Application Of Fe₂O₃ Composite Nanomaterials Derived From Metal-organic Gel In Photocatalytic Degradation Of Rhodamine B

With the current rapid development of industry,the serious pollution of water environment has attracted more and more attention.Among them,a variety of organic dyes that are discharged in the water environment along with commercial wastewater have become a research hotspot because of their toxicity-causing and hard-to-degrade characteristics.Traditional organic removal technologies include precipitation,adsorption,etc.,while photocatalytic degradation is a new technology that can use photocatalysts to absorb sunlight to degrade pollutants in the environment,possessing characteristics such as low cost,environmental friendly,green and non-toxic,which has attracted wide interest of people.Therefore,it is of great importance to develop efficient photocatalysts.Among many photocatalysts,ferric oxide（Fe₂O₃）,as an n-type semiconductor with high absorption of solar energy and cheap and abundant energy storage,is considered as a very promising photocatalytic material.At present,the methods for preparing Fe₂O₃ have the problems of numerous synthesis steps and harsh reaction conditions,as well as the disadvantages of low photogenerated carrier separation efficiency of the obtained Fe₂O₃ in the photocatalytic process.Therefore,simple and mild preparation methods as well as heterojunction strategies for improving photocatalytic performance are attracting increasing attention.Based on this,the corresponding Fe₂O₃composites were obtained by calcination using iron-based metal organogels（Fe-MOG）and silver-and iron-based bimetallic organogels（Ag/Fe-MOG）synthesized in one step at room temperature as precursors and applied to the degradation of the organic dye rhodamine B（Rh B）in this paper.The specific research content is as follows:1.Fe-MOG-derived Carbon skeleton/Fe₂O₃ nanosheets for photo-Fenton degradation of rhodamine BIn this work,Fe₂O₃ of two morphologies,skeleton/flakes（namely 300-Fe₂O₃ and400-Fe₂O₃）and spheres（namely 500-Fe₂O₃ and 600-Fe₂O₃）were obtained by calcinating sheet-like iron-based metal-organic gel（Fe-MOG）synthesized with Fe³⁺and 1,10-phenanthroline-2,9-dicarboxylic acid（PDA）in one step at room temperature,and were used for photo-Fenton degradation of rhodamine B（Rh B）.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,infrared spectroscopy（FT-IR）and N₂ adsorption-desorption test were used to investigate the morphology and structure of the photocatalyst materials.The existence of oxygen vacancy in 400-Fe₂O₃ was verified by electron spin test（ESR）and X-ray photoelectron spectroscopy（XPS）.The light absorption and band gap（Eg）of derived Fe₂O₃ were obtained by solid diffuse reflection spectroscopy（DRS）.The conduction band（CB）of400-Fe₂O₃ was obtained by Mott-schottky curve test,and the valence band（VB）was obtained by further calculation.The result was in agreement with the XPS test analysis.Transient photocurrent response test and electrochemical impedance map（EIS）were used to characterize its photoelectric properties.Among them,400-Fe₂O₃ exhibited excellent electron transport performance and high photogenerated charge separation efficiency,endowing it with remarkable catalytic activity.In addition,the existence of oxygen vacancy in 400-Fe₂O₃promoted the formation of Fe²⁺,which was the key factor to enhance the photo-Fenton activity.In the presence of H₂O₂,400-Fe₂O₃ photodegraded97.5%of Rh B within 60 min,and its catalytic performance was 2.7 times higher than that of commercial Fe₂O₃.The recycling test showed that 400-Fe₂O₃ possessed good photostability and the Rh B degradation efficiency was still 85.3%after five consecutive recycling experiments.The degradation effect of Rh B in the 400-Fe₂O₃/H₂O₂ system at different p H values was investigated,and 400-Fe₂O₃ was found to show the best catalytic activity under neutral conditions.The mechanism of the photocatalytic reaction was further determined by electron spin resonance tests and active species capture experiments,and the degradation pathway of Rh B molecules was inferred using mass spectrometry detection data.Under visible light irradiation,a part of the photogenic electron（e^?）generated by 400-Fe₂O₃ reacted with O₂to generate superoxide anion radical（·O₂^?）,the other part of e^?reduced Fe³⁺to Fe²⁺in situ.Subsequently,Fe²⁺can catalyze the decomposition of H₂O₂ into hydroxyl radicals（·OH）,and participated in the photodegradation of Rh B together with·O₂^?.The 400-Fe₂O₃/H₂O₂ system also had good photocatalytic effects on other cationic dyes methyl orange（MO）,anionic dyes Congo red（CR）and the antibiotic ciprofloxacin（CIP）.The degradation rate of pollutants could reach more than 80%.2.Ag/Fe-MOG-derived Ag₂O/Fe₂O₃ p-n heterojunction composites for photocatalytic degradation of rhodamine BThe construction of heterojunctions is an effective strategy to improve the photogenerated carrier separation of catalysts.Here,we obtained Fe₂O₃ heterojunction composite oxides with enhanced photocatalytic activity by adjusting the composition as well as the ratio of metal nodes of MOG precursors.A series of novel bimetallic organogels（Ag/Fe-MOG）were synthesized at room temperature using PDA as ligand and Ag⁺and Fe³⁺as metal nodes.Three kinds of Ag₂O/Fe₂O₃-x（x=1,3,5）p-n heterocomplex were obtained by direct calcination using Ag/Fe-MOG as precursors.The morphology and structure of precursor MOG and derived Ag₂O/Fe₂O₃-x photocatalyst materials were analyzed by scanning electron microscopy,X-ray diffraction and Fourier infrared spectroscopy.Taking Ag₂O/Fe₂O₃-3 as an example,the morphology and composition of the derived oxides were analyzed by transmission electron microscopy and X-ray photoelectron spectroscopy.The light absorption and band gap of Fe₂O₃ were obtained by solid diffuse reflection spectroscopy.The photoelectric properties of Fe₂O₃were characterized by transient photocurrent response test and electrochemical impedance spectroscopy.Among them,Ag₂O/Fe₂O₃-3 had good crystallinity,small band gap and high photogenerated carrier separation efficiency.Under visible light irradiation,the photocatalytic degradation rate of Ag₂O/Fe₂O₃-3 was 96.1%within 60 min,which was 3.5 times and 2.8 times of that of Ag₂O and Fe₂O₃ alone.In addition,the effects of pollutant concentration,photocatalyst dosage and p H on the removal of pollutants in the photocatalytic system were discussed.Ag₂O/Fe₂O₃-3 also possessed excellent reusability,with a degradation efficiency of 83.5%for Rh B after four cycles of degradation experiments.Finally,the energy band structure of the semiconductor material was determined by Mott-Schottky test and the mechanism of the photocatalytic reaction was further determined by electron spin resonance test and active species capture experiment.It was shown that the photogenerated holes were transferred from the valence band of Fe₂O₃ to that of Ag₂O in time by the built-in electric field within Ag₂O/Fe₂O₃-3 under the light illumination,which effectively suppressed the complexation of photogenerated carriers,promoted the generation of a large number of active species,and improved the photocatalytic performance of the catalyst.Additionally,Ag₂O/Fe₂O₃-3 photocatalyst also showed good degradation performance in the mixed solution with methylene blue（MB）Congo red（CR）and Rh B,which could make the color of the mixed solution fade from red to colorless.In summary,in this paper,iron-based mono-and bimetallic organogel gel were prepared by a simple one-step precursor synthesis strategy at room temperature,which were calcined to obtain carbon skeleton/Fe₂O₃ and Ag₂O/Fe₂O₃ p-n junction composites,and applied to the photocatalytic degradation of Rh B and other organic dyes to explore the mechanism of photocatalytic degradation,and this study provides a new strategy for the preparation of Fe₂O₃ composites with high photocatalytic activity.