Study Of Triangular Silver Nanoparticles/triangular Silver Nanocomposites And Graphene Quantum Dots

Nanostructured materials,known as nanomaterials,is defined as a material with any external dimension in the nanoscale or having internal structure or surface structure in the nanoscale.Especially,the special physical and chemical properties of metal nanomaterials make them widely used in many fields such as optics,photoelectricity,sensing technology,biological detection and so on.The size,shape and composition of nanomaterials all affect their chemical and physical properties,so the research on the preparation and optical properties of nanomaterials has important scientific significance.In this thesis,triangular silver nanoparticles,triangular silver nanocomposites and graphene quantum dots,which can be used for Raman surface enhancement,have been prepared and studied.First of all,the research work of triangular silver nanoparticles is carried out.Using sodium borohydride as reducing agent and sodium citrate as modifier,homogeneous triangular silver nanoparticles with particle size of about 50 nm were prepared in the presence of hydrogen peroxide by liquid phase method.On this basis,the effect of different dosage of PVP on triangular silver nanoparticles was studied.The results show that with the increase of PVP dosage,the color of triangular silver nanoparticles sol gradually deepens,and the position of in-plane bipolar resonance peak at 620 nm is blue shifted.After that,the influence of different amount of hydrogen peroxide on the triangular silver nanocrystalline was studied.Through TEM experiment,it was found that,,with the increase of the dosage of hydrogen peroxide in the range of 40 μL to 60 μL(remaining other parameters the same),the irregular silver particles in triangular silver nanoparticles gradually decreased,and the yield of triangular silver nanoparticles increased.Finally,the thermal stability of triangular silver nanoparticles was studied.When heating the triangular silver sol at 100℃,it was found that the morphology of the sol decomposed gradually and the triangular shape of silver began to become irregular.The peaks of 540 nm ~ 620 nm in the UV-Vis spectrum were all deviated during the heating process of the sol.It is inferred from above experiments that the size of triangular silver nanoparticles may be related to the absorption peak of 620 nm,and the change of the solution color shows that the absorption peak at 450 nm of triangular silver nanoparticles may be related to the shape of the particles.The absorption peak at the triangular silver nanocrystalline 340 nm may be related to silver crystal plane(111)and does not change with the size and shape,which could be deduced from the phenomenon that the spectral shift of the absorption peak of silver nanoparticles during dissolution process.The second work of this thesis is the preparation and study of graphene quantum dots.Firstly,graphene quantum dots were prepared by controlling pyrolysis time and pyrolysis temperature.The UV-Vis absorption spectra of graphene quantum dots show that with the increase of heating time or temperature,the peak position of graphene quantum dots deviated,which may be related to the size of quantum dots.When keeping the pyrolysis temperature at 2000 C,TEM experiments found that the size of graphene quantum dots(QDs)increases with the increase of heating time.When the heating time reaches to 33 minutes,not only the thickness of graphene quantum dots increases,but also the shape of the graphene quantum dots become irregular At the same preparation temperature,when the p H value changing from acidic to alkali,the fluorescence peak of graphene quantum dots red shifted.but with different This phenomena may be due to the different electrical properties of the groups in the QDs in different acid-base solutions.At different preparation temperatures,the shift of the fluorescence peak of the graphene quantum dots maybe rely to the different band gap of the quantum dots with different crystallinity obtained at different temperature.When the triangular silver nanoparticles are combined with graphene quantum dots,the fluorescence of the composite is blue shifted relative to the silver fluorescence of the quantum dots,which may be caused by electrons transfer or energy transfer between the two kinds of composites.The third work of this thesis is Raman enhancement.The triangular silver / quartz substrate and triangular silver @ graphene quantum dot / quartz substrate were prepared by using the prepared triangular sol and graphene quantum dots.The triangular silver / graphene / quartz substrate was used as a Raman enhanced substrate to detect the Rhodamine probe molecule of 10-5 mol/l,and the triangular silver / graphene / quartz substrate was the best.The triangular silver @ graphene quantum dot / quartz substrate was the second.The fourth work of this thesis is to prepare composite nanomaterials.The network structure of triangular nano-silver / xanthan gum was prepared by the combination of triangular nano-silver and xanthan gum.The number of nano-silver in the composite network with different proportions was calculated to be in accordance with the volume of silver sol in the composite material at 1:15:2.A more uniform composite network structure with more repeatability and controllability is obtained by using the mechanism of spin coating.