Screening Of Biomass For Biosynthesis Of Gold/Silver Nanoparticles And Preliminary Exploration Of Their Reducing Components

In recent years,the research to develop environmentally benign processes to synthesize nanoparticle has been attracting more and more eyeballs,and biosynthesis of nanoparticles at room temperature is the very example.Biosynthesis of nanoparticles which owns virtues of low energy and environment consumption and can make full use of rich bioresources can produce stable nanoparticles protected by certain biocomponents in biomass.Meanwhile, considering the extremely important role played by the noble metal catalysts in chemical industry by right of their unique catalytic activity and selectivity,consequently it is believed of great interest to develop supported noble metal catalysts through bioreduction.Herein the study aims to screen a variety of plant biomass in and around Xiamen city and microorganisms available in our lab in terms of their ability to rapidly synthesize gold/silver nanoparticles at mild condition,so as to provide biomass sources for preparation of supported gold catalysts used in catalytic oxidation of propylene and supported silver catalysts used in catalytic oxidation of ethylene.Moreover,in order to explore a convenient and feasible method to screen plant extracts for biosynthesis of nanopartilcles and to find out the key components responsible for the reduction of AuCl₄^- ions,correlations between various parameters of plant extracts and conversion of AuCl₄^- ions were evaluated.Gold or silver nanoparticles were acquired by merely adding biomass extracts to aqueous chloroaurate or silver nitrate/diamine silver complex,and different techniques such as UV-Vis-NIR spectroscopy,transmission electron microscopy(TEM) or scanning electron microscopy(SEM) and atomic absorption spectophotometry(AAS) spectroscopy were employed to characterize this bioprocess.The results demonstrated that 24 kinds of plant extracts,such as Vat alboflava,Acacia confuse,Delonix regia,Dimocarpus longan,Litchi chinensis and so on,could rapidly synthesize well-distributed gold nanoparticles and their size varied greatly from plant to plant, which consequently indicated that gold nanoparticles with controllable sizes could be achieved by merely altering the species of plant extracts.In addition,it is found that gold nanotriangles could be assembled at room temperature by 6 kinds of plant extracts,including Morus alba,Cassia siamea,Cinnamomum japonicum,Citrus limon,Eriobotrya japonica and Lophatherum gracile.On the other hand,for the screened microorganisms,the experimental results indicated that 6 kinds of microorganisms,including Aspergillus niger(A.niger),Pichia pastoris GS115 (P.pastoris GS115),Saccharomyces cerevisiae(S.cerevisiae),Lactolacillus fermentum(L. fermentum),Bacillus licheniformis R08(B.licheniformis R08) and Penicillium minioluteum (P.minioluteum) could rapidly synthesize well-distributed gold nanoparticles at 60℃. Besides,extracts of Staphylocossus aureus(Staph.aureus),A.niger and P.minioluteum could synthesize gold nanotriangles.Among them,the yield of gold nanotriangles synthesized by extracts of P.minioluteum got to 45%.Similarly,a batch of biomass which could synthesize silver nanoparticles was also discovered.Six kinds of plant extracts,including Celtis sinensis,Psidium guajava,Aleurites moluccana,Bombax malabaricum,Cassia fstula and Canarium album could rapidly synthesize well-distributed silver nanoparticles at room temperature.Different plant extracts could afford silver nanoparticles of different size and as a result,size control of silver nanoparticles could be realized by changing the kind of plant extracts.It is worth mentioning that previously we reported that biosynthesis of silver nanowires could be achieved using both extracts of Canarium album and Cassia fistula,and as well,polygonal silver nanoplates could be obtained by extracts of Mangifera indica.Among microorganism extracts,extracts of A. niger and P.minioluteum own the strongest capability to reduce diamine silver complex to silver nanoparticles,of which the conversion of diamine silver complex after reacting time of 6 days got to 99.1%and 90.7%,respectively.Furthermore,through the evaluation of correlations between various parameters of plant extracts and conversion of AuCl₄^- ions,it can be found that concentration of reducing sugar and total flavonoids of plant extracts had a good linear correlation with conversion of AuCl₄^-ions respectively,indicating that reducing sugar and total flavonoids of plant extracts are mainly responsible for the reduction of AuCl₄^- ions.In addition,DPPH free radical scavenging capacity of plant extracts were also observed with a better linear correlation with conversion of AuCl₄^- ions.Therefore,by simply measuring the DPPH free radical scavenging capability,we can know whether or how fast the plant extracts can reduce AuCl₄^- ions.