Design, synthesis and applications of core-shell, hollow core, and nanorattle multifunctional nanostructures

With the evolution of nanoscience and nanotechnology, studies have been focused on manipulating nanoparticle properties through the control of their size, composition, and morphology. As nanomaterial research has progressed, the foremost focus has gradually shifted from synthesis, morphology control, and characterization of properties to the investigation of function and the utility of integrating these materials and chemical sciences with the physical, biological, and medical fields, which therefore necessitates the development of novel materials that are capable of performing multiple tasks and functions. The construction of multifunctional nanomaterials that integrate two or more functions into a single geometry has been achieved through the surface-coating technique, which created a new class of substances designated as core-shell nanoparticles. Core-shell materials have growing and expanding applications due to the multifunctionality that is achieved through the formation of multiple shells as well as the manipulation of core/shell materials. Moreover, core removal from core-shell-based structures offers excellent opportunities to construct multifunctional hollow core architectures that possess huge storage capacities, low densities, and tunable optical properties. Furthermore, the fabrication of nanomaterials that have the combined properties of a core-shell structure with that of a hollow one has resulted in the creation of a new and important class of substances, known as the rattle core-shell nanoparticles, or nanorattles. The design strategies of these new multifunctional nanostructures (core-shell, hollow core, and nanorattle) are discussed in the first part of this review. In the second part, different synthesis and fabrication approaches for multifunctional core-shell, hollow core-shell and rattle core-shell architectures are highlighted. Finally, in the last part of the article, the versatile and diverse applications of these nanoarchitectures in catalysis, energy storage, sensing, and biomedicine are presented.

Iron oxide nanoparticles immobilized to mesoporous NH2-SiO2 spheres by sulfonic acid functionalization as highly efficient catalysts

A novel SiO2 nanosphere was synthesized by the post-synthetic grafting of sulfonic acid groups on to anionic-surfactant-templated mesoporous NH2-silica (AMAS). This one-pot post-functionalization strategy allowed more metal ions to be homogeneously anchored into the channel of the meso-SiO2 nanosphere. After hydrothermal and calcination treatment, the in situ growth of α-Fe2O3 on sulfonic acid-functionalized mesoporous NH2-SiO2 (SA-AMAS) exhibited much higher activity in the visible-light assisted Fenton reaction at neutral pH than that for AMAS or meso-SiO2 nanospheres. By analysis, the grafted sulfonic acid group can not only enhance the acid strength of the catalyst, but can also bring more orbital-overlapping between the active sites (Fe(II) and Fe(III)) and the surface peroxide species, to facilitate the decomposition of H2O2 to hydroxyl radical. The present results provide opportunities for developing heterogeneous catalysts with high-performance in the field of green chemistry and environmental remediation.

Silica composite nanoparticles containing fluorescent solid core and mesoporous shell with different thickness as drug carrier

Nonporous silica transitional approach was employed to create core-shell architectural nanocomposites, which performed particularly well in morphology and controllable synthesis. The silica nanocomposites containing fluorescent solid SiO2 core and mesoporous silica shell (F-nSiO2/mSiO2) presented distinct structures of narrow size distribution, stable and shell thickness independent fluorescence, and high specific surface area. Furthermore, the thickness of mesoporous shell could be precisely tailored by the amount of TEOS and solid SiO2 seeds. Drug delivery study of F-nSiO2/mSiO2 with different mesoporous thicknesses were carried out, and Peppas equation was adopted to demonstrate the controlled releasing mechanism of doxorubicin (DOX). The diffusion rate of DOX from F-nSiO2/mSiO2 nanocomposites depended on the thickness of mesoporous shell and electrostatic interaction between drug and silanol group, which facilitated an enhanced drug releasing activity at pH 5.5 than 7.4. What's more, particles loaded DOX showed similar cytotoxicity compared with pure DOX, while no obvious cytotoxicity of carrier was observed in MTT tests for blank particles. These characteristics mentioned above implied that core/shell structured F-nSiO2/mSiO2 had a great potential for controlled drug delivery system.