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Article

Enhancement of Electron Transfer Between Fe/Mn Promotes Efficient Activation of Peroxomonosulfate by FeMn-NBC

by
Xiaoni Lin
1,
Qiang Ge
2,
Xianbo Zhou
3,
Yan Wang
1,4,*,
Congyun Zhu
2,
Kuanyong Liu
3 and
Jinquan Wan
1,4
1
School of Environment and Energy, South China University of Technology, Guangzhou 510006, China
2
China CEC Engineering Corporation, Changsha 410114, China
3
Pengsheng (Group) Paper Corporation, Qianxinan 562400, China
4
State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou 510640, China
*
Author to whom correspondence should be addressed.
Water 2025, 17(11), 1700; https://doi.org/10.3390/w17111700
Submission received: 25 April 2025 / Revised: 19 May 2025 / Accepted: 22 May 2025 / Published: 4 June 2025
(This article belongs to the Section Wastewater Treatment and Reuse)
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Abstract

Bimetallic catalysts can effectively enhance the catalytic degradation efficiency of peroxymonosulfate (PMS), which is usually attributed to the enhancement of electron transfer, but currently, there is no clear explanation of the mechanism of how the electron transfer is enhanced. A nitrogen-doped Fe/Mn composite biochar (FeMn-NBC) was co-constructed by hydrothermal synthesis and high-temperature calcination. The FeMn-NBC activated PMS more efficiently than the monometallic one due to the enhanced electron transfer between Fe and Mn. The FeMn-NBC/PMS system activated PMS with Mn as the active center, and the high oxidation state of Mn4+ promoted the acceleration of the PMS adsorption of the generation of Mn2+/Mn3+. This gaining effect accelerated the electron cycling between Fe2+/Fe3+ and Mn2+/Mn3+/Mn4+, which enhanced the PMS catalysis to generate free radicals (•OH, SO4•− and •O2−) and non-radicals (1O2) for the efficient degradation of diisobutyl phthalate (DIBP). Benefiting from this gaining effect, the degradation rate of DIBP by the FeMn-NBC/PMS system was increased by 2.43 and 3.38 times compared to Fe-NBC and Mn-NBC. The bimetallic-enhanced electron transfer mechanism proposed in this study facilitated the development of efficient catalysts for more efficient and selective removal of organic pollutants.

1. Introduction

Phthalates (PAEs) are the most widely used, varied, and produced plasticizers [1,2,3]. DIBP, as one of the most commonly used plasticizers among PAEs, poses a threat to human health through its adverse effects on organisms, such as reproductive developmental toxicity, genotoxicity, and endocrine-disrupting effects [4,5,6]. According to available studies, PAEs can hardly be removed by conventional wastewater treatment processes currently used in wastewater treatment plants [7,8]. Therefore, the task of developing efficient degradation techniques to eliminate PAEs is imminent.
The sulfate radical-based advanced oxidation processes are new technologies capable of efficiently removing organic pollutants from water [9,10]. Carbon materials doped with heteroatoms (N, B, S, etc.) [11,12,13] and doped with transition metals (Fe, Mn, Cu, Co, etc.) [14,15,16,17] have been proved to efficiently activate PMS to degrade pollutants due to their low energy consumption and high catalytic efficiency. Biochar is widely available and inexpensive, and the presence of abundant oxygen-containing functional groups on its surface can be used as a carrier for metal loading to catalyze PMS [18,19]. Although iron-based biochar catalysts have been shown to have great catalytic efficiency performance, they suffer from the disadvantages of poor iron cycling and easy leaching [20,21]. Whereas, doping another metal in the iron-based catalyst can solve these problems associated with monometallic iron-based catalysts [22,23]. The reduction potential of Fe (Fe3+/Fe2+ = 0.77 eV) is much lower than that of Mn (Mn3+/Mn2+ = 1.51 eV). When forming a bimetallic catalyst with Mn, Fe can easily construct a redox cycle with Mn, which can accelerate the internal electron transfer rate and improve its catalytic efficiency for PMS [24,25]. Zhang et al. [24] synthesized FeMn-CA300 catalysts for non-homogeneous catalytic PMS, which could achieve 100% removal of the surface activator benzalkonium chloride.
When biomass was co-pyrolyzed with nitrogen-containing polymers, the oxygen-containing can capture more nitrogen from the polymers to be immobilized on BC. N-heterocyclic structures such as pyridine N, pyrrole N, and graphite N are formed on the surface of BC, which promotes the electron transfer cycle with PMS [26,27]. Co-doping of metals with non-metals can also modulate the electronic structure of carbon-based catalysts, simplify the recycling process of materials, and significantly reduce metal leaching [28,29]. Studies have shown that the formation of M-N bonds in nitrogen-doped metal catalysts can not only enhance their catalytic activity but also significantly inhibit metal leaching and improve catalyst stability [30]. Therefore, on the basis of ensuring that the Fe-Mn bimetallic composite biochar catalyst has high catalytic activity, this experiment introduces nitrogen doping into the Fe-Mn bimetallic composite biochar catalyst to improve its catalytic activity while reducing metal leaching and enhancing its stability.
So far, the synergies of Fe and Mn have been shown to efficiently activate the degradation of pollutants by PMS, but the electron transfer pathways and the mechanism of electron transfer enhancement between Fe and Mn on nitrogen-doped iron–manganese bimetallic carbon catalysts remain unclear. Therefore, in this paper, N-doped Fe/Mn bimetallic catalysts, FeMn-NBC, prepared using biochar as a precursor, were synthesized in a two-step process by hydrothermal synthesis and high-temperature calcination. The activation efficiency of FeMn-NBC for the degradation of pollutants by PMS was tested by taking DIBP as the target contaminant. Analyze the reactive oxygen species (ROS) in the FeMn-NBC/PMS system through free radical quenching experiments and electron paramagnetic resonance (EPR) analysis. The attack sites of the FeMn-NBC/PMS system on DIBP were analyzed by density functional theory (DFT). Combining the intermediate products of DIBP degradation detected by HPLC-MS, the possible degradation pathways of DIBP were proposed. By studying the degradation mechanism of DIBP in the FeMn-NBC/PMS system, the electronic cycling and synergistic effect between bimetallic materials were explored. The toxicity of the degradation products was evaluated using the toxicity assessment software tool (T.E.S.T.). This study provides a theoretical reference value for analyzing the electron transfer enhancement mechanism of bimetallic catalysts and valuable approaches for developing efficient and selective catalysts.

2. Materials and Methods

2.1. Chemicals and Reagents

Ferric nitrate hydrate (Fe(NO3)3·9H2O, ≥99%), manganese nitrate tetrahydrate (Mn(NO3)2·4H2O, ≥99%), urea (CH4N2O, >99.5%), diisobutyl phthalate (DIBP, 99%), bisphenol A ((CH3)2C(C6H4OH)2, 98%), trichlorophenol (C6H3Cl3O, 98%), potassium persulfate (2KHSO5·KHSO4·K2SO4, ≥47%), p-benzoquinone (BQ, ≥99%), tert-butanol (TBA, ≥99%), ethanol (EtOH, ≥99.9%), methanol (Meth, ≥99.8%), dimethylsulfoxide (DMSO, ≥99.8%), methylphenylsulfoxide (MPSO, >98%), L-histidine (L-his, 98%), 2,2,6,6-tetramethylpiperidine (TEMP, 99%), 5,5-dimethyl-1-pyrroline-N-oxide (DMPO, 99%), KI (99%), and humic acid (HA, >90%) were purchased from Aladdin Biochemistry Co. in Shanghai; Na2SO4 (99%), NaCl (99%), Na2HPO4 (99%), NaHCO3 (99%), HCl (>99.7%), and NaOH (99%) were purchased from MackLin Biochemical Co. Ltd (Shanghai, China). The rice straw powder was purchased from Suryo Agricultural Products Processing Plant (Jiangsu, China). All chemicals were of analytical grade and required no further purification. Ultrapure water with a resistivity of 18.2 MΩ cm was used throughout the experiments.

2.2. Preparation of Catalysts

Fe(NO3)3·9H2O and Mn(NO3)2·4H2O (Fe (mol)/Mn (mol) = 5, 3, 1, 0.333, 0.2), rice straw powder and urea were weighed according to the mass ratio of bimetallic/urea/rice straw of 2:1:1. All the chemicals were dissolved in the 50 mL of ultrapure water, stirring for 1 h to make the reagents mixed uniformly, then was heated at 160 °C for 10 h in polytetrafluoroethylene high-pressure reactors. The product was centrifuged at 8000 rpm in a high-speed centrifuge for 5 min, placed in a vacuum drying oven at 60 °C for 24 h, and then ground to powder. The corresponding FeMn-NBC was obtained by calcining the FeMn-NBC precursor in the N2 atmosphere with target temperatures (500 °C, 600 °C, 700 °C and 800 °C) for 2 h at an elevated rate of 5 °C/min.

2.3. Characterization of Catalysts

The crystal structure of the catalysts was detected by X-ray diffraction (XRD, Rigaku-MiniFLex 600, Tokyo, Japan). The surface functional group species of the catalysts were detected using Fourier transform infrared spectroscopy (FTIR, Thermo Fisher, Nicolett iS5, Waltham, MA, USA). The catalysts’ surface morphology and element atomic percentages were analyzed using a scanning electron microscope equipped with Energy-Dispersive X-ray Spectroscopy (SEM-EDS, Nova Nano SEM 430, Hillsboro, OR, USA). The chemical composition of the catalyst surface was analyzed using X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha, Waltham, MA, USA). The peak of C1s at 284.8 eV indeterminate carbon was used to calibrate all binding energies. The ionic leaching of both Fe and Mn was determined by inductively coupled plasma atomic absorption spectroscopy (ICP-AAS, TAS-990, Beijing, China). The degree of defects and graphitization of the catalysts were obtained by Raman spectroscopy (Ramna, Withch alpha 300R, Oxford, UK). Electron spin resonance (ESR) spectra were recorded on a Bruker 5000 spectrometer (Waltham, MA, USA) at reaction times of 0, 5, and 10 min using DMPO and TEMP as spin traps. The ESR signals were collected under conditions of a center magnetic field strength of 3505 G, sweep width of 500 G, and liquid nitrogen temperature (77 K). Detection of intermediates produced in the degradation system by high-performance liquid chromatography mass spectrometry (HPLC-MS, Agilent 1290 Infinity II, Santa Clara, CA, USA).

2.4. Experimental Methods

The degradation reaction was carried out by adding FeMn-NBC and PMS in 10 mg/L DIBP, shaking at 25 °C and 180 rpm for 60 min on a constant temperature shaker. DIBP was measured by taking 1 mL of sample and mixing it with 1 mL of methanol to terminate the oxidation reaction at preset time intervals, then filtering it through a 0.22 µm membrane. The concentration of DIBP in the filtered sample was detected by high-performance liquid chromatography (HPLC; Agilent 1290 series, Santa Clara, CA, USA) equipped with an Agilent XDB-C18 (Santa Clara, CA, USA) column (5 μm, 4.6 mm × 150 mm) and a UV diode array detector. The column temperature and detection wavelength were set at 30 °C and 228 nm. The mobile phase consisted of acetonitrile and water in a volume ratio of 9:1 at a flow rate of 1.0 mL min−1 with an injection volume of 20 μL and a peak time of 10 min. The intermediates of DIBP degradation were identified by HPLC-MS analysis. In order to evaluate the reusability and stability, the catalysts were collected by centrifugation after the reaction and washed with ultrapure water several times, then added into a new DIBP solution for the catalytic degradation reaction. All experiments were performed in three parallel groups, and the mean ± standard deviation was used as the final experimental results.

2.5. Toxicity Analysis and DFT Calculation

The results of toxicity analysis of DIBP and its degradation products were obtained by T.E.S.T. software 4.2.1 using a consistent prediction method based on quantitative constitutive relationship prediction (QSAR) [31] The geometrical configuration and frequencies of the molecules were optimized at the RB3LYP/def2-SVP level using Gaussview 6.0, Gaussian 16W and Multiwfn software 3.7 [32], and the Fukin function, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) orbitals, as well as electrostatic potential (ESP) of the DIBP, were computed through the DFT method.

3. Results and Discussion

3.1. Catalyst Characterization

The surface morphology of FeMn-NBC was investigated by SEM (Figure 1a). It was observed that the surface of FeMn-NBC was complicated, forming a loose and rough surface structure with a large number of pores. In addition, a large number of small irregular particles were uniformly aggregated on the surface of FeMn-NBC, which was a phenomenon caused by the attachment of FeMn oxides on the surface of biochar. Meanwhile, there was a flower-shaped appearance morphology on the surface of FeMn-NBC, which could increase the surface area of FeMn-NBC due to the presence of folds and facilitated contact with more oxidants. C, O, N, Fe, and Mn could be detected and uniformly distributed on the surface of FeMn-NBC, as shown by the EDS of FeMn-NBC in Figure 1c.
To gain insight into the crystal type and structure of the catalysts, X-ray diffraction spectroscopy (XRD) was used to analyze BC, NBC, Fe-NBC, Mn-NBC, and FeMn-NBC. As shown in Figure 2a, FeMn-NBC had formed the crystal structure Fe19Mn and (FeO)0.099 (MnO)0.901, indicating the successful synthesis of FeMn-NBC. The diffraction peaks of FeMn-NBC at 44.6° and 64.91° belonged to the (110) and (200) crystal planes of Fe19Mn (JCPDS#65-7528), the diffraction peaks at 34.04°, 40.68°, and 58.89° belong to the (111), (200), and (220) crystal planes of (FeO)0.099 (MnO)0.901 (JCPDS#77-2362), the diffraction peaks at 43.58° and 50.76° belong to the (111) and (200) crystal planes of Fe3N (JCPDS#75-2127), and 31.13° belong to the (113) crystal plane of Fe2O3 (JCPDS#75-2127). The FeMn-NBC samples were multiphase composite crystals encapsulated with complex compositions.
Raman spectroscopy was applied to investigate the bonding state and crystallinity of carbon atoms in catalysts. The characteristic peaks of the catalyst near 1342 cm−1 (D-band) and 1595 cm−1 (G-band), respectively, represent defects and graphite structures (Figure 2b). Theoretically, the peak intensity ratio (ID/IG) of the D-band and G-band can reflect the structural defects and graphitization of carbonaceous materials. The larger the ID/IG ratio, the higher the degree of defects, and vice versa, the higher the degree of graphitization [33]. The degree of defects in the material of FeMn-NBC (0.98) was larger than that of Fe-NBC (0.92) and Mn-NBC (0.91), which indicates that the simultaneous introduction of transition metal elements into FeMn-NBC enhances the defect degree of the catalyst. The defects in the catalyst will disrupt the periodicity of the crystal lattice, form electron traps or donors, and change the electron configuration of surrounding atoms. In addition, the defective carbon sites in the carbon matrix transfer electrons to the surface metal sites through the π-electron delocalization effect, forming an efficient electron transfer path, thereby promoting the redox reaction between the catalyst and PMS [34,35].
The activation capacities of BC, NBC, Fe-NBC, Mn-NBC, and FeMn-NBC on PMS were compared by DIBP degradation experiments (Figure 3a). To exclude the effect of adsorption on pollutant removal, the adsorption test was performed on FeMn-NBC within 90 min. It showed that FeMn-NBC exhibited a low adsorption efficiency for DIBP, removing only 27.7% of DIBP after 90 min of adsorption. At the same time, the PMS alone was also barely able to degrade DIBP (2.9%). When PMS and catalyst were simultaneously added, the degradation rate of DIBP by FeMn-NBC/PMS system was 90.4% at 60 min, and the reaction leveled off at 30 min. In contrast, the degradation of DIBP by Fe-NBC/PMS and Mn-NBC/PMS systems stabilized at 60 min, with removal rates of 67.7% and 50.7%. As shown in the reaction rate constant (kobs) for DIBP removal in Figure 3b, the kobs of the FeMn-NBC/PMS system (0.0382 min−1) was 2.43 times higher than that of the Fe-NBC/PMS system (0.0157 min−1), and 3.38 times higher than that of the Mn-NBC/PMS system (0.0113 min−1). This also indicated that FeMn-NBC has a higher catalytic ability for PMS under the same conditions.
In this experiment, five groups of Fe/Mn bimetallic ratios (5:1, 3:1, 1:1, 1:3, 1:5) were set up to investigate the effect of Fe/Mn bimetallic ratios on the degradation of DIBP by FeMn-NBC/PMS system (Figure 3c). Overall, the degradation effect of the FeMn-NBC/MPS system on DIBP increased with the increase in the Mn/Fe ratio. The FeMn-NBC/PMS system showed the best degradation of DIBP when Mn/Fe was 5, with 94.6% degradation of DIBP at 60 min. However, the degradation rate of DIBP was only improved by 3.3% relative to the degradation rate of DIBP at Fe/Mn of 1 (91.3%). Combining the material properties and cost, FeMn-NBC with Fe/Mn of 1 was finally selected in this study. It can be seen that Mn acted as the activated center of FeMn-NBC. The effect of the calcination temperature of the tube-in-tube furnace on the catalytic properties of the FeMn-NBC was also compared (Figure 3d), and the optimum calcination temperature was 800 °C.

3.2. Catalytic Performance

3.2.1. Effects of Operational Parameters

The DIBP degradation rate increased from 75.4% to 89.4%, and the kobs rapidly increased from 0.0177 min−1 to 0.0382 min−1 as FeMn-NBC dosage in the range of 0.05 to 0.2 g/L (Figure 4a,b). In this range, with the increase in FeMn-NBC dosage, more active sites could be provided for the reaction to activate more PMS to produce ROS. Nevertheless, there was no significant improvement in the efficiency and rate of DIBP degradation when the FeMn-NBC dosage increased to 0.3 and 0.4 g/L. In the range of 1 mM to 3 mM, the more PMS was added, the higher the degradation rate and kobs (increased from 0.0227 min−1 to 0.0382 min−1) of DIBP by the FeMn-NBC/PMS system (Figure 4c,d). However, the degradation rate of DIBP decreased to 85.7%, and the kobs decreased to 0.0307 min−1 when the PMS dosage increased to 5 mM, which was mainly attributed to the over-addition of PMS, which caused SO4·− to undergo self-quenching in solution and reduced the amount of free radicals for pollutant degradation.
Figure 4c shows that the kobs of the FeMn-NBC/PMS system at different initial pH follow the order: pH 9 > pH 11 > pH 3 > pH 5 > pH 7. The FeMn-NBC degraded the DIBP better under alkaline conditions. The reason for the lower degradation to DIBP of the FeMn-NBC/PMS system under acidic conditions may be that acid conditions lead to higher leaching of Fe and Mn, thus reducing the number of active sites in the catalyst [36]. However, the FeMn-NBC surface became more negatively charged, thereby inhibiting the migration of PMS when pH > 9, which was also negatively charged, to the surface of FeMn-NBC by electrostatic repulsion, which ultimately resulted in a slight decline in the reaction rate [37].

3.2.2. Inorganic Anions and Natural Organic Matters

Natural organic matter (NOM) and inorganic anions (including Cl−, HCO3−, SO42−, and H2PO4−) are important factors that affect the degradation performance of the reaction system [38]. Humic acid (HA) is a key component of NOM, which is widely found in a variety of water bodies [39]. The background substances reacted to the system with certain effects in the order of Cl− < SO42− < HA < HCO3− < H2PO4− (Figure 5). In particular, Cl− addition not only had no inhibitory effect on DIBP degradation but also promoted the degradation of the pollutant. When the concentration of Cl− reached 10 mM, the removal rate of DIBP reached 90% at 30 min, which increased by 3.3% relative to the removal rate of DIBP without Cl− (86.7%). This was attributed to the fact that excess free Cl− in the solution could directly react with PMS to form hypochlorous acid and more SO42−, accelerating the overall degradation reaction rate [40,41]. SO42− showed a slight inhibitory effect on the degradation of DIBP (73.6%), which was due to the fact that excess SO42− in the reaction system reverses the reversible reactions generated by free radicals [42,43]. When 10 mM of HCO3− and H2PO4− were present in the solution, the degradation of DIBP decreased to 66% and 65.1%, which was due to the following: (1) HCO3− and H2PO4− reacted with free radicals, thus quenching or generating free radicals with lower redox potentials, and (2) HCO3− and H2PO4− may chelate with multivalent metal ions on the FeMn-NBC surface and occupied the active sites, thus hindering the catalytic effect of the FeMn-NBC on PMS [44,45]. For example, H2PO4− may stabilize and occupy the Fe III, thus reducing the reactivity of iron-based catalysts. The inhibitory effect of HA on the degradation of DIBP was gradually evident as HA concentration increased, which was because of the coordination reaction between HA and Fe in the catalyst, occupying the active site of FeMn-NBC. Meanwhile, HA, as an organic substance, competed with DIBP as a reactive substance. Overall, FeMn-NBC could still show high resistance to the interference of NOM and common anions.

3.2.3. Stability and Practical Application

Reusability and stability are indicators for assessing catalyst performance (Figure 6). In the first three cycle experiments, the FeMn-NBC/PMS system maintained high degradation efficiency and rate for DIBP within 30 min (90.25%, 92.74%, and 92.03%). Starting from the fourth cycle experiment, the degradation efficiency and rate of the FeMn-NBC/PMS system for DIBP gradually decreased (83.37%), dropping to 73.7% in the fifth cycle experiment. Excessive leaching of iron and manganese may turbid water bodies, disrupt the balance of water quality in terms of acid–base and redox potential, and affect human health [46,47]. In this experiment, very low leaching concentrations of Fe and Mn were observed in the metal ion leaching experiments, which reduced the risk of secondary pollution to the environment (Figure 6b, Table 1). With the increase in cycles, the leaching of Fe and Mn showed a decreasing trend: the leaching concentrations were 1.46 and 1.11 mg/L, and the absolute loss ratios (leaching volume/the volume of metal added to the catalyst) were 0.119% and 0.144% in the first round of the experiment, then gradually decreased in the subsequent four rounds. In the fifth cycle experiment, the leaching of Fe and Mn was only 0.02 and 0.01 mg/L, with absolute loss ratios of 0.002% and 0.002%. Therefore, it can be concluded that the FeMn-NBC/PMS system reduces the risk of secondary pollution to the environment. Additionally, after five reaction cycles, the peak shape and intensity of the XRD spectrum of FeMn-NBC changed (Figure 6c). XRD characterization of the used FeMn-NBC showed the presence of (FeO)0.099(MnO)0.901, Fe3N, and Fe2O3 structures, with the loss of the Fe19Mn structure compared to the fresh FeMn-NBC. It is speculated that since the Fe19Mn alloy is not directly bound to the carbon material but adheres to the catalyst surface, it dissolves into the solution during the reaction. The positions of the FTIR characteristic peaks showed no obvious changes, but the peak intensities decreased significantly (Figure 6d). In conclusion, the compositional structure and surface functional groups of FeMn-NBC were relatively stable after five cycles, exhibiting great reusability and stability.
The FeMn-NBC/PMS system was applied to real water bodies to further explore its prospects for practical application (Figure 7a). The degradation effect of FeMn-NBC/PMS on DIBP in tap water was almost unaffected. After filtering out the excessive suspended matter in lake water, the removal rate of DIBP reached 74%. This indicated that the FeMn-NBC/PMS system has great application prospects in real water bodies. In addition, the ability of the FeMn-NBC/PMS system to eliminate other pollutants was also verified (Figure 7b). The results showed that the FeMn-NBC/PMS system could completely remove TCP in 40 min, while the complete removal of BPA only required 30 min, which proved its wide applicability and great potential in wastewater treatment.

3.3. Mechanism of Catalysts System

3.3.1. Identification of Active Species

In order to explore the ROS species and their contribution to the degradation of DIBP in the FeMn-NBC/PMS system, the system was subjected to active species quenching experiments. EtOH and TBA were selected to determine the extent of the contribution of •OH and SO4•− to the degradation of DIBP. The degradation of DIBP was inhibited from 88.7% to 60.7% (TBA) and 52.9% (EtOH) at 30 min when TBA = EtOH = 1000 mM (Figure 8b,c). The addition of L-his and BQ to the system as scavengers of 1O2 and O2•− inhibited the degradation rate of DIBP from 88.7% to 60.7% (L-his) and 43.4% (BQ) (Figure 8c,d). Given the strong hydrophobic gravitational force between the scavenger and catalyst, the substance coverage effect affects the activation of PMS, thus exaggerating the quenching effect [48]. Therefore, we performed electron paramagnetic resonance (ESR) experiments by TEMP and DMPO as a spin-trapping agent to further examine the generation of ROS in the FeMn-NBC/PMS system. The characteristic peaks of •OH with intensity 1:2:2:1 and another set of peaks with intensity 1:1:1:1:1:1:1 representing SO4•− can be observed (Figure 8f) [49]. In addition, the signal intensity of ESR spectra at 10 min was significantly higher than that at 5 min, suggesting that FeMn-NBC activated PMS efficiently and consistently [50]. Meanwhile, we utilized TEMP to further capture the potential 1O2 in the reaction system (Figure 8g), the intensity of the unique triple signal peaks representing TEMP-1O2 enhanced with the increase in catalytic time. In addition, we also detected a strong signal of DMPO-O2•− in the reaction system (Figure 8h). Both radical quenching experiments and ESR characterization show that the FeMn-NBC/PMS system degrades DIBP through the combined action of free radicals dominated by O2•− and non-radical processes.
Research indicates that catalytic systems can directly degrade pollutants through electron transfer processes, and the existence of electron transfer pathways in the system can be jointly verified by pre-mixing experiments and electrochemical characterization [51,52]. If direct electron transfer-mediated degradation of DIBP occurs in the FeMn-NBC/PMS system, the pre-mixing of FeMn-NBC and PMS should theoretically have no impact on pollutant degradation, as the absence of electron-donating pollutants would prevent consumption of reactive oxidative complexes formed between the catalyst and PMS. However, experimental results demonstrated that pre-mixing FeMn-NBC with PMS reduced the DIBP removal efficiency from 88.7% to 77.3% (Figure 9a), confirming the presence of electron transfer-driven direct degradation of DIBP in the FeMn-NBC/PMS system.
To further elucidate the electron transfer mechanism in the FeMn-NBC/PMS system, this study employed electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) for comprehensive analysis (Figure 9b,c). LSV, a robust electrochemical technique, was utilized to verify the electron-shuttling capability of the carbon matrix and to identify the non-radical pathway mechanism (i.e., carbon-mediated electron transfer) in the FeMn-NBC/PMS/DIBP system. LSV profiles revealed a significant current enhancement at the FeMn-NBC-loaded electrode upon PMS introduction, indicative of interactions between PMS and FeMn-NBC that generated metastable reactive complexes. Subsequent addition of DIBP further amplified the electrode current, demonstrating that FeMn-NBC facilitates direct electron transfer through surface-bound metastable complexes to oxidize DIBP. Transient microcurrent bursts observed at the electrode interface provided dynamic evidence of the electron transfer process, confirming that the coexistence of organic pollutants (as electron donors) and PMS (as electron acceptors) constitutes an essential prerequisite for initiating electron transfer pathways.
For a comprehensive evaluation of FeMn-NBC’s electrochemical performance, comparative EIS analyses were conducted on Fe-NBC, Mn-NBC, and FeMn-NBC materials. The semicircle diameter in Nyquist plots inversely correlates with charge transfer resistance. Experimental data revealed that FeMn-NBC exhibited the smallest semicircle diameter among the three materials, indicating superior electrical conductivity and minimized charge transfer resistance. This characteristic endows FeMn-NBC with enhanced electron transfer capabilities, thereby optimizing catalytic efficiency in the reaction system.

3.3.2. Identification of High-Valent Active Species

In order to prove that the FeMn-NBC/PMS system might contain high-valent metal–oxide species, dimethyl sulfoxide (DMSO) was added to the system. DMSO can be oxidized by high-valent metals through the oxygen-atom transfer reaction, which competes with the pollutants for the high-valent metals and makes the degradation rate of pollutants decrease [53]. Notably, the DIBP removal rate was significantly slowed down as the DMSO dose increased to 20 mM with a final kobs of 0.02225 min−1 (Figure 10a,b). In addition, methyl phenyl sulfoxide (MPSO) has been known to be oxidized by the high valence states of metals, intermediates to form methyl phenyl sulfone (MPSO2) [54,55]. Compared to the system without PMS, significant MPSO loss and MPSO2 generation were detected in the FeMn-NBC/PMS system (Figure 10c,d). All of the above could confirm the presence of high-valent metal–oxide species in the FeMn-NBC/PMS system.

3.3.3. Catalytic Mechanism of FeMn-NBC

In order to understand the activation sites of FeMn-NBC-activated PMS and the synergistic effect between Fe and Mn, XPS was used to characterize the valence state changes of all elements on the surface of the material before and after the reaction. Peaks of C 1s, N 1s, O 1s, Fe 2p, and Mn 2p were observed in the FeMn-NBC spectra before and after the reaction (Figure 11a). The decrease in the C=O content and the increase in the C-O content shown in Figure 11b indicated that after the catalytic reaction, part of the C=O was converted to C-O. It was speculated that C=O could act as a Lewis base site to effectively increase the electron density of the surrounding carbon layer, thus triggering the redox reaction with the pollutant. The N compound fractions changed significantly (Figure 11c). The contents of graphite N and Fe-N/Mn-N decreased from 19.78% and 63.34% to 6.41% and 24.69%, respectively. On the contrary, pyrrole N increased from 15.56% to 40.54%. This suggested that graphite N and Fe-N/Mn-N can be used as potential active sites for PMS activation. In particular, graphite N can greatly enhance the adsorption of PMS on the catalyst and promote 1O2 production [56].
It is known that Fe2+ and Fe3+ can activate PMS by providing electrons to generate free radicals to degrade pollutants (Equations (1) and (2)). Fe2+/Fe3+ can form a cycle itself when catalyzing PMS, but the rate of the cycle is very slow [57]. Similarly, from Equations (3)–(6), there is a cycle among Mn2+/Mn3+/Mn4+ when catalyzing PMS. Based on the fact that the redox potential of Mn3+/Mn2+ (1.51 V) is higher than that of Fe3+/Fe2+ (0.77 V), Fe2+ can thermodynamically reduce Mn3+ (Equation (7)). In addition, according to the redox potential of Mn4+/Mn3+ (0.51 V), which is lower than the redox potential of Fe3+/Fe2+ (0.77 V), Fe3+ can oxidize Mn3+ (Equation (8)). From Table 2, the content of Fe2+ in FeMn-NBC increased from 26.06% before the reaction to 33.26% after the reaction, while the content of Fe3+ decreased from 30.65% to 27.22%. Meanwhile, Mn2+ increased from 16.42% before reaction to 30.84% after reaction, Mn3+ decreased from 42.81% to 32.09%, and Mn4+ decreased from 35.63% to 22.84%. There was also a cycle between Fe2+/Fe3+ and Mn2+/Mn3+/Mn4+. It was noteworthy that the reduction reaction of PMS activated by Mn4+ is more difficult, but XPS showed a significant decrease in Mn4+, which was attributed to the fact that Mn4+ was more readily bound to PMS. The adsorption of more PMS by Mn4+ increased the chances for the generation of Mn2+/Mn3+ and the direct activation of PMS by Mn2+ and Mn3+, which collectively explained the high catalytic activity for PMS activation [58]. •OH and SO4•− were continuously generated during the reaction. The cyclic reaction favored the continuous production of SO4•− and •OH, which could continuously and effectively act on the degradation of pollutants. In addition, the formation of •OH and •O2− based on the reaction of PMS with H2O/OH− could promote the production of 1O2. Moreover, PMS could also release electrons through OH bond breaking and decompose into SO5•− to further generate 1O2 (Equations (10)–(18)). The reaction mechanism of FeMn-NBC-activated PMS is shown in Figure 12. Specifically, the FeMn-NBC/PMS system mainly took Mn as the active center, and Mn4+ adsorption of PMS accelerated the generation of Mn2+/Mn3+, which in turn accelerated the cycle between Fe2+/Fe3+ and Mn2+/Mn3+/Mn4+, and facilitated the efficient catalysis of PMS in order to generate free radicals and non-radicals to jointly enhance the degradation of DIBP.
Fe2+ + HSO5•− → Fe3+ + SO4•− + OH−
Fe3+ + HSO5•− → Fe2+ + SO4•− + H+
Mn2+ + HSO5•− → Mn3+ + SO4•−+ OH−
Mn3+ + HSO5•−→ Mn4+ + SO4•− + OH−
Mn3+ + HSO5•− → Mn2+ + SO4•− + H+
Mn4+ + HSO5•− → Mn3+ + SO4•− + H+
Mn3+ + Fe2+ → Mn2+ + Fe3+
Mn3+ + Fe3+ → Mn4+ + Fe2+
Fe 0 + Fe3+ → 3Fe2+
2SO4•− + H2O → SO4•− + H+ +•OH
2SO4•− + OH— → SO42− +•OH
H2O + HSO5•− → H2O2 + HSO4−
H2O2 +•OH → H2O + HO2•
HO2•→ H+ + •O2−
•O2− +•OH → H2O2 + 1O2
2•O2− + 2H+ → H2O2 + 1O2
2SO5•− → S2O82− + 1O2
2SO5•− → 2SO42− + 1O2

3.4. Degradation Pathways and Toxicity Evaluation

In order to investigate the degradation process of DIBP by the FeMn-NBC/PMS system, the molecular structure of DIBP was analyzed through DFT, and its surface electrostatic potential (ESP), HOMO/LUMO [59,60], and Fukin function were calculated in to investigate the most vulnerable sites in DIBP molecule. DIBP underwent ESP calculations to analyze its surface electron clusters. Apparently, the negative charge pairs were mainly concentrated around O atoms on chemical base, which are most vulnerable to electrophilic or activation attacks [61]. The HOMO orbitals of DIBP were mainly concentrated around the C atoms of the benzene ring that could easily lose electrons (Figure 13c). The LUMO orbitals were mainly concentrated around the C atoms of the benzene ring that could easily gain electrons, as well as the C and O atoms on the attached ester group (Figure 13d). As shown in Table 3, 1 C (Δf = −0.0156), 12 O (Δf = −0.0301), and 14 O (Δf = −0.0801) showed higher values of electrophilic attack, all of which were susceptible to attack by electrophilic species radicals. In contrast, the 2 C (Δf = 0.0368), 5 C (Δf = 0.0266), and 7 C (Δf = 0.0539) sites were reactive nucleophilic sites, which had higher nucleophilic attack values and f+ (r) values.
HPLC-MS detection was performed on the degradation intermediates of DIBP (Table 4). Based on these intermediates, possible degradation pathways of DIBP were proposed (Figure 14). As shown in pathway (1), the ester group on the branched chain of the DIBP molecule was first attacked by •O2− radicals and underwent an ester hydrolysis reaction to form P1 (m/z 221). For P1, there were two degradation pathways: on the one hand, the carboxyl group on the benzene ring of P1 was susceptible to decarboxylation reaction by 1O2 attack and was replaced by ·OH to form P4 (m/z 193); on the other hand, P1 continued to undergo ester hydrolysis reaction to form P5 (m/z 165). The benzene ring of P5 was attacked by 1O2 to open the ring to form P8 (m/z 117). In pathway (2), the alkyl group on the branched chain of the DIBP molecule was first attacked by free radicals to undergo dealkylation to form P2 (m/z 249). The P2 molecule (i) underwent decarboxylation to form P5. (ii) the C1 on the benzene ring of the P2 molecule was more readily available for binding to hydroxyl groups as an electron-rich region, and the hydroxylation of the P2 underwent a hydroxylation reaction to form P6 (m/z 266), and the P9 underwent a ring opening to form P8. (iii) underwent decarboxylation reaction to form P7 (m/z 163). In pathway (3), the DIBP benzene ring was attacked by nucleophilic attack on C3, C5, C6, and C4 was attacked by SO4•− and ring opening to form P3 (m/z 127). Ultimately, all obtained intermediates were decomposed into organic compounds with smaller molecular weights and mineralized into H2O and CO2. In the FeMn-NBC/PMS system, the degradation of DIBP mainly involved dealkylation, decarboxylation, hydroxylation, hydrolysis, and ring-opening reactions.
In order to clarify whether the products generated from the degradation of DIBP by the FeMn-NBC/PMS system pose a biotoxicological risk to the environment, the toxicity of DIBP and its degradation products was analyzed by using a consistent prediction method based on QSAR through the T.E.S.T. software [62]. DIBP was toxic to Daphnia nigra and Daphnia magna (Figure 15a,b). P1, P2, P3, P4, and P7 in the degradation products were toxic; most of the degradation products turned out to be harmful, and P8 in the degradation final product was non-toxic. Overall, the toxicity of the final products P3, P4, P7, P8, and most of the other intermediate degradation products decreased in comparison to the toxicity of DIBP. The bioconcentration factors (BCFs) of all degradation products decreased from 1.39 to 0.09, 1.07, 1.2, and −0.22 for the final products P3, P4, P7, and P8, respectively (Figure 15d). DIBP and its degradation products were mutagenic-negative (Figure 15e). The toxicity evaluation showed that the FeMn-NBC/PMS system was not only effective in the oxidative degradation of DIBP but also effective in reducing the toxicity of DIBP, and it will not produce highly toxic degradation products.

4. Conclusions

In this study, FeMn-NBC was co-constructed by hydrothermal synthesis and high-temperature calcination. FeMn-NBC comprises a complex crystalline structure of bimetallic composite oxides (FeO)0.099 (MnO)0.901 and M–Nx coordination configurations. Nitrogen doping introduces pyridinic N, pyrrolic N, and M–Nx coordination configurations, which significantly optimize the electronic structure of the material. These features, coupled with active sites such as Fe2+, Mn4+, and C=O groups, endow FeMn-NBC with high catalytic activity. Concurrently, the M–NX coordination enhances metal dispersion on the FeMn-NBC surface, mitigates particle agglomeration, and stabilizes active centers, thereby substantially improving the material’s structural stability. In the FeMn-NBC/PMS system for pollutant degradation, Mn4+ preferentially adsorbed PMS to accelerate Mn2+/Mn3+ generation, while Fe2+/Fe3+ activated PMS to produce sulfate radicals (SO4•−) and hydroxyl radicals (•OH). Multivalent transitions of Mn2+/Mn3+/Mn4+ further facilitated PMS decomposition. The oxidation of Mn3+ by Fe2+ generated Fe3+ and Mn2+, driving a dynamic redox cycling between Fe2+/Fe3+ and Mn2+/Mn3+/Mn4+. This synergistic interplay enhanced the efficient activation of PMS to generate both radical species (•OH, SO4•− and •O2−) and non-radical species (1O2 and high-valent metal-oxo intermediates).
Under optimized conditions (Fe/Mn = 1, calcination temperature 800 °C), FeMn-NBC achieved a DIBP degradation efficiency of 90.4%, with a reaction rate 2.3–3.4-fold higher than single-metal systems. After five consecutive cycles, FeMn-NBC retained 73.71% DIBP degradation efficiency via PMS activation, with cumulative Fe/Mn leaching amounts as low as 0.087 mg/L and 0.052 mg/L, respectively, demonstrating exceptional stability. The system exhibited robust anti-interference capability across a wide pH range (3–11) and in complex water matrices (e.g., Cl−, humic acid), maintaining over 80% degradation efficiency. Intermediate products from DIBP degradation in the FeMn-NBC/PMS system were identified via LC-MS, and degradation pathways were proposed based on DFT calculations of reactive sites. DIBP degradation primarily involved dealkylation, decarboxylation, hydroxylation, hydrolysis, and ring-opening reactions, with intermediates ultimately mineralized into H2O and CO2.

Author Contributions

Conceptualization, X.L., Q.G., X.Z., Y.W. and K.L.; methodology, J.W.; software, X.L.; validation, C.Z.; formal analysis, X.L.; investigation, X.L. and C.Z.; resources, Q.G., X.Z. and K.L.; data curation, X.L.; writing—original draft preparation, X.L.; writing—review and editing, Y.W. and J.W.; visualization, X.L.; supervision, Q.G., X.Z., Y.W., J.W. and K.L.; project administration, Q.G., X.Z., K.L. and J.W.; funding acquisition, Y.W. and J.W. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Natural Science Foundation of Guangdong Province: (No.2023A1515011186); National Natural Science Foundation of China (No.22278156); Guangdong Innovation Projects Foundation for Ordinary Universities (No.2022KTSCX005).

Data Availability Statement

The data supporting the findings of this study are included in the article.

Conflicts of Interest

Qiang Ge and Congyun Zhu were employed by China CEC Engineering Corporation. Xianbo Zhou and Kuanyong Liu were employed by Pengsheng (Group) Paper Corporation. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Liu, B.; Lv, L.; Ding, L.; Gao, L.; Li, J.; Ma, X.; Yu, Y. Comparison of phthalate esters (PAEs) in freshwater and marine food webs: Occurrence, bioaccumulation, and trophodynamics. J. Hazard. Mater. 2024, 466, 133534. [Google Scholar] [CrossRef] [PubMed]
  2. Zheng, X.; Lu, G.; Liu, J.; Jiang, R. Phthalate esters in municipal sewage treatment plants: Occurrence level, removal rate and optimum combination technology. Front. Environ. Eng. 2023, 2, 1208689. [Google Scholar] [CrossRef]
  3. Belinda, M.; Chang, H.; Emma, K.; Mueller, J.F.; Benjamin, T. Bisphenols and phthalates in Australian wastewater: A statistical approach for estimating contributions from diffuse and point sources. Water Res. 2023, 246, 120680. [Google Scholar] [CrossRef]
  4. Liu, M.; Du, X.; Chen, H.; Bai, C.; Lan, L. Systemic investigation of di-isobutyl phthalate (DIBP) exposure in the risk of cardiovascular via influencing the gut microbiota arachidonic acid metabolism in obese mice model. Regen. Ther. 2024, 27, 290–300. [Google Scholar] [CrossRef]
  5. Safar, A.M.; Santacruz-Márquez, R.; Laws, M.J.; Meling, D.D.; Liu, Z.; Kumar, T.R.; Nowak, R.A.; Raetzman, L.T.; Flaws, J.A. Dietary exposure to an environmentally relevant phthalate mixture alters follicle dynamics, hormone levels, ovarian gene expression, and pituitary gene expression in female mice. Reprod. Toxicol. 2023, 122, 108489. [Google Scholar] [CrossRef]
  6. Tan, H.; Gao, P.; Luo, Y.; Gou, X.; Xia, P.; Wang, P.; Yan, L.; Zhang, S.; Guo, J.; Zhang, X.; et al. Are New Phthalate Ester Substitutes Safer than Traditional DBP and DiBP? Comparative Endocrine-Disrupting Analyses on Zebrafish Using In Vivo, Transcriptome, and In Silico Approaches. Environ. Sci. Technol. 2023, 57, 13744–13756. [Google Scholar] [CrossRef]
  7. Sun, J.; Wei, B.; Mei, Q.; An, Z.; Wang, X.; Han, D.; Xie, J.; Zhan, J.; Zhang, Q.; Wang, W.; et al. Theoretical investigation on the degradation of dibutyl phthalate initiated byOH and SO 4 ·—In aqueous solution: Mechanism, kinetics and ecotoxicity assessment. Chem. Eng. J. 2020, 382, 122791. [Google Scholar] [CrossRef]
  8. Pang, X.; Sarvothaman, V.P.; Nathan, S.; Wang, Z.; Rooney, D.W.; Ranade, V.V.; Robertson, P.J. Kinetic modelling of the photocatalytic degradation of Diisobutyl phthalate and coupling with acoustic cavitation. Chem. Eng. J. 2022, 444, 136494. [Google Scholar] [CrossRef]
  9. Tufail, A.; Price, W.E.; Mohseni, M.; Pramanik, B.K.; Hai, F.I. A critical review of advanced oxidation processes for emerging trace organic contaminant degradation: Mechanisms, factors, degradation products, and effluent toxicity. J. Water Process Eng. 2020, 40, 101778. [Google Scholar] [CrossRef]
  10. Tang, M.; Wan, J.; Wang, Y.; Ye, G.; Yan, Z.; Ma, Y.; Sun, J. Overlooked role of void-nanoconfined effect in emerging pollutant degradation: Modulating the electronic structure of active sites to accelerate catalytic oxidation. Water Res. 2024, 249, 120950. [Google Scholar] [CrossRef]
  11. Li, Y.; Liu, Z.; Sun, Z. A novel Co-N-doped carbon catalyst to activate peroxymonosulfate for efficient removal of sulfamethazine: Role of singlet oxygen and high-valent cobalt-oxo species. J. Water Process Eng. 2024, 63, 105398. [Google Scholar] [CrossRef]
  12. Luo, Y.; Liu, C.; Wang, X.; Zhang, Q.; Yao, C.; Huang, D.; Liu, X.; Lu, Y.; Song, W.; Chen, S.; et al. A novel, low-cost, and efficient separation strategy based on S-doped C3N4 for the analysis of PCDD/Fs and dioxin-like PCBs. J. Environ. Chem. Eng. 2024, 12, 112529. [Google Scholar] [CrossRef]
  13. Long, L.; Wang, X.; Fu, H.; Qu, X.; Zheng, S.; Xu, Z. Robust Activity and Stability of P-Doped Fe-Carbon Composites Derived from MOF for Bromate Reduction. Acs Appl. Mater. Inter. 2024, 16, 21838–21848. [Google Scholar] [CrossRef] [PubMed]
  14. Liu, Z.; Liu, Q.; Zhang, X.; Shi, B.; Qin, D.; Wang, J.; Zhang, A.; Liu, Y. Degradation of phenol by Cu-Ni bimetallic-doped sludge biochar as a fenton-like catalyst: Mechanistic study and practical application. Sep. Purif. Technol. 2024, 347, 127554. [Google Scholar] [CrossRef]
  15. Zhao, Y.; An, H.; Dong, G.; Feng, J.; Ren, Y.; Wei, T. Elevated removal of di-n-butyl phthalate by catalytic ozonation over magnetic Mn-doped ferrospinel ZnFe2O4 materials: Efficiency and mechanism. Appl. Surf. Sci. 2020, 505, 144476. [Google Scholar] [CrossRef]
  16. Leal, T.W.; Lourenço, L.A.; de L Brandão, H.; da Silva, A.; de Souza, S.G.; de Souza, A. Low-cost iron-doped catalyst for phenol degradation by heterogeneous Fenton. J. Hazard. Mater. 2018, 359, 96–103. [Google Scholar] [CrossRef]
  17. Zhou, T.; Wang, H.; Dong, W.; Du, T.; Li, X.; Wang, F.; Zhao, Z. Electron transfer-mediated peroxymonosulfate activation through monoatomic Fe–pyridinic N4 moiety in biochar-based catalyst for electron-rich pollutants degradation in groundwater. Chem. Eng. J. 2024, 492, 152158. [Google Scholar] [CrossRef]
  18. Lai, C.; Wang, N.; Xu, F.; Zhang, M.; Huang, D.; Ma, D.; Zhou, X.; Xu, M.; Li, L.; Yan, H.; et al. Pomelo peel biochar supported nZVI@Bi0 as a persulfate activator for the degradation of acetaminophen: Enhanced performance and degradation mechanism. Sep. Purif. Technol. 2024, 350, 127966. [Google Scholar] [CrossRef]
  19. Tong, S.; Chen, D.; Jiang, X.; Xu, Z.; Liu, X.; Shen, J. Persulfate activation by Fe3O4-doped biochar synthesized from Fenton sludge and sewage sludge for enhanced 1-H-1,2,4-triazole degradation. Chem. Eng. J. 2023, 461, 142075. [Google Scholar] [CrossRef]
  20. Hao, M.; Wang, Q.; Yu, F.; Guan, Z.; Zhang, X.; Sun, Y. Efficient degradation of 2,4-dichlorophphenol in groundwater using persulfate activated by nitrogen-doped biochar-supported nano zero-valent iron. J. Clean. Prod. 2024, 458, 142415. [Google Scholar] [CrossRef]
  21. Qiu, Y.; Zhang, Q.; Wang, Z.; Gao, B.; Fan, Z.; Li, M.; Hao, H.; Wei, X.; Zhong, M. Degradation of anthraquinone dye reactive blue 19 using persulfate activated with Fe/Mn modified biochar: Radical/non-radical mechanisms and fixed-bed reactor study. Sci. Total Environ. 2021, 758, 143584. [Google Scholar] [CrossRef] [PubMed]
  22. Zhou, J.; Li, X.; Yuan, J.; Wang, Z. Efficient degradation and toxicity reduction of tetracycline by recyclable ferroferric oxide doped powdered activated charcoal via peroxymonosulfate (PMS) activation. Chem. Eng. J. 2022, 441, 136061. [Google Scholar] [CrossRef]
  23. Li, L.; Zhang, Q.; She, Y.; Yu, Y.; Hong, J. High-efficiency degradation of bisphenol A by heterogeneous Mn–Fe layered double oxides through peroxymonosulfate activation: Performance and synergetic mechanism. Sep. Purif. Technol. 2021, 270, 118770. [Google Scholar] [CrossRef]
  24. Zhang, T.; Xue, Y.; Xu, M.; Zhu, Z.; Zhang, Q.; Hong, J. Efficient degradation of benzalkonium chloride by FeMn-CA300 catalyst activated persulfate process: Surface hydroxyl potentiation mechanism and degradation pathway. Environ. Pollut. 2023, 333, 121986. [Google Scholar] [CrossRef]
  25. Li, L.; Lai, C.; Huang, F.; Cheng, M.; Zeng, G.; Huang, D.; Li, B.; Liu, S.; Zhang, M.; Qin, L.; et al. Degradation of naphthalene with magnetic bio-char activate hydrogen peroxide: Synergism of bio-char and Fe–Mn binary oxides. Water Res. 2019, 160, 238–248. [Google Scholar] [CrossRef]
  26. Xu, L.; Wu, C.; Liu, P.; Bai, X.; Du, X.; Jin, P.; Yang, L.; Jin, X.; Shi, X.; Wang, Y. Peroxymonosulfate activation by nitrogen-doped biochar from sawdust for the efficient degradation of organic pollutants. Chem. Eng. J. 2020, 387, 124065. [Google Scholar] [CrossRef]
  27. Zhu, Q.; Xiang, T.; Chen, C.; Zhang, J.; Wu, Z.; Rao, S.; Li, B.; Yang, J. Enhancing activity and stability of FeNC catalysts through co incorporation for oxygen reduction reaction. J. Colloid. Interf. Sci. 2024, 663, 53–60. [Google Scholar] [CrossRef]
  28. Xiang, M.; Wang, Y.; Ren, X.; Yang, Z.; Huang, Y.; Zhu, S.; Chen, L.; Zhang, J.; Li, H. Efficient degradation of tetrabromobisphenol A by metal-organic framework-derived N-doped Fe/Fe3C@NC catalysts in sequential reduction-oxidation system. Sep. Purif. Technol. 2024, 340, 126672. [Google Scholar] [CrossRef]
  29. Lu, J.; Jv, A.; Zhao, H.; Che, G.; Feng, B.; Zhang, Y.; Liu, C.; Guan, R. Fc-COOH modified MIL-101(Cr) as enhanced photocatalyst to efficiently degrade tetracycline under visible light. Sep. Purif. Technol. 2024, 346, 127442. [Google Scholar] [CrossRef]
  30. Hu, C.; Xing, G.; Han, W.; Hao, Y.; Zhang, C.; Zhang, Y.; Kuo, C.H.; Chen, H.; Hu, F.; Li, L.; et al. Inhibiting demetalation of Fe-N-C via Mn sites for efficient oxygen reduction reaction in Zinc-Air batteries. Adv. Mater. 2024, 36, 2405763. [Google Scholar] [CrossRef]
  31. Bai, J.; Cheng, L.; Liu, S.; Lian, Y.; Deng, Y.; Zhou, Q.; Xiang, M.; Tang, Y.; Su, Y. Construct N-doped carbon anchored CoFe alloy nanoparticles with high content graphitic-N for electrocatalytic oxygen reduction. J. Colloid. Interf. Sci. 2024, 653, 1785–1791. [Google Scholar] [CrossRef] [PubMed]
  32. Lu, T.; Chen, F. Multiwfn: A multifunctional wavefunction analyzer. J. Comput. Chem. 2012, 33, 580–592. [Google Scholar] [CrossRef] [PubMed]
  33. Meng, H.; Nie, C.; Li, W.; Duan, X.; Lai, B.; Ao, Z.; Wang, S.; An, T. Insight into the effect of lignocellulosic biomass source on the performance of biochar as persulfate activator for aqueous organic pollutants remediation: Epicarp and mesocarp of citrus peels as examples. J. Hazard. Mater. 2020, 399, 123043. [Google Scholar] [CrossRef] [PubMed]
  34. Zhang, Y.; Pan, H.; Murugananthan, M.; Sun, P.; Dionysiou, D.D.; Zhang, K.; Khan, A.; Zhang, Y. Glucose and melamine derived nitrogen-doped carbonaceous catalyst for nonradical peroxymonosulfate activation. Carbon. 2020, 156, 399–409. [Google Scholar] [CrossRef]
  35. Xu, L.; Fu, B.; Sun, Y.; Jin, P.; Bai, X.; Jin, X.; Shi, X.; Wang, Y.; Nie, S. Degradation of organic pollutants by Fe/N co-doped biochar via peroxymonosulfate activation: Synthesis, performance, mechanism and its potential for practical application. Chem. Eng. J. 2020, 400, 125870. [Google Scholar] [CrossRef]
  36. Wang, H.; Guo, W.; Liu, B.; Wu, Q.; Luo, H.; Zhao, Q.; Si, Q.; Sseguya, F.; Ren, N. Edge-nitrogenated biochar for efficient peroxydisulfate activation: An electron transfer mechanism. Water Res. 2019, 160, 405–414. [Google Scholar] [CrossRef]
  37. Chen, X.; Oh, W.; Hu, Z.; Sun, Y.; Webster, R.; Li, S.; Lim, T. Enhancing sulfacetamide degradation by peroxymonosulfate activation with N-doped graphene produced through delicately-controlled nitrogen functionalization via tweaking thermal annealing processes. Appl. Catal. B Environ. 2018, 225, 243–257. [Google Scholar] [CrossRef]
  38. Han, Y.; Zhao, C.; Zhang, W.; Liu, Z.; Li, Z.; Han, F.; Zhang, M.; Xu, F.; Zhou, W. Cu-doped CoOOH activates peroxymonosulfate to generate high-valent cobalt-oxo species to degrade organic pollutants in saline environments. Appl. Catal. B Environ. 2024, 340, 123224. [Google Scholar] [CrossRef]
  39. Wu, Z.; Wang, Y.; Xiong, Z.; Ao, Z.; Pu, S.; Yao, G.; Lai, B. Core-shell magnetic Fe3O4@Zn/Co-ZIFs to activate peroxymonosulfate for highly efficient degradation of carbamazepine. Appl. Catal. B Environ. 2020, 277, 119136. [Google Scholar] [CrossRef]
  40. Lee, Y.; Kim, Y.T.; Kwon, E.E.; Lee, J. Biochar as a catalytic material for the production of 1,4-butanediol and tetrahydrofuran from furan. Environ. Res. 2020, 184, 109325. [Google Scholar] [CrossRef]
  41. Xu, Z.; Zhou, Y.; Sun, Z.; Zhang, D.; Huang, Y.; Gu, S.; Chen, W. Understanding reactions and pore-forming mechanisms between waste cotton woven and FeCl3 during the synthesis of magnetic activated carbon. Chemosphere 2020, 241, 125120. [Google Scholar] [CrossRef] [PubMed]
  42. He, Y.; Yang, Y.; Ye, X.; Lv, Y.; Liu, Y.; Liu, M. Enhanced persulfate activation for sulfadiazine degradation by N, S self-doped biochar from sludge and sulfonated lignin: Emphasizing the roles of graphitic nitrogen and thiophene sulfur. J. Environ. Chem. Eng. 2024, 12, 112407. [Google Scholar] [CrossRef]
  43. He, Y.; Qin, H.; Wang, Z.; Wang, H.; Zhu, Y.; Zhou, C.; Zeng, Y.; Li, Y.; Xu, P.; Zeng, G. Fe-Mn oxycarbide anchored on N-doped carbon for enhanced Fenton-like catalysis: Importance of high-valent metal-oxo species and singlet oxygen. Appl. Catal. B Environ. 2024, 340, 123204. [Google Scholar] [CrossRef]
  44. Ye, S.; Zeng, G.; Tan, X.; Wu, H.; Liang, J.; Song, B.; Tang, N.; Zhang, P.; Yang, Y.; Chen, Q.; et al. Nitrogen-doped biochar fiber with graphitization from Boehmeria nivea for promoted peroxymonosulfate activation and non-radical degradation pathways with enhancing electron transfer. Appl. Catal. B Environ. 2020, 269, 118850. [Google Scholar] [CrossRef]
  45. Xie, D.; Guo, P.; Zhong, K.; Sheng, G. Highly dispersed Co/Fe bimetal in carbonaceous cages as heterogeneous Fenton nanocatalysts for enhanced sulfamethoxazole degradation. Appl. Catal. B Environ. 2022, 319, 121923. [Google Scholar] [CrossRef]
  46. El Batouti, M.; Al-Harby, N.F.; Elewa, M.M. A Review on Promising Membrane Technology Approaches for Heavy Metal Removal from Water and Wastewater to Solve Water Crisis. Water 2021, 13, 3241. [Google Scholar] [CrossRef]
  47. Punnoy, P.; Aryal, P.; Hefner, C.E.; Brack, E.; Rodthongkum, N.; Potiyaraj, P.; Potiyaraj, P.; Henry, C. Smartphone-assisted dual-sided capillary microfluidic device for multiplex detection of heavy metals and nutrients in drinking water. Anal. Chim. Acta 2025, 1356, 344031. [Google Scholar] [CrossRef]
  48. Yu, Y.; Li, N.; Lu, X.; Yan, B.; Chen, G.; Wang, Y.; Duan, X.; Cheng, Z.; Wang, S. Co/N co-doped carbonized wood sponge with 3D porous framework for efficient peroxymonosulfate activation: Performance and internal mechanism. J. Hazard. Mater. 2022, 421, 126735. [Google Scholar] [CrossRef]
  49. Gao, Y.; Chen, Z.; Zhu, Y.; Li, T.; Hu, C. New Insights into the Generation of Singlet Oxygen in the Metal-Free Peroxymonosulfate Activation Process: Important Role of Electron-Deficient Carbon Atoms. Environ. Sci. Technol. 2020, 54, 1232–1241. [Google Scholar] [CrossRef]
  50. Wang, Z.; Chen, Z.; Li, Q.; Zhao, Z.; Cheng, X. Non-Radical Activation of Peracetic Acid by Powdered Activated Carbon for the Degradation of Sulfamethoxazole. Environ. Sci. Technol. 2023, 57, 10478–10488. [Google Scholar] [CrossRef]
  51. Chen, D.; Bai, X.; Chen, Y.; Wang, Y.; Zhu, Y. Efficient removal of sulfamethoxazole by activated peroxodisulphates using Fe/N co-doped biochar: The minimal role of high-valent iron species. Sep. Purif. Technol. 2024, 343, 127078. [Google Scholar] [CrossRef]
  52. Chen, Y.; Liu, L.; Wei, J.; Liu, Z.; Wang, H.; Zhu, Y.; Shao, Q.; Xie, P. Efficient bimetallic activation of sulfite by CoFe-LDH for bisphenol A removal: Critical role of Co/Fe ratio on ROS generation. Chem. Eng. J. 2024, 492, 152171. [Google Scholar] [CrossRef]
  53. Wang, Z.; Nengzi, L.; Zhang, X.; Zhao, Z.; Cheng, X. Novel NiCo2S4/CS membranes as efficient catalysts for activating persulfate and its high activity for degradation of nimesulide. Chem. Eng. J. 2020, 381, 122517. [Google Scholar] [CrossRef]
  54. Feng, Y.; Liao, C.; Kong, L.; Wu, D.; Liu, Y.; Lee, P.; Shih, K. Facile synthesis of highly reactive and stable Fe-doped g-C3N4 composites for peroxymonosulfate activation: A novel nonradical oxidation process. J. Hazard. Mater. 2018, 354, 63–71. [Google Scholar] [CrossRef] [PubMed]
  55. Gong, W.; He, D.; Wang, X.; Yan, Y. The role of Fe(IV) in the zero-valent iron biochar activated persulfate system for treatment of contaminants of emerging concern. Chem. Eng. J. 2024, 487, 150553. [Google Scholar] [CrossRef]
  56. Sun, Y.; Zhao, Y.; Zhan, X.; Gao, R.; Chen, L.; Yu, J.; Wang, H.; Shi, H. A ZIF-8-derived copper-nitrogen co-hybrid carbon catalyst for peroxymonosulfate activation to degrade BPA. Chemosphere 2022, 308, 136489. [Google Scholar] [CrossRef]
  57. Huang, M.; Wang, X.; Liu, C.; Fang, G.; Gao, J.; Wang, Y.; Zhou, D. Mechanism of metal sulfides accelerating Fe(II)/Fe(III) redox cycling to enhance pollutant degradation by persulfate: Metallic active sites vs. reducing sulfur species. J. Hazard. Mater. 2021, 404, 124175. [Google Scholar] [CrossRef]
  58. Guo, Z.; Li, C.; Gao, M.; Xiao, H.; Zhang, Y.; Zhang, W.; Li, W. Mn-O Covalency Governs the Intrinsic Activity of Co-Mn Spinel Oxides for Boosted Peroxymonosulfate Activation. Angew. Chem. Int. Ed. 2020, 60, 274–280. [Google Scholar] [CrossRef]
  59. Niu, H.; Dong, Z.; Guo, H.; Yang, Y.; Yang, W.; Yan, M.; Niu, C.; Li, J. Cu inanchored MnO/carbonaceous frameworks trigger peroxymonosulfate activation for enrofloxacin degradation: ROS generation and pollutant attacking processes. J. Environ. Chem. Eng. 2024, 12, 113243. [Google Scholar] [CrossRef]
  60. Yan, C.; Li, J.; Sun, Z.; Chen, L.; Sun, X.; Wang, X.; Xia, S. Engineering sulfur vacancies on Mo-doped FeS2 nanosheets grown on activated carbon fibers enhances peroxymonosulfate activation for efficient elimination of sulfamethazine, antibiotic resistant bacteria and antibiotic resistance genes: The dominant role of singlet oxygen. Chem. Eng. J. 2024, 493, 152643. [Google Scholar] [CrossRef]
  61. Yao, J.; Yu, Y.; Qu, R.; Chen, J.; Huo, Z.; Zhu, F.; Wang, Z. Fe-Activated Peroxymonosulfate Enhances the Degradation of Dibutyl Phthalate on Ground Quartz Sand. Environ. Sci. Technol. 2020, 54, 9052–9061. [Google Scholar] [CrossRef]
  62. Chen, X.; Chen, Y.; Li, S.; Cheng, X.; Liu, D.; Huang, W. Unraveling the crucial role of Mo2N from Fe/Mo bimetal MOF-derived catalyst in initiating Fe3+/Fe2+ redox cycle to activate peroxymonosulfate for dibutyl phthalate degradation. Chem. Eng. J. 2023, 476, 146693. [Google Scholar] [CrossRef]
Water 17 01700 g001
Figure 1. (a) SEM images, (b) SEM-EDS energy spectrum, (c) elemental mapping of FeMn-NBC.
Figure 1. (a) SEM images, (b) SEM-EDS energy spectrum, (c) elemental mapping of FeMn-NBC.
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Figure 2. (a) XRD patterns, (b) Raman spectra of catalysts.
Figure 2. (a) XRD patterns, (b) Raman spectra of catalysts.
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Figure 3. (a) DIBP removal in different systems; (b) the relevant pseudo-first-order kinetics of PMS oxidation systems; DIBP removal by FeMn-NBC; (c) synthesized with different Fe/Mn atomic ratios; (d) synthesized at different temperatures. Reaction conditions: [DIBP] = 10 mg/L, [PMS] = 3 mM, [catalyst] = 0.2 g/L.
Figure 3. (a) DIBP removal in different systems; (b) the relevant pseudo-first-order kinetics of PMS oxidation systems; DIBP removal by FeMn-NBC; (c) synthesized with different Fe/Mn atomic ratios; (d) synthesized at different temperatures. Reaction conditions: [DIBP] = 10 mg/L, [PMS] = 3 mM, [catalyst] = 0.2 g/L.
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Figure 4. Effects of (a) FeMn-NBC dosage; (c) PMS concentration; and (e) initial pH on the DIBP degradation performance. (b,d,f) Corresponding kobs. Reaction conditions: [DIBP] = 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L.
Figure 4. Effects of (a) FeMn-NBC dosage; (c) PMS concentration; and (e) initial pH on the DIBP degradation performance. (b,d,f) Corresponding kobs. Reaction conditions: [DIBP] = 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L.
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Figure 5. Effect of (a) Cl−, (b) HCO3−, (c) H2PO4−, (d) SO42−, and (e) HA on DIBP degradation in the FeMn-NBC/PMS system. Reaction conditions: [DIBP] = 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L.
Figure 5. Effect of (a) Cl−, (b) HCO3−, (c) H2PO4−, (d) SO42−, and (e) HA on DIBP degradation in the FeMn-NBC/PMS system. Reaction conditions: [DIBP] = 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L.
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Figure 6. Effects of (a) recycling times on DIBP removal in FeMn-NBC/PMS system and (b) leaching of Fe and Mn ions in FeMn-NBC/PMS system. Reaction conditions: [DIBP] = 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L. (c) XRD and (d) FTIR spectra of FeMn-NBC before and after use.
Figure 6. Effects of (a) recycling times on DIBP removal in FeMn-NBC/PMS system and (b) leaching of Fe and Mn ions in FeMn-NBC/PMS system. Reaction conditions: [DIBP] = 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L. (c) XRD and (d) FTIR spectra of FeMn-NBC before and after use.
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Figure 7. The degradation of (a) DIBP in different real water, (b) other pollution in FeMn-NBC/PMS system. Reaction conditions: [DIBP]/[TCP]/[BPA]= 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L.
Figure 7. The degradation of (a) DIBP in different real water, (b) other pollution in FeMn-NBC/PMS system. Reaction conditions: [DIBP]/[TCP]/[BPA]= 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L.
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Figure 8. Effects of (a) different scavengers, (b) EtOH, (c) TBA, (d) BQ, and (e) L-histidine on DIBP removal in FeMn-NBC/PMS system and (f) ESR spectra of •OH and SO4•−, (g) 1O2, and (h) O2•−. Reaction conditions: [DIBP]= 10mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L.
Figure 8. Effects of (a) different scavengers, (b) EtOH, (c) TBA, (d) BQ, and (e) L-histidine on DIBP removal in FeMn-NBC/PMS system and (f) ESR spectra of •OH and SO4•−, (g) 1O2, and (h) O2•−. Reaction conditions: [DIBP]= 10mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L.
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Figure 9. (a) Pre-mixing FeMn-NBC and PMS on DIBP degradation. (b) LSV profiles of different systems, (c) EIS profiles of various catalysts. Reaction conditions: [DIBP]= 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L, initial pH.
Figure 9. (a) Pre-mixing FeMn-NBC and PMS on DIBP degradation. (b) LSV profiles of different systems, (c) EIS profiles of various catalysts. Reaction conditions: [DIBP]= 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L, initial pH.
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Figure 10. (a) Effect and (b) the relevant pseudo-first-order kinetics of DMSO on DIBP degradation in the FeMn-NBC/PMS system, MPSO consumption, and MPSO2 generation in different systems: (c) FeMn-NBC alone system, (d) FeMn-NBC/PMS system. Reaction conditions: [DIBP]= 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L, [PMSO] = 0.1 mM.
Figure 10. (a) Effect and (b) the relevant pseudo-first-order kinetics of DMSO on DIBP degradation in the FeMn-NBC/PMS system, MPSO consumption, and MPSO2 generation in different systems: (c) FeMn-NBC alone system, (d) FeMn-NBC/PMS system. Reaction conditions: [DIBP]= 10 mg/L, [PMS] = 3 mM, [FeMn-NBC] = 0.2 g/L, [PMSO] = 0.1 mM.
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Figure 11. High resolution XPS spectra of FeMn-NBC before and after reaction: (a) the wide scan survey (b) C 1s, (c) N 1s, (d) O 1s, (e) Mn 2p, (f) Fe 2p.
Figure 11. High resolution XPS spectra of FeMn-NBC before and after reaction: (a) the wide scan survey (b) C 1s, (c) N 1s, (d) O 1s, (e) Mn 2p, (f) Fe 2p.
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Figure 12. The reaction mechanism of the FeMn-NBC-activated PMS degradation of the DIBP system.
Figure 12. The reaction mechanism of the FeMn-NBC-activated PMS degradation of the DIBP system.
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Figure 13. (a) DIBP molecule structure; (b) the ESP of DIBP; (c) the HOMO orbitals map; (d) the LUMO orbitals map.
Figure 13. (a) DIBP molecule structure; (b) the ESP of DIBP; (c) the HOMO orbitals map; (d) the LUMO orbitals map.
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Figure 14. The proposed degradation pathways of DIBP in the FeMn-NBC/PMS system.
Figure 14. The proposed degradation pathways of DIBP in the FeMn-NBC/PMS system.
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Figure 15. The toxicity analysis of DIBP in FeMn-NBC/PMS system: (a) Fathead minnow LC50 (96 h), (b) Daphnia magna LC50 (48 h), (c) Developmental Toxicity, (d) Bioaccumulation factor, (e) Mutagenicity.
Figure 15. The toxicity analysis of DIBP in FeMn-NBC/PMS system: (a) Fathead minnow LC50 (96 h), (b) Daphnia magna LC50 (48 h), (c) Developmental Toxicity, (d) Bioaccumulation factor, (e) Mutagenicity.
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Table 1. The metal leaching of FeMn-NBC.
Table 1. The metal leaching of FeMn-NBC.
Cycles12345
FeLeaching concentration (mg/L)1.4641.2940.6290.1670.021
Absolute metal loss ratio (%)0.1190.1050.0510.0130.002
MnLeaching concentration (mg/L)1.1060.9370.7320.2460.013
Absolute metal loss ratio (%)0.1440.1220.0960.0320.002
Table 2. Element at% of fresh FeMn-NBC and used FeMn-NBC.
Table 2. Element at% of fresh FeMn-NBC and used FeMn-NBC.
CatalystsElement
Fresh FeMn-NBCN 1s (%)Pyridinic NPyrrolic NGraphic NFe-N/Mn-N
1.3615.5619.7863.34
Fe 2p (%)Fe 0Fe2+Fe3+
21.2226.0630.65
Mn 2p (%)Mn2+Mn3+Mn IV
16.4242.8135.63
Used FeMn-NBCN 1s (%)Pyridinic NPyrrolic NGraphic NFe-N/Mn-N
28.3640.546.4124.69
Fe 2p (%)Fe 0Fe2+Fe3+
14.5432.727.22
Mn 2p (%)Mn2+Mn3+Mn IV
30.8432.0922.84
Table 3. The Fukin index of DIBP.
Table 3. The Fukin index of DIBP.
Atomq (N)q (N + 1)q (N − 1)f−f+f0Δf
1 (C)−0.0286−0.10020.05850.08720.07160.0794−0.0156
2 (C)−0.0234−0.11650.03290.05630.09310.07470.0368
3 (C)−0.0243−0.06360.01190.03620.03930.03770.0031
4 (C)0.0029−0.06180.0640.06110.06480.06290.0037
5 (C)−0.0087−0.07860.03460.04330.06990.05660.0266
6 (C)−0.0273−0.07490.00950.03690.04760.04220.0107
7 (C)0.21480.14290.23270.0180.07190.04490.0539
8 (C)0.21650.18370.24840.03190.03280.03230.0009
9 (O)−0.1157−0.1457−0.08330.03240.030.0312−0.0023
10 (O)−0.261−0.3434−0.19480.06620.08240.07430.0162
11 (C)0.03980.030.05050.01060.00980.0102−0.0008
12 (O)−0.12−0.1314−0.07850.04150.01140.0264−0.0301
13 (C)0.0410.03380.05080.00970.00720.0085−0.0025
14 (O)−0.2666−0.3274−0.12560.1410.06090.1009−0.0801
15 (C)−0.011−0.0124−0.00670.00440.00140.0029−0.003
16 (C)−0.076−0.083−0.06910.00690.0070.0070.0001
17 (C)−0.0829−0.0858−0.07860.00430.00280.0036−0.0015
18 (C)−0.0114−0.0129−0.00610.00530.00150.0034−0.0038
19 (C)−0.0839−0.0861−0.07880.00510.00220.0037−0.0029
20 (C)−0.0768−0.0829−0.06870.00810.00610.0071−0.0021
21 (H)0.04430.00190.08330.0390.04240.04070.0034
22 (H)0.0457−0.00240.07960.0340.04810.0410.0141
23 (H)0.04650.01530.07250.0260.03120.02860.0053
24 (H)0.04070.00990.06740.02680.03080.02880.004
25 (H)0.03520.01780.05220.0170.01740.01720.0004
26 (H)0.03310.02260.0420.00890.01050.00970.0017
27 (H)0.03560.02730.04580.01010.00830.0092−0.0019
28 (H)0.03470.02310.05360.01890.01160.0152−0.0073
29 (H)0.02870.02960.03040.0017−0.00090.0004−0.0026
30 (H)0.03180.01860.04490.01320.01320.01320
31 (H)0.0260.0160.03590.00990.010.010.0001
32 (H)0.03110.0250.03660.00560.00610.00580.0006
33 (H)0.02930.01620.04290.01360.01320.0134−0.0004
34 (H)0.02480.03070.0208−0.004−0.0059−0.0049−0.002
35 (H)0.02490.01530.03490.01010.00960.0098−0.0005
36 (H)0.0270.02590.03140.00440.00110.0028−0.0033
37 (H)0.02540.03120.0229−0.0025−0.0058−0.0042−0.0033
38 (H)0.02730.0150.04290.01560.01220.0139−0.0034
39 (H)0.02410.01680.03570.01160.00730.0095−0.0043
40 (H)0.03030.0180.04580.01560.01230.0139−0.0033
41 (H)0.03070.02490.03780.00710.00580.0065−0.0013
42 (H)0.02550.01750.03690.01150.00790.0097−0.0035
Table 4. The intermediates of DIBP during the FeMn-NBC/PMS oxidation process identified by HPLC-MS.
Table 4. The intermediates of DIBP during the FeMn-NBC/PMS oxidation process identified by HPLC-MS.
ProductsMass-to-Charge Ratio (m/z)FormulaChemical Structure
1DIBP278C16H22O4Water 17 01700 i001
2P1221C12H14O4Water 17 01700 i002
3P2249C14H18O4Water 17 01700 i003
4P3127C7H12O2Water 17 01700 i004
5P4193C11H14O3Water 17 01700 i005
6P5165C8H6O4Water 17 01700 i006
7P6266C14H18O5Water 17 01700 i007
8P7163C10H12O2Water 17 01700 i008
9P8117C4H4O4Water 17 01700 i009
10P9181C8H6O5Water 17 01700 i010
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Lin, X.; Ge, Q.; Zhou, X.; Wang, Y.; Zhu, C.; Liu, K.; Wan, J. Enhancement of Electron Transfer Between Fe/Mn Promotes Efficient Activation of Peroxomonosulfate by FeMn-NBC. Water 2025, 17, 1700. https://doi.org/10.3390/w17111700

AMA Style

Lin X, Ge Q, Zhou X, Wang Y, Zhu C, Liu K, Wan J. Enhancement of Electron Transfer Between Fe/Mn Promotes Efficient Activation of Peroxomonosulfate by FeMn-NBC. Water. 2025; 17(11):1700. https://doi.org/10.3390/w17111700

Chicago/Turabian Style

Lin, Xiaoni, Qiang Ge, Xianbo Zhou, Yan Wang, Congyun Zhu, Kuanyong Liu, and Jinquan Wan. 2025. "Enhancement of Electron Transfer Between Fe/Mn Promotes Efficient Activation of Peroxomonosulfate by FeMn-NBC" Water 17, no. 11: 1700. https://doi.org/10.3390/w17111700

APA Style

Lin, X., Ge, Q., Zhou, X., Wang, Y., Zhu, C., Liu, K., & Wan, J. (2025). Enhancement of Electron Transfer Between Fe/Mn Promotes Efficient Activation of Peroxomonosulfate by FeMn-NBC. Water, 17(11), 1700. https://doi.org/10.3390/w17111700

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