Rapid Biosynthesis Of Silver Nanoparticles And Its Composite By Plants Extract And Their Structure,Properties Assessment

Silver nanoparticles?Ag NPs?and its composite NPs have unique properties,including good electrical conductivity,high surface to volume ratios,catalytic properties,antimicrobial properties and quantum effects.AgNPs take on immense applications in pharmaceuticals,electronic,food and many others field.There are many methods for AgNPs synthesis.Compared to physical and chemical methods,the biological method has many advantages such as efficient,fast,simple,eco-friendly and low-cost.So,it attracts more and more attention from the research circles.In fact,compared to the synthesis of AgNPs used plants or plant extract,the most reports are about microbiological methods.Therefore,as a novel study,the present work is aimed to synthesize AgNPs and its composite NPs using green tea leaf,ginkgo biloba leaf,apple pomace and pomegranate peel aqueous extract as the reducing and stabilizer agent.The main research contents and the results obtained are as follows:?1?Green tea leaf,ginkgo biloba leaf,apple pomace and pomegranate peel extract were used as the raw materials to synthesize AgNPs or?Ag/Ag⁺/Ag3?NPs from Ag NO3 solution.The AgNPs and(Ag/Ag⁺/Ag³⁺)NPs were analyzed by UV-vis,XRD,TEM.FTIR spectra of aqueous extract of plants before and after used to synthesize AgNPs were carried out to explant the formation of AgNPs or(Ag/Ag⁺/Ag³⁺).The suitable conditions for syntheses of AgNPs and its composite were confirmed by single factor experiment.The results showed that when the material ratio is 1:30?g/mL?,adding AgNO₃ solution?10mmol/L?into the green tea extract solution at the ratio of 5:1?mL/mL?can result in smaller sized?13.6 nm?AgNPs.And when the material ratio is 1:20?g/mL?,adding AgNO₃ solution?15 mmol/L?into apple pomace extract solution at the ratio of 4:1?mL/mL?can result in smaller sized?16.0 nm?AgNPs.The obtained AgNPs have a good stability,high crystallinity and smaller size.With Ginkgo biloba extract as the raw material,when the material ratio is 1:50?g/mL?,adding AgNO₃ solution?5 mmol/L?into the extract solution at the ratio of 8:1?mL/mL?,the obtained(Ag/Ag⁺/Ag³⁺)NPs is dispersed,high crystallinity,the average size of AgNPs is 13.8 nm and that of AgONPs is 24.6 nm.At pH=8,material ratio is 1:15?g/mL?and AgNO₃ concentration of 10 mmol/L,using pomegranate peel extract to synthesize(Ag/Ag⁺/Ag³⁺)NPs,the results showed that the size of the achieved composites are between 18-35 nm with a spherical shape and high crystallinity.FTIR analysis revealed that biological macromolecules in plant extract such as polyphenols,flavonoids,vitamins,proteins distributes on the surface of the nanoparticles as the role of reducing and protective agent.?2?In order to determine the strength of the antioxidant of the plants extract,free radicals clearance rate of the plant aquous extracts on ·OH,O₂^-· and DPPH were measured,taking Vc as reference.The reduction rates of Ag⁺ under the synthesis conditions of AgNPs and(Ag/Ag⁺/Ag³⁺)NPs were determined and the stabilities of the synthesized AgNPs and its composite NPs were also tested.The results showed that green tea extract has a stronger ability to remove free radicals than Vc,but the other three plants extract are weaker to remove that.In the four tested free radicals,any one of the four plants extract has the best scavenging ability to DPPH free radicals.With the plants extract as a reducing agent,the Ag⁺ reduction rate or conversion rate can reach more than 99% and the obtained AgNPs and its composite NPs have a better stability.?3?The antibacterial ability of AgNPs and(Ag/Ag⁺/Ag³⁺)NPs against E.coli and S.aureus were measured using antibacterial circle method and minimum inhibitory concentration method?MIC?.The results showed that any biosynthesized AgNPs exhibit a good antibacterial activity against gram-negative bacteria and gram-positive bacteria and(Ag/Ag⁺/Ag³⁺)NPs have a stronger antibacterial activity than AgNPs by 2-3 times.The MIC of AgNPs against E.coli and S.aureus is about 1.15×10^-4 mol/L,and that of(Ag/Ag⁺/Ag³⁺)NPs is about 2.90×10^-5 mol/L.After treated at 500°C,the MIC of the AgNPs and(Ag/Ag⁺/Ag³⁺)NPs are increased to 2.31×10^-4 mol/L and 5.80×10^-5 mol/L respectively.After heattreated at 200,350 and 500°C the obtained AgNPs were investigated by UV-vis.It is found that the size and crystallinity of AgNPs and composite NPs increased,while the Ag⁺ and Ag³⁺ in(Ag/Ag⁺/Ag³⁺)NPs were decomposed.With ESEM observation,it is found that morphologies of any obtained nano-powders were changed.The results of SEM observation showed that as the temperature rises,the nanoparticles begin to aggregate.Therefore,the average particle size of AgNPs increased from about 15 nm to about 100 nm and(Ag/Ag⁺/Ag³⁺)NPs increased from about 20 nm to about 130 nm.After treated at 500°C,the antibacterial properties of the AgNPs and the composite NPs are significantly reduced.Antibacterial capacity of the NPs before heattreated is 2 to 3 times of that of after heattreated.Therefore,heat-treatment can affect or change the morphology,size,crystallinity and antibacterial activity of the nano-powder.The results of the FTIR spectrograms of AgNPs and(Ag/Ag⁺/Ag³⁺)NPs before and after treated showed that absorption peaks corresponding to polyphenols,flavonoids,protein and other macromolecules are disappeared,proving that these large material molecules covered on the surface of nanoparticles and are decomposed at high temperature.?4?The mechanisms of AgNPs and(Ag/Ag⁺/Ag³⁺)NPs formation,theirs inhibiting bacterial growth were explored.The AgNPs formation mechanism includes the adsorption,reduction,complexation between Ag⁺ and macromolecules in plants extract.The characteristic action in inhibition of bacteria is multivalent interactions between NPs and bacteria.This study provides some new ideas and the theoretical basis for using plants or plants extract to synthesize AgNPs and its composite NPs.