Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Key Laboratory for Advanced Energy Devices, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi'an 710119, China.
College of Science, China University of Petroleum, Qingdao, Shandong 266580, China.
Nanoscale. 2018 Mar 28;10(12):5607-5616. doi: 10.1039/c8nr00327k. Epub 2018 Mar 12.
The catalytic activity of metal nanocrystals is mainly tuned through the control of their shapes and sizes. However, the shapes and sizes of many metal nanocrystals are difficult to control and therefore their catalytic activity is hard to tune. Here, we demonstrate another approach, using differently charged surfactants, for tuning the catalytic activity of metal nanocrystals. Au and Pd nanocrystals capped with cationic cetyltrimethylammonium bromide (CTAB) and anionic citrate are chosen to study the effect of surfactant charges on the catalytic activity. The oxidation of o-phenylenediamine to 2,3-diaminophenazine by HO is selected as a model reaction. The prepared Au and Pd nanocrystals are initially capped with CTAB, which is changed to citrate through surfactant exchange. Owing to the relatively weak electrostatic interaction of CTAB with the nanocrystals, the surfactant exchange does not induce observable changes in nanocrystal shapes and sizes. In contrast, the catalytic activity is greatly improved by the surfactant exchange. XPS analysis and theoretical calculations indicate that the adsorption of anionic citrate enriches the electrons of the nanocrystal surfaces, while the adsorption of CTAB depletes the electrons of the nanocrystal surfaces. The different catalytic activities of CTAB and citrate-capped nanocrystals arise from the different behaviors of electron transfer between the surfactants and the nanocrystal surface. Since the surfacants that electrostatically bind to the metal nanocrystals are facile to exchange into other surfactants, our findings provide an effective way to tuning the catalytic activity of metal nanocrystals.
金属纳米晶体的催化活性主要通过控制其形状和尺寸来调节。然而，许多金属纳米晶体的形状和尺寸难以控制，因此其催化活性难以调节。在这里，我们展示了另一种方法，使用带不同电荷的表面活性剂来调节金属纳米晶体的催化活性。选择带正电荷的十六烷基三甲基溴化铵（CTAB）和带负电荷的柠檬酸盐稳定的 Au 和 Pd 纳米晶体来研究表面活性剂电荷对催化活性的影响。选择 HO 将邻苯二胺氧化为 2,3-二氨基吩嗪作为模型反应。所制备的 Au 和 Pd 纳米晶体最初被 CTAB 稳定，通过表面活性剂交换将其转换为柠檬酸盐。由于 CTAB 与纳米晶体之间的静电相互作用相对较弱，因此表面活性剂交换不会引起纳米晶体形状和尺寸的可观察到的变化。相比之下，表面活性剂交换大大提高了催化活性。XPS 分析和理论计算表明，阴离子柠檬酸盐的吸附增加了纳米晶体表面的电子，而 CTAB 的吸附耗尽了纳米晶体表面的电子。CTAB 和柠檬酸盐稳定的纳米晶体的不同催化活性源于表面活性剂和纳米晶体表面之间电子转移的不同行为。由于静电结合在金属纳米晶体上的表面活性剂易于交换成其他表面活性剂，因此我们的发现为调节金属纳米晶体的催化活性提供了一种有效方法。
