USEPA Office of Research and Development, National Risk Management Laboratory, 26 West Martin Luther King Drive, Cincinnati, OH 45224, United States.
Sci Total Environ. 2010 Feb 1;408(5):999-1006. doi: 10.1016/j.scitotenv.2009.11.003. Epub 2009 Nov 27.
Most recently, renewed interest has arisen in manufactured silver nanomaterials because of their unusually enhanced physicochemical properties and biological activities compared to the bulk parent materials. A wide range of applications has emerged in consumer products ranging from disinfecting medical devices and home appliances to water treatment. Because the hypothesized mechanisms that govern the fate and transport of bulk materials may not directly apply to materials at the nanoscale, there are great concerns in the regulatory and research communities about potential environmental impacts associated with the use of silver nanoparticles. In particular, the unlimited combinations of properties emerging from the syntheses and applications of silver nanoparticles are presenting an urgent need to document the predominant salt precursors, reducing agents and stabilizing agents utilized in the synthesis processes of silver nanoparticles to guide the massive efforts required for environmental risk assessment and management.
The primary objective of this study is to present an evidence-based environmental perspective of silver nanoparticle properties in syntheses and applications. The following specific aims are designed to achieve the study objective: Aim 1--to document the salt precursors and agents utilized in synthesizing silver nanoparticles; Aim 2--to determine the characteristics of silver nanoparticles currently in use in the scientific literature when integrated in polymer matrices to form nanocomposites and combined with other metal nanoparticles to form bimetallic nanoparticles; Aim 3--to provide a summary of the morphology of silver nanoparticles; and (4) Aim 4--to provide an environmental perspective of the evidence presented in Aims 1 to 3.
A comprehensive electronic search of scientific databases was conducted in support of the study objectives. Specific inclusion criteria were applied to gather the most pertinent research articles. Data and information extraction relied on the type of synthesis methods, that is, synthesized silver nanoparticles in general and specific applications, nanocomposites, and bimetallic techniques. The following items were gathered for: type of silver salt, solvent, reducing agent, stabilizing agent, size, and type of application/nanocomposite/bimetallic, and template (for nanocomposites). The description of evidence was presented in tabular format. The critical appraisal was analyzed in graphical format and discussed.
An analysis of the scientific literature suggests that most synthesis processes produce spherical silver nanoparticles with less than 20nm diameter. Silver nanoparticles are often synthesized via reduction of AgNO(3), dissolution in water, and utilization of reductants also acting as capping or stabilizing agents for the control of particle size to ensure a relatively stable suspension. Two of the most commonly used reductants and stabilizing agents are NaBH(4) and citrate which yield particles with a negative surface charge over the environmental pH range (3-10). The environmental perspectives of these parameters are discussed.
It is expected that the antibacterial property of bulk silver is carried over and perhaps enhanced, to silver nanoparticles. Therefore, when one examines the environmental issues associated with the manufacture and use of silver nanoparticle-based products, the antibacterial effects should always be taken into account particularly at the different stages of the product lifecycle. Currently, there are two arguments in the scientific literature about the mechanisms of antimicrobial properties of silver nanoparticles as they relate to colloidal silver particles and inonic silver. Methodologies of risk assessment and control have to account for both arguments.
最近，由于制造的银纳米材料具有异常增强的物理化学性质和生物活性，与母体材料相比，人们对其重新产生了兴趣。从消毒医疗器械和家用电器到水处理，各种消费品都出现了广泛的应用。由于控制大块材料命运和迁移的假设机制可能不适用于纳米尺度的材料，因此监管和研究界非常关注与使用银纳米粒子相关的潜在环境影响。特别是，银纳米粒子的合成和应用中出现的无限组合的特性，迫切需要记录银纳米粒子合成过程中使用的主要盐前体、还原剂和稳定剂，以指导大量环境风险评估和管理所需的工作。
本研究的主要目的是从环境角度介绍银纳米粒子在合成和应用中的特性。为了实现研究目标，设计了以下具体目标：目的 1-记录合成银纳米粒子中使用的盐前体和试剂；目的 2-确定当前在科学文献中整合到聚合物基质中形成纳米复合材料并与其他金属纳米粒子结合形成双金属纳米粒子时使用的银纳米粒子的特性；目的 3-提供银纳米粒子形态的总结；和（4）目的 4-从目的 1 到 3 提供所呈现证据的环境角度。
为了支持研究目标，对科学数据库进行了全面的电子搜索。具体的纳入标准被应用于收集最相关的研究文章。数据和信息提取依赖于合成方法的类型，即一般合成的银纳米粒子和特定应用、纳米复合材料和双金属技术。收集了以下项目：银盐的类型、溶剂、还原剂、稳定剂、尺寸和应用/纳米复合材料/双金属的类型，以及模板（用于纳米复合材料）。证据的描述以表格形式呈现。以图形格式分析并讨论了批判性评价。
对科学文献的分析表明，大多数合成工艺生产的银纳米粒子的直径小于 20nm。银纳米粒子通常通过还原 AgNO3、溶解在水中以及使用还原剂来合成，还原剂还充当控制粒径的帽或稳定剂，以确保相对稳定的悬浮液。两种最常用的还原剂和稳定剂是 NaBH4 和柠檬酸盐，它们在环境 pH 范围（3-10）下产生带负电荷的表面。讨论了这些参数的环境观点。
预计块状银的抗菌性能会被传递并得到增强，从而转移到银纳米粒子上。因此，当人们研究与制造和使用基于银纳米粒子的产品相关的环境问题时，特别是在产品生命周期的不同阶段，都应该考虑到抗菌效果。目前，科学文献中有两种关于银纳米粒子抗菌性能的机制的论点，即与胶体银颗粒和离子银有关。风险评估和控制的方法必须考虑到这两个论点。
