This study is carried out for a comparative screening of three groups of biomasses; soft or non-woody (peanut shell); intermediate woody (walnut shell) and hard woody (pine wood) for the development of adsorbents/activated carbons for post-combustion CO2 capture (over N2 balance). Three different groups of biomass residues are selected to study the role and nature of the material in adsorption and selection of the raw material for CO2 adsorbents synthesis for future researches because of the hot issue of anthropogenic CO2 emissions. The adsorption isotherms studied by the thermal gravimetric analyser (TGA) revealed that CO2 adsorption capabilities are in the range of 2.53–3.92 mmol/g (over N2 balance) at 25 °C. The newly synthesised activated carbons (ACs) exhibited a fast rate of adsorption as 41–94% in the initial 2 min. Porous surface development with catalytic KOH activation is seen clearly through SEM surface morphological analyses and mathematically confirmed from SBET ranges from 146.86 to 944.05 m2/g. FTIR and XRD peaks verify the generation of basic or inorganic O2-rich moieties that help in acidic CO2 capture. It has also been observed from adsorption isotherms that the order of higher adsorption groups is as; peanut shell > pine wood > walnut shell, while the best activation mass ratio (sample/KOH) is 1:3. The synthesised low cost ACs with an amount of 1.93 US$ per kg production could help to overcome the environmental hazards and problems caused by CO2 and biomass waste.