Do polymer ligands block the catalysis of metal nanoparticles? Unexpected importance of binding motifs in improving catalytic activity
Do polymer ligands block the catalysis of metal nanoparticles? Unexpected importance of binding motifs in improving catalytic activity
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DOI：
10.1039/d0ta03906c
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发表时间：
2020-08
影响因子：
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通讯作者：
Lei Zhang;Zichao Wei;Michael Meng;G. Ung;Jie He
中科院分区：
文献类型：
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作者：
Lei Zhang;Zichao Wei;Michael Meng;G. Ung;Jie He
由合成聚合物连接的金属纳米粒子在自组装、纳米医学和催化等领域具有广泛的应用前景。聚合物配体中的结合基序通常作为聚合物的末端官能团，大多限于硫醇盐。由于结合基序仅代表聚合物中许多重复单元的一小部分，因此其重要性常常被忽视。本文报道了聚合物N-杂环卡宾（NHC）配体在提供氧化稳定性和促进贵金属NP的催化活性方面的独特性。开发了两种用于聚合物NHC的“接枝”方法，用于在各种溶剂中和具有不同尺寸的预合成的金属NP。值得注意的是，咪唑鎓封端的聚苯乙烯可以在2分钟内修饰金纳米粒子（AuNPs），同时达到与聚苯乙烯-硫醇（SH）相似的接枝密度，需要6小时的修饰。我们证明聚合物NHC在空气中的高温下极其稳定。有趣的是，聚合物配体的结合基序主导金属纳米颗粒的催化活性。聚合物NHC改性的金属NP显示出改善的活性，而与表面拥挤无关。在AuNP的情况下，用聚苯乙烯NHC修饰的AuNP的活性比柠檬酸盐封端的AuNP高约5.2倍，比用聚苯乙烯硫醇盐修饰的AuNP高22倍。鉴于配体控制的金属纳米颗粒的催化性能，我们的研究结果说明了在过去被忽视的结合基序的重要性。
Metal nanoparticles (NPs) tethered by synthetic polymers are of broad interest for self-assembly, nanomedicine and catalysis. The binding motifs in polymer ligands usually as the end functional groups of polymers are mostly limited to thiolates. Since the binding motif only represents a tiny fraction of many repeating units in polymers, its importance is often ignored. We herein report the uniqueness of polymeric N-heterocyclic carbene (NHC) ligands in providing oxidative stability and promoting the catalytic activity of noble metal NPs. Two “grafting to” methods were developed for polymer NHCs for pre-synthesized metal NPs in various solvents and with different sizes. Remarkably, imidazolium-terminated polystyrene can modify gold NPs (AuNPs) within 2 min while reaching a similar grafting density to polystyrene-thiol (SH) requiring 6 h modification. We demonstrate that polymer NHCs are extremely stable at high temperature in air. Interestingly, the binding motifs of polymer ligands dominate the catalytic activity of metal NPs. Polymer NHC modified metal NPs showed improved activity regardless of the surface crowdedness. In the case of AuNPs, AuNPs modified with polystyrene NHCs are approximately 5.2 times more active than citrate-capped ones and 22 times more active than those modified with polystyrene thiolates. In view of ligand-controlled catalytic properties of metal NPs, our results illustrate the importance of binding motifs that has been overlooked in the past.