Effect of Methacrylic Acid in PNNPAM Microgels on the Catalytic Activity of Embedded Palladium Nanoparticles

• Published in: Macromolecular chemistry and physics 2022-06, Vol.223 (11), p.n/a
• Main Authors: Sabadasch, Viktor, Fandrich, Pascal, Annegarn, Marco, Hellweg, Thomas
• Format: Article
• Language: English
• Subjects: catalysis; Catalytic activity; Charge density; Copolymerization; Copolymers; Methacrylic acid; Microgels; Nanoparticles; Nitrophenol; Palladium; Photon correlation spectroscopy; Rate constants; Spectrum analysis; Titration
• ISSN: 1022-1352; 1521-3935
• DOI: 10.1002/macp.202200045

Poly‐N‐n‐propylacrylamide based microgels with embedded Pd‐nanoparticles are synthesized with varying amounts (5–25 mol%) of methacrylic acid (MAc) comonomer. The microgels are characterized to investigate the influence of the comonomer content on catalytic activity of the hybrid particles. Since the acidity changes significantly upon copolymerization, the incorporated amount and apparent p Ka value of the MAc via potentiometric titration are determined. The thermoresponsive properties of the microgels are characterized by means of photon correlation spectroscopy at pH values of 4 and 10, which correspond to the protonated and deprotonated state of the acidic copolymer according to the determined p Kavalues. MAc shows tremendous influence on the thermoresponsivity of the microgels not only related to the amount of MAc but especially upon change in pH. The prepared microgel systems are subsequently loaded with palladium nanoparticles. Their catalytic activity is investigated by the reduction of 4‐nitrophenol. The catalytic degradation of the educt is monitored via UV–vis spectroscopy and the observed absorbance decay is analyzed by a pseudo‐first order kinetic. Derived reaction rate constants are normalized with respect to the surface area of the palladium nanoparticles, revealing that the charge density and hydrophilicity within the microgel template greatly affect reactivity of embedded nanoparticles. The effect of methacrylic acid (MAc) copolymerized within poly‐N‐n‐propylacrylamide microgels on the reactivity of embedded palladium nanoparticles is investigated. The catalytic activity is tested via the reduction of 4‐nitrophenolate to 4‐aminophenol. Palladium nanoparticles contained in microgels with increased MAc content showed significantly lower catalytic activity than systems with low MAc content.