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.