Salt-Enhanced CO₂-Responsiveness of Microgels

Abstract

Here, we report a distinct mechanism for harnessing CO2-responsiveness through enhancing CO2 capture ability. The finding is demonstrated on the microgels that are composed of oligo­(ethylene glycol) and sulfonate moieties. Laser light scattering studies on dilute aqueous dispersion of these microgels indicated a low CO2-responsivity, which can be significantly enhanced by adding NaCl and other salts. This salt-enhanced CO2-responsiveness of microgels can be elucidated by the antipolyelectrolyte behavior and its superposition of forming cross-links physically with CO2 as an intermediate. Further results of the filtration experiments on microgel translocation through pores suggest the feasibility of the explanation. The finding is also supported by the CO2 capture-release experiments on the dispersion, which can reversibly absorb and desorb CO2.

CO2-responsive gels

“…Wang et al 316 showed that the responsiveness of CO 2 -responsive PIL microgels could be enhanced through the addition of salts to microgel dispersions in water. In this study, the authors used weak Lewis bases [oligo(ethylene glycol) and sulfonate] as functional groups on the microgels instead of traditional amine groups.…”

Insect-Inspired Strategy for Conferring Reversible, High Responsivity on Microgels to Dilute-Source CO2

“…Stimuli-responsive polymers have received increased attention and seem to continue to be one critical topic in several disciplines, owing to their adaptive ability similar to living organisms . In particular, CO 2 -responsive polymers recently went through a rapid development because of the appeal of greenhouse gas CO 2 as a trigger, rather than liquid acid or base as in conventional pH-responsive systems. − A variety of functional moieties, such as base groups, including guanidines, imidazoles, amidines and tertiary, secondary, or primary amines, carboxylic acid groups, and more recently, frustrated Lewis pairs, have been incorporated into polymer chains through direct polymerization or postmodification to impart CO 2 -responsiveness. − Those functional moieties can react with CO 2 in water following an acid–base principle to introduce a significant change in their hydrophilicities and polarities, which can recover to their original state upon CO 2 removal by purging with an inert gas (e.g., argon, nitrogen) or heating, thus, free of any contamination by accumulated chemical agents. However, the reversible nature of CO 2 -responsiveness also makes the application of the developed responsive materials heavily limited by the input side, since CO 2 with a relatively high purity or concentration (≥5 vol % usually) is required. − The uptake of CO 2 from a gas mixture with an even lower CO 2 concentration poses a much greater challenge thermodynamically, which needs favorable and selective CO 2 binding energetics on functional moieties. − Unfortunately, with a high binding affinity, the release of the captured CO 2 becomes difficult, which inevitably leads to a poor reversibility under mild conditions.…”

“…126 ppm, and the peaks of bicarbonate and carbonate ions (ca. 161–169 ppm) were not observed. , These results suggest that the responsivity of the microgels to dilute CO 2 should obey a distinct mechanism, unlike the responsivity of amine-containing polymers to concentrated CO 2 reported previously that essentially is the pH-responsive behavior. − In Figure d the observation of the lower SW in the PC/water mixture for a high CO 2 of ≥25.0 vol %, compared to results of no PC, should also reflect the existence of CO 2 (aq) (even if not all), thus, indirectly support the possibility of obeying a different CO 2 -response mechanism. Considering the CO 2 -unresponsivity of a control sample without feeding DEAEMA (Figure S11), , we therefore tentatively ascribed the vital role of amines of DEAEMA unit to promotion on the CO 2 capture ability of microgels (Figure S9) without significant CO 2 hydrolysis.…”

“…23 At temperatures below LCST, these polymers were hydrophilic and became relatively hydrophobic upon heating to form gel particles, resulting in spherical-like, nearly monodispersed microgels (harvested after polymerization for 5 h; Figure 1a). 11,21,22 The composition of microgels was confirmed by IR analysis (Figure S1), in which characteristic bands for O−C stretching vibration (1041 cm −1 ) of methyl ether oxygen on MEO 2 MA unit, C−N stretching vibration (1020 cm −1 ) of tertiary amine on DEAEMA unit, and C−O−C stretching vibration (1113 cm −1 ) of either oxygen on the OEGDMA unit were detected. 11,24,25 To verify the synthesis, the feeding molar ratio r MEO2MA:DEAEMA of MEO 2 MA to DEAEMA was varied (Table S1), which leaded to microgels of different particle sizes in water (Figure S2).…”

“…11,21,22 The composition of microgels was confirmed by IR analysis (Figure S1), in which characteristic bands for O−C stretching vibration (1041 cm −1 ) of methyl ether oxygen on MEO 2 MA unit, C−N stretching vibration (1020 cm −1 ) of tertiary amine on DEAEMA unit, and C−O−C stretching vibration (1113 cm −1 ) of either oxygen on the OEGDMA unit were detected. 11,24,25 To verify the synthesis, the feeding molar ratio r MEO2MA:DEAEMA of MEO 2 MA to DEAEMA was varied (Table S1), which leaded to microgels of different particle sizes in water (Figure S2). The synthesis was reproducible, with a yield of ≥84%.…”