The synthesis of iron(III) terephthalate metal–organic frameworks MOF-235(Fe) and MIL-101(Fe) has long been plagued by inconsistencies in reported surface areas and phase purity. Despite the use of a standard solvothermal protocol involving a 3:5 molar ratio of Fe(III) to terephthalic acid (TPA), heating in a 1:1 DMF:ethanol mixture at 80 °C for 24 hours, many studies report widely varying BET surface areas ranging from as low as 9.6 to over 540 m² g⁻¹. This variability suggests that the products are often not pure phases but mixtures of both MOF-235 and MIL-101, which have fundamentally different structures and porosities. To address this issue, we systematically investigated the influence of key synthesis parameters—Fe(III):TPA ratio, DMF:ethanol solvent ratio, equilibration time (teq), and reaction temperature—on phase formation and surface area.
Our findings reveal that the DMF:ethanol ratio is the most critical factor determining the final product. A higher DMF content favors the formation of MOF-235, while a lower DMF fraction promotes MIL-101.GPER1 Antibody Technical Information Using a stoichiometric 4:3 Fe(III):TPA ratio combined with a 3:1 DMF:ethanol ratio resulted in a nearly pure MOF-235 product with a BET surface area of 295 m² g⁻¹ and a yield of 67%. Conversely, maintaining a 1:1 DMF:ethanol ratio under the same reagent ratio produced high-surface-area MIL-101(Fe) with SABET exceeding 2400 m² g⁻¹ and a yield of up to 95%, achieved at a previously unreported low temperature of 80 °C—significantly below the typical 110–150 °C required in literature protocols. This represents a major advancement in sustainability, reducing energy consumption and minimizing solvent decomposition.
In situ medium-angle X-ray scattering (MAXS) confirmed that no transformation occurs between MOF-235 and MIL-101 during synthesis. At 80 °C, only MOF-235 crystallizes; at 85 °C and 90 °C, only MIL-101 forms.PRKRA Antibody Data Sheet This indicates independent nucleation pathways rather than phase conversion. The presence of ethanol appears essential for stabilizing the initial MOF-235 structure, as no solid product formed in pure DMF at 80 °C. Additionally, equilibration time plays a non-linear role: longer teq does not uniformly improve crystallinity or surface area, suggesting post-synthesis structural rearrangement or degradation may occur at room temperature.PMID:34978373
XPS analysis confirmed the presence of Fe³⁺ in both frameworks, with minimal differences in elemental composition between samples. However, MIL-101 showed lower nitrogen and chlorine content, likely due to reduced solvent incorporation. Methylene blue adsorption tests demonstrated superior performance for MIL-101(Fe) (425 mg g⁻¹) compared to MOF-235(Fe) (276 mg g⁻¹), despite electrostatic repulsion between the positively charged dye and the slightly positive zeta potential of both materials (~+20 mV). This highlights the importance of pore size and accessibility over surface charge in adsorption capacity.
In conclusion, precise control of solvent composition and reagent stoichiometry enables the selective synthesis of either high-surface-area MIL-101(Fe) or phase-pure MOF-235(Fe). Our optimized protocol reduces environmental impact by lowering temperature and solvent usage while achieving reproducible, high-quality materials suitable for applications in catalysis, gas storage, and water purification.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com