Photocatalytic activity of sol-gel self-combustion derived MCr2O4 (M= Mg, Ni) spinel chromites for photodegradation of organic dyes

Herein, MCr2O4 (M= Mg, Ni) chromite photocatalysts were synthesized via sol-gel self-combustion route and sintered at 1000 °C. The Rietveld refined X-ray powder diffraction profiles confirmed the single-phase formation of MgCr2O4 (MCO) and NiCr2O4 (NCO) chromites crystalized in the face-centered cubic and tetragonal spinel structures having Fd3̅m and I41/amd space group symmetries, respectively. The polyhedral geometrical shape and sizes of the grains were determined by the surface micrographs obtained from the field emission scanning electron microscopy (FESEM). The oxidation states and cations distribution investigated by the x-ray photoelectron spectroscopic (XPS) analysis professed the charge balance in the compounds. The photocatalytic performance of the chromite nanoparticles was examined using malachite green (MG) and crystal violet (CV) organic dyes at 5 ppm in solutions irradiated under sunlight. The photodegradation studies revealed the degradation efficacy of 70% and 85% for MCO, and 90% and 95% for NCO catalysts for the degradation of the MG and CV dye pollutants within 120 min, without utilizing H2O2. Furthermore, the kinetic studies were carried out and the experimental equilibrium data were observed to follow the pseudo-second-order and intraparticle diffusion models which described the synergetic adsorption-photodegradation procedures. Thus, NCO exhibited a high percentage for the removal of MG and CV organic pollutants compared to MGO, indicating that the tetragonally distorted NiCr2O4 nanocatalyst is an efficient candidate for the potential environmental purification of toxic organic contaminants. [Display omitted]