Preparation And Application Of H-MoO₃/TiO₂ Nanotube Study On The Mechanism Of Degradation Of MB Under Visible Light

With the rapid development of the dye industry,the number and types of dyes entering the environment are increasing day by day.According to incomplete statistics,national textile enterprises discharge about 3 to 4 million tons of wastewater every day.Dye wastewater has the characteristics of high p H value,deep chroma,and high biochemical oxygen demand.If the wastewater is not treated or does not meet the discharge requirements,it will cause harm to human health and even destroy the ecosystem.As a typical traditional dye,methylene blue（MB）is widely used in production and life and is used in a large amount,so it is urgent to solve its pollution problem.Photocatalytic technology is widely used due to its advantages of high degradation efficiency,wide application range,and no secondary pollution by utilizing solar energy to treat dye wastewater.As the most commonly used photocatalyst,TiO₂has the advantages of low price,stable performance and no toxicity.However,due to its own wide band gap（3.2 e V）,it can only be excited under ultraviolet light,and the holes,Electrons recombine very easily,resulting in very low quantum yields for absorbed light and limited degradation rates under visible light.Doping with semiconductors on the basis of modified TiO₂structure and morphology is a common method to improve the performance of TiO₂.In this study,the structure of nano-TiO₂was modified and composited with h-MoO₃to synthesize h-MoO₃/TiO₂nanotube composite photocatalytic material with high photocatalytic activity,and its degradation performance and degradation mechanism of MB were studied.The main research conclusions are as follows:（1）A composite material loaded with h-MoO₃on TiO₂nanotubes was prepared.In this study,through a two-step hydrothermal method,the structure and morphology of nano-TiO₂particles were first modified to obtain TiO₂nanotubes,and h-MoO₃was prepared by hydrothermal method and then supported on TiO₂nanotubes by calcination method to obtain a composite material.In order to understand the characteristics of h-MoO₃/TiO₂,the materials were characterized as follows:X-ray diffraction（XRD）can be used to know that h-MoO₃/TiO₂nanotube composites are composed of h-MoO₃independent crystals and anatase phase TiO₂;The characterization by Fourier transform infrared spectroscopy（FTIR）proved that h-MoO₃was successfully loaded onto TiO₂nanotubes;X-ray photoelectron spectroscopy（XPS）confirmed that h-MoO₃had been nucleated on the surface of TiO₂nanotubes,while electrons It will migrate from TiO₂to h-MoO₃;the microscopic appearance of the composite material is observed by scanning electron microscope（SEM）calculation,and the results show that h-MoO₃is successfully loaded on TiO₂nanotubes;based on fluorescence spectroscopy（PL）and electrochemical impedance spectroscopy（EIS）proved that the generation of Mo-O-Ti bonds can make the separation and transfer of photogenerated carriers more rapidly.（2）When the doping ratio of h-MoO₃was 5%,h-MoO₃/TiO₂nanotubes exhibited the best MB photocatalytic activity,and the degradation rate was 100%at the end of the 90 min photocatalytic reaction.The photocatalytic degradation of MB by the composite material follows first-order kinetics,and the k value of 5%h-MoO₃/TiO₂nanotubes is the highest of 0.038mg·L^-1·min^-1,which is the highest of unmodified TiO₂(k=0.008 mg·L^-1·min^-1)4.75 times.The photocatalytic activity of 5%h-MoO₃/TiO₂nanotubes on MB is affected by the substrate concentration and catalyst dosage.When the substrate concentration is greater than 10 mg·L^-1and the catalyst dosage is greater than 0.2 mg·L^-1,with the increase of the concentration and the increase of the catalyst dosage,the degradation rate is continuously decreasing;at the same time,the activity increases with the increase of temperature;the activity is the strongest at p H=6.In addition,the composites maintained high stability in 5 degradation cycles,and the MB removal rate reached more than 90%.The experiment selected three typical dyes,Rhodamine B,Reactive Yellow and Congo Red.It was found that the composite materials had good degradation effect on three different dyes.After 120 min of photocatalytic reaction,the degradation rate could reach more than 95%,indicating that the composite material has wide applicability for the degradation of dye wastewater and is an excellent photocatalytic material.（3）The photocatalytic degradation of MB by h-MoO₃/TiO₂nanotube composites was proved.DRS characterization results show that compared with TiO₂,the h-MoO₃/TiO₂nanotube composite has a reduced band gap width and stronger visible light absorption ability.The electron transfer from TiO₂to h-MoO₃occurs in the 5%h-MoO₃/TiO₂nanotube material.This is the reason for the improvement of the photocatalytic ability of the material.According to the analysis of the way of quenching free radicals,it is known that·OH and h⁺are the main active oxides in the process of catalytic degradation of MB by the composite material,and·OH plays the most important role.Electron spin resonance spectroscopy（EPR）analysis showed that the signal intensity of·OH was the strongest,followed by h⁺radicals,and the signal intensity of·O^2-was the weakest,which was consistent with the quenching test results.