Preparation And Photocatalytic Properties Of Near-infrared Responsive Porous Silica Fiber-based Supported Catalyst

Semiconductor titanium dioxide(Ti02)has the characteristics of abundant source,low price,safe and non-toxic,and excellent photocatalytic performance.Hence,it has broad applied prospects in the fields of waste water,waste gas organic pollutant control and renewable new energy.Due to its own wide bandgap nature,TiO2 can only absorb a specific wavelength of ultraviolet light(UV).Therefore,the utilization efficiency of solar energy is relatively low.In addition,in the process of practical use,there exist problems such as extremely easy agglomeration inactivation and difficulty in recycling.Therefore,in this thesis,by introducing rare earth upconversion luminescent materials(UC),Ti02 was coated on the surface of UC to form NaYF4:Yb,Tm@TiO2 composite particles with core-shell structure,which indirectly broadened the photo-response range of TiO2 to the near-infrared(NIR)region.The composite particles were loaded onto porous silica fibers(SiO2)to obtain a novel supported catalyst of NaYF4:Yb,Tm@TiO2/P-SiO2.The effects of synthesis conditions on UC,the control of shell-thickness,the regulation and preparation of porous SiO2 fibers,the preparation and photocatalytic properties of supported catalysts were studied.The main contents of this thesis were as follows:(1)The NIR responsive NaYF4:Yb,Tm nanocrystals were prepared by the hydrothermal method.The effects of rare earth nitrate concentrations,rare earth doping concentrations and reaction time on the crystal structure,morphology,size and fluorescence intensity of NaYF4:Yb,Tm were investigated.Through SEM,EDX,TEM and upconversion fluorescence tests,it was found the optimal synthesis conditions of NaYF4:Yb,Tm nanocrystals were as follows:the rare earth nitrate concentration was 0.02mol/L;the reaction time was 3h;the Yb3+ doping concentration was 20%;the Tm3+doping concentration was 0.5%.The optimal NaYF4:Yb,Tm and different concentrations of tetrabutyl orthotitanate(TBOT)were combined to prepare NaYF4:Yb,Tm@TiO2 composite particles with different shell-thickness,and their structures,morphologies and upconversion fluorescences were investigated.When the amount of TBOT was 0.02ml,the composite particles exhibited the best fluorescence performance.(2)Porous SiO2 fibers were successfully prepared via electrospinning combined with a templating method.The optimal spinning conditions of PAN/PEG composite fibers were determined:the spinning solution concentration was 18.6wt.%;the spinning speed was 1mL/h;the voltage was 15kV;the distance from the drum to the nozzle was 15cm;the rotation speed of the drum was 300rpm.The mass ratio of PAN/PEG was adjusted to control the morphology and structure of porous SiO2 fibers.When the mass ratio was 1,the diameter of porous SiO2 fibers was uniform,and their pores were relatively large.The high specific surface area was 221.12m2/g and the average pore diameter was 6.87nm.(3)Based on the preparation of porous SiO2 fibers,TiO2 nanoparticles and NaYF4:Yb,Tm@TiO2 composite particles were separately added to the SiO2 precursor to obtain TiO2/P-SiO2 and NaYF4:Yb,Tm@TiO2/P-SiO2 supported catalyst.The specific surface area of TiO2/P-SiO2 supported catalyst was as high as 186.87m2/g and the average pore diameter was 3.67nm,which greatly improved the dispersibility of TiO2 particles.The photocatalytic degradation of methyl orange(MO)by the Ti02/P-SiO2 supported catalyst under UV light irradiation showed that the degradation rate was up to 91.9%within 15min,twice as much as Ti02 powders.In NaYF4:Yb,Tm@TiO2/P-SiO2 supported catalyst,NaYF4:Yb,Tm@TiO2 composite particles were dispersed on the core and surface of porous SiO2 fibers.Photocatalytic degradation of MO solution by the NaYF4:Yb,Tm@TiO2/P-SiO2 supported catalyst under NIR light showed that the degradation rate reached 48.8%within 10 hours,which was 1.5 times of the degradation rate of NaYF4:Yb,Tm@Ti02 composite particles.