A series of Brønsted acid-surfactant-combined catalysts (BASCs) functionalised with different acids have been synthesized and applied to catalyze the three-component Mannich reaction with aldehyde, acetone and amine at 25 °C in water. The effects of cation tail length and ions of the ionic liquid and the recyclability of the catalysts and BASC acidity (H₀) were investigated. The results demonstrated that the 3-(N,N-dimethyloctylammonium) propanesulfonic acid toluene sulfate ([DOPA][Tos]) provide the best catalytic activity because of the formation of emulsions during the reaction. The catalytic procedure was simple and the catalyst could be recycled 9 times by simple separating processes without noticeably decreasing the catalytic activity.

Covalent organic polymers (COPs) are a kind of promising material for carbon dioxide (CO₂) reutilization. Herein, a series of covalent organic crown-based polymers (COCP–H, COCP–OH, COCP–CH₃, COCP–Bu, COCP–NH₂) were designed and synthesized. These synthesized COCPs were characterized by FT-IR, SEM, BET and ¹³C CP MAS NMR. Notably, the novel COCP–OH catalyst with hydroxyl and crown ether groups on the framework simultaneously was particularly effective in cycloaddition reactions, giving a cyclic carbonate yield of 94.8% after 24 h at 70 °C with 1 bar of CO₂, using 0.0735 mmol of KI and 71 mg of COCP–OH. It is worth considering that there is a synergetic effect between the hydroxyl group and KI activated by the crown ether fragment, which plays a crucial role in accelerating the reaction rate. The coordinated interaction of crown ether with KI was also confirmed by X-ray photoelectron spectroscopy (XPS). Thus, this study provides a new approach to fabricate multifunctional COP materials for the coupling reaction of CO₂ under mild conditions.

Quaternary ammonium geminal Brønsted acid ionic liquids (GBAILs) based on zwitterionic 1,2-bis[N-methyl-N-(3-sulfopropyl)-alkylammonium]ethane (where the carbon number of the alkyl chain is 4, 8, 10, 12, 14, 16, or 18) and p-toluenesulfonic acid monohydrate were synthesized. The catalytic ionic liquids were applied in three-component Mannich reactions with an aldehyde, ketone, and amine at 25 °C in water. The effects of the type and amount of catalyst and reaction time as well as the scope of the reaction were investigated. Results showed that GBAIL-C₁₄ has excellent catalytic activity and fair reusability. The catalytic procedure was simple, and the catalyst could be recycled seven times via a simple separation process without noticeable decreases in catalytic activity.

The synergistic interaction of KI and NUPs plays an important role in the fixation reaction of CO₂ and epoxides.