College of Chemistry and Materials Science , Sichuan Normal University , Chengdu 610068 , P. R. China.
Key Laboratory of Land Resources Evaluation and Monitoring in Southwest , Sichuan Normal University, Ministry of Education , Chengdu 610066 , P. R. China.
ACS Appl Mater Interfaces. 2018 Oct 10;10(40):34332-34339. doi: 10.1021/acsami.8b12989. Epub 2018 Sep 28.
Developing amphiphilic colloid catalysts is essentially important for realizing environmentally benign biphasic catalysis under atmospheric conditions. Herein, a linear structured plant polyphenol was employed as an amphiphilic stabilizer for preparing a series of amphiphilic Pd nanoparticles (PdNPs) colloids. For the as-prepared PdNPs colloids, the phenolic hydroxyls of plant polyphenols were responsible for the stabilization of PdNPs, whereas the rigid aromatic scaffold of plant polyphenols effectively suppressed the PdNPs from aggregation by providing a high steric effect. Thanks to the coexistence of hydrophilic phenolic hydroxyls and hydrophobic aromatic rings, the plant polyphenols induced tunable amphiphilic properties into the PdNPs, allowing an easier wetting of PdNPs with the substrate molecules. By tuning the content of plant polyphenols in the colloid, the particle size (3.17-4.73 nm) and the dispersity of the PdNPs were facilely controlled. When applied for atmospheric oxidation of insoluble alcohols in water by air, the amphiphilic PdNPs preferentially absorbed the alcohol substrates to create a relatively high-substrate-concentration microenvironment, which improved the mass transfer in the biphasic catalysis, allowing the proceeding of low-temperature (50 °C) atmospheric oxidation of diverse alcohols with high catalytic conversion, including aliphatic alcohols, cyclic aliphatic alcohols, and aromatic alcohols. Furthermore, the amphiphilic PdNPs colloid also exhibited excellent reusability with a conversion yield high up to 97.96% in the fifth cycle. In contrast, the control catalysts of poly(vinylpyrrolidone)- and poly(ethylene glycol)-stabilized PdNPs were completely inactivated in the fifth cycle. As a consequence, our findings provided a new route for developing an environmentally benign aqueous colloid catalyst that is both highly active and recyclable for mild biphasic oxidation reaction systems.
开发两亲胶体催化剂对于在大气条件下实现环境友好的两相催化至关重要。在此，我们使用线性结构的植物多酚作为两亲稳定剂，制备了一系列两亲钯纳米粒子（PdNPs）胶体。对于所制备的 PdNPs 胶体，植物多酚的酚羟基负责稳定 PdNPs，而植物多酚的刚性芳环结构通过提供高空间位阻有效地抑制了 PdNPs 的聚集。由于亲水性的酚羟基和疏水性的芳环的共存，植物多酚诱导可调两亲性进入 PdNPs，使 PdNPs 更容易润湿底物分子。通过调节胶体中植物多酚的含量，可以轻松控制 PdNPs 的粒径（3.17-4.73nm）和分散性。当用于空气中在水中对不溶性醇的大气氧化时，两亲 PdNPs 优先吸附醇底物，从而创造出相对高底物浓度的微环境，这改善了两相催化中的传质，允许在低温（50°C）下进行各种醇的大气氧化，包括脂肪醇、环状脂肪醇和芳香醇。此外，两亲 PdNPs 胶体还表现出优异的可重复使用性，在第五个循环中转化率高达 97.96%。相比之下，聚乙烯吡咯烷酮和聚乙二醇稳定的 PdNPs 的对照催化剂在第五个循环中完全失活。因此，我们的发现为开发高效且可回收的环境友好型水性胶体催化剂提供了一条新途径，该催化剂适用于温和的两相氧化反应体系。
