Synthesis And Photocatalytic Properties Of Multistage Porous ZIF-8 Materials

Zeolite imidazole framework materials（ZIFs）are novel metal organic framework materials（MOFs）with zeolite topologies that combine the advantages of MOFs and zeolite materials with high specific surface area and structural tunability.With high chemical stability and thermal stability,it has become a new type of porous material with great research potential.Among the ZIFs series materials,ZIF-8material is a ZIFs material composed of metal zinc salt and dimethylimidazole.The presence of Zn²⁺makes the material have good photocatalytic degradation ability.At present,ZIF-8 materials have problems in application of macromolecular adsorption and catalysis caused by too small pore size.To overcome such problems and improve the application performance of ZIF-8 materials,this paper uses the template method to use CTAB and P123 respectively.Soft templating agent,mesoporous silica material as a hard templating agent combined with colloidal chemistry to synthesize multi-stage poreZIF-8 material.In this paper,X-ray diffraction（XRD）,N₂ adsorption-desorption experiments,scanning electron microscopy（SEM）and thermogravimetric analysis（TG-DTG）were used to study and analyze the pores of multi-stage pore ZIF-8 materials.The structure,crystal morphology and thermal stability are the best synth-etic methods for the synthesis of multi-stage pore ZIF-8 materials by template method.In the photocatalytic degradation of methylene blue and rhodamine B in multi-stage ZIF-8 materials,the photocatalytic degradation of methylene blue and rhodamine B by multi-stage ZIF-8 materials was discussed by analyzing different reaction conditions and combining photocatalytic kinetics models.Optimal condition.The main research contents are as follows:（1）The ZIF-8 material was synthesized by colloidal chemical synthesis.The experimental results show that the colloidal chemical method is feasible in the synthesis of ZIF-8 material.The total pore volume and mesoporous pore volume of the synthesized ZIF-8 material are 0.42cm³g^-11 and 0.00cm³g^-1.the pore diameter is1.65 nm,indicating that the material is a microporous structural material;the specific surface area is 927 m² g^-1,the crystal morphology is a large crystal structure,and the heat resistance temperature is about 600K.（2）Multistage pore ZIF-8 materials were prepared by using colloidal chemical synthesis method using CTAB and P123 as soft templating agents,respectively.The results show that the multi-stage pore ZIF-8 material synthesized by CTAB and P123as template can maintain the crystal structure of ZIF-8 material itself;the total pore volume of two multi-stage pore ZIF-8 materials(CTAB is 0.51cm³g^-1),P123 is0.62cm³g^-1)and mesoporous pore volume(CTAB is 0.13cm³g^-1,P123 is 0.23cm³g^-1)compared with ZIF-8 material,and the pore diameter is mesoporous（CTAB is2.34nm,P123 was 2.41 nm）.（3）The multi-stage pore ZIF-8 material synthesized by the soft template method is a layered structure formed by agglomeration of small particulate matter.Although CTAB is a templating agent,it can synthesize multi-stage pore ZIF-8 materials to a certain extent,but the specific surface area and heat-resistant temperature are lower,respectively 750m²g^-1and 500K.P123 is a templating agent,and the multi-stage pore ZIF-8 material has smaller particles and a more regular shape.The specific surface area is 1053m²g^-1,and the heat resistance temperature is similar to that of ZIF-8 material,which is 600K,which basically maintains the thermal stability of ZIF-8 material.The combination of（2）shows that in the soft template synthesis of multi-stage pore ZIF-8 material,P123 is more suitable as a template than CTAB.（4）The multi-stage pore ZIF8 material was synthesized by P123,and the optimal conditions for synthesizing the multi-stage pore ZIF-8 material were determined by different reaction conditions.The results show that when the mass ratio of zinc salt to P123 is 1/0.3,the molar ratio of zinc salt to dimethylimidazole is 1/8,the crystal size of the multi-stage pore ZIF-8 material synthesized at 12h is the most uniform.The morphology is the most uniform,and the specific surface area and pore volume are the largest,which are 1053m³g^-11 and 0.62cm³g^-1,respectively.（5）A multi-stage pore ZIF-8 material was prepared by a hard template method using synthetic mesoporous silica as a hard templating agent.The experimental results show that the synthesized multi-stage pore ZIF-8 material can maintain the original structural framework of ZIF-8 material;the total pore volume(0.53cm³g^-1)and mesoporous pore volume(0.18cm³g^-1)are both ZIF-8 The material is improved,and the pore diameter is mesoporous（2.35nm）.In terms of morphology,the multi-stage pore ZIF-8 material synthesized by hard template method is composed of small hexagonal particles with uniform morphology and layered structure..Compared with the soft templating method,the multi-stage pore ZIF-8 material synthesized by the hard template method has the characteristics of smaller crystal particles and more uniform morphology,but the specific surface area can only be kept similar to the ZIF-8 material(903m²g^-1)The total pore volume and mesoporous pore volume are also small compared to the soft template method.（6）After the preparation and characterization experiments of multi-stage pore ZIF-8 materials,the experiments of photocatalytic degradation of methylene blue and rhodamine B simulated wastewater were carried out using multi-stage pore ZIF-8material prepared with P123 as template.The experimental results show that the synthesized multi-stage pore ZIF-8 material shows good performance for the degradation of macromolecular organic dye contaminants methylene blue and rodan B.When the pH is 5 and the dosage is 50 mg,the removal rate of methylene blue by multi-stage pore ZIF-8 material is 98%,and the removal rate of rhodamine B is 99%;the first-order kinetics is related to the 0-order kinetics.The comparison of the coefficients found that the photocatalytic degradation of methylene blue and rhodamine B in the multi-stage pore ZIF-8 material under different reaction conditions accorded with the photocatalytic first-order kinetic model;after the regeneration simulation cycle experiment was carried out 5 times,the synthesized multi-stage pore ZIF The degradation rate of-8 materials for methylene blue and rhodamine B was over 80%,indicating that the materials have good recyclability.Figure 54,table 20,reference 155...