Synthesis, Characterization, and Ammonia Adsorption Properties of Mesoporous Metal–Organic Framework (MIL(Fe))–Graphite Oxide Composites: Exploring the Limits of Materials Fabrication

Abstract

Composites of MIL‐100(Fe) and graphite oxide (GO) were prepared with various ratios of the two components and tested for ammonia removal in dynamic conditions. The initial and exhausted samples were characterized by X‐ray diffraction, nitrogen adsorption, thermal analysis, Fourier Transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy. The results indicate that the formation of well‐defined MIL‐100(Fe)/GO composites is not favored. This is linked to the specific geometry of MIL‐100(Fe). The attachment of the GO carbon layers to the spherical cages of MIL‐100(Fe) (via coordination between the oxygen groups of GO and the metallic sites of the metal–organic framework) prevents the proper formation of the MIL‐100(Fe) structure. Therefore, the composite with the highest GO content has a lower porosity and smaller ammonia adsorption capacity than those calculated for the physical mixture of MIL‐100(Fe) and GO. The main mechanism of ammonia retention is via Brönsted interactions between ammonia and the water molecules present in MIL‐100(Fe). Nevertheless, the presence of excess water in the system lowers the acidity of the MIL material, and consequently causes a decrease in the ammonia adsorption. The Lewis interactions between ammonia and the metal centers in MIL also take place during the adsorption process.