Synergy of CO2-response and aggregation induced emission in a small molecule: renewable liquid and solid CO2 chemosensors with high sensitivity and visibility

A tetraphenylethylene (TPE) derivative (N,N-dimethyl-N'-(4-(1,2,2-triphenylvinyl)phenyl)acetimidamide, TPE-amidine) was designed and synthesized, and used to prepare visible CO₂ chemosensors, TPE-amidine-L (liquid) and TPE-amidine-S (solid). The hydrophilicity of TPE-amidine thoroughly changed because of the unique reversible reaction between the amidine group and CO₂, which controlled the molecular aggregation extent in water by CO₂. Combining with the well-known aggregate-induced emission effect, the highly selective CO₂ chemosensor TPE-amidine-L was developed, which has the lowest CO₂ detection limit of 24.6 ppm compared with other reported CO₂ chemosensors, and can be regenerated within 10 s by adding triethylamine. With the aim of being safer and more convenient to use, a polyacrylamide hydrogel containing TPE-amidine was prepared as a renewable CO₂ sensing "tape" (TPE-amidine-S). The flexibility, adhesivity, CO₂ sensitivity and reversibility of the "tape" is systematically investigated, showing great potential for "on-site" and "real-time" CO₂ detection in practical applications.

Structure Design of Low-Temperature Regenerative Hyperbranched Polyamine Adsorbent for CO2 Capture

A novel low-temperature regenerative hydroxy-functionalized hyperbranched polyamine adsorbent (0.16OH-HBPA) for CO₂ capture was readily prepared using glutaraldehyde to cross-link amino-terminated hyperbranched polymers (HBP) and functionalized with glycidol, followed by the reduction of the imino groups of 0.16OH-HBPA to alkyl aminos using NaBH₄. Here, the HBP has been prepared through the one-pot reaction between pentaethylenehexamine and methyl acrylate. The as-prepared 0.16OH-HBPA adsorbent showed a high adsorption capacity (4.05 mmol/g) for CO₂ (concentration, 10%) in the presence of water at 25 °C, and the alkyl amino utilization efficiency reached 73%. More importantly, the CO₂-adsorbed 0.16OH-HBPA showed excellent regenerative performance at low temperatures (85 °C, under pure CO₂ gas) due to the introduced hydroxyl that can cooperatively adsorb CO₂ via the amino groups to form stable carbamic acid. This process suppressed the formation of open-chain urea and cyclic urea and could overcome the disadvantages of high regeneration temperatures (≥90 °C, under pure inert gas) of CO₂-adsorbed traditional solid amine adsorbents.

LCST-Type Hyperbranched Poly(oligo(ethylene glycol) with Thermo- and CO2 -Responsive Backbone

A novel hyperbranched lower critical solution temperature (LCST) polymer with sharp temperature and CO₂ -responsive behaviors is presented in this study. The target polymer of hyperbranched poly(oligo(ethylene glycol) (HBPOEG) is constructed using POEG as the backbone and tertiary amines as branch points. Phase transition of HBPOEG in aqueous solution is investigated by heating and cooling the system; the results indicate that HBPOEG in aqueous solution has a concentration-dependent phase transition behavior with excellent repeatability. Moreover, LCST of HBPOEG can be tuned by bubbling CO₂ into the solution, as the tertiary amines can be protonated and the solubility of the polymer would increase by bubbling CO₂ into the system, leading to an increase of LCST of the polymer. Further bubbling N₂ to remove CO₂ can reversibly turn back the LCST to its original value. This backbone-based hyperbranched LCST polymer with both CO₂ and temperature responsiveness can be applied in application areas like drug delivery, gene transfection, functional coatings, etc.