Abstract:
Tandem catalysis can perform multi-step catalytic reactions in one-pot
sequentially, which not only improves the efficiency of reactions significantly, but
also decreases time, energy and the amounts of reagents needed. However, as
there is always more than one active site (catalyst) in tandem reactors, it is critical
to separate different sites and ensure each step is conducted individually.
Moreover, it is often challenging to control the whole reaction processes due to
the complexity of the systems. In this research, several bio-inspired catalytic
reactors were proposed and developed to address the two challenges of site
separation and smart control of tandem catalysis.
First of all, the goal of sites separation has been achieved in this work through an
enzyme-inspired molecularly imprinted polymer reactor MIP-Au-NP-BNPC and a
core-shell structure catalytic nanoreactor AMPS@AM-Ag. Two molecularly
imprinted cavities were created in MIP-Au-NP-BNPC. The different channels of
the two catalytic sites in the reactor enabled different catalytic reactions to occur
in different regions, resulting in the process of tandem reactions. As a result of
the radial distribution of catalytic sites and mass transfer, the core-shell structure
of AMPS@AM-Ag enabled the nanoreactor to perform different catalytic
processes sequentially. Hence, the nanoreactor demonstrated the ability to
conduct tandem catalysis with successful site separation.
Then a biomimetic switch was introduced into the reactor to achieve the smart
control of the catalytic process. Firstly, a new type of catalytic reactor consisting
of a three-layer mussel-inspired polymer, MIP-AgPRS, was developed. The
smart switchable layer composed of mussel-inspired self-healing copolymer was
prepared between two MIP layers. This middle smart layer was able to react to
different temperatures, permitting either simple or tandem reactions by closing
and opening the access of the intermediate products.
Secondly, a bilayer polymer reactor, DPR, composed of two different
temperature-sensitive polymer layers was prepared. The two functional layers
were not only able to respond to different specific temperatures, but each also
contained different catalytic sites. Because of the two different phase transition
processes of the two layers, the polymer reactor demonstrated to be able to
perform simple/tandem catalysis in different temperature regions. As a result, this
new type of bilayer polymer reactor was capable of achieving smart control of the
tandem reactions.
Finally, a three-layer switchable polymer reactor, PRS, with two MIP layers and
a PNIPAM-PAM switchable layer in the middle was prepared. In an aqueous
environment, when the temperature was low (lower than 47 °C), it exhibited an
open access (hydrophilic condition), while when the temperature was high (higher
than 47 °C), it became closed (hydrophobic condition). Furthermore, a
comonomer (AM) was introduced in the middle layer with different ratios to adjust
the responsive temperature range, enabling a more comprehensive range of
practical uses. Therefore, a fast responsive and stable polymer reactor with self-
controlled catalytic property was obtained.
By preparing different types of new catalytic reactors, the research carried out
here has shown the ability to achieve a smart control of the tandem catalysis
while separating the catalytic sites effectively. Therefore, this study has
highlighted new solutions to address the challenges present in tandem catalysis
and has provided novel inspiration on how to exploit functional polymers while
performing complicated catalytic reactions.