Self-reinforcing photocatalytic decomplexation of heavy metal complexes and in-situ metal recovery via a BN/C3N4 S-scheme heterojunction.

Photocatalysis promises efficient treatment of toxic heavy metal complexes in wastewater, yet simultaneously achieving high catalytic performance and in-situ recovery of released metal ions remains challenging. This study reports a metal-free boron nitride/carbon nitride (BN/C3N4) S-scheme heterojunction, fabricated via simple ball-milling and calcination, for streamlined removal of Cu-ethylenediaminetetraacetic acid (Cu-EDTA) through photocatalytic activation of low-dose peroxymonosulfate (PMS). Theoretical calculations unveil that the internal electric field across the S-scheme heterojunction boosts charge transfer and separation, thereby promoting the generation of 1O2 and h+ as the primary active species for Cu-EDTA decomplexation. Consequently, the optimized BN/C3N4 photocatalyst achieves 99.6 % removal of Cu-EDTA within 180 min, with a photocatalytic efficiency 6.2 and 15.9 times higher than those of pristine C3N4 and BN, respectively. Moreover, the released Cu2+ ions can be spontaneously captured by BN/C3N4 and serve as new active sites to further activate PMS, creating a self-accelerating effect that enables near-complete Cu-EDTA removal over eight consecutive cycles. The BN/C3N4 photocatalyst also exhibits exceptional stability in the presence of coexisting ions and can be extended to other metal-EDTA complexes (e. g., Fe, Zn, Ni, Pb, Cr). This work provides a novel strategy for photocatalytic decomplexation of heavy metal complexes with simultaneous recovery of valuable metal resources.