One step fabrication of carbon supported cobalt pentlandite (Co₉S₈) via the thermolysis of lignin and Co₃O₄

This work proposed a new method for one step fabrication of carbon supported (biochar) Co₉S₈ composite via the thermo-chemical process of cobalt oxide (Co₃O₄) and lignin under CO₂ atmosphere. A series of pyrolysis were conducted in N₂ and CO₂ environment, and their thermal degradation behaviors were characterized. The thermogravimetric analysis tests revealed that CO₂ did not affect physical aspects of the thermal degradation. However, the influence of CO₂ on chemical aspects governing the thermal degradation mechanisms was apparent. As an example of it, carbon supported (biochar) Co₉S₈ composite was only generated in CO₂ environment. The surface morphology and structural matrix of biochar generated from CO₂ environment was characterized using various spectroscopic instruments, which confirmed the formation of Co₉S₈. The formation of Co₉S₈ was highly affected by the pyrolytic parameters such as temperature and duration for isothermal run. Furthermore, use of CO₂ as the reaction medium provided an effective way for modifying pore structure of biochar. More importantly, the formation of highly porous structure and Co₉S₈ in the presence of CO₂ imparted strong catalytic capability. The reaction kinetics of p-nitrophenol (PNP) reduction using CO₂-700 °C and CO₂-760 °C biochar was 9 × 10^-3 and 18 × 10^-3 s^-1, respectively, of which performance was superior to other catalytic materials in the literature. Lastly, the successive PNP reduction tests revealed the invulnerable catalytic capability up to 10 PNP reduction cycles. Thus, all experimental findings in this study suggests that Co₉S₈ could be synthesize from the waste materials and CO₂. Moreover, Co₉S₈ could be employed as an effective catalyst in the environmental applications.