An in situ investigation of the thermal decomposition of metal-organic framework NH2-MIL-125 (Ti)

Mian Zahid Hussain , Mounib Bahri (1, 2) , Werner R. Heinz , Quanli Jia , Ovidiu Ersen (1, 2) , Tim Kratky , Roland A. Fischer , Yanqiu Zhu , Yongde Xia

1 IPCMS - Institut de Physique et Chimie des Matériaux de Strasbourg
2 IPCMS - Institut de Physique et Chimie des Matériaux de Strasbourg

Titanium based metal-organic frameworks (MOFs) are interesting self-sacrificial precursors to derive semiconducting porous nanocomposites for highly efficient heterogeneous catalysis. However, there is a lack of systematic and in-depth mechanistic understanding of the pyrolytic conversion of MOF precursors into the desired functional composite materials. In this work, TGA-MS and in situ STEM/EDX combined with other characterization techniques were employed to investigate the evolution of the structural, physicochemical, textural and morphological properties of NH2-MIL-125(Ti) pyrolysis at different temperatures in an inert gaseous atmosphere. In situ thermal analysis of NH2-MIL-125(Ti) reveals the presence of 3 rather defined stages of thermal transformation in the following order: phase-pure, highly porous and crystalline MOF -> intermediate amorphous phase without accessible porosity -> recrystallized porous phase. The three stages occur from mom temperature till 300 degrees C, between 350 and 550 degrees C and above similar to 550 degrees C respectively. It is found that the framework of NH2-MIL-125(Ti) starts to collapse around 350 degrees C, accompanied with the cleavage of coordination and covalent bonds between organic linkers [O2C-C6H3(NH2)-CO2](6) and the Ti oxo-cluster Ti8O8(OH)(4). The organic linker continues fragmentation at 450 degrees C causing the shrinkage of particle sizes. The dominant pore size of 0.7 nm for NH2-MIL-125(Ti) gradually expands to 1.4 nm at 800 degrees C along with the formation of mesopores. The derived disc-like particles exhibit an approximately 35% volume shrinkage compared to the pristine MOF precursor. Highly crystalline N and/or C self-doped TiO2 nanoparticles are homogeneously distributed in the porous carbon matrix. The original 3D tetragonal disc-like morphology of the NH2-MIL-125(Ti) remains preserved in derived N and/or C doped TiO2/C composites. This study will provide an in-depth understanding of the thermal conversion behavior of MOFs to rationally select and design the derived composites for the relevant applications.

Domaines: Matériaux

Mian Zahid Hussain, Mounib Bahri, Werner R. Heinz, Quanli Jia, Ovidiu Ersen, et al.. An in situ investigation of the thermal decomposition of metal-organic framework NH2-MIL-125 (Ti). Microporous and Mesoporous Materials, 2021, 316, ⟨10.1016/j.micromeso.2021.110957⟩. ⟨hal-03450335⟩