Boosting the degradation of antibiotics via peroxymonosulfate activation with a Cu-based metal–organic framework

Abstract

Highly efficient degradation of antibiotics is a huge challenge due to the extremely stable molecules and the potential for biological resistance. However, conventional degradation methods are limited to lower degradation rate, higher energy consumption and secondary pollution. Herein, we report a new Cu-based metal–organic framework (MOF), featuring classical planar trinuclear [Cu₃(µ₃-O)]⁴⁺ clusters within the pores. The presence of the rich open metal sites and the large pore ratio, as well as the high catalytic activity of Cu²⁺ ions, are conducive to boosting the degradation of various antibiotics (>95%) under the activation of peroxymonosulfate. Remarkably, this is the first MOF to achieve such exceptional catalytic performance under neutral and even alkaline conditions, which exceeds those of most reported materials. Mechanism investigation demonstrates that multiple active species were produced and promoted the degradation synergistically during the advanced oxidation processes.

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Introduction

Antibiotics have been extensively used in the treatment of bacterial diseases, but most of them are non-metabolized and discharged into water directly, resulting in serious environmental pollution.¹ The traditional degradation methods (biological treatment and chlorination) are limited by the time-consuming processes and high-toxicity by-products. Therefore, highly effective methods are urgently needed for degrading the residual antibiotics.

As an emerging degradation technology, advanced oxidation processes (AOPs) based on the activation of persulfate (PS) or peroxymonosulfate (PMS) with other technologies can produce highly reactive species (hydroxyl radicals (HO˙), sulfate radicals (SO₄˙^–), singlet oxygen (¹O₂), superoxide radicals (O₂˙^–), etc.) for target degradation.^2,3 Among them, ¹O₂ and O₂˙^–, as the dominant reactive species, possess excellent resistance to the background components (inorganic ions, natural organic materials) of water, in contrast to the common radicals (HO˙ and SO₄˙^–). Furthermore, compared to the activation by UV light and heat, which is limited by the high energy consumption and complex operation, heterogeneous catalytic activation possesses more outstanding activity by virtue of the multi-functionality (metal activation) and stability (avoiding secondary pollution from the materials).^4–7 Therefore, the development of functional materials with high activity and stability, as well as being environmentally friendly, is still a huge challenge.⁸

Metal–Organic frameworks (MOFs) are well-known for the highly designable, tunable structures and pore surfaces, and have been applied in diverse fields,⁹ including catalytic oxidation.^10–12 However, the application of pure MOFs for degrading antibiotics in AOPs is rarely reported, while the majority focus is on the degradation of dyes. For example, [Fe₃O(TBA)₃(OH)(H₂O)₂] (MIL-88A(Fe), H₂TBA = trans-2-butenedioic acid) and defective [Fe₃O(ATA)₃(OH)(H₂O)₂] (MIL-88B(NH₂)(Fe), H₂NBDC = 2-amino-1,4-benzene dicarboxylic acid) have been reported as catalysts, achieving more than 90% degradation of tetracycline (TC) and sulfamethoxazole (SMX) via activating the oxidants, demonstrating that the open metal sites (OMSs) are more conducive to the activation of PMS.^13,14 Nevertheless, the high dosage of catalysts and the extra energy requirements, as well as the narrow pH range, significantly limit the application. On the other hand, the pores within MOFs usually act as confined space to load other functional molecules or metal nanoparticles to obtain composites, which can be used in the activation of PMS. For example, composite materials of Fe@C and CoS_x–CuS_x/CF derived from MOFs can degrade SMX with more than 95% degradation efficiencies.^15,16 However, poor yield, high loss and limited OMSs for composite materials hinder the degradation performance.¹⁷ As far as we know, most of the literature reports on heterogeneous catalysts for degradation of organics are focused on Fe-, Co-based catalysts. However, Cu²⁺ ions are more environment-friendly in comparison with Co²⁺ ions. On the other hand, the standard redox potential of E₀(Cu²⁺/Cu⁺) (1.7 V) is much higher than that of E₀(Fe³⁺/Fe²⁺) (0.77 V), which is more favorable for the production of active species by activating PMS.¹⁸ Therefore, it is still a tremendous challenge to find functional MOFs that can achieve efficient degradation of antibiotics with high stability and numerous catalytically active sites.

Here, we synthesized a new MOF, [Cu₃(µ₃-O)(pypz)₃]NO₃‧guest, namely MAF-wyu2 (1, Hpypz = 4-(1H-pyrazol-4-yl)pyridine), which is a new member of metal-azolate frameworks (MAFs),¹⁹ and possesses rich OMSs based on the planar trinuclear [Cu₃(µ₃-O)]⁴⁺ clusters. By virtue of the higher catalytic activity of Cu²⁺ ions and remarkable thermal and chemical stability, 1 can degrade common antibiotics (including SMX, oxytetracycline (OTC), sulfamethazine (SMZ), ciprofloxacin (CIP), TC) with high efficiency (95%+) within 30 minutes. In particular, the degradation performance for SMX, the most stable antibiotic, in AOPs reaches 100% based on PMS even in strong alkaline environments (pH = 11.0) with a low catalyst concentration (25 mg L⁻¹). 1 is the first MOF that can achieve such superior catalytic oxidation performance, and superior to most of the reported materials. The reactive oxygen species (ROS) quenching experiments and electron paramagnetic resonance (EPR) measurements verified the degradation mechanisms, suggesting that O₂˙^– and ¹O₂ are the dominant active substances. Multi-cycle experiments and common ion interference tests proved that this MOF possesses good reusability and anion resistance.

Results and discussion

Solvothermal reaction of Cu(NO₃)₂·4H₂O, Hpypz and 1H-1,2,4-triazole in N,N-dimethylacetamide (DMA) yielded the crystals of 1. Single-crystal X-ray diffraction revealed that 1 crystallizes in the cubic space group I43d, containing one Cu²⁺ ion, one pypz⁻ ligand, one-third of µ₃-O and one-third of NO₃⁻ counter anion in an asymmetric unit (Fig. S1 and Table S1†). Three Cu²⁺ ions are bridged by the pyrazolate groups from three pypz⁻ ligands and µ₃-O into a classic planar trinuclear [Cu₃(µ₃-O)]⁴⁺ cluster, exposing numerous OMSs within the pores (Fig. S2†). Each [Cu₃(µ₃-O)]⁴⁺ cluster connects with the other six clusters through pypz⁻ ligands, obtaining an extended 3D framework (Fig. 1a and S4†). The counter NO₃⁻ anions are located near the trinuclear clusters in the pores. Regarding the planar trinuclear [Cu₃(µ₃-O)(Rpz)₃(Rpy)₃]⁺ as 6-connected nodes and linear pypz⁻ as 2-connected linkers, the whole network forms a new 6-connected topology with the point symbol of {8⁶12⁹}{8}3 (Fig. S3†). Interestingly, there are 3D interconnected channels, with diameters of 8.6 × 8.6 Ų and 8.9 × 11.7 Ų along the a-axis, respectively (Fig. 1b and S4†). After ignoring the NO₃⁻ anions and solvate molecules, the pore ratio reaches 69.6% (Fig. 1b).

Fig. 1 (a) 3D coordination framework and (b) pore surface structure of 1.

The powder X-ray diffraction (PXRD) pattern of as-synthesized 1 matches well with the simulated one, indicating the high purity and crystallinity (Fig. S5†). The scanning electron microscopy (SEM) image of 1 shows that there is a smooth polyhedral morphology with a uniform particle size of about 25 µm (Fig. S6a and S6b†). Thermogravimetry analysis of 1 showed no obvious plateau, which can be attributed to the gradual removal of the high boiling point DMA molecules. After methanol (MeOH) exchange, 1 can be stable up to 200 °C (Fig. S7†). It is worth noting that 1 retained its framework after being immersed in aqueous solutions of pH range from 3.0 to 11.0 for six months, as well as in various organic solutions (N,N-diethylformamide (DEF), ethanol (EtOH), MeOH, acetonitrile (MeCN), diethyl ether (DEE)) for six months, indicating high chemical stability (Fig. S5†). It is worth noting that the PXRD patterns of the activated sample by various methods (direct heating activation, MeOH-exchanged activation and supercritical CO₂ (SC–CO₂) activation) were further obtained and indicated that the host-framework has been transformed into the amorphous state, probably owing to the large surface tension caused by the removal of guest molecules within the pores. Therefore, the N₂ adsorption isotherm of the host-framework cannot be measured. Interestingly, this amorphous state can be recovered to the as-synthesized phase after immersing in DMA, indicating that the structural transformations from the crystalline to the amorphous state are reversible (Fig. S8†).

Considering the excellent structural stability, and numerous OMSs within the framework,^20–221 may be a promising catalyst for efficient degradation of antibiotics by activating PMS. As far as we know, there are various types of antibiotics (e.g. tetracyclines, macrolides, quinolones, sulfonamides, etc), and sulfonamides (SAs, especially SMX) possess the most stability and poor biodegradability, leading to efficient degradation being extremely difficult. Therefore, degradation experiments were performed and showed that the degradation efficiency of SMX reached 100% within 20 min at pH = 7.0 by activating PMS (Fig. 2a and S9a†). In order to exclude the influence from the oxidation of PMS self-decomposition or the adsorption capacity of 1, the solely PMS or 1 exhibits insignificant degradation (about 10%) and adsorption efficiency (about 20%), respectively (Fig. 2a and S9a†). Specifically, the adsorption rate of SMX to the host-framework is rapid owing to the coulombic interactions between the SMX⁻ and the cationic host-framework. However, the adsorption capacity of SMX is limited due to the large molecular size of SMX. In contrast, the catalytic performance boosted significantly with the addition of both 1 and PMS, achieving complete degradation within 20 min (k_obs increased to 0.389 min⁻¹). These results indicate that the OMSs within the host-framework can accelerate the activation of PMS and facilitate the degradation. At the same time, the morphology, particle size and PXRD patterns of 1 are maintained after degradation, except that the crystal surface was slightly rough and the cracks increased (Fig. S6c and S6d†).

Fig. 2 (a) Comparison of the degradation performance in adsorption and/or catalysis. The influence of (b) catalyst concentrations, (c) pH, and (d) oxidant concentrations on the degradation of SMX. (e) The effect of the presence of common ions/molecules (1.0 mmol L⁻¹) on the degradation. (f) Recycling stability experiment for 5 times. (Experimental conditions: pH = 11.0, SMX = 5 µM, Catalyst = 25 mg L⁻¹, PMS = 100 µM, T = 25 °C.)

Since the reaction parameters (such as pH, catalyst and oxidant concentrations) play crucial roles in the production of ROS, different experiments were performed to explore the degradation efficiency in PMS-based AOPs.²³ Initially, the effect of catalyst concentrations shows that the degradation efficiencies are positively correlated with the catalyst concentrations due to the increasing OMSs, which is conducive to producing more ROS by activating PMS.²⁴ Notably, the degradation efficiency reached 100% within 30 min with the catalyst increased to 25 mg L⁻¹ (Fig. 2b), corresponding to the k_obs value of 0.282 min⁻¹ (Fig. S9b†). However, the degradation efficiency slightly decreases to 99% as the concentration increases to 50 mg L⁻¹, which is attributed to the quenching effect resulting from the reduction of ROS by the higher catalyst concentration.²⁵ These results indicate that the optimum catalyst concentration of 25 mg L⁻¹ not only can avoid agglomeration effectively, but also produce sufficient ROS.

Besides, considering the different pH of various wastewaters and the stability of 1, the SMX degradation in various pH shows that 1 possesses excellent degradation performance under a wide pH range from 5.0 to 11.0.²⁶ Specifically, the degradation efficiency of SMX reaches 98% at pH = 7.0. Considering SMX as a kind of dibasic acid (corresponding to pK_a1 = 1.7 and pK_a2 = 5.7), there are various forms of SMX with the pH changes according to the literature. The anionic form (SMX⁻) prevails at pH > 5.7 and exhibits optimal reaction activity owing to the activation of the aniline portion within SMX, which is more susceptible to electrophilic attacks by PMS.²⁷ In other words, the excellent catalytic performances of 1 under neutral and alkaline conditions are attributed to the fact that the anionic SMX⁻ is not only more susceptible to attack by PMS by virtue of the coulombic interactions, but also adsorption to the cationic host-framework. The degradation efficiencies increase from 72% (0.057 min⁻¹) to 98% (0.154 min⁻¹) within the pH various from 5.0 to 9.0 (Fig. 2c and S9c†). Therefore, the synergistic interactions between SMX⁻, the host-framework and ROS (generated by PMS activated with 1) facilitate the degradation. At the same time, PMS is inclined to produce more ROS (e.g.¹O₂, O₂˙^–) to accelerate the degradation under alkaline condition and the degradation efficiency reaches 100% (0.282 min⁻¹) at pH = 11.0. To the best of our knowledge, there are rare materials with excellent catalytic performance in such a wide pH range, and most of them work under neutral/weak alkaline conditions (Table S2†). In other words, 1 is the first MOF that can degrade SMX efficiently at pH = 11.0.

Additionally, the effect of oxidant concentrations (ranging from 0.05 mM to 0.20 mM) shows that the k_obs values are significantly correlated with the oxidant concentrations (providing more ROS), corresponding to that the oxidant concentrations increase from 0.083 min⁻¹ at 0.05 mM to 0.321 min⁻¹ at 0.20 mM (Fig. S9d†). It's worth noting that the k_obs increased slightly with the concentrations increasing from 0.10 mM to 0.20 mM, due to the presence of conversion and scavenging of highly oxidative ROS.^25,28 Therefore, the optimum oxidant concentration can be determined as 0.10 mM (Fig. 2d).

It was reported that the activation of PMS in AOPs can produce various active species for degradation.^29–31 To determine the dominant active species under the optimal degradation conditions (25 mg L⁻¹1, 0.10 mM PMS and pH = 11.0), MeOH, L-ascorbic acid (AA) and furfuryl alcohol (FFA) can be employed as quenchers of hydroxyl radicals (HO˙), sulfate radicals (SO₄˙^–), superoxide radicals (O₂˙^–) and singlet oxygen (¹O₂), respectively.³² It is clear that the degradation rates were slightly reduced (from 0.282 min⁻¹ to 0.196 min⁻¹), whereas the efficiency (>97%) exhibits insignificant change in the presence of 10 mM MeOH, indicating that neither SO₄˙^– nor HO˙ are dominant active species (Fig. 3a and S10†). In contrast, the degradation efficiencies and k_obs values are closely related to the quenching agents of AA and FFA, corresponding to 10% (0.003 min⁻¹) and 19% (0.008 min⁻¹) at 10 mM AA/FFA (Fig. 3a, S11 and S12†). Obviously, the non-radical pathway of O₂˙^– and ¹O₂ plays key roles in the degradation process. Alternatively, the presence of the active species (SO₄˙^–, HO˙, O₂˙^– and ¹O₂) can be further confirmed by EPR measurements by using the spin traps of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 2,2,6,6-tetramethyl-4-piperidinol (TEMP).³³ It is noted that no radical signal was observed with the addition of individual DMPO or PMS, while the typical adduct signals of DMPO-HO˙, DMPO-SO₄˙^–, as well as the typical sextuple signal of O₂˙^– were detected in the presence of 1 and PMS,³⁴ which indicate that HO˙, SO₄˙^– and O₂˙^– are produced in the AOPs (Fig. 3b and c). Moreover, there is a stronger triple signal of TEMP-¹O₂ after adding TEMP (Fig. 3d).³⁵ These results are consistent with the quenching experiments, demonstrating that the ¹O₂ and O₂˙^– play dominant roles in degrading SMX.

Fig. 3 (a) Effect of different scavengers on SMX degradation. (b) EPR spectra obtained with DMPO/HO˙ and DMPO/SO₄˙^–, (c) DMPO/O₂˙^– and (d) TEMP/¹O₂. High-resolution XPS spectra of Cu 2p (e) before and (f) after the degradation. (Experimental conditions: pH = 11.0, SMX = 5 µmol L⁻¹, Catalysts = 25 mg L⁻¹, PMS = 100 µmol L⁻¹, T = 25 °C, MeOH = 10 mmol L⁻¹, ascorbic acid = 10 mmol L⁻¹, FFA = 10 mmol L⁻¹.)

In order to investigate the recycling performance of 1, multiple cycle tests were performed and showed that the degradation efficiencies remain above 95%, indicating the significant reusability and stability (Fig. 2f). To ensure the stability of the MOF during the degradation and eliminate the possibility of Cu²⁺ leaching, ICP measurement of Cu²⁺ ion leaching concentration after degradation was performed, and there was only 0.76 mg L⁻¹, which is lower than the value specified in the standard (<1.0 mg L⁻¹ based on GB 25467-2010 or < 2.0 mg L⁻¹ based on the European Union standard).¹⁶ In addition, a comparison experiment at 0.8 mg L⁻¹ Cu²⁺ ion concentration (based on Cu(NO₃)₂) was also conducted and showed limited catalytic efficiency (36.62%) and k_obs (0.019 min⁻¹) (Fig. 2a and S9a†). In addition, considering that the complex components in sewage affect the degradation performance, degradation experiments in the presence of common ions (e.g., chloride ions (Cl⁻), bicarbonate ions (HCO₃⁻))/molecules showed insignificant effects on the degradation efficiency, except for humic acid (HA) (Fig. 2e, S13 and S14†).^36–38 Interestingly, the degradation efficiencies and k_obs values decreased from 100% (0.282 min⁻¹) to 38% (0.017 min⁻¹) with the concentrations of HA increasing from 0 mg L⁻¹ to 10 mg L⁻¹ (Fig. S15†), owing to the functional groups in HA competing with SMX for ROS, as well as the blocking of HA on the OMSs of the material surface.^39,40 These results show that the system exhibits great resistance to environmental anions in actual water and possesses strong degradation effects after filtering HA.

To further elucidate the relationship between ROS production and catalyst conductivity in the catalytic oxidation process, electrochemical and X-ray photoelectron spectroscopy (XPS) experiments were performed. First, the cyclic voltammetry curve of 1 exhibits strong reduction capacity, as well as electron transfer performance by virtue of the numerous OMSs and large specific surface area (Fig. S16a†). It is well known that the reaction rate of the material and electrode is related to the electron transfer resistance, corresponding to the smaller radius with lower impedance.⁴¹ Electrochemical impedance spectroscopy of 1 exhibits a smaller semicircular diameter, demonstrating the lower electron transfer impedance and higher charge transfer efficiency (Fig. S16b†). In addition, XPS results clearly show the presence of C, N, O and Cu in 1, and the spectra of other elements were calibrated by the binding energies of C (284.8 eV). Specifically, the peaks at 932.3 eV, 952.2 eV and 934.7 eV, 954.6 eV correspond to Cu(I) and Cu(II), respectively (Fig. 3e and f), illustrating the valence change of Cu in the degradation.⁴² It is noteworthy that the relative ratio of Cu(II) decreases from 46.2% to 29.3%, while that of Cu(I) increases from 53.8% to 70.7%, demonstrating that a portion of Cu(II) within the host-framework has been converted to Cu(I) in AOPs. These results indicated that there is a reduction process of Cu(II) to Cu(I) due to the transfer of the peaks in Cu 2p_1/2 and Cu 2p_3/2 towards the region of lower binding energy.

Based on the above results, the mechanism of degradation can be proposed as follows: PMS is activated by the Cu²⁺ ions in 1, facilitating the generation of ROS in the free radical and non-radical pathways and the transition of the metal valence state, as well as the formation of intermediates/products during the degradation (Fig. 4). First, for the free radical pathway, HSO₅⁻ (PMS) ions are decomposed into SO₅²⁻ ions at pH > 9.4 (eqn (1)), generating O₂˙^– species in the aqueous solution simultaneously (eqn (2)). Furthermore, the Cu²⁺ ions as the intermediate mediators obtain electrons from PMS more efficiently, triggering the decomposition of HSO₅⁻ and generation of O₂˙^– and SO₅˙^– (eqn (3) and (4)). Simultaneously, the Cu⁺ ions react with HSO₅⁻, producing HO˙ and SO₄˙^– (eqn (5) and (6)). It is worth noting that SO₄˙^– are only available at pH < 10.0. Therefore, SO₄˙^– are hydrolyzed to produce a large amount of HO˙ under extremely alkaline conditions, which is conducive to the degradation (eqn (7)). On the other hand, in the non-radical pathway, the Cu²⁺ ions can activate HSO₅⁻ to form SO₅˙^–, and subsequently generate ¹O₂ by recombination (eqn (8) and (9)). Consequently, SMX can be degraded to various products with lower toxicity than SMX in the presence of ROS (HO˙, SO₄˙^–, O₂˙^–, ¹O₂) (eqn (10)), and even to CO₂ and H₂O (Fig. 4 and S17†).¹⁸

Fig. 4 The proposed mechanism of SMX degradation by PMS activation with 1.

Since the application of pure MOFs for antibiotic degradation is rarely reported, various types of classical MOFs, such as [Fe(OH)(BDC)] (MIL-53(Fe), H₂BDC = 1,4-benzene dicarboxylic acid), [Fe₃(µ₃-O)Cl(H₂O)₂(BDC)₃] (MIL-101(Fe)), [Cu₃(µ-OH)(pzca)₃(H₃O)] (H₂pzca = 1H-pyrazole-4-carboxylic acid), [Cu₃(BTC)₂(H₂O)₃] (HKUST-1, H₃BTC = benzene-1,3,5-tricarboxylic acid), [Co₂(dhbdc)(H₂O)₂] (MOF-74, H₄dhbdc = 2,5-dihydroxyterephthalic acid), [(Zn₄O)₃(Cu₃(PyCA)₃)₄(BDC)₃] (FDM-6, H₂PyC = 4-pyrazolecarboxylic acid), [Cu₂Zn₃(BTDD)₃Cl₄] (Cu-MFU-4l, H₂BTDD = bis(1H-1,2,3-triazolo[4,5-b],[4′,5′-i])dibenzo[1,4]dioxin), and a coordination compound of [Cu₃(PyCA)₃] (HPyCA = 1H-pyrazole-4-carbaldehyde), were selected as catalysts to evaluate the SMX degradation performance under the same conditions to verify the effects of the types of OMSs or various metal ions for the degradation performance. Interestingly, both MIL-53 and MIL-101 containing the OMSs of Fe³⁺ ions, and MOF-74 containing the OMSs of Co²⁺ ions, exhibit poor degradation efficiencies of less than 40%, while the degradation performance of HKUST-1 containing the OMSs of Cu²⁺ ions reaches 71% (k_obs = 0.047 min⁻¹). Although the standard redox potential of E₀(Co³⁺/Co²⁺) (1.92 V) is much higher than E₀(Cu²⁺/Cu⁺) (1.7 V) and E₀(Fe³⁺/Fe²⁺) (0.77 V), the larger pore ratio of 1 is more favorable for the diffusion of the antibiotics into the pores than other MOFs. These results imply that the degradation performance is not only related to the types of OMSs, but also to the porosity of the host-framework. To further demonstrate the role of planar trinuclear clusters, the degradation performance of [Cu₃(µ-OH)(pzca)₃(H₃O)], FDM-6, Cu-MFU-4l and [Cu₃(PyCA)₃] containing similar planar trinuclear units showed that 1 possesses the most significant degradation efficiency and rate constant (100%, 0.282 min⁻¹) compared to [Cu₃(µ-OH)(pzca)₃(H₃O)] (71%, 0.043 min⁻¹) [Cu₃(PyCA)₃] (83.4%, 0.059 min⁻¹), FDM-6 (59.3%, 0.039 min⁻¹) and Cu-MFU-4l (71.7%, 0.053 min⁻¹) (Fig. 5a and Table S3†), indicating that the significant degradation performance is the result of synergistic effect of the cationic host-framework and density of OMSs, as well as the porosity. At the same time, the Turnover Number (TON) and Turnover Frequency (TOF) were also calculated and indicated that the TOF and TON of 1 are 0.038 and 0.008 min⁻¹, respectively, which are superior to those of the selected materials (Table S3†).⁴³ In addition, the PXRD patterns of catalysts were retained after the degradation (Fig. S18†).

Fig. 5 (a) The SMX degradation performance based on various materials, and (b) the degradation of different antibiotics by PMS activated by 1. (Experimental conditions: pH = 11.0, antibiotics = 5 µmol L⁻¹, catalysts = 25 mg L⁻¹, PMS = 100 µmol L⁻¹, T = 25 °C.)

Considering that there are various antibiotics in the actual water, the degradation efficiencies of 1 towards OTC, SMZ, CIP, and TC were also tested. The results show that 1 can activate PMS to achieve high-efficiency degradation (>95% within 30 min) of other common antibiotics, demonstrating that 1 possesses excellent activity and adaptability for various organic contaminants (Fig. 5b).

Conclusions

In summary, a new Cu-based MOF with planar trinuclear [Cu₃(µ₃-O)]⁴⁺ clusters was synthesized. By virtue of the combination of excellent stability, rich OMSs in the framework and high activity of Cu²⁺ ions, as well as the large pore ratio, this MOF can effectively activate peroxymonosulfate to degrade various antibiotics by producing highly active species. Remarkably, the degradation is applicable not only for lower catalyst concentrations (25 mg L⁻¹), but also in a wide pH range. In particular, the degradation rate can reach 0.282 min⁻¹ at pH = 11.0. Mechanism studies demonstrate that the redox circulation between Cu(II) and Cu(I) promotes the participation of free and non-free radicals (including, HO˙, SO₄˙^–, O₂˙^–, ¹O₂) in the process of degradation, among which O₂˙^– and ¹O₂ are dominant. These results provide insights into designing potent catalysts with outstanding activity and long-term stability for degrading organic pollutants.

Data availability

All experimental supporting data are available in the ESI.†

Author contributions

Ying Wu: investigation, data curation, writing – original draft. Gang Liang: methodology, data curation, resources. Wen-Bin Li: methodology, data curation, resources. Xiao-Feng Zhong: resources, methodology. Yang–Yang Zhang: resources, methodology. Jia-Wen Ye: writing – review & editing. Tao Yang: writing – original draft, writing – review & editing, formal analysis. Zong-Wen Mo: project administration, funding acquisition, writing – original draft, writing – review & editing, formal analysis. Xiao-Ming Chen: supervision, project administration, funding acquisition.

Conflicts of interest

The authors declare no competing financial interest.

Acknowledgements

This work was supported by the NSFC (22101210), Municipal Science and Technology Bureau (Jiangke 2021-76), the Foundation of Department of Education of Guangdong Province (2023KTSCX152, 2022ZDJS027).

Notes and references

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Footnote

† Electronic supplementary information (ESI) available. CCDC 2309034. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d4sc02850c

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