Adsorption of Carbon Dioxide with Ni-MOF-74 and MWCNT Incorporated Poly Acrylonitrile Nanofibers.

Among the new adsorbent forms, nanofiber structures have attracted extra attention because of features such as high surface area, controllable properties, and fast kinetics. The objective of this study is to produce the polyacrylonitrile (PAN) electrospun nanofibers loaded with Ni-MOF-74/MWCNT to obtain maximum CO2 adsorption. The prepared PAN/MWCNT/MOF nanofiber based on the Box-Behnken design (BBD) model suggests the CO2 adsorption of about 1.68 mmol/g (at 25 °C and 7 bar) includes 14.61 w/v%, 1.43 w/w%, and 11.9 w/w% for PAN, MWCNT, and MOF, respectively. The results showed the effective CO2 adsorption of about 1.65 ± 0.03 mmol/g (BET = 65 m2/g, pore volume = 0.08 cm3/g), which proves the logical outcomes of the chosen model. The prepared PAN/MWCNT/MOF nanofiber was characterized using different analyzes such as SEM, TEM, TG, XRD, FTIR, and N2 adsorption-desorption isotherms. More MOF mass loading on the nanofiber surface via secondary growth method resulted in 2.83 mmol/g (BET = 353 m2/g, pore volume = 0.22 cm3/g, 43% MOF mass loading) and 4.35 mmol/g (BET = 493 m2/g, pore volume = 0.27 cm3/g, 65% MOF mass loading) CO2 adsorption at 7 bar for the first and second growth cycles, respectively. This indicates that secondary growth is more effective in the MOF loading amount and, consequently, adsorption capacity compared to the MOF loading during electrospinning.

Introducing a dual-step procedure comprising microwave and electrical heating stages for the morphology-controlled synthesis of chromium-benzene dicarboxylate, MIL-101(Cr), applicable for CO2 adsorption.

MIL-101(Cr) crystals were synthesized through a dual-step procedure consisting of a short term nucleation step in which the solution mixture was heated using microwave irradiation (MW phase) followed by a long-term growth step in which conventional electrical heating (CE phase) was used as a source of energy. The primary objective of such segregation is to increase the nuclei population at the end of the nucleation step. As a result of the high population density of nuclei, it is expected that the total time required to grow crystals in the CE phase decreases. The results showed that using the dual-step procedure led to a significant reduction in total synthesis time. The results also revealed that increasing pH from around 1.5 to 3 at the beginning of the CE phase resulted in producing octahedral crystals instead of a multifaceted sphere. Octahedral crystals exhibit higher CO2 adsorption capacity than the multifaceted ones. Using the dual step procedure, one can not only control the morphology but also reduce the total synthesis time of MIL-101(Cr) crystals.