Synthesis Of Silver Nanoparticles Under Solar Radiation Using The Aqueous Extract Of Cyperus Rptundus L.bulb And Their Applications

With the development of nanotechnology,the demand for metal nanoparticles had gradually increased.Silver nanoparticles（AgNPs）have been widely used in nanotechnology due to their broad-spectrum antibacterial properties,biocompatibility,efficient thermal and electrical conductivity.Common methods for synthesizing metal nanoparticles include physical methods and chemical methods.Physical methods are usually energy-intensive and have high requirement for equipment.And the chemical methods always need chemical reagents that may cause harm to ecological environment.Biosynthesis methods have developed rapidly in recent years because of its biocompatibility and harmlessness to the environment.In the biosynthesis methods,plant extracts are the preferred materials for biosynthesis due to the advantages of easy availability and non-contamination compared with the longer culture period of biosynthesis by microbes.However,medicinal plants get attention because they contain active ingredients that are beneficial to humans and can increase the biocompatibility of nanoparticles.The main research contents of this subject are as follows:1.AgNPs were rapidly synthesized photochemically using the aqueous extract of Cyperus rotundus L.bulbs.The synthesized AgNPs were characterized by ultraviolet–visible spectroscopy（UV-vis）,dynamic light scattering（DLS）,X-ray diffraction（XRD）,transmission electron microscopy（TEM）and electron selective diffraction（SADE）.The results showed that the entire synthesis reaction was completed within 90 min by this method.It was confirmed that the AgNPs were successfully synthesized by visual observation and UV-vis characterization.The DLS result showed that the synthesized AgNPs had a hydradynamic particle size of 124.7 nm and a polydispersity index（PDI）of 0.205.The TEM characterization found that the synthesized AgNPs were approximately spherical with an average particle size of 11 nm.The characterizations by XRD,high-resolution transmission electron microscopy（HRTEM）and SADE showed that the synthesized AgNPs exhibited the same face-centered cubic crystal structure as metallic silver,and preferentially oriented in the（111）crystal plane.The effect of different p H value of the aqueous extract of Cyperus rotundus L.bulbs was also studied on the synthesis of AgNPs.It was found that the synthesis rate of AgNPs was faster under alkaline conditions than that under neutral and acidic conditions,and the synthesized AgNPs had smaller particle size and better stability.The AgNPs synthesized under acidic and neutral conditions had smaller PDI values,among which the AgNPs synthesized under neutral condition of p H=7 had the smallest PDI.2.The catalytic activity of the AgNPs was investigated using common organic dye pollutants including methylene blue（MB）,methyl orange（MO）,Congo red（CR）,p-nitrophenol（4-NP）and rhodamine B（Rh-B）.The results showed that MB,MO,CR.4-NP and Rh-B faded completely in 5 s,1 min,16 min,16 min and 2 min under the catalysis of the AgNPs,respectively,indicating that the AgNPs had effective catalytic effect on the reduction of MB,MO,CR,4-NP and Rh-B.3.The synthesized AgNPs were added to sodium alginate（SA）,and a composite coating was formed through the cross-linking of SA and 2%Ca Cl₂.The effect of different AgNPs contents on the physicochemical properties of the composite film was discussed.The FT-IR characterization indicated that adding AgNPs weakened the hydrogen bonds of SA-based composite films,and the weakening degree of hydrogen bonds by 3%and 5%AgNPs was greater than that by 1%AgNPs.The ultraviolet-visible diffuse reflectance spectrum（UV-vis-DRS）characterization results showed that the higher the content of AgNPs was,the greater the influence on the absorbance of SA-based composite films would be.In the experiment of the dissolution rate,it was found that the increase of AgNPs reduced the dissolution rate of the SA matrix film,and the SA-AgNPs-1%composite film had the lowest dissolution rate,and then the dissolution rate of the composite film increased with the increase of AgNPs content.The measurements of contact angle showed that the hydrophobicity of SA-based films increased with the increase of AgNPs content.4.The SA-AgNPs-1%composite film was selected for morphological characterization and fruit preservation experiments.In SEM characterization,it was found that the addition of AgNPs caused cracks on the surface of the composite film.In AFM characterization,the SA-AgNPs-1%composite film had a rougher surface morphology and smaller pore size than the SA film.In the fruit preservation experiments,both SA film and SA-AgNPs-1%composite film helped to delay the lesions or spoilage in the appearance of strawberries and bananas.Compared with SA film,SA-AgNPs composite film could effectively delay the increase of weight loss rate.In conclusion,the photochemical synthesis of AgNPs using the aqueous extract of Cyperus rotundus L.bulb was an efficient and environmentally friendly method for the synthesis of metal nanoparticles,and the synthesized AgNPs had good catalytic effect and fruit preservation ability.