Optical And Antibacterial Properties Of Silver Nanoparticles And Their Composites

Silver nanoparticles(Ag NPs)have received widespread attention due to their good optical,catalytic,and antibacterial properties.At present,there are many methods for preparing Ag NPs,but the particle size and degree of dispersion of Ag NPs prepared by different methods are different.We can even change the external temperature and other parameters or add different metal ions to change the structure of Ag NPs to improve its performance.In addition to antibacterial properties,the color of Ag NPs have also received wide attention,including molecular detection(enhanced surface Raman),metal ion detection and surface treatment of Ag NPs(fabric finishing agents,coatings,antibacterial coatings,etc.).Polyvinyl alcohol(PVA)has a good water solubility,and it usually can be used as a dispersant and protective agent to prepare nanomaterials.However,its stabilization needs a certain time to achieve,the Ag NPs prepared just after using PVA has a certain instability at low concentrations.From the appearance,it will be reflected in the color of the Ag NPs itself.At the same time,the internal structure of the Ag NPs(particle size,particle arrangement)will also change.These can be determined by UV-visible spectroscopy(UV-vis),transmission electron microscopy(TEM).Ag NPs in a stable state shows different colors according to the shape and size of the particles.In actual use,these appearance colors may affect it in the application range.In this work,we first take the metastable Ag NPs of PVA as the research object,and find that the color of low concentration(such as 10 ppm Ag NPs)can change from yellow to wine red,and finally to black.Using TEM,through the analysis of its appearance and particle size,combined with the analysis of UV-vis spectra,the internal change mechanism of Ag NPs was studied,and compared with the appearance performance,it was considered that the color change of Ag NPs was the result of the chain aggregation of particles to coarsening into irregular aggregation,and we proposed the physical process of theoretical change.Secondly,through the autocatalytic property of Ag NPs,it is found that by adjusting the concentration of added copper ions,a colorless and antibacterial silvercopper nanoparticles solution is prepared at a higher temperature.This kind of silvercopper core-shell nanoparticles has a specific and good antibacterial property.At the same time,it can realize colorless Ag NPs and be used for antibacterial treatment of fabrics.We combined TEM and UV-vis spectroscopy to study mechanism of the structure.Finally,the stability of Ag NPs in sodium chloride solution was studied.It was found that Ag NPs could become completely colorless in appropriate sodium chloride environment,but no silver chloride precipitate was formed.TEM analysis showed that the size of particles decreased in sodium chloride environment.It was believed that the environment of sodium chloride resulted in the release of silver ions from particles and the formation of silver ion aqueous solution.These results prove that although sodium chloride helps to reduce the color of Ag NPs and make the yellow lighter,it is also convert Ag NPs to silver ions and cause a significant decrease in antibacterial properties.