Nanoscale CuFe2O4 monodispersedly anchored on reduced graphene oxide as excellent peroxydisulfate catalyst for removal of gaseous elemental mercury

Abstract

This paper synthesized a magnetic and robust catalyst, CuFe2O4@rGO, by hydrothermal method and evaluated its catalytic activity towards peroxydisulfate (PDS) for removal of gaseous Hg0. The structure–function relationship of the prepared catalysts was revealed according to the characterization results of XRD, SEM-EDS, TEM, BET, FTIR and XPS. By incorporating into rGO, the catalytic activity of CuFe2O4 was greatly improved because the introduced rGO increased the large specific surface area and enlarged the pore volume, making the CuFe2O4 nanocrystals mono-dispersedly anchoring on the surface of rGO, increasing the accessible reactive sites. The carbon-based groups owing to rGO also acted as the auxiliary catalyst to facilitate PDS activation. CuFe2O4@rGO0.25 was determined as the best catalyst. The influences of key reaction conditions on Hg0 removal were assessed, such as catalyst dosage, PDS concentration, reaction temperature, solution pH, and the concentrations of SO2 and NO. The Hg0 removal efficiency was > 98% under the best conditions. The CuFe2O4@rGO0.25 hybrid catalyst possessed good magnetism, thus was easily separated by applying an external magnetic field, and also kept good catalytic activity after successively used for 10 h, with tiny Cu leaching (0.69%). According to the results of XPS, XRD, FTIR, ESR and radical quenching experiments, the reactivity order of the oxidizing species towards Hg0 removal was concluded as SO4•-> •OH > PDS. The redox reactions including ≡Cu(II)/≡Cu(I), ≡Cu(II)/≡Cu(III) and ≡Fe(II)/≡Fe(III) contributed to the PDS activation, with O2•-/S2O8•− as the reductants. This study gives a new insight into the method of SO4•--induced oxidation for effective removal of gaseous Hg0.