Preparation Of Up-conversion Luminescent Materials/TiO₂ Photonic Crystal Tandem Films For Photocatalytic Wastewater Treatment

Since the 21st century,with the rapid development of economy,human society is faced with two major problems:energy shortage and environmental pollution.As the basic pillar industry of China,coal chemical industry has a series of serious environmental pollution problems,especially the industrial wastewater has the characteristics of large discharge,complex pollutant composition,high concentration,high toxicity,and difficult degradation.It is urgent to develop efficient and clean advanced treatment technology of coal chemical wastewater.Photocatalysis takes solar energy as the main energy source,which has the advantages of high efficiency,cheapness,no secondary pollution,and small damage to the environment.It is an ideal advanced oxidation technology for advanced wastewater treatment with high efficiency.TiO₂is cheap and easily available,stable in nature,non-toxic and harmless,and has high photocatalytic activity,so it is currently recognized as the most likely to achieve industrial application of photocatalyst.The large-scale application of TiO₂photocatalytic process is limited by its limited light absorption performance（It only absorbs ultraviolet light）,high electron/hole composite rate and low surface area,which greatly reduces the photocatalytic efficiency of TiO₂.In order to solve the problem that TiO₂can only absorb UV light,this thesis proposes a novel up-conversion luminescent materials/tandem photonic crystal films photocatalyst.The up-conversion luminescent material has the advantages of low autofluorescence interference,high conversion efficiency,narrow emission frequency,low toxicity,good biocompatibility and stability,which can be used to convert visible and infrared light into ultraviolet light that can be absorbed by TiO₂.Photonic crystals have optical properties such as"photonic band-gap"and"slow photon"effect.The up-conversion luminescent materials/tandem photonic crystal film composite catalysts uses the optical properties of the photonic crystal to accurately segment the solar spectrum,and then converts sunlight into ultraviolet light under the action of the up-conversion material,which is then absorbed by TiO₂for the photocatalytic process.In principle,it can realize the effective utilization of the full spectrum of sunlight.At the same time,the abundant pore structure inside the photonic crystal is conducive to the diffusion and migration of the reactants,which can make full use of the high specific surface area and improve the utilization rate of the reactive site,thus greatly improving the photocatalytic degradation of pollutants and hydrogen production ability of TiO₂.This paper focuses on the preparation of tandem photonic crystal films;Preparation of up-conversion luminescent materials and regulation of luminescent properties;The preparation and evaluation of photocatalytic activity of up-conversion materials/tandem photonic crystal film composite photocatalysts.At present,based on the above research ideas,the main achievements are as follows:（1）A high-quality up to five layers opal photonic crystal film is prepared.At the microscopic scale,it can be observed that the front of the photonic crystal is a large area of hexagonal densely packed colloidal microspheres arranged in regular order,and the orderly stacking of colloidal microspheres of different sizes can be clearly observed in the cross section.Ultraviolet-visible reflection spectrums show multiple reflection peaks corresponding to photon band-gap peaks of each layer colloidal microspheres.High quality opal photonic crystal films are the basis for the subsequent preparation of inverse-opal films.（2）The tandem inverse opal photonic crystal films were prepared,the impregnation rate and impregnation time were optimized,and the influence of impregnation conditions on the microstructure of the inverse opal films was investigated,which laid the foundation for the subsequent evaluation experiment of photocatalytic activity.（3）Carbon based up-conversion luminescent material C₃N₄was successfully prepared by thermal polymerization method,and the layered structure of C₃N₄nanosheets was obtained by acetic acid vapor etching.The changes of its structure,optical properties and photocatalyst activity were explored.Rare earth up-conversion luminescent materials NaYF₄:Yb:Er and NaYF₄:Yb:Tm were prepared by hydrothermal method and their preparation conditions were optimized.（4）The up-conversion luminescent materials/TiO₂photonic crystal tandem film photocatalyst was successfully prepared,its optical regulation behavior was studied,and a series of photocatalytic activity evaluation experiments were carried out,and it was found that the photocatalytic activity of the composite film photocatalyst was significantly improved.