Application Of Montmorillonite Micro-nano Sheets In Composite Gel And Composite Bi₂O₃ Photocatalytic Material

Montmorillonite is a typical 2:1 layered silicate mineral,because of its special structure,it has been widely used in many aspects.The montmorillonite nanosheets obtained by ultrasonic stripping treatment have a large amount of negative surface charges and abundant functional groups,and are ideal materials for manufacturing inorganic gels.Montmorillonite can also be used as a carrier for semiconductor photocatalytic materials.Bismuth oxide is a semiconductor material with high photocatalytic activity,but in the photocatalytic process of the liquid phase system,its powder is easy to agglomerate,and it is more difficult to separate and recover.In this paper,montmorillonite is used as the raw material.After ultrafine dispersion,the montmorillonite composite gel is prepared by vacuum freeze-drying method,and the Bi₂O₃/MMT composite photocatalytic material is prepared by hydrothermal method.The characteristics and performance were studied.In the preparation of montmorillonite composite gels,montmorillonite nanosheets,chitosan and sodium carboxymethyl cellulose are used as raw materials to prepare binary composite hydrogels and ternary composite hydrogels by self-assembly,And get the xerogel by vacuum freeze-drying method.The effects of raw material mass ratio,montmorillonite slurry concentration,pH adjustment,surfactant and ultrasonic treatment on the composite gel were investigated.The experimental results show that when montmorillonite is subjected to ultrasonic treatment,it is easier to form a gel;when the concentration of montmorillonite is higher,it is easier to form a gel;when the mass ratio of montmorillonite to polymer material is larger,The easier it is to form a gel;adjusting the pH of the polymer solution to weakly alkaline is also beneficial to the formation of the gel;adding surfactants is not conducive to the formation of the gel;compared to the ternary composite gel,the binary gel is more Difficult to form.For the prepared ternary system MMT/CS/CMC composite gel,the preferred process is to adjust the pH value of chitosan to weakly alkaline,using nano-concentration of1%concentration Under the condition that the mass ratio of MMT/CS/CMC is 10:1:1,the prepared CS-CMC-19 sample has the best adsorption effect for methylene blue.The adsorption capacity is 268mg/g,the thermal conductivity is 0.039W/m·K,and the thermal insulation effect is excellent.In the preparation of photocatalysts,pure phase bismuth oxide was synthesized by hydrothermal method,and the Bi2O3/MMT composite photocatalyst was prepared under the optimal hydrothermal pH conditions,and the hydrothermal pH value and loading were investigated respectively Effect on the structure and catalytic performance of composite samples.The experimental results show that the presence of montmorillonite can hinder the change of the crystal structure of bismuth oxide,and also increase the pH range of the synthesis of highly active bismuth oxide.The optimal synthesis process is determined as follows:the loading mass ratio of Bi₂O₃/MMT is 4:1,the system pH value is 7.5⁸.5,and the hydrothermal reaction is carried out at a hydrothermal temperature of 180℃ for 10 hours.Under this optimal process,the degradation rate of methyl orange can be as high as 90%or more when the composite photocatalyst is irradiated by visible light for 8 hours;100%degradation of methyl orange can be achieved by ultraviolet light irradiation for 2hours.The results of photoelectrochemical testing and photocatalytic reaction active species capture experiments show that the excellent photocatalytic activity of the composite photocatalyst is mainly due to the recombination of montmorillonite,so that the structure of the composite photocatalytic material can more effectively separate electron holes and reduce The width of the forbidden band of bismuth oxide is reduced,and the response to visible light is enhanced,and the oxidation of photogenerated holes is the key to promoting the entire photocatalytic degradation process.