Zircon-Type CaCrO₄ Chromite Nanoparticles: Synthesis, Characterization, and Photocatalytic Application for...

The degradation of organic dye pollutants is a critical environmental issue that has garnered significant attention in recent years. To address this problem, we investigated the potential of CaCrO₄ chromite (CCO) as a photocatalyst for the degradation of cationic and anionic dye solutions under sunlight irradiation. CaCrO₄ was synthesized via a sol-gel auto-combustion route and sintered at 900 °C. The Rietveld refined XRD profile confirmed the zircon-type structure of CaCrO₄ crystallized in the tetragonal unit cell with I41/amd space group symmetry. The surface morphology of the sample was investigated by field emission scanning electron microscopy (FESEM), which revealed the polyhedral texture of the grains. Energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) studies were carried out to analyze the elemental composition and chemical states of the ions present in the compound. Fourier transform infrared (FT-IR) spectroscopy analysis revealed the vibrational modes corresponding to the tetrahedral and dodecahedral metal oxide bonds. The optical band gap was approximated to be in the range of 1.928 eV by using the Tauc relation. The CaCrO₄ catalyst with different contents (5, 20, 35, and 50 mg) was investigated for its photocatalytic performance for the degradation of RhB dye solution under sunlight irradiation using a UV-Vis spectrometer over the experimental wavelength range of 450-600 nm. The degradation efficacy increased from 70.630 to 93.550% for 5-35 mg and then decreased to 68.720% for 50 mg in 140 min under visible light illumination. The comparative study demonstrates that a higher degradation rate was achieved for cationic than anionic dyes in the order RhB > MB > MO. The highest deterioration (93.80%) was achieved for the RhB dye in 140 min. Equilibrium and kinetic studies showed that the adsorption process followed the Langmuir isotherm and pseudo-second-order models, respectively. The maximum adsorption capacity of 21.125 mg/g was observed for the catalyst concentration of 35 mg. From the cyclic test, it has been observed that the synthesized photocatalyst is structurally and morphologically stable and reusable. The radical trapping experiment demonstrated that superoxide and hydroxyl radicals were the primary species engaged in the photodegradation process. A possible mechanism for the degradation of RhB has been proposed. Hence, we conclude that CaCrO₄ can be used as an efficient photocatalyst for the remediation of organic dye pollutants from the environment.