Design, Preparation And Application Of Water Purification Of Bi-system Visible Light Photocatalysts

Semiconductor photocatalysis has received much attention as a potential solution to theworldwide energy shortage and counteracting environmental degradation. Visible-light-drivenphotocatalysts with high activity and stability had attracted a great deal of attention. It wasnecessary to make the band gap of photocatalysts match with that of the solar energy and toexploit way to enhance the photo-generated electron-hole separation. In this paper, in view ofthe market demand, the BiOI/Bi2WO6-base visible light photocatalysts with excellentphtocatalytic activity and recycling was designed. Meanwhile, Synthesis of K2SiF6: Mn4+phosphor and their application in warm-white LED(1) A series of crystal continuously changing from Bi7O9I3to BiOI were successfullyfabricated using an ethylene glycol-assisted solvothermal process by adjusting theconcentration of precursor with different I/Bi molar ratios of1,1.5,2,3, and5. The productcan be determined as Bi7O9I3, based on the results of X-ray diffraction and thermogravimetryanalysis. Bi7O9I3uniform flowerlike hollow microspheres with a hole in its shell have beenobtained with larger BET specific surface area (68.86m2·g). The special structural feature ofthe hollow Bi7O9I3microsphere structure and crystal had special anisotropic growth along the(110) plane lead to high photocatalytic activity under visible light irradiation. In addition, themicro-structure of Bi7O9I3is regulated by adding a small amout of water duing preparation.All samples on the degradation of RhB under visible light irradiation exhibited higherphotocatalytic activity than that of hollow Bi7O9I3microsphere structure.(2) Electrospinning-derived TiO2nanofibers of anatase phase were decorated with BiOInanosheets, constructing TiO2@BiOI composite fibers. Size, morphology, together withpopulation density of the BiOI nanosheets can be readily adjusted by controlling the initialconcentration of Bi(NO3)3and incubation time in the hydrothermal reaction. Compared withpristine TiO2nanofibers, the TiO2@BiOI composite fibers exhibit faster decomposition ofRhB under visible light irradiation, and meanwhile possess high separation convenience inwater purification. Photoluminescence and transient photocurrent response results evidencethe formation of p-n junction at the interface of TiO2and BiOI, which contributes a lot inpromoting the photocatalytic performance of TiO2@BiOI fibers through enhanced separation efficiency of photogenerated charge carriers. In addition, the TiO2@BiOI fibers alsodemonstrate excellent chemical stability, making their repeated reuse in water purificationfeasible. To further improve the mechanical properties of TiO2@BiOI, the SiO2@TiO2@BiOIcomposite films is synthesized by combining the electrospinning technique, soaking andsolvothermal method. The results showed that the morphology of BiOI on the surface ofSiO2@TiO2similar to those on the TiO2@BiOI, meaning SiO2@TiO2@BiOI have both thephotocatalytic activity of TiO2@BiOI and flexibility of SiO2fiber.(3) The hierarchical SiO2@Bi2WO6composite nanofibers membranes were successfullyfabricated by combining the electrospinning technique and solvothermal method. Size,morphology, together with population density of the Bi2WO6nanosheets can be readilyadjusted by controlling the initial concentration of Bi(NO3)3in the hydrothermal reaction.Bi2WO6is dispersed on the surface of SiO2fibers not only prevent agglomeration of Bi2WO6during the photocatalytic reaction but also could be recycled easily by sedimentation. X-raydiffraction, scanning electron microscope and mechanical properties of films before and afterheat treatment results evidence that the composite fibers have excellent thermal stability andtensile strength. In order to improve the photocatalytic activity of SiO2@Bi2WO6, theSiO2@TiO2@Bi2WO6composite films is synthesized by combining the electrospinningtechnique, soaking and solvothermal method. The results showed that SiO2@TiO2@Bi2WO6has excellent photocatalytic activity and flexibility.(4) Highly bright K2SiF6: Mn4+red phosphors with a quantum efficiency of74%weresynthesized from silicon dioxide by redox reaction in HF/KMnO4solution. The opticalproperties of LEDs containing different ratios of K2SiF6: Mn4+phosphor and commercialCe3+-doped garnets(YAG-40) yellow-green phosphor were studied. A warm-white LED, withcolor temperature of3510K and color rendering index of90.9and efficacy of81.56lm/Wwas demonstrated. These prominent optical properties together with its low-cost and highefficient fabrication approach endow the as-synthesized K2SiF6: Mn4+phosphors greatpotential for commercial applications in warm-white LED.