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Authors Tzounis, L. ; Dona, M. ; Lopez-Romero, J. M. ; Fery, A. ; Contreras-Caceres, R.
Title Temperature controlled catalysis by core-shell-satellites AuAg@pNIPAM@Ag hybrid microgels: A highly efficient catalytic thermo-responsive nanoreactor
Date 29.07.2019
Number 57001
Abstract A novel wet-chemical protocol is reported for the synthesis of “temperature programmable” catalytic colloids consisting of bimetallic core@shell AuAg nanoparticles (AuAgNPs) encapsulated into poly(N-isopropylacrylamide) (pNIPAM) microgels with silver satellites (AgSTs) incorporated within the microgel structure. Spherical AuNPs of 50 nm in diameter are initially synthesized and used for growing a poly(N-Isoproylacrylamide) microgel shell with temperature stimulus response. A silver shell is subsequently grown on the Au core by diffusing Ag salt through the hydrophilic pNIPAM microgel (AuAg@pNIPAM microgel). The use of allylamine as co-monomer during pNIPAM polymerization facilitates the coordination of Ag+ with the NH2 nitrogen lone pair of electrons, which are reduced to Ag seeds (~14 nm) using a strong reducing agent, obtaining thus AuAg@pNIPAM@Ag hybrid microgels. The two systems are tested as catalysts towards the reduction of 4-nitrophenol (4-Nip) to 4-aminophenol (4-Amp) by NaBH4. Both exhibit extremely sensitive temperature-dependent reaction rate constants, with the highest K1 value of the order of 0.6 L/m2s, which is one of the highest values ever reported. The presence of plasmonic entities is confirmed by UV-vis spectroscopy. Dynamic light scattering (DLS) prove the temperature responsiveness in all cases. Transmission electron microscopy (TEM) and EDX elemental mapping highlight the mondispersity of the synthesized hybrid nanostructured microgels, as well as their size and metallic composition. The amount of gold and silver in both systems is obtained by thermogravimetric analysis (TGA) and the EDX spectrum. The reduction reaction kinetics is monitored by UV-vis spectroscopy at different temperatures for both catalytic systems, with the AuAg@pNIPAM@Ag microgels showing superior catalytic performance at all temperatures due to the synergistic effect of the AuAg core and the AgSTs. The principal novelty of this study lies in the “hierarchical” design of the metal-polymer-metal core@shell@satellite nanostructured colloids exhibiting synergistic capabilities of the plasmonic NPs for among others temperature controlled catalytic applications.
Publisher ACS Applied Materials & Interfaces
Wikidata
Citation ACS Applied Materials & Interfaces 11 (2019) 29360-29372
DOI https://doi.org/10.1021/ACSAMI.9B10773
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