Nanostructured materials: Synthetic strategies and their expanding roles in catalysis, drug delivery, and environmental remediation

Nanostructured materials comprising both discrete nano-objects with at least one external dimension below approximately 100 nm and nanostructured bulk or hierarchical materials that are assembled from nanoscale structural units even though the object itself can be macroscopic have grown from laboratory curiosities to becoming a key platform in the development of applications for controlling pollution, precision medicine, and catalysis. Through manipulation of size, shape, composition and surface chemistry, they can be precisely engineered to exhibit desired reactivity, optical properties, transport behaviour, and surface functionality arising from their high surface-to-volume ratio and unique quantum and interfacial effects. This review discusses the critical role of the different synthesis strategies, like top-down physical processes, bottom-up wet-chemical processes, template-directed processes, self-assembly processes, green and biogenic processes, and metal-organic framework (MOF) based processes, on particle size, shape, crystallinity, and surface features. Progress in heterogeneous catalysis and single-atom catalysis is reviewed, considering increased accessibility of the active sites and better selectivity. Applications to nanomedicine and drug delivery are developed, including stimuli responsive and targeted nanocarriers in the form of polymeric, lipidic, magnetic or MOF materials. The review also covers nanomaterial applications for environmental remediation in the field of heavy metal, dye, and emerging contaminant adsorption and sequestration applications. Finally, toxicity, classification of environmental fate, scalability, repeatability, and the impact of nanomanufacturing are examined. The next steps will require a combination of proven synthetic methods and application specific design and sustainable manufacturing strategies.