| Among the preparation methods of silver nanoparticles(Ag NPs),biological method has been widely concerned because of its green,high efficiency,rapidity etc.The biological organic matter used in biological method included microorganisms,plant extract etc.,among which the plant extract was the most widely used.In the application of Ag NPs,a large number of studies were mainly aimed at their antibacterial properties,and many researchers have published a considerable number of papers.The relationship between the structural characteristics of Ag NPs and the catalytic degradation efficiency of the Ag NPs prepared by various plant extracts,as well as the mechanism of the Ag NPs to the catalytic degradation of various kinds of dyes,has not been studied yet,and the related papers published abroad were mainly focused on some indicators reduction(such as methyl orange,methyl blue,methyl red,etc.),and the research on the catalytic degradation of synthetic dyes was not seen.In this paper,Ag NPs were prepared by green reduction of plant-intermediate polyphenols(tea polyphenols,grape seed and Eucommia ulmoides extract).The effects of effective components and various reaction conditions on the dispersion stability,UV-vis absorption spectrum,particle size distribution and morphology of Ag NPs dispersion system were studied,and the reaction mechanism of green reduction preparation of Ag NPs was also studied.For the biological preparation of Ag NPs,the effective preparation of silver nanoparticles was confirmed by measuring the UV-Vis absorption spectrum of the solution and the EDS energy spectra of the particles.The TEM images of tea polyphenol,grape seed extract and Eucommia ulmoides extract Ag NPs showed that they were basically spherical or ellipsoid.It was found that the particle size distribution of the three kinds of plant polyphenol Ag NPs was extensive,mainly in the range of 1?10 nm and 10?100 nm.At the same time,various reaction conditions(such as reaction temperature,p H value of solution and concentration of precursor silver nitrate)would affect the preparation of silver nanoparticles,which would also affect the catalytic degradation of dyes by Ag NPs.In the catalytic degradation experiments of dyes,the reductant used was sodium borohydrate,while the target dyes were monoazo dyes,diazo dyes and oxygen anthracene dyes.Under the condition that the Ag NPs catalyst was not added,the sodium borohydride reducing agent had certain reactivity to the monoazo dye(such as Acid Orange 7 and the Acid Red B)and the heterocyclic dye(such as rhodamine 6G and rhodamine B).The addition of the Ag NPs catalyst greatly improved the reaction speed,and the color of the dye solution after the reaction had changed obviously.The mechanism of the catalytic reduction and degradation of the azo-type dye was determined by the related experiments,and the deactivation of the azo group and the imino group were determined,and the parent structure of the azo dye after the reaction was destroyed,and new organic decomposition products were generated.The dye solution produced a new absorption peak or absorption band in the ultraviolet region.The catalytic performance of plant polyphenol Ag NPs prepared under different reaction conditions was very different,and Eucommia ulmoides extract Ag NPs prepared at lower temperature showed higher catalytic efficiency in catalytic degradation of Direct Violet 1 and Direct Orange 26 dyes.When the target degradation dye contains more functional groups that could be involved in the reaction,Eucommia ulmoides extract Ag NPs prepared at higher temperature showed higher catalytic efficiency.Because the Ag NPs prepared under the condition of higher p H value had smaller particle size and higher effective concentration,they showed the highest catalytic activity.Totally,the catalytic efficiency of Ag NPs was the result of the particle size distribution,particle concentration and the number of functional groups involved in the reductive degradation reactions. |
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