Removal of citrate-coated silver nanoparticles from aqueous dispersions by using activated carbon

• Adsorption of Ag nanoparticles on activated carbon followed Freundlich and Langmuir isotherms.
• Adsorption of Ag nanoparticles on activated carbon depended on the presence of electrolytes.
• Increased deposition of Ag nanoparticles on activated carbon was observed at high electrolyte concentration.
• Ag nanoparticles could be completely removed from aqueous dispersions.

This article describes studies on the efficiency of activated carbon as adsorbent for water-dispersible silver nanoparticles. Nanoparticles of average size around 60 nm and negative zeta-potential were synthesized by reduction of Ag(I) ions with sodium citrate in aqueous medium. Activated carbon (Norit® CA1) intended for water purification was found to be an efficient adsorbent for silver nanoparticles. It was found that nanoparticle adsorption on activated carbon could be described by Freundlich and Langmuir isotherms. The presence of electrolytes favored nanoparticle deposition on the surface of activated carbon. When electrolytes were used above their critical coagulation concentration aggregated nanoparticles were settling down along with the carbon particles, where carbons were acting as filter aid. This allowed complete removal of nanoparticles from the aqueous dispersions. It is expected that these studies could be important for better understanding of the interactions between nanoparticles and solid–liquid interfaces, for preparation of nanoparticle/carbon composite materials, as well as for designing of methods for removal of metal nanoparticles from contaminated water during treatment of nanowastes.

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