Influence Of Yb, N, F, B And Ga Doped Er³⁺：Y₃Al₅O₁₂ On Sonocatalytic Activity Of TiO₂

With the development of the dyeing industries, a large number of toxicwastewater was produced and released to the nature. These highly colored effluentsnot only led to our environment to be not beautiful but also badly broke the ecologicalbalance. Particularly, many azo dyes and their breakdown products may lead tocarcinogenesis, teratogenesis and mutagenesis, which has already threaten humanhealth. Hence, searching and improving the rapidly effective methods to treat dyewastewater is an urgent task at present. As is well-known, semiconductor oxides TiO₂have been recognized to be preferable materials for catalytic processes, due to theirhigh photosensitivity, non-toxic nature, low cost and chemical stability. However,semiconductor oxides TiO₂are not suitable for the treatments of non-orlow-transparent organic dye wastewaters, which apparently limit the application intreatment of high concentration and dark color of dye wastewaters.Fortunately, several papers have appeared on ultrasonic treatment of wastewaterin recent years. Because of the special transmission mode, the ultrasound should be avery effective way to mineralize dyes in non-or low-transparent dye effluents.According to the theoretical and experimental investigations, sonochemistry arerelated to sonoluminescence because all of them originate from the high temperatureand pressure conditions inside the collapsing bubbles. This is also one of the wellknown mechanisms. The spectrum of sonoluminescence has a fairly wide rang ofwavelength in a liquid and has a part of high intensity of ultraviolet light emission.Recently, the sonocatalytic degradation of some organic pollutants in aqueoussolution using TiO₂powder as sonocatalyst has been reported. Nevertheless,whenever the heightening of catalytic activity and shortening of degradation time areour eternal task and pursuance. However, because of the wide band gap of TiO₂, onlya small fraction （ultraviolet light） of sonoluminescence can be utilized to carry outsonocatalytic degradation. That is, the insufficient supply of ultraviolet light fromsonoluminescence restrains the catalytic activity of TiO₂. This reminds us that the applications of up-conversion luminescence agent may resolve this problem. It isbecause the up-conversion luminescence agent can be succeed in converting thevisible light to the ultraviolet light that can effectually activate the TiO₂. Moreover,for further expanding the spectral response range of the sonocatalyst used today,combining the semiconductor with some improved up-conversion luminescenceagents has been also taken into consideration by us.Thus, this study is mainly about the influence of some doping atoms （Yb, N, F,B, Ga） on the performance of up-conversion luminescence ofEr³⁺：Y₃Al₅O₁₂.Experientially, the doping of Yb can sensitizeEr³⁺：Y₃Al₅O₁₂, which contributes toenhancing the performance of up-conversion luminescence. And the doping of N andF used to replace O atom inEr³⁺：Y₃Al₅O₁₂can broaden the scope of absorptionspectrum and enhance the intensity emission spectrum for their differentelectronegativity and radius from O atom. And Al is replaced by B and Ga atoms,which have small and big ionic diameter compared with Al. For this reason, as e/rchanging great, the intensity of crystal field inside will be transformed.It can besupposed that the host crystal inEr³⁺：Y₃Al₅O₁₂may be changed by doping of N, F, Band Ga. That is, N, F, B and Ga can decrease and increase the difference of orbitalenergy levels, respectively, meanwhile also reduce the symmetry of crystal fieldaround Er³⁺, which helpsEr³⁺：Y₃Al₅O₁₂to absorb much more expansive range andlarger amount of visible light. And then, Yb, N, F, B and Ga dopedEr³⁺：Y₃Al₅O₁₂isput into TiO₂for enhancing the sonocatalytic performance.In the study, several up-conversion luminescence agents were synthesized usingsol-gel method. And then, the corresponding sonocatalyst were prepared by sol-gelcoating process. The synthesized up-conversion luminescence agents and their coatedcomposites were characterized by X-ray diffraction （XRD） and scanning electronmicroscope （SEM）. And that, the sonocatalytic activities were detected through thedegradation of Azo Fuchsine （AF） dye in aqueous solution by UV-vis spectroscopy.Some key influences such as heat-treated temperature and heat-treated time on thesonocatalytic activity of Er³⁺:Yb_aY2.99-aNxFyAl5O12-x-y/TiO₂coated composite andEr³⁺:Yb_aY_2.99-aB_xGa_yAl_5-x-yO₁₂/TiO₂coated composite, as well as ultrasonicirradiation time and initial dye concentration on the sonocatalytic degradation were studied. At last, the experiments also indicated that the sonocatalyst has a goodsonocatalytic activity to degrade other organic dyes under ultrasonic irradiation.