Development and thermal evolution of silver clusters in hybrid organic–inorganic sol–gel coatings

https://doi.org/10.1016/j.surfcoat.2011.06.018Get rights and content

Abstract

A silver doped hybrid organic–inorganic sol–gel coating was developed through the hydrolytic condensation of tetraethoxysilane (TEOS) and methyl-triethoxysilane (MTES). Silica nanoparticles were added in order to give a mechanical reinforcement and silver nitrate as the supplier of Ag+ ions, which have a potential effect as a biocide component. Synthesis of precursor sol and the evolution of silver clusters in the whole process were analyzed through Attenuated Total Reflectance Fourier Transformed Infrared spectroscopy (ATR-FTIR) and UV–visible spectroscopy. A high thermal sensitivity of sub-nanometric silver particles was determined by Small Angle X-ray Scattering (SAXS) carrying to formation of higher agglomerates or silver nanoparticles. Lixiviation tests show long-term and gradual silver releasing without worsening of the structural integrity of coatings.

Research Highlights

►This article exposes the development of silver doped hybrid organic–inorganic coatings. ►Evolution of silver clusters was analyzed by UV–visible spectroscopy and SAXS. ►A gradual silver release was determined by XRF in water immersed coatings.

Introduction

The development of new materials enriched with noble metal ions, such as silver, cobalt or copper, is of great interest in the field of hygienic and healthiness products due to its action against fungus and bacteria. Although a large number of commercial products are chemically active against microorganisms, they are usually limited to fabrics for medical bandages and sportswear in order to avoid, respectively, infections and odors. Although many of those products are based on the biocide properties of silver nanoparticles, it is well known that Ag+ ions have an effective action against bacteria life inhibiting their DNA replication process, increasing the permeability of the cytoplasmic membrane and inhibiting the respiratory enzymes, causing asphyxia of the bacteria. Taking this feature in account, reduction of silver ions must be avoided in order to maximize the biocide character of the functional coating.

Natural trend of silver to reduce and form metallic particles makes its incorporation as ions or small clusters quite difficult in hybrid organic–inorganic solid matrixes. This property is usually leveraged to synthesize suspensions of spherical nanoparticles, through emulsion routes [1], [2], [3], [4], [5], or solid materials loaded with “in situ” generated nanoparticles [6], [7], [8], [9].

In this work, the development of silver doped hybrid organic–inorganic sol–gel coatings is focused. A hybrid organic–inorganic matrix was obtained through the hydrolytic condensation of tetraethoxysilane (TEOS) and methyl-triethoxysilane (MTES). Silver nitrate (AgNO3) was added as supplier of Ag+ and silica nanoparticles were added to increase the coating density and to improve the mechanical properties.

A characterization was performed in sols and in the resulting dip-coated films in order to determine the evolution of silver ions and clusters along the whole process. Small Angle X-ray Spectroscopy (SAXS) was performed with synchrotron light, which is a powerful tool for characterization of size distribution of particles, even sub-nanometric and small clusters [3], [7], [8], [9], [10], [11], [12], [13]. Silver lixiviation process was studied on immersed samples through X-ray Fluorescence Spectroscopy (XRF).

Section snippets

Experimental

Hybrid sols were prepared by the chemical reaction of tetraethoxysilane (TEOS) and methyl-triethoxysilane (MTES) in presence of an aqueous dispersion, 40 vol.%, of colloidal silica (SiO2 NP, LUDOX AS-40 Aldrich, mean size: 6 nm). TEOS/MTES/SiO2 (NP) molar ratio was kept at 36/54/10. Besides of the water supplied by Ludox, an additional aliquot was added in order to reach a molar ratio ethoxy groups/water of 2. Hydrolytic condensation was acid catalyzed at room temperature by the addition of

Synthesis and characterization of sols

FTIR analysis allows the observation of the whole process trough the following of bands corresponding to the chemical groups involved. Table 1 displays the main FTIR bands appearing. Hydrolytic condensation of TEOS and MTES in presence of the aqueous suspension of silica nanoparticles occurs fast and spontaneously after addition of HNO3 to catalyze the chemical reaction. Fig. 1 shows FTIR spectra of main reagents and its resulting sol. Suspension of silica nanoparticles presents a sharp band

Conclusions

Silver doped hybrid organic–inorganic sol–gel coatings were synthesized by hydrolytic condensation of TEOS and MTES in presence of silica nanoparticles. Pyridine coordination of silver ions carried to the development of Ag2+ and Ag42+ clusters and allowed the stabilization of sols for more than two months of aging in dark conditions at 4 °C without precipitation or loosening of colorless. Upon thermal treatment, silver clusters undergo agglomeration leading to formation of nanometric and

Acknowledgments

Authors want to acknowledge the National Synchrotron Light Laboratory, Campinas, Brazil (LNLS, Project 6780/2010, proposal D11A-SAXS1-10004) and the Argentine National Agency for Scientific and Technological Promotion (ANPCyT PICT-2007-01161) for the financial support. Also the Argentine National Council of Scientific and Technical Researches (CONICET) is gratefully acknowledged.

References (39)

  • A. Ledo et al.

    Physica B

    (2007)
  • J. Compton et al.

    Polymer

    (2006)
  • V. Purcar et al.

    Appl. Catal. A

    (2009)
  • J. Wang et al.

    Nanostruct. Mater.

    (1996)
  • J.H. Osborne et al.

    Prog. Org. Coat.

    (2001)
  • A. Conde et al.

    Prog. Org. Coat.

    (2003)
  • L.Y.L. Wu et al.

    Thin Solid Films

    (2008)
  • S. Pellice et al.

    J. Non-Cryst. Solids

    (2004)
  • D.R. Brown et al.

    J. Phys. Chem.

    (1986)
  • E.M. Egorova et al.

    Colloids Surf. A

    (2000)
  • N.C. Rosero-Navarro et al.

    Surf. Coat. Technol.

    (2009)
  • A. Henglein et al.

    Electrochim. Acta

    (1991)
  • M. Arada et al.

    Eng. Aspects

    (2008)
  • M. Arada et al.

    J. Colloid Interface Sci.

    (2010)
  • M. Andersson et al.

    Langmuir

    (2005)
  • C. Petit et al.

    J. Phys. Chem.

    (1993)
  • E.V. Shtykova et al.

    Nanotechnol. Russ.

    (2009)
  • T. Saraidarov et al.

    Phys. Status Solidi C

    (2010)
  • A.M. Signori et al.

    Langmuir

    (2010)
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      The presence of the bands corresponding to the LO mode, at 1130 and 1170 cm− 1 (sh), is attributed to the porous structure in the silica network [16,17], while the TO bands, around 1020, 1045 and 1100 cm− 1, correspond to structural units of isolated cyclosiloxanes or terminal rings, with larger SiOSi angles and SiO bond lengths [18–20]. On the other hand, taking into account that the gel conversion of a pure silica sol, from TEOS in acidic conditions, corresponds to the condensation of at least 80% of the hydrolysable groups [21] and that if a fraction of TEOS (tetrafunctional) is replaced by a trifunctional alkoxyde (MTES) the gel conversion should be even higher [22] the contribution of the bands of residual alkoxide groups, that do not become into a SiOSi bond nor to a SiOH group, should be strongly overlapped by the corresponding ones of the silica network of the gelled and thermally treated films [13]. Therefore, the bands at 770 and 793 cm− 1 can be certainly attributed to the symmetric stretching of the SiOSi bonds [23,24].

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