Novel sulfur vacancies featured MIL-88A(Fe)@CuS rods activated peroxymonosulfate for coumarin degradation: Different reactive oxygen species generation routes under acidic and alkaline pH

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Abstract

A novel rod-shaped MIL-88A(Fe)@CuS featured with sulfur vacancies (SV) were constructed as heterogeneous catalysts for activating peroxymonosulfate (PMS) for coumarin (COU) degradation. A series of xMIL@CuS were obtained according to the mass content of MIL-88A(Fe) in the composites (x, wt% = 50 %, 65 %, and 80 %). Among them, 65 % MIL@CuS hold the best performance, and realized a complete COU removal (30 μM) in 7 min (0.2 g/L 65 %MIL@CuS and 0.5 mM PMS). The degradation was much more favorable in acidic initial pH than alkaline initial pH. The calculated reaction rate constants at initial pH of 3.0, 5.0, 6.0 and 9.0 were 0.903, 0.729, 0.650 and 0.095 min−1, respectively. Electron paramagnetic resonance (EPR) analysis, radical scavenging tests and mechanism exploration indicated that the main difference in degradation under acidic and alkaline pH came from the yield of 1O2. In initial pH = 3.0 condition, SV and lattice oxygen on 65 %MIL@CuS participated in the generation of 1O2, greatly increasing the content of 1O2 (11.6 × 10−11 M) and promoting the degradation. While under initial alkaline condition (pH = 9.0), 1O2 were basically produced from the reaction between Cu(II) and PMS, resulting in a low yield (1.7 × 10−11 M) and lower degradation. Besides, 65 %MIL@CuS maintained excellent reusability with low metal ions leaching, and the degradation exceeded 98.0 % even in the fifth run. Overall, this work provided an efficient and stable activator for activating PMS to degrade refractory organics, and managed to disclose the activation mechanisms under acidic and alkaline pH.

Introduction

The pleasant fragrance of coumarin (COU) makes it frequently used in perfumes, soaps, and cosmetics products, resulting in the release of the substance into the aquatic environment (Zeng et al., 2021a). COU has been reported to induce estrogenic responses in fish species and exacerbate hepatotoxicity and tumor development in rodents (Montanaro et al., 2017, Blanco et al., 2019). It is also a potential endocrine disruptor for mammals and some of people are much more susceptible to its toxicity (Abraham et al., 2010). As a result, there is a growing demand to seek efficient water treatment technologies to remove COU from water matrix.

Advanced oxidation processes (AOPs), certified as an efficient and promising technique, have been extensively utilized in hazardous organics removal (Zeng et al., 2020). Some AOPs methods have been attempted to remove COU. Görmez et al. investigated the electro-Fenton and subcritical water oxidation processes to degrade COU, achieving 99 % and 88 % COU degradation, respectively (Görmez et al., 2022). Montanaro et al. used boron-doped diamond anodes and UV irradiation to degrade COU via electrochemical oxidation, and 50 mg/L COU was complete removal and mineralized after 3 h (Montanaro et al., 2017). However, UV and electrochemical oxidation are uneconomical and unsustainable due to the additional energy required. Sulfate radical (SO4•−) based AOPs (SR-AOPs) are considered as a preference on account of the wide adaptive pH range, higher redox potential, longer half-life and excellent selectivity of SO4•− (Zeng et al., 2021b). Generally, transition metals like Cu, Fe, Ni, Co, and Mn have been regarded as effective activators for PMS and no energy input is required (Wang and Wang, 2018, Zeng et al., 2022, Zhu et al., 2022, Xia et al., 2022). Yet, metal ions addition in homogeneous reaction system greatly limits its application because of the inevitable secondary pollution and metal sludge (Dong et al., 2019). Thus, it is necessary to construct novel heterogeneous catalysts building on transition metals with high activity and stability (Zhang et al., 2021, Zhu et al., 2021).

Metal organic frameworks (MOFs) have received a surge of interest in the fields of adsorption/separation (Zhou et al., 2014, Yang et al., 2013), photo-catalysis (Tian et al., 2019) and catalysis (Zhou et al., 2021, Zhang et al., 2018), owing to excellent properties of large pore volume, high apparent surface areas, well-defined structure (Liao et al., 2019), and fine dispersion of active metal sites (Duan et al., 2018). Especially, iron-based MOFs have received tremendous attention in environmental remediation due to their environmental friendliness and unique structural characteristics (Liu et al., 2017, Luo et al., 2021). For example, MIL-101 (Fe), MIL-100 (Fe), MIL-53 (Fe), and MIL-88B (Fe) have been developed to remove acid orange 7 (AO7) via adsorption and persulfate activation (Li et al., 2016). Among numerous iron-based MOFs, MIL-88A(Fe) possesses impressive water/chemical stability (Liu et al., 2018, Amaro-Gahete et al., 2019) and excellent swelling properties (Mellot-Draznieks et al., 2005). Wang et al. synthesized a series of MIL-88A(Fe) in diverse preparation conditions to activate persulfate and realized the removal of 96.4 % Orange gelb (Wang et al., 2016). However, as the coordination spheres of metal ions in MOFs are completely connected or obstructed by organic linkers, the intrinsic shortage of free unsaturated metal sites in MOFs limits their ability to degrade organic contaminants (Liu et al., 2014). In view of this, an effective method has been attempted to produce more active metal sites by introducing metal complexes to connect with organic linkers in MOFs (Wu et al., 2013).

Copper sulfide (CuS), a natural mineral, has been served as photo-catalysts due to its fantastic optical property. Recently, copper sulfide (CuS) and its derivatives have been applied as activators for H2O2 (Zhang et al., 2021, Nie et al., 2013), PMS (Wang et al., 2020), and PS (Peng et al., 2018) for organics elimination. It was reported that the unsaturated S atoms distributed on the surface of metal sulfides could facilitate the conversion of Fe(III)/Fe(II) (Xing et al., 2018). Zhang el al. found that the sulfur in Fe3O4@CuS nanoparticles promoted the conversion of Cu(II)/Cu(I) and Fe(III)/Fe(II), and the reaction kinetic rate constant achieved by Fe3O4@CuS was more than 20 times higher than that of Fe3O4 (Zhang et al., 2021). Yan et al. also reported that the ciprofloxacin degradation obtained by CuS/Fe2O3/Mn2O3 nanocomposite (81.6 %) was much higher than Fe2O3/Mn2O3 (~ 30 %) (Huang et al., 2020). In addition, sulfur vacancies (Sv) have been studied to adjust the surface electronic and geometric structure of nanomaterials to improve the catalytic activity and adsorption free energy (Gao et al., 2020). Our previous study demonstrated that Sv in CuS@MIL-101(Fe) could boost the metal reduction and enhance the catalytic activity (Zhou et al., 2021). Kuang et al. also verified that Sv in MoS2 improved the adsorption energy of Fe3+ to accelerate the Fenton reaction process (Kuang et al., 2021). Benefiting from the well-defined structure of MIL-88A(Fe) and Sv in CuS, incorporating CuS onto MIL-88A(Fe) is expected to be a more efficient approach for PMS activation (Chen et al., 2021). Unfortunately, to the best of our knowledge, no attempt has been made to construct MIL-88A(Fe)@CuS as heterogeneous catalyst for activating PMS for organics degradation. Besides, initial acidic and alkaline pH are considered to hold a crucial influence on reactive oxygen species (ROS) production in heterogeneous PMS activation, but the mechanism of the effect remains underdeveloped and needs further clarification.

Herein, a novel MIL-88A(Fe)@CuS rod featured with abundant sulfur vacancies was successfully synthesized by in-situ growing CuS on rod-like MIL-88A(Fe). The morphology, crystal structure, and chemical composition of the as-synthesized catalysts were characterized. The catalytic activity of MIL@CuS toward PMS activation for COU degradation was studied systematically. The generation routes of reactive oxygen species (ROS) in the catalytic system under acidic and alkaline pH were unveiled. The possible activation mechanisms and degradation pathways of COU were proposed.

Section snippets

Materials

FeCl3·6H2O, CuCl2·2H2O, Thiourea (CH4N2S), NaCl, NaNO3, Na2SO4, NaHCO3, H2SO4, NaOH, ethyl alcohol (EtOH), N,N-Dimethylformamide (DMF), methanol (MeOH), nitrobenzene (NB), furfuryl alcohol (FFA) were purchased from Sinopharm Chemical Reagent Co., Ltd. Fumaric acid (FA) and p-hydroxybenzoic acid (HBA) were obtained from Shanghai Macklin Biochemical Co., Ltd. Sigma-Aldrich Chemical Co. Ltd., (China) provided Sulfamethoxazole (SMX), sulfadiazine (SDZ), carbamazepine (CBZ), bisphenol A (BPA),

Catalysts characterization

The surface morphology and microstructure of MIL-88A(Fe), CuS, and 65 %MIL@CuS were examined using SEM as depicted in Fig. 1. MIL-88A(Fe) exhibits a rod-like crystal morphology with a diameter of 4 µm and a length of around 13 µm (Fig. 1a and b). CuS displays a flower-like sphere with a diameter of 2 µm (Fig. 1c and d). In Fig. 1e and f, the as-synthesized 65 %MIL@CuS remains the rod-shape structure just like MIL-88A(Fe), with CuS nanoparticles uniformly attached on the surface of MIL-88A(Fe).

Conclusions

In this work, we synthesized novel sulfur vacancies featured MIL-88A(Fe)@CuS rod and used it as PMS activator for the COU degradation. The loading amount of MIL-88A(Fe) greatly affected on the catalytic performance. 0.2 g/L of the as-synthesized 65 %MIL@CuS and 0.5 mM of PMS could completely remove 30 μM of COU in 7 min, and the reaction rate constant was 0.650 min−1. The initial solution pH greatly influenced activation mechanisms. EPR and radicals scavenging tests identified that OH and 1O2

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We were grateful to the financial support from The Science and Technology Innovation Program of Hunan Province (2021RC3039) and Natural Science Foundation of Hunan Province (2021JJ40069).

References (71)

  • B. Lake

    Coumarin metabolism, toxicity and carcinogenicity: relevance for human risk assessment

    Food Chem. Toxicol.

    (1999)
  • C. Li et al.

    Peroxymonosulfate activation for efficient sulfamethoxazole degradation by Fe3O4/β-FeOOH nanocomposites: coexistence of radical and non-radical reactions

    Chem. Eng. J.

    (2019)
  • X. Li et al.

    Fe-based MOFs for efficient adsorption and degradation of acid orange 7 in aqueous solution via persulfate activation

    Appl. Surf. Sci.

    (2016)
  • Y. Li et al.

    Efficient degradation of sulfamethazine via activation of percarbonate by chalcopyrite

    Water Res.

    (2021)
  • X. Liao et al.

    Synthesis of (100) surface oriented MIL-88A-Fe with rod-like structure and its enhanced fenton-like performance for phenol removal

    Appl. Catal. B: Environ.

    (2019)
  • N. Liu et al.

    Ultrathin graphene oxide encapsulated in uniform MIL-88A(Fe) for enhanced visible light-driven photodegradation of RhB

    Appl. Catal. B: Environ.

    (2018)
  • H. Luo et al.

    Application of iron-based materials in heterogeneous advanced oxidation processes for wastewater treatment: a review

    Chem. Eng. J.

    (2021)
  • D. Montanaro et al.

    UV-assisted electrochemical degradation of coumarin on boron-doped diamond electrodes

    Chem. Eng. J.

    (2017)
  • G. Nie et al.

    Fabrication of polyacrylonitrile/CuS composite nanofibers and their recycled application in catalysis for dye degradation

    Appl. Surf. Sci.

    (2013)
  • W.-D. Oh et al.

    Surface–active bismuth ferrite as superior peroxymonosulfate activator for aqueous sulfamethoxazole removal: performance, mechanism and quantification of sulfate radical

    J. Hazard. Mater.

    (2017)
  • J. Peng et al.

    Degradation of atrazine by persulfate activation with copper sulfide (CuS): kinetics study, degradation pathways and mechanism

    Chem. Eng. J.

    (2018)
  • C. Qi et al.

    Activation of peroxymonosulfate by base: implications for the degradation of organic pollutants

    Chemosphere

    (2016)
  • D. Roy et al.

    Mechanistic investigation of photocatalytic degradation of Bisphenol-A using MIL-88A(Fe)/MoS2 Z-scheme heterojunction composite assisted peroxymonosulfate activation

    Chem. Eng. J.

    (2022)
  • M. Saranya et al.

    Enhanced visible light photocatalytic reduction of organic pollutant and electrochemical properties of CuS catalyst

    Powder Technol.

    (2015)
  • H. Tian et al.

    Removal of MC-LR using the stable and efficient MIL-100/MIL-53 (Fe) photocatalyst: the effect of coordinate immobilized layers

    Appl. Catal. B: Environ.

    (2019)
  • J. Wang et al.

    Activation of persulfate (PS) and peroxymonosulfate (PMS) and application for the degradation of emerging contaminants

    Chem. Eng. J.

    (2018)
  • X. Wang et al.

    Efficient activation of peroxymonosulfate by copper sulfide for diethyl phthalate degradation: performance, radical generation and mechanism

    Sci. Total Environ.

    (2020)
  • F. Wu et al.

    Copper nanoparticles embedded in metal–organic framework MIL-101 (Cr) as a high performance catalyst for reduction of aromatic nitro compounds

    Inorg. Chem. Commun.

    (2013)
  • X. Wu et al.

    A mechanistic study of amorphous CoSx cages as advanced oxidation catalysts for excellent peroxymonosulfate activation towards antibiotics degradation

    Chem. Eng. J.

    (2020)
  • M. Xing et al.

    Metal sulfides as excellent co-catalysts for H2O2 decomposition in advanced oxidation processes

    Chem

    (2018)
  • J. Ye et al.

    2D/2D confinement graphene-supported bimetallic Sulfides/g-C3N4 composites with abundant sulfur vacancies as highly active catalytic self-cleaning membranes for organic contaminants degradation

    Chem. Eng. J.

    (2021)
  • X.-H. Yi et al.

    Photocatalysis-activated SR-AOP over PDINH/MIL-88A(Fe) composites for boosted chloroquine phosphate degradation: performance, mechanism, pathway and DFT calculations

    Appl. Catal. B: Environ.

    (2021)
  • R. Yuan et al.

    Self-assembled hierarchical and bifunctional MIL-88A (Fe)@ ZnIn2S4 heterostructure as a reusable sunlight-driven photocatalyst for highly efficient water purification

    Chem. Eng. J.

    (2020)
  • H. Zeng et al.

    Peroxymonosulfate-assisted photocatalytic degradation of sulfadiazine using self-assembled multi-layered CoAl-LDH/g-C3N4 heterostructures: performance, mechanism and eco-toxicity evaluation

    J. Water Process Eng.

    (2020)
  • H. Zeng et al.

    Novel Prussian blue analogues@MXene nanocomposite as heterogeneous activator of peroxymonosulfate for the degradation of coumarin: the nonnegligible role of Lewis-acid sites on MXene

    Chem. Eng. J.

    (2021)
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    Haojie Zhang and Chan Zhou contributed equally to this article.

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