Improved mechanochemical synthesis of MIL-100(Fe) and MIL-100(Fe)@Carbon Metal-Organic Framework composite for PFAS polluted waters remediation

MOFs are a class of crystalline solids with permanent porosity. They are coordination polymers made up of metal ions or metal clusters linked together by organic ligands. MOFs are promising materials for application in the chemical industry of the future due to their outstanding properties. Their porosity and the high tunability of internal surface open many possibilities for their use in different fields such as catalysis, gas storage and separation4. However, their application is often hindered by the cost of the precursor and by the demanding synthetic conditions. Moreover, the manufacturing of MOFs containing materials is still in early development. One of the most promising MOF is MIL-100 (Fe): it was firstly synthetized by Férey et al. and possesses large cages with diameters of about 25 and 29 Å1 with reported Langmuir surface area up to 2800 m2/g. One big advantage of this MOF is that is built by inexpensive and non-toxic constituent such as Iron and trimesic acid. However, its synthetic procedure requires toxic organic solvents, such as DMF and hazardous synthetic additives (i.e. hydrofluoric acid or nitric acid), and high temperature and pressure1. Recently there were some attempts to prepare this material in a greener way and a water-based synthesis for MIL-100 (Fe) was developed2. However, the use of water as solvent is still problematic since it consumes an important resource and produces a lot of wastewaters rich in inorganic salts and acids. As a result, solvent free synthesis seems to offer an ideal mean to obtain this material. It was recently reported that hand grinding of the precursor powders and subsequent annealing of the mixed powder at high temperature followed by immersion in water can produce MIL-100 (Fe)3. Here we propose a new synthetic method which replaces hand grinding with the use of a ball miller to improve reproducibility and scalability of the production of MIL-100 (Fe). This process offers advantages over the previous methods since it is more rapid, preventing waste of time, and it uses lower temperature and less water, thus improving energy efficiency and reducing waste and resource consumption. Moreover, we could extent this procedure to a new method for the creation of a new composite material made of intimately bonded MIL-100 (Fe) on carbon particles. This material opens the possibility of improved manufacturing of MOFs since this powder can be formed in a pellet that better fit existing technology for adsorption of gases or molecules from liquid phase. We assessed the crystallinity of the materials using X-ray powder diffraction and their gas adsorption properties through N2 adsorption isotherms. We also tested these materials for the removal of perfluoroalkyl substances, PFASs, from water, with promising results.