Self-reinforcing photocatalytic decomplexation of heavy metal complexes and in-situ metal recovery via a BN/C3N4 S-scheme heterojunction
Shenghu Wang, Huanji Song, Dongcheng Li, Yuyang Dong, Xianying Xu, Shihao Yang, Weiyang Lv
Abstract
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/C 3 N 4 ) 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 1 O 2 and h + as the primary active species for Cu-EDTA decomplexation. Consequently, the optimized BN/C 3 N 4 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 C 3 N 4 and BN, respectively. Moreover, the released Cu 2+ ions can be spontaneously captured by BN/C 3 N 4 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/C 3 N 4 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.