Efficient approach for preparing silver nanoparticles on layered double hydroxides: synthesis, characterization and properties

Novel functional materials have been obtained supporting metal nanoparticles (NPs) on solids having different dimensionality as clay, carbon nanotubes, graphite or graphene sheets. It is believed that the nature of the support utilized plays an important role in controlling the metal particle size and the interaction between the NPs and the supports, which can consequently affect the performance of the NPs supported. Such hybrid have applications in many technologically important fields such as catalysis, photophysics, photochemistry and biomedicine. Materials for electro-chemical devices and biochemical application can be obtained using the layered double hydroxides (LDH) surface as a substrate for growing and anchoring metallic nanocrystals. The use of LDH as a support allows to combine the NPs properties with the biocompatibility, compositional flexibility and ion exchange properties of LDH. In this contest a method to produce silver nanoparticles supported on ZnAl-LDH was developed. NPs of AgCl were precipitatedon the ZnAl-LDH surface by using AgNO3 as silver source. The ZnAl-LDH in chloride form acts as nucleating agent and, depending on the pH of the LDH dispersion, AgCl NPs with different dimension were obtained. In particular AgCl NPs with diameter of 55 nm were precipitated at pH 5 (Figure 1). The AgCl NPs supported on LDH sheets were reduced by different reducing agents (NaBH4, formaldehyde, sodium hyaluronate) resulting in silver NPs with diameter of 10-15 nm. The silver chloride and silver dimensions were evaluated by x-ray powder diffraction, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). UV-Vis spectra of the samples upon reduction showed a band centered at 415 nm due to the surface plasmon resonance of silver with dimension of about 10 nm, in agreement with the TEM analysis. The ZnAl-LDH7Ag nanocomposites can be designed as systems for advanced wound care dressing because of their ability to release zinc and silver ions in physiological media. The nanocomposites were used as inorganic filler of hyaluronate based films to be applied as advanced dressing. Preliminary antimicrobial tests indicate that the films were able to inhibit the growth of both bacteria and yeasts.