Kinetics of ZIF-8 Thermal Decomposition in Inert, Oxidizing, and Reducing Environments

Abstract

Zeolitic imidazolate frameworks (ZIFs) have been foregrounded as structures with exceptional, intrinsic chemical and thermal stability. However, there has yet to be a systematic study of the isothermal stability of ZIFs, specifically the well-studied ZIF-8. In this work, ZIF-8 isothermal TGA decomposition kinetics were studied in air, argon, H 2 /CO 2 , and nitrogen environments by exposing ZIF-8 to each gas for 20 h at temperatures of 200, 250, and 300 °C, respectively. ZIF-8 crystallinity was preserved under the experimental isothermal conditions at 200 °C in each atmosphere, but crystallinity was increasingly eliminated at higher temperatures. Decomposition kinetics data show that the rate of ZIF-8 carbonization significantly increases at temperatures above 200 °C irrespective of environment. ZIF-8 decomposition in the H 2 /CO 2 reducing mixture exhibits the slowest decomposition kinetics at all temperatures and the greatest morphological change. At 300 °C, oxidative effects enhance ZIF-8 decomposition in air. At lower temperatures the decomposition rate in air behaves more similarly to that of nitrogen and argon. Arrhenius activation energy parameters enable postulation that the temperature dependency of ZIF-8 thermal decomposition after carbonization at 300 °C is more similar upon decomposition in inert and reducing environments as compared to decomposition in oxidizing atmosphere. Four chemical equations inferring the residual carbonized ZIF structure after decomposition at 300 °C were developed based upon EDS quantification and FTIR/azirine formation models. The FTIR/azirine derived model postulates a heterogeneous carbonized ZIF-8 structure containing 2-methylimidazole and azirine rings coordinated to zinc and more precisely agreed with TGA weight decomposition data than the EDS derived model.

Conductivity study of Zeolitic Imidazolate Frameworks, Tetrabutylammonium hydroxide doped with Zeolitic Imidazolate Frameworks, and mixed matrix membranes of Polyetherimide/Tetrabutylammonium hydroxide doped with Zeolitic Imidazolate Frameworks for proton conducting applications

“…In the TGA curve of the Z8T, a plateau appears from 200 °C to 310 °C and then the material exhibits a weight loss of 41.3%, which is related to the ZIF-8 decomposition. This behavior agrees with that previously reported [14]. The TGA curve of Z67T, on the other hand, shows a continued weight loss without a plateau after the removal of guest molecules (See Fig.…”

“…The decomposition temperatures of the ZIFsT structures determined in this work are low compared to those previously reported for ZIFs [14,15], demonstrating that TBAH doping affects the thermal stability of the microporous materials. Table 2 shows the values obtained in nitrogen sorption/desorption study for the series of materials ZIFs and ZMixT.…”

“…2). The characteristic absorption band of the imidazole ring, which appears at 1140 cm −1 , was compared with the absorption band of the methylene group of TBAH, which appears at 2875 cm −1 [14]. It was assumed that there is no decomposition of the 2-methylimidazole ring in the analyzed temperature range, therefore, the 1140 cm −1 band was taken as a reference to calculate the relative concentration of methylene groups upon heat treatment.…”

Zeolitic imidazolate framework-8 was coated with silica and investigated as a flame retardant to improve the flame retardancy and smoke suppression of epoxy resin

“…3,3 0 -Dichloro-4,4 0 -diaminodiphenylmethane (MOCA) was obtained from Guangzhou Fufei Chemical Corporation. Deionized water was produced at our laboratory.…”

“…[3][4][5][6][7][8] Due to the diversity of nanometer ZIF-8 materials, their new functions are being explored. Therefore, the application of ZIF-8 as a ame retardant has also attracted attention.…”