Study On The Preparation And Properties Of Upconversion Materials And NaYF₄:Er,Yb/TiO₂ Composite Catalysts

Photocatalytic technology as a green,efficient and energy-efficient technology,can degrade the pollutants in the environment through photocatalytic reaction.The most important part of photocatalytic technology is catalyst.semiconductor TiO₂ is the most maturely and widely used semiconductor catalyst because of its excellent properties.However,due to its larger band gap of TiO₂ can only absorb a small amount of ultraviolet light from the sunlight and waste a large part of the sunlight energy.So researchers explored semiconductor TiO₂ catalyst modification research and obtained certain achievements,that expand the TiO₂ light response to visible light and near infrared parts,and can greatly improve the effective utilization rate of the light from the sun.Due to the unique electronic layer structure and low phonon energy of the doped rare earth ions in the upconversion material,the ability to absorb low-energy light and convert it into high-energy light has become a widely studied field.The luminescence intensity of the upconversion materials varies greatly when the species of rare earth elements and the amount of doping are different.Based on previous research,this paper used the upconversion material that can absorb long wavelengths to transform short wavelength light feature to modify semiconductor TiO₂ photocatalyst with the method.In this paper,the solvother-mal method was firstly used to constantly change the experimental conditions,and the experimental process was optimized to prepare the upconversion material NaYF₄:Er,Yb.The test of the performance of the upconversion material was carried out through a series of characterization methods.Then,the NaYF4:Er,Yb/TiO2 composite catalyst was prepared.Finally,the photocatalytic performance of photocatalytic degradation of pollutants in visible light was studied.The main contents are as follows:?1?Solvothermal method was used to prepare NaYF₄:Er,Yb upconversion nanoparticles based on NaYF₄ as substrate and doped with two rare earth ions Er and Yb.The morphology,particle size,morphology and luminescence characteristics of NaYF₄:Er,Yb nanoparticles were analyzed by XRD,TEM,SEM,UV-vis.In the preparation process,the conditions such as oleic acid content,temperature and heating time have a great influence on the crystal shape and particle size of NaYF₄:Er,Yb nanoparticles,and then affect the luminescence properties.The results showed that the NaYF₄:Er,Yb nanoparticles exhibited hexagonal crystals with a particle size of about 30 nm and good upconversion fluorescence properties when prepared in 15 ml of oleic acid and heated at 180?for 24 h.?2?Byhydrothermalmethodandultrasonicmethodtoprepare NaYF₄:Er,Yb/TiO₂ catalysts whit the NaYF₄:Er,Yb nanoparticles prepared above.NaYF4:Er,Yb/TiO2 catalyst was characterized by a series of characterization means such as XRD,TEM,SEM,UV-vis,BET and so on.Finally,the photocatalytic performance analysis experiment was carried out.The experimental results show that NaYF₄:Er,Yb/TiO₂ nanoparticles catalyst prepared by the two methods have higher the catalytic performance than the pure TiO₂.?3?In order to further improve the catalytic effect of NaYF₄:Er,Yb/TiO₂nanoparticle catalyst,NaYF₄:Er,Yb nanoparticles were treated by Lemieux-von Rudloff reagent and then NaYF₄:Er,Yb/TiO₂ nanoparticles catalyst were prepared.Oleic acid was present on the surface of NaYF₄:Er,Yb nanoparticles prepared by solvothermal method,which greatly affects its composite effect with TiO₂ and further influences the photocatalytic effect.Therefore,surface active agents were used to treat the surface of NaYF₄:Er,Yb nanoparticles.After being treated,the NaYF₄:Er,Yb/TiO₂ nanoparticle catalyst was prepared by compounding with TiO₂.After a series of characterization tests,the results show that the composite effect of the treated NaYF₄:Er,Yb nanoparticles have greatly improved compared with the untreated NaYF₄:Er,Yb.Meanwhile,the photocatalytic performance was also improved.