Study On The Pyrolysis And Carbonization Mechanism Of Typical Metal-organic Frameworks Based On TG-MS

MOFs-derived carbon-based materials have a wide range of applications in the fields of gas phase adsorption,electrochemistry,and environmental catalysis due to its excellent conductivity,porosity and good stability.However,directly carbonization of MOFs in high temperature may destroy the topological structure,cause the skeleton to collapse,decrease the specific surface area,and reduce the active sites,which will adversely affect its performance.Therefore,it has great guiding significance for more reasonable design and preparation of MOFs derived carbon-based materials with good performance and structure by studying the pyrolysis and carbonization process of MOFs.In this paper,three typical MOFs(HKUST-1,MIL-101(Cr)and ZIF-67)were concerned,and the pyrolysis mechanism and path were studied studied through TG-MS combined technology in an inert atmosphere(He).The research results are as follows:(1)The pyrolysis and carbonization process of the three MOFs can be roughly divided into three stages,which were called the pre-pyrolysis stage,pyrolysis carbonization stage and deep carbonization stage,respectively.Among them,the loss of surface adsorption water or crystal water caused weight loss in the pre-pyrolysis stage,and the weight loss rate was less than 3%;In the pyrolysis carbonization stage,the organic ligands were cracked by high temperature with the weight loss rate of more than 30%,and the carbon-based materials were generated here;In the deep carbonization stage,the residual organic matter inside the carbon-based material was further carbonized due to high temperature,and the weight loss rate was about 10%;(2)The E values of HKUST-1 and MIL-101(Cr)in the pre-pyrolysis stage were both less than 100 k J·mol^-1,and both followed the chemical reaction mechanism;(3)There were slightly different of the reaction order of the most probable mechanism among the three MOFs in the pyrolysis carbonization stage,and they all followed the random nucleation and subsequent growth mechanism with the E value between 180?235k J·mol^-1;(4)In the deep carbonization stage,HKUST-1 followed the chemical reaction mechanism with the E value of 564.36 k J·mol^-1,while MIL-101(Cr)followed the three-dimensional diffusion mechanism with the E value of 387.60 k J·mol^-1,which was caused because of the differences in the properties of the two carboxylic acid MOFs.