In this study, we developed a feasible and cost-effective method for obtaining porous carbon from cattail biomass as a promising material to be applied in various applications. The obtained carbon was further treated via CO2 activation without any other chemical reagents. The results showed that the as-prepared activated carbon had a high specific surface area of 441.12 m(2)/g after CO2 activation. Besides, the activated carbon showed excellent capacity to adsorb malachite green dye, and the effects of initial dye concentration, adsorption time, initial pH, and adsorption temperature were studied. Moreover, the activated carbon exhibited exceptional electrochemical performance as supercapacitors, with specific capacitance reaching 126.5 F/g at a current density of 0.5 A/g within a potential range of 1.0 to 0 V in a 6 M KOH solution. The excellent adsorption capacities and electrochemical performance suggested that the obtained activated carbon could be a promising candidate as an adsorbent and supercapacitor. (C) 2017 Elsevier B.V. All rights reserved.