Hyojong Yoo

Nano Metal-Organic Framework-Derived Inorganic Hybrid Nanomaterials: Synthetic Strategies and Applications

Nano- (or micro-scale) metal-organic frameworks (NMOFs), also known as coordination polymer particles (CPPs), have received much attention because of their structural diversities and tunable properties. Besides the direct use, NMOFs can be alternatively used as sacrificial templates/precursors for the preparation of a wide range of hybrid inorganic nanomaterials in straightforward and controllable manners. Distinct advantages of using NMOF templates are correlated to their structural and functional tailorability at molecular levels that is rarely acquired in any other conventional template/precursor. In addition, NMOF-derived inorganic nanomaterials with distinct chemical and physical properties are inferred to dramatically expand the scope of their utilization in many fields. In this review, we aim to provide readers with a comprehensive summary of recent progress in terms of synthetic approaches for the production of diverse inorganic hybrid nanostructures from as-synthesized NMOFs and their promising applications.

Synthesis of highly fluorescent silica nanoparticles in a reverse microemulsion through double-layered doping of organic fluorophores

Water-soluble, highly fluorescent double-layered silica nanoparticles (FL-DLSN) have been successfully synthesized through a reverse (water-in-oil) microemulsion method. The microemulsion was prepared by mixing a surfactant (Brij35), co-surfactant, organic solvent, water, and fluorescein as an organic fluorophore. The sizes of the silica nanoparticles were successfully controlled in the reverse microemulsion using Brij35 by changing the water-to-Brij35 ratio and by adding HCl. Initially, tetraethylorthosilicate was hydrolyzed by adding NH4OH as a catalyst and then polymerized to generate core fluorescent silica nanoparticles with fluorescein. 3-(Aminopropyl)triethoxysilane (APTS) was sequentially added into the reaction mixture, and reacted on the surface of pre-generated core silica nanoparticles to form the second layer in the form of a shell. The second silica layer that was derived from the condensation of APTS effectively protected the fluorescein dye within the silica matrix. This is a novel and simple synthetic approach to generate highly fluorescent, monodispersed silica nanoparticles by doping organic molecules into a silica matrix.Graphical Abstract

Finely tunable fabrication and catalytic activity of gold multipod nanoparticles

Gold multipod nanoparticles (Au Multipod NPs) containing multi-branches with sharp edges and tips were synthesized in high yield through a facile seed-mediated method using cetyltrimethylammonium bromide (CTAB), Brij35, Au seed nanoparticles, Ag(+) ions, ascorbic acid, and sodium salicylate. The branch lengths of Au Multipod NPs were finely controlled by adjusting the molar ratio of mixed surfactants, and in particular by changing the amount of sodium salicylate. A formation mechanism for the star-shaped topologies was proposed and experimentally proved. The catalytic activity of the synthesized Au Multipod NPs was evaluated in ethanol electrooxidation reaction. The dependence of the catalytic performances on the nanostructural morphology was investigated.

Synthesis of cobalt cluster-based supramolecular triple-stranded helicates

A cobalt cluster-based triple-stranded helicate, Co8(PDA)6(PTA)3(DMF)3(H2O)3 () (PDA = 2,6-pyridinedicarboxylate, PTA = benzene-1,3-dicarboxylate, DMF = dimethylformamide) was successfully synthesized and fully characterized. Complex can be used as a supramolecular building block in constructing a higher-order helix-of-helix structure, [Co8(PDA)6(PTA)3(DMF)2(H2O)4-0.51(Co(OHn)2)] (n = 1 or 2) ().

Fabrication of nickel oxide nanostructures with high surface area and application for urease-based biosensor for urea detection

Uniform nanostructured nickel-based coordination polymer particles with multilayered morphologies (mL-NiCPPs) were successfully fabricated through a two-step heating process. To increase the surface area by reducing the size of mL-NiCPPs, pyridine and acetic acid were added as size modulators during the growth process. The resultant coordination polymer nanoparticles were then calcinated at a controlled temperature in order to produce nickel oxide nanostructures (mL-NiOs), which have a regular multilayered morphology and a high degree of crystallinity. Moreover, the mL-NiOs had a relatively high BET specific surface area (112 m2 g−1) and a well-defined pore size (10 nm), hence exhibited significant potential for use in a variety of applications. The synthesized mL-NiOs were successfully deposited onto indium tin oxide (ITO) serving as an efficient matrix for the immobilization of urease (Ur), which was used for urea detection. The prepared bioelectrode (Ur/NiO/ITO/glass) was employed for urea sensing using cyclic voltammetry (CV). The prepared electrodes showed a high sensitivity and a linear dependence of the current on the urea concentration.

A Cobalt Supramolecular Triple-Stranded Helicate-based Discrete Molecular Cage

We report a strategy to achieve a discrete cage molecule featuring a high level of structural hierarchy through a multiple-assembly process. A cobalt (Co) supramolecular triple-stranded helicate (Co-TSH)-based discrete molecular cage (1) is successfully synthesized and fully characterized. The solid-state structure of 1 shows that it is composed of six triple-stranded helicates interconnected by four linking cobalt species. This is an unusual example of a highly symmetric cage architecture resulting from the coordination-driven assembly of metallosupramolecular modules. The molecular cage 1 shows much higher CO2 uptake properties and selectivity compared with the separate supramolecular modules (Co-TSH, complex 2) and other molecular platforms.

High catalytic performance of raspberry-like gold nanoparticles and enhancement of stability by silica coating

Raspberry-like gold nanoparticles (Au RLNPs) synthesized through reduction of HAuCl4 by using Brij35 surfactant and NaOH show high catalytic activity in the reduction of 4-nitrophenol and ethanol electrooxidation. The enhanced catalytic activity of Au RLNPs is mainly due to their high surface roughness. However, Au RLNPs are easily changed to spherical or aggregated nanoparticles by treatment with acids, thiols, and cationic surfactants (e.g., CTAB), making it difficult to sustain the catalytic activity. To improve the stability and applicability in a wide range of environments without degrading the original Au RLNP morphology, silica-coated Au RLNPs (Au RLNP@SiO2 NPs) were successfully synthesized through a sol–gel process using poly(vinylpyrrolidone) (PVP) as a primer. In comparison with Au RLNPs and other Au nanoparticles, Au RLNP@SiO2 NPs are more easily recovered and recycled in repeated catalytic reactions.

Synthesis, structure, and ligand exchange of a copper(II)-based molecular helix with 2,6-pyridinedicarboxylates

An one-dimensional (1-D) metal–organic polymer, [Cu2(PDA)2(DMF)2]n (PDA = 2,6-pyridinedicarboxylate, DMF = dimethylformamide), was synthesized by reaction of copper(II) nitrate hemi(pentahydrate) and 2,6-pyridinedicarboxylic acid in DMF. The complex shows a molecular helix structure consisting of five-coordinate Cu(II) building blocks with distorted square pyramidal geometry. Tridentate chelating PDA, DMF, and an oxygen from the carboxylate of the adjacent Cu(II) building unit are coordinated to the copper(II) center. The weakly coordinated DMF groups in [Cu2(PDA)2(DMF)2]n easily exchange with a pyridine to generate a pyridine-coordinated non-helical 1-D metal–organic polymer with six-coordinate pseudooctahedral Cu(II) units.

Controllable synthesis of multi-layered gold spirangles

Hexagonal multi-layered gold spirangles were successfully synthesized in high yield through a simple process in aqueous solution. Commercially available Brij 700 surfactant was used as the reducing, capping, and shape-directing agent. The growth of single- and multi-layered gold crystals including spirangles was controllably changed through the change of reaction temperature.

Acoustic Anomalies and Fast Relaxation Dynamics of Amorphous Progesterone as Revealed by Brillouin Light Scattering

The amorphous state of pharmaceuticals has attracted much attention due to its high bioavailability and other advantages. The stability of the amorphous state in relation with the local molecular mobility is important from both fundamental and practical points of view. The acoustic properties of amorphous progesterone, one of the representative steroid hormones, were investigated by using a Brillouin inelastic light scattering technique. The Brillouin spectrum of the longitudinal acoustic mode exhibited distinct changes at the glass transition and the cold-crystallization temperatures. The acoustic dispersions of the longitudinal sound velocity and the acoustic absorption coefficient were attributed to the fast and possibly the secondary relaxation processes in the glassy and supercooled liquid states, while the structural relaxation process was considered as the dominant origin for the significant acoustic damping observed even in the liquid phase. The persisting acoustic dispersion in the liquid state was attributed to the single-molecule nature of the progesterone which does not exhibit hydrogen bonds in the condensed states.