Enhanced Carbon\nSequestration of Sustainable Biochar\nvia Metal Salt Regulation: Insight into Reaction Mechanism and Carbon\nFootprint

Sustainable biochar can sequester carbon and therefore,\nmitigate\nclimate change. However, only a small fraction of biomass carbon is\nretained during biochar synthesis, greatly restricting its carbon-sequestration\ncapacity. A significant boost of the carbon-sequestration potential\nof biochar has so far been a challenge. This study reveals that when\nbiochar is modified by FeCl<sub>3</sub>, its carbon-sequestration\ncapacity is boosted to 247.73% of that of pristine biochar derived\nat 500 °C. Meanwhile, pristine biochar retains only 43.18% of\nits biomass carbon, while FeCl<sub>3</sub>-modified biochar retains\n75.20% of its carbon by forming complexes between the iron salts and\nthe carboxyl- and hydroxyl-rich organic compounds derived from biomass\npyrolysis. As react proceeds, the complexes are further converted\ninto ferrites and organic carbon. The resulting minerals provide physical\nbarriers against carbon decomposition, further enhancing the long-term\nstability of biochar. Life cycle assessment results further show that\nferric salt can markedly enhance the greenhouse gasreduction\npotential of <i>biomass-to-biochar-to-soil</i> systems.\nThe more cycles from biomass to upgraded biochar, the more potent\nthe carbon-negative effect is. Undoubtedly, such discoveries hold\nsignificant implications for accelerating carbon neutrality.