Heterogeneous activation of persulfate by reduced graphene oxide-elemental silver/magnetite nanohybrids for the oxidative degradation of pharmaceuticals and endocrine disrupting compounds in water

Reduced graphene oxide hybridized with zero-valent silver and magnetite nanoparticles (NPs) (rGO-Ag-0/Fe3O4 nanohybrids) prepared via in situ nucleation and crystallization was used to activate peroxydisulfate (PDS) for degradation of pharmaceuticals and endocrine disrupting compounds (phenol, acetaminophen, ibuprofen, naproxen, bisphenol A, 17 beta-estradiol, and 17 alpha-ethinyl estradiol). The deposition of Ag-0 and Fe3O4 in rGO nanosheet enhanced the catalytic removal of phenol in the heterogeneous activation of PDS. The adsorption capacities of rGO-Ag-0/Fe3O4 for 10 mu M phenol were 1.76, 1.33, and 2.04 mu mol g(-1)-adsorbent at pH 4, 7, and 10, respectively, which are much higher than those of single NPs studied (Ag-0, nanoscale zero-valent iron, and rGO). The rGO-Ag-0/Fe3O4 effectively activated PDS to produce strong oxidizing SO4 center dot(-) and facilitate an electron transfer on the surface of the nanohybrid. The initial pseudo-first-order rate (k(ini)) constant for phenol degradation in PDS/rGO-Ag-0/Fe3O4 system was 0.46 h(-1) at pH 7, which is approximately eight times higher than that in the presence of single NPs (k(ini) = 0.04-0.06 h(-1)) due to the synergistic effects between adsorption and catalytic oxidation. Among various organic contaminants tested, the simultaneous use of rGO-Ag-0/Fe3O4 (0.1 g/L) and PDS (1 mM) achieved more than 99% degradation of acetaminophen and 17 beta-estradiol at pH 7. The radical scavenging studies with methanol and natural organic matter indicated that phenol was more likely to be degraded via free SO4 center dot(-) and center dot OH formation or a non-radical oxidative pathway. Our findings indicate that the rGO-Ag-0/Fe3O4 nanohybrids can be used as an efficient magnetically-separable nanocatalyst for removal of organic compounds in water and wastewater treatment.