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-Ag0/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, 17β-estradiol, and 17α-ethinyl estradiol). The deposition of Ag0 and Fe3O4 in rGO nanosheet enhanced the catalytic removal of phenol in the heterogeneous activation of PDS. The adsorption capacities of rGO-Ag0/Fe3O4 for 10 μM phenol were 1.76, 1.33, and 2.04 μmol g-1-adsorbent at pH 4, 7, and 10, respectively, which are much higher than those of single NPs studied (Ag0, nanoscale zero-valent iron, and rGO). The rGO-Ag0/Fe3O4 effectively activated PDS to produce strong oxidizing SO4·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-Ag0/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-Ag0/Fe3O4 (0.1 g/L) and PDS (1 mM) achieved more than 99% degradation of acetaminophen and 17β-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·- and ·OH formation or a non-radical oxidative pathway. Our findings indicate that the rGO-Ag0/Fe O nanohybrids can be used as an efficient magnetically-separable nanocatalyst for removal of organic compounds in water and wastewater treatment.