Study On The Construction Of Hierarchical Micro-nano Materials In Ethanol/water System And Their Degradation Of Organics

The global industrialization has caused the increasingly serious problem of water pollution.Many water treatment technologies have been developed to deal with the harmful organic pollutants in water.However,severe energy crisis and strict environmental protection policy put forward increasingly high requirements for water treatment technology.In recent years,the emergence of nanotechnology and micro-nano materials has made it possible to efficiently treat pollutants.The excellent physical and chemical properties and the low secondary pollution of 3D hierarchical micro-nano materials have attracted much attention.However,the hierarchical micro-ano materials are always faced with many problems such as complex preparation process,environmental pollution and unsatisfactory performance.In order to solve these problems,we developed a low-carbon,environmentally friendly,simple process method,and successfully synthesized a variety of 3D hierarchical micro-nano materials with high efficiency of degradation of organic pollutants such as Congo red and phenol in water.Using ethanol and water solvent system,we successfully developed a Fe₃O₄-assisted low-temperature?72 oC?hydrothermal method to synthesize 3D F-ZnO hierarchical structure.The morphology,crystal structure and visible light response capability of 3D F-ZnO were studied by SEM,XRD and DRS.3D F-ZnO with the diameter of ? 4.5 ?m was composed of a large number of asymmetric conical zinc oxide nanorods growing around the center of Fe₃O₄ nanosphere.According to the experimental results,the formation mechanism of 3D F-ZnO was proposed.The enhanced visible light degradation performance of 3D F-ZnO toward Congo red was studied,and the adaptability of catalyst in real environment was further studied.The influence of external factors such as heavy metal ions,acid ions and water sources on the photodegradation efficiency of Congo red was studied.According to the results of material photoelectric performance and trapping activity experiment,the reason of enhanced visible light catalytic performance was proposed.In order to further reduce energy consumption and pollution in the process of preparing 3D hierarchical micro-nano materials,a green one-step injection method at room temperature?? 25 oC?with simple preparation process was developed based on ethanol and water solvent system.After 1.35 M Na₂CO₃ solution was rapidly injected into the Ag NO3 anhydrous ethanol solution at room temperature,the Ag₂O/Ag₂CO₃ nanoparticles of ? 30 nm were successfully assembled into 3D hierarchical micro-nano structures.It was found that the reaction temperature could change the morphology of the products.The effect of calcining temperature on the morphology of the samples was also studied.Through the study of the formation process of Ag₂O/Ag₂CO₃ 3D hierarchical structure,it is found that sodium carbonate has the specific function of forming hollow 3D crystal with a trumpet flower-like structure on the surface,which plays the role of template in the formation of Ag₂O/Ag₂CO₃ 3D hierarchical materials.The preparation mechanism of one-step injection method was deduced and analyzed.It was the Langmuir isothermal adsorption process for the adsorption of Congo red to the hierarchical materials.The photodegradation rate of Ag₂O/Ag₂CO₃ on Congo red reached 87.5% in 25 min under visible light.·OH,h+ and ·O2– active substances were produced in the degradation process.The photodegradation mechanism was analyzed through mott-schottky theory and energy band theory.Because one-step injection has obvious eco-friendly and cost advantages over low-temperature hydrothermal method,it is more important to further study one-step injection method,a BiOI/Bi₂O₂CO₃ 3D hierarchical structure assembled with ultra-thin two-dimensional nanosheet was prepared by one-step injection based on the ethanol/water system and slow etching by Na₂CO₃ aqueous solution at room temperature.The characteristics of heterojunction,defects and lattice distortion were observed in the BiOI/Bi₂O₂CO₃ crystal.The changes of thickness and internal crystal structure of the original BiOI/Bi₂O₂CO₃ nanosheet during Na₂CO₃ etching were determined.These changes can significantly affect the photoelectronic properties of the BiOI/Bi₂O₂CO₃ complex.The etch of Na₂CO₃ can also change the specific surface area and pore size distribution of the materials.It was also found that CO₃^2– can replace I– of [Bi₂O₂]²⁺ interlayer in the etching process.Accrording to these results,the template-induced assembly mechanism with Na₂CO₃ and the ion substitution mechanism in the [Bi₂O₂]²⁺ interlayer were proposed.The visible degradation performance of different BiOI/Bi₂O₂CO₃ samples toward phenol were carried out,among which BiOI/Bi₂O₂CO₃-15 min had the best visible degradation effect on phenol with the degradation efficiency up to 99%.In the photodegradation process,the active substances of ·OH,h+ and ·O₂^– were generated to degrade phenol at the surface.The enhanced photocatalytic ability was closely related to the synergistic changes of internal crystal structure and ultrathin properties.In order to verify the universality of one-step injection method,the 3D hierarchical structure of flower-like Fe?OH?₃ was synthesized by rapid injection of Na₂CO₃ solution into FeCl₃ anhydrous ethanol.The results showed that the pore structure was evenly distributed on the surface of the materials.Although the sample morphology was influenced by the reactant concentration and reaction temperature,the high-temperature calcination can't change the morphology of Fe?OH?₃.The composition of the sample was determined by various techniques.It was found that the flower like Fe?OH?₃ had good adsorption and Fenton-like degradation ability toward Congo red.The adsorption and degradation of Fe?OH?₃ toward Congo red obeyed pseudo-second-order kinetics and second-order reaction kinetics,respectively.The results of isothermal adsorption experiments showed that the maximum adsorption capacity of Fe?OH?₃ for Congo red was 308 mg/g.