Interaction of ferric ions with europium metal organic framework and application to mineral processing sensing

Metal organic frameworks (MOFs) have numerous practical applications including hydrogen storage, drug delivery, separation processes and sensing. Sensing is particularly important in the mineral processing sector, where the success of mineral leaching processes depends upon the development of reliable and efficient methods for the detection of ferric ions (Fe3+). Here, we examine the atomic interactions between a hydrated ferric ion and an europium-based MOF with a view to the development of a sensing device capable of determining the ferric ion concentration in an analyte solution. Using a continuum approach together with the Lennard-Jones potential, we determine the Lennard-Jones (van der Waals) interaction energy and force between a hydrated ferric ion and a MOF pore. The hydrated ferric ion is modelled as a point at the centre of two concentric spheres, while the MOF pore is modelled by a semi-infinite cylinder. The model predicts that it is energetically more favourable for the hydrated ferric ion to reside inside the MOF pore and that the greatest attractive force is experienced at the entrance of the MOF pore. However, the hydrated ferric ion is unlikely to enter the MOF pore because it is geometrically larger than the free space inside. This means that in practice the hydrated ferric ion will remain on the surface of the MOF crystal, considerably simplifying ion removal. This property will be useful for washing and reusing the sensor.