Magnetically recyclable and remarkably efficient visible-light-driven photocatalytic hexavalent chromium removal based on plasmonic biochar/bismuth/ferroferric oxide heterojunction.

The development of easily recyclable non-noble metal plasmonic photocatalysts with high performance is highly desired for the removal of Cr(VI). Herein, the in-situ growth of plasmonic-bismuth (Bi) combined with magnetic ferroferric (Fe3O4) nanoparticles on biochar (BC) was realized by a facile high temperature calcination. BC/Bi/Fe3O4 exhibits broad photoabsorption from 200 to 2000 nm. The weaker photoluminescence (PL) spectrum or stronger photocurrent density confirmed its higher separation efficiency of photogenerated carriers than that of BC or Bi/Fe3O4. Under visible light irradiation, BC/Bi/Fe3O4 exhibits excellent adsorption-photocatalytic performance for Cr(VI) (95%) in 180 min. With BC/Bi/Fe3O4 as a working electrode, the higher removal efficiency (97%) was achieved than that using BC/Bi (65%), BC/Fe3O4 (79%) or Bi/Fe3O4 (66%) after 160 min under visible light irradiation, rooting from wide spectral absorption and efficient separation of photogenerated carriers. BC/Bi/Fe3O4 can be easily recycled by magnetism with good stability. This work not only provides ideas for the preparation of surface plasma resonance (SPR) semiconductor photocatalyst for removing heavy metal, but also realizes the resource utilization of agricultural and forestry waste.