Preparation Of WO₃ Nanomaterials With Different Crystalline Phases And Methods For Improving Photocatalytic Activity

Tungsten trioxide（WO₃）is a kind of n-type transition metal oxide.Its band gap can be adjusted in a wide range（2.4-3.2eV）.It also has good charge transport characteristics and is very stable under acidic illumination conditions.These characteristics make WO₃ have great potential in the application of photocatalysis.In addition to these excellent properties,the d^0-electronic configuration of WO₃ is also very beneficial for photocatalytic activity.Tungsten trioxide has many different crystalline phases,such as orthogonal,monoclinic,cubic,hexagonal and so on.The size,morphology and physical and chemical properties of tungsten trioxide in different crystalline phases are also different.These factors will affect the photocatalytic performance.Therefore,this paper focuses on the preparation of WO₃ nanocrystals with different crystalline phases and their photocatalytic properties.At the same time,the effects of morphology and doping rare earth elements on photocatalytic activity are discussed.The experimental results are as follows:1.Orthogonal WO₃ nanoparticles were prepared by hydrothermal method.The samples synthesized by hydrothermal method were annealed at different temperatures in vacuum.After annealing,three WO₃ samples with uniform morphology but different crystalline phases were obtained.2.The photocatalytic activity of WO₃ nanoparticles with different crystalline phases was studied using methyl blue simulated wastewater.It was found that the photocatalytic activity of WO₃ nanoparticles with different crystalline phases was significantly different.The photocatalytic activity of WO₃ nanoparticles was tetragonal>orthogonal>hexagonal.3.Orthogonal phase WO₃ was synthesized by hydrothermal method and annealed in air to obtain three WO₃ nanoparticles with the same crystal phase but different morphology.The aggregation degree,size and shape of the three samples were different.The results of photocatalytic activity test and analysis show that when the morphology of WO₃ is identical,the photocatalytic activity of WO₃ with layered structure and small aggregation degree is higher than that of WO₃ with monoclinic phase.4.Rare earth element Er-doped WO₃ was prepared by hydrothermal method.It was found that with the increase of Er doping concentration,WO₃ nanoparticles first decreased and then increased,indicating that appropriate Er doping could inhibit the growth of WO₃ grains,and the sample size with Er atomic molar ratio of 0.4%was the smallest in the period.The results of photocatalytic activity test also showed that the sample with Er doping concentration of 0.4%had the best photocatalytic activity.