Shi Yunlei, Xiong Dazhen, Li Zhiyong, Wang Huiyong, Qiu Jikuan, Zhang Hucheng, Wang Jianji
Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, P. R. China.
State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R. China.
ACS Appl Mater Interfaces. 2020 Nov 25;12(47):53385-53393. doi: 10.1021/acsami.0c13157. Epub 2020 Nov 10.
In recent years, metal-organic frameworks (MOFs) have been explored as emulsifiers for the fabrication of Pickering emulsions and then used for hybrid material synthesis and interface catalysis. Nevertheless, stimuli-responsive Pickering emulsions stabilized by MOFs have been rarely reported so far, although they are of great importance for fundamental research studies and practical applications. Herein, for the first time, triethylenetetramine (TETA)-functionalized MOFs (ZIF-90/TETA) have been designed, synthesized, and used for fabricating CO-/N-response Pickering emulsions. It is shown that even at the ZIF-90/TETA content of 0.25 wt %, the functional MOF can still efficiently emulsify -hexane and water to form a high internal phase Pickering emulsion. Importantly, the Pickering emulsion can be easily and reversibly switched between emulsification and demulsification by bubbling of CO and N alternatively at atmospheric pressure. The possible mechanism of the CO/N switchable emulsion is investigated by zeta potential, water contact angle, interfacial tension, C NMR spectroscopy, and an optical microscope. It is found that the acid-base reaction of CO with TETA anchored on the surface of ZIF-90 leads to the production of hydrophilic ammonium bicarbonate and carbamate, which results in the emulsification of the Pickering emulsion. However, when N is bubbled to remove CO, the reverse reaction takes place to cause the demulsification of the Pickering emulsion. Moreover, the CO/N switchable Pickering emulsion has been successfully used as a microreactor for Knoevenagel reactions to demonstrate a highly efficient integration of chemical reaction, product separation, and ZIF-90/TETA recycling for a sustainable chemical process.
近年来，金属有机框架材料（MOFs）已被探索用作制备皮克林乳液的乳化剂，并随后用于杂化材料合成和界面催化。然而，迄今为止，由MOFs稳定的刺激响应性皮克林乳液鲜有报道，尽管它们对于基础研究和实际应用都非常重要。在此，首次设计、合成了三乙烯四胺（TETA）功能化的MOFs（ZIF-90/TETA），并将其用于制备CO₂/N₂响应性皮克林乳液。结果表明，即使在ZIF-90/TETA含量为0.25 wt%时，功能化MOF仍能有效地乳化正己烷和水，形成高内相比皮克林乳液。重要的是，通过在常压下交替鼓入CO₂和N₂，皮克林乳液能够轻松、可逆地在乳化和破乳之间切换。通过zeta电位、水接触角、界面张力、¹³C核磁共振光谱和光学显微镜研究了CO₂/N₂可切换乳液的可能机理。研究发现，CO₂与锚定在ZIF-90表面的TETA发生酸碱反应，生成亲水性碳酸氢铵和氨基甲酸盐，从而导致皮克林乳液乳化。然而，当鼓入N₂以去除CO₂时，会发生逆反应，导致皮克林乳液破乳。此外，CO₂/N₂可切换皮克林乳液已成功用作Knoevenagel反应的微反应器，以证明化学反应、产物分离和ZIF-90/TETA循环利用的高效整合，实现可持续化学过程。
