Rapid Synthesis Of Sheet-like Bi₂WO₆ By Low Temperature Molten Salt Method And Its Photocatalytic Properties

With the global energy consumption and environmental pollution problems becoming more and more serious,the traditional methods cannot completely solve the problems caused by environmental pollution and energy shortage due to their own shortcomings?easy to cause secondary pollution?.Therefore,using photocatalytic technology to degrade organic pollutants and developing new photocatalysts with high efficiency and activity has become a key topic in the field of photocatalysis research.As a new type of semiconductor photocatalytic material,Bi₂WO₆ has attracted much attention due to its excellent photocatalytic performance.Its morphology has a great influence on photocatalytic performance.Bi₂WO₆ with sheet-like and flower structure can improve its photocatalytic performance.At present,Bi₂WO₆ in the form of sheet-like,flower and fiber,is mostly synthesized by hydrothermal method.Although sheet-like Bi₂WO₆ is also synthesized by molten salt method,the time required is too long.In this study,a large number of attempts were made to find a fast and efficient method for synthesis of sheet-like Bi₂WO₆,which has a high photocatalytic performance.The main research work and results of this thesis are as follows:In the KNO₃ or NaNO₃ molten salt medium,Bi?NO₃?₃·5H₂O and Na₂WO₄·2H₂O were used as reaction materials,and sheet-like Bi₂WO₆ was synthesized at a relatively low temperature in a very short time.Studies have shown that different reaction temperatures,different reaction times,different feeding sequences and different molten salt media have no significant effect on the phase structure of Bi₂WO₆.In a certain feeding sequence,the sheet-like Bi₂WO₆ was obtained under different reaction sequences,different reaction temperatures,different reaction times and different molten salt media.However,the morphology of Bi₂WO₆ synthesized by changing the feeding sequence was different,with overlapping laminates or multi-species flower-like structures formed by interlacing laminates.It was found by XPS and FT-IR analysis that different synthesis conditions had no significant effect on the composition and structure of the sheet-like Bi₂WO₆.The BET test found that different synthesis conditions have a great effect on the specific surface area of the product.Through UV-Vis DRS,DRS,PL and transient photocurrent response test analysis,the absorption band edge,band gap,fluorescence intensity and transient photocurrent of sheet-like Bi₂WO₆ obtained under different synthesis conditions were significantly different.Studies on the photocatalytic performance of synthesized sheet-like Bi₂WO₆ showed that it has high visible light catalytic activity.Taking KNO₃ as molten salt medium,sheet-like Bi₂WO₆ sample was synthesized at 380 oC and the reaction time was 1min.Under visible light for 60 min,sheet-like Bi₂WO₆ degradation rate of Rhodamine B?RhB?reached 98.09%.Cyclic tests showed that the sheet-like Bi₂WO₆ has good stability.The experimental results show that the high visible light photocatalytic activity of the sheet-like Bi₂WO₆ is mainly attributed to the sheet-like structure or the self-assembled flower-like structure.Visible light degradation of rhodamine B?RhB?is the result of both electrons and holes working together,in which hole plays a dominant role.