Electron transfer mediated contaminant activates periodate to generate 1O2 by charge-confined single-atom catalyst

doi:10.21203/rs.3.rs-4671921/v1

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Electron transfer mediated contaminant activates periodate to generate ¹O₂ by charge-confined single-atom catalyst

https://doi.org/10.21203/rs.3.rs-4671921/v1

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published 05 Nov, 2024

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The electron transfer process (ETP) is able to avoid the redox cycling of catalysts by capturing electrons from contaminants directly. However, the ETP usually leads to the formation of oligomers and the reduction of oxidants to anions. Herein, the charge-confined Fe single-atom catalyst (Fe/SCN) with Fe-N₃S₁ configuration was designed to achieve ETP-mediated contaminant activation of the oxidant by limiting the number of electrons gained by the oxidant to generate ¹O₂. The Fe/SCN-activate periodate (PI) system shows excellent contaminant degradation performance due to the combination of ETP and ¹O₂. Experiments and DFT calculations show that the Fe/SCN-PI* complex with strong oxidizing ability triggers the ETP, while the charge-confined effect allows the single-electronic activation of PI to generate ¹O₂. In the Fe/SCN + PI system, the 100% selectivity dechlorination of ETP and the ring-opening of ¹O₂ avoid the generation of oligomers and realize the transformation of large-molecule contaminants into small-molecule biodegradable products. Furthermore, the Fe/SCN + PI system shows excellent anti-interference ability and application potential. This work pioneers the generation of active species using ETP’s electron to activate oxidants, which provides a new perspective on the design of single-atom catalysts via the charge-confined effect.

Earth and environmental sciences/Environmental sciences

Physical sciences/Chemistry/Environmental chemistry/Pollution remediation

Advanced oxidation processes (AOPs) have been widely used for contaminants disposal driven by their high efficiency and strong oxidation capacity^1–3. In conventional AOPs, an oxidant is activated by one electron from the catalyst to generate strongly oxidizing active species for the degradation of contaminants^4,5. Although the activation process of oxidants by catalysts significantly improved the degradation of contaminants, the difficult redox cycling of the active sites of catalysts makes the catalysts-activated AOPs suffer from the consumption of catalysts and the low utilization of oxidants^6–8.

Recently, the electron transfer process (ETP) has been found to degrade contaminants via catalyst-mediated electron transfer from contaminants to oxidants, which realizes the efficient utilization of oxidants and avoids the redox cycling of catalysts^9–11. Unfortunately, the absence of active species in the ETP system enables the contaminants that have lost electrons to polymerize with each other to form oligomers and occupy the active sites on the catalyst^12,13. In this way, the catalyst still exhibits poor reusability. However, the deep treatment of contaminants is habitually overlooked in the ETP systems, and current endeavors are mostly focused on the use of catalysts with excellent conductivity to mediate the electron transfer between reactants^14,15. Based on the uneven dispersion of active sites as well as the excellent conductivity of the catalyst, the unlimited transfer of electrons induces the oxidants (PI, PMS, and PDS, etc.) in the ETP system to get two electrons to be directly reduced to anions, resulting in the absence of active species^16–18. If the oxidant obtains only one electron from contaminants via the ETP, the active species will be generated. Meanwhile, the advantages of catalytic-activated AOPs and ETP will be combined in a single system. Therefore, it is necessary to design catalysts that can control the number of electrons transferred from contaminants to oxidants.

Heptazine-based carbon nitride (C₃N₄) forms a C-N conjugated framework due to the sp² hybridized π-conjugated structure within the heptazine unit. Whereas, the bridged N atoms are sp³-hybridized and are unable to form a conjugation together with the heptazine ring^19,20. Consequently, C₃N₄ can confine the charge within each heptazine unit, which is an ideal candidate for controlling the number of transferred electrons²¹. However, the lack of adsorption sites for reactants makes it difficult to induce the ETP reaction^22,23. The dual-site catalysts have been validated to enable the adsorption of different reactants^24,25. Compared with the dual metal sites, the metal-nonmetal dual-site catalysts can provide active sites for C₃N₄ without changing the charge-confined properties. Especially, the noncovalent interactions between halogen elements ( i.e., S···O) provide a robust basis for appropriate interactions between nonmetal sites and reactants^26,27. In addition, the coordination between nonmetal and metal single atoms is able to serve as a channel for rapid and directional charge transfer^22,28. Hence, the single atom catalyst supported by nonmetal-doped C₃N₄ will achieve electron transfer mediated the activation of oxidants by contaminant to generate active species via charge confinement.

In this work, the S-doped C₃N₄-loaded Fe single-atom catalyst (Fe/SCN) has been successfully prepared. The atomic level distribution of Fe and the coordination configuration of the active site as Fe-N₃S₁ are confirmed. The Fe/SCN + PI system exhibits excellent degradation performance for 4-CP via the synergistic mechanism of ETP and ¹O₂. Furthermore, it does confirm that ¹O₂ is derived from the activation of PI by electrons conducted from contaminants rather than the activation of PI by the Fe/SCN itself. DFT calculations verify that the charge channel of the Fe-S bond and the charge-confined active site enables electrons from 4-CP to be transferred to PI via a single-electron pathway, resulting in the generation of ¹O₂. The dechlorination of 4-CP is accomplished by the ETP in the Fe/SCN + PI system, while the ring-opening of the intermediates is further achieved by the ¹O₂ generated from the contaminants-activated PI, thus avoiding the generation of oligomeric products. This study proposes the concept of the charge-confined single-atom catalyst and applies it to the rational design of the Fe/SCN, which realizes the activation of PI by the electron from the contaminant to generate ¹O₂ via the ETP system.

Characterization of catalysts. The Fe/SCN was synthesized according to our previous work with a slight modification²⁹. The X-ray diffraction (XRD) patterns and Fourier-transform infrared spectroscopy (FTIR) spectra indicate that the Fe/SCN possesses a graphitic carbon nitride texture, and no Fe nanoparticles or iron sulfides are detected (Supplementary Fig. 1). Additionally, the Fe/SCN exhibits a lamellar morphology without visible Fe nanoparticles (Fig. 1a and b), indicating the excellent dispersion of Fe. As shown in Fig. 1c, the tiny bright spots in the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) image prove the atomic dispersion of Fe atoms in the Fe/SCN³⁰. Energy-dispersive X-ray (EDX) elemental mapping images (Fig. 1d) demonstrate that Fe and S are evenly distributed in the Fe/SCN. The precise Fe content is confirmed to be 6.20 wt% by inductively coupled plasma-optical emission spectrometry (ICP-OES). The specific surface area of the Fe/SCN (76.194 m² g^− 1) is larger than that of CN, SCN, and Fe/CN (Supplementary Fig. 2 and Table 1), which can provide more active sites for catalytic reactions³¹.

X-ray adsorption was employed to explore the chemical state and coordination environment of the Fe atoms in the Fe/SCN. The Fe K-edge X-ray absorption near edge structure (XANES) spectrum of the Fe/SCN is located between that of FeO and Fe₂O₃ (Fig. 1e), indicating that the oxidation state of Fe in the Fe/SCN is between + 2 and + 3³². As shown in Fig. 1f, the Fourier transform extended X-ray absorption fine structure (FT-EXAFS) spectrum of the Fe/SCN has only one dominant peak located at 1.53 Å. The peaks of Fe-Fe (2.21 Å) and Fe-O (2.67 Å) are not detected, consistent with the wavelet transform images (Supplementary Fig. 3), showing that the Fe in the Fe/SCN is atomically dispersed²⁹. The maximum peak of the Fe/SCN displays a slight positive shift than that of the FePc (Fig. 1f and Supplementary Fig. 3), showing that the atoms coordinated with Fe in the Fe/SCN are heteroatoms with a larger atomic radius than N³³. Additionally, the Fe-N and Fe-S peaks are detected in the N 1s and S 2p spectra of the Fe/SCN, respectively, indicating that both S and N are coordination atoms of Fe (Supplementary Fig. 4). The EXAFS-fitting results (Fig. 1g and Supplementary Table 2) show that the average coordination numbers of Fe-N and Fe-S are 3.3 and 0.9, respectively. From the above results, it is worth noting that the isolated Fe atom in the Fe/SCN is coordinated with three N atoms and one S atom to form the Fe-N₃S₁ moiety.

Periodate activation by Fe/SCN. The catalytic activities of the as-prepared samples were evaluated by activating PI to degrade 4-CP. As shown in Fig. 2a, the adsorption performances of the as-prepared catalysts for 4-CP are weak, and all of them are less than 5%. When the PI is added, neither CN nor SCN can degrade 4-CP, indicating that they cannot activate PI. The homogeneous Fe²⁺ or Fe³⁺ also have no performance on degrading 4-CP (Supplementary Fig. 5), whereas the Fe/CN has a rapid 4-CP degradation ability, demonstrating that the anchored Fe single atom is the active site for activating PI. Using the Fe/SCN to activate PI, the degradation rate of 4-CP is further improved. The optimization apparent reaction rate constant (k_obs, min^− 1) for the Fe/SCN (0.189 min^− 1) to decompose 4-CP is 2.3-fold higher than that of the Fe/CN (Supplementary Fig. 6–9), indicating that the Fe and S have a synergistic enhancement effect on the activation of PI.

To explore the reactive species, quenching experiments and electron paramagnetic resonance (EPR) tests were conducted. Tert-butanol (TBA), p-benzoquinone (p-BQ), furfuryl alcohol (FFA), and potassium dichromate (K₂Cr₂O₇) were used as scavengers of ·OH, ·O₂⁻, ¹O₂, and e⁻, respectively^34,35. For the Fe/CN + PI system, the active species of ·OH, ·O₂⁻, and ¹O₂ are verified by quenching experiments and EPR (Fig. 2b and Supplementary Fig. 10). Moreover, the ETP and Fe(Ⅳ) species are not detected (Fig. 2b and Supplementary Fig. 11). Hence, the degradation of 4-CP by Fe/CN-activated PI is a process accomplished synergistically by radicals and nonradicals. As demonstrated in Fig. 2b and c, the TBA does not affect the degradation rate of 4-CP, and the EPR characteristic signal of ·OH is not detected, showing that there is no ·OH in the Fe/SCN + PI system. As shown in Fig. 2c, the DMPO-·O₂⁻ and TEMP-¹O₂ adducts are detected, consistent with the results of the quenching experiments (Fig. 2b), confirming the generation of ·O₂⁻ and ¹O₂ in the Fe/SCN + PI system. As shown in Fig. 2d, the SOD can completely inhibit the generation of ¹O₂, suggesting that all of the ¹O₂ in the Fe/SCN + PI system are generated by the intermediate ·O₂ ^− 36. The presence of ETP in the Fe/SCN + PI system was further investigated. For the Fe/SCN + PI system, quenching electrons can significantly inhibit the degradation of 4-CP, tentatively suggesting that ETP plays a role in the degradation of 4-CP (Fig. 2b). Compared with the Fe/CN + PI system, the Fe/SCN + PI system has lower oxidant consumption in the case of degrading the same amount of 4-CP (Fig. 2e), which is one of the characteristics of the ETP system³⁷. Additionally, the removal of 4-CP and the consumption of PI have a very good linear correlation (Fig. 2f), indicating that the decomposition of 4-CP and PI simultaneously occurs¹⁷. As shown in Fig. 2g, the Fe/SCN displays an obvious change in current response when PI and 4-CP are added successively, corresponding to the formation of the catalyst-PI* complexes and the trigger of the ETP reaction, respectively^12,38. Correspondingly, the increase in potential after adding PI proves that the formed catalyst-PI* complexes induce a higher redox potential (Fig. 2h), which can facilitate the subsequent oxidation of contaminants³⁹. A more significant decrease in potential is observed at the Fe/SCN compared to the Fe/CN after the addition of 4-CP, confirming that the catalyst-PI* complex is directly consumed by 4-CP⁴⁰. The results of the oxidant consumption test and electrochemical experiments fully prove the existence of the ETP in the Fe/SCN + PI system. In conclusion, both ¹O₂ and ETP act on the degradation of 4-CP in the Fe/SCN + PI system.

Mechanism investigation of Fe/SCN + PI system. The relationship between ¹O₂ and ETP in the Fe/SCN + PI system is further explored. In Fig. 3a, different atmospheres (Air, O₂, and Ar) do not affect the catalytic performance of the Fe/SCN + PI system, showing that the reactive oxygen species are all from PI and are not related to dissolved oxygen²⁹. Moreover, the concentration of PI in the Fe/SCN + PI system remains unchanged for 30 min before the addition of 4-CP, while decreases over time after the addition of 4-CP (Supplementary Fig. 12), indicating that 4-CP is the initiator of the Fe/SCN + PI system⁴¹. The EPR signal of ·O₂⁻ increases obviously after the addition of 4-CP (Supplementary Fig. 13), verifying that the electrons provided by 4-CP promote the generation of reactive oxygen species²⁸. As depicted in Fig. 3b, the K₂Cr₂O₇ greatly suppresses the signal intensity of ¹O₂. Moreover, the fluorescence signal of DMA (a classical chemical probe that can react with ¹O₂ to form DMA-O₂) decreases significantly only after the addition of 4-CP as the electron donor (Fig. 3c and d)⁴². All of the above results demonstrate that the Fe/SCN + PI system is triggered by ETP, and then the electron from 4-CP activates PI to generate ¹O₂.

In order to figure out the electron transfer route in the Fe/SCN system, the adsorption sites of the reactants on the Fe/SCN surface are explored. As shown in Fig. 2h, the open-circuit potential of the SCN after the addition of PI is higher than that of the Fe/CN, indicating that the S may be the adsorption site of PI. As illustrated in the high-resolution I 3d XPS spectra (Supplementary Fig. 14), neither the CN nor the Fe/CN possess the adsorption capacity of PI, while the SCN and Fe/SCN exhibit obvious peaks of I 3d, revealing that the S site is essential for the interaction between the Fe/SCN and PI. When 4-CP and PI simultaneously exist, a comparison is made between the energies of the Fe and S dual sites for different modes of co-adsorption of the reactants (Fig. 3e). In comparison, the co-adsorption model, in which 4-CP interacts with the Fe site at the Cl-terminus and the PI adsorbs at the S site, has a much lower energy than the other model, which is consistent with the above XPS results. This provides the underlying conditions for the rapid transfer of electrons from 4-CP to PI via the Fe-S transport channel. As demonstrated in Fig. 3f, a large number of electrons are enriched at the PI molecule after the co-adsorption of 4-CP and PI. The number of charges received by the PI molecule is 0.88 e as evidenced by Bader charge calculations. The differential charge density analysis of the Fe/SCN reveals that the conjugate distribution of charges inside the heptazine ring enables electrons to move inside the heptazine ring easily (Fig. 3g), whereas it is difficult for the electrons to cross over and undergo long-range transfer between heptazine rings. Thus, the reactions of each Fe-N₃S₁ active moiety do not interfere with each other due to the unique charge-confined nature of heptazine units. In addition, it is clarified by the rotating ring-disk electrode test that the electron transfer number during the degradation of 4-CP by the Fe/SCN + PI system converges to 1 (Fig. 3h), thus realizing the generation of reactive oxygen species from the activated PI via single-electron transfer. In conclusion, the Fe/SCN achieved the activation of PI by the electron from contaminants to generate ¹O₂ via the single-electron transfer.

Contaminant degradation pathways. After figuring out the electron transfer process and PI activation mechanism in the Fe/SCN + PI system, the degradation pathway of this system towards 4-CP is further explored. As illustrated in Fig. 4a, when the degradation ratio of 4-CP is 92%, the dechlorination ratio is only 31% in the Fe/CN + PI system, whereas the Fe/SCN + PI system achieves 100% dechlorination of 4-CP. In addition, the change in PI concentration before and after the addition of 4-CP indicates that the Fe/SCN + PI system is triggered by ETP (Supplementary Fig. 12). The DFT calculations prove that 4-CP is adsorbed on the Fe site of the Fe/SCN by the terminal Cl (Fig. 3e). Hence, the degradation of 4-CP in the Fe/SCN + PI system originates from dechlorination induced by ETP. When the p-benzoquinone (the product obtained after 4-CP dechlorination) is used as the target contaminant in the Fe/SCN + PI system, the p-benzoquinone and PI concentrations show no obvious change (Fig. 4b). The results indicate that the ETP only accomplished the dechlorination of 4-CP without further degradation. Unlike traditional ETP, oligomers are easily produced after dechlorination, while no oligomers are detected in the Fe/SCN + PI system (Fig. 4c). As can be seen from Fig. 4d and Supplementary Fig. 15, the concentration of macromolecule products (C₆H₆O₂ and C₆H₄O₂) shows a trend of increase and then a decrease, while the concentration of micromolecule products (C₄H₄O₄, C₃H₄O₂, and C₂H₄O₃) continues to increase, suggesting that 4-CP is gradually converted into the small-molecule products after dechlorination in the presence of ¹O₂, an active species with good ring-opening properties⁴³. The total organic carbon (TOC) test results also demonstrate that the Fe/SCN + PI system can degrade the macromolecule organic pollutants to micromolecule products (Supplementary Fig. 16). The degradation pathway of 4-CP by the Fe/SCN + PI system is summarized (Fig. 4e). Firstly, the Cl of 4-CP is removed by ETP to produce p-benzoquinone, while the electrons from the ETP activate PI to produce ¹O₂. Then, the p-benzoquinone is further ring-opened by ¹O₂ to generate micromolecular products. Advantageously, the continuous generation of small molecule products with good microbial degradability in the Fe/SCN + PI system facilitates further biochemical treatment of the actual organic wastewater. In addition, the Fe/SCN + PI system shows good degradation of different halophenols (Fig. 4f), presenting the universality of the contaminant-triggered ETP and ¹O₂ synergistic degradation mechanism for halophenol degradation in this system.

Evaluation of practical application potential. The potential of the Fe/SCN for practical applications is verified. In Fig. 5a and b, the Fe/SCN + PI system shows excellent degradation performance for 4-CP over a wide pH range (pH = 2.5–10.5) and natural waters, which demonstrates that the Fe/SCN has superior environmental adaptability. As shown in Fig. 5c, the degradation rate of 4-CP has no obvious decrease in five cycles. Furthermore, the texture does not change before and after the five cycles, and the leaching amount of Fe is lower than that of the Fe/CN (Supplementary Fig. 17–18), which proves that the Fe/SCN has excellent reusability. When phenol is added to the Fe/SCN + PI system, no iodinated phenols such as 4-IP and 2-IP are detected (Supplementary Fig. 19a), which can rule out the existence of HOI⁴⁴. The IO₄⁻ is almost stoichiometrically converted to non-toxic IO₃⁻ during the reaction (Supplementary Fig. 19b). The I₂/I₃⁻ are also ruled out by starch colorimetry (Supplementary Fig. 19c)⁴⁵. These results confirm that the Fe/SCN + PI system does not form the low-valence iodine species containing potential environmental risks. The exclusion of toxic byproducts is also consistent with the results of the E. coli culture experiments (Supplementary Fig. 20). To evaluate the persistent reactivity of the system, a continuous-flow reactor consisting of a catalyst-filled column was constructed (Fig. 5d and Supplementary Fig. 21). Continuous degradation of 4-CP is achieved by activating PI using the prepared Fe/SCN-sodium alginate gel spheres as column packing. As shown in Fig. 5e, the degradation rate of 4-CP can be maintained at nearly 100% during the continuous reaction up to 270 h, indicating that the Fe/SCN has favorable potential for practical application.

In this work, the charge-confined Fe single-atom catalysts (Fe/SCN) with Fe-N₃S₁ configuration are successfully synthesized. The Fe/SCN + PI system shows efficient degradation of 4-CP by combining the ETP and ¹O₂. DFT calculations verify that the co-adsorption of reactants and the charge-confined active sites enable the electrons conducted by the contaminants to be further utilized in the activation of PI to generate ¹O₂. The 100% selective dechlorination of the ETP and the subsequent ring-opening of ¹O₂ realize the transformation of contaminants into small-molecule biodegradable products without the generation of oligomers. In addition, the Fe/SCN not only exhibits a wide pH tolerance and good recyclability but also presents continuous degradation up to about 270 hours. This work first achieves the activation of oxidants by the contaminant’s electron in the ETP system via the charge-confined Fe/SCN, which provides a new perspective on the design of single-atom catalysts.

Synthesis of Fe/SCN. Melamine (MA, 8 mmol) and Cyanuric acid (CA, 5.6 mmol) were dissolved into 100 mL and 105 mL of deionized water, respectively. Fe(NO₃)₃·9H₂O (1.2 mmol) and OA (2.4 mmol) were dissolved in 45 mL of deionized water and then added into CA solution. Following 5 min stirring, the mixed solution was added gradually to MA solution and stirred consistently for 4 h. The precursor was obtained by filtration and dry at 60°C overnight. 2.5 g of the precursor was mixed well with a certain amount of thiourea and then put into a crucible and placed in a tube furnace, and then calcined at 600°C for 4 h under Ar atmosphere. After natural cooling, the Fe/SCN was obtained.

Synthesis of Fe/CN. The synthesis process of the Fe/CN was identical to that of the Fe/SCN except that the precursor powder was calcined directly without the addition of thiourea.

Synthesis of SCN. The synthesis process of the SCN was identical to that of the Fe/SCN except that Fe(NO₃)₃·9H₂O was not added.

Synthesis of CN. The synthesis process of the CN was identical to that of the Fe/CN except that Fe(NO₃)₃·9H₂O was not added.

Material characterizations. The powder X-ray diffraction (XRD) pattern was conducted on a Bruker D8 Advance, and the source uses a Cu-Kα line at 0.1541 nm in a 2θ range from 5° to 70° with a scan rate of 2° min^− 1. The Fourier-transform infrared (FT-IR) spectra were performed using a VERTEX70 Fourier Transform Microscopic infrared spectrometer. Transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy were performed on the Tecnai F20 at 200 kV. High-angle annular dark-field (HAADF) images were acquired with a JEM-ARM200F TEM/STEM with a spherical aberration corrector working at 300 kV. The content of Fe in as-prepared catalysts was examined by an inductively coupled plasma atomic emission spectrometer (ICP-AES, ICAP 7200). X-ray photoelectron spectroscopy (XPS) was performed using a VG Escalab 250 spectrometer with an Al anode (Al-Kα = 1486.7 eV) radiation source and peak positions were corrected by the C 1s spectrum at 284.8 eV. Fe K-edge XAFS analyses were performed with Si(111) crystal monochromators at the BL14W Beam line at the Shanghai Synchrotron Radiation Facility (SSRF) (Shanghai, China). Before the analysis at the beamline, samples were placed into aluminum sample holders and sealed using Kapton tape film. The XAFS spectra were recorded at room temperature using a 4-channel Silicon Drift Detector (SDD) Bruker 5040. Fe K-edge extended X-ray absorption fine structure (EXAFS) spectra were recorded in transmission/fluorescence mode. Negligible changes in the line-shape and peak position of Fe K-edge XANES spectra were observed between two scans taken for a specific sample. The XAFS spectra of these standard samples were recorded in transmission mode. The spectra were processed and analyzed by the software codes Athena. The Brunauer-Emmett-Teller (BET) specific surface area of obtained catalysts were performed on a BELSORP-MAX Automatic specific surface area analyzer. The free radicals (such as ·OH and ·O₂⁻) and singlet oxygen (¹O₂) were recorded on electron paramagnetic resonance (EPR) spectrometer (Bruker A300, Germany) with 60.0 mM of DMPO and TEMP as the spin-trapper agent, respectively.

Catalytic performance. The catalytic degradation experiments for the model pollutant 4-CP (0.1 mM) were carried out at room temperature without special instructions. The beaker was always placed on a magnetic stirrer with a constant stirring speed during the reaction. The catalyst (25 mg, 0.5 g·L^− 1) was evenly dispersed in the 4-CP solution (49.5 mL, 0.1 mM). After continuous stirring for 30 min, PI (0.5 mL of 0.25 M) was added to start the degradation reaction. At fixed time intervals, 1 mL of the reaction solution was withdrawn and filtered using a filter fitted with a nylon membrane with a pore size of 0.22 µm to remove the catalyst, and after filtration, the obtained reaction solution was injected into a centrifuge tube containing 0.1 mL of methanol for subsequent testing. Scavenging experiments were carried out on ·OH, ·O₂⁻, ¹O₂, and e⁻ using TBA, p-BQ, FFA, and K₂Cr₂O₇, respectively, to determine the active species in the reaction system. The amount of each scavenger was determined as a molar ratio to the PI, where TBA: PI = 1000:1, p-BQ: PI = 20:1, FFA: PI = 50:1 and K₂Cr₂O₇: PI = 20:1. At least three parallel control groups were set up for each experiment to ensure the accuracy of the experimental data.

Analysis methods. Conditions for high-performance liquid-phase testing of organic pollutants, DMA probe experiments, detection of iodinated byproducts, electrochemical testing conditions, E. coli culture experiments, and preparation of the Fe/SCN-sodium alginate gel spheres were described in supplementary information. Details of DFT calculations were also included.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Competing interests

The authors declare no competing interests.

Author contributions

L.Z., T.M. and J.Z. conceived the ideas and co-wrote the manuscript. J.Z. supervised the entire project. Q.T., B.W., X.H., W.R., and Y.C. prepared, characterized, and tested the catalysts. L.Z., Q.T., L.L., and L.T. analyzed the data. Q.S. and Z.K. designed and performed the DFT calculations. All the authors participated in the discussion of the results and manuscript preparation and revision.

Acknowledgments

We gratefully acknowledge the financial support of the National Natural Science Foundation of China (52100186 and 52170082), the Natural Science Foundation of Jiangxi Province (20225BCJ23003, 20212ACB203008, and 20223AEI91001), and the support by Key Laboratory of Jiangxi Province for Persistent Pollutants Prevention Control and Resource Reuse (No. 2023SSY02061).

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Electron transfer mediated contaminant activates periodate to generate ¹O₂ by charge-confined single-atom catalyst

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