Comparative Study of Loading of Anodic Porous Alumina with Silver Nanoparticles Using Different Methods

Abstract

Three different routes were used to infiltrate the pores of anodic porous alumina templates with silver nanoparticles, selected as an example of a bioactive agent. The three methods present a continuous grading from more physical to more chemical character, starting from ex situ filling of the pores with pre-existing particles, moving on to in situ formation of particles in the pores by bare calcination and ending with in situ calcination following specific chemical reactions. The resulting presence of silver inside the pores was assessed by means of energy dispersive X-ray spectroscopy and X-ray diffraction. The number and the size of nanoparticles were evaluated by scanning electron microscopy of functionalized alumina cross-sections, followed by image analysis. It appears that the best functionalization results are obtained with the in situ chemical procedure, based on the prior formation of silver ion complex by means of ammonia, followed by reduction with an excess amount of acetaldehyde. Elution of the silver content from the chemically functionalized alumina into phosphate buffer saline has also been examined, demonstrating a sustained release of silver over time, up to 15 h.

Keywords: anodic porous alumina; elution; filling factor; nanoparticles; silver.

Figure 1

Scanning electron microscope (SEM) images of Ag-loaded anodic porous alumina (APA) substrates prepared from different methods; (a)–(b) direct filling with commercial nanoparticles (NPs); (c)–(d) physical method; (e)–(f) chemical method. Magnification is 1300× for the left column images (a), (c) and (e), and 20,000× for the right column images (b), (d) and (f). (b) is not representative of the typical surface, but is rather selected on purpose in a region of high NPs aggregation.

Figure 2

(a) Energy-dispersive X-ray microanalysis (EDS) spectrum of one APA substrate Ag-loaded with the chemical method; (b) X-ray diffraction (XRD) spectrum for the same sample.

Figure 3

Results of EDS analysis of Ag-loaded APA from different methods.

Figure 4

Typical curves of eluted Ag concentration per unit surface area from APA loaded with the three different loading methods up to the first two days, with respective fitting parameters to an exponential growth model. The symbols legend for experimental datapoints is as follows: Squares (□) are used for chemical loading, circles (○) for physical loading and triangles (Δ) for NPs filling.