This study embarks on the synthesis of activated carbon (AC) from cashew nut shells using a potassium carbonate (K2CO3) activation process, with a specific focus on its practical application in high-pressure gas adsorption. Among the synthesized samples, MCAK85 emerged as the most efficient, demonstrating a specific surface area of 1693 m2/g and total and micropore volumes of 0.839 cm3/g and 0.641 cm3/g, respectively. Importantly, this bioorganic activated carbon exhibited high sorption capacities for CO2 and CH4, with uptake values of 11.0 mmol/g and 5.5 mmol/g at 10 bar at 25°C, and a CO2/CH4 selectivity range between 9.1 and 1.8. A comprehensive range of characterization techniques were employed to analyze the structural and chemical properties of the synthesized AC, providing valuable insights into the functional groups and molecular structure. The morphology of the AC was examined using SEM, while the point of zero charge was determined to understand the surface charge characteristics. Additionally, TGA was utilized to assess the thermal stability and composition of the AC. This study underscores the potential of utilizing agricultural waste, specifically cashew nut shells, in the creation of effective materials for gas storage and purification applications. The high-pressure adsorption capacity of the produced AC, coupled with its sustainable and eco-friendly nature, underscores its suitability for environmental and industrial applications, particularly in areas focusing on greenhouse gas capture and air purification, thereby inspiring further research and development in this field. Display omitted •Cashew shells transformed into activated carbon, optimizing waste utilization.•MCAK85: Outstanding textural features - 1693 m2/g surface, 0.839 cm3/g pore volume.•MCAK85 shows high adsorption: 11.0 mmol/g CO2, 5.5 mmol/g CH4 uptake at 25°C, 10 bar.•MCAK85's attributes suggest environmental viability in gas storage and air purification.•Activated carbons exhibits CO2/CH4 selectivity from 9.1 to 1.8.