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[Display omitted] • H 2 O 2 generated from PMS is critical precursors of 1O 2. • Co sites in ZIF-L@Fe 28 denote all 1O 2 , SO 4 ·−, ⋅O 2 −, ·OH and H 2 O 2 generation. • Fe sites prefer 1O 2 and H 2 O 2 generation via PMS*→H 2 O 2 →1O 2 pathway. Verifying the role of H 2 O 2 is a critical challenge for deepening the understanding of the mechanism of peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs). In this research, Co, Fe bimetallic organometallic frameworks (ZIF-L@Fe 28) were prepared, and their ultrahigh activities via H 2 O 2 generation at Fe and Co sites were experimentally and theoretically verified. The important contribution of H 2 O 2 to 1O 2 production was identified through the quantifications of the mutual transformation of active species. Co sites were identified as the most active positions for PMS activation because of they strongly triggered 1O 2 , SO 4 ·−, ⋅O 2 −, ·OH, and H 2 O 2. However, the self-quenching of active species suppressed the efficiency and selectivity of 1O 2 generation at Co sites. In contrast to Co sites, Fe sites had selective preference for H 2 O 2 generation, and the transformation of H 2 O 2 to 1O 2 further enhanced the performance of ZIF-L@Fe 28. The supplementary discussion from the perspective of H 2 O 2 will enable the further application of the PMS activation mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co-MOF/GO activated PMS could remove BAC in a wide pH range of 3–11. • SO 4 − and OH were identified as critical precursors for 1O 2 generation rather than DO and O 2 –. • Co (II) and Co (III) act as dominant active sites for PMS attachment. Peroxymonosulfate (PMS)-triggered non-radical pathways have potential for environmental application due to the high activity and pH tolerance of singlet oxygen (1O 2). However, the mechanism of 1O 2 generation remains unclear. Herein, new insights into 1O 2 generation are discussed based on the postulated precursors of PMS, DO, O 2 –, SO 4 −, and OH with Co-MOF/GO catalyst. According to experimental results and theoretical calculation, Co (II) and Co (III) were identified as dominant active sites for PMS attachment, leading to the simultaneous breakage of S-O and O-O bonds and the generation of SO 4 −, OH, and 1O 2. SO 4 − and OH were critical precursors for 1O 2 generation, while PMS self-decomposition had a small contribution. DO and O 2 – acted more likely as quenchers than vital precursors of 1O 2. Results provide in-depth understanding of the mechanism of 1O 2 generation to broaden the application prospects of PMS oxidation technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni and S atoms in Ni 3 (HTTP) 2 /GO had negligible contributions for catalysis directly. • Electron transfer via "GO-C-O-S-C-Ni 3 (HTTP) 2 " bridge was important for catalysis. • S atoms were more favorable for generating connection bridges than N and O atoms. Electron transfer capability as crucial properties of anode is directly related to electrocatalytic performance. However, the contributions of electron transfer were always under estimated due to the ambiguous mechanism of electrocatalysis. In this paper, a new electron transfer bridge was constructed in Ni 3 (HTTP) 2 /GO to provide a new insight into electrocatalytic performance enhancement. The contributions of active sites candidates, including metal sites, ligands (metal bridging atoms), and electron transfer bridges were innovatively separated. As replacement experimental results (of metal sites and metal bridging atoms), both metal sites and metal bridging atoms contributed slightly as the active center directly for the electrocatalytic degradation of tetracycline hydrochloride (TCH). The great improvement was attributed to the generation of "GO-C-O-S-C-Ni 3 (HTTP) 2 " bridges, in which S atoms from ligands were critical anchoring sites for the connection of two 2D layers (Ni 3 (HTTP) 2 and GO layer). The experimental and density functional theory results showed Ni 3 (HTTP) 2 could donate electrons to GO layers, leading the electrostatic imbalance of charge density to facilitate electron withdrawal from pollutions (not only TCH, but also dyes and complex microbial flora). The results of this paper provide a new strategy for improving electrocatalytic efficiency by adjusting electron transfer for novel practical applications of Ni 3 (HTTP) 2 /GO composites. [ABSTRACT FROM AUTHOR]