Preparation And Characterization Of ZIF-67 Membrane Coated On Paper-like Stainless Steel Fibers For Isopropanol Removal

Volatile organic compounds（VOCs）,as major air pollutants,endanger the environment safety and human health.Metal organic framework materials（MOFs）have a unique framework structure,large surface area and good thermal stability,which were increasingly used in gas adsorption and separation,catalytic degradation and other fields.Microfiber composite materials possess developed voidage,which could effectively reduce bed pressure drop and improve contact efficiency when used in fixed bed.In this study,PSSF were used as a support,and a continuous defect-free ZIF-67 membrane was synthesized on the surface of the support by the seed secondary growth method.The adsorption performance of isopropanol over ZIF-67/PSSF composite was studied in a structured fixed bed.A series of Co₃O₄ catalysts supported on PSSF were prepared by MOFs template,impregnation and chemical vapor deposition methods and applied for catalytic combustion of isopropanol.Firstly,ZIF-67/PSSF composite prepared by the seed secondary growth method,and adsorption dynamics of isopropanol in the structured fixed bed based on ZIF-67/PSSF composite was studied.The PSSF support prepared by wet papermaking and sintering process was modified by APTES,then ZIF-67 membrane coated on it by the seed secondary growth method.XRD,SEM,FT-IR,N₂ adsorption and desorption,XPS and other characterization test results shown that continuous dense ZIF-67 membrane uniformly grown on the surface of PSSF,ZIF-67/PSSF composite possessed large specific surface area of 363.8 cm²/g with gradient porous structure and good thermal stability.Comparing with ZSM-5 particles,the adsorption experimental results indicated that the structured fixed bed based on ZIF-67/PSSF composite could enhance mass transfer and improve the adsorption efficiency due to its three-dimensional structure with large specific surface area.The fitting results of Yoon-Nelson and BDST models were in good agreement with the adsorption experimental data.With the flow rate increased from 50 ml/min to 150 ml/min,the rate constant k、of ZIF/PSSF composite increased from0.0563 min^-1 to 0.0641 min^-1.Secondly,the preparation process of Co₃O₄ catalysts supported on PSSF and its application in the catalytic combustion of isopropanol were investigated.The obtained Co₃O₄ catalysts were characteristic by SEM,TEM,XRD,N₂ adsorption-desorption,H₂-TPR,XPS techniques.SEM and TEM results shown that the calcination temperature in the MOFs-template method had a significant effect on micro morphology of Co₃O₄ catalysts.As the calcination temperature raised from 350℃to 450℃,the morphology of precursor ZIF-67 crystallized membrane gradually shrunk to the collapse of the skeleton.The N₂ adsorption and desorption test results shown that the higher calcination temperature,the greater specific surface area loss of the Co₃O₄catalysts compared to the precursor ZIF-67/PSSF composite.The specific surface area of Co₃O₄（M）-350,Co₃O₄（M）-400 and Co₃O₄（M）-450 catalysts were 11.79 m²/g,7.567 m²/g and5.911 m²/g,respectively.Compared with Co₃O₄ catalysts prepared by impregnation and CVD methods,the gradient porous Co₃O₄ catalysts supported on PSSF were prepared by MOFs template method.XPS analysis results shown that the surface Co³⁺/Co²⁺values and chemisorption oxygen content of the Co₃O₄（M）-X catalyst increased firstly and then decreased with the calcination temperature increasing.Among them,Co₃O₄（M）-400 shown the highest values of Co³⁺/Co²⁺（1.25）and O_c/O_c+O_a+O_l（0.63）.The effects of preparation method,catalyst bed height,space velocity and isopropanol inlet concentration on the catalytic activity of Co₃O₄ catalysts supported on PSSF were investigated.The experimental results shown that the catalytic activity of Co₃O₄ catalysts prepared by MOFs template method was higher than those of Co₃O₄（IM）and Co₃O₄（CVD）.Among the as-synthesized catalysts,Co₃O₄（M）-400exhibited the highest activity for the catalytic combustion of isopropanol with the T₅₀ and T₉₀values of 258℃and 281℃,respectively.