Preparation And Properties Of Organic-inorganic Composite Bismuth Tungstate Photocatalytic Materials

The treatment of water pollution is related to the survival and development of human society.However,traditional treatment methods have problems such as long time,high cost,and secondary pollution.Therefore,photocatalytic technology with the advantages of environmental protection,high efficiency and reproducibility has gradually become a current research hotspot.However,most single photocatalysts have problems such as poor response to visible light,high photo-generated electron-hole pair recombination rate,easy aggregation of catalyst powder,difficult recovery,and poor cycle stability,which restrict their wide application in actual sewage treatment.As one of the most commonly photocatalytic semiconductors,bismuth tungstate（Bi₂WO₆）has a narrow band gap and has a good response to visible light.However,the development of bismuth tungstate is still limited due to the high photo-generated charge recombination rate,low oxidation potential,and easy aggregation.In order to greatly improve its application performance,this study prepared organic-inorganic hybrid semiconductor photocatalyst PW₁₂/CN@Bi₂WO₆ by introducing conjugated organic small molecule phytic acid and melamine.The introduction of small conjugated organic molecules helps to solve the disadvantages of poor stability of Bi₂WO₆ photocatalyst.At the same time,small conjugated organic molecules act as a"bridge"to form a Z-type heterojunction structure with bismuth tungstate and phosphotungstic acid,which inhibits the recombination of photo-generated charges and significantly improves the separation efficiency of photo-generated charges,thereby solving the problem of low catalytic activity.In order to promote the PW₁₂/CN@Bi₂WO₆ powder photocatalyst to be widely used in industrial wastewater treatment,air purification,public transportation internal air treatment and other fields,this article uses commonly used cotton fabric as a carrier to load it to improve its recyclability and recovery performance.The construction of an organic-inorganic hybrid system is an important strategy to improve the photocatalytic performance of photocatalysts,and it also provides a new way for the development of photocatalysts.Based on this,the main research work of this paper is carried out from several aspects:preparation,structural characterization,degradation mechanism analysis,TC degradation product tracking,and loading performance of the composite photocatalyst,as follows:1.Preparation of composite photocatalyst:The organic-inorganic hybrid PW₁₂/CN@Bi₂WO₆semiconductor photocatalytic material was synthesized by simple hydrothermal method using phosphotungstic acid,melamine,phytic acid and Bi₂WO₆ semiconductor as raw materials,and the preparation conditions were optimized.The results show that when the doping ratio of PW₁₂/CN composite is 10%,the p H value is 3,the temperature is 180℃,and the preparation time is 8 h,all organic-inorganic hybrid composites have the best photocatalytic performance.Characterization of the structure of the composite catalyst:The microscopic morphology,structural crystal form,surface element composition,specific surface area and pore structure of the prepared PW₁₂/CN@Bi₂WO₆composite catalyst were characterized by SEM,TEM,XRD,XPS and BET.2.Degradation performance of composite photocatalyst:In addition,tetracycline solutions prepared with different inorganic salt ions and different water quality were used as substrates for degradation to evaluate their photocatalytic performance in practical applications.The results show that the prepared PW₁₂/CN@Bi₂WO₆ composite materials have high efficiency photocatalytic degradation performance,proving that it has a wide range of value in practical applications.3.Degradation mechanism of composite photocatalyst and analysis of TC degradation process:Through free radical capture and electron spin resonance（ESR）experiments,it is proved that the active groups that play a major role in the photocatalytic oxidation reaction are h⁺and·O₂^-.Combined with the conduction band position obtained by the Mott-Schottky curve and the calculated valence band position,it is inferred that it is the photocatalytic mechanism of the Z-type heterojunction.In addition,three-dimensional fluorescence spectroscopy and liquid-mass spectrometry technology are used to track and monitor the intermediate process of tetracycline degradation.4.Preparation and performance analysis of the supported photocatalyst:The PW₁₂/CN@Bi₂WO₆ composite photocatalyst powder is anchored on the cotton fabric through the"amine-formaldehyde reaction"to realize the close combination of the photocatalyst and the fiber fabric.Solve the problem that the powdered photocatalyst is easy to aggregate in the solution and difficult to recycle.The system has excellent photocatalytic efficiency,mild reaction conditions,easy recycling and no secondary pollution.