pH-driven HO•/Cu(III) trade-off mediated by surface CuxO shell in zerovalent copper-activated peracetic acid process

pH switches reactive species in ZVC/PAA: HO • at pH 3, Cu(III) at pH 7. • Surface Cu x O shell is the key site governing the generation of reactive species. • HO • -dominated system rapidly removes diverse sulfonamides with non-selectivity. • Cu(III) system selectively degrades sulfonamides containing heterocyclic rings. • ZVC demonstrates higher reusability and lower Cu ions leaching at pH 7. Zerovalent copper (ZVC) has garnered considerable attention in Fenton-like reactions, but the surface properties of ZVC that regulate reactive species (RSs) generation remain elusive. Herein, we systematically investigated the pH-dependent regulation of hydroxyl radical (HO • ) and high-valent copper (Cu(III)) generation during peracetic acid (PAA) activation by ZVC for the degradation of sulfonamide antibiotics (SAs). Characterization results revealed that ZVC has a core-shell structure, in which the surface copper oxide (Cu x O) layer serves as the primary active site. Theoretical and experimental analyses elucidated that pH modulates the surface properties of ZVC. At pH 3, the protonation of Cu x O promotes the generation of HO • in the ZVC/PAA system; conversely, under neutral conditions (pH 7.0), the unprotonated state favors the formation of Cu(III) as the dominant RSs. This trade-off between HO • and Cu(III) generation leads to distinct degradation performance for SAs degradation. HO • -dominated system achieved non-selective removal (>96 %) of various SAs; whereas the Cu(III) pathway selectively degraded SAs with heterocyclic rings at pH 7. The Cu(III) pathway outperformed the HO • system in terms of humic acid tolerance and catalyst recyclability in the ZVC/PAA process. This work clarifies the decisive role of surface protonation of ZVC in steering HO • versus Cu(III) pathways and provides a theoretical basis for designing pH‑specific Fenton-like reaction processes. Download: Download high-res image (355KB) Download: Download full-size image