Silver nanoparticles were synthesized and supported on thin nylon membranes by means of a simple method of impregnation and chemical reduction of Ag ions at ambient conditions. Particles of less than 10 nm were obtained using this methodology, in which the nylon fibers behave as constrained nanoreactors. Pores on nylon fibres along with oxygen and nitrogen from amide moieties in nylon provide effective sites for
Research on the synthesis of mesoporous materials containing nanoparticles represents a fast-developing area of nanoscience and nanotechnology. This interest is stimulated by several possible application areas of these materials including catalytic [
Nylon is an electron-rich and polar synthetic polymer (polyamide) usually made from the monomers adipoyl chloride and hexamethylene diamine to form a linear molecular chain (Figure
Characteristic synthesis of nylon-6,6 fibers.
In this work, a facile synthesis of silver nanoparticles of less than 10 nm in diameter with a narrow size distribution, using porous nylon fibers as unique nanoreactors to generate a nylon-6,6/silver nanoparticles composite, is reported.
All chemical reagents were analytical grade and were used without further purification.
In a typical experiment, nylon-6,6 membranes (Millipore Co., cat. number: GNWP02500; 150
UV-visible absorption spectra were recorded, using a nylon-6,6 membrane as the reference, on a Cary 5000 UV-Vis-NIR scanning spectrophotometer. Scanning electron microscopy (SEM) observations were performed on a Philips XL30 electron scanning microscope. Transmission electron microscopy (TEM) observations were carried out on a JEOL JEM-2010F instrument with a point resolution of 1.9 Å and equipped with high-angle annular dark-field or
The measurements of lattice-fringe spacing and angles were made using digital image analysis of reciprocal space parameters, according to Akamatsu et al. [
X-ray photoelectron spectroscopy (XPS) was performed using an UHV system of VG Microtech ESCA3000 Multilab, with an Al
The membranes used in this work are composed of nylon-6,6 fibers in the micrometer range, as shown in Figure
SEM image of the nylon-6,6 membrane.
These pores may allow guest molecules to enter. Thus, when a nylon membrane is immersed in aqueous AgNO3, Ag+ ions are readily impregnated into the nylon membrane fibers through the pores. Most of the incorporated Ag+ ions are bound to nylon macromolecules probably via electrostatic (i.e., ion-dipole) interactions, because the electron-rich oxygen and nitrogen atoms of polar amides groups are expected to interact with positive metal ions. The posterior rinse with ethanol (ca. 30 s) removes Ag+ ions that were not anchored to nylon fibres. Figure
Nylon-6,6 without and with Ag nanoparticles formed at different AgNO3 concentrations.
Energy-dispersive X-ray spectroscopy (EDX) spectrum in Figure
EDX spectrum of nylon-6,6 membrane coated with Ag nanoparticles.
UV-Vis spectra of the nylon-6,6/silver nanoparticles composites are shown in Figure
UV-Vis spectra of silver nanoparticles in nylon-6,6 membranes. Nanoparticles were prepared using aqueous AgNO3 at 0.5 mM, 1.0 mM, and 1.5 mM, respectively.
These assumptions are confirmed by TEM observations. As shown in Figure
TEM micrograph and size distribution histogram of Ag nanoparticles in nylon-6,6 membranes (AgNO3 0.05 mM).
Figure
HAADF images and size distribution of Ag nanoparticles obtained from (a), (c) AgNO3 1.0 mM; (b), (d) AgNO3 1.5 mM.
Because of the porous structure of nylon fibre and the strong interactions between Ag+ ions and the carbonyl and amide groups of nylon macromolecule, Ag+ ions were uniformly and tightly anchored to the nylon fibres [
The HRTEM image in Figure
HRTEM image of Ag nanoparticles (top) and their corresponding Fourier transforms (FFT) (bottom) pattern.
In order to examine the chemical composition of the nylon-6,6/Ag nanoparticles fibre composite, as well as the possible interaction of silver metal with the nylon moieties, after formation of Ag nanoparticles, X-ray photoelectronic spectroscopy (XPS) was used. Figure
XPS spectra of nylon-6,6 and three different nylon-6,6/Ag composites.
Figure
In order to obtain more information about the chemical state of the Ag nanoparticles present in the composite a curve fit of the various signals was made and is shown in Figure
The XPS deconvolution for C 1s, O 1s, N 1s, and Ag 3d core levels.
Table
The binding energy position by XPS of nylon-6,6- and Ag-containing samples core levels Ag 3d, C 1s, O 1s, and N 1s.
N 1s | O 1s | Ag 3d5/2 |
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Sample | O=C | O–Ag | Ag | AgO |
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0.5 mM |
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1.0 mM |
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1.5 mM |
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From Table
It was demonstrated that using an aqueous Ag ion impregnation of nylon fibres followed by a reduction with NaBH4, a composite of Ag nanoparticles attached to the polymer can be formed. The whole process is carried out at ambient conditions. SEM, HRTEM, and XPS studies confirmed the presence of such Ag nanoparticles in the fibres, with an average size of 3.3 nm. This very simple and versatile synthetic route could be applied to obtain other composites made of metal nanoparticles and natural or synthetic polymer fibres. Moreover, an interaction between nitrogen of amides moieties of nylon-6,6 and silver nanoparticles has been found by X-ray photoelectron spectroscopy.
Financial support of this work was provided by Universidad Autónoma del Estado de México (UAEM) (Project no. 3246/2012U). The authors are indebted to Fernando Ureña (ININ), Samuel Tehuacanero (IFUNAM) for their assistance in SEM and image digitalisation, respectively.