Systematic utilization of carbonated Mg-Al layered double hydroxide (LDH) nanosheets on methyl orange removal was investigated with a respect to particle dimension. LDHs with smallest dimension were synthesized carefully to have a small lateral size as well as high dispersibility. The other particles with medium and large sizes were prepared by hydrothermal treatment and urea hydrolysis to have larger size and higher crystallinity. According to kinetics and isotherm analyses, the smallest sized LDH showed effective adsorption of methyl orange (1250 mg/g-LDH) which was remarkable higher than the other LDHs with the larger lateral sizes. Compared with the larger lateral sized LDHs, the small sized ones were verified to utilize all the accessible adsorption sites of the nanosheets generating nanoconfinement of the methyl orange molecules. Transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD) patterns definitely indicated that the LDHs with ~40 nm of the lateral dimension could fully utilize the interlayer nanospace of the LDH. Monte-Carlo simulation suggested the intercalated methyl orange could be stabilized not only through electrostatic interaction with the LDH layer but also by π-π stacking between the methyl orange molecules, which is thought to be the driving force to replace carbonate anion.

A hierarchical silver nanostructure with improved antibacterial property was fabricated utilizing silver coordination polymer. Octadecanethiolate–silver polymer was synthesized to have a layered structure and was coated on silicon wafer by drop-casting method utilizing hydrophobic–hydrophobic interaction. Thus, the silver coordination polymer was calcined under reductive condition to produce zero-valent silver with a hierarchical nanostructure. X-ray diffraction patterns revealed that layered silver coordination polymer successfully transformed to hexagonal silver upon calcination. According to scanning electron and atomic force microscopy, silver coordination polymer with ~145.5 nm size was homogeneously coated on the surface before calcination, and it evolved micrometer-sized lumps and grooves which were composed of ~58.8 nm sized Ag nanoparticles. The hierarchical structure—micrometer lump/groove consisting of Ag nanoparticles—would be advantageous to kill bacteria; micrometer-grooves provide physical condition (pocket for bacteria capture) and the Ag nanoparticles from the neighboring lump endow chemical condition (antibacterial property of released Ag+). The antibacterial activity test on Escherichia coli via colony forming inhibitory assay indeed exhibited an improved antibacterial activity of hierarchical Ag nanostructure compared with the surface simply coated with Ag nanoparticles. From the line profile of atomic force microscopy, the bacterium trapped in the hierarchical Ag nanostructure was shown to interact intimately with Ag surface.

The immobilization of antimicrobial drugs can be used to expand the application of antibacterial properties to consumer products. The purpose of this study was to stabilize an antimicrobial agent, levofloxacin (LVX), for sustained antibacterial activity by immobilizing the drug molecules in a layered double hydroxide (LDH) and embedded in a polyurethane substrate. As-prepared MgAl-LDH was calcined at 400°C and reconstructed with LVX for intercalation. The X-ray diffraction patterns and cross-sectional transmission electron microscopy images showed lattice expansion along the crystallographic c axis upon LVX intercalation, suggesting successful loading of the drug. Fourier-transform infrared spectra revealed that the structure of LVX was well preserved between LDH layers. Elemental analysis indicated that the loading capacity of LVX in the hybrid was 41.7%. Bacterial-colony forming inhibitory assay on Bacillus subtilis exhibited ~100% antibacterial activity of both LVX alone and LVX-LDH hybrid (LL). To determine sustainability of antibacterial activity by the hybrid, either LVX alone or LL hybrid was loaded in the polyurethane (PU) substrate for which antibacterial activity was evaluated before and after immersion in a phosphate-buffered saline for 3 days. The LVX-composited PU showed a dramatic decrease in antibacterial activity, down to 0% after buffer treatment; LL-composited PU still contained antibacterial activity (~34% of colony suppression) after phosphate-buffered saline immersion.

Matching of charge periodicity between a guest and a host enabled effective immobilization of highly water soluble antibiotic drug, gentamicin C, in a bentonite clay by cation exchange. X-ray diffraction,...