Pyrolytic synthesis of graphene-encapsulated zero-valent iron nanoparticles supported on biochar for heavy metal removal
Tharindu N. Karunaratne, R.M. Oshani Nayanathara, Chanaka Navarathna, Prashan M. Rodrigo, Rooban Venkatesh K.G. Thirumalai, Charles U. Pittman, Yunsang Kim, Todd Mlsna, Jilei Zhang, Xuefeng Zhang
Abstract
Abstract Biochar (BC)-supported graphene-encapsulated zero-valent iron nanoparticle composites (BC-G@Fe 0 ) are promising engineering nanocomposites that can be used to scavenge heavy metal from wastewater. However, the production of BC-G@Fe 0 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@Fe 0 using bamboo as the carbon source. The first route impregnated Fe ions (Fe 2+/3+ ) into unpyrolyzed bamboo particles initially, followed by carbonization at 600–1000 °C. This process produced BC-G@Fe 0 dominated by iron carbide (Fe 3 C), which led to low heavy metal removal efficiency (i.e., Cu 2+ 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 Pb 2+ , Cu 2+ , 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@Fe 0 were also investigated. This study revealed the formation mechanisms of BC-G@Fe 0 through biomass carbothermal reduction, which could guide the application-oriented design of multifunctional iron-BC composites for water remediation. Graphical Abstract