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

• Published in: Microporous and mesoporous materials Vol. 316; p. 110957
• Main Authors: Hussain, Mian Zahid, Bahri, Mounib, Heinz, Werner R., Jia, Quanli, Ersen, Ovidiu, Kratky, Tim, Fischer, Roland A., Zhu, Yanqiu, Xia, Yongde
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.03.2021; Elsevier
• Subjects: Carbon; Chemical Sciences; Material chemistry; MOF; MOF derivative; Nanocomposite; Thermal decomposition; TiO2; MOF derivative; Nanocomposite; MOF; Thermal decomposition; Carbon; TiO2
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2021.110957

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 room temperature till 300 °C, between 350 and 550 °C and above ~550 °C respectively. It is found that the framework of NH2-MIL-125(Ti) starts to collapse around 350 °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 °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 °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. [Display omitted] •A number of techniques used in the characterization of the MOF decomposition process.•Some characterization techniques were carried out in situ to study MOF decomposition.•MOF NH2-MIL-125 (Ti) thermally decomposes to composites via 3 well defined stages.•TiO2/C with developed mesopores maintains particle shapes with 35% sizes shrinkage.