Versatile pathways for oxidating organics via peroxymonosulfate activation by different single atom catalysts confining with Fe–N4 or Cu–N4 sites

Efficient diclofenac removal by superoxide radical and singlet oxygen generated in surface Mn(II)/(III)/(IV) cycle dominated peroxymonosulfate activation system: Mechanism and product toxicity

Transition metal single-atom embedded on N-doped carbon as a catalyst for peroxymonosulfate activation: A DFT study

Multi-pathway on peroxymonosulfate activation by single cobalt atoms incorporated on CuO with enriched oxygen vacancies for high-efficient oxidation of tetracycline

Bioinspired axial S-coordinated single-atom cobalt catalyst to efficient activate peroxymonosulfate for selective high-valent Co-Oxo species generation

Precise modulation of the axial coordination microenvironment in single-atom catalysts (SACs) to enhance peroxymonosulfate (PMS) activation represents a promising yet underexplored approach. This study introduces a pyrolysis-free strategy to fabricate SACs with well-defined axial-FeN4+1 coordination structures. By incorporating additional out-of-plane axial nitrogen into well-defined FeN4 active sites within a planar, fully conjugated polyphthalocyanine framework, FeN4+1 configurations are developed that significantly enhance PMS activation. The axial-FeN4+1 catalyst excelled in activating PMS, with a high bisphenol A (BPA) degradation rate of 2.256 min-1, surpassing planar-FeN4/PMS systems by 6.8 times. Theoretical calculations revealed that the axial coordination between N and the Fe sites forms an optimized axial FeN4+1 structure, disrupting the electron distribution symmetry of Fe and optimizing the electron distribution of the Fe 3d orbital (increasing the d-band center from -1.231 to -0.432eV). Consequently, this led to an enhanced perpendicular adsorption energy of PMS from -1.79 to -1.82eV and reduced energy barriers for the formation of the key reaction intermediate (O*) that generates 1O2. This study provides new insights into PMS activation through the axial coordinated engineering of well-defined SACs in water purification processes.

Directing the persulfate activation reaction pathway by control of Fe-Nx/C single-atom catalyst coordination

The microenvironment regulation of Fe-N4 single atom catalysts (SACs) critically governs peroxymonosulfate (PMS) activation. Although conventional heteroatom substitution in primary coordination enhances activity, it disrupts Fe-N4 symmetry and compromises stability. Herein, we propose oxygen doping in the secondary coordination shell to construct Fe-N4-C6O2 SAC, which amplifies the localized electric field while preserving the pristine coordination symmetry, thus trading off its activity and stability. This approach suppresses Fe-N bond structural deformation (bond amplitude reduced from 0.875–3.175 Å to 0.925–2.975 Å) during PMS activation by lowering Fe center electron density to strengthen Fe-N bond, achieving extended catalytic durability (>240 h). Simultaneously, the weakened coordination field lowers the Fe=O σ* orbital energy, promoting electrophilic σ-attack of high-valent iron-oxo towards bisphenol A, and increasing its degradation rate by 41.6-fold. This work demonstrates secondary coordination engineering as a viable strategy to resolve the activity-stability trade-off in SAC design, offering promising perspectives for developing environmental catalysts.

Single atom catalysts (SACs) are atomic-level-engineered materials with high intrinsic activity. Catalytic centers of SACs are typically the transition metal (TM)-nonmetal coordination sites, while the functions of coexisting non-TM-bonded functionalities are usually overlooked in catalysis. Herein, the scalable preparation of carbon-supported cobalt-anchored SACs (CoCN) with controlled Co─N sites and free functional N species is reported. The role of metal- and nonmetal-bonded functionalities in the SACs for peroxymonosulfate (PMS)-driven Fenton-like reactions is first systematically studied, revealing their contribution to performance improvement and pathway steering. Experiments and computations demonstrate that the Co─N3C coordination plays a vital role in the formation of a surface-confined PMS* complex to trigger the electron transfer pathway and promote kinetics because of the optimized electronic state of Co centers, while the nonmetal-coordinated graphitic N sites act as preferable pollutant adsorption sites and additional PMS activation sites to accelerate electron transfer. Synergistically, CoCN exhibits ultrahigh activity in PMS activation for p-hydroxybenzoic acid oxidation, achieving complete degradation within 10min with an ultrahigh turnover frequency of 0.38min-1, surpassing most reported materials. These findings offer new insights into the versatile functions of N species in SACs and inspire rational design of high-performance catalysts in complicated heterogeneous systems.

Degradation of chlorophenols via peroxymonosulfate activation by Fe-Co bimetallic single-atom catalyst

Theoretical study of local S coordination environment on Fe single atoms for peroxymonosulfate-based advanced oxidation processes

Bio-porphyrin supported single-atom iron catalyst boosting peroxymonosulfate activation for pollutants degradation: A Singlet Oxygen-dominated nonradical pathway

Water contamination by refractory organics is one of the most critical and challenging problems in industrialization. Advanced oxidation processes based on peroxymonosulfate (PMS) activation is increasingly becoming popular due to its high ability to completely decompose toxic and refractory organic pollutants. Heteroatom-doped nanocarbons have attracted considerable attention over the conventional metal-based catalysts (e.g., Fe- or Co-based catalyst, etc.) to activate PMS, because carbocatalysts with the environmentally benign nature, corrosion resistance and biocompatibility can overcome the sintering and metal leaching problems caused by metal-based catalysts. The main objective of this study is to fabricate carbocatalysts to activate PMS for the degradation of recalcitrant organic contaminants, especially sulfonamide antibiotics in the aqueous environment. In the first part of this study, nitrogen-doped graphenes (NG) was fabricated to activate PMS for sulfacetamide (SAM) degradation. The contents of reactive functional groups and catalytic performance of NG were delicately controlled by adjusting thermal annealing temperature. NG600 (NG thermally annealed at 600°C) with the optimized amount of N species and C=O group exhibited a better PMS-activating activity than NGs prepared under other thermal annealing temperatures or via other optimized synthesis methods. Quenching experiment, electron paramagnetic resonance (EPR) study and Density Functional Theory (DFT) calculations revealed that non-radical pathway with surface activated PMS as the key reactive oxygen species (ROS) contributed more to SAM degradation than radical pathway in the NG/PMS/SAM system. The effect of catalyst loading, PMS dosage and common matrix species on PMS activation by NG600 for SAM degradation, the SAM degradation pathway, and the reusability of NG600 were investigated. In the second part of this study, nitrogen and boron-co-doped graphene was synthesized through two-step thermal annealing (2sNBG) and one-step thermal annealing (1sNBG). Boron-doped graphene was also synthesized via thermal annealing (BG). The carbocatalysts were employed as PMS activators to degrade SAM. The concentration of the main reactive functionalities and catalytic activity of 2sNBGs were delicately maneuvered through tuning the thermal annealing temperatures. 2sNBG800 (prepared at 800°C) with the highest N and B doping levels, the highest contents of pyridinic N and BC3 (substitutional B) that serve as the main active sites, and absence of hexagonal boron nitride (h-BN), performed best to activate PMS for SAM degradation. By contrast, the 1sNBG contained h-BN which could hamper its catalytic activity. The catalytic performances of the various doped graphenes prepared in this study followed the order of 2sNBG800 > 2sNBG900 > 2sNBG700 > 2sNBG600 > NG600 > 1sNBGs > BG800. Both radical quenching experiment and DFT calculation revealed that the introduction of B into NG can facilitate the shift of reaction pathway from a non-radical oxidation dominating in the NG/PMS system to the coexistence of non-radical and radical oxidations in the 2sNBG/PMS system. The synergistic coupling effect from bonding configuration of B-C-C-C-pyridinic N was the main reason for the enhanced catalytic activity of 2sNBG800 to activate PMS for SAM degradation. The SAM degradation was negligibly influenced by NO3- in the 2sNBG800/PMS/SAM system, while Cl- and humic acid led to 33% and 64% decrease in kapp, respectively. The transformation of the aromatic amino group and subsequent mineralization of SAM can effectively minimize the hazardous potentials of sulfonamides to the environment. Nevertheless, the adsorbed intermediates could deactivate 2sNBG to some extent. In the third part of this study, nitrogen-doped chitosan-derived carbon nanosheets (CNUs) were synthesized as a renewable, cheap and easily accessible alternative to the graphene-based carbocatalyst. The contents of reactive functionalities, graphitization degree and porous structure of CNU can be effectively tailored by pyrolysis temperature (Tp). The outstanding PMS-activating activity of CNU800 (prepared at Tp = 800°C) for SAM degradation can be attributed to its high level of C=O/C and graphitic N/C, relatively high graphitization degree, and its large specific surface area and hierarchically porous structure. The introduction of urea with the presence of NaHCO3 during chitosan pyrolysis facilitated formation of the graphene-like carbocatalyst with hierarchically porous structure and an enhanced PMS-activating activity. Quenching experiment and EPR collectively revealed that non-radical oxidation with singlet oxygen (1O2) as the main ROS was the dominant catalytic pathway in the CNU800/PMS/SAM system. The effect of catalyst loading, PMS dosage and common matrix species on PMS activation by CNU800 for SAM degradation, SAM degradation pathway, and reusability of CNU800 were probed.

Ornidazole degradation by PMS activated by Co-Zr-TiO2 with abundant oxygen vacancies: Performance, mechanism and degradation pathway

A novel combination of bioelectrochemical system with peroxymonosulfate oxidation for enhanced azo dye degradation and MnFe2O4 catalyst regeneration

N-doped carbon nanosheets supported-single Fe atom for p-nitrophenol degradation via peroxymonosulfate activation