Preparation Of Fe-MOFs@PANI Composite Materials And Its Photocatalytic Performance

With the speeding up of the process of industrialization,a large number of toxic pollutants are discharged into water bodies,including heavy metals and organic pollutants,posing a potential threat to the environment and even human health.Therefore,in water treatment technology,photocatalysis as an efficient and energy-saving technology has gradually attracted attention.This technology can use sunlight to reduce highly toxic Cr???to low toxic Cr???,and it can also degrade difficult-to-biodegradable macromolecular organic pollutants into non-toxic small-molecule substances,and even completely mineralize to CO₂ and H₂O.Metal-organic framework?MOF?as a photocatalyst has been widely used in the field of environmental restoration.Among them,Fe-MOFs can photocatalytically reduce heavy metals under visible light or ultraviolet visible light,and can also effectively photocatalytically oxidize organic pollutants.In order to further enhance the Fe-MOFs'photocatalytic activity,conductive polymers-polyaniline?PANI?was used to modify Fe-MOFs to build more powerful photocatalytic materials.In this research,we chose MIL-100?Fe?,MIL-88A?Fe?and PANI were used as raw materials to synthesize a series of composite photocatalysts.The properties of composite materials for photocatalytic Cr???reduction and organic pollutants degradation were explored,and the factors affecting the photocatalytic activity were investigated.The reaction mechanism was proposed and verified.The main work of this paper is as follows:1.Series of Z-scheme heterojunction MIL-100?Fe?/PANI was prepared by using a simple mechanical ball milling method using structurally stable metal-organic framework material MIL-100?Fe?and conductive polymer material polyaniline?PANI?as raw materials.As-synthetic materials were characterized by powder X-ray diffraction?PXRD?,Fourier transform infrared spectroscopy?FT-IR?,thermogravimetric analysis?TGA?,transmission electron microscopy?TEM?,scanning electron microscopy?SEM?,high-resolution transmission electron microscopy?HRTEM?,photoluminescence emission spectroscopy?PL?,X-ray photoelectron spectroscopy?XPS?,and UV-Vis diffuse reflectance spectroscopy?UV-vis DRS?and so on.The photocatalytic activity of MIL-100?Fe?/PANI for Cr???reduction under white light was studied.The results show that the rate of MP9%photocatalytic Cr???reduction was more than 6 times more efficient than the original MIL-100?Fe?.The effects of ethanol as a hole consumption,pH value?2-8?and coexisting ions?ions in tap water and lake water?on Cr???reduction over MP9%were also investigated.And under white light irradiation,MP9%also showed good photocatalytic degradation efficiency for the tetracycline?TC?.In addition,the photocatalytic behavior of MP9%in a mixed system of Cr???and tetracycline was also studied.Compared with the photocatalytic performance of the single-component system,the degradation efficiency of Cr???and tetracycline in the mixed system is improved,which indicates that MP9%has a coordinated promotion effect on the degradation of the two pollutants.Based on the results of electrochemical characterization and electron spin resonance experiments,a possible reaction mechanism was proposed and verified.Photocatalytic reduction of Cr???cycle experiments also showed that MP9%has good reusability and stability as a photocatalyst.This can also be confirmed by photoluminescence emission spectroscopy and electrochemical impedance spectroscopy.2.In order to verify that PANI modified other Fe-MOF to improve the universality of photocatalytic activity,other Fe-MOF was selected for further investigation.A series of PANI/MIL-88A composites?named Px@M88,x represents the initial mass ratio of FeCl₃·6H₂O:PANI?with different ratios were prepared by one-pot hydrothermal method using visible light excited MIL-88A and PANI as raw materials.Powder X-ray diffraction,UV-visible diffuse reflectance,Fourier transform infrared spectroscopy,morphology characterization?scanning electron microscopy,transmission electron microscopy,high-resolution transmission electron microscopy?,X-ray photoelectron spectroscopy and photoluminescence emission spectroscopy were used to characterize them.Px@M88 was investigated the photocatalytic performance of Cr???reduction under white light.The efficiency of photocatalytic reduction of Cr???by Px@M88 composite material is also greatly improved compared with alone MIL-88A.The best photocatalyst P9@M88 was selected to investigate the effects of pH?2,3,4,5,6,7,and 9?small organic compounds?tartaric acid,citric acid and oxalic acid?and foreign ions?ions in tap water,lake water,etc.?on Cr???reduction.The results show that the rate of photocatalytic reduction of Cr???by Px@M88 is 3.5 times higher than that of pure MIL-88A.The photocatalytic reduction of Cr???cycle experiments also showed that P9@M88 has reusability and stability as a photocatalyst.The possible mechanism of P9@M88 photocatalytic Cr???reduction was proposed based on electrochemical analysis,X-ray photoelectron spectroscopy and electron spin resonance experimental.3.Considering the existence of Fe-O clusters in the Px@M88 composites prepared by in situ hydrothermal method,Fenton advanced oxidation reaction can be activated by H₂O₂ to improve the degradation efficiency of organic pollutants.In the Fenton degradation experiment,the photocatalytic activity of P9@M88 on the degradation of organic pollutants was investigated with bisphenol A?BPA?,methylene blue?MB?and rhodamine B?RhB?as the targets.In the presence of H₂O₂ and light source,P9@M88 has the best photodegradation efficiency for three organic pollutants,which is attributed to the reaction between iron-oxygen clusters and hydrogen peroxide in MIL-88A which can generate hydroxyl radicals,which are the main oxide species in the Fenton system can promote the degradation of organic pollutants.The P9@M88 catalyst exhibits better organic pollutant degradation efficiency than the MIL-88A catalyst,which is due to the enhanced charge transfer ability between the type II heterojunction interfaces formed by the P9@M88complex.The path of BPA degradation was deduced based on the flight mass spectrometry test.The reaction mechanism of this material to degrade organic pollutants was proposed and verified.And explore the recyclability and stability of materials.