Removal of silver nanoparticles coated with different stabilizers from aqueous medium by electrocoagulation

This study evaluated the removal of silver nanoparticles (AgNPs), coated with different stabilizers, from aqueous media using the electrocoagulation technique. The AgNPs dispersions were synthesized by chemical reduction with silver nitrate as precursor, sodium borohydride as reducing agent and sodium carboxymethylcellulose (CMC), polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) as stabilizers with initial concentrations of 1 and 3% (w/v). The dispersions were named AgNPs-CMC1, AgNPs-CMC3, AgNPs-PVA1, AgNPs-PVA3, AgNPs-PVP1, and AgNPs-PVP3. Electrocoagulation treatments of AgNPs-PVA1, AgNPs-PVP1 and AgNPs-PVP3 dispersions resulted in total silver removals above 99.90% in 10 min. For the AgNPs-PVP3 dispersion 99.98% of removal was obtained in 20 min. After 15 min of electrolysis, The AgNPs-CMC1 and AgNPs-CMC3 dispersions showed a reduction in total silver concentration of 71.72 and 52.15%, respectively. Therefore, these results showed that the removal of AgNPs from the aqueous medium by electrocoagulation is possible, but their efficiency and viability depends on the nature, the molecular structure and the concentration of stabilizers. Furthermore, the toxicity analysis using the Vibrio fischeri bacteria demonstrated that only the dispersions stabilized with PVP became suitable for disposal after the electrocoagulation treatment.