Enhanced porosity in marine biomass-derived activated carbon via two-step CO₂ activation and acidic decontamination

Marine biomass (MB) is gaining attention as a sustainable and eco-friendly carbon source within the carbon cycle, particularly in regions with extensive coastlines. However, the high content of alkali and alkaline earth metals (AAEMs) in MB poses challenges in producing functional carbon materials, like activated carbon (AC), with a high specific surface area (SSA). In this study, we employed a two-step CO₂ activation process, coupled with acid treatment, to successfully convert MB into highly porous AC. Preheating followed by nitric acid washing reduced AAEM content from 22.4 to 2.5 wt%, and subsequent atmospheric CO₂ activation produced AC with an SSA of 1700 m²/g and mesopores of 3–5 nm. A further treatment with a mixed acid solution of nitric and acetic acids reduced impurities to below 1.0 wt%. A second pressurized CO₂ activation at 1 MPa yielded AC with an SSA exceeding 2100 m²/g, with mesopores accounting for more than 50% of the total pore volume. This method demonstrates an effective approach to producing high-performance AC from MB for advanced applications.