Controllable Synthesis And Photocatalytic Performance Of Polymorphic AgVO₃

Crystal phase structure is considered to be one of the fundamental reasons for the origin of photocatalytic activity among many of the influencing factors,as it is directly related to the generation,separation,and transfer of photogenerated carriers.Many polymorph photocatalysts,such as TiO₂,Ga₂O₃,WO₃,Bi₂O₃,BiVO₄,have shown distinct photocatalytic activity due to their various crystal structure.Silver vanadate,AgVO₃,is a known indirect band gap semiconductor,and is mainly used in the fields of battery,gas sensor,photocatalysis and so on.AgVO₃ is also a polymorph semiconductor material.Four AgVO₃ polymorphs including?,?,?and?have been reported,among which?-and?-AgVO₃ are seldom reported and only stay in the theoretical research stage,?-AgVO₃ has good sterilization performance but no any photocatalytic activity towards dye degradation and water splitting into oxygen,while the most studied?-AgVO₃ displays excellent visible light photocatalytic activity for the degradation of RhB,MB and other organic dyes.In addition,some unknown AgVO₃ appear as impurity phase.Thus,the synthesis of AgVO₃ polymorph photocatalysts with high purity and the investigation of their structure-activity relationship are of great significance for the understanding of the basic principles of photocatalysis and the development of highly efficient photocatalysts.Nevertheless,due to the limitation of synthesis chemistry,there is no systematic study on the correlation between photocatalytic activity and crystal structure of AgVO₃.Herein,we developed a simple hydrothermal method to achieve a novel metastable and high purity AgVO₃phase,which is named as?'-AgVO3,and systematically investigated its crystal structure and photochemical properties.We further compared the photocatalytic activity of?'-AgVO₃ with two common?-and?-AgVO₃ and revealed the activity difference of them from the viewpoint of crystal structure and electronic structure.This thesis not only develops a new and simple solution chemistry strategy to prepare the metastable phase AgVO₃,but also enriches the photocatalytic applications and structure-activity relationship of AgVO3 polymorphs.The specific research contents are as follows:?1?A seldom reported metastable phase?'-AgVO₃ with high purity has been prepared by a simple hydrothermal reaction by introducing I^-in the system.The XRD refinement results show that?'-AgVO3 is a Orthorhombic phase,Pnma?62?,with cell parameter of a=14.3492?4??,b=3.5949?2??,c=5.1598?2??,V=266.16?1??,Z=4.The DFT calculation reveals that?'-AgVO3 is an indirect semiconductor with band gap of 1.93 eV and a candidate visible light material.?'-AgVO3 demonstrates the metastable phase characteristics during the heat treatment.In-situ XRD and TG results show that?'-AgVO₃ begins to undergo a phase transition at 350°C and completely transforms into a thermodynamic stable?phase at 500°C.Raman and XPS results prove the important role of I^-in the formation of?'-AgVO₃.The discovery of high purity?'-AgVO3 enriches the polymorphism of AgVO3,which is of great significance to the investigation of synthesis chemistry and properties of AgVO3.?2?Three AgVO₃ polymorphs including?-,?-and?'-AgVO₃ have been synthesized by the simple solution chemistry.The crystal phase,composition,morphology and optical properties of the three AgVO₃ polymorphs were characterized by XRD,SEM,XPS,and Raman techniques.The photocatalytic activity was evaluated by the degradation of Rhodamine B?RhB?under visible light irradiation.The results show that?'-AgVO3 exhibits excellent photocatalytic performance under visible light,and its photocatalytic degradation rate is about 6 times of?-and?-AgVO₃.The better activity of?'-AgVO₃ can be attributed to its extremely distorted polyhedral configuration and highly dispersed band structure,which are more benefiting for the separation of photogenerated carriers.