Pyrolytic synthesis of graphene-encapsulated zero-valent iron nanoparticles supported on biochar for heavy metal removal
Tharindu N. Karunaratne, R. M. Oshani Nayanathara, Chanaka M. Navarathna, Prashan M. Rodrigo, Rooban V. K. G. Thirumalai, Charles U. Pittman, Yunsang Kim, Todd Mlsna, Jilei Zhang, Xuefeng Zhang
Biochar ›› 2022, Vol. 4 ›› Issue (1) : 0.
Pyrolytic synthesis of graphene-encapsulated zero-valent iron nanoparticles supported on biochar for heavy metal removal
| • | BC-G@Fe0 nanocomposite was produced through two carbothermal reduction routes. |
| • | The biomass impregnating-carbonizing route produced graphene-encapsulated iron carbide (Fe3C) nanoparticles. |
| • | The pyrolyzing-biochar-impregnating-carbonizing route produced graphene-encapsulated nanoscale zero-valent iron particles. |
| • | BC-G@Fe0 nanocomposites exhibited good heavy metal ion removal performance. |
Biochar (BC)-supported graphene-encapsulated zero-valent iron nanoparticle composites (BC-G@Fe0) are promising engineering nanocomposites that can be used to scavenge heavy metal from wastewater. However, the production of BC-G@Fe0 through carbothermal reduction using biomass as a carbon source remains challenging because of biomass pyrolysis complications. Here, we examined two carbothermal reduction routes for preparing BC-G@Fe0 using bamboo as the carbon source. The first route impregnated Fe ions (Fe2+/3+) into unpyrolyzed bamboo particles initially, followed by carbonization at 600–1000 °C. This process produced BC-G@Fe0 dominated by iron carbide (Fe3C), which led to low heavy metal removal efficiency (i.e., Cu2+ capacity of < 0.3 mmol g−1). In the second route, bamboo particles were pyrolyzed (600 °C) to biochar first, followed by impregnating this biochar with Fe ions, and then carbonized at 600–1000 °C. This route produces zero-valent iron nanoparticles, which resulted in high heavy metal removal capacities (i.e., 0.30, 1.58, and 1.91 mmol g−1 for Pb2+, Cu2+, and Ag+, respectively). The effects of carbonization temperature (600–1000 °C), iron source (i.e., iron nitrates, iron sulfate, ferrous chloride, and ferric chloride), and iron loading (5–40%) on the morphology, structure, and heavy metal ion aqueous uptake performance of BC-G@Fe0 were also investigated. This study revealed the formation mechanisms of BC-G@Fe0 through biomass carbothermal reduction, which could guide the application-oriented design of multifunctional iron-BC composites for water remediation.
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