Recent advances in the development of engineered biochar for CO2 adsorption: Research on heteroatom-doped biochar

With rising atmospheric CO2 levels driving global warming, carbon capture and storage (CCS) technologies are critical. Biochar, an eco-friendly and cost-effective carbon material, has gained attention for low-temperature CO2 capture due to its sustainable adsorption properties. However, raw biochar’s limited pore structure and surface chemistry hinder its efficiency. Among modification strategies, heteroatom doping is particularly effective. By enriching functional groups and tuning the carbon framework, this approach significantly improves CO2 capture performance. This review explores recent advancements in the development of engineered biochar for CO2 adsorption, with a focus on heteroatom doping techniques. Additionally, key quantitative performance metrics were compiled and compared, including adsorption capacities and isosteric heats of adsorption (Qst) (and, where available, selectivity/working capacity), to quantify how different doping strategies alter gas uptake and binding strength and to establish structure-performance relationships. Among various dopants (such as nitrogen, sulfur, phosphorus, and boron), nitrogen doping has attracted much attention due to its significant enhancement in the ability to capture CO2. This is mainly because nitrogen atoms can more effectively regulate the electronic structure and pore structure of the material in a coordinated manner, thereby enhancing the dual effects of physical and chemical adsorption on CO2. A critical comparison is made between pre-modification doping (incorporating heteroatoms during biomass carbonization) and post-modification doping (treating already-formed biochar), revealing that pre-modification generally offers superior doping efficiency and structural stability. Moreover, the review examines co-doping strategies, where synergistic effects between multiple elements, as exemplified by nitrogen-phosphorus co-doping or nitrogen-sulfur co-doping of biochar, further optimize the adsorption capacity. Finally, critical barriers to industrialization, including techno-economic feasibility and regeneration energy costs, are discussed. Future perspectives emphasize the integration of machine learning for rational design, standardized characterization protocols, and life-cycle assessments (LCA) to accelerate the deployment of biochar in practical CCUS applications. The review highlights the mechanisms of CO2 capture, emphasizing the balance between physical adsorption and chemisorption. The challenges for development of engineered biochar for CO2 capture are prospected. Further research on improving chemical adsorption performance while preserving physical adsorption properties is still required to improve biochar’s application in sustainable CO2 capture technologies.