| Catechin is a natural plant antioxidant with a wide range of biological,pharmacological and antioxidant activities.Catechin can be used as a reducing and stablizing agent for the green preparation of metal nanomaterials,which has the advantages of safety and environmental protection effect.In this study,we explored the hydrothermal synthesis method to synthesis of catechin-silvernanocomposite,catechin-zinc oxide nanocomposites and catechin-ZnO/Ag nanocomposites in which catechin was served as a reducing and stablizing agent.The obtained products were characterized by UV-visible absorption spectrum(UV-Vis),infrared absorption spectrum(FTIR),transmission electron microscope(TEM),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The antimicrobial activity and removal of organic dyes of these nanocomposite materials was also investigated.1.Silver nanoparticles were prepared by hydrothermal synthesis with green tea extract,and the size and particle size distribution of the nanoparticles were uniform.Because the main component of green tea extract is catechin,we further prepared the catechin-silver nanocomposite by one-step hydrothermal method using pure catechin.The pH value of the reaction solution,the concentration of catechin solution and the addition amount of silver nitrate solution were optimized.The optimized preparation conditions were obtained as follows:40 mL 0.32 mM catechin solution was mixed with 0.4 mL 5%silver nitrate solution,the pH of the reaction solution was adjusted to 7.0,and the reaction temperature was set at 140? for 4h.The products characterized by UV-Vis and TEM showed that the silver nanocomposites were mainly spherical particles with uniform distribution and an average size of 22.7nm.XRD measurements show that the silver nanocomposite has a high crystalline structure.The bacteriostatic experiments results showed that the catechin-silver nanomaterial had a strong inhibitory effect on Escherichia coli,staphylococcus aureus and coccus albicans.2.Preparation of catechin-zinc oxide nanocomposite and study on its antibacterial activity and removal of organic dye methylene blue.The pH value of the reaction solution and the amount of zinc chloride solution were optimized for the synthesis.The optimized synthetic conditions were obtained as follows:40mL 0.32 mM catechin solution was mixed with 0.4 mL 5%zinc chloride solution,the pH of the reaction solution was adjusted to 8.0,and the reaction temperature was set at 140? for 4h.UV-Vis and XPS measurement results demonstrated the presence of nanometer zinc oxide in the nanocomposite.FTIR results showed the adsorption of catechin molecules on the surface of ZnO nanocomposite.TEM results showed that the nanocomposite is composed of many small particles with a nanocluster structure.The bacteriostatic results showed that the catechin-ZnO nanocomposite had a strong inhibitory effect on both bacteria and fungi.The removal experiments results for organic dye showed that the catechin-ZnO nanomaterial had a very high removal rate for methylene blue.The removal rate of 20 mg/L methylene blue dye was as high as 99%and that of 35 mg/L methylene blue dye was 96%with 0.3 g/L catechin-ZnO nanocomposites.3.Preparation and antibacterial activity of catechin-ZnO/Ag nanocomposites.The molar ratio of zinc chloride and silver nitrate in the initial reaction solution was 1:1,and the pH was adjusted to 8.0.The catechin-ZnO/Ag nanocomposite was prepared by one-step hydrothermal synthesis in which catechin is served as reducing and stablizing agent.The results of TEM and XPS showed that there were bar-like nanometer zinc oxide and spherical silver nanoparticles in the nanocomposite.The results of bacteriostatic studies of the catechin-ZnO/Ag nanocomposites show that they have a very strong inhibitory effect on both bacteria and fungi,and their bacteriostatic effect on Escherichia coli and staphylococcus aureus exceeds that of the catechin-zinc oxide nanomaterials and the catechin-silver nanomaterials. |
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