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Article

Fabrication of MoS2@Fe3O4 Magnetic Catalysts with Photo-Fenton Reaction for Enhancing Tetracycline Degradation

1
College of Jilin Emergency Management, Changchun Institute of Technology, Changchun 130012, China
2
Key Lab of Groundwater Resources and Environment, Ministry of Education, Jilin University, Changchun 130021, China
3
College of Life and Environmental Science, Wenzhou University, Wenzhou 325035, China
*
Author to whom correspondence should be addressed.
Water 2025, 17(2), 235; https://doi.org/10.3390/w17020235
Submission received: 9 December 2024 / Revised: 14 January 2025 / Accepted: 14 January 2025 / Published: 16 January 2025

Abstract

:
Tetracycline (TCs) is widely used in the treatment of human and animal infectious disease. TCs gives rise to a growing threat to the human health and environment protection due to its overuse. Therefore, it is important to remove TCs contaminants from waste effluents. In this work, MoS2@Fe3O4 catalytic material was fabricated by the simple hydrothermal method, which was applied in the photo-Fenton system to degrade TCs. The crystal structure, surface morphology, elemental composition, chemical state, electrochemical properties, and separability of MoS2@Fe3O4 catalytic materials were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), conventional and high-resolution transmission electron microscopy (TEM/HRTEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and vibrating sample magnetometry (VSM). Furthermore, MoS2@Fe3O4 could degrade 98.6% of TCs within 60 min under the optimum reaction conditions (the catalyst dosage of 3 g/L, H2O2 concentration of 5 mmol/L, the initial TCs concentration of 50 mg/L, and the initial pH of 5), which was a significant increase compared with pure Fe3O4. MoS2 can accelerate the Fe3+/Fe2+ cycle through electron transfer from Mo4+ to Fe3+, resulting in the improvement in the degradation efficiency of TCs. The quenching and electron paramagnetic resonance (EPR) results showed that OH and photogenic hole h+ was the main active species in the photo-Fenton system. What is more, MoS2@Fe3O4 catalytic materials had remarkable stability and reusability, and can be handily regained via magnetic separation technology in a real scenario.

1. Introduction

Compared with other antibiotics, tetracycline (TCs) is widely used in animal husbandry, aquaculture industry, and the medical industry due to its advantages of low cost, good effects, and wide antibacterial range [1,2]. Because it is biologically active, stable, and non-biodegradable, TCs has now been detected in surface water, groundwater, and sediments [3]. Residual TCs in the environment can threaten the aquatic and microbial community structure and increase the risk posed by antibiotic-resistant pathogens, which can be transferred throughout the food chain, causing longer-term harm to the environment and human health [4,5]. Therefore, how to efficiently remove TCs pollutants has gradually become a research hotspot.
Several methods, including physical adsorption [6,7], membrane treatment [8], biodegradation [9,10], advanced oxidation processes (AOPs) such as photocatalytic degradation [11], ozonation [12], Fenton and Fenton-like technology [13,14], and photo-Fenton processes [15], are utilized to remove TCs from polluted water. Specifically, the heterogeneous photo-Fenton process, which combined the features of photocatalysis and Fenton method, can realize the rapid degradation of TCs. Due to the use of sunlight as a light source, the photocatalytic reaction process is green non-pollution and huge energy release. Meanwhile, the introduction of hydrogen peroxide (H2O2) can boost the yield of OH, form an iron cycle reaction, reduce the drainage of ferrous ions (Fe2+), and avoid the generation of iron sludge.
In recent years, thanks to the excellent catalytic properties and magnetic characteristics, transition elements hybrid oxides have become promising catalysts in oxidative degradation. Some studies have suggested that Fe3O4 nanoparticles can effectively catalyze the decomposition of H2O2 to produce OH, and their pH range is wide, playing a leading role in the Fenton reaction. Meanwhile, Fe3O4 nanoparticles after reaction can be quickly separated using its magnetic properties, which reduced the formation of iron sludge [16,17,18]. Due to the inverse spinel structure of Fe3O4, electrons can transmit between Fe2+ and Fe3+ at the octahedral location, promoting the mineralization of pollutants. However, after several reaction cycles, its catalytic activity gradually decreased, and due to the rapid recombination of photoelectron hole pairs, its photocatalytic performance was not ideal, so it is necessary to modify it to enhance their catalytic activity and increase the separation rate of photo generated electron hole pairs [16,19].
MoS2 is a typical transition-metal dichalcogenide (TMD) which features a 2D layered structure similar to that of graphene, with high edge molecular activity and an adjustable band gap [20]. MoS2 can be transformed from an indirect band gap semiconductor to a direct band gap semiconductor as the number of layers decreases. Correspondingly, the band gap increases from 1.29 eV to 1.97 eV, extending the absorption spectrum to the visible region [21]. At the same time, MoS2 with small sizes or fewer layers has excellent peroxidase-like activity, through which H2O2 can be efficaciously converted to OH [22,23]. Therefore, MoS2 exhibits amazing catalytic activity, excellent optical absorption, and high photothermal efficiency. Recent evidence demonstrated that MoS2 can accelerate the Fe3+/Fe2+ cycle through electron transfer from Mo4+ to Fe3+, which was attributed that the standard redox potential of Mo4+ (E0 = 0.65 V) being lower than that of Fe3+ (E0 = 0.77 V) [24,25]. Therefore, the combination of Fe3O4 nanoparticles and MoS2 enhances the H2O2 activation, and facilitates the Fe3+/Fe2+ rapid cycle by MoS2.
In this study, a series of magnetic MoS2 @Fe3O4 catalysts was fabricated by a simple hydrothermal process, and its catalytic performance was explored through photo-Fenton experiments used TCs as the target pollutant. The morphology, structure, chemical composition, and electrochemical properties of the catalysts were determined using XRD, SEM, TEM, XPS, EIS, and VSM. The effects of catalyst dosage, H2O2 concentration, TCs initial concentration, and pH on the TCs degradation performance were studied. The stability and reusability of MoS2 @Fe3O4 catalysts were verified by repeatability experiments and magnetic recovery experiments. The possible degradation mechanism was also discussed.

2. Materials and Methods

2.1. Materials and Reagents

Analytical-grade FeSO4·7H2O, Na2S2O3·5H2O, H2O2, and NaOH were purchased from Sinopharm Chemical Reagents Co., Ltd. (Shanghai, China). Tetracycline hydrochloride (TCs, analytical reagent) was obtained from Rhawn Technology Development Co., Ltd. (Shanghai, China). Ammonium molybdate (H8MoN2O4, analytical reagent) and L-cysteine (C3H7NO2S, analytical reagent) were obtained from Tianjin Damao Chemical reagent Factory (Tianjin, China).

2.2. Catalyst Synthesis

Fe3O4 powder was fabricated by the hydrothermal method [26]. They were synthesized as follows: FeSO4·7H2O (2.78 g) and Na2S2O3·5H2O (2.48 g) were dissolved in 50 mL distilled water to form solution A. Then, 0.8 g of NaOH were dissolved in 10 mL distilled water to form solution B. Solution A and B were mixed and evenly stirred for 20–30 min. Subsequently, the mixture was added into 100 mL Teflon-lined autoclave chamber and hydrothermally treated at 140 °C for 12 h. After cooling to room temperature, the solid was separated from the mixture by centrifugal separation, then washed three times with distilled water and anhydrous ethanol, and dried in an oven at 60 °C for 12 h. The final product was crushed to obtain the Fe3O4 powder.
In the synthetic process of MoS2@Fe3O4, ammonium molybdate (0.5 g) were dissolved in 70 mL distilled water, then L-cysteine (1.4 g) was added and stirred evenly for 20 min. A certain amount of Fe3O4 powder was immersed in the previous solution. After ultrasonic dispersion, the solution was filled into a 100 mL hydrothermal reactor and treated at 200 °C for 24 h. Afterward, the solid was centrifuged at 10,000 rpm and rinsed repeatedly in ethanol. Subsequently, the product was dried under the vacuum condition at 60 °C. According to the mass ratio of MoS2 and Fe3O4 (2%, 4%, and 6%) in the MoS2@Fe3O4, the samples were denoted as 2% MoS2@Fe3O4, 4% MoS2@Fe3O4, and 6%MoS2@Fe3O4.

2.3. Characterization Method

The physical phase and crystal structure of the sample were characterized by D8-FOCUS X-ray diffraction (XRD) in the scanning range of 5° to 70° at 2°/min using Cu-Ka as the radiation source (Bruker, Bremen, Germany). Apreo 2C scanning electron microscopy (SEM) (Thermo Fisher Scientific, Shanghai, China) was used to observe the apparent morphology of the samples, as well as to conduct EDS (EDS XD-3) (Shimadzu, Shanghai, China) analyses. The microstructure of the material was characterized by transmission electron microscopy (TEM) (JEOL, Tokyo, Japan), and the lattice of the material was characterized by HRTEM with SEAD. The elemental and chemical valence states of the materials was characterized by ESCALAB 250 X-ray photoelectron spectrometer (XPS) with Al-Kα radiation (Thermo Fisher Scientific, Shanghai, China). The Mott–Schottky test was performed by the CHI760E electrochemical workstation (Austin, TX, USA). The magnetic strength of the material in a magnetic field of 10,000 Oe was analyzed by a magnetometer (Westerville, OH, USA).

2.4. Degradation Performance Evaluation

The photo-Fenton degradation experiment was conducted with 50 mg/L TCs as the target pollutant, and a 400 W xenon lamp bulb with cut-off filters for λ = 420 nm as the light source. A certain amount of catalyst was added to 200 mL of the TCs solution, and then a certain concentration of H2O2 was added to the solution; then, the light source was turned on to trigger the photo-Fenton reaction. Subsequently, 4.0 mL suspension was collected every 10 min and filtered through a 0.45 μm filter. Finally, the concentration of TCs was measured using a UV spectrophotometer at 357 nm. The reusability and comparative study of MoS2@Fe3O4 were further examined under the same conditions for five runs.

3. Results

3.1. Characterization

The crystal structure and phase composition of the prepared samples were analyzed by XRD, which are shown in Figure 1. The diffraction peaks at 30.3°, 35.6°, 43.4°, 57.4°, and 63.0° for the pure phase Fe3O4 sample corresponded to the characteristic peaks of the (220), (311), (400), (422), (511), and (440) crystal planes of the cubic crystal system (equiaxial crystal system) magnetite Fe3O4 (JCPDS card 19-0629), respectively [27]. The characteristic diffraction peaks of each crystal plane of Fe3O4 can be clearly seen in the MoS2@Fe3O4 samples synthesized with different mass ratios of MoS2 and Fe3O4. The diffraction peak of Fe3O4 showed a gradually weakening trend with the increase in the MoS2 mass, indicating that the introduction of MoS2 did not affect the crystal plane structure of Fe3O4. The characteristic diffraction peak of MoS2 was not recognized in the XRD patterns, implying that MoS2 was amorphous in the sample. As shown in JCPDS card 37-1492, the diffraction peaks of pure MoS2 at 2θ(002) = 14.39, 2θ(004) = 29.03, 2θ(100) = 32.69, 2θ(101) = 33.52, 2θ(102) = 35.87, 2θ(103) = 39.55, 2θ(006) = 44.16, 2θ(105) = 49.80, 2θ(106) = 55.98, 2θ(110) = 58.34, 2θ(114) = 64.14, 2θ(108) = 70.16, 2θ(203) = 72.79, and 2θ(116) = 75.99 corresponded to hexagonal structure having space group P63/mmc [28]. The peak intensity of MoS2 phase is noticeably weak or absent in 2% MoS2@Fe3O4; however, in case of 4% MoS2@Fe3O4, the intensity of the XRD characteristic peaks of MoS2 has been improved. In fact, the main peaks of MoS2 corresponding to planes (100), (102), and (114) are clearly visible in 4% MoS2@Fe3O4, which confirmed the MoS2 phase was introduced into the Fe3O4 phase.
As depicted in Figure 2a,b, the apparent morphology of 4% MoS2@Fe3O4 catalyst was analyzed by scanning electron microscopy (SEM). It can be observed that Fe3O4 presented a polyhedral structure with uniform particle size between 50 and 80 nm, and good dispersity. The elemental distribution of MoS2@Fe3O4 was also investigated by EDS element mapping. Figure 2c shows that the O, Fe, Mo, and S elements were uniformly distributed in the surface of sample, which confirmed the successful preparation of MoS2@Fe3O4. Because MoS2 attached to the Fe3O4 surface, the map of Mo and S elements was clearer.
In order to further analyze the microstructure, 4% MoS2@Fe3O4 catalyst was characterized by TEM and HRTEM, and the results are shown in Figure 3. From Figure 3a, it can be seen that the MoS2 was successfully loaded on the surface of Fe3O4 particles, and the MoS2 had better dispersity and no aggregation phenomenon. At the same time, Fe3O4 presented a polyhedral structure with a particle size of about 50–80 nm, which was consistent with the SEM spectra. In Figure 3b, two kinds of lattice fringes can be clearly observed by high-resolution HRTEM. The measured lattice spacing of 0.27 nm corresponded to the (100) crystallographic plane of MoS2, while that of 0.297 nm corresponded to the (110) crystal plane of Fe3O4 [29], which confirmed that MoS2@Fe3O4 catalyst was successfully synthesized.
An XPS measurement was conducted to reveal the surface elemental composition and chemical state of 4% MoS2@Fe3O4. Figure 4a is the wide scan spectrum of MoS2@Fe3O4 catalyst, indicating the existence of Mo, S, Fe, and O elements on the MoS2@Fe3O4 surface. Meanwhile, the high-resolution XPS spectra of Fe 2p, O 1s, Mo 3d, and S 2p were detected. As shown in Figure 4b, the peaks at 712.64 eV and 726.44 eV were consistent with Fe3+ at Fe 2P3/4 and Fe 2p1/2, respectively, and the peaks at 709.44 eV and 723.1 eV were fitted with Fe2+ at Fe 2P3/4 and Fe 2p1/2, respectively [18,30]. The O 1s spectrum in Figure 4c exposed two obvious peaks at 530.3 eV and 531.6 eV, which belonged to Fe−O of Fe3O4 and Fe−OH/−OH groups, respectively [31]. The peaks at 232.2 V and 229.3 eV represented Mo 3d5/2 and Mo 3d3/2, respectively, which indicated the predominant presence of Mo4+ (Figure 4d) [32]. In the S 2p spectrum (Figure 4e), the presence of two peaks at 163.1 eV and 161.8 eV correspond to S 2p3/2 and S 2p1/2 stated in metal sulfides [33], respectively.
To investigate the electrochemical properties, pure Fe3O4, MoS2, and MoS2@Fe3O4 were tested by AC impedance. As shown in Figure 5, the Nyquist arc radius of 4% MoS2@Fe3O4 was significantly smaller than that of pure Fe3O4 and MoS2 sample, which implied a smaller charge transfer resistance as a result of the fast migration of photogenerated carriers after the introduction of MoS2 [34]. During the photo-Fenton reaction, the conversion between Fe3+ and Fe2+ can be promoted, which in turn improved the catalytic activity.

3.2. Evaluation of MoS2@Fe3O4 Photo-Fenton Catalytic Activity

3.2.1. Photo-Fenton Degradation Performance

To evaluate the effect of different mass ratios on the photo-Fenton catalytic performance of MoS2@Fe3O4, three samples were tested under the same reaction conditions: the concentration of TCs was 50 mg/L, solution volume was 200 mL, H2O2 concentration was 5 mmol/L, catalyst dosage was 3 g/L, pH was 5.0, and temperature was room temperature. It can be seen from Figure 6a that the TCs degradation efficiency of 2% MoS2@Fe3O4, 4% MoS2@Fe3O4, and 6% MoS2@Fe3O4 materials was 90.8%, 98.6%, and 93.9%, respectively, of which 4% MoS2@Fe3O4 had the best catalytic activity. When the content of MoS2 was too small, too high an Fe3O4content would hinder the absorption of visible light by MoS2, so that the quantum yield of light was low and the photocatalytic efficiency was low. When the content of MoS2 was too large, too low an Fe3O4 content would reduce the efficiency of the dominant Fenton reaction. Therefore, 4% MoS2@Fe3O4 had the best photo-Fenton degradation efficiency of TCs, and the latter experiments were chosen 4% MoS2@Fe3O4 as catalyst.
To further investigate the catalytic activity of 4% MoS2@Fe3O4, the TCs degradation processes were compared with among different systems, involving vis-Fe3O4, Fe3O4-H2O2, vis-Fe3O4-H2O2, vis-MoS2@Fe3O4, MoS2@Fe3O4-H2O2, and vis-MoS2@Fe3O4-H2O2 systems, and the results are shown in Figure 6b (Catalyst = 3 g/L, H2O2 = 5 mmol/L, TCs = 50 mg/L, pH = 5, 200 mL). As depicted in Figure 6b, the photocatalytic degradation of TCs was not obvious under visible light irradiation and pure Fe3O4 as catalyst. When the MoS2@Fe3O4 catalyst was added, the TCs degradation efficiency during photocatalysis reached 28%. The Fenton system using pure Fe3O4 as catalyst exhibited significantly lower TCs degradation efficiency compared to using MoS2@Fe3O4 (39%). Under the condition of photo-Fenton, using MoS2@Fe3O4 as catalyst, the degradation efficiency of TCs reached 98.6%, which was significantly higher than that of pure Fe3O4. It indicated that visible light and the Fenton reaction had a synergistic effect, which significantly enhanced the degradation efficiency. Meanwhile, the introduction of MoS2 can accelerate the Fe3+/Fe2+ cycle through electron transfer from Mo4+ to Fe3+, resulting in the improvement in degradation efficiency of TCs. At the same time, MoS2 can enhance the transfer efficiency of photogenerated electron holes and restrain the recombination of electron holes, thus improving the performance of photo-Fenton process. This result was consistent with the previous result of AC impedance.

3.2.2. Different Influencing Factors

The influences of various reaction conditions such as catalyst dosage, H2O2 concentration, TCs concentration, initial pH on the photo-Fenton reaction were investigated. The catalytic efficiency of TCs at different catalyst dosage is depicted in Figure 7a (H2O2 = 5 mmol/L, TCs = 50 mg/L, pH = 5, 200 mL). The degradation efficiency of TCs increased from 85.1% to 98.6% when the catalyst dosage increased from 1 to 3 g/L, and then reduced to 89.4% with elevated 4% MoS2@Fe3O4 dosage to 5 g/L. The excessive catalyst dosage inhibited the absorption of visible light, reduced the production of photogenerated electrons and holes, and thus lowered the catalytic efficiency. Meanwhile, the scavenging of OH radicals by excessive Fe2+ led to a decline in OH radical generation [35]. Therefore, the catalyst dosage of 3 g/L was selected in subsequent experiments.
Figure 7b demonstrated that the catalytic efficiency of TCs increased from 82% to 98.6% with the increase in H2O2 concentration from 3 mmol/L to 5 mmol/L, and then the efficiency had a slight decline with the further rise in the H2O2 concentration to 9 mmol/L (Catalyst = 3 g/L, TCs = 50 mg/L, pH = 5, 200 mL). This might be due to the fact that H2O2 was responsible for the formation of OH, and a higher concentration of H2O2 would promote to product more OH. However, excessed H2O2 may further react with OH and convert it into HO2. which was in poor reactivity because of its lower oxidation potential [14]. Therefore, although the H2O2 concentration was high, the OH production decreased, resulting in a lower TCs degradation efficiency. Therefore, 5 mmol/L was selected as the addition concentration of H2O2 for subsequent experiments.
The concentration of TCs changed in the range of 40 to 60 mg/L, and the photo-Fenton experiment was carried out (Catalyst = 25 mg, H2O2 = 5 mmol/L, pH = 5, 200 mL). As displayed in Figure 7c, the photocatalytic performance of TCs reduced with the increase in TCs concentrations. This was because the amount of catalyst and oxidizer was fixed, so the same number of active species was formed. Meanwhile, high concentrations of TCs may reduce catalyst activity by adsorbing and blocking the surface of the catalyst, or consume H2O2 by depleting reactive oxygen species, and trigger side reactions [36]. Considering that the economy, 50 mg/L was determined as the appropriate TCs concentration.
Figure 7d shows the degradation curves of TCs at different pH (Catalyst = 3 g/L, H2O2 = 5 mmol/L, TCs = 50 mg/L, 100 mL). The TCs degradation increased from 90% to 98.6% after 60 min with the increase in pH from 3 to 5. According to the pH value of the solution, TCs exists in three forms, specifically, the cationic form when pH < 3.3, the zwitterionic form with a pH of 3.3–7.7, and the anionic form in alkali environment (pH > 7.7) [37]. The cationic form is less vulnerable to reactive oxygen than the zwitterionic form. Consequently, under the condition of pH = 3, TCs cations were formed by protonation, which reduced the degradation efficiency of TCs slightly. When pH further increased to 9 the degradation efficiency of TCs decreased to 62%. This might be due to the quick consumption of H2O2 in an alkaline environment. Therefore, pH = 5 was applied in the follow-up experiment.

3.2.3. Stability and Recyclability of MoS2@Fe3O4

In order to evaluate the stability and recyclability of MoS2@Fe3O4 catalyst, the degradation of TCs in recycling experiments was carried out (Catalyst = 3 g/L, H2O2 = 5 mmol/L, TCs = 50 mg/L, pH = 5, 200 mL), and the experimental results are displayed in Fig8a. The catalytic efficiency of TCs reduced from 98.6% to 92.1% after five cycles, demonstrating its remarkable stability and reusability. The reason for the slight decrease in degradation efficiency was that the active sites were blocked by the adsorbed TCs and TCs degradation intermediates after repeated use of the catalyst [38]. At the same time, ICP results showed the concentration of the leached iron and molybdenum were 0.021mg/L and 0.009 mg/L, also indicated the MoS2@Fe3O4 catalyst had a better stability. In addition, the MoS2@Fe3O4 catalyst could be easily separated by a magnet after use. To analyze the magnetic characteristics of the samples, hysteresis loop analysis was performed on 4% MoS2@Fe3O4, as shown in Figure 8b. It can be seen that the magnetic saturation value of pure Fe3O4 was 63.0 emu/g under an external magnetic field of 10,000 Oe, while that of MoS2@Fe3O4 sample was 43 emu/g, indicating that the magnetism of the catalyst reduced after the introduction of MoS2. The inset of Figure 8b showed the dispersion of MoS2@Fe3O4 sample in an aqueous solution and in solution after 1 min under an applied magnetic field. MoS2@Fe3O4 sample can be adsorbed by a magnet and the solution became clarified, which indicated that the magnetic properties of the MoS2@Fe3O4 were weaker than those of pure Fe3O4, but can still be easily separated and reused under the action of applied magnetic field.

3.3. Degradation Mechanism

In the MoS2@Fe3O4 photo-Fenton system, tertiary-butanol (t-BA), p-benzoquinone (p-BQ), sodium azide (NaN3) and ammonium oxalate (250 mmol/L) were used as OH, O2•−, O21 and hole (h+) inhibitors, and dominant active species were evaluated by the quenching experiments. As described in Figure 9a, the order of inhibiting effect on TCs degradation was t-BA > ammonium oxalate > p-BQ > NaN3. When t-BA was added to the degradation system, the degradation efficiency of TCs dropped nearly to 25.63%, illustrating that OH was the main free radical, because t-BA is a strong quenching agent of OH. When the degradation of TCs in the quenched h+ system was 72.68%, indicating that photogenerated holes were also the important part of active species in the photo-Fenton system. In contrast, the catalytic efficiency of TCs was hardly affected and was still 90.85% and 96.72% after inhibition of O2•− and O21. Therefore, OH and h+ were the main active groups of TCs degradation in the MoS2@Fe3O4 photo-Fenton system.
Electron paramagnetic resonance spectroscopy (EPR) trapping tests were used to identify the dominant radical species in in the photo-Fenton system, which further supported the above conclusions. 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was as a radical scavenger of OH and O2•− in the MoS2@Fe3O4 photo-Fenton system, and the results are shown in Figure 9b,c. The signal with an intensity ratio of 1:2:2:1 observed under the ultrapure aqueous phase test conditions belonged to the characteristic peak of typical DMPO-OH, confirming the formation of OH in the MoS2@Fe3O4 photo-Fenton system (Figure 9b). At the same time, six characteristic peaks with almost equal intensity ratio observed under the methanol phase test conditions belonged to the characteristic peaks of typical DMPO-O2•−, confirming the formation of O2•− in the MoS2@Fe3O4 photo-Fenton system (Figure 9c). The results of ESR spectra were in good agreement with the quenching experimental results.

4. Conclusions

In this study, a serial of MoS2@Fe3O4 magnetic catalysts were fabricated by a simple hydrothermal process, which had an excellent photo-Fenton catalytic performance. The optimal reaction conditions were evaluated to be the catalyst dosage of 3 g/L, H2O2 concentration of 5 mmol/L, initial TCs concentration of 50 mg/L, and pH of 5. The photocatalytic degradation of TCs reached 98.6% within 60 min under the optimal conditions, which was a remarkable growth compared to the pure Fe3O4. MoS2 can accelerate the Fe3+/Fe2+ cycle through electron transfer from Mo4+ to Fe3+, resulting in the improvement in degradation efficiency of TCs. EPR analysis and free radical quenching experiments results showed that OH and photogenic hole h+ played a great distribution on TCs degradation. Furthermore, MoS2@Fe3O4 catalytic materials had significant stability and reusability, and can be conveniently collected by a magnet in a real scenario, which would reduce the cost of catalyst separation and recovery.

Author Contributions

Z.-L.L. contributed to overall organizing of all experiments, and writing—original draft preparation. J.-H.S. contributed to gas sensing properties experiments, data analysis. B.L. contributed to sample characterizing and data analysis. Y.-N.C. contributed to sample preparation. W.F. contributed to providing ideas for all the experiments, methodology, and supervision. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Jilin Science and Technology Development Planning Project [Nos. 20210203006SF, YDZJ202201ZYTS630], the Sixth Batch of Young Science and Technology Talents Promotion Program of Jilin Province [QT202216] and the Educational Department of Jilin Province in China (No. JJKH20210304KJ).

Data Availability Statement

Data are contained within the article.

Acknowledgments

We are grateful to all the authors for their contributions and financial help.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. XRD pattern of MoS2@Fe3O4 catalysts with different ratios.
Figure 1. XRD pattern of MoS2@Fe3O4 catalysts with different ratios.
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Figure 2. (a,b) SEM pictures, and (c) EDS element mapping of 4% MoS2@Fe3O4 catalyst.
Figure 2. (a,b) SEM pictures, and (c) EDS element mapping of 4% MoS2@Fe3O4 catalyst.
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Figure 3. (a) TEM and (b) HRTEM of 4% MoS2@Fe3O4 catalyst.
Figure 3. (a) TEM and (b) HRTEM of 4% MoS2@Fe3O4 catalyst.
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Figure 4. XPS spectra: (a) the wide scan, (b) Fe 2p, (c) O 1s, (d) Mo 3d, and (e) S 2p of 4% MoS2@Fe3O4 catalyst.
Figure 4. XPS spectra: (a) the wide scan, (b) Fe 2p, (c) O 1s, (d) Mo 3d, and (e) S 2p of 4% MoS2@Fe3O4 catalyst.
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Figure 5. EIS curves of pure Fe3O4, MoS2, and 4% MoS2@Fe3O4 catalyst.
Figure 5. EIS curves of pure Fe3O4, MoS2, and 4% MoS2@Fe3O4 catalyst.
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Figure 6. (a) The photo-Fenton degradation efficiency of TCs with different mass ratio of MoS2@Fe3O4 and (b) Effect of different systems on the degradation of TCs.
Figure 6. (a) The photo-Fenton degradation efficiency of TCs with different mass ratio of MoS2@Fe3O4 and (b) Effect of different systems on the degradation of TCs.
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Figure 7. The photo-Fenton degradation efficiency of TCs with (a) catalyst dosage, (b) H2O2 concentrations, (c) TCs concentrations, and (d) initial pH.
Figure 7. The photo-Fenton degradation efficiency of TCs with (a) catalyst dosage, (b) H2O2 concentrations, (c) TCs concentrations, and (d) initial pH.
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Figure 8. (a) Recycling experiments of the degradation system and (b) Hysteresis curve of pure Fe3O4 and 4% MoS2@Fe3O4 catalyst (the insert represent the collection of 4% MoS2@Fe3O4 by a permanent magnet).
Figure 8. (a) Recycling experiments of the degradation system and (b) Hysteresis curve of pure Fe3O4 and 4% MoS2@Fe3O4 catalyst (the insert represent the collection of 4% MoS2@Fe3O4 by a permanent magnet).
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Figure 9. (a) Effects of various inhibitors on degradation of TCs, ESR spectra of (b) DMPO-OH and (c) DMPO-O2•− in the MoS2@Fe3O4 photo-Fenton system.
Figure 9. (a) Effects of various inhibitors on degradation of TCs, ESR spectra of (b) DMPO-OH and (c) DMPO-O2•− in the MoS2@Fe3O4 photo-Fenton system.
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MDPI and ACS Style

Liu, Z.-L.; Sun, J.-H.; Liu, B.; Chen, Y.-N.; Feng, W. Fabrication of MoS2@Fe3O4 Magnetic Catalysts with Photo-Fenton Reaction for Enhancing Tetracycline Degradation. Water 2025, 17, 235. https://doi.org/10.3390/w17020235

AMA Style

Liu Z-L, Sun J-H, Liu B, Chen Y-N, Feng W. Fabrication of MoS2@Fe3O4 Magnetic Catalysts with Photo-Fenton Reaction for Enhancing Tetracycline Degradation. Water. 2025; 17(2):235. https://doi.org/10.3390/w17020235

Chicago/Turabian Style

Liu, Zong-Lai, Jia-Hong Sun, Bing Liu, Ya-Nan Chen, and Wei Feng. 2025. "Fabrication of MoS2@Fe3O4 Magnetic Catalysts with Photo-Fenton Reaction for Enhancing Tetracycline Degradation" Water 17, no. 2: 235. https://doi.org/10.3390/w17020235

APA Style

Liu, Z.-L., Sun, J.-H., Liu, B., Chen, Y.-N., & Feng, W. (2025). Fabrication of MoS2@Fe3O4 Magnetic Catalysts with Photo-Fenton Reaction for Enhancing Tetracycline Degradation. Water, 17(2), 235. https://doi.org/10.3390/w17020235

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