A Novel Approach for Synthesizing Ultra–Small Silver Nanoparticles Using Covalent Organic Frameworks as Template, Stabilizer and Reductant at Room Temperature

The preparation of ultra–small silver nanoparticles (average diameter ≤10 nm) is a technical problem because of their aggregation tendency. Therefore, the preparation conditions are usually harsh and complex. It is widely recognized that covalent organic frameworks (COFs) represent a novel class of porous crystalline compounds with broad applications in various fields. In this work, an environmentally and economically friendly new method has been developed for synthesizing ultra–small silver nanoparticles by reducing silver ions in ethanol solution with a covalent organic framework (TPB–DMTP–COF) as a template and reductant at room temperature. Interestingly, the TPB–DMTP–COF not only serves as a template and reductant but also functions as a stabilizer. Moreover, the TPB–DMTP–COF can be utilized repeatedly as a reductant. The morphology and structure of the silver nanoparticles were examined using transmission electron microscopy and showed that they were spherical with an average particle size of approximately 7.5 nm. Compared with the previously reported silver nanoparticles, the silver nanoparticles synthesized by this new method are not coated with Surfactant, such as Polyvinylpyrrolidone (PVP). As a result, they possess a larger exposed surface area, exhibit increased activity, and demonstrate excellent antimicrobial properties against both Gram–negative Escherichia coli and Gram–positive bacteria Staphylococcus aureus.