Cobalt titanate nanocatalyst for enhanced photodegradation of atrazine: kinetics, degradation efficiency, and mechanistic analysis

In this study, cobalt titanate nanoparticles (CoTiO₃ NPs) were synthesized and applied as a photocatalyst to degrade atrazine. Scanning electron microscopic (SEM) analysis showed irregularly shaped particles prone to agglomeration, while X-ray diffraction (XRD) confirmed the formation of a rhombohedral CoTiO₃ phase with a crystallite size of 3.76 nm. Raman spectroscopic analysis showed vibrations typical for Ti-O and Co-O bonds and confirmed a well-defined cobalt titanate structure. Thermogravimetric analysis (TGA) showed that the nanoparticles remained stable up to 800 °C. The photocatalytic activity of CoTiO₃ NPs was tested under sunlight irradiation and the results obtained demonstrated excellent efficiency compared to the photolysis reaction. The efficiency was influenced by concentration (20-50 ppm), catalyst dosage (0.5-2.0 mg/L), pH (4.21-10.22), and irradiation time (0-120 min). The synthesized nanoparticles exhibited a surface area of 32.5 m²/g (DFT) and 828.03 m⁻¹ (BET), a pore volume of 0.03925 m³/g, and a bandgap energy of 2.66 eV. Kinetic studies demonstrated that the degradation followed the Langmuir-Hinshelwood model, with the photocatalytic reaction being the rate-determining step. Adsorption rate constants were found to range from 0.03828 to 0.166528 min⁻¹, while photocatalytic rate constants ranged from 0.373692 to 0.977135 min⁻¹. The CoTiO₃ NPs also showed excellent recyclability, maintaining high degradation efficiency after five cycles. Scavenger experiments confirmed that hydroxyl radicals (HO•) are responsible for atrazine degradation while GCMS analysis confirmed the complete mineralization of atrazine with carbon dioxide (CO₂) and water (H₂O) as the final degradation products.