Catalytic activity towards H2O2 reduction of carbon composites containing MFe2O4 nanoparticles.

FABIANA A. GUTIERREZ; EVA MAZARIO; MARIA D. RUBIANES; GUSTAVO A. RIVAS; PILAR HERRASTI; SOLEDAD BOLLO; JOSE H. ZAGAL; F. JAVIER RECIO

Angra dos Reis

Congreso; 16th Topical Meeting of the International Society of Electrochemistry; 2015

International Society of Electrochemistry

Among magnetic oxides, magnetite nanoparticles supported on graphite powder have well-established catalytic properties for many reactions such as decomposition of alcohols, selective oxidation of carbon monoxide, decomposition of hydrogen peroxide and discoloration of synthetic dyes, and have been extensively studied for environmental applications and biosensors [1, 2]. The integration of nanoparticles (NPs) and carbon nanomaterials as supported material in nanocomposites has recently become a hot topic of research due to their new and/or enhanced functionalities that cannot be achieved by either component alone, and therefore holds great promise for a wide variety of applications in catalysis, biomedical fields, drug delivery, energy storage and removal of contaminants from wastewater. The present work inform a systematic study of the effect of different carbon supported nanomaterials (nanotubes and graphene) on the catalytic activity of three kinds of MFe2O4 nanoparticles (M = Mn, Co, Fe) at pH 13. Nanostructured ferrites were electrochemically synthesized according to ref. 3, and stabilized with citrate. X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersed spectroscopy (EDS) were used for chemical and structural characterization. The ferrite nanoparticles shown a similar size (20 nm) and shape. The dispersions were obtained by mixing Np and carbon nanomaterials in mass ratio (1:4) with 5 mL of a mixture of water, isopropanol and nafion, followed by sonication for 30 min. Before modification, the GCEs were polished with alumina slurries of 1.0, 0.30, and 0.05 ìm for 2 min each. After that, they were modified by dropping 10 ìL of the given dispersion on the top of the surfaces followed by the evaporation of the solvent. The modified electrodes were evaluated by Scanning Electrochemical Microscopy (SECM), Cyclic voltammetry (CV), Amperometry and Electrochemical Impedance Spectroscopy (EIS). Electrochemical characterization experiments were performed at de-oxygenated pH 13 solution (NaOH 0.1M) at room temperature. The catalytic activity of the nanocomposites was performed by cathodic polarization at 5mV/s in presence of 10 mM H2O2 and evaluated by their onset potential. The sensitivity was determined as the slope of the calibration plots obtained from the amperometric recordings. The charge transfer resistance (Rct), associated with the electrocatalytic activity of the nanoparticles, was obtained of the EIS The catalytic activity of nanoparticles are higher than nanotubes or graphene evaluated independently, following the next sequence (Mn>Co>Fe). However, a clear decrease of the onset potential is detected when both kind of nanocomposites (MWNT-NP and GORT-NT) with different nanoparticles are evaluated. The higher analytical sensitivity and and lower Rtc of nanoparticles was detected when Co or Mn and MWNT were used follow by Fe. The best synergic effect of the C nanocomposites are evaluated taking into account the relative increase of sensitivity and the decrease in Rct respect the bare Np. In the case of the use of graphene a similar increase of 1.5 times are detected independent of the Nanoparticle tested. However the effect of nanotubes is dependent of the cation with an increased of 6, 2.8 and 1.8 for Fe, Mn and Co respectively. In conclusion, the use of ferrite-C nanocomposites have shown a clear increase in the catalytic activity and sensitivity of bare nanoparticles, the synergic effect of the C materials if higher when CNT are used and is dependent of the chemical composition of the nanoparticles.