Studies On The Green Preparation And Applications Of Ag And Ag/ZnO Nanomaterials

Due to a range of fascinating properties,nanocrystals have been applied in catalysis,electronics,information storage,photonics,sensing,imaging,medicine and among others.In recent years,much success have been made to control the poperties of nanomaterials with aprropriate size and shape for efficient utilization in some fields.However,with the increasing concern to the enviromental,it still remains a great challenge to develop the facile,clean and high-yield synthesis methods for nanomaterials.In this paper,some greener methods have been developed to synthesize the nanocystals of triangular Ag nanoplates and Ag/ZnO nanocomposites.In the preparation process,the green solvent of ionic liquids and the biocompatible materials such as ascorbic acid,tyrosine and sodium alginate have been used. Fouthermore,their enviromental applications in anti-bacteria,SERS detection and degradation of dye pollutants are also studied.The main contents of each chapter are as follows.Chapter 1.The progress in the green preparation of nanomaterials,such as the use of green solvent,the biopreparion and the clean process,are reviewed.Chapter 2.The triangular Ag nanoplates were prepared from a [C₆mim][PF₆]-H₂O two phase systerm.Then the structures of the prepared Ag nanoplates were characterized by XRD,TEM,and SAED.Finally,their antibacterial activities for both Escherichia coli and Staphylococcus aureus were evaluated and their applications as active substrate for SERS detection of 4-ATP were also examined.The results show that,the slow reduction of Ag⁺made the process kinetically controlled for formation of triangular Ag nanoplates.The observations from TEM and SAED suggested that the upper and lower bases were bound by{111}planes and the l/3{422}spots were originated from the planar defects.However,the dark bands on the surface in TEM observation were from the bending countour.Due to the increase of the {111}active planes,the Ag nanoplates showed a better antibacterial effect than Lee-meisal Ag,and the MIC values for Escherichia coli and Staphylococcus aureus were found to be 15 and 20μg/mL,respectively.As the SERS active substrates,the Ag nanoplates can detect 4-ATP at the concentration of 10^-7M,and the SERS signals envolved the mechanism of the electromagnetic enhancement and the chemical effects of charge transfer.Chapter 3.The ID Ag/ZnO nanorod were prepared though a facile one-pot hydrothermal method.The prepared samples were structurally characterized by XRD,SEM,TEM,and XPS.Then,their photocatalytic performance for degradation of Orange G and their antibacterial activities were evaluated, respectively.It was shown that the added tyrosine served both as a reducing agent of Ag+ion and as a shape conductor for the formation of ZnO faceted nanorods, and that the concentration of tyrosine and the volume of the added ammonia solution significantly influence the final morphology of the products.The structure characterizations indicated that the Ag nanoparticles were embedded in the ZnO nanorods.In the photocatalytic process under UV irradiation,Ag nanoparticles on the ZnO surface may serve as electron sinks,promoting the separation of photogenerated electron-hole pairs,and thus increased their photocatalytic activity. While in antibacterial tests,the nanocomposites showed enhanced and synergistic antibacterial activities for both gram-negative and gram-positive bacteria,due to the strong interaction between metallic Ag and semiconductor ZnO.Chapter 4.Firstly,the Ag modified three-dimensional(3D)ZnO hollow microspheres were prepared through a facile one-step hydrothermal method.Then the as-prepared samples were structurally characterized by XRD,FESEM, HRTEM and XPS.The influence of deposited Ag on the electronic structure and surface property of ZnO had been emphasized.Finally,the photocatalytic performance of the prepared Ag/ZnO samples with different Ag contents for the degradation of Orange G was systematically explored.The structural characterizations showed that the wall of the hollow microsphere is composed of oriented nanorods,which were aligned with their growth axes perpendicular to the surface of the microsphere.In addition to the effects of enhanced separation of the photogenerated electron-hole pairs,Ag deposits with appropriate contents also increased the surface hydroxyl contents of ZnO microspheres.This facilitated the trapping of the photoinduced electrons and holes to form more active hydroxyl radicals,and thus enhanced the photocatalytic efficiency of ZnO.