Structural and catalytic properties of sol–gel derived iron-doped calcium cobalt oxide Ca₃Co_2−xFe_xO₆

This study presents a novel cobalt-based catalyst, iron-doped calcium cobalt oxide (Ca₃Co_2−xFeₓO₆, with x ranging from 0 to 0.3) for the reduction of 4-nitrophenol with NaBH₄ in aqueous solutions. The catalyst was synthesized using a sol–gel method, and then examined for the structure and catalytic performance. Based on FTIR analysis, the optimal synthesis conditions were an annealing temperature of 1000 °C for 10 h, resulting in high purity and crystallinity. Scanning electron microscopy (SEM) analysis showed increased particle sizes with higher iron content. X-ray diffraction (XRD) analysis confirmed the phase purity of the samples and an average crystallite size of 21.6 ± 0.2 nm. Brunauer–Emmett–Teller (BET) equation analysis of nitrogen physisorption at 77 K revealed that iron doping significantly influenced the surface area and porosity of Ca₃Co_2−xFeₓO₆, with an optimal doping level (x = 0.1) maximizing these properties, while higher concentrations led to a decline due to potential pore blockage or densification. These nitrogen physisorption results correlated well with the catalytic activity, as the Ca₃Co_1.9Fe_0.1O₆ composition exhibited the highest reaction rate for reducing 4-nitrophenol, with optimal performance achieved at a pH of 8. Reusability tests demonstrated that the catalyst remained relatively stable over 5 reuse cycles. This research provides valuable insights into the synthesis, structure, and catalytic performance of iron-doped calcium cobalt oxide materials, which have potential applications in environmental remediation and energy-related processes.