Activated carbon (AC) has proven to be an effective adsorbent for gas and liquid. However, the production of AC involves high energy consumption and the use of limited nonrenewable resources as feedstock. In this study, activated carbon was synthesized through hydrothermal carbonization (HTC) at a low temperature using coconut shells and microalgae. The adsorbents were characterised by Fourier Transform Infrared Spectroscopy (FTIR) to determine the surface function. The results indicate that the coconut shell activated carbon (CSAC) precursor had a higher yield compared to microalgae-based activated carbon (MAAC). However, the carbon dioxide (CO2) uptake of MAAC at 1.0 bar is 115.4 higher. A combination of algae and coconut shells as feedstock resulted in competitive activated carbon compared to MAAC (7.74 wt instead of 8.28 wt). The results of this study suggest that waste biomass hydrochars could be considered as low-cost adsorbents for carbon dioxide removal and that this would be useful in environmental applications for post-combustion carbon capture. © 2023 Institute of Physics Publishing. All rights reserved.