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.

Enhanced porosity in marine biomass-derived activated carbon via two-step CO2 activation and acidic decontamination
    Abstract
        Graphical Abstract
    1 Introduction
    2 Experimental
        2.1 Preparation of precursor from MB
        2.2 Preparation of AC from precursor
        2.3 Characterizations
    3 Results and discussion
    4 Conclusion
    Acknowledgements 
    References

• Jueun Choi(Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Hyeonseok Yi(Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan, Institute for Materials Chemistry and Engineering, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Seong‑Ho Yoon(Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan, Institute for Materials Chemistry and Engineering, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Koji Nakabayashi(Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan, Institute for Materials Chemistry and Engineering, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Hyeonseok Yi(Institute for Materials Chemistry and Engineering, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Keiko Ideta(Institute for Materials Chemistry and Engineering, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Takaaki Shimohara(Institute for Materials Chemistry and Engineering, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Toru Kato(Environment and Process Research Department, The Japan Research and Development Center for Metals, 1‑5‑11 Nishishinbashi, Minato‑ku, Tokyo 105‑0003, Japan)
• Koji Saito(Nippon Steel Technology Co., Ltd., 1‑6‑1 Otemachi, Chiyoda‑ku, Tokyo 100‑0004, Japan)
• Hiroko Watanabe(Nippon Steel Technology Co., Ltd., 1‑6‑1 Otemachi, Chiyoda‑ku, Tokyo 100‑0004, Japan)
• Yoong Ahm Kim(Department of Polymer Engineering, Graduate School and School of Polymer Science and Engineering, Chonnam National University, 77 Yongbong‑ro, Buk‑gu, Gwangju 61186, Republic of Korea) Corresponding author