Comparative study of the photocatalytic activity for hydrogen evolution of MFe2O4 (M = Cu, Ni) prepared by three different methods

Abstract

In this work, CuFe2O4 and NiFe2O4 were synthesized by three different methods solid state reaction, polymer precursor method, and hydrothermal synthesis. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), Brunauer Emmett-Teller method (BET) and electrochemical measurements were employed to study the structural, morphological, optical, textural and electrical properties of the products. In all the cases (solid state, polymer precursor, and hydrothermal method) we confirmed through XRD analysis the obtention of the tetragonal phase for CuFe2O4 and the cubic phase for NiFe2O4. The influence of the preparation routes on the physicochemical properties of the materials was investigated in detail. The catalytic activity of the materials was tested under different irradiation sources: UV light (254 nm and 365 nm) and visible light, exhibiting activity only under 254 nm. The materials prepared by solid state method exhibited the highest activity for hydrogen evolution, due to their higher crystallinity and lower recombination of charges photogenerated. CuFe2O4 showed higher hydrogen evolution rate (336 μmol g−1 h−1) than NiFe2O4 (234 μmol g−1 h−1) attributed to the more negative character of the conduction band and higher photocurrent response of CuFe2O4. The photocatalytic activity of the materials was further analyzed in the presence of a sacrificial agent (0.25 M Na2SO3 – 0.35 Na2S), increasing more than 10 times the activity of the compounds obtained by solid state.