Browsing by Author "Li, Songjun"

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    Self-switchable polymer reactor with PNIPAM-PAm smart switch capable of tandem/simple catalysis
    (Elsevier, 2021-10-11) Wei, Wenjing; Thakur, Vijay Kumar; Li, Songjun; Chianella, Iva
    In this paper, we report a novel three-layer polymer reactor capable of simple/tandem self-controlled catalysis. The top and bottom layers were composed of two different molecularly imprinted polymers respectively containing two catalytic sites (an acidic site catalyzing hydrolysis and metal nanoparticles catalyzing reduction), performing two selective tandem reactions without interference between each other. The middle layer was composed of a copolymer of poly-N-isopropylacrylamide (PNIPAM) and polyacrylamide (PAm) in different ratio, acting as a temperature-responsive switch for the tandem catalysis process. In an aqueous environment, when the temperature is lower than the Lower Critical Solution Temperature (LCST) of the copolymer, the reactor exhibited an open middle access (hydrophilic condition) of intermediate, allowing the tandem processes from hydrolysis to reduction. When the temperature is higher than the LCST, the channels of the middle layer were closed (hydrophobic condition), which obstructed the access of reactants. As a result, the reactor could only conduct simple hydrolysis processes. Therefore, with the three-layer structure, the polymer reactor has led to a self-controlled catalysis. This new multi-layer polymeric reaction concept can expand the practical use of functional catalysts by permitting the control of processes in large temperature ranges.
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    Smart bilayer polymer reactor with cascade/non-cascade switching catalyst characteristics
    (Elsevier, 2020-05-06) Wei, W.; Xiao, Panpan; Thakur, Vijay Kumar; Chianella, Iva; Li, Songjun
    In this work, a new method is proposed to meet the challenge of preparing new catalysts with cascade/non-cascade switching catalytic property. Inspired from “soft” characteristics and divisional isolation function in natural biological systems, this objective was accomplished by developing a new class of hydrogels made of two unique functional layers with different temperature responses where each may self-govern coupled processes at a specific temperature. This hydrogel polymer reactor exhibited almost no catalytic activity at low-temperature range (<37 °C) as both channels of bilayer hydrogel polymer catalyst were closed. At modest temperatures (between 37 °C and 50 °C), the first step of the tandem reaction (the hydrolysis of p-nitrophenyl acetate (NPA)) showed significant reactivity that arises from the relaxing of the weak polymer complexes in the hydrogel layer. This enabled NPA the access to the acidic catalytic active center of the hydrogel. At range of higher temperatures (>50 °C), the hydrogel catalytic polymer reactor further exhibited significant efficiency towards the hydrolysis reaction of NPA as well as the reduction of the intermediate product p-nitrophenol (NP). This mainly resulted from the opening of both the weak polymer complexes and the stronger polymer complexes hydrogel layers, allowing entrance to both the acidic catalytic active center and the metal nanoparticles active center. As a result, the novel hydrogel polymer reactor could be used to control cascade/non-cascade catalysis reactions. This new protocol enables efficient control of switchable tandem reactions, inspiring for difficulty to control tandem catalytic reactors
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    Towards next generation “smart” tandem catalysts with sandwiched mussel-inspired layer switch
    (Elsevier, 2020-05-18) Wei, Wenjing; Thakur, Vijay Kumar; Chew, Y. M. John; Li, Songjun
    In this paper, we prepared a novel reactor with switchable ability to address present challenges in tandem catalyst. By introducing mussel-inspired moiety, this goal was achieved via preparing a “smart” polymer reactor which can open or closes the entry tunnel of the targeted substrate in cascade reactions. The catalyst consisted of two functional layers acting as tandem catalytic parts and one smart layer with mussel-inspired moieties as a controlled middle switch. The top and the bottom layer were made of molecularly imprinted polymers and catalytic components, like acidic parts and metal nanoparticles, respectively. The middle layer made of polymeric dopamine (PDPA) and acrylamide with self-healing ability will allow or inhibit the intermediate product for the reaction, thus controlling the process of the tandem catalysis. As a result, the novel catalyst exhibited self-controlled tandem catalysis, which provides new opportunities to design smart tandem catalysts, showing a promising prospect in this area.