Carbon dots (CDs) have attracted increasing attention in applications such as bio-imaging, sensors, catalysis, and drug delivery. However, unlike metallic and semiconductor nanoparticles, the transfer of CDs between polar and non-polar phases is little understood. A class of amine-terminated CDs is developed and their phase transfer behavior has been investigated. It is found that these CDs can reversibly transfer between aqueous and organic solvents by alternatively bubbling and removing CO at atmospheric pressure. The mechanism of such CO -switched phase transfer involves reversible acid-base reaction of amine-terminated CDs with CO and the reversible formation of hydrophilic ammonium salts. By using the CDs as catalysts, the phase transfer is applied in the Knoevenagel reaction for efficient homogeneous reaction, heterogeneous separation, and recycling of the catalysts.
Stimuli-responsive ionic liquid microemulsions can be reversibly switched from W/O monophase to oil–water phase separation upon alternate bubbling and removal of CO2.
Surfactant-free microemulsions (SFMEs)
have shown great potential
in many aspects such as chemical reactions and material preparation.
Ionic liquid (IL)-based SFME is a promising member in this family.
However, switchable phase separation of nonaqueous IL SFMEs has not
been reported up to now although it is of great importance for the
separation of products and recycling of the systems. Herein, a new
kind of CO2-responsive SFMEs composed of quaternary ammonium
IL, dimethyl sulfoxide, and ethyl acetate has been developed. It is
worth noting that the microemulsion can be reversibly switched between
emulsification and complete phase separation upon alternative CO2 and N2 bubbling at atmospheric pressure. The microstructures
and phase behavior of the systems before and after CO2 bubbling
have been systematically studied by phase diagrams, electrical conductivity,
dynamic light scattering, optical microscopy, and atomic force microscopy,
respectively. Mechanism studies verify that the reversible switching
is attributed to the generation and restoration of more hydrophilic
carbamate salts from the reaction of CO2 with IL anions,
which results in poor solubility of ILs in the nonaqueous microemulsions
and thus reversible breaking and rebuilding of the microemulsions.
Based on this unique phase behavior, the CO2-switchable
SFMEs are used as a microreactor for room temperature synthesis of
Zn-based metal–organic frameworks, and effective reaction and
microemulsion recycling have been achieved. This study may provide
a new strategy for the integration of reaction, separation, and recycling
procedures to obtain sustainable chemical processes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.