Preparation And Properties Of Zr-MOFs-based Z-scheme Heterojunction Composite Photocatalyst

With the continuous development of economy,the situation of environmental pollution is becoming more and more serious,especially the problem of water environmental pollution.Therefore,it is urgent to find a green and efficient sewage treatment method.Photocatalysis technology has attracted much attention because of its mild reaction conditions and high economic benefits.As a Zr-based metal organic frameworks（Zr-MOFs）,MOF-808 is a photocatalytic material with high specific surface area,adjustable structure,excellent stability and good adsorption properties,which shows good application potential in the field of photocatalysis.However,the wide band gap of MOF-808 and the low utilization rate of visible light affect its photocatalytic activity to some extent.From the perspective of improving the light absorption capacity and promoting the separation of photogenerated carriers,this paper focused on modifying the MOF-808 material to enhance its photocatalytic activity.The photocatalytic performance of the catalysts was evaluated by the photodegradation efficiency of antibiotics.Specific research contents are as follows:（1）The MOF-808/Bi OBr（MB）composite photocatalysts were successfully prepared by solvothermal method and water bath method.The morphology,composition and optical properties of the as-prepared photocatalytic materials were tested by a series of characterization methods.Tetracycline hydrochloride（TC）was selected as the target pollutant to evaluate the photocatalytic activity of the materials.The experimental results showed that the adsorption capacity of MOF-808/Bi OBr composites was higher than that of Bi OBr single component,and the degradation capacity was also significantly enhanced.In particular,the MB-50 composite with 50%Bi OBr loading showed the best degradation performance,and the TC degradation efficiency reached 91.52%in 80 min.In addition,the results of radical capture experiments and ESR tests showed that·OH,·O₂^-and h⁺played a major role in the photodegradation process.Therefore,it can be speculated that a direct Z-scheme heterojunction was formed between MOF-808 and Bi OBr,which enhanced the visible light absorption and promoted the separation and transfer of charges.Combined with the enrichment effect of TC by MOF-808,the photocatalytic activity of the materials was effectively enhanced.（2）The MOF-808/Ag I（MA）composite photocatalytic materials were prepared by simple ion exchange precipitation method.A series of characterization tests were carried out to study the as-prepared catalyst materials.The characterization results of XPS showed that a small amount of Ag nanoparticles was deposited on the surface of the composite during the illumination process.The experimental results of TC degradation showed that the degradation performance of MOF-808/Ag I composites was significantly enhanced,among which the composite with a Ag I loading of 40%（MA-40）showed the best degradation performance with a 93.65%degradation rate in 80 min.The results of radical capture experiments and ESR tests showed that·O₂^-,¹O₂ and h⁺were the main active species in TC degradation process.Combined with the results of band structure analysis,it can be inferred that an all-solid Z-sheme heterojunction was constructed between MOF-808 and Ag I.Ag can be used as electron transfer medium,which can effectively promote the transfer of photogenerated carriers under the action of Schottky barrier,thus enhancing the photocatalytic activity of the materials.（3）The dye-sensitization Eosin Y/MOF-808/Cd S（EMC）composites were prepared by solvothermal method and chemical precipitation method,and were studied by various characterization methods.The characterization results of UV-vis DRS showed that the dye-sensitization of Eosin Y successfully extended the light absorption range of MOF-808 to the visible light region,and effectively improved the low light utilization rate of MOF-808.The PL and EIS analysis results showed that the loading of Cd S promoted the separation and migration of photogenerated charges.In addition,the TC degradation efficiency of Eosin Y/MOF-808/Cd S composites has been enhanced,especially the EMC-30 with a Cd S mass ratio of 30%,which could degrade 91.46%of TC within 80 min.A possible photocatalytic degradation mechanism with h⁺,·O₂^-and ¹O₂as the main active species was proposed based on the analysis of radical capture experiments and ESR tests.It can be speculated that the charge of photoexcited dye would transfer to MOF-808,and a direct Z-scheme heterostructure was formed betweem Cd S and Eosin Y/MOF-808,which could effectively promote the separation and migration of photogenerated electron-hole pairs,and further enhance the photocatalytic activity of the materials.In addition,the degradation effects of the three as-prapared photocatalysts were tested by mixing different antibiotic solutions to simulate industrial wastewater.The results of total organic carbon analysis showed that the photocatalysts had good mineralization ability and displayed good potential in practical application.In recent years,great progress has been made in the preparation and properties of Zr-MOFs materials.It is believed that the structure types of Zr-MOFs will continue to increase with the deepening of research,and there will be further breakthroughs in practical application.