Biological and environmental degradation of metal-organic frameworks and related mechanisms

Metal-organic frameworks (MOFs) are composed by metal ions (or metal clusters) and bridging organic ligands, which have shown great application potential in biomedicine and environment fields. However, MOFs would inevitably be transformed or degraded in the environment and/or organisms during applications, which could change their structures and limit the applications. At the same time, MOFs could bring potential risks to human and environmental health. Therefore, the effects of simulated biological physiological conditions (such as pH, ions, protein/enzyme, microorganism) and environmental conditions (such as moisture, redox substances, light, temperature) on the degradation of MOFs are systematically summarized in this review, and the related degradation mechanisms are discussed. In the human digestive system and blood, pH and PO43− are the main factors that affect the degradation of MOFs, respectively, which could lead to the degradation of MOFs by directly destroying coordination bonds in MOFs and acting on metal centers in MOFs. While in the environment, water molecules are the key factors that affect the stability of MOFs, which could replace the organic ligands in MOFs through substitution reaction or destroy the coordination bonds in MOFs through hydrolysis, resulting in the degradation of MOFs. This review provides support for clarifying the degradation behaviors of MOFs and the impact of degradation products on human health and environmental fate. Finally, combining with existing issues, this article highlights the prospects and suggestions for future research perspectives of MOFs degradation, providing a theoretical basis for the green and sustainable application of MOFs.