Abstract 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.