https://doi.org/10.1016/j.ccst.2022.100059
“The application of biochar is of significant potential in CO2 capture due to its abundant sources, developed pore structures and relatively high adsorption capacity. However, there are still some shortcomings and limitations on its application in CO2 capture, and some more efforts has to be carried out as follows:
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CO2 adsorption capacity of biochar is lower than commercial activated carbon and the adsorption performance needs to be further optimized and improved. Possible approaches include optimizing the synthesis conditions and raw material selection to reduce the presence of contaminants in the raw material and reaction process, increasing the specific surface area, pore volume and surface functional groups of biochar, introducing surface functional groups, loading alkali and alkaline earth metals to improve the adsorption performance of biochar.
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For biochar with co-pyrolysis of multiple feedstocks, further analysis is also needed to determine whether the components of the different types interact with each other and whether the prepared biochar interacts with each other during the adsorption process. Furthermore, in the future, it could be investigated whether co-decomposition of biomass by adding another non-biomass (e.g., waste plastics, coal, and chemicals) could produce biochar with high adsorption capacity.
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Different modification methods have various effects on the physicochemical properties of biochar. In addition to the traditional physical and chemical modifications, there are also some emerging modification methods, including ultrasonic modification, microwave modification, plasma modification and electrochemical modification techniques that can adjust the surface functional groups and surface area of biochar. Therefore, more modification methods can be developed, and even combined modification of two or more methods can be attempted.
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Many studies have been conducted on various biochar production technologies and processes, but they are all general studies without detailed evaluation of the definite correlation between biochar characteristics and raw materials, manufacturing processes, or modifications that can be established to produce biochar with higher CO2 capture capacities. This work can benefit with raw material selection, production process adjustments and optimization, together with more efficient biochar applications.
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Currently, most of the studies on the adsorption of CO2 by modified biochar have been conducted in the lab scale. The practical environment is more complex and harsher than the laboratory environment, which may contain additional gasses such as nitrogen oxides and sulfur oxides, leading to uncertainties in the environmental impact of modified biochar. For the practical application of activated biochar, the dynamic adsorption, capturing CO2 from complex gas mixtures at different temperatures and pressures, and its deactivation resistance in harsh practical environments need to be studied in details.
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Biochar is stable and persists in the environment for a long time. Therefore, the development of environmentally friendly biochar composites is an important research direction. The potential ecotoxicity of biochar materials should be assessed before their introduction, the conversion process of biochar should be further studied and followed. The life cycle of biochar should be accurately evaluated, and various pollutants need to be assessed both after production and after application to reduce secondary pollution.
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