Optimisation of the Flame Spheroidisation Process for the Rapid Manufacture of Fe3O4-Based Porous and Dense Microspheres

The rapid, single-stage, flame-spheroidisation process, as applied to varying Fe3O4:CaCO3 powder combinations, provides for the rapid production of a mixture of dense and porous ferro-magnetic microspheres with homogeneous composition, high levels of interconnected porosity and microsphere size control. This study describes the production of dense (35-80 µm) and highly porous (125-180 µm) Ca2Fe2O5 ferromagnetic microspheres. Correlated backscattered electron imaging and mineral liberation analysis investigations provide insight into the microsphere formation mechanisms, as a function of Fe3O4/porogen mass ratios and gas flow settings. Optimised conditions for the processing of highly homogeneous Ca2Fe2O5 porous and dense microspheres are identified. Induction heating studies of the materials produced delivered a controlled temperature increase to 43.7 °C, indicating that these flame-spheroidised Ca2Fe2O5 ferromagnetic microspheres could be highly promising candidates for magnetic induced hyperthermia and other biomedical applications

Rapid synthesis of magnetic microspheres and the development of new macro–micro hierarchically porous magnetic framework composites †

Magnetic framework composites (MFCs) are a highly interesting group of materials that contain both metal–organic frameworks (MOFs) and magnetic materials. Combining the unique benefits of MOFs (tuneable natures, high surface areas) with the advantages of magnetism (ease of separation and detection, release of guests by induction heating), MFCs have become an attractive area of research with many promising applications. This work describes the rapid, scalable synthesis of highly porous magnetic microspheres via a flame-spheroidisation method, producing spheres with particle and pore diameters of 206 ± 38 μm and 12.4 ± 13.4 μm, respectively, with a very high intraparticle porosity of 95%. The MFCs produced contained three main iron/calcium oxide crystal phases and showed strong magnetisation (Ms: 25 emu g−1) and induction heating capabilities (≈80 °C rise over 30 s at 120 W). The microspheres were subsequently surface functionalised with molecular and polymeric coatings (0.7–1.2 wt% loading) to provide a platform for the growth of MOFs HKUST-1 and SIFSIX-3-Cu (10–11 wt% loading, 36–61 wt% surface coverage), producing macro–micro hierarchically porous MFCs (pores > 1 μm and <10 nm). To the best of our knowledge, these are the first example of MFCs using a single-material porous magnetic scaffold. The adaptability of our synthetic approach to novel MFCs is applicable to a variety of different MOFs, providing a route to a wide range of possible MOF–microsphere combinations with diverse properties and subsequent applications

Evaluating the purification and activation of metal-organic frameworks from a technical and circular economy perspective

Metal-organic frameworks (MOFs) are highly porous materials consisting of metal ions or clusters linked by organic molecules. The high value of MOFs arises from the amount of empty space within their structure (up to 90%) and their tuneable structures and functionalities. To take full advantage of their porosity, MOFs must first be purified and activated whereby pore blocking agents present after synthesis are removed from the pores of the MOF thus exposing their high internal surface areas. Purification and activation can be challenging from both a technical perspective, due to possible framework collapse, and a sustainability perspective, due to high energy and resource demands. The circular economy model aims to eliminate waste and avoid continual use of finite resources whilst balancing considerations of society, the economy, and the environment. Its application to the chemical industry has resulted in the field of sustainable chemistry which focuses on the design, manufacture, and use of efficient and more environmentally benign chemical products and processes. In this contribution we critically evaluate the technical benefits and challenges of current MOF purification and activation methods, including against principles from the circular economy model, focusing on considerations for scalability, waste reduction, material reuse, and energy efficiency. We also discuss how a circular economy approach could inform the design and manufacture of future economically and environmentally sustainable MOF purification and activation processes which are key to realising the immense opportunities offered by these materials

Optimisation of the Flame Spheroidisation Process for the Rapid Manufacture of Fe3O4-Based Porous and Dense Microspheres

The rapid, single-stage, flame-spheroidisation process, as applied to varying Fe3O4:CaCO3 powder combinations, provides for the rapid production of a mixture of dense and porous ferromagnetic microspheres with homogeneous composition, high levels of interconnected porosity and microsphere size control. This study describes the production of dense (35–80 µm) and highly porous (125–180 µm) Ca2Fe2O5 ferromagnetic microspheres. Correlated backscattered electron imaging and mineral liberation analysis investigations provide insight into the microsphere formation mechanisms, as a function of Fe3O4/porogen mass ratios and gas flow settings. Optimised conditions for the processing of highly homogeneous Ca2Fe2O5 porous and dense microspheres are identified. Induction heating studies of the materials produced delivered a controlled temperature increase to 43.7 °C, indicating that these flame-spheroidised Ca2Fe2O5 ferromagnetic microspheres could be highly promising candidates for magnetic induced hyperthermia and other biomedical applications.</jats:p