Synthesis of composite based on submicron sized silver particles hosted on microspheres of surface-functional porous crosslinked copolymer networks

doi:10.1016/j.matlet.2006.10.061

Materials Letters

Volume 61, Issues 14–15, June 2007, Pages 2993-2999

https://doi.org/10.1016/j.matlet.2006.10.061 Get rights and content

Abstract

This study presents a different colloidal silver (Ag)/polymer system where Ag submicron particles are anchored onto surface-functional porous microspheres of various commercial copolymers networks, namely Amberlite® GT73 (resin containing thiol group) and Amberlyst® 15WET from Rohm and Haas Co. and Lewatit® VPOC1800 from Bayer Co., both containing sulfonic acid group. The Ag/microsphere composites were prepared via in situ reduction of Ag salt (AgNO₃) by employing three different reductants, namely hydrazine, hydroxylamine and formaldehyde (under alkaline pH). The formation and morphology of the composite microspheres were characterized by scanning electron microscopy (SEM) equipped with backscattered electrons detector (BSE). Energy dispersive X-ray spectroscopy (EDS) coupled to SEM allowed the observation of submicron particles in the 50–500 nm size range, which chemical microanalysis of emitted X-rays revealed the presence of metal on the microspheres surface. The significance of the present report is that owing to the affinity between Ag and functional groups of the different copolymers studied on the large surface of the microspheres, it was possible to have an insight on the influence of the functional group in the Ag particles dispersion profile in the composite. Thus Ag particles were observed to be incorporated evenly into the deep pores of the beads with fine size and narrow size distribution in GT73 resin, while non-uniform coarse precipitation was observed in VPOC1800 and 15WET resins. It appears that the morphological features could be strongly influenced by the chemical composition.

Introduction

Metal composites have received a vast deal of interest in many fields, such as adsorptive, separation and purification processes, catalysis and also water treatment, which is attributed to their distinctive physicochemical properties [1], [2], [3], [4], [5]. Actually, the high performance in these composite materials is attained by tailoring their phase structure in the micro-sized range. A versatile methodology is used to produce them in the presence of solid carrier, such as polymeric materials [5], [6], [7].

Silver powders having ultrafine and uniformly distributed sizes are of large current use in chemical industry, electronics, medicine due to singular properties such as high electrical and thermal conductivity, high resistance to oxidation, bactericidal action (colloid silver), etc. Silver is a durable (persistent) biocide with high temperature stability and very low volatility compared to other usual biocide agents, such as chlorine, bromine and iodine. In this regard, nanosized powders and silver colloidal dispersions have attracted great attention in recent years. Many methods, such as chemical reduction [8], [9], [10], photochemical or radiation-chemical reduction [11], [12], metallic wire explosion [13], sonochemical [14] and polyol methods [15] have been currently applied to prepare ultrafine silver powders. From a practical point of view, the method of chemical reduction from aqueous solutions is most preferable for obtaining nanosized powders and silver colloidal dispersions.

The method of chemical reduction involves the reduction of relevant metal salts in the presence of a suitable protecting agent, which is necessary for controlling the growth of metal colloids through agglomeration. Generally, synthetic polymers such as gelatin, polyvinylpirrolidone (PVP), polyvinylalcohol (PVA) are used as protecting agents. According to Tosun and Glicjsman [16], silver powder with particle size 0.1–1.0 mm can be obtained by reduction of silver nitrate with alkylacid phosphate in the presence of gelatin. It has been shown that vinyl polymers improve on other substances, including gelatin, in protective characteristics. The reduction of preheated silver nitrate solution in the presence of PVP allows the production of silver powder with a particle size of ∼ 300 nm [17], [18]. However, the size of silver particles can be diminished to 100 nm, if the reduction of silver nitrate is conducted by hydrazine in the presence of PVP [9].

Porous solid materials based on copolymer networks are of practical importance for a useful support owing mostly to their good mechanical and thermal properties, interconnected pores structure, small pores and large surface area [5], [6]. In order to optimize the advantages of those porous materials, it is a promising approach to introduce functional groups by means of suitable chemical modification of a basic polymer or the use of a polymer that contains functional monomeric units [1], [6]. The production of colloidal metal particles with controlled morphology and size is of paramount significance due to the intensive dependence of physical and chemical properties of these particles on their shapes and sizes [19], [20].

Literature has pointed out that many parameters are determinants of the size and morphology of these metal particles. It has been demonstrated that the shape of the template has an important role on particle formation. In addition, researchers have also discovered that the concentration and type of stabilizer agents, as well as the concentration of cations and the reaction time, have a remarkable impact on the morphology of the particles. Fundamentally, the morphology and size of submicron particles are quite susceptible to the type and concentration of reducing reagent, and support polymer employed during their preparation [19], [20], [21], [22], [23], [24].

The preparation of submicron silver particles has been conducted by the reduction of metal salt using sodium formaldehydesulfoxylate [20], [22], NH₂NH₂ [6], [19], [20], [25], NH₂OH, NaBH₄ [20], [22], glucose/NaOH [10], [20], HCHO/NaOH/Na₂CO₃ [20], ascorbic acid [4], [21], citric acid [19] among other reductants. Additionally, methods based on physical agents, such as UV [7], [21] or gamma irradiation [20], metal evaporation or sputtering [7] and sonochemical pulsing [14], [19] have also been used for the preparation of silver film.

The silver supported on crosslinked polymer composites combines the excellent high thermal stability of polymeric carrier with the intrinsic antimicrobial property of silver [5], [6], [7]. Silver-based antimicrobials have received much attention not only due to the non-toxicity of the active Ag to human cells, but due also to their innovation.

In this paper, we describe a method for synthesizing colloidal silver composites that were created by the precipitation of silver submicron particles hosted in surface-functional porous microspheres with different porosities and surface functionalities (namely, thiol and sulfonic acid groups). Our focus is on the effect of these copolymer characteristics on the attaching of Ag particles on the beads surface and the morphology of the final microspheres.

Section snippets

Materials

The commercial resins were kindly supplied by Rohm and Haas Co., namely Amberlite® GT73 (resin containing thiol group, exchange capacity = 1.2 mmol/g of resin, apparent density = 0.78 g/cm³ data informed by the supplier) and Amberlyst® 15WET (macroreticular resin, exchange capacity = 1.7 mmol/g of resin, surface area = 45 m²/g, pore diameter = 300 Å, pore volume = 0.40 cm³/g, apparent density = 0.77 g/cm³ data informed by the supplier) and by Bayer Co., namely Lewatit® VPOC1800 (gel-like resin, apparent

Results and discussion

Two ion exchanger copolymer networks with the –SO₃H group (namely, VPOC1800 and 15WET) and other resins with –SH as mostly the coordinating group (namely, GT73) were employed for anchoring silver particles. PVP was used as a protector colloid to prepare binary materials containing nanosized silver particles dispersed on the copolymers surface [9]. In order to investigate the influence of the type of functional group and the reducing agent on the formation of silver particle structure and silver

Conclusions

It is important to point out that the size and shape of the silver particles and their distribution on the surface (internal or external) of porous copolymer network containing ion-exchange (–SO₃H) or chelating (–SH) groups can be easily attained using SEM techniques. In addition, the use of BSE images permitted suitable observation of the silver particles dispersed on the surface of the copolymer microspheres. The silver particle distribution and size depended on the type and amount of

Acknowledgements

We thank to CNPq, CAPES, FAPERJ and CETREINA/UERJ for financial support. We also wish to express our thanks to Rohm and Haas and Bayer for resins donation.

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Synthesis of composite based on submicron sized silver particles hosted on microspheres of surface-functional porous crosslinked copolymer networks

Abstract

Introduction

Section snippets

Materials

Results and discussion

Conclusions

Acknowledgements

Electrochem. Commun.

J. Colloid Interface Sci.

Biomaterials

Polymer

Mater. Sci. Eng., C, Biomim. Mater., Sens. Syst.

Mater. Res. Bull.

J. Solid State Chem.

Mater. Chem. Phys.

Acta Metall.

Solid State Ionics

J. Colloid Interface Sci.

Mater. Lett.

Mater. Chem. Phys.

Mater. Chem. Phys.

Chemosphere