition, and the sintering of CaO grains does not occur at 800 °C because the Tammann temperature of CaO is 1313 °C [26], we suppose that only the Van der Waals forces provide the connection between CaO grains inside the nanofibers.”
“Figure 3. The microstructure of electrospun CaAA/PAN fibers annealed at 800 °C.”
“Figure 4. The DTG curves of CaO nanofibers carbonation and decarbonation processes.”https://doi.org/10.3390/nano12101677
“Figure 5. The carbonation–decarbonation cycle profiles of CaO nanofibers upon carbonation in the gaseous stream containing 15 vol.% CO2 and 85 vol.% N2; and in pure N2.” https://doi.org/10.3390/nano12101677
“According to the performed DTG analysis, CaO nanofibers most intensively sorb CO2 in the temperature range of 610–633 °C, which is determined by the carbonation-rate peak width at half height (Figure 4). The carbonation rate attains the maximum value at 618 °C. Therefore, the given temperature was chosen as the carbonation temperature.”
“During carbonation the mass of CaO nanofibers increases by 72.15 wt.% that corresponds to the CO2-uptake capacity of 16.4 mmol/g. The fabricated CaO nanofibers show a rather high capacity since the stoichiometric capacity of CaO is 17.9 mmol/g. The observed absence of a change in the weight of the sorbent upon carbonation in pure N2 indicates that it does not sorb N2 in the temperature range of 500–800 °C. The CO2-uptake capacity of CaO nanofibers is inferior to that of the nanosized powder CaO sorbent that was fabricated using flame-spray pyrolysis [10] and exceeds, for example, the capacity of nanosized powder CaO sorbents produced by the calcination method [28], the sol-gel technique [29] and mechanical milling [12]. The characteristics of synthetic CaO sorbents produced by various methods are presented in Table 1.”
