Photocatalytic reduction of chromate oxyanions on MMnFe2O4 (M=Zn, Cd) nanoparticles

Spinel MxMn1−xFe2O4 ferrites (M=Zn or Cd) synthesized via the co-precipitation method were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance UV–vis and Mössbauer spectroscopy. MnFe2O4 exhibited mainly cubic structure when Cd was incorporated, whereas the Zn incorporation stimulated a mixed phase consisting of MnFe2O4 and ZnMnFe2O4. The IR spectra of both Cd- and Zn modified MnFe2O4 samples revealed vibration of the chemical bond Fe2+O2− in A location of the tetrahedron which infers that dopants were uniformly distributed over the system. The optical band gap energy showed large variations; a smaller value was determined for Cd0.2Mn0.8Fe2O4 (1.46 eV) when compared with those of MnFe2O4 (2.16 eV) and Zn0.2Mn0.8Fe2O4 (2.8 eV). The analysis of Mössbauer spectra gave inversion values of Fe3+ distribution in tetrahedral coordinated sites of 24%, 57% and 65% in MnFe2O4, Zn0.2Mn0.8Fe2O4 and Cd0.2Mn0.8Fe2O4, respectively. It was found that Cd0.2Mn0.8Fe2O4 exhibited the best performance in the photocatalytic reduction of Cr(VI) to Cr(III) having a maximum value of 96% within 30 min, and the experimental data obeyed pseudo-second-order rate kinetic model. Also, the linear model of Langmuir attained a maximum adsorption capacity of 37 mg g−1 for Cd0.2Mn0.8Fe2O4.