Mechanism of gold metal ion reduction, nanoparticle growth and size control in aqueous amphiphilic block copolymer solutions at ambient conditions.
Mechanism of gold metal ion reduction, nanoparticle growth and size control in aqueous amphiphilic block copolymer solutions at ambient conditions.
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DOI：
10.1021/jp046221z
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发表时间：
2005-03
期刊：
影响因子：
--
通讯作者：
T. Sakai;P. Alexandridis
中科院分区：
文献类型：
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作者：
T. Sakai;P. Alexandridis
在室温下，在空气饱和的聚环氧乙烷-聚环氧丙烷-聚环氧乙烷（PEO-PPO-PEO）嵌段共聚物水溶液中，由四氯金酸（III）水合物（HAuCl4.3H2O）自发形成并有效稳定平均直径为7约20 nm的金纳米颗粒 在没有任何其他还原剂的情况下的温度。这里基于吸收光谱的嵌段共聚物浓度依赖性、AuCl4-还原的时间依赖性（动力学）以及颗粒尺寸的嵌段共聚物浓度依赖性来考虑颗粒形成机制。通过研究几种 PEO-PPO-PEO 嵌段共聚物，探讨了嵌段共聚物特性（例如分子量 (MW)、PEO 嵌段长度、PPO 嵌段长度和临界胶束浓度 (cmc)）的影响。我们的观察表明，AuCl4-形成金纳米颗粒包括三个主要步骤：（1）溶液中的嵌段共聚物还原金属离子，（2）金簇上嵌段共聚物的吸收和这些金簇表面金属离子的还原，以及（3）嵌段共聚物稳定的金属颗粒的生长。虽然 PEO 和 PPO 嵌段都有助于 AuCl4 还原（步骤 1），但 PEO 的贡献似乎占主导地位。在步骤2中，由于嵌段共聚物的两亲特性（PPO的疏水性），嵌段共聚物在金簇表面发生吸附。与 PEO 均聚物系统相比，PEO-PPO-PEO 嵌段共聚物系统获得的颗粒形成效率要高得多，这可归因于嵌段共聚物促进的吸附和生长过程（步骤 2 和 3）。产生的金纳米粒子的尺寸由上述机制决定；尺寸随着嵌段共聚物总分子量引起的反应活性的增加而增加，并且由于嵌段共聚物的两亲特性而受到吸附的限制。
Spontaneous formation and efficient stabilization of gold nanoparticles with an average diameter of 7 approximately 20 nm from hydrogen tetrachloroaureate(III) hydrate (HAuCl4.3H2O) were achieved in air-saturated aqueous poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer solutions at ambient temperature in the absence of any other reducing agent. The particle formation mechanism is considered here on the basis of the block copolymer concentration dependence of absorption spectra, the time dependence (kinetics) of AuCl4- reduction, and the block copolymer concentration dependence of particle size. The effects of block copolymer characteristics such as molecular weight (MW), PEO block length, PPO block length, and critical micelle concentration (cmc) are explored by examining several PEO-PPO-PEO block copolymers. Our observations suggest that the formation of gold nanoparticles from AuCl4- comprises three main steps: (1) reduction of metal ions by block copolymer in solution, (2) absorption of block copolymer on gold clusters and reduction of metal ions on the surface of these gold clusters, and (3) growth of metal particles stabilized by block copolymers. While both PEO and PPO blocks contribute to the AuCl4- reduction (step 1), the PEO contribution appears to be dominant. In step 2, the adsorption of block copolymers on the surface of gold clusters takes place because of the amphiphilic character of the block copolymer (hydrophobicity of PPO). The much higher efficiency of particle formation attained in the PEO-PPO-PEO block copolymer systems as compared to PEO homopolymer systems can be attributed to the adsorption and growth processes (steps 2 and 3) facilitated by the block copolymers. The size of the gold nanoparticles produced is dictated by the above mechanism; the size increases with increasing reaction activity induced by the block copolymer overall molecular weight and is limited by adsorption due to the amphiphilic character of the block copolymers.