Removal of trichloroethene by iron-based biochar from anaerobic water: Key roles of Fe/C ratio and iron carbides

Nanoscale zero-valent iron (nZVI) is widely studied for environmental remediation in recent years. However, its easy agglomeration, vulnerable oxidation, and runoff limit its practical application. Herein, iron-based lignin-derived biochar composites (Fe-LBC) with different Fe/C ratios were synthesized using a facile carbothermal reduction method and applied for trichloroethene (TCE) removal from anaerobic water. The synthesized Fe-LBC was equipped with higher specific surface area, more uniform nanoparticles distribution, and higher iron carbide content with the decrease of Fe/C ratio from about 1:5 (Fe-LBC 5 ) to 1:30 (Fe-LBC 30 ). TCE removal by Fe-LBC firstly increased as the Fe/C ratio increased from 1:10 6 to 1:10 3 , and then decreased with the Fe/C ratio further increased to 1:5. The removal efficiency remained largely stable (97.0–98.5%) within the Fe/C ratio range of 1:10 4 -1:30. Fe-LBC 30 (1.0 g L −1 ) could remove 97.4% of TCE (10.4 mg L −1 ), and owned the highest dechlorination efficiency (30.0%). Iron carbides but not Fe 0 could mainly contribute to the dechlorination. The quenching experiment reveals atomic hydrogen (H*) formed under the catalysis of iron carbides, and 1,2-dichloroethene was identified as the main degradation product derived from hydrogenolysis; electrochemical analyses suggest iron carbides could also serve as electron donors to TCE. Moreover, Fe-LBC 30 maintained excellent TCE removal efficiency in various water matrixes and pH range of 3–9, revealing its high application potential in practical groundwater remediation. This work firstly demonstrated the reductive dechlorination action of iron carbides rather than nZVI in iron-biochar hybrid materials, boosting our knowledge and potential application of iron-based materials.