Persulfate activation by two-dimensional MoS2 confining single Fe atoms: Performance, mechanism and DFT calculations
Graphical abstract
Introduction
Developing technologies for efficient removal of persistent organic pollutants is strongly desired during water treatment and wastewater reclamation process. Advanced oxidation processes (AOPs) are believed as one of the most promising technologies to obtain this goal. Hydroxyl radical (HO), which is highly reactive towards nearly all persistent organic pollutants, is the most used oxidants generated from ozone or H2O2 in AOPs. Using ozone as a HO source require complex and high-cost ozone generation system which hinders its large scale application (Lee et al., 2017). H2O2 generate HO via Fenton process (Fe2+ + H2O2→ Fe3+ + HO + OH−), which requires acidic pH (Chakma and Moholkar, 2014). Thus, a large amount of acid and base is needed for pH adjustment. Sludge production and disposal during Fenton process is also a great environmental concern (Zeng et al., 2019).
Sulfate radical (SO4−) has been recently recognized as one of the most highly reactive oxidants, as superior as hydroxyl radical (HO), for degradation of organic pollutants in AOPs. Persulfate (PS) has been widely utilized as a precursor to generate sulfate radicals. PS can be activated via various catalysts, alkaline, heat, UV irradiation and electrochemical method to generate SO4− (Ahmad et al., 2013; Johnson et al., 2008; Furman et al., 2010; Kim et al., 2018; Matzek et al., 2018). In contrast to the high energy consumption and high chemical dosage for most of these activation methods, transitional metal-based catalyst has been proved to be efficient and cost-effective to activate PS in potential practical applications (Zhang et al., 2013). Transitional metal ions dissolved in homogeneous solutions are one type of efficient catalysts for PS activation (Huang and Huang, 2009). Unfortunately, the formation of metal sludge and the potential health hazards caused by free metal ions in water is of great concern. Thus, a variety of metal nanomaterials have been developed and used as heterogeneous catalysts for the activation of PS (Rong et al., 2019; Xu et al., 2019; Zhou et al., 2019; Liu et al., 2014). Metal nanomaterials are relatively stable for catalysis and can be reused after separation from the treated water. However, the low activity is always the issue compared to homogeneous metal ions (Zhang et al., 2018). The intrinsic reason is that PS activation only occurs on the surface of metal nanomaterials, and any metal atoms inaccessible by PS molecules are not involved in the catalytic process. Single-atom catalysts (SACs), with atomically distributed active sites on supports, are believed to have the advantages of both homogeneous catalysts (high reactivity) and heterogeneous catalysts (stable, easy to separate and reuse, no secondary pollution) in water treatment applications (Chen et al., 2018). Application of SACs in AOPs has been scarcely studied although it is one of the most promising strategies to maximize the efficiency of AOPs in potential practical applications (Li et al., 2018; Guo et al., 2019; Yin et al., 2019; An et al., 2018).
The surface free energy is extremely high for SACs, thus the aggregation of SACs is a big problem during their application. This problem can be solved by anchoring single metal atoms on suitable catalyst support (Zhang et al., 2018). Various supports have been developed to confine SACs, including 3D (carbon, metal oxide, MoC, metal-organic frameworks etc.) and 2D supports (graphene, g-C3N4, and MoS2) (Lin et al., 2013; Pei et al., 2015; Qiu et al., 2015; Yan et al., 2015; Jones et al., 2016; Li et al., 2016; Liu et al., 2016; Yin et al., 2016; Wang et al., 2019; Sun et al., 2019). SACs confined in 2D supports have several unique features compared to 3D supports such as more coordinatively unsaturated single atoms, expedited mass-transfer on both sides of the 2D structure, and the well-defined 2D motif allowing catalytic performances interpreted theoretically (Wang et al., 2019). Also, the interaction between SACs and supports significantly influence the activity, selectivity, and stability of the catalysts (Zhang et al., 2018). Recent studies have shown that MoS2 can act as co-catalyst in homogeneous Fenton-like reaction (Xing et al., 2018; Liu et al., 2018). Thus, we hypothesize that Fe SACs confined in 2D MoS2 support may lead to strong SACs-supports interaction and lead to high activity in AOPs.
In this work, we report the in-plane doping of single Fe atoms in 2D MoS2 with various Fe content (designated as FexMo1-xS2) and demonstrate that FexMo1-xS2 is a highly active catalyst for PS activation, thereby leading to complete mineralization of aniline, a persistent organic pollutant widely detected in surface and ground waters. The high activity of FexMo1-xS2 derives from the synergistic catalysis between the atomically distributed Fe and Mo sites, as revealed by experiments and theoretical calculations. Sulfate radicals are demonstrated to be the major reactive oxygen species responsible for the oxidative degradation of aniline. Furthermore, the FexMo1-xS2/PS system can degrade a wide range of other persistent organic pollutants and work well in a real water environment, testifying the great potential of FexMo1-xS2/PS system for practical water treatment applications.
Section snippets
Chemicals and materials
The FexMo1-xS2 nanosheets were synthesized via a biomolecule-assisted hydrothermal synthetic route (Chang and Chen, 2011; Miao et al., 2015). FeSO4·7H2O, Na2MoO4·2H2O, and L-cysteine were used as iron, molybdenum and sulfur source, respectively. A 200 mL aqueous solution consists of Na2MoO4·2H2O, FeSO4·7H2O and L-cysteine were used as a precursor for hydrothermal synthesis. The FexMo1-xS2 with different x was synthesized by varying Na2MoO4·2H2O/FeSO4·7H2O ratios of 1/1, 1/3 and 3/1 with the sum
Experimental and theoretical characterization of FexMo1-xS2
STEM images show FexMo1-xS2 has a nanosheet morphology similar to MoS2 (Fig. 1a). No nanoparticles or distinct clusters can be observed by TEM, implying impurities such as ferrous sulfide does not exist in FexMo1-xS2. EDS elemental mapping in HAADF-STEM images demonstrates the homogeneous distribution of Fe, Mo, and S in the FexMo1-xS2 nanosheets (Fig. 1b-d). The atomically dispersion of Fe atoms in MoS2 matrix was evidenced by the dispersed white dots in the MoS2 matrix observed by spherical
Conclusion
Two-dimensional MoS2 confining single Fe atoms (FexMo1-xS2) was synthesized to activate PS for aniline degradation. Aniline can be complete mineralized to CO2 and H2O as confirmed by the TOC analysis. Fe0.36Mo0.64S2 shows good reusability and stability during PS activation. FexMo1-xS2/PS system can effectively remove various persistent organic pollutants and FexMo1-xS2 show high reactivity in most AOP systems. The slightly decreased degradation efficiency of aniline in real polluted water can
CRediT authorship contribution statement
Li-Zhi Huang: Conceptualization, Methodology, Writing - original draft, Project administration, Funding acquisition. Chu Zhou: Validation, Investigation. Miaolong Shen: Validation, Investigation. Enlai Gao: Formal analysis. Chunbo Zhang: Formal analysis. Xin-Ming Hu: Writing - review & editing. Yiqun Chen: Supervision, Funding acquisition. Yingwen Xue: Supervision. Zizheng Liu: Supervision, Funding acquisition.
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 funded by the National Natural Science Foundation of China (Grant No. 51978537, 41807188, 51508423 and 51508423), the National Natural Science Foundation of China and the Russian Foundation for Basic Research (NSFC–RFBR 51811530099).
References (47)
- et al.
Single-atom catalysis: bridging the homo- and heterogeneous catalysis
Chin. J. Catal.
(2018) - et al.
A fast and robust algorithm for Bader decomposition of charge density
Comput. Mater. Sci.
(2006) - et al.
Behavioral evidence of the dominant radicals and intermediates involved in Bisphenol A degradation using an efficient Co2+/PMS oxidation process
J. Hazard. Mater.
(2009) - et al.
Single-atom dispersed Co-N-C catalyst: structure identification and performance for hydrogenative coupling of nitroarenes
Chem. Sci.
(2016) - et al.
Molybdenum sulfide Co-catalytic Fenton reaction for rapid and efficient inactivation of Escherichia colis
Water Res.
(2018) - et al.
Sulfate radicals induced from peroxymonosulfate by magnetic ferrospinel MFe2O4 (M=Co, Cu, Mn, and Zn) as heterogeneous catalysts in the water
Appl. Catal. B
(2015) - et al.
The magnetic biochar derived from banana peels as a persulfate activator for organic contaminants degradation
Chem. Eng. J.
(2019) - et al.
Metal sulfides as excellent co-catalysts for H2O2 decomposition in advanced oxidation processes
Chem
(2018) - et al.
Persulfate activation towards organic decomposition and Cr(VI) reduction achieved by a novel CQDs-TiO2-x/rGO nanocomposite
Chem. Eng. J.
(2019) - et al.
Persulfate-based advanced oxidation processes (AOPs) for organic-contaminated soil remediation: a review
Chem. Eng. J.
(2019)
Molybdenum disulfide (MoS2): a versatile activator of both peroxymonosulfate and persulfate for the degradation of carbamazepine
Chem. Eng. J.
Mechanism of persulfate activation by phenols
Environ. Sci. Technol.
High-density ultra-small clusters and single-atom Fe sites embedded in graphitic carbon nitride (g-C3N4) for highly efficient catalytic advanced oxidation processes
ACS Nano
Projector augmented-wave method
Phys. Rev. B
Investigations in synergism of hybrid advanced oxidation processes with combinations of sonolysis + Fenton process + UV for degradation of bisphenol A
Ind. Eng. Chem. Res.
L-cysteine-assisted synthesis of layered MoS2/graphene composites with excellent electrochemical performances for lithium ion batteries
ACS Nano
Triggering the electrocatalytic hydrogen evolution activity of the inert two-dimensional MoS2 surface via single-atom metal doping
Energy Environ. Sci.
Mechanism of base activation of persulfate
Environ. Sci. Technol.
Single-atom Mn–N4 site-catalyzed peroxone reaction for the efficient production of hydroxyl radicals in an acidic solution
J. Am. Chem. Soc.
Oxidation of dodecanoate intercalated iron(II)–iron(III) layered double hydroxide to form 2D iron(III) (hydr)oxide layers
Eur. J. Inorg. Chem.
Hierarchical MoS2 nanosheets on flexible carbon felt as an efficient flow-through electrode for dechlorination
Environ. Sci.-Nano
Persulfate persistence under thermal activation conditions
Environ. Sci. Technol.
Thermally stable single-atom platinum-on-ceria catalysts via atom trapping
Science
Cited by (73)
Metal sulfides as emerging materials for advanced oxidation of wastewater: Recent developments, challenges, and prospects
2024, Coordination Chemistry ReviewsDegradation of phenol in high-salt wastewater by three-dimensional FeCu co-doped materials: Interaction of FeCu with g-C<inf>3</inf>N<inf>4</inf>–rGO and synergistic catalytic mechanism
2024, Journal of Environmental Chemical EngineeringEnhanced peroxymonosulfate activation by MoS<inf>2</inf>/NiCo<inf>2</inf>S<inf>4</inf> composite catalyst for efficient elimination of tetracycline hydrochloride
2024, Journal of Environmental Chemical EngineeringMultifunctional roles of MoS<inf>2</inf> in persulfate-based advanced oxidation processes for eliminating aqueous organic pollutants: A review
2024, Applied Catalysis B: EnvironmentalRecent advances in nanomaterial-enhanced persulfate activation for organic pollutants removal: Electron transfer, surface reactions, and radical generation
2023, Journal of Environmental Chemical Engineering