Preparation Of Quantum Dots And Study On Modified SA-CMC Blend Membranes

Because quantum dots(QDs)have surface effect,small size effect and macroscopic quantum tunneling effect,people are interested in the application of quantum dots in optical and electrical fields.By dispersing quantum dots in biofilm,the composite film has excellent properties such as high fluorescence,excellent thermal stability and flexibility.It can be used in photoelectric applications such as light emitting diodes(LED),flexible electronic displays and filter devices.In this dissertation,three kinds of quantum dots(QDs)were prepared,namely zinc oxide quantum dots(ZnOQDs),silicon quantum dots(SiQDs)and Si-ZnO hybrid quantum dots.The morphology,surface groups,chemical bond composition and optical properties of quantum dots were analyzed by transmission electron microscopy(TEM),fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and fluorescence spectroscopy(PL).The zinc oxide quantum dots were prepared by an improved sol-gel method,which obviously shortened the reaction time compared with the experimental conditions reported in the literature.Fluorescence spectra confirmed that the ratio of zinc acetate to lithium hydroxide was 1:1.5 and the reaction time was 20 minutes,which was the best reaction condition for the preparation of ZnOQDs.The maximum fluorescence emission wavelength of ZnOQDs is 525 nm,the average particle size is(3.2±0.2)nm,and the lattice spacing is 0.28 nm.Silicon quantum dots with fluorescence stabilization were synthesized by hydrothermal method using ethanol as reaction solvent,silicic acid and sodium borohydride as reaction materials;The optimum reaction conditions were determined as follows:the molar ratio of silicic acid to sodium borohydride is 1.2:1,the reaction temperature was 200?,and the reaction time was 3 h;The lattice spacing of the prepared SiQDs is 0.31 nm,corresponding to the(111)crystal plane of silicon,and the structure is stable;It mainly contains C-Si and Si-Si bonds;The hydrophobicity of SiQDs is greater than that of hydrophilicity;The maximum fluorescence emission wavelength of SiQDs is 440 nm,and SiQDs is wavelength-dependent.Two kinds of quantum dots,zinc oxide and silicon,were used to synthesize Si-ZnO hybrid quantum dots.FTIR and XRD analyses show that there are both Si and ZnO components in Si-ZnO quantum dots.The chemical bonding of Si-ZnO was confirmed by XPS.The fluorescence emission wavelengths of Si-ZnO quantum dots obtained by reactants with different mass ratios are different.Moreover,Si-ZnO quantum dots have the properties of adjustable fluorescence emission centers.Three kinds of quantum dots were dispersed into sodium alginate(SA)and sodium carboxymethyl cellulose(CMC).When the mass ratio of SA to CMC is 3:7,the mechanical properties of SA-CMC blend membranes are the best The composite materials of three quantum dots and blend membranes exhibit different central fluorescence emission wavelengths and show different colors under ultraviolet lamp irradiation.The central fluorescence emission wavelengths of the prepared ZnOQDs/CMC and ZnOQDs/SA-CMC composites are 525 nm,which show yellow light under 365 nm ultraviolet lamp irradiation and have wide ultraviolet absorption properties.The central fluorescence emission wavelength of SiQDs/SA-CMC composites is 440 nm,which shows obvious wavelength dependence.When the SiQDs content is 0.4 g,the composites have the best thermal stability and the highest fluorescence intensity.Under 365 nm ultraviolet lamp,it shows blue light,which is consistent with the color of SiQDs.The prepared Si-ZnO/SA-CMC composite is different from the first two composite membranes.It has a good absorption of mid-wave ultraviolet and appears blue-green under 245 nm ultraviolet lamp irradiation.When the addition of Si-ZnO is 0.3 g,the thermal stability of the composite film is the best.