Degradation of sulfamethaxazole by persulfate assisted micrometric Feº in aqueous solution :assessment of bimetallic and trimetallic iron-based systems -

Abstract

Persulfate (PS) chemical activation using micrometric Feº particles (MIPs) was tested on sulfamethoxazole (SMX) solution (39.5 M). MIPs load (0.89-17.85 mM), PS content (0.4-1.0 mM), pH (5.50-8.30) and alkalinity (bicarbonate) were the main parameters investigated for the improvement of SMX degradation. Optimum conditions for the enhancement of the reaction stoichiometric efficiency (RSE = 5.2percent) were developed. The HPLC-MS supported results confirmed that in the absence of PS, SMX was converted into its reduced form through cleavage of the isoxazole N-O bond. The resulting unstable radical anion yielded a stable end-product identified as b-aminoenone after acceptance of electrons originated from the MIPs surface oxide. However, in the presence of PS, results did not show the presence of b-aminoenone. This suggested that PS activation into sulfate radicals (SRs) was responsible for the rapid degradation of SMX and its transformation product as well. Different water matrices were evaluated in order to understand the role that can play dissolved ions on the reaction degradation rate. Successive experiments (n = 3) of 1 h each conducted on remaining Feº showed complete SMX degradation. The mineralization extent of SMX under the experimental conditions reached 37percent making from Fe0-PS system an excellent source of SRs able to sustain oxidation reactions in aqueous media of slightly acidic pH. This work was extended to investigate the potential of different iron-based systems to activate persulfate (PS) into sulfate radicals (SRs) through catalytic electron transfer reactions. SRs in their turn are then used to degrade sulfamethoxazole (SMX) in water. PS activators like Fe²⁺, Feº, AgFe and CoFe (bimetallics), AgCoFe and CoAgFe (trimetallics) were tested on SMX solution (39.5 M) spiked with PS (1.0 mM). Results on SMX degradation showed better kinetics and efficiency in case of non-plated iron particles used compared to bimetallic and trimetallic systems as well as Fe²[u2