Temperature-Controlled Catalysis by Core-Shell-Satellite AuAg@pNIPAM@Ag Hybrid Microgels: A Highly Efficient Catalytic Thermoresponsive Nanoreactor

Lazaros Tzounis; Manuel Doña; Juan Manuel Lopez-Romero; Andreas Fery; Rafael Contreras-Caceres

doi:10.1021/acsami.9b10773

Temperature-Controlled Catalysis by Core-Shell-Satellite AuAg@pNIPAM@Ag Hybrid Microgels: A Highly Efficient Catalytic Thermoresponsive Nanoreactor

ACS Appl Mater Interfaces. 2019 Aug 14;11(32):29360-29372. doi: 10.1021/acsami.9b10773. Epub 2019 Aug 1.

Authors

Lazaros Tzounis^{1

2}, Manuel Doña³, Juan Manuel Lopez-Romero³, Andreas Fery^{4

5

6}, Rafael Contreras-Caceres^{3

7}

Affiliations

¹ Department of Materials Science & Engineering , University of Ioannina , GR-45110 Ioannina , Greece.
² Printed Electronic Devices of Things P.C. (PDoT) , Makrinitsis 122 , GR-38333 Volos , Greece.
³ Departamento de Química Orgánica, Facultad de Ciencias , Universidad de Málaga , 29071 Málaga , Spain.
⁴ Leibniz-Institut für Polymerforschung Dresden e.V. , Hohe Str. 6 , 01069 Dresden , Germany.
⁵ Physical Chemistry of Polymeric Materials , Technische Universität Dresden , 01069 Dresden , Germany.
⁶ Cluster of Excellence Centre for Advancing Electronics Dresden (cfaed) , Technische Universität Dresden , 01062 Dresden , Germany.
⁷ Department of Chemistry in Pharmaceutical Sciences, Faculty of Pharmacy , Complutense University of Madrid , Plaza Ramon y Cajal , 28040 Madrid , Spain.

PMID: 31329406
DOI: 10.1021/acsami.9b10773

Abstract

A novel wet-chemical protocol is reported for the synthesis of "temperature-programmable" catalytic colloids consisting of bimetallic core@shell AuAg nanoparticles 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 pNIPAM 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 a 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 toward 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/m² s, which is one of the highest values ever reported. The presence of plasmonic entities is confirmed by UV-vis spectroscopy. Dynamic light scattering proves the temperature responsiveness in all cases. Transmission electron microscopy and energy-dispersive X-ray (EDX) elemental mapping highlight the monodispersity 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 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 because of 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.

Keywords: bimetallic nanoparticles; core@shell@satellite structure; heterogeneous catalysis; nanoreactors; pNIPAM microgels; silver satellites; thermo-responsive behavior.