Study On The Effect Of Er³⁺: Y₃Al₅O₁₂ And Er³⁺: YAlO₃ On Photocatalytic Activity Of TiO₂ And ZnO

Photocatalytic processes to degrade organic pollutants in water by utilizing a catalyst have been the subject of research recently. Semiconductor oxides such as TiO₂ and ZnO have been recognized to be preferable materials for photocatalytic processes, due to their high photosensitivity, non-toxic nature, low cost and chemical stability. The semiconductor photocatalysis is initiated by the surface trapping of photo generated electrons (e-) and holes (h+), which induces interfacial electron-transfer reactions with adsorbed substrates. However, because of the wide band gap of TiO₂ and ZnO, only a small ultraviolet fraction of solar light (3-5 %) can be utilized. Therefore, the effective utilization of solar energy still remains a challenge in photocatalytic applications.For long time, much attention had been drawn on extending the range of absorption wavelength of TiO₂ and ZnO catalyst, namely, making the TiO₂ and ZnO powder as photocatalyst absorb the sun light at large region. In earlier investigations, some researchers tried to ameliorate the properties of TiO₂ and ZnO particles by doping transition-metal ions in order to slow down the recombination rate of the photogenerated electron-hole pairs and to enhance the interfacial charge transfer efficiency. Later, others had started to use anionic nonmetal dopants to extend the photocatalytic activity into the visible-light region because the related impurity states are near the valence band edge. All these methods did its work in extending the range of absorption wavelength of TiO₂ and ZnO catalyst, but the absorption spectra of these compounds in the visible region were relatively small, and they also suffered from a thermal instability, an increase of carrier-recombination centers, the increased recombination of photogenerated electron-hole pairs, the requirement of an expensive ion-implantation facility and complex treated process.In this paper, Er³⁺:Y₃Al₅O₁₂/TiO₂ composite, Er³⁺:YAlO₃/TiO₂ composite, Er³⁺:YAlO₃/TiO₂ coating agent, Er³⁺:YAlO₃/ZnO composite, Er³⁺:YAlO₃/ZnO coating agent and Er³⁺:YAlO₃/ZnO/TiO₂ composite, which could use the sun energy, have been prepared. In succession, these composites were characterized by XRD, SEM or TEM. Azo dyes are the most important class of synthetic organic dyes used in the textile industry and are therefore common industrial pollutants. They are produced in large amounts and may enter the environment during the production and manufacturing process. Here, the Acid Red B is selected as the primary model contaminant to detect the photocatalytic activity of the Er³⁺:Y₃Al₅O₁₂/TiO₂ composite, Er³⁺:YAlO₃/TiO₂ composite, Er³⁺:YAlO₃/TiO₂ coating agent, Er³⁺:YAlO₃/ZnO composite, Er³⁺:YAlO₃/ZnO coating agent and Er³⁺:YAlO₃/ZnO/TiO₂ composite under solar light irradiation.In addition, the effects of Er³⁺:Y₃Al₅O₁₂ or Er³⁺:YAlO₃ content, heat-treated temperature and heat-treated time on photocatalytic activity of these composites were reviewed through the degradation of Acid Red B dye under solar light. And, the parameters such as dye solution initial concentration, prepared photocatalyst amount, solution acidity and solar light irradiation time for the photocatalytic degradation of Acid Red B dye under solar light have been investigated with the existence of the prepared photocatalyst. The mechanism for the great improvement for the activity of the prepared photocatalyst is proposed as well. Compared to the conventional method, this kind of new composites photocatalyst can supply ample UV light for the genuine requirement of TiO₂ and ZnO partilcles. Furthermore, it may be easy to discover the raw materials and prepare the composite. Thereafter, it is possible to provide a new way to utilize TiO₂ and ZnO under solar light and reduce the cost for wastewater treatment.