Performance of NiFe₂O₄-SiO₂-TiO₂ Magnetic Photocatalyst for the Effective Photocatalytic Reduction of Cr(VI) in Aqueous Solutions

Abstract

Investigation into the reduction of Cr(VI) in aqueous solution was carried out through some batch photocatalytic studies. The photocatalysts used were silica coated nickel ferrite nanoparticles (NiFe 2 O 4 -SiO 2 ), nickel ferrite titanium dioxide (NiFe 2 O 4 -TiO 2 ), nickel ferrite silica titanium dioxide (NiFe 2 O 4 -SiO 2 -TiO 2 ), and titanium dioxide (TiO 2 ). The characterization of the materials prepared via stepwise synthesis using coprecipitation and sol-gel methods were carried out with the aid of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), and vibrating sample magnetometry (VSM). The reduction efficiency was studied as a function of pH, photocatalyst dose, and contact time. The effects of silica interlayer between the magnetic photocatalyst materials reveal that reduction efficiency of NiFe 2 O 4 -SiO 2 -TiO 2 towards Cr(VI) was higher than that of NiFe 2 O 4 -TiO 2 . However, TiO 2 was observed to have the highest reduction efficiency at all batch photocatalytic experiments. Kinetics study shows that photocatalytic reduction of Cr(VI) obeyed Langmuir-Hinshelwood model and first-order rate kinetics. Regenerability study also suggested that the photocatalyst materials can be reused.