H3PO4 activation mediated the iron phase transformation and enhanced the removal of bisphenol A on iron carbide-loaded activated biochar

Zero valent iron-loaded biochar (Fe0-BC) has shown promise for the removal of various organic pollutants, but is restricted by reduced specific surface area, low utilization efficiency and limited production of reactive oxygen species (ROS). In this study, iron carbide-loaded activated biochar (Fe3C-AB) with a high surface area was synthesized through the pyrolysis of H3PO4 activated biochar with Fe(NO3)3, tested for removing bisphenol A (BPA) and elucidated the adsorption and degradation mechanisms. As a result, H3PO4 activated biochar was beneficial for the transformation of Fe0 to Fe3C. Fe3C-AB exhibited a significantly higher removal rate and removal capacity for BPA than that of Fe0-BC within a wide pH range of 5.0-11.0, and its performance was maintained even under extremely high salinity and different water sources. Moreover, X-ray photoelectron spectra and density functional theory calculations confirmed that hydrogen bonds were formed between the COOH groups and BPA. 1O2 was the major reactive species, constituting 37.0% of the removal efficiency in the degradation of BPA by Fe3C-AB. Density functional reactivity theory showed that degradation pathway 2 of BPA was preferentially attacked by ROS. Thus, Fe3C-AB with low cost and excellent recycling performance could be an alternative candidate for the efficient removal of contaminants.

Automated summary

This study synthesized iron carbide-loaded activated biochar with a high surface area, which exhibited higher removal rate and capacity for bisphenol A (BPA) compared to traditional zero valent iron-loaded biochar. The adsorption and degradation mechanisms were explored, showing that hydrogen bonds were formed between the COOH groups and BPA and that 1O2 was the major reactive species in the degradation process. Density functional reactivity theory also revealed the preference of ROS attacking degradation pathway 2 of BPA. Therefore, this iron carbide-loaded biochar can be a cost-effective and efficient alternative for contaminant removal.