Quantum Dots/Bi₂WO₆ Photocatalysts Synthesized By Microwave And Their Activity In Degradation Of Organic Wastewater

In recent years,the discharge of wastewater from the country has been increasing year by year.In particular,the discharge of organic wastewater has remained at a high level,seriously endangering the environment and endangering human health.Traditional physical and chemical wastewater treatment technologies are not ideal for the treatment of organic wastewater containing POPs(persistent organic pollutants),and have the disadvantages of high energy consumption and secondary pollution.Photocatalytic technology has been widely applied in the degradation of organic wastewater due to its low energy consumption,thorough degradation,and no secondary pollution.The traditional photocatalyst TiO2 can only be excited by ultraviolet light and cannot use the visible light that accounts for the largest proportion of sunlight,limiting its application and promotion.In recent years,new photocatalysts such as bismuth tungstate(Bi2WO6)have become the hot spots in photocatalysis due to their visible light response characteristics,stable performance,and green non-toxicity.At present,Bi2WO6 is still not industrialized,mainly due to the following reasons:1.Bi2WO6 itself is easier to complex with photoelectrons and electrons,the photocatalytic activity needs to be further improved;2.The pure Bi2WO6 visible light response range is relatively small,and it still needs to be substantially at this stage.Improve the utilization of visible light;3,Bi2WO6 commonly used hydrothermal preparation,preparation cycle is long,and there are crystal defects caused by uneven heating.Based on the above issues,this paper proposes the preparation of Bi2WO6 composite photocatalysts with carbon quantum dots and graphene quantum dots prepared by microwave hydrothermal synthesis.The sample prepared by microwave hydrothermal synthesis method and traditional hydrothermal method has controllable morphology and high purity.In addition,it has the advantages of rapid heating,heat source and medium separation,and even heating,which can solve the defects of the traditional hydrothermal method.Greatly reduce the preparation cycle.The carbon quantum dots have photoluminescence-dependent properties,and can reduce the bandgap of the composite photocatalyst,thus significantly improving the visible light utilization of the composite photocatalyst.The graphene quantum dots inherit the excellent properties of graphene.The conjugated fluorene bonds contained in the graphene quantum dots give excellent electron transport and storage ability,which facilitates the rapid electron transfer,improves the carrier separation efficiency of the composite photocatalyst and thus enhances the light.Catalytic activity.At the same time,the graphene quantum dots have a certain photoluminescence ability,which helps to improve the visible light response ability of the composite photocatalyst.The main research contents of this paper include:(1)Graphene quantum dots(GQDs)were prepared by redox-dialysis method,and carbon quantum dots(CQDs)were synthesized by hydrothermal method and compounded with Bi2WO6 to obtain GQDs/Bi2WO6 and CQDs/Bi2WO6 samples,respectively,GQDs(CQDs)were investigated.The effects of the content,microwave synthesis temperature,time and other conditions on the morphology of the catalyst samples were investigated.The photocatalytic degradation of simulated wastewater was investigated.The activity of the simulated wastewater was investigated,and the"structure-activity" relationship was explored.(2)The photoelectron-hole separation efficiency of GQDs(CQDs)/Bi2WO6 samples was measured by PL photoluminescence spectra and transient photocurrent It curves,and the GQDs(CQDs)/Bi2WO6 samples were characterized by UV-Vis diffuse reflectance spectroscopy.Visible light response performance was analyzed by SEM,TEM,XRD,etc.The morphology and phase structure of the synthesized samples were analyzed.It was found that after the modification of carbon quantum dots and graphene quantum dots,the phase structure of Bi2WO6 did not change.The visible light response performance has been greatly improved,and the electron recombination rate of photogenerated holes has been significantly reduced,thereby improving the photocatalytic performance of the composite photocatalyst.The photocatalytic performance of the 3%GQDs/Bi2WO6 composite photocatalyst was the strongest,and 100 ml of RhB solution with a concentration of 20 mg/L could be almost completely degraded in 20 min(degradation rate>99%).Compared with the current report,the photocatalytic performance of Bi2WO6 has been greatly improved.It has a guiding role in the theoretical design of novel photocatalysts and photocatalytic research.