Study on the Production of Silver/Modified Clay Nanocomposites
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Study on the Production of Silver/Modified Clay Nanocomposites Natália F. N. Pessanha1 and Gerson L. V. Coelho1 1
Separation Process Laboratory, Department of Chemical Engineering, Federal Rural University of Rio de Janeiro, Seropédica, Rio de Janeiro, Brazil.
ABSTRACT The aim of this study was to investigate the application of modified clay as a support in the synthesis of silver nanoparticles. Silver nitrate (AgNO3) was used as the silver precursor in several concentrations (0.005 M, 0.01 M, 0.02 M, 0.05 M, and 0.1 M) to obtain Ag-MMT purified and modified clay nanocomposites. The properties of nanocomposites were also studied as a function of the concentration of the reducing agent, sodium borohydride (NaBH4). It was observed through X-ray Diffraction that the MMT purified structure was gradually exfoliated with increased concentrations of AgNO3, while the modified clay structure remained intact. As observed through UV-vis spectra, samples of Ag+-MMT were reduced with NaBH4 to produce Ago and its particle diameter is dependent on the concentration of NaBH4. INTRODUCTION Silver (Ag) has been recognized for its oligodynamic activity since ancient times and its effects on cellular activity in living organisms even at low concentrations. The use of Ag as an antimicrobial material proved to be advantageous because it presents the highest degree of toxicity to more than 650 pathogenic microorganisms and still shows low toxicity to animal cells. It has been observed throughout the years that the antimicrobial activity of Ag was enhanced when it is presented in the colloidal form, i.e., in nanometer sizes (from 10-9 m to 10-6 m). Nano Ag provides increased number of particles per unit area [1,2,3]. The preparation of Ag nanoparticles consists mostly of two steps: reduction of Ag cations mainly from AgNO3 solutions and stabilization of the resulting Ag nanoparticles. Therefore, clay montmorillonite (MMT) has a lamellar structure, swelling capacity in aqueous media, and cation exchange capacity. The lamellar surface has charge-compensating cations (Ca2+, Na+ and Li+), which can be exchanged for other metal ions. The reduction of these metal ions leads to nano-sized particles because the lamellar spacing serves as a nano-reactor limiting the size of particles preventing agglomeration, and ensuring optimal dispersion of particles on the clay’s surface [4]. Given that Ag-MMT nanocomposites have been produced, and considering its known antimicrobial activity, the aim of this study was to synthesize Ag nanoparticles in modified clay to increase the basal spacing with a quaternary salt that develops higher adsorption capacity of nanometer metallic silver.
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EXPERIMENTAL DETAILS The commercial sodium bentonite clay (Argel CN 35) from Brazil has a cation exchange capacity (CEC) of 100 meq/100 g, was used in this study, and codified as MMT. The synthesis of nanocomposite comprises five steps: clay purification and modification, Ag adsorption and reduction, and characterization of the materials produced during these steps. Fi
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