Insights into the mechanism of enhanced peroxymonosulfate degraded tetracycline using metal organic framework derived carbonyl modified carbon-coated Fe0

https://doi.org/10.1016/j.jhazmat.2021.127640Get rights and content

Highlights

  • Carbonyl modified carbon-coated Fe0 by one step calcination.

  • Roles of C, Fe0 and Cdouble bondO in PMS activation were investigated.

  • Degradation mechanism was proposed by experiment and DFT.

  • Toxicity of the intermediates was evaluated.

Abstract

Tetracycline (TC) is a commonly used antibiotic that has gained wide spread notoriety owing to its high environmental risks. In this study, rich carbonyl-modified carbon-coated Fe0 was obtained by pyrolysis of MIL-100(Fe) in an Ar atmosphere, and used to activate peroxymonosulfate (PMS) for the degradation of tetracycline in water. The roles of Fe0, carbon and surface carbonyl on PMS activation were investigated. Fe0 continuously activated PMS, acted as a sustained-release source of Fe2+, and could effectively activate PMS to produce SO4•−, O2•− and •OH. Carbon was found to do responsible for electron transportation during the activation of PMS and slow down the oxidation of Fe0. The carbonyl group on the carbon surface layer was the active site of 1O2, which explains the enhanced performance for TC degradation. When Ca = 0.1 g/L and C0 = 0.4 mM, TC degradation rate reached 96%, which was attributed to the synergistic effect of radicals (i.e., SO4•−, O2•−, •OH) and non-radical (i.e., 1O2). Finally, the degradation pathway was proposed by combining density functional theory (DFT) calculations with liquid chromatography-mass spectrometry (LC-MS), toxicities of the intermediate products were also evaluated. All results show that carbonyl-modified carbon-coated Fe0 possesses promising capacity for the removal of antibiotics from water.

Introduction

The antibiotic tetracycline (TC) is widely used to treat diseases in humans and animals, and as an additive in cattle feed. These applications are ascribed to its broad-spectrum activity and low cost (Gopal et al., 2020). TC has even been reported in current literature as a potential treatment for COVID-19 (Sodhi and Etminan, 2020). Unfortunately, only 25% of TC is metabolized by the human body, while the rest is released into the environment (Lundstrom et al., 2016). Residual TC can affect the growth and development of aquatic flora and fauna, potentially endanger human health through the biological food chain, and lead to endocrine disorders, mutagenicity, and antibiotic resistance (Gao et al., 2012, Xu et al., 2021). A method for removing TC from water is thus urgently needed.

So far, several methods, have been invested for the removal of pollutants from water, such as adsorption (Yang et al., 2020), photocatalysis (Jia et al., 2021, An et al., 2020, Yang et al., 2021, Yang et al., 2021, Liu et al., 2021), Microwave catalysis (Wang et al., 2021a), and advanced oxidation (Wang et al., 2021b, Wang et al., 2022). However, adsorption cannot decompose target pollutants (Guo et al., 2020, Guo et al., 2020, Guo et al., 2020), and the antibacterial properties of TC limit the efficiency of TC removal using biological methods (Bai et al., 2020). Based on different free radicals, advanced oxidation processes can be classified into Fenton systems represented by H2O2 (•OH), as well as systems represented by peroxymonosulfate (PMS) and persulfate (PDS) (SO4•−). Compared with •OH (1.8–2.7 V and 20 ns), SO4•− had a higher oxidative power (2.5–3.1 V) and longer half-life (30–40 μs) (Huang et al., 2021, Huang et al., 2021, Huang et al., 2021, Xiao et al., 2020), which rendered it superior for degrading aqueous pollutants.

SO4•− is obtained by adding light radiation (Ao et al., 2019, Shi et al., 2020), ultrasound (Asadzadeh et al., 2021) and electricity (Bai et al., 2021, Tang et al., 2021a) (see Table S1), furthermore, the activation of PMS using an asymmetric structure requires less energy (Kohantorabi et al., 2021). To reduce energy consumption, transition metals, such as Co (Liu et al., 2021, Liu et al., 2021, Liu et al., 2021), Mn, Fe (Yang et al., 2018) and Cu (Guo et al., 2021), were used as activators for PMS to degrade TC. However, as they can leach toxic ions (e.g., Co2+) and have long reaction times, their applicability is limited. Among them, Fe is considered a suitable activator for PMS because of its cost-effectiveness and eco-friendliness. However, traditional Fe2+ catalysts can rapidly activate PMS to form Fe3+, leading to the termination of the reaction (see Eq. 1). Additionally, excessive Fe2+ quenches the SO4•− generated (see Eq. 2) and excessive Fe3+ will consume PMS, resulting in a low PMS utilization efficiency (see Eq. 3). Cao et al. (2019) used Fe0 as a PMS activator for the removal of TC, which reached approximately 88% degradation efficiency within 5 min. This could be attributed to Fe0 being a sustained-release source of Fe2+ (see Eq. 4), and the Fe3+ generated could thus be reduced by Fe0 (see Eq. 5). However, Fe0 is difficult to preserve as it easily undergoes oxidation and agglomeration, thus highlighting the need for devising a methodology to slow down its oxidation.Fe2+ + HSO5- → Fe3+ + SO4•− + OH-Fe2+ + SO4•− → Fe3+ + SO42-Fe3+ + HSO5- → Fe2+ + SO5•− + H+Fe0 + O2 + 2H+ → Fe2+ +H2O2Fe0 + 2Fe3+ → 3Fe2+

In recent years, porous carbon materials have attracted widespread attention as PMS activators (Hu et al., 2021). The metal particles encapsulated in the hierarchical carbon layer of such materials can slow down the oxidation of Fe0. Their excellent electron transport capacity and the tunable surface chemistry of the carbon layer are additional favorable factors for PMS activation (Huang et al., 2021, Huang et al., 2021, Huang et al., 2021, Ahsan et al., 2020). Metal organic frameworks (MOFs) are highly ordered porous materials, with metal ions or clusters in their center and organic ligands as bind (Ye et al., 2020). MOFs have found extensive application in adsorption (Zhang et al., 2022), catalytic oxidation (Zhang et al., 2021, Zhang et al., 2021, Bi et al., 2021, Yang et al., 2022), and other such process. Recently, MOF-derived carbon materials have been widely studied for the activation of PDS and PMS, because of their high surface area and porosity, adjustable pore size, high conductivity and stability (Hao et al., 2021). For example, Ding et al. (2020) encapsulated CoFe alloy particles in nitrogen-doped graphitic carbon in an in-situ conversion from a Prussian blue precursor through a two-step carbonization route for the degradation of norfloxacin via coupling with PMS. Tang et al. Tang and Wang (2019) successfully prepared a three-dimensional flower-like catalyst comprising iron-copper bimetallic NPs within a mesoporous carbon shell (i.e., FeCu@C) through simple pyrolysis of a [Fe, Cu]-BDC precursor, which was then applied to the degradation of sulfamethazine. Cu species improved •OH generation by facilitating fast Fe3+/ Fe2+ redox cycles. He et al. (2021) successfully synthesized carbon nanocubes with abundant FeNx active sites by calcining xFe@ZIF-8, since the introduction of FeNx sites regulates the electronic structure of the catalysts. Such electron-deficient Fe centers act as electron acceptors to receive electrons transmitted by the adsorbed PMS, thus generating highly reactive 1O2 for rapid phenol oxidation. Li et al., 2020, Li et al., 2020 synthesized iron/carbon composites by the pyrolysis of MIL-88A(Fe) for realizing the degradation of phenol by activating PDS, during which, the optimized catalyst FexC-600 performed excellently. The advantage of carbon-coated metal nanoparticles, which are obtained by calcining MOFs at high temperatures in an Ar atmosphere, is the uniform distribution of metal particles throughout the carbon layer. In addition, the encapsulation of metal particles by carbon can inhibit their agglomeration (Liu et al., 2018).

In this work, MIL-100 (Fe) was synthesized using different iron sources as a template to obtain carbonyl-rich carbon-coated Fe0 material at high temperatures. The physical and chemical properties of the materials were characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The effects of various factors on the activation of PMS and the role of carbon and iron in the degradation of TC were also investigated. By combining intermediate product analysis with density functional theory (DFT) calculations, a reasonable degradation path was proposed. In addition, toxicity analysis showed that the M(Fe)-N-8/PMS system significantly reduced the ecotoxicity of TC, indicating that this material has potential practical applications for degradation of antibiotics in water.

Section snippets

Chemicals

The reagents used for the synthesis of MIL-100(Fe) were ferric nitrate nonahydrate (Fe(NO3)3.9H2O), iron powder, ferrous sulfate heptahydrate (FeSO4.7H2O), nitric acid (HNO3), hydrofluoric acid (HF) and 1,3,5-Benzenetricarboxylic acid (H3BTC), all of which were obtained from Sinopharm Chemical Reagent Co., Ltd., China. Ethanol (C2H5OH), ferrous ammonium sulfate hexahydrate ((NH4)2Fe(SO4)2.6H2O), peroxymonosulfate (2KHSO5·KHSO4·K2SO4, PMS), sodium persulfate (Na2S2O8, PDS), hydrogen peroxide (H2O

The effect of iron precursors

To explore the influence of different iron precursors on the synthesis of nanometer-scale zero-valent iron (nZVI), MIL-100(Fe) was synthesized using three different iron precursors. Fig. S1(A) presents the XRD patterns of MIL-100(Fe) synthesized using these different iron sources as precursors. It can be observed that the synthesized MIL-100(Fe) matches well with those reported in the literature (Costa et al., 2008), indicating that the synthesis of MIL-100(Fe) was successful. Remarkably,

Conclusions

In summary, MIL-100(Fe) was calcined as a template at high temperatures in an Ar atmosphere to form carbonyl-modified carbon-coated Fe0, which could effectively activate PMS to degrade tetracycline. Under the condition of Ca = 0.1 g/L and C0 = 0.4 mM, the degradation rate of tetracycline reaches 96%, which was ascribed to the slow release of Fe2+, excellent electron transport performance of carbon layer and enhancement efficiency of carbonyl group. Additionally, experimental results showed that

CRediT authorship contribution statement

Yiqiong Yang, Writing - original draft, Funding acquisition, Wenqing Ji, Writing - original draft preparation, Xingyu Li, Software, Visualization, Huidong Lin, Software, Hongjia Chen, Visualization, Fukun Bi, Visualization, Zenghui Zheng, Data curation, Jingcheng Xu, Data curation, Xiaodong Zhang, Writing - review & editing, Conceptualization.

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.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 12075147, 12075152).

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