Pickering interfacial
catalysis provides an excellent platform
for biphasic reactions, but the separation and recycling of nanocatalysts
is a challenge because of high adsorption energy of nanocatalysts
at the liquid–liquid interface. In this work, we represent
a new type of versatile Pickering emulsion based on magnetic and CO2-responsive nanohybrids Fe3O4@SiO2@P(TMA–DEA). The smart nanoparticles can stabilize
the water-in-oil Pickering emulsion in the biphasic system and achieve
the subsequent demulsification by bubbling CO2 ascribed
to their reversible switching surface. In the absence of energy barrier,
the nanohybrids can be easily captured in situ by magnetic field in
2 min and showed excellent recyclability. In the Anelli system for
alcohol oxidation, the nanocatalyst exhibited threefold enhancement
in catalytic efficiency in comparison with an unemulsified two-phase
and little loss on activity after five cycles. The conceptually novel
dual-responsive system offers a green and energy-saving strategy for
effective recycling of the nanocatalyst and intensification of biphasic
reaction.
We
report in this paper the design and synthesis of a pH-responsive
polymeric interfacial catalyst (PIC) via one-step grafting of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) onto a polyaryletherketone having pendant
benzimidazole groups (SCBI-PAEK-6F). The TEMPO-functionalized polymer
has been systematically characterized with 1H nuclear magnetic
resonance, Fourier-transform infrared spectroscopy, elemental analysis,
contact angle, and transmission electron microscopy. Moreover, this
well-designed polymer has been applied in the oxidation of alcohols
under Montanari conditions. It is found that the functionalized polymer
can aggregate at the water–oil interface and act as an efficient
stabilizer to facilitate the formation of a stable Pickering emulsion,
which shows outstanding catalytic activity for alcohol oxidation through
the microreactor mechanism. Moreover, the PIC is featured with desirable
high pH responsiveness due to the valuable benzimidazole groups. De-emulsification
of the Pickering emulsion reaction system can be conveniently triggered
by simply tuning the system pH value to 3, thus facilitating the facile
recovery of the PIC. In addition, the sustainable catalyst can be
reused for subsequent cycles of alcohol oxidation without appreciable
loss in catalytic activity or selectivity.
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