前驱体水解对纳米铂形状控制合成的影响

Effect of Precursor Hydrolysis on Shape-controlled Synthesis of Pt Nanocrystals

以聚丙烯酸钠 (NaPA :Mw≈ 2 10 0 )为保护剂 ,对比研究了H2 还原K2 PtCl4和K2 PtCl6水溶液制备纳米铂晶粒的形状选择性 ,揭示了前驱体的水解对纳米铂晶粒的形状控制合成具有显著影响 .文献中通常采用的合成立方体形状纳米铂的K2 PtCl4前驱体在水溶液中不稳定 ,避光静置一周会析出黑色沉淀 .这种不稳定性导致了以K2 PtCl4为Pt前驱体的合成结果难以重复 .相比而言 ,避光静置的K2 PtCl6水溶液很稳定 ,以它为前驱体合成的纳米铂通常为削角八面体 .K2 PtCl6水溶液暴露于室内光线中会出现 [PtCl6] 2 -的光致水解 .当 [PtCl6] 2 -的紫外特征吸收峰 ( 2 60nm)由于光致水解完全消失后 ,以聚丙烯酸钠为保护剂 ,通过H2 还原可以有选择性地 (约 80 %)合成由 {10 0 }晶面包裹的立方体形状的纳米铂 .

With sodium polyacrylate (NaPA : M-w approximate to 2100) as a protector, H-2 reduction of aqueous K2PtCl4 and K2PtCl6 were performed for shape-controlled synthesis of platinum (Pt) nanocrystals. It was found that the hydrolysis of the Pt precursors affected significantly the shape of Pt nanocrystals synthesized. Aqueous K2PtCl4, which was frequently used in earlier literature works for producing cubic Pt nanocrystals, proved not stable in the present work, it was hydrolyzed to form a black deposit when the solution was aged in dark for a week. While the aqueous K2PtCl6 was fairly stable in the dark aging, synthesis with fresh K2PtCl6 solution produced mainly truncated-octahedral Pt nanocrystals by H-2 reduction with NaPA as the protector. An exposure to ambient light was shown to induce a hydrolysis of [PtCl6](2-) in the K2PtCl6 solution. When the characteristic absorption of [PtCl6](2-) ions (260 nm) disappeared entirely by exposing the K2PtCl6 solution to the ambient light, cubic Pt nanocrystals enclosed with {100} facets were produced selectively (ca. 80%) from thereafter H-2 reduction under NaPA protection. It is emphasized that a proper control of the hydrolysis or light-induced hydrolysis of the Pt precursors is crucial for the,synthesis of cubic Pt nanocrystals.