Lanthanide Ion-doped Upconversion Nanocrystals @ Zno-Based Hetero-Nanostructures:Their Controlled Synthesis And Photocatalytic Performances

ZnO is one of the most promising photocatalyst due to its virtue of excellent biocompatibility,nontoxicity and low cost.However,with relatively wide band-gap(?3.37 eV),it can only absorb the ultraviolet light which constitutes only 5%of the solar light to perform the photocatalytic reaction,thus greatly restrict its application and spreading.NaYF4-based upconversion nanoparticles can turn the infrared lights into visible light or ultraviolet light which can be absorbed by the ZnO or ZnO-based materials when doped with Er3+ or Tm3+ activator ions upon NIR-light excitation.Thus,combiningthe upconversion luminescent materials with ZnO or ZnO-based materials can expand the light response range and elevate the reaction activity of the photo-generated electrons and holes,resultingin a significant improvement of photocatalytic activity of ZnO.Thus,this dissertation is focused on the synthesis and photocatalytic application of fluorides upconversion luminescent materials @ZnO-based hetero-nanostructures.The composite materials display notable photocatalytic performance and antibacterial activity.The specific contents of this paper were illustrated as below:1.Controlled synthesis of NaYF4:Yb,Er@SiO2@Zn1-xtnxO nanoparticles with improved photocatalytic degradation and antibacterial activityA series of NaYF4:Yb,Er nanoparticles were prepared via a microwave-assisted process.The effects of the reactants NH4F,doped concentration and solvents-ratio on the morphology,phase and the intensity of upconversion luminescent were investigated.Subsequent silica coating on the UCN core was done by using NaYF4:Yb,Er as core materials.By changing the amount of TEOS,the thickness of SiO2 shell could be easily controlled from 3 to 30 nm.The influence of the SiO2 shell thickness on the Zeta potential and upconversion luminescent were studied.At last,Zn1-xMnxO layer were coated on the surface of NaYF4:Yb,Er@SiO2 sample which has the highest effective upconversion luminescence to form a NaYF4:Yb,Er@SiO2@Zn1-xMnxO composite structure.The effect of Mn doping concentration on photocatalytic activity of the hetero-nanostructure composites is also studied.The photocatalytic results shows that the products display obviously enhanced performanceunder NIR light,due to the effcient utilization of UC emissions.The working mechanism of the hybrid photocatalysts is also proposed.Tert-butyl alcohol and potassium bromate were used to detecte the main active groups in the process of photocatalytic antibacterial activity.The result suggests that ·OH is the dominant reactive species under NIR light irradiation.Cytotoxicity assay shows the composite materials exhibit good biocompatibility and low cytotoxicity for cells.2.Synthesis of NaYP4:Yb,Tm,Nd@NaYF4:Yb,Nd@SiO2@ZnO nanocomposites and their photocatalytic propertiesWe employ a seed-mediated synthetic approach to prepare homogenous NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd active-core/active-shell nanostructure via two-step pyrolysis method.The optimum doped amount was choosed by comparing the intensity of luminescence of the samples with different amounts of activator and sensitizer ions.The silica coating on the synthesized UCNPs core was performed with a reverse microemulsion method,following by ZnO coating.The thickness of the ZnO shell was adjusted by changing the content of Zn(CH3COO)2·2H2O,which lead to the changing of the intensity of luminescence and photocatalytic activities.Our results suggest that the obtained NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd@SiO2@ZnO hetero-nanostructures possessed the improved photocatalytic degradation and antibacterial activity.In addition,the main active groups in the process of photocatalytic degradation were detected by using different radical scavengers,such as isopropanol,benzoquinone and ethylene diamine tetraacetic acid,revealing that ·OH radicals were the dominant reactive species.Cytotoxicity assay also shows the composite materials exhibit low cytotoxicity for cells.3.NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd-decorated ZnO nanosheets-assembled flowerlike microspheres:Their synthesis and photocatalytic applicationsThe as-prepared NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd active-core/active-shell NPs were deposited on the surface of nanosheets assembled flower-like ZnO microspheres by ultrasonic dispersion and centrifugation method.A series of samples with different deposition quantities of NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd nanoparticles was synthesized through altering the volume of UCNPs-cyclohexane dispersions,and their photocatalytic activities were explored by degradation of RhB and antibacterial against Bacillus subtilis under NIR light irradiation.The results showed that both the photocatalytic activity and its antibacterial activity of the developed composites exhibit the highest efficiency under the NIR light when the addition of UCNPs-cyclohexane dispersions is 3 mL.