Halide removal from waters by silver nanoparticles and hydrogen peroxide

Abstract

The objective of this study was to remove halides from waters by silver nanoparticles (AgNPs) and hydrogen peroxide (H₂O₂). The experimental parameters were optimized and the mechanism involved was also determined. The AgNP/H₂O₂ process proved efficacious for bromide and chloride removal from water through the selective precipitation of AgCl and AgBr on the AgNP surface. The optimal AgNP and H₂O₂ concentrations to be added to the solution were determined for the halide concentrations under study. The removal of Cl^- and Br^- anions was more effective at basic pH, reaching values of up to 100% for both ions. The formation of OH, O₂^-, radicals was detected during the oxidation of Ag(0) into Ag(I), determining the reaction mechanism as a function of solution pH. Moreover, the results obtained show that: i) the efficacy of the oxidation of Ag(0) into Ag(I) is higher at pH11, ii) AgNPs can be generated by the O₂^- radical formation, and iii) the presence of NaCl and dissolved organic matter (tannic acid [TAN]) on the solution matrix reduces the efficacy of bromide removal from the medium due to: i) precipitation of AgCl on the AgNP surface, and ii) the radical scavenger capacity of TAN. AgNPs exhausted can be regenerated by using UV or solar light, and toxicity test results show that AgNPs inhibit luminescence of Vibrio fischeri bacteria.

Keywords: Halides; Hydroxyl radicals; Precipitation; Silver-nanoparticles.