In this study, a carbonaceous material was obtained from the thermal decomposition of a non-pretreated rice husk in a pyrolysis system with controlled nitrogen at 700, 800, 900, and 1000 °C. The characterization of the material was performed using various analytical techniques. The results of these characterizations indicate that the obtained carbonaceous material can achieve a surface area of 450 m²/g, with a microporous volume of 0.15 cm³/g. Furthermore, the presence of oxygenated function groups, predominantly hydroxyl (C-OH) and epoxy (C-O-C), along with amorphous silicon, was identified. Additionally, the material’s CO₂ adsorption capacity was assessed, revealing a maximum capacity of 1.0 mmol/g. The findings of this study suggest that the CO₂ adsorption effectiveness can be impacted by the presence of specific functional groups. These groups have been shown to enhance the material’s affinity for CO₂, along with its porosity and surface area. In this sense, a notable correlation was identified between the oxygenated function group content and CO₂ adsorption capacity. Also, the adsorption isotherm modeling showed an excellent fit to the Langmuir model, indicating monolayer adsorption on a homogeneous surface.