Process Optimization Of Nano Silver Synthesis By Citrus Peel Extract And Characterization Of The Nano Silver

AgNPs is a novel material due to its special surface effect,small size effect,surface plasmon resonance effect and macroscopic quantum tunneling effect.AgNPs used as an antibacterial agent is the most widely known application for public.Due to some notable advantages such as high efficiency,broad-spectrum and non-pollution,AgNPs is widely used in the field of medical and health,textile and food packaging.The chemical method has been widely used to synthesis AgNPs.However,most of the chemical reduction regents are toxic,which pollute the environment and limit the application of AgNPs in the field of medical and health and food packaging.In recent years,the green method that used natural plant extracts as reduction agent and stabilizer has attracted more attention.This method has some characteristics such as the wide source,low cost,green and so on.At the same time,AgNPs showed a high capability of dispersion and good stability,thus it has great potential in the application of food application.Citrus peel have many antioxidants such as flavonoids,soluble phenolic acids,vitamin C and so on,which laid the theoretical foundation that it can be used as green reduction materials to synthesis AgNPs.Under this background,the contents of this research are as follows:Firstly,flavonoids,soluble phenolic acids and vitamin C were extracted from the citrus peels of eight different varieties,respectively.The content of the constituents and their antioxidant activities were determined.Then this research was explored the relationship between the contents of antioxidant components and antioxidant activity;Secondly,AgNPs was then synthesized separately using the extracts of these citrus peels,with the determination of reduction efficiency and size of AgNPs.Then correlation analysis were conducted between the contents of antioxidant components and the reduction ratio,the aim of this research was to explore the relationship between the contents of antioxidant components and reduction efficiency in different citrus peels;Thirdly,Amakusa peel extract which has the best reduction effect were used as the green reduction agent to synthesis AgNPs,the reaction time,temperature and AgNO₃concentration were optimized by single factor and orthogonal experiment.Furthermore,the effects of the reaction time,reaction temperature,and AgNO₃ concentration on the reduction ratio of the extract,as well as the average particle size,size distribution and zeta potentials of the synthesized AgNPs were investigated,then the conditions were optimized;Fourthly,two kinds of AgNPs?G-AgNPs and C-AgNPAgNPs?were synthesized using the aqueous extract of Amakusa peels as the green reduction agent and NaBH₄ as the chemical reduction agent,respectively.The reduction ratio,particle size and morphologies,crystal structure,and chemical components of G-AgNPs and C-AgNPs were characterized by XRD,TEM,FT-IR and some other characteristics methods;Finally,the difference of bacteriostasis between G-AgNPs and C-AgNPs towards to some food-borne gram positive bacteria?Staphylococcus aureus and Bicillus subtilis?and gram negative bacteria?Escherichia coli and Salmonella typhi?were explored.In the meanwhile,the difference of G-AgNPs and C-AgNPs in dispersion and antioxidant properties were compared.Based on these studies,the main results obtained are as follows:1.The content of flavonoids,phenolic acids and vitamin C in Citrus peels were significantly different among varieties.The content of antioxidant components and antioxidant activity in peels of Amakusa are superior to other varieties.Its antioxidant activity is correlated with the contents of new hesperidin and erucic acid.The peels of Amakusa showed the best performance to synthesize AgNPs among the eight varities of citrus tested in this study.It showed the highest reduction efficiency and the lowest size of AgNPs.The reduction efficiency of Citrus peel extracts towards AgNPs was significantly correlated with the antioxidant activities of flavonoids,phenolic acids and vitamin C in Citrus peesls,and was also significantly correlated with the contents of new hesperidin of flavonoids,erucic acid of phenolic acids,and vitamin C.2.The results of single factor and orthogonal experiment revealed that the effects of these factors on the synthetic ratio of AgNP from large to small was reaction temperature>AgNO₃concentration>reaction time.The optimum reaction conditions were reaction time of 2 h,reaction temperature of 90?,and AgNO₃ concentration of 10 mmol/L.The reduction ratio of the extract towards Ag⁺,the average particle size,size distribution and zeta potentials of the synthesized AgNPs were also influenced by these reaction conditions.Under the optimum reaction conditions,the reduction ratio of the extract reached 91.1%,while the synthesized AgNPs had an average particle size of 29.8 nm with a narrow distribution,and a zeta potential value of-30.8±0.10 mv,which showed a high capability of dispersion and good stability.3.It was found that the reduction ratio of two reduction agents towards AgNPs both exceeded 90%.G-AgNPs and C-AgNPs were observed to be spherical or nearly spherical crystals with face-centred cubic structure.The size distribution of G-AgNPs was narrower than C-AgNPs,and presented smaller average particle size and median size?D50?,which were 29.81nm and 28.21 nm,respectively.Furthermore,G-AgNPs absorbed some active components of the Amakusa peel extract,which reduce the agglomeration of AgNPs.4.Both of G-AgNPs and C-AgNPs showed strong inhibitory activities towards some food-borne gram positive bacteria?Staphylococcus aureus and Bicillus subtilis?and gram negative bacteria?Escherichia coli and Salmonella typhi?.However,G-AgNPs had generally better antimicrobial activities compared to C-AgNPs.Owing to the active compounds absorbed on the surface,G-AgNPs showed a significantly higher decolourization rate towards methylene blue?MB?was significantly higher than C-AgNPs,indicating their strong antioxidant activities.When the redispersive solution of G-AgNPs after standing for 7 days,its changes in UV-vis absorbency was smaller than that of C-AgNPs.Therefore,G-AgNPs showed better dispersion capability and stability compared to C-AgNPs.