Engineering of specific composite silica nanoarchitectures with d-transition metal ions, complexes, oxides and sulfides for MRI contrast agents and nanocatalysts

The practical significance of silica nanoparticles (SNPs) loaded with metal ions/complexes and/or metal oxides/sulfides stimulates the search for optimal one-pot synthesis methods that allow controlling both the size, shape, polydispersity of composite nanoparticles and changes occurring with metal compounds during the synthesis. To achieve this goal, it is necessary to understand the fundamental aspects of the synthetic loading of SNPs with metal compounds. These aspects include the influence of coordination and oxidative transformations of metal compounds, as well as their interaction with silica seeds, on the colloidal and functional properties of composite SNPs. The influence of the ligand, metal ion, or synthesis method, with or without surfactants, is considered as a tool for controlling the properties of composite SNPs. A comparative analysis of the use of the Stöber and water-in-oil microemulsion methods for growing SNPs containing iron/copper oxides/sulfides, 3(4)d metal ions, and their complexes as practically significant additives is also presented. Both the influence of accompanying additives and the variation of the time conditions of their stepwise introduction into the synthesis are considered as a powerful tool for controlling practically significant characteristics of the metal compounds included in SNPs, such as their accessibility to water molecules and leachability. Special attention is paid to the importance of the identified trends in the management of functional properties such as catalytic activity or acceleration of magnetic relaxation of protons of water molecules, as a prerequisite for the use of such composite SNPs as nanocatalysts or contrast agents in MRI. The bibliography includes 112 references.