Sabadasch Viktor, Wiehemeier Lars, Kottke Tilman, Hellweg Thomas
Physical and Biophysical Chemistry, Bielefeld University, Germany.
Soft Matter. 2020 Jun 21;16(23):5422-5430. doi: 10.1039/d0sm00433b. Epub 2020 Jun 3.
Responsive core-shell microgels are promising systems for a stabilization of Pd nanoparticles and control of their catalytic activity. Here, poly-N-n-propylacrylamide (PNNPAM) was copolymerized with methacrylic acid to yield microgel core particles, which were subsequently coated with an additional, acid-free poly-N-isopropylmethacrylamide (PNIPMAM) shell. Both core and core-shell systems were used as pH- and temperature-responsive carrier systems for the incorporation of palladium nanoparticles. The embedded nanoparticles were found to have a uniform size distribution with diameters at around 20 nm. Their catalytic activity was investigated by following the kinetics of the reduction of p-nitrophenol to p-aminophenol using UV-vis spectroscopy. For the PNNPAM microgel core, the temperature dependence of the rate constant followed the Arrhenius equation, which is an unusual behaviour for thermoresponsive carrier systems but common for passive systems such as polyelectrolyte brushes. In contrast, the catalytic activity of nanoparticles embedded in microgel core-shell systems decreased drastically at the volume phase transition temperature (44 °C) of the PNIPMAM shell. Accordingly, a promising architecture of passive nanoparticle-carrying core and thermoresponsive shell was realized successfully.
响应性核壳微凝胶是用于稳定钯纳米颗粒并控制其催化活性的有前景的体系。在此，聚-N-正丙基丙烯酰胺（PNNPAM）与甲基丙烯酸共聚以产生微凝胶核颗粒，随后用额外的无酸聚-N-异丙基甲基丙烯酰胺（PNIPMAM）壳进行包覆。核体系和核壳体系均用作pH和温度响应性载体体系以掺入钯纳米颗粒。发现嵌入的纳米颗粒具有均匀的尺寸分布，直径约为20 nm。通过使用紫外可见光谱跟踪对硝基苯酚还原为对氨基苯酚的动力学来研究其催化活性。对于PNNPAM微凝胶核，速率常数的温度依赖性遵循阿仑尼乌斯方程，这对于热响应性载体体系来说是不寻常的行为，但对于诸如聚电解质刷等被动体系来说是常见的。相比之下，嵌入微凝胶核壳体系中的纳米颗粒的催化活性在PNIPMAM壳的体积相变温度（44℃）时急剧下降。因此，成功实现了一种有前景的由被动纳米颗粒承载核和热响应性壳组成的结构。
