Biosynthesis,Characterization And Environmental Behavior Of Nanoparticles

Nanoparticles(NPs)would inevitably enter into the environment and pose a threat to the environment and organisms with the extensive consumption.In addition,the hazardous chemical agents are inevitably introduced to the process of synthesis and co-existed with the synthesized NPs,which could affect NPs’ biological compatibility and restrict their usage eventually.Therefore,with the increasing demand of NPs as well as the importance of nano-environmental health,it is urgent to develop a green and sustainable route to synthesize NPs.Biosynthesis of NPs based on natural biota has been regarded as a green way to control NPs’ pollution from the source and has been received enormous attentions.In the biosynthesis procedure,bio-compounds in plants or microorganisms,including proteins,phenols,flavonoids,sugars and enzymes,can serve as both reducing and capping agents to synthesize NPs in one pot.Among various species,plant mediated method for production of NPs shows a better application prospect than microbes because it eliminates the elaborate course of maintaining microbial cultures.This dissertation focused on the preparation,’growth mechanism and environmental behavior of silver and gold nanoparticles(AgNPs and AuNPs)synthesized using plant extract.In the first part,we successfully synthesized AgNPs and AuNPs using different plants extracts,and studied the effects of extract concentration,reaction temperature and pH on the size,shape as well as the synthesis efficiency.In addition,UV-visible(UV-vis),transmission electron microscopy(TEM),energy-dispersive X-ray(EDS),X-ray diffraction(XRD),and Fourier transform infrared spectroscopy(FTIR)were used to characterize the synthesized NPs.Furthermore,these biosynthesized NPs exhibited good catalytic,antioxidant and antimicrobial activities.Among used plants,persimmon extract could synthesize highly stable AgNPs,which was used in the following experiments.In order to investigate the involved bioactive components and the possible mechanism of biosynthesis,complex persimmon extract was fractionated by solvent with different polarity to collect relatively homogeneous molecules at first.Then Fourier Transform Ion Cyclotron Resonance Mass Spectrometry(FT-ICR MS)was carried out to identify the biomolecules in each fraction.The results showed that phenols and flavonoids are responsible for reduction of metal ions,while lipids and proteins could absorb on the surface of NPs to protect them from agglomeration.In addition,nitrogen-containing lipids played an important role in anisotropic growth of AuNPs.This work has the significance for controlling synthesis of NPs.Given that the coexistence of residual ions and biomolecules caused problems in biosynthesized NPs’storage and further usages,TX-114 based cloud point extraction(CPE)was developed for separation and concentration of biosynthesized AgNPs from remained bio-compounds for the first time.Maximum extraction efficiency was obtained at 20 mM of Na2S2O3,10%(w/v)of TX-114,pH 3,incubation time of 40 min,and temperature of 40℃.TEM images showed that AgNPs were extracted into TX-114-rich phase with the preserved size and shape.The residual Ag+ions and biomolecules were remined in the TX-114-aqueous phase,which was confirmed by the analysis of hollow fiber flow field-flow fractionation(HF5)coupled with UV-vis.Under the optimum conditions,other types of AgNPs synthesized using various plants’ extracts also showed good extraction efficiencies(81-102%).In the last part,the environmental behavior of biosynthesized NPs under relevant environmentally conditions were examined using persimmon capped AgNPs(bio-AgNPs)as a model.We observed that environmental factors like dissolved matter(DOM),pH,Ca2+/Mg2+,S2-and Cl-affected the morphology and chemical transformation of bio-AgNPs in the same way of polyvinyl pyrrolidone(PVP)and citrate coated AgNPs.Specifically,release of Ag+ ions and regeneration of AgNPs could happen in aquatic environment containing dissolved organic matter(DOM).Ca2+/Mg2-,S2-and Cl-and pH variation within environmental levels did not affect the tendency.However,due to a combination of electrostatic repulsion and steric effects aroused from the absorbed biomolecules on their surface,bio-AgNPs showed a greater degree of colloidal stability and less ion release in comparison with PVP-AgNPs and Cit-AgNPs.