TY - JOUR
T1 - Surface-enhanced CO2 capture in ionic liquid-silica nanocomposites via sol-gel synthesis in the low partial pressure range
AU - Leeuwen, Marieke van
AU - Plankensteiner, Nina
AU - Maity, Rahul
AU - Loe, Jesus Gandara
AU - Denayer, Joeri F.M.
AU - Ameloot, Rob
AU - Vereecken, Philippe M.
N1 - Funding Information:
The N2 adsorption/desorption profiles at 77 K in Fig. 3 a are characteristic of an entirely mesoporous silica matrix and a meso/microporous material for composites synthesized with x = 1 and x = 2 mol [BMP][TFSI]: mol SiO2, respectively. The small extent of open hysteresis in the adsorption/desorption profiles strongly suggests a well ordered porosity and a connected porous network. The different microstructures observed for nanocomposites of composition x = 2 supports the observations from SEM that two domains are present for x = 2, highlighting the presence of larger \u201Cdistribution\u201D canals interconnected with smaller pores. Surface area and average pore diameter for the remaining silica after [BMP][TFSI] extraction of the nanocomposites were quantified from the sorption isotherms at 77 K (Fig. 3a) via the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) method. The respective BET surface area amounted to 169 and 293 m2/g for x = 1 and x = 2 mol IL: mol SiO2, and the average pore width based on the BJH desorption branch was 14 and 24 nm (Table 2). For smaller ionic liquid-to-silica content, i.e., for x = 1, most of the pore volume can be accounted for by pores ranging from 5 to 10 nm radius, as shown in black in the pore size distribution derived from the BJH analysis (Fig. 3b). For higher ionic liquid content, i.e., for x = 2, some domains can be differentiated. Pores of radius around 20 and 40 nm account for a large volume fraction of the silica host matrix, as visible from the wide distribution in Fig. 3b, and can be related to the bronchiole's highways observed in Fig. 2. Smaller domains inferior to 10 nm are also found and can be related to the smaller alveoli. The sol-gel synthesis route created an interconnected porous silica network with high ionic liquid retention, thereby standing out from previous ionogel compositions in CO2 sorption studies (Table 1). The total pore volume amounts 0.63 cm3/g and 0.88 cm3/g for the x = 1 and x = 2 extracted nanocomposites, as calculated from the BJH method from the isotherms presented in Fig. 3a (see methods and SI). This translates to 59 and 66 vol %, respectively, using a density for amorphous silica of 2.2 g/cm3 [36].The enhancement factor is significantly higher for composites at lower partial pressures, as can be observed in Fig. 10. At partial pressures of 1 bar, the measured uptake is 1.6\u20131.7 times higher than the expected uptake from SiO2 and the [BMP][TFSI] ionic liquid for x = 1 (black) and x = 2 (red). In this range, bulk ionic liquids are typically more performant than at low partial pressures. The possible enhancement due to interface effects is therefore expected to be less significant than at lower partial pressures as shown in Fig. 8, and the enhancement factor would be expected to be closest to 1. The EF in the higher pressure range is within an order of magnitude of the heuristically expected value. The difference obtained might originate from the assumptions made and their respective variation, but overall, it supports the validity of the assumptions made for the EF model. At lower partial pressures, the enhancement factor goes up to 5 for iolnic liquid-to-silica ratios of 1 and 2. The high enhancement in uptake compared to expected values for the nanocomposites highlights the beneficial effect of ionic liquid immobilization at low partial pressures.The authors thank Seger Witteveen his contributions to the DSC data. MvL gratefully acknowledges the support of the PhD fellowship (Grant No. 1SD5923N) from the Research Foundation Flanders (FWO) and JGD acknowledges the support of the FWO Junior Postdoctoral Fellowship (12E5123N). All the authors are grateful to VLAIO for financial support (HBC.2020.2615).
Funding Information:
The authors thank Seger Witteveen his contributions to the DSC data. MvL gratefully acknowledges the support of the PhD fellowship (Grant No. 1SD5923N) from the Research Foundation Flanders ( FWO ) and JGD acknowledges the support of the FWO Junior Postdoctoral Fellowship (12E5123N). All the authors are grateful to VLAIO for financial support (HBC.2020.2615).
Publisher Copyright:
© 2024
PY - 2025/1/15
Y1 - 2025/1/15
N2 - Ionic liquid-containing silica nanocomposites enable the capture of carbon dioxide from gas mixtures containing nitrogen, oxygen, and methane. Synthesis methods explored for such nanocomposites include impregnating porous silica and one-pot synthesis via a sol-gel process. This research investigates a non-hydrolytic sol-gel route for nanocomposite materials enabling CO2 capture at low partial pressures (0.1–0.4 bar). The tetraethyl orthosilicate (TEOS) precursor condensation resulted in a silica matrix formed around ionic liquid domains, for bis(trifluorosulfonylimide) (TFSI−)-based ionic liquids with 1-butyl-1-methylpyrrolidinium (BMP+), 1-butyl-3-methylimidazolium (BMI+), 1-ethyl-3-methylimidazolium (EMI+) and 1-hexyl-3-methylimidazolium (HMI+) cations. Using a one-pot synthesis method enables exploring CO2 sorption in such nanocomposites for ionic liquid-to-silica contents up to fourteen times higher than in previously reported studies. Moreover, the selected synthesis method provides greater tunability in deposition methods and their control. The silica host matrix was characterized by N2 adsorption isotherms at 77 K after solvent extraction and supercritical drying of the material for ionic liquid removal. The pore size distribution of the freestanding silica network was observed via Scanning Electron Microscope (SEM) imaging and assessed with the Barrett-Joyner-Halenda (BJH) method for nanocomposites of different [BMP][TFSI]-to-silica ratio. The CO2 uptake at pressures down to 0.1 bar was evaluated from CO2 adsorption isotherms at 303 K. The confinement of [BMP][TFSI] resulted in a beneficial effect for the CO2 uptake at lower partial pressures, with an uptake five times higher than the sum of the individual uptake expected from the contained ionic liquid and silica. The reported results show the advantage of a one-pot synthesis method for broader tunability of the nanocomposite, both regarding its content and application, as well as increased performance at lower partial pressures compared to the nanocomposite's individual constituents.
AB - Ionic liquid-containing silica nanocomposites enable the capture of carbon dioxide from gas mixtures containing nitrogen, oxygen, and methane. Synthesis methods explored for such nanocomposites include impregnating porous silica and one-pot synthesis via a sol-gel process. This research investigates a non-hydrolytic sol-gel route for nanocomposite materials enabling CO2 capture at low partial pressures (0.1–0.4 bar). The tetraethyl orthosilicate (TEOS) precursor condensation resulted in a silica matrix formed around ionic liquid domains, for bis(trifluorosulfonylimide) (TFSI−)-based ionic liquids with 1-butyl-1-methylpyrrolidinium (BMP+), 1-butyl-3-methylimidazolium (BMI+), 1-ethyl-3-methylimidazolium (EMI+) and 1-hexyl-3-methylimidazolium (HMI+) cations. Using a one-pot synthesis method enables exploring CO2 sorption in such nanocomposites for ionic liquid-to-silica contents up to fourteen times higher than in previously reported studies. Moreover, the selected synthesis method provides greater tunability in deposition methods and their control. The silica host matrix was characterized by N2 adsorption isotherms at 77 K after solvent extraction and supercritical drying of the material for ionic liquid removal. The pore size distribution of the freestanding silica network was observed via Scanning Electron Microscope (SEM) imaging and assessed with the Barrett-Joyner-Halenda (BJH) method for nanocomposites of different [BMP][TFSI]-to-silica ratio. The CO2 uptake at pressures down to 0.1 bar was evaluated from CO2 adsorption isotherms at 303 K. The confinement of [BMP][TFSI] resulted in a beneficial effect for the CO2 uptake at lower partial pressures, with an uptake five times higher than the sum of the individual uptake expected from the contained ionic liquid and silica. The reported results show the advantage of a one-pot synthesis method for broader tunability of the nanocomposite, both regarding its content and application, as well as increased performance at lower partial pressures compared to the nanocomposite's individual constituents.
KW - CO capture
KW - Ionogel
KW - Nanocomposite
KW - Physisorption
UR - http://www.scopus.com/inward/record.url?scp=85206949616&partnerID=8YFLogxK
U2 - 10.1016/j.micromeso.2024.113374
DO - 10.1016/j.micromeso.2024.113374
M3 - Article
AN - SCOPUS:85206949616
VL - 382
JO - Microporous and Mesoporous Materials
JF - Microporous and Mesoporous Materials
SN - 1387-1811
M1 - 113374
ER -