Egcg As A Reducing Agent Of Silver Nano Material Preparation And Application Of Green

The polyhydroxy compound of epigallocatechin gallate (EGCG), extracted from plants, has good biocompatibility and reducibility, which can be used to synthesize noble metal nanomaterials via facile green approaches. In this paper, silver nanoparticles (Ag NPs) with different sizes and morphologies were prepared through varying the experimental conditions, including the concentration of EGCG, the reaction temperature and the addition of different surfactants, etc. Surface-enhanced Raman scattering (SERS) spectra of several molecular probes on the as-prepared silver nanostructures of various shapes were measured and their shape-dependent properties were evaluated. Since EGCG-stabilized silver hydrosol possessed unique optical property, the addition of heavy metal ions could immediately result in a gradual bathochromic shift in its plasmon absorption band, accompanied by the change of the silver hydrosol color, which could be used to detect heavy metal ions.The main work completed in this thesis could be summarized as following:1. The EGCG-stabilized silver hydrosol could be prepared through the reduction of AgNO3with EGCG as the reducing and protecting agent. The sizes of the as-prepared Ag NPs became smaller with the concentration of EGCG increasing and the reaction temperature rising. The amount of HAuCl4solution previously added had a distinct effect on the uniformity of as-prepared Ag NPs. The Au core Ag shell (Au@Ag) NPs with various sizes and morphologies could be controllably obtained by the Au-seed-mediated method. Surface-enhanced Raman scattering (SERS) spectra of R6G on the as-prepared silver nanostructures of various shapes as well as sizes were measured and their size-dependent or shape-dependent properties were evaluated. The result indicated that the stronger the SERS signal was. the more irregular the shape of Ag nanostructures got and the larger the size of Ag NPs became. 2. Silver nanomaterials with different structural architectures, from hexagonal plates, triangular plates, nanowires, and nanocubes to spheres were synthesized successfully in high yield by EGCG reducing AgNO3in the presence of the protecting agent polyvinylpyrrolidone (PVP). With the molar ratio of PVP/AgNO3increasing, the obtained Ag NPs varied from silver nanoplates to nanowires, nanocubes and spheres. When the concentration of EGCG was enhanced, silver nanostructures changed from silver nanowires to the mixture of nanoplates and spheres, the average sizes of which gradually decreased. As the reaction temperature went up, the shapes of Ag NPs transformed from irregularity to nanowires, nanoplates and spheres. While the amount of AgNO3was raised, the yield of Ag nanowires firstly increased and then decreased. The SERS spectra of several molecule probes (R6G,4-MPY and RB) on the as-prepared silver nanostructures of various shapes were measured, revealling that all silver nanostructures exhibited enhanced SERS properties.3. The high yield of Ag nanowires could be obtained by using EGCG in situ reducing Ag+ions in the presence of the directing agent polyacrylic acid (PAA). The obtained Ag NPs varied from silver spheres to nanowires and big spheres with the concentration of PAA increasing. The shapes of Ag NPs gradually changed from spheres to nanowires and then short nanorods while the concentration of EGCG increased. Ag NPs transformed from short nanowires to long nanowires and then spheres when the reaction temperature enhanced. The length of Ag nanowires firstly strengthened and then shortened with the amount of AgNO3increasing. The experimental result demonstrated the R6G molecular on Ag nanowires exhibited an intense SERS property and Ag nanowires could serve as a high-sensitivity substrate for SERS-based measurements.4. EGCG-stabilized silver hydrosol possessed unique optical property, but the addition of heavy metal ions could immediately induce the aggregation of Ag NPs, which resulted in a red shift in its plasmon absorption band and a change of its color. The discernment of heavy metal ions was successfully realized through the conjugation of EGCG-stabilized silver hydrosol and heavy metal ions. The result indicated a high sensitivity as well as a good selectivity of EGCG-stabilized Ag NPs toward Pb2+ions.