Crystallization Behavior of 2,4,6-Trinitrotoluene Confined in Hierarchical Macro-Microporous ZIF-8 Frameworks and Its Impact on Thermal Decomposition

The crystallization behavior of 2,4,6-trinitrotoluene (TNT) confined within a hierarchical macro-microporous ZIF-8 (SOM-ZIF-8) framework and its impact on thermal decomposition are systematically investigated. TNT is incorporated into the porous host via evaporative crystallization, resulting in composites with varying TNT loadings. The well-defined macropores serve as templates for the confined growth of TNT nanospheres, while the intrinsic micropores are expected to facilitate the adsorption of key decomposition intermediates, potentially promoting autocatalytic decomposition pathways. XPS analysis reveals a negative shift of Zn 2p peaks and a positive shift of the –NO 2 N 1s peak, indicating electron transfer from the nitro groups to the Zn 2+ centers─an interfacial interaction further supported by the blue shift of –NO 2 vibrations in FTIR. This confined crystallization dramatically alters the thermal decomposition behavior: the peak decomposition temperature decreases from 320 °C for pristine TNT to as low as 180 °C for the composite, and the apparent activation energy is reduced from 131.6 kJ·mol –1 to 75.1 kJ·mol –1 . Combustion tests reveal significantly enhanced flame intensity and a maximum temperature increase from 889.5 to 1216.0 °C. The optimal loading (TNT: SOM-ZIF-8 = 5:1 by mass) achieves a balance between microporous catalysis and macroporous nanoconfinement, leading to the most efficient energy release. This work demonstrates that confined crystallization within hierarchically porous MOFs is an effective crystal-engineering strategy to tailor the thermal decomposition kinetics of conventional explosives, offering new insights into structure–property relationships in energetic materials.