2O4 nanoparticles with temperature varying from 500 to 800°C. The two ferrite samples calcined at 500–600°C were obtained as single spinel phase with peaks at 220, 311, 400, 511, and 440, corresponding to the cubic spinel structure (JCPDS card. no. 01-071-1232) . It is showed that the increase in temperature is associated with the improvement of MgFe2O4 powders. However, from 700 to 800°C, new phases of ?-Fe2O3 were observed. The spinel phase of MgFe2O4 was confirmed by five XRD peaks at 220, 311, 400, 511, and 440 crystal planes. Results reported in Table 1 also indicate that the crystallite size of MgFe2O4 was positively associated with the calcination temperature. As temperature moved from 500 to 800°C with 100°C interval, the average crystallite size was expanded from 18 to 61 nm. For the “a” lattice parameter, XRD spectra showed that for MgFe2O4 nanoparticles, the value fell in the range of 8.344–8.378 A.
The SEM images of different samples of MgFe2O4 nanoparticles corresponding to four calcination temperature points of 500°C, 600°C, 700°C, and 800°C are shown in Figures 3(a)–3(d). Visually, the images showed consistent implication with the XRD results. To be specific, particle size of the prepared samples were found to be proportionally increasing with temperature. This could possibly be due to the aggregation and coalescence during desiccation.
The TEM image of MgFe2O4 synthesized at 500°C is presented in Figure 4(a). Evidently, the magnesium ferrite nanoparticles resulted from the solution combustion method were uniform in terms of morphology and crystallite size and reached the particle size of approximately 30 nm.
Figure 4(b) shows chemical purities and elemental composition of the MgFe2O4 materials produced by energy dispersive X-ray analysis (EDX). The existence of Mg, O, and Fe was determined by their corresponding peaks and the absence of other characteristic peaks. On the contrary, the synthesized sample was pure and installment loans in Michigan did not contain any other elements.
The UV-Visible absorption spectrum was obtained to investigate the optical properties of magnesium ferrite calcined at 500–600°C as shown in Figure 5. By using the Kubelka–Munk equation, the band gap of MgFe2O4 samples was determined from reflectance spectra via conversion to absorbance . The band gap energy Eg (eV) of the synthesized photocatalyst is calculated by the following equation:
In addition, significant and proportional decline of peak intensity with respect to irradiation time was also recognized in these two spectra
where , , and are the Planck constant (6. ?34 J·s·photon ?1 ), the speed of light (3.10 ?8 m·s ?1 ), and the wavelength at the absorption edge (nm), respectively . At wavelengths 500 and 600°C, of the samples was calculated to be 679 nm and 687 nm, respectively. Therefore, the calculated band gap energy values are 1.83 eV and 1.81 eV for the MgFe2O4 samples calcined at 500°C and 600°C, respectively.
3.2. Photocatalytic Activity of Magnesium Ferrite Nanoparticles
Nanoparticles of the MgFe2O4 were tested for catalytic activities by performing photo-Fenton-like degradation of MB. Figures 6(a)–6(e) show different UV-Visible spectra of MB with MgFe2O4 photocatalyst corresponding to varying conditions including the calcination temperature of the absorbent, availability of H2O2, and presence of light irradiation.
The presence of methylene blue is indicated by the two absorption peaks at 609 nm and 664 nm . It is visibly observed that the color of the MB solution gradually changed from blue to light blue and finally to colorless, which is presumably due to the estrangement of the chromophoric group. In the first two spectra where H2O2 was absent, MB degradation efficiency reached 6.51% (in the dark) and % (under light irradiation) after 240 minutes, suggesting the positive influence of light on the degradation efficiency. In comparison with the first spectrum, the third spectrum involved the introduction of H2O2, showing a significantly higher efficiency at %. The last two spectra demonstrated the effect of calcination temperature with the presence of H2O2 and light irradiation. The measured efficiencies were % and % corresponding to MgFe2O4 calcined at 500°C and 600°C, respectively. These results suggested that light irradiation, ferrite catalyst, and H2O2 were all required for efficient photo-Fenton degradation of MB dye. Similar results have been reported for NiFe2O4 nanoparticles and CuFe2O4 spheres by various studies [11, 41].