Origin of the Excellent Activity and Selectivity of a Single-Atom Copper Catalyst with Unsaturated Cu-N₂ Sites via Peroxydisulfate Activation: Cu(III) as a Dominant Oxidizing Species

Abstract

As an efficient active oxidant for the selective degradation of pollutants in wastewater, the high-valent copper species Cu­(III) with persulfate activation has attracted substantial attention in some Cu-based catalysts. However, the systematic study of a catalyst structure and mechanism about Cu­(III) with peroxydisulfate (PDS) activation is challenging owing to the coexistence of multiple Cu species and the structural symmetry of PDS. Herein, we anchored a Cu atom with two pyridinic N atoms to synthesize a single-atom Cu catalyst (CuSA-NC). Experimental characterizations and theoretical calculations complemented each other well because of the uniform atomic active sites. The single-atom Cu was identified as the active site, and the unsaturated Cu-N2 configuration was more conductive to PDS activation than the saturated Cu-N4 configuration. Benefiting from the generation of Cu­(III), CuSA-NC exhibited an obvious selective and anti-interference performance for pollutant degradation in a complex matrix. The superior catalytic activity of CuSA-NC compared with that of other reported Cu-based catalysts and good durability in a continuous-flow experiment further revealed the potential of CuSA-NC for practical applications. This work strongly deepens the understanding of the generation of Cu­(III) in a single-atom Cu catalyst with unsaturated Cu-N2 sites under PDS activation and develops an efficient approach for actual water purification.

Ozone Micronano-bubble-Enhanced Selective Degradation of Oxytetracycline from Production Wastewater: The Overlooked Singlet Oxygen Oxidation

“…In addition, in the TEMP-trapping EPR experiments at pH 11.0 (Figure e), the characteristic signals of the TEMP– 1 O 2 adducts ( a N = 17 G, triplet lines with a height ratio of approximately 1:1:1) provide more direct evidence. The signal intensity increases over time in the ozone MNB system and is significantly higher than those in the conventional ozone system.…”

Electrocatalytic Hydrogenation Boosts Reduction of Nitrate to Ammonia over Single-Atom Cu with Cu(I)-N3C1 Sites

“…The rational design of coordination environment around the single-atom Cu catalyst would be very important; for example, utilizing the unsaturated Cu–N 2 is beneficial to NO 3 RR and peroxydisulfate activation. , The special coordination environment and electronic structure caused by the oxidation state of copper atoms (Cu­(I)-N 3 C 1 ) allow for the adsorption of nitrate and hydrogen atoms at adjacent sites, which provide the following advantages for electrocatalytic reactions: (i) avoiding competition for active sites (e.g., HER), (ii) alleviating the desorption of intermediates, and (iii) facilitating the simultaneous adsorption-electrocatalytic hydrogenation due to the matched adsorption energy of reactants and *H. This finding can also provide fundamental basis for designing more efficient electrocatalysts for some hydrogenation reactions (electrocatalytic dechlorination, etc. ).…”

“…In Figure 2g, the Cu MNC-7 exhibits adsorption intensity between Cu 2 O and CuO at the rising-edge of ∼8978 eV, suggesting that the oxidation state of Cu sites is between +1 and +2, which is consistent with the XPS analysis. Only one prominent peak is observed at 1.53 Å in the Fourier transformed EXAFS (FT-EXAFS) spectrum of Cu MNC-7 (Figure 2h), which is attributed to the first coordination shell of Cu−N, 36 and there is no contribution of Cu−Cu bonds at 2.14 Å from Cu foil. Although the distances of Cu−N and Cu−O paths are similar in R-space, the Wavelet transform (WT) EXAFS contour of the Cu MNC-7 only plots one intensity maximum at 4.85 Å −1 in the k-space (Figure S9), corresponding to the Cu−N(C) pair and no intensity ascribed to the Cu oxides confirms the atomically dispersed Cu sites.…”

Single-Atom MnN5 Catalytic Sites Enable Efficient Peroxymonosulfate Activation by Forming Highly Reactive Mn(IV)–Oxo Species

“…The coordination number of M–N moieties in SACs strongly affects the geometric and electronic properties, as well as the catalytic activity of SACs. While SACs with a coordination number higher than four have been used for selective conversion of hydrocarbons and oxygen reduction reactions − and play prominent roles in biomimetic and enzymatic oxidation reactions, − the five-nitrogen coordinated SACs are seldom explored for persulfate activation except for Fe–N 5 SACs. , This represents a fundamental knowledge gap and a missed opportunity for coordination chemistry using other transition metal SACs (such as Co, Mn, Cu, and Ni) to boost PMS activation and enhance the degradation of recalcitrant organic pollutants. For instance, while Mn SACs have been tested for HVMO-dominated persulfate activation, five-nitrogen coordinated Mn SACs have not.…”