Department of Civil & Environmental Engineering, University of Cincinnati, Cincinnati, OH, USA.
Environ Sci Technol. 2010 Feb 15;44(4):1260-6. doi: 10.1021/es902240k.
The impact of capping agents and environmental conditions (pH, ionic strength, and background electrolytes) on surface charge and aggregation potential of silver nanoparticles (AgNPs) suspensions were investigated. Capping agents are chemicals used in the synthesis of nanoparticles to prevent aggregation. The AgNPs examined in the study were as follows: (a) uncoated AgNPs (H(2)-AgNPs), (b) electrostatically stabilized (citrate and NaBH(4)-AgNPs), (c) sterically stabilized (polyvinylpyrrolidone (PVP)-AgNPs), and (d) electrosterically stabilized (branched polyethyleneimine (BPEI)-AgNPs)). The uncoated (H(2)-AgNPs), the citrate, and NaBH(4)-coated AgNPs aggregated at higher ionic strengths (100 mM NaNO(3)) and/or acidic pH (3.0). For these three nanomaterials, chloride (Cl(-), 10 mM), as a background electrolyte, resulted in a minimal change in the hydrodynamic diameter even at low pH (3.0). This was limited by the presence of residual silver ions, which resulted in the formation of stable negatively charged AgCl colloids. Furthermore, the presence of Ca(2+) (10 mM) resulted in aggregation of the three previously identified AgNPs regardless of the pH. As for PVP coated AgNPs, the ionic strength, pH and electrolyte type had no impact on the aggregation of the sterically stabilized AgNPs. The surface charge and aggregation of the BPEI coated AgNPs varied according to the solution pH.
本研究考察了封端剂和环境条件（pH 值、离子强度和背景电解质）对银纳米粒子（AgNPs）悬浮液表面电荷和聚集势的影响。封端剂是用于纳米粒子合成以防止聚集的化学物质。本研究中考察的 AgNPs 如下：（a）未涂层 AgNPs（H₂-AgNPs），（b）静电稳定的（柠檬酸盐和 NaBH₄-AgNPs），（c）空间稳定的（聚乙烯吡咯烷酮（PVP）-AgNPs），和（d）电动稳定的（支化聚乙烯亚胺（BPEI）-AgNPs））。未涂层的（H₂-AgNPs）、柠檬酸盐和 NaBH₄ 涂层的 AgNPs 在较高的离子强度（100 mM NaNO₃）和/或酸性 pH（3.0）下聚集。对于这三种纳米材料，氯离子（Cl(-)，10 mM）作为背景电解质，即使在低 pH（3.0）下，水动力直径也几乎没有变化。这是由于残留银离子的存在，导致形成稳定的带负电荷的 AgCl 胶体。此外，即使在 pH 值较低的情况下，10 mM 的 Ca²+（10 mM）的存在也会导致三种先前确定的 AgNPs 的聚集。对于 PVP 涂层的 AgNPs，离子强度、pH 值和电解质类型对空间稳定的 AgNPs 的聚集没有影响。BPEI 涂层的 AgNPs 的表面电荷和聚集状态随溶液 pH 值而变化。
