Oxygen vacancy-dominated activation of peroxydisulfate and removal of tetracycline：The synergistic contribution of dual-metal cycling and the prominent role of non-radical pathway

Abstract

In this study, a nitrogen-rich porous carbon substrate (NC) doped with NiO and Mo2N-γ was prepared using zeolitic imidazolate framework-8 (ZIF-8) through processes of acid etching and calcination to create a bimetallic catalyst with optimized oxygen vacancies (NiMo-NC/A(2)). This catalyst displayed remarkable peroxydisulfate (PDS) activation, achieving a 90.9% of tetracycline (TC) removal in 60min. The NiMo-NC/A(2)/PDS system showed superior resilience to various interferences, performing well over a wide range of pH levels (3-11) and in wastewater with different background ions and organic substances. This research revealed that the strategic incorporation of OVs into the catalyst not only could substantially amplify its PDS adsorptive affinity, consequently lowering the PDS activation energy threshold and bolstering the production of singlet oxygen (1O2) and some superoxide anions (O2·-), but was also able to propel the redox cycling of the Ni and Mo constituents, thereby invigorating the PDS activation to yield a series of reactive oxygen species (ROS). The Ni-Mo metal sites on the catalyst's surface were capable of adsorbing PDS molecules, forming metastable complexes (PDS*), which hastened the electron transfer-mediated TC adsorption. Meanwhile, the pyrrolic and graphitic N embedded within the carbon matrix accelerated the PDS activation by adsorbing both TC and PDS, assisting the TC's removal. In summary, this work highlighted the critical impact of optimal OVs content on enhancing the catalytic efficiency of the bimetallic catalyst, elucidated the mechanism of PDS activation for effective TC removal, and offered a new direction for developing eco-friendly catalysts for PDS-based contaminant removal.