Controllable Synthesis And Photocatalytic Properties Of Nano-composites Derived From CAU-17

In recent years,with the rapid development of industrial factories,organic pollutants,such as organic dyes and tetracycline,have been poured into rivers in large quantities.The increase in the content of tetracycline drugs in water will increase the drug resistance of human bodies.Organic dyes,such as rhodamine B,methyl orange and methyl blue,are at risk of cancer if they are drunk.At present,photocatalytic degradation of sewage technology provides a good idea for solving sewage treatment.In this technology,efficient photocatalyst is the key.Efficient photocatalyst usually needs to have good space charge separation rate,considerable visible light absorption range and absorption intensity.However,there is a problem that the band gap of photocatalyst is too wide,which makes the material only absorb ultraviolet light,which is less than 5%of the solar light source,so the research focus is on improving its utilization rate of visible light.At present,one of the main methods is to construct heterojunction,and use the synergy and the matching energy band structure between them to enhance the separation and transfer of photo-generated electron-hole pairs of photocatalyst,so as to generate more active free radicals to remove pollutants.In recent years,metal-organic framework（MOFs）materials have been widely used in the field of photocatalysis because of their good pore structure and many active sites.In 2016,CAU-17 was prepared for the first time.Because of its low preparation price and large pore structure,it has become one of the emerging photocatalysts.CAU-17 is one of Bi-based MOFs,and its band gap is wide and its absorption range is limited.Therefore,we can improve the absorption range by forming heterojunction with other materials or using it as the precursor of Bi source to form Bi-based semiconductor heterojunction.In this paper,we use CAU-17 as the precursor,design double MOFs heterojunction and Bi-based semiconductor heterojunction,and aim at improving the separation of photo-generated carriers,and construct CAU-17@MIL-100 heterojunction,BiOCl/Bi₂O₃ heterojunction excited by single photon path and MOF-BiOCl/Mo S₂ heterojunction excited by two electron channels.The details are as follows:（1）In order to improve the light absorption range of CAU-17,we construct CAU-17@MIL-100 double MOFs heterojunction.It was found from various characterization tests that the synergy between the two MOFs formed a single-photon excitation pathway from MIL-100 to CAU-17.The existence of the single-photon transfer pathway promoted the separation and transfer of photo-generated carriers in CAU-17@MIL-100 system.（2）Bi-based heterojunction BiOCl/Bi₂O₃ was prepared by halogenation with CAU-17 as the precursor.Its morphology maintained the rod-like structure of CAU-17,and nanosheets of Bi-based semiconductor was formed on the surface.Because more active adsorption sites were obtained,and it was found through analysis that the heterojunction transferred charges through single photon,which formed an effective space charge separation.Through characterization,it is found that a built-in electric field is formed between the two semiconductors,and the charge flow direction is transferred from Bi₂O₃ to BiOCl,which makes BiOCl with a wide band gap gain visible light absorption ability,and improves the photon utilization rate through this single photon transfer pathway.（3）MOF-BiOCl/Mo S₂ heterojunction was prepared by a step-by-step method with CAU-17 as the precursor.It was found that the photocatalytic degradation performance was improved because BiOCl nanosheets were synthesized in situ by Bi-MOFs,which avoided the aggregation of single BiOCl nanosheet and obtained more adsorption sites.In addition,built-in electric fields were formed between heterojunctions,and charges were transferred through an S-scheme pathway,which resulted in effective space charge separation.