Effects of apparent activation energy in pyrolytic carbonization on the synthesis of MOFs-carbon involving thermal analysis kinetics and decomposition mechanism

Abstract

Pyrolysis process of metal-organic frameworks (MOFs) was analyzed by thermal analysis kinetics for the study of the synthesis of MOFs-based carbon materials with high adsorption performance. The process was studied based on the thermogravimetric mass spectrometry (TG-MS), through which the gas products of the pyrolysis process were detected. The HKUST-1 and MIL-101 were prepared by solvothermal method and characterized by XRD, BET, SEM and TEM. The characterization results showed that HKUST-1 and MIL-101 have been successfully prepared with cubic octahedral morphology and specific surface areas up to 1477.50 m2/g and 2239.88 m2/g, respectively. The data of TG-DTG showed that the pyrolysis of HKUST-1 and MIL-101 could be divided into three stages and seven stages, respectively. The kinetic triplets of different pyrolysis stages were calculated by iso-conversional methods, and the gas products decomposed were analyzed, through which the pyrolysis mechanism of MOFs was inferred. The first pyrolysis stages of HKUST-1 and MIL-101 were both dehydration stages, the E values of both were less than 100 kJ/mol, and the pyrolysis mechanism of both two materials at this stage were the chemical reaction mechanism. The average apparent activation energy of the main pyrolysis carbonization stages of both was about 180 kJ/mol, and both followed the random nucleation and subsequent growth mechanism, indicating that there were some uniformities between the two materials in the main pyrolysis stage. The main gas products in this stage were CO, CO2 and benzene. The apparent activation energy of the final deep carbonization stage were 564.36 and 387.60 kJ/mol, respectively, and mechanisms followed were chemical reactions and three-dimensional diffusion mechanisms, meaning that there were some differences between the two materials in the deepening stage.