Study On The Structure And Size Control Of TiO₂ Microspheres And Their Photocatalytic Coupling With Flat Microfiltration Membrane Separation Proces

The coupling technology of suspended photocatalysis membrane separation combines the efficient interception and phase change free separation characteristics of membrane separation technology with suspended photocatalysis technology,which can achieve the separation,recovery,and reuse of photocatalysts.This technology can not only have the high specific surface area and high reaction efficiency of suspended TiO₂ photocatalysts,but also improve the hydraulic retention time（HRT）of photocatalysts,while achieving the goal of separating photocatalysts from the reaction environment and effectively removing pollutants from the aqueous medium.Therefore,suspended photocatalysis membrane separation coupling technology is one of the effective ways for photocatalysis technology to move towards application.In the research of suspended photocatalysis pressure driven membrane separation technology,the biggest problem of the coupling process between photocatalysis technology and pressure driven membrane separation is the deposition of nano photocatalysts suspended in the reaction medium on the membrane surface and even blockage of pores,resulting in a decrease in membrane permeability and further membrane pollution.In order to overcome membrane fouling caused by nano photocatalysts,domestic and foreign scholars and technicians have attempted to solve this problem by using methods such as cross flow filtration,aeration,stirring,intermittent operation,and p H regulation.However,facing the requirements of practical applications,they have not achieved the desired results.At the same time,the micrometer level TiO₂ spherical hierarchical structure not only has unique advantages in preventing the aggregation,structural and morphological stability,improving the specific surface area and light capture performance of low-dimensional nanostructures,but also finds that the micrometer level TiO₂ spherical structure can prevent its deposition and formation of filter cake layers on the surface,causing pressure driven membrane pollution,Thus improving the comprehensive performance of suspended photocatalysis membrane separation coupling technology.Based on this judgment,the following research content has been completed in this paper.In this paper,the solid,hollow and flower shaped TiO₂ microspheres photocatalyst materials with an average diameter of 341 nm～5430 nm and good uniformity were prepared by Sol gel method,solvothermal method and alkaline solvothermal method,respectively.The structure activity relationship of the TiO₂ microspheres was determined through structural characterization and experimental testing.On this basis,a TiO₂ microsphere photocatalytic flat microfiltration membrane separation integrated reactor was designed.Three types of flat microfiltration membranes（PVDF-1,PET-2,and PET-3,）were used for membrane separation experiments to study the effects of process parameters such as TiO₂ microsphere diameter,TiO₂microsphere aggregation state,and membrane pore size on membrane flux decay rate.The stability of suspended TiO₂ photocatalytic flat microfiltration membrane integration was investigated through continuous operation experiments.The research results show that the Si O₂-TiO₂ solid microspheres with different Si O₂contents with an average diameter of 236 nm have achieved uniform distribution of Ti,O and Si elements,and have good monodispersity and structural stability.The doping of Si O₂ leads to a decrease in the Zeta potential and isoelectric point on the surface of Si O₂-TiO₂microspheres,which enhances the adsorption of positively charged pollutants such as MB on the surface,while also improving their dispersibility and preventing aggregation.However,due to the critical diameter corresponding to zero net force on the surface of the microfiltration membrane,good dispersion actually intensifies the deposition of Si O₂-TiO₂ microspheres on the surface of the microfiltration membrane,resulting in higher flux attenuation rates for flat microfiltration membranes with different pore sizes than solid TiO₂ microspheres of the same size.In order to solve the problem of flat microfiltration membrane fouling caused by TiO₂photocatalytic materials,an innovative Sol gel method and self template solvothermal method were proposed.By adjusting the H₂O/TBOT molar ratio in the range of 0.75 to 3.75,TiO₂microspheres with flower like,hollow,and solid structures were synthesized,achieving the regulation of TiO₂ hollow sphere diameter in the range of 1 to 1820 nm.During the solvothermal process,the crystallization process of amorphous TiO₂ on the surface of the microspheres into TiO₂-B and the Ostwald aging process occur on the surface and inside of the microspheres,respectively.During the calcination process,the high-strength TiO₂-B dense layer not only ensures that the structure of the microspheres will not fracture,but also suppresses the crystal growth process,leading to an increase in crystal phase transition temperature and macroscopic stress between the lattice,while also resulting in a relatively low specific surface area of the material.The experiment of photocatalytic mineralization of 20mg·L^-1 phenol solution showed that after 24 hours of solvent thermal reaction at R_w=1.5,the prepared TiO₂ microspheres had the best photocatalytic activity and were superior to commercially available P25 photocatalysts.Through membrane separation experiments,it was found that as the diameter of TiO₂ microspheres with the above structure increased,the membrane flux decay rate significantly decreased.When the diameter is≥1820 nm,the membrane flux decay rate is less than 5%,which not only achieves good photocatalytic activity but also achieves good separation performance of the flat microfiltration membrane.This paper continues to expand the research on the structure and size of TiO₂ microspheres.TiO₂ solid microspheres prepared by gel gel method are used as precursors,H₂O₂ is used as structure controller,and different micron TiO₂ flower shaped microspheres are prepared by alkaline hydrothermal method.With the increase of hydrothermal time within the range of 4 to24 hours,and through calcination and crystallization,the diameter of TiO₂ flower shaped microspheres was regulated within the range of 2200 to 5430 nm.TiO₂ flower shaped microspheres not only exhibit good photocatalytic activity for the degradation of 20mg·L-1phenol solution,but also ensure a low membrane decay rate（≤1%）in the separation experiment of flat microfiltration membrane.On this basis,this paper comprehensively compares the membrane separation performance of TiO₂ microsphere photocatalytic materials with different structures and sizes prepared,and experimentally determines the optimal process conditions:when TMP=0.05Mpa,aeration rate is 0.5 L·min^-1,and TiO₂ dosage is 0.5 g·L^-1,when the diameter of TiO₂ microsphere is≥1820 nm,its value has exceeded the critical diameter dc reported in the literature,and the membrane flux attenuation rate is≤1%.Under the above optimal conditions,the stability experiment of suspended TiO₂ photocatalysis flat microfiltration membrane integration was conducted.Through 5 cycles of suspended TiO₂ photocatalysis flat microfiltration membrane separation alternating operation experiments,the TiO₂ hollow sphere photocatalyst with an average diameter of 1820 nm and a dosage of 0.5 g·L^-1 showed good photocatalytic activity,And the use of PVDF-1 flat microfiltration membrane can achieve stable and efficient membrane separation of TiO₂ hollow sphere photocatalysts under the optimal membrane separation process parameters.