Hydrochar supported strategy for nZVI to remove bisphenol A and Cr(VI): Performance, synergetic mechanism, and life cycle assessment

Abstract

To comprehensively overcome the shortcomings and extend the application of nanoscale zero-valent iron (nZVI), a promising hydrochar supported strategy was provided. nZVI/Eupatorium adenophorum hydrochar (nZVI/EaHC) composite was attained under relatively mild reaction condition, and life cycle assessment revealed that the greenhouse gases emission, ecotoxicity, and resource consumption of nZVI/EaHC fabrication processes largely reduced in comparison with nZVI and pyrolysis biochar supported nZVI (nZVI/EaBC). Moreover, nZVI/EaHC exhibited an outstanding potential in reduction and immobilization of Cr(VI) as well as degradation of bisphenol A (BPA) via Fenton-like system. The static experiment showed that the removal efficiency achieved 99.21 % within 1 h for Cr(VI) and 97.9 % within 1 min for BPA, which significantly exceeded the performance of nZVI/EaBC, accompanied by a significant detoxification to non-harmful level and mineralization of 87.9 % within 10 min. The dynamic continuous flow column experiment indicated that 90 % Cr(VI) was removed within 40 min and 90 % BPA within 180 min under ultra-low-dosage of catalyst and H₂O₂. Furthermore, hydrochar supported strategy may reduce the economic cost and avoid secondary pollution due to the outstanding stability under aerobic condition and recyclability in magnetic field. The synergetic mechanisms were further revealed, the abundant oxygen-containing functional groups on EaHC facilitated the generation of electron-rich/poor centers via chemical bond bridge (COFe) and Fe-π interaction, which further enhanced the electron transfer to reduce Cr(VI) or promote the production of multiple reactive species including OH, O₂^–, and ¹O₂ to degrade BPA, additionally, persistent free radicals on EaHC also contributed to the degradation of BPA. Therefore, this efficient, applicable, and sustainable strategy may have a greatly practical outlook on nZVI application together with a comprehensive control and utilization of biomass including invasive plants.