Cobalt oxide (Co₃O₄) catalysts synthesized using green methods were studied in the context of sodium borohydride (NaBH₄) hydrolysis, with in-situ reduction observed during the reaction. The research focuses on the impact of varying ratios of Solanum lycopersicum (tomato) leaf extract and cobalt acetate hexahydrate, as well as calcination temperatures, on the catalysts’ structural and catalytic properties. X-ray diffraction (XRD) analysis confirmed the face-centered cubic structure of the synthesized nanoparticles, with characteristic peaks corresponding to specific crystallographic planes. The study highlights that higher calcination temperatures (up to 900 °C) improved crystallinity, as evidenced by sharper diffraction peaks in samples like PWB600 and PWB900 compared to those calcined at lower temperatures.
The thermal stability of the Co₃O₄ catalysts was verified up to 900 °C, with no detectable phases of carbon species or cobalt compounds such as Co(OH)₂ or CoO. Magnetic properties observed in PWB600 and PWB900 catalysts were attributed to in-situ reduction during NaBH₄ hydrolysis. XRD patterns remained consistent before and after the reaction, indicating structural retention despite peak intensity reductions. Energy-dispersive X-ray (EDX) spectroscopy confirmed elemental composition, while scanning electron microscopy (SEM) images revealed morphological variations across different synthesis conditions.
Crystal Structure and Thermal Stability
The XRD patterns of calcined Co₃O₄ catalysts at varying temperatures and extract ratios confirmed a face-centered cubic structure, with peaks matching JCPDS card No. 03-065-3103. Key diffraction planes included (111), (220), (311), (222), (400), (422), (511), and (440), indicating high purity and crystallinity. The cubic phase remained stable up to 900 °C, with increased calcination temperatures correlating with sharper, more intense peaks. This suggests improved crystallinity at higher temperatures, as observed in PWB600 and PWB900 samples compared to lower-temperature counterparts.
Effect of Calcination Temperature on Crystallinity
Calcination temperature played a critical role in determining the crystallinity of Co₃O₄ nanoparticles. At 600 °C and 900 °C, the (311) plane exhibited narrower peaks, indicating enhanced crystallinity. The study notes that calcination above 700 °C may introduce mixed phases like CoO due to oxygen vacancies, but the cubic structure of Co₃O₄ remained dominant. These findings show that precise temperature control is important for synthesizing high-performance catalysts.
Catalytic Performance and Structural Retention
Post-reaction XRD analysis of the PWB600 catalyst revealed no changes in chemical structure, though peak intensities decreased. This suggests the catalyst retained its crystalline form during NaBH₄ hydrolysis, with magnetic properties arising from in-situ reduction. The absence of amorphous CoₓB phases, which can interfere with crystallinity, was confirmed through comparisons with prior studies. While the research emphasizes structural and thermal characteristics, specific catalytic activity metrics for hydrogen generation were not detailed in the source material.