Research On Preparation And Sterilization Performance Of Visible-ultraviolet β-NaYF₄:Pr³⁺,Li⁺ And Its Composite Photocatalytic Sterilization Materials

Drinking water containing pathogenic microorganisms can cause a variety of diseases,such as legionella,cholera,pneumonia,and acute gastritis.At present,common chlorine disinfection,ozone disinfection and ultraviolet disinfection technologies at home and abroad have the disadvantages of high energy consumption and easy to produce disinfection by-products.If we can devlope a visible light sterilizing material with high bactericidal efficiency,wide applicability,good stability and recyclability,the existing water pollution situation will be greatly improved.The upconversion material can achieve visible-to-ultraviolet conversion due to its unique upconversion characteristics,and the rare earth element praseodymium（Pr）can generate UVC band（200-280nm）ultraviolet light with the best sterilization effect under the excitation of visible light.Photocatalytic materials can use optical energy to generate active species with strong redox properties.They not only can efficiently inactivate microorganisms,but also have good stability,showing good application prospects as germicidal materials.An up-conversion bactericidal materialβ-NaYF₄:Pr³⁺,Li⁺（NYF）that can convert visible light to UVC was developed.Then,using NYF as the core,TiO₂ and BiOCl were supported on the outer layer of NYF to form a core-shell composite photocatalytic sterilization materialsβ-NaYF₄:Pr³⁺,Li⁺@TiO₂（NYF-Ti）andβ-NaYF₄:Pr³⁺,Li⁺@BiOCl（NYF-Bi）,systematically explore the basic properties,sterilization performance and sterilization mechanism of materials.The main research results of this article are as follows:（1）NYF,NYF-Tiand NYF-Bisterilization materials were prepared by hydrothermal method and sol-gel method.Diffraction of X-rays（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and X-ray photoelectron spectroscopy（XPS）were used to characterize the crystal structure,morphology and ion valence state of the materials.The results show that hexagonal prismβ-NaYF₄ with a height of about 3-5μm and a diameter of about 2-3μm was successfully prepared,and Pr³⁺and Li⁺were successfully doped therein.At the same time,anatase flocculent TiO₂ and tetragonal flaky BiOCl were prepared and successfully loaded on NYF surface to form core-shell structure NYF-Tiand NYF-Bi.（2）The optical performance of three bactericidal materials were characterized by UV-Vis DRS.The result shows that NYF-Tihas the narrowest forbidden band width and the strongest light absorption intensity;NYF has the widest forbidden band width and the weakest light absorption intensity;NYF-Biis somewhere in between.It is shown that the addition of TiO₂ and BiOCl can effectively improve the light absorption performance of composite materials,and NYF-Tihas the best light absorption performance among the three materials.（3）The single-factor experiment was used to investigate the bactericidal performance and optimal conditions of NYF,NYF-Tiand NYF-Bion E.coli.The results showed that the optimal dosage of bactericidal material was 0.15g/L,and the optimal light intensity was 1000W.NYF-Tihas the highest sterilization efficiency among the three materials.Under the best experimental conditions,the three-hour sterilization efficiency of E.coli with an initial concentration of 10⁶CFU/mL can reach 99.9999%.The effects of cyclic sterilization experiments on NYF-Tihave been investigated.The results show that NYF-Tihas good stability and recyclability and is a promising photocatalytic sterilization material.（4）The light intensity and corresponding sterilization efficiency of NYF under different doping concentrations were investigated.The results show that the sterilization efficiency of NYF is directly related to the ion doping concentration and the luminous intensity of the UVC band,and the doping concentration with the best sterilization efficiency isβ-NaYF₄:1.5%Pr³⁺,9%Li⁺.Electron paramagnetic resonance（EPR）,transient fluorescence,electrochemical impedance spectroscopy（EIS）,and photoluminescence spectroscopy（PL）were used to investigate the photoelectric performance of the three materials.The results show that NYF-Tihas the most free radicals,the strongest photocurrent,the highest carrier mobility,and the best photoelectric performance,so it has the best sterilization effect.（5）The sterilization mechanism of NYF and NYF-Tiwas analyzed,and the results showed that NYF mainly realized the transition from the ground state to the excited state through the excitation state absorption（GSA）,ground state absorption（ESA）and energy transfer upconversion（ETU）processes inside Pr³⁺,and destroyed the DNA and RNA of E.coli by emitting UVC band ultraviolet light.NYF-Timainly generates internal electron transition by absorbing ultraviolet light generated by NYF to generate active substances such as h⁺,·O₂^-and·OH,which destroy the structure and intracellular organic matter of E.coli,so as to achieve sterilization.