Facile Synthesis of Iron-Based MIL-101 Metal-Organic Framework as a Potential Hydrogen Storage Material

Conventional approaches for metal-organic framework synthesis have shortcomings that may be circumvented through unconventional approaches, which offer fast reactions and scale-up opportunities. This work reports the successful preparation of iron-based MIL-101 utilizing unconventional precursors: iron extracted from acid mine water and terephthalic acid derived from waste polyethylene terephthalate. Three methods were employed including conventional solvothermal, unconventional microwave-assisted and unconventional sonochemical-assisted synthesis and the resulting Fe-MIL-101 was evaluated as an adsorbent for hydrogen. Unconventional synthesis drastically reduced synthesis duration from 20 h (solvothermal) to 4 h (sonochemical-assisted) and 2 h (microwave-assisted). The prepared materials displayed comparable surface areas, with the sample from microwave-assisted synthesis exhibiting a surface area of 512 m² g^{− 1} while that from sonochemical and conventional solvothermal methods exhibited surface areas of 702 and 717 m² g^{− 1}, respectively. Correspondingly, the highest hydrogen uptake (1.03 wt% at 1 bar, 77 K) was attained for the solvothermal Fe-MIL-101. The feasibility of synthesizing Fe-MIL-101 holistically from these specific waste sources using unconventional methods, with an advantage of shortened reaction times, has been proven in this study.