Improved Smart Microgel Carriers for Catalytic Silver Nanoparticles

Abstract

Acrylamide-based, thermoresponsive core–shell microgels with a linear phase transition region are used as improved carriers for catalytically active silver nanoparticles in the present study. In this context, we investigated the swelling behavior of the carriers and the stability of the silver nanoparticles inside the polymer network with photon correlation spectroscopy, transmission electron microscopy, and by following the surface plasmon resonance of the nanoparticles. Depending on the cross-linker content of the microgel core, we observed very good stability of the nanoparticles inside the microgel network, with nearly no bleeding or aggregation of the nanoparticles over several weeks for core cross-linker contents of 5 and 10 mol %. The architecture of the hybrid particles in the swollen state was investigated with cryogenic transmission electron microscopy. The particles exhibit a core–shell structure, with the silver nanoparticles located mainly at the interface between the core and shell. This architecture was not used before and seems to grant advanced stability to the nanoparticles inside the network in combination with good switchability of the catalytic activity. This was measured by following the reduction of 4-nitrophenole, which is a well-studied model reaction. The obtained Arrhenius plots show that similar to previous works, the swelling of the core and shell can influence the catalytic activity of the silver nanoparticles. As mentioned before, the cross-linker content of the core seems to be a very important parameter for the switchability of the catalytic activity. A higher cross-linker content of the core seems to be connected to a stronger influence of the carrier swelling degree on the catalytic activity of the silver nanoparticles.

Microgel organocatalysts: modulation of reaction rates at liquid–liquid interfaces

“…Here, microgels have been investigated as responsive carrier colloids for catalytically active materials, naming metal nanoparticles, metallic complexes, organocatalysts and enzymes. [21][22][23][24][25][26] In particular, the most explored catalytic systems are LCST-type microgel hydrides containing metallic nanoparticles. 21,22,27 A more recent report focuses on exploring upper critical solution temperature type microgels (UCST-type) as nanocatalyst platforms for silver nanoparticles.…”

“…[21][22][23][24][25][26] In particular, the most explored catalytic systems are LCST-type microgel hydrides containing metallic nanoparticles. 21,22,27 A more recent report focuses on exploring upper critical solution temperature type microgels (UCST-type) as nanocatalyst platforms for silver nanoparticles. 23 In this work, silver nanoparticles were applied to catalyse the reduction of 4nitrophenol whereas the temperature induced UCST-type collapse of the microgel network was used to control the velocity of this reaction.…”

Recent advances in stimuli-responsive core-shell microgel particles: synthesis, characterisation, and applications

“…These microgels comprise epoxy groups in the core which can be subsequently modified by reaction with 2-aminoethane thiol to introduce SH and also NH 2 groups [66,67]. Brändel et al optimised catalytic response of silver NPs also located around the core in core-shell microgels with linear thermoresponse, the structure of which will be further discussed below [68]. Suzuki and Kawaguchi also achieved high loadings of in situ synthesised magnetic particles in the spherical microgel core using again copolymerisation of glycidyl methacrylate to introduce immobilising functions [69], whereas Xu et al provided an example of a cylindrical core-shell structure loaded with magnetite particles stabilised by the shell.…”

“…Especially the last system shows a drastic change of the reaction rate. Reproduced from reference [68], American Chemical Society ACS Omega swelling behaviour even if confined to a solid interface (Siwafer) [57]. In this work, we have used ellipsometry to measure the film thickness as a function of temperature while the wafers were immersed in water.…”

Artificial reactor containing polymeric bilayer architectures for the formation of self-controlled tandem catalytic-ability

“…The use of self-controlled tandem catalysts in chemical synthesis would allow the ongoing tandem reactions to run in a controllable and tunable way, endowing the systems with catalytic one-pot ability [4,5]. This privilege often arises from the careful control of the structure-activity relationship at the undergoing catalysts (such as the adoption of smart hydrogels [6], functional microspheres [7] and hierarchical structures [8]), which leads to a restriction on either the substrate channeling or access to the catalytic sites in these catalysts. In this way, the use of self-controlled catalysts leads to the occurrence of self-controlled catalytic ability.…”