Homogeneous dispersion of amorphous nanoscale zero-valent iron supported on chlorella-derived biochar: In-situ synthesis and application mechanism for Cr(VI) removal over a wide pH range

[Display omitted] •Chlorella pyrenoidosa (CP) biochar rich in acidic functional groups was synthesized.•Effective Cr (VI) removal by nZVI@CP-BC over a wide pH range (3.0–11.0).•Prominent synergistic effect activated high-efficiency of Cr(VI) removal.•Detailed passivation mechanism of nZVI in reaction was investigated.•CP-BC mediated pH changes potentially contributed to Cr(VI) removal. Novel recyclable chlorella pyrenoidosa-derived biochar (CP-BC) supported nanoscale zero-valent iron composite (nZVI@CP-BC) was developed via an in-situ liquid-phase chemical reduction-deposition method. The obtained adsorbent kept prominent hexavalent chromium (Cr(VI)) removal capacity with a broad pH range (3.0–11.0). Also, these findings revealed that the removal performance of Cr(VI) via nZVI@CP-BC was 1.37, 6.67 and 1.25 times more than that of pristine nZVI, unmodified CP-BC and nZVI + CP-BC, respectively. The exceptional Cr(VI) removal benefited from the combination of high-reactivity nZVI and CP-BC resulting in an effective synergy. The physicochemical property of the nZVI@CP-BC was systematically elucidated utilizing multiple characterizations. It is launched that the Cr(VI) molecules were converted into Cr(Ⅲ) mainly via surface adsorption and chemical reduction. And CP-BC may regulate beneficial conditions for Cr(VI) chemical reduction reaction via largely mediating solution pH and electron transfer, which showed a rational reaction mechanism of promoted removal of Cr(VI) under a broad working pH range. The corrosion mechanism of nZVI in the whole reaction was also studied thoroughly. This work indicates that this novel nZVI@CP-BC would be a prominent material for the preferable remediation of Cr(VI)-bearing wastewater.