The effect of cationic surfactant on the structure, morphology and optical band gap of ferrites synthesized by a microwave sol–gel auto-combustion method

Cu and Ni ferrites as the semiconductor materials were synthesized by a microwave sol-gel auto-combustion method. Two cationic surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), were applied and the influence of surfactants on the properties of the Cu and Ni ferrite particles was studied. The samples were characterized by X-ray powder diffraction (XRD) pattern, scanning electron microscope analysis (SEM), Fourier transform infrared (FT-IR) spectroscopy and diffuse reflectance spectra (DRS). Powder XRD analysis and FT-IR spectroscopy confirmed the formation of ferrite spinel phase. The crystallite size was calculated to be 50-95 nm using Scherrer’s equation. The morphology and size of the synthesized nanoparticles have been observed by scanning electron microscopy. The particles were agglomerated without using surfactant. Using CTAB leads to the samples with layer shapes, and  using SDS leads to  the samples  with pyramidal shapes. The energy band gaps  calculated from UV–DRS absorption by using Kubelka-Munk equation were 1.68-1.77 eV, indicating that band gap of Cu ferrites becomes small and band gap of Ni ferrites becomes large in the presence of surfactant.