Pollutants transformation by metal nanoparticles in confined nanospaces

Large-scale applications of metal nanoparticles (MNPs) in waste treatment and environmental remediation are challenging due to declining activity and stability of nanoparticles that arises from rapid aggregation during synthesis and deactivation under environmental conditions. A potential approach to overcome these problems is to confine the highly reactive MNPs in porous frameworks. In confined nano-architectures, dispersed MNPs are more stable and accessible to pollutants while integration of the support can further improve catalytic degradation of pollutants with high metal utilization. In this perspective, emerging environmental applications of confined-MNP nanocomposites are discussed, focusing on the removal of toxic heavy metals, degradation of organic pollutants and catalytic denitrification. The confinement effects are emphasised, including spatial restriction in material synthesis, enrichment and selective adsorption of reactants, and electronic interactions between metal and support. Understanding the confinement effects to guide the design of confined materials for targeted pollutants, and especially for single-atom catalysts and heteroatom doping, is highlighted.