Preparation Of Metal Bridged Fe-MOFs Composite And Study On Fenton-Like/Photo Synthetic Degradation Of Thiacloprid

Thiacloprid belongs to the second generation of neonicotinoid insecticides and has been widely used in modern agriculture because of its highly effective and specific control effect on sucking and chewing pests.However,the good solubility and structural stability of thiacloprid allow it to remain in the water for a long time without been degraded,causing many negative problems such as ecological imbalance and environmental pollution.Therefore,finding a method that can efficiently degrade and mineralize thiacloprid is an urgent problem to be solved.Fenton-like/photo catalytic technology belongs to a class of typical advanced oxidation technologies,which has advantages as mild reaction conditions and thorough mineralization.The Fenton-like/photo catalytic technology is widely used for the efficiently degrade of organic pollutants in water.The catalyst with the dual function of photo-Fenton is the key to this chemical process.At present,the catalysts used in photo-Fenton degradation of organic pollutants are suffer in degraded incompletely and susceptible to the effects of free radicals and photogenic carriers.Herein,the metal bridge strategy is proposed to enhance the interface of catalyst and improved its stability as well degradation effect.The metal bridge realized the efficient degradation and rapid mineralization of thiacloprid under UV-vis light irradiation.This strategy provided a new catalysts and treatment method for green environmental protection degradation of other similar pesticide pollutants.The main research contents and results obtained in this thesis are as follows:（1）Preparation of Cu₂O/MIL（Fe/Cu）based on in-situ Cu-bridge and applied in the Fenton-like/photo degradation of thiacloprid.The photosensitive semiconductor Cu₂O was grown on MIL-100（Fe）with in-situ Cu-bridge strategy to prepare a tight heterojunction interface in Cu₂O/MIL（Fe/Cu）,which can perform efficiency synthetic Fenton-like/photo degradation of thiacloprid.The Scanning Electron Microscope（SEM）,X-ray Diffraction Spectra（XRD）,X-ray Photoelectron Spectroscopy（XPS）,N₂ adsorption and desorption isotherms were used to characterize the crystal morphology and structure,element type and content,pore structure of materials.The photoelectric properties of Cu₂O/MOFs were analyzed by UV-vis spectrophotometer（UV-vis DRS）and electrochemical analysis（CV,EIS）.The characterization results show that:Cu₂O/MIL（Fe/Cu）showed a similar crystal form and pore structure to MIL（Fe）,which broadened the absorption range of MIL（Fe）from UV to UV-vis region,and the band gap value of MIL（Fe）also decreases from 2.5 e V to 1.3 e V;The in-situ Cu-bridge promotes the formation of tight interface within Cu₂O and MIL（Fe/Cu）,accelerating the transfer of photogenerated electron and the conversion of Fe²⁺/Fe³⁺.As a result,the reaction pathway of photoinduced electron excitation to Fenton-like reactions generate free radicals was shortened.The catalytic performance shows that:the degradation rate of thiacloprid over Cu₂O/MIL（Fe/Cu）was 2-40 times faster than other catalysts reported in recent years,which also show efficiency mineralization（82.3%with 80 min）and excellent catalytic cycle stability（degradation rate remains 98%in 10 experiments）;semi-in-situ tracking detection of thiacloprid degradation process was carried out by combining High Performance Liquid Chromatography/Mass Spectrometry（HPLC/MS）and Surface Enhanced Raman Spectroscopy（SERS）characterization methods,which obtained the degradation path and intermediate products of thiacloprid,and the cyanoimino group was proved to be the main attack target in the degradation process.（2）Preparation of MXene（Fe）-POR-MOFs based on in-situ Fe-bridge and Fenton-like/photo synthetic degradation of thiacloprid.In order to achieve the efficient degradation of thiacloprid without adding H₂O₂,MXene（Fe）was obtained by modifying two-dimensional material MXene with metal substitution method,then added into MOFs with porphyrin to obtain MXene（Fe）-POR-MIL（Fe）.The morphology and pore structure of materials were characterized by SEM,XRD,N₂ adsorption and desorption isotherms,etc.,the photoelectric properties and thermal stability were characterized by UV-vis DRS,CV,EIS and TGA.The characterization results show that:MXene（Fe）-POR-MIL（Fe）showed similar crystal structure and particle size to MIL（Fe）.Porphyrin could significantly improve the light absorption performance of pure MIL（Fe）and reduce the band gap value of MIL（Fe）by 0.5 e V;The in-situ addition of porphyrin as ligand to MIL（Fe）significantly improved the thermal stability of the material and increased the thermal decomposition temperature of MIL（Fe）by 27°C;MIL（Fe）can be tightly connected to the Fe anchor point on MXene（Fe）and form a Schottky junction to promote the separation of electron holes,which can improve the photocatalytic stability of materials.The catalytic performance showed that:without the addition of H₂O₂,MXene（Fe）-POR-MIL（Fe）can directly promote the water to produce·OH and completely degrade thiameprid within 120 min,and TOC removal rate reached70%in 7 h;MXene（Fe）-POR-MIL（Fe）exhibits excellent catalytic cycle stability,which show high degradation effect in 5 cycle experiments;According to the free radical capture experiment of degradation for thiacloprid over MXene（Fe）-POR-MIL（Fe）,·OH is the main active material in degradation.The VB value of MXene（Fe）-POR-MIL（Fe）（3.65 e V）was obtained by Ultraviolet Photospectrometric（UPS）,which concluded the degradation mechanism of thiacloprid over MXene（Fe）-POR-MIL（Fe）.