Construction of 3D sheet-packed hierarchical MoS2/BiOBr heterostructures with remarkably enhanced photocatalytic performance for tetracycline and levofloxacin degradation

Construction of 3D sheet-packed hierarchical MoS2/BiOBr heterostructures with remarkably enhanced photocatalytic performance for tetracycline and levofloxacin degradation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Construction of 3D sheet-packed hierarchical MoS2/BiOBr heterostructures with remarkably enhanced photocatalytic performance for tetracycline and levofloxacin degradation Zhanying Ma, Xiaobo Li, Guang Fan, lingjuan Deng, Yangqing He This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2186761/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 04 Apr, 2023 Read the published version in Environmental Science and Pollution Research → Version 1 posted 6 You are reading this latest preprint version Abstract In this paper, MoS 2 nanosheets were prepared and deposited on BiOBr microflowers to fabricate MoS 2 /BiOBr heterojuncitons through deposition-hydrothermal strategy. The SEM and TEM images evidenced that few-layer MoS 2 were grafted on BiOBr surface to yield 3D sheet-packed MoS 2 /BiOBr heterostructures. The obtained MoS 2 /BiOBr samples exhibited tremendous enhanced catalytic activity in comparison with pure BiOBr and the degradation rate reached 92.96% and 90.31% for tetracycline and levofloxacin degradation, respectively. The remarkably enhanced performance could be attributed to the synergistic effect of strong visible-light harvesting ability and the formation of heterojunction between MoS 2 and BiOBr. The reactive species capturing experiments evidenced that photo-generated holes and ⋅OH radicals played the dominant roles in the whole photocatalytic decomposition process. A plausible mechanism for the enhanced photocatalytic capability was also proposed. MoS2/BiOBr Photocatalysis Antibiotic residues removal Heterojunctions Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction In the last two decades, antibiotic residues were inevitably discharged into in various water bodies since the antibiotics were enormously produced and extensively used for medical therapy because of its excellent activity against bacterial infection (Li et al. 2019 ; Hu et al. 2021 ). Antibiotics polluted wastewater would provoke potential threats to the public health and ecosystem due to its toxic nature. Therefore, it is urgent to explore an efficient technology to eliminate the antibiotics residues before discharge. Among various wastewater treatment techniques, semiconductor photocatatysis has been considered as an effective approach to remove antibiotics pollutants due to its non-toxicity, cost-effective and ambient operating condition (Chen et al. 2019 ; Pirhashemi et al 2018 ). Bismuth oxybromide (BiOBr) is a V-VI-VII ternary oxide semiconductor material with layered tetragonal matlockite structure. The [Bi 2 O 2 ] 2+ positive slices were embedded in double Br negative slabs to yield [Br-Bi-O-Bi-O-Br] layers (Xu et al. 2014 ). Then [Br-Bi-O-Bi-O-Br] layers interacted together through van der Waals forces rather than closely packed, resulting in larger BET surface area and ideal absorption abilities (Xiong et al. 2014 ). As reported, BiOBr has been evidenced as a promising visible-light-induced photocatalyst to decompose organic effluents due to its high stability against photocorrosion, appropriate band gap (1.7–3.2 eV) and relatively excellent photocatalytic performance (Xue et al. 2014 ). For instance, Mao reported that square BiOBr nanoplates synthesized by ionic liquid-assisted hydrothermal method could degrade RhB thoroughly within 90 min (Mao et al. 2014 ). Xue et al. ( 2014 ) demonstrated that BiOBr porous microflowers displayed excellent photocatalytic activities for RhB decomposition under visible-light illumination. Nevertheless, the low separation ability of photo-generated electron/hole pairs severely hindered its practical applications. Previous investigations had specified that coupling BiOBr and another semiconductor with suitable band gap to form heterojunction was an efficient strategy to promote separation rate of charge carriers (Meng and Zhang 2015 ; Wang et al. 2014 ). Up to now, various BiOBr-based heterojunctions with improved photocatalytic activities over those comprised of a single component had been extensively investigated, such as BiOAc/BiOBr (Liu et al. 2021 ), BiOBr/BiFeWO 6 (Lu et al. 2021 ), BiOBr/BiOCl (Liao et al. 2021 ), BiSbO 4 /BiOBr (Van et al. 2022 ), BiOBr/C 3 N 4 (Ma et al. 2019a ), and so on. The outstanding degradation performance of these photocatalysts depended on their preferable optical-absorption characteristics, high separation efficiency of excited charge carriers and long-term stability. Molybdenum disulfide (MoS 2 ) has a similar layered structure to BiOBr, in which Mo atoms were sandwiched covalently between S atoms to form S-Mo-S layers. Then each formed S-Mo-S layer vertically connected together by Van Der Waals interactions, which facilitated the exfoliation of 2D MoS 2 nanosheets from bulk MoS 2 . This typical layered structure not only significantly improved the utilization of active center, but also greatly shortened transfer path of photo-induced charge carriers, intermediates and products, which allowed it to be an ideal co-catalyst (Fang et al. 2017 ; Ma et al. 2019a ). Various semiconductors such as C 3 N 4 (Li et al. 2019 ), CdS (Darsara et al. 2018 ), Bi 2 S 3 (Iqbal et al. 2022 ), ZnO (Benavente et al. 2018 ), Bi 2 O 3 (Ma et al. 2019b ), had been coupled with MoS 2 to increase the photocatalytic performance. Interestingly, the band gap of BiOBr matched well with that of MoS 2 and coupling BiOBr with MoS 2 can form a staggered structure, which was helpful for absorbing more photons across a wide range of light response and effectively conquer the defects of monomer catalyst. Previously, some inspiring investigations of BiOBr/MoS 2 heterojunctions for eliminating organic pollutants have been documented (Zhang et al. 2021 ; Di et al. 2014 ). For example, Zhang et al. ( 2021 ) designed BiOBr/MoS 2 heterojunctions, exhibiting remarkably enhanced photocatalytic activity towards of organic dye elimination and Cr (VI) reduction with the help of peroxymonosulfate. Lee et al. ( 2017 ) synthesized MoS 2 /BiOBr hybrid photocatalyst, which exhibited more than 1.4 times of enhancement over pure BiOBr in the degradation of RB5. Zhang et al. ( 2022 ) successfully synthesized MoS 2 quantum dots (QDs) decorated BiOBr heterojunction photocatalyst, and exhibited remarkably increased visible light photocatalytic ability for the RhB and ciprofloxacin removal. Concerning the frequently emergencies of global epidemic and pandemic viral illnesses such as novel coronavirus disease-2019 (COVID-19), which are in certain point associated with the long-term propagation and evolution of antibiotic resistant genes of viruses, bacteria, and protozoa promoted by the discharged antibiotic residues. It is urgently desirable to develop highly effective BiOBr-based photocatalysts towards throughly removal antibiotic residues contaminants from the aquatic environment. What’s more, the morphology, phase structure and surface chemical state of photocatalyst have important effect on the catalytic performance. Considering the unique properties of few-layered MoS 2 , in this work, MoS 2 nanosheets were fabricated firstly by a simple hydrothermal-dialysis method, and then deposited on the surface of BiOBr microflowers via a deposition-hydrothermal process. As a result, few-layer MoS 2 nanosheets coupled with BiOBr heterojunctions MoS 2 /BiOBr were successfully fabricated. The visible-light absorption capacity was enhanced and the separation or transfer efficiency of excited charge carriers was remarkably promoted. The photocatalytic performance of as-synthesized MoS 2 /BiOBr microflowers was evaluated by degradation of tetracycline and levofloxacin antibiotics. The detailed relationship between the unique structure and the excellent catalytic performance of MoS 2 /BiOBr microflowers was explored. The possible enhanced photocatalytic mechanism was also proposed based on various experimental investigations. Furthermore, this fabrication method could be extended into a general strategy for the formation of other 2D few-layered heterojunctions. 2. Experimental 2.1 Materials Sodium molybdate [Na 2 MoO 4 ], thiourea [CH 4 N 2 S], bismuth nitrate pentahydrate [Bi(NO 3 ) 3 ·5H 2 O], cetyltrimethylammonium bromide (CTAB), anhydrous ethanol (EtOH), tetracycline and levofloxacin were used without further purification. 2.2 Preparation of MoS 2 nanosheets 0.6 g of Na 2 MoO 4 was dissolved in deionized water with continuous ultrasonication for 10 min to obtain the transparent Na 2 MoO 4 solution, followed by the addition of CH 4 N 2 S (0.5 g). The as-obtained mixture solution was migrated into a 50 mL Teflon-lined stainless steel autoclave and kept at 190°C for 24 h to get MoS 2 suspension. After centrifuge at 10,000 rpm for 10 min, the supernatant was transferred to dialysis bag and kept on dialysis for 2 days. Finally, MoS 2 nanosheets dispersion was obtained for the following step. 2.3 Preparation of MoS 2 /BiOBr heterojunctions The MoS 2 /BiOBr heterojunctions were prepared via a simple deposition-hydrothermal method. Typically, 0.729 g of CTAB was dissolved in a specified amount of anhydrous ethanol, followed by the addition of bismuth nitrate pentahydrate (0.9702 g). After ultrasonication for 30 min, 4 mL of MoS 2 nanosheets dispersion was added. The obtained suspension was added into a 100 mL Teflon-lined stainless-steel autoclave and heated for 17 h at 160 °C. The product was cooled down to 25 °C and separated by filtration. The obtained precipitate was swilled with anhydrous ethanol and dried at 60 °C to obtain MoS 2 /BiOBr samples, marked as 4-MoS 2 /BiOBr. Pure BiOBr was also synthesized using the similar procedure to MoS 2 /BiOBr without the addition of MoS 2 nanosheets dispersion. By changing the volume amounts of MoS 2 nanosheets dispersion, 6-MoS 2 /BiOBr, 8-MoS 2 /BiOBr, 10-MoS 2 /BiOBr samples were also prepared with other parameters unchanged for comparison. 2.4 Characterization of the prepared samples Crystal structure was studied by X-ray diffractometer (D8 ADVANCE A25, Cu Kα, λ = 1.54056Å). The morphology was investigated by scanning electron microscopy (S-3000N) and field emission transmission electron microscopy (G2F30). The surface chemical state was detected using X-ray photoelectron spectroscope (AXIS ULtrabld), operating at 3.0×10 − 10 mbar. The optical absorption property was investigated by Lambd 950 UV-visible diffuse reflectance spectrophotometer. The photoluminescence spectra were measured by using RF-6000 Fluorescence spectrophotometer. 2.5 Photocatalytic experiment Photocatalytic capability of the samples was evaluated by elimination of tetracycline and levofloxacin antibiotics. The detailed process was described in our previous work (Ma et al. 2019a ). In a typical process, under the dark condition, 10 mg of the samples were applied to degrade 40 mL tetracycline (20 mg/L) or levofloxacin (20 mg/L) solution with vigorous stirring for 20 min to obtain the equilibrium of adsorption/desorption. Then the dispersion was continuously irradiated with a 250 W Xe lamp. 4 mL suspension was sequentially collected at each 10 min interval and centrifuged through membrane filters (0.22 µm) to take away the solid photocatalyst. The obtained filtrate was transferred into a quartz cuvette to investigate the absorption spectra (200–750 nm) by using a UV-3200 spectrophotometer. The long-term stability was studied as follows. 6-MoS 2 /BiOBr heterojunctions were recycled through centrifugation after the degradation of tetracycline and levofloxacin, respectively, then rinsed with deionized water and recycled to another run. 3. Results And Discussion 3.1 Crystal phase structure analysis The XRD patterns of BiOBr, MoS 2 and MoS 2 /BiOBr composites (4-MoS 2 /BiOBr, 6-MoS 2 /BiOBr, 8-MoS 2 /BiOBr, 10-MoS 2 /BiOBr) were displayed in Fig. 1 . For BiOBr sample, the main detected peaks could be well indexed to (001), (002), (101), (102), (110), (112), (200) and (212) planes of tetragonal phase structure (JCPDS No. 09-0393). The diffraction signals of MoS 2 were assigned to (002), (100) and (110) planes of the hexagonal phase (Chandrabose et al. 2021 ). While for MoS 2 /BiOBr composites, all detected peaks were well matched to tetragonal BiOBr and no distinct diffraction peaks of MoS 2 were observed because the content of MoS 2 was too low to detect. 3.2 Morphology analysis The morphology, size and lattice were characterized by SEM, TEM and HRTEM techniques. Results were showed in Fig. 2 . From Fig. 2 a, it was clearly observed that MoS 2 showed accumulated states of thin nano-plates with the smooth surface. The TEM in Fig. 2 b displayed that MoS 2 exhibited a string of nano-sheets with wrinkled layer outlook and sufficient exposed edges, further confirming the thin size and smooth surface of MoS 2 nano-sheet. The 0.947 nm lattice spacing in the The SEM image in the HRTEM of MoS 2 (Fig. 2 c) could be indexed to its (002) facet (Hu et al. 2020 ). Figure 2 d indicated that 6-MoS 2 /BiOBr composites had a micro-flowers morphology, with the diameter of 2 ~ 3 µm, fabricated by some interlaced nano-sheets with thickness of 35 nm. The enlarged SEM (inset of Fig. 2 d) further indicated that 6-MoS 2 /BiOBr micro-flowers were self-assembled by numerous BiOBr nano-sheets and MoS 2 nano-plates (marked by yellow arrow) were attached on the surface of BiOBr. The TEM images as shown in Fig. 2 e confirmed the as-prepared 6-MoS 2 /BiOBr were sheet-packed 3D hierarchical structures. To confirm the formation of heterojunction between MoS 2 and BiOBr in 6-MoS 2 /BiOBr composites, HRTEM technique was employed and results were showed in Fig. 2 f. An obvious tight contact boundary (marked by a yellow line) between MoS 2 and BiOBr was evidently observed, which proved that MoS 2 was closely attached to the BiOBr microstructure, which was helpful for the charge separation in the electron-hole transfer process for photocatalytic tetracycline degradation (Liu et al. 2018 ). Notably, clear lattice fringes with a spacing of 0.278 and 0.282 nm were obvious, which could be ascribed to (102) and (110) facet of BiOBr. Figure 3 was the elemental mapping results of 6-MoS 2 /BiOBr composites. The Bi, Br, O, Mo and S elements were distributed in the selected district and had a good synergistic correspondence with the whole scanning region, indicating that MoS 2 were attached or immersed well into BiOBr microstructure. This result further proved that MoS 2 /BiOBr composites were successfully prepared. 3.3 XPS analysis To further prove the interaction between MoS 2 and BiOBr in the heterojunctions and explore the chemical states of 6-MoS 2 /BiOBr, X-ray photoelectron spectroscopies (XPS) were carried out and results were showed in Fig. 4 . Figure 4 a showed the full spectra of BiOBr and 6-MoS 2 /BiOBr. Bi, O and Br elements could be observed in the spectrum of BiOBr. From the spectrum of 6-MoS 2 /BiOBr, Mo and S elements were detected in addition to Bi, O, Br, implying the successful synthesis of 6-MoS 2 /BiOBr. Figure 4 b-f was the XPS high resolution spectra of Mo 3d, S 2p, Bi 4f, O 1s and Br 3d. From Fig. 4 b, the two strong Mo 3d signals at 235.53 and 232.29 eV could be ascribed to Mo 3d 3/2 and Mo 3d 5/2 , respectively, demonstrating the valence of molybdenum in 6-MoS 2 /BiOBr sample was + 4. The XPS peaks at 164.56 and 159.2 eV shown in Fig. 4 c could be attributed to S 2p 1/2 and S 2p 3/2 (Li et al. 2018 ). From Fig. 4 d, two peaks at 164.4 and 159.1 eV for BiOBr sample corresponding to Bi 4f 5/2 and Bi 4f 7/2 were shifted to higher binding energies by 0.1 and 0.16 eV for 6-MoS 2 /BiOBr sample, respectively. The O 1s signal at 529.9 eV of BiOBr in Fig. 4 e could be ascribed to Bi-O bond (Li et al. 2023 ), which was shifted to 530.1 eV with apparent decreased intensity owning to the coupling of MoS 2 in 6-MoS 2 /BiOBr sample. Two signals with binding energies at 69.13 and 68.24 eV presented for pure BiOBr belonging to Br 3d 3/2 and Br 3d 5/2 were shifted to 69.31 and 68. 4 eV for 6-MoS 2 /BiOBr heterojunctions. All these distinct shifts of Bi 4f, O 1s and Br 3d orbits further proved the formation of heterojunction between MoS 2 and BiOBr in 6-MoS 2 /BiOBr heterojunctions. 3.4 Photocatalytic degradation of tetracycline and levofloxacin The photocatalytic capabilities of BiOBr and MoS 2 /BiOBr heterostructures were investigated by photocatalytic removal of antibiotics tetracycline and levofloxacin aqueous solution and the results were given in Fig. 5 . As seen from Fig. 5 a and 5 b, the degradation efficiency of tetracycline and levofloxacin in the existence of BiOBr was only about 69.99% and 66.08%, respectively. Remarkable enhancement of photocatalytic performance was obtained by the MoS 2 /BiOBr heterojunctions. As shown, the photocatalytic activity of the clearly depended on the coupling amount of MoS 2 and 6-MoS 2 /BiOBr exhibited the best photoactivity, 92.96% for tetracycline and 90.31% for levofloxacin after 70 min Xe lamp illumination. With the increase of MoS 2 coupling amount, excess MoS 2 particles were aggregated and increase the recombination rate of photo-generated charge carriers (Zarezadeh et al. 2019 ), thus leading to the lower photocatalytic activity. Figure 5 c and 5 d showed the dependence of UV-vis absorbance for tetracycline and levofloxacin in the absence and presence of heterojunctions. The intensity of major absorption peak for both tetracycline at 370 nm and levofloxacin at 287 nm gradually diminished with prolonging the illumination time and almost disappeared after 70 min, indicating the broken of molecular structure and the conjugated π system in the tetracycline and levofloxacin molecules. This result is very important for the practical antibiotics wastewater decontamination, since the 6-MoS 2 /BiOBr heterojunctions displayed remarkable photocatalytic performance in degradation of tetracycline and levofloxacin, the major effluents from therapeutic medicine, feed supplements and pharmaceutical factory. Long-term stability of the photocatalysts is significant for the actual applications. To evaluate the durability of 6-MoS 2 /BiOBr heterojunctions, the recycling degradation experiments for both tetracycline and levofloxacin were examined. The detailed process was based on our reported reference (Ma et al. 2019a ). Typically, 6-MoS 2 /BiOBr composites were collected by centrifugation after each run and washed with deionized water and recycled to another run. The experimental results were shown in Fig. 6 . It was clear that the degradation efficiency of 6-MoS 2 /BiOBr exhibited high stability and potential applications for eliminating antibiotics pollutants, since 85% of tetracycline and 81% of levofloxacin could still be efficiently degraded after 3 runs. To investigate the migration, transfer and separation properties of photo-generated electron/hole (e − /h + ) pairs during the photocatalytic process in the presence of BiOBr and 6-MoS 2 /BiOBr, the UV-vis diffuse reflectance spectra (DRS), photoluminescence (PL) spectroscopy, electrochemical impedance Nyquist (EIS) and transient photocurrent were employed. As evidenced in Fig. 7 a, the incorporation of MoS 2 displayed a synergistic effect with significantly improved visible light harvesting in the region of 400−600 nm for 6-MoS 2 /BiOBr, in comparison with that of BiOBr. Furthermore, the PL intensity (Fig. 7 b) and the EIS Nyquist radius (Fig. 7 c) of 6-MoS 2 /BiOBr dramatically decreased compared with that of BiOBr, implying that the recombination of e − /h + pairs in 6-MoS 2 /BiOBr was strongly inhibited (Wu et al. 2020 ). The transient photocurrent shown in Fig. 7 d displayed that BiOBr had weak response signal while the heterojunction 6-MoS 2 -BiOBr exhibited stronger photocurrent than BiOBr, further proving that the efficient separation of photocarriers in 6-MoS 2 /BiOBr was promoted. The above PL, EIS and photocurrent results were in accordance with the previous photocatalytic performance. 3.5 Detection of reactive species To specify the main reactive species involved in tetracycline and levofloxacin photo-degradation by 6-MoS 2 /BiOBr, reactive radical capture experiments were conducted and ethylene di-ammine tetra acetic acid disodium (Na 2 EDTA), isopropanol (IPA), benzoquinone (BQ) were employed to capture h + , •OH, and •O 2 – , respectively. From Fig. 8 a, it could be seen that the degradation efficiency of tetracycline was dramatically suppressed from 92.96–54.78% and 63.23% with the addition of Na 2 EDTA and IPA in tetracycline degradation process. However, the addition of BQ had a negligible effect on tetracycline degradation. This phenomenon depicted that h + and •OH were the main reactive reagents in tetracycline degradation and the same results were observed in levofloxacin degradation (Fig. 8 b). 3.6 Mechanism of enhanced photocatalytic performance A plausible enhanced photocatalytic mechanism for tetracycline and levofloxacin degradation over MoS 2 /BiOBr heterojunctions was proposed and illustrated in Fig. 9 . As irradiated by the visible-light, both MoS 2 and BiOBr could be inspired and produce electron/hole (e − /h + ) pairs. Based on our previous work, the conduction band potential ( E CB ) and valence band potential ( E VB ) for MoS 2 is 0.33 eV, 1.33 eV (Ma et al. 2019b ), whereas it is 0.19 eV, 3.17 eV for BiOBr (Ma et al. 2019a ). Thus, the heterojunciton structure formed in MoS 2 /BiOBr system could be classified in type-I (Marschall 2014 ). Since E CB value of MoS 2 was larger than that of BiOBr, the photo-induced electrons were partly migrated from the CB of BiOBr to that of MoS 2 . The CB of both MoS 2 and BiOBr were more positive than the oxidation potential of O 2 /•O 2 − (-0.33 eV vs NHE (Liu et al. 2022 ; Liu 2017). So •O 2 − radicals cannot be produced by both MoS 2 and BiOBr, which had been confirmed by the radical capturing experiments (Fig. 9 ). The E VB of MoS 2 was lower than that of the reduction potential of ·OH/OH − (1.99 eV vs NHE and ·OH/H 2 O (2.27 V vs NHE (Li et al. 2018 ). While the BiOBr had a more positive E VB value than 1.99 and 2.27 eV, so the OH − or H 2 O could be oxidized to ·OH radicals by BiOBr but not by MoS 2 . The ·OH radicals possess strong oxidation ability and could degrade organic molecules to small molecules. The participation of ·OH radicals in the degradation process had been approved by radical capturing experiments (Fig. 8 ). In a word, the fabrication of type-I heterojunction structure at the interface of MoS 2 and BiOBr facilitated the transfer and separation of photo-generated e − /h + pairs, which could be confirmed by the diminished PL intensity, the decreased EIS Nyquist radius and increased photocurrent signal shown in Fig. 7 . The reaction procedure involved in photo-degradation of tetracycline and levofloxacin was depicted with the following equations: MoS 2 /BiOBr + hv → MoS 2 (e − ) + Bi 2 O 3 (h + ) + MoS 2 (h + ) + BiOBr (h + ) (1) h + (BiOBr) + H 2 O → •OH + H + (2) h + (BiOBr) + OH − → •OH (3) •OH + tetracycline or levofloxacin → intermediates → CO 2 + H 2 O (4) h + + tetracycline or levofloxacin → intermediates → CO 2 + H 2 O (5) 4. Conclusion In this paper, 3D sheet-packed hierarchical MoS 2 /BiOBr type-I scheme heterojunctions were fabricated via a simple deposition-hydrothermal method. In comparison with pure BiOBr, the MoS 2 /BiOBr heterojunctions demonstrated enhanced photocatalytic capability in removal of tetracycline and levofloxacin. The enhanced photocatalytic ability could be accredited to the synergistic effect of stronger photo-absorption and the fabrication of type-I heterojunction at the interface of MoS 2 and BiOBr, which was facilitated the separation and migration of photo-induced e − /h + pairs. Photo-generated holes and ·OH radicals acted as a key role in the whole degradation process. This MoS 2 /BiOBr heterojunction was a promising photocatalysts suitable for eliminating antibiotics in wastewater. Declarations Funding This work was supported by the Natural Science Foundation of Shaanxi Province (2019JQ-221) Author contribution Zhanying Ma: Visualization, Investigation. Yangqing He: Conceptualization, Methodology, Writing - Original Draft, Writing - Review & Editing, Supervision. Xiaobo Li, Guang Fan and Lingjuan Deng: Formal analysis. 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Lu C, Wu WD, Zhou HF (2021) In situ fabrication of BiOBr/BiFeWO 6 heterojunction with excellent photodegradation activity under visible light. J Solid State Chem 303: 122465. Ma ZY, Deng LJ, Fan G, He YQ (2019a) Hydrothermal synthesis of p-C 3 N 4 /f-BiOBr composites with highly efficient degradation of methylene blue and tetracycline. Spectrochim. Acta A 214: 103–110. Ma ZY, Hu LL, Li XB, Deng LJ, Fan G, He YQ (2019b) A novel nano-sized MoS 2 decorated Bi 2 O 3 heterojunction with enhanced photocatalytic performance for methylene blue and tetracycline degradation. Ceram Int 45: 15824–15833. https://doi.org/10.1016/j.ceramint.2019.05.085 Mao DJ, Lü XM, Jiang ZF, Xie JM, Lu XF, Wei W, Hossain AMS (2014) Ionic liquid-assisted hydrothermal synthesis of square BiOBr nanoplates with highly efficient photocatalytic activity. Mater Lett 118: 154–157. https://doi.org/10.1016/j.matlet.2013.12.049 Meng XC, Zhang ZS (2015) Facile synthesis of BiOBr/Bi 2 WO 6 heterojunction semiconductors with high visible-light-driven photocatalytic activity. J Photoch Photobio A 310: 33–44. https://doi.org/10.1016/j.jphotochem.2015.04.024 Marschall R (2014) Semiconductor composites: strategies for enhancing charge carrier separation to improve photocatalytic activity. Adv Funct Mater 242: 421–2440. https://doi.org/10.1002/adfm.201303214 Pirhashemi M, Habibi-Yangjeh A, Pouran SR (2018) Review on the criteria anticipated for the fabrication of highly efficient ZnO-based visible-light-driven photocatalysts. J Ind Eng Chem 62: 1-25. https://doi.org/10.1016/j.jiec.2018.01.012 Van ND, Huong NT, Le NTH, Nam MH (2022) One-pot synthesis of BiSbO 4 /BiOBr nanocomposite with excellent UV-photocatalytic activity. Ceram Int 48: 8715-8720. https://doi.org/10.1016/j.ceramint.2021.12.022 Wang J, Dong C, Jiang BB, Wu KL, Sun J, Li XZ, Zhang WJ, Zhang B, Wei XW (2014) Preparation of visible light-driven Ag 2 CO 3 /BiOBr composite photocatalysts with universal degradation abilities. Mater Lett 131: 108-111. Wu J, Xie Y, Ling Y, Si JC, Li X, Wang JL, Ye H, Zhao JS, Li SQ, Zhao QD, Hou Y (2020) One-step synthesis and Gd 3+ decoration of BiOBr microspheres consisting of nanosheets toward improving photocatalytic reduction of CO 2 into hydrocarbon fuel. Chem Eng J 400: 125944. https://doi.org/10.1016/j.matlet.2014.05.153 Xiong JY, Dong QS, wang T, Jiao ZB, Lu GX, Bi YP (2014) Direct conversion of Bi nanospheres into 3D flower-like BiOBr nanoarchitectures with enhanced photocatalytic properties. RSC Adv 4: 583–586. https://doi.org/10.1039/C3RA46088F Xu ZK, Han L, Lou BH, Zhang XW, Dong SJ (2014) High-performance BiOBr ultraviolet photodetector fabricated by a green and facile interfacial self-assembly strategy. Nanoscale 6: 145–150. https://doi.org/10.1039/C3NR04496C Xue C, Xia JL, Wang T, Zhao SS, Yang GD, Yang BL, Dai YZ, Yang G (2014) A facile and efficient solvothermal fabrication of three-dimensionally hierarchical BiOBr microspheres with exceptional photocatalytic activity. Mater Lett 133: 274–277. https://doi.org/10.1016/j.matlet.2014.07.016 Zarezadeh S, Habibi-Yangjeh A, Mousavi M (2019) Fabrication of novel ZnO/BiOBr/C-Dots nanocomposites with considerable photocatalytic performances in removal of organic pollutants under visible light. Adv Powder Technol 301: 197–1209. https://doi.org/10.1016/j.apt.2019.03.016 Zhang BF, Zhang MT, Zhang L, Bingham PA, Tanaka M, Li W, Kubuki S (2021) BiOBr/MoS 2 catalyst as heterogenous peroxymonosulfate activator toward organic pollutant removal: Energy band alignment and mechanism insight. J Colloid Interf Sci 594: 635–649. https://doi.org/10.1016/j.jcis.2021.03.066 Zhang ML, Luo FF, Lan JH, Li LX, Zhan JW, Chu LL, Wang,CB (2022) Decoration engineering induced MoS 2 QDs/BiOBr heterostructures for significantly enhancing visible light photocatalytic capability for the organic dyes and antibiotics removal. Appl Surf Sci 583: 152544. https://doi.org/10.1016/j.apsusc.2022.152544 Cite Share Download PDF Status: Published Journal Publication published 04 Apr, 2023 Read the published version in Environmental Science and Pollution Research → Version 1 posted Editorial decision: Major Revision 06 Jan, 2023 Reviewers agreed at journal 03 Dec, 2022 Reviewers invited by journal 02 Dec, 2022 Editor invited by journal 14 Nov, 2022 Editor assigned by journal 28 Oct, 2022 First submitted to journal 24 Oct, 2022 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2186761","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":157028369,"identity":"f84c7d60-3f49-44fb-bf71-c308179c9c57","order_by":0,"name":"Zhanying Ma","email":"","orcid":"","institution":"Xianyang Normal University","correspondingAuthor":false,"prefix":"","firstName":"Zhanying","middleName":"","lastName":"Ma","suffix":""},{"id":157028370,"identity":"7e7b49a0-7ff0-459a-bff7-a03e1289fc38","order_by":1,"name":"Xiaobo Li","email":"","orcid":"","institution":"Xianyang Normal University","correspondingAuthor":false,"prefix":"","firstName":"Xiaobo","middleName":"","lastName":"Li","suffix":""},{"id":157028371,"identity":"06f6afe4-347e-4834-a310-8a0b895d1ae6","order_by":2,"name":"Guang Fan","email":"","orcid":"","institution":"Xianyang Normal University","correspondingAuthor":false,"prefix":"","firstName":"Guang","middleName":"","lastName":"Fan","suffix":""},{"id":157028372,"identity":"fe4e9704-59ef-4de7-a094-dfb1499f0d59","order_by":3,"name":"lingjuan Deng","email":"","orcid":"","institution":"Xianyang Normal University","correspondingAuthor":false,"prefix":"","firstName":"lingjuan","middleName":"","lastName":"Deng","suffix":""},{"id":157028373,"identity":"179fd726-afe0-457b-a6ef-d934c9d14a53","order_by":4,"name":"Yangqing He","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAx0lEQVRIiWNgGAWjYFACHgaGDxUINnFaGGecAdJspGhh5mwjRYvB8dyDjxnnHZY3uN/A+OBtG4O8OUEtZ94lGxduSzPccIyB2XBuG4PhzgZCWm7kmEnP3GbDCNTCJs3bxpBgcICwFvPfvHMk7IFa2H8Tq8WMmbfBJhFkCzNRWiTPvDGWnHEsLXnmscRmyTnnJAw3ENLCdzzH8MOHmsO2fYcPH/zwpsxGnqAtCgcSYEzGBiAhQUA9EMg3JBBUMwpGwSgYBSMdAAAwS0HLkDJq0wAAAABJRU5ErkJggg==","orcid":"","institution":"Xi'an University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Yangqing","middleName":"","lastName":"He","suffix":""}],"badges":[],"createdAt":"2022-10-20 12:33:40","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2186761/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2186761/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11356-023-26740-9","type":"published","date":"2023-04-04T20:23:03+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":29970935,"identity":"91a34206-a201-4a7d-ae3b-e1d09a2b9abe","added_by":"auto","created_at":"2022-12-06 15:39:51","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":177608,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of BiOBr, MoS\u003csub\u003e2\u003c/sub\u003e and MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites with different weight percentage of MoS\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-2186761/v1/0b5e2f21654ef67ea067fd0d.png"},{"id":29970125,"identity":"5bfd6564-0317-4ce7-8e6c-2dae4acab0a5","added_by":"auto","created_at":"2022-12-06 15:23:51","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":693239,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of MoS\u003csub\u003e2\u003c/sub\u003e (a) and 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites (d), TEM images of MoS\u003csub\u003e2\u003c/sub\u003e (b) and 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites (e), HRTEM images of MoS\u003csub\u003e2\u003c/sub\u003e (c) and 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites (f)\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-2186761/v1/35c0db06d89c075b92a46ce7.png"},{"id":29970934,"identity":"8ff9829f-c60e-488e-963a-71f2cf17ba8c","added_by":"auto","created_at":"2022-12-06 15:39:51","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":361695,"visible":true,"origin":"","legend":"\u003cp\u003eElemental distribution maps of 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-2186761/v1/296f4894ccf0a5ddc6074925.png"},{"id":29970126,"identity":"2664fcbb-a27c-4d45-be31-67bb47dba262","added_by":"auto","created_at":"2022-12-06 15:23:51","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":186222,"visible":true,"origin":"","legend":"\u003cp\u003eXPS spectra of BiOBr and 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions (a) full spectra, (b) Mo 3d, (c) S 2p, (d) Bi 4f, (e) O 1s and (f) Br 3d\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-2186761/v1/70b088d75cfc354c6b6a817b.png"},{"id":29971415,"identity":"48a922f6-7519-479b-91de-a16394f45a24","added_by":"auto","created_at":"2022-12-06 15:47:52","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":166184,"visible":true,"origin":"","legend":"\u003cp\u003eDecomposition of tetracycline (a) and levofloxacin (c) under Xe lamp irradiation by BiOBr and MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions, UV-vis absorption spectra of tetracycline (b) and levofloxacin (d) during the photocatalytic degradation process by 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterounctions\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-2186761/v1/d2772e7b549129465cdf5945.png"},{"id":29970550,"identity":"105b2729-f15b-448c-a4f3-c44d842b4771","added_by":"auto","created_at":"2022-12-06 15:31:51","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":109685,"visible":true,"origin":"","legend":"\u003cp\u003eRecycling experiments by 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr under visible light irradiation\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-2186761/v1/d68291e86356a46fe13efdc5.png"},{"id":29970132,"identity":"3ed6db1e-30db-4dc9-9365-1416817235d3","added_by":"auto","created_at":"2022-12-06 15:23:52","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":79273,"visible":true,"origin":"","legend":"\u003cp\u003eUV-vis diffuse reflectance spectra (a), the photoluminescence spectroscopy (b), electrochemical impedance Nyquist (c) and transient photocurrent (d) curves of BiOBr and 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-2186761/v1/3c9f4469bc216df48c6e38ea.png"},{"id":29971414,"identity":"2030b79b-11ad-4155-b510-c91f9e8f09c0","added_by":"auto","created_at":"2022-12-06 15:47:51","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":62835,"visible":true,"origin":"","legend":"\u003cp\u003eThe degradation efficiency of tetracycline (a) and levofloxacin (b) over the 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions in the presence of scavengers\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-2186761/v1/1a1ed3ed5e4498fe9611fba2.png"},{"id":29970133,"identity":"8712b7a4-afa8-42dc-948b-a4bb5b63d967","added_by":"auto","created_at":"2022-12-06 15:23:52","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1053913,"visible":true,"origin":"","legend":"\u003cp\u003eThe proposed mechanism of enhanced photocatalytic performance over MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-2186761/v1/fb36afeeae0abf0d78b6aa38.png"},{"id":44724377,"identity":"4cb99303-d7ad-463b-9e24-23391a65b504","added_by":"auto","created_at":"2023-10-16 20:29:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3108202,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2186761/v1/0803ad26-2505-446c-9428-80b17765ef63.pdf"}],"financialInterests":"","formattedTitle":"Construction of 3D sheet-packed hierarchical MoS2/BiOBr heterostructures with remarkably enhanced photocatalytic performance for tetracycline and levofloxacin degradation","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eIn the last two decades, antibiotic residues were inevitably discharged into in various water bodies since the antibiotics were enormously produced and extensively used for medical therapy because of its excellent activity against bacterial infection (Li et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Hu et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Antibiotics polluted wastewater would provoke potential threats to the public health and ecosystem due to its toxic nature. Therefore, it is urgent to explore an efficient technology to eliminate the antibiotics residues before discharge. Among various wastewater treatment techniques, semiconductor photocatatysis has been considered as an effective approach to remove antibiotics pollutants due to its non-toxicity, cost-effective and ambient operating condition (Chen et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Pirhashemi et al \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBismuth oxybromide (BiOBr) is a V-VI-VII ternary oxide semiconductor material with layered tetragonal matlockite structure. The [Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e2+\u003c/sup\u003e positive slices were embedded in double Br negative slabs to yield [Br-Bi-O-Bi-O-Br] layers (Xu et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Then [Br-Bi-O-Bi-O-Br] layers interacted together through van der Waals forces rather than closely packed, resulting in larger BET surface area and ideal absorption abilities (Xiong et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). As reported, BiOBr has been evidenced as a promising visible-light-induced photocatalyst to decompose organic effluents due to its high stability against photocorrosion, appropriate band gap (1.7\u0026ndash;3.2 eV) and relatively excellent photocatalytic performance (Xue et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). For instance, Mao reported that square BiOBr nanoplates synthesized by ionic liquid-assisted hydrothermal method could degrade RhB thoroughly within 90 min (Mao et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Xue et al. (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) demonstrated that BiOBr porous microflowers displayed excellent photocatalytic activities for RhB decomposition under visible-light illumination. Nevertheless, the low separation ability of photo-generated electron/hole pairs severely hindered its practical applications. Previous investigations had specified that coupling BiOBr and another semiconductor with suitable band gap to form heterojunction was an efficient strategy to promote separation rate of charge carriers (Meng and Zhang \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Up to now, various BiOBr-based heterojunctions with improved photocatalytic activities over those comprised of a single component had been extensively investigated, such as BiOAc/BiOBr (Liu et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), BiOBr/BiFeWO\u003csub\u003e6\u003c/sub\u003e (Lu et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), BiOBr/BiOCl (Liao et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), BiSbO\u003csub\u003e4\u003c/sub\u003e/BiOBr (Van et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), BiOBr/C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e (Ma et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019a\u003c/span\u003e), and so on. The outstanding degradation performance of these photocatalysts depended on their preferable optical-absorption characteristics, high separation efficiency of excited charge carriers and long-term stability.\u003c/p\u003e \u003cp\u003eMolybdenum disulfide (MoS\u003csub\u003e2\u003c/sub\u003e) has a similar layered structure to BiOBr, in which Mo atoms were sandwiched covalently between S atoms to form S-Mo-S layers. Then each formed S-Mo-S layer vertically connected together by Van Der Waals interactions, which facilitated the exfoliation of 2D MoS\u003csub\u003e2\u003c/sub\u003e nanosheets from bulk MoS\u003csub\u003e2\u003c/sub\u003e. This typical layered structure not only significantly improved the utilization of active center, but also greatly shortened transfer path of photo-induced charge carriers, intermediates and products, which allowed it to be an ideal co-catalyst (Fang et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Ma et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019a\u003c/span\u003e). Various semiconductors such as C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e (Li et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), CdS (Darsara et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), Bi\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e (Iqbal et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), ZnO (Benavente et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (Ma et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019b\u003c/span\u003e), had been coupled with MoS\u003csub\u003e2\u003c/sub\u003e to increase the photocatalytic performance. Interestingly, the band gap of BiOBr matched well with that of MoS\u003csub\u003e2\u003c/sub\u003e and coupling BiOBr with MoS\u003csub\u003e2\u003c/sub\u003e can form a staggered structure, which was helpful for absorbing more photons across a wide range of light response and effectively conquer the defects of monomer catalyst. Previously, some inspiring investigations of BiOBr/MoS\u003csub\u003e2\u003c/sub\u003e heterojunctions for eliminating organic pollutants have been documented (Zhang et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Di et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). For example, Zhang et al. (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) designed BiOBr/MoS\u003csub\u003e2\u003c/sub\u003e heterojunctions, exhibiting remarkably enhanced photocatalytic activity towards of organic dye elimination and Cr (VI) reduction with the help of peroxymonosulfate. Lee et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) synthesized MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr hybrid photocatalyst, which exhibited more than 1.4 times of enhancement over pure BiOBr in the degradation of RB5. Zhang et al. (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) successfully synthesized MoS\u003csub\u003e2\u003c/sub\u003e quantum dots (QDs) decorated BiOBr heterojunction photocatalyst, and exhibited remarkably increased visible light photocatalytic ability for the RhB and ciprofloxacin removal. Concerning the frequently emergencies of global epidemic and pandemic viral illnesses such as novel coronavirus disease-2019 (COVID-19), which are in certain point associated with the long-term propagation and evolution of antibiotic resistant genes of viruses, bacteria, and protozoa promoted by the discharged antibiotic residues. It is urgently desirable to develop highly effective BiOBr-based photocatalysts towards throughly removal antibiotic residues contaminants from the aquatic environment. What\u0026rsquo;s more, the morphology, phase structure and surface chemical state of photocatalyst have important effect on the catalytic performance.\u003c/p\u003e \u003cp\u003eConsidering the unique properties of few-layered MoS\u003csub\u003e2\u003c/sub\u003e, in this work, MoS\u003csub\u003e2\u003c/sub\u003e nanosheets were fabricated firstly by a simple hydrothermal-dialysis method, and then deposited on the surface of BiOBr microflowers \u003cem\u003evia\u003c/em\u003e a deposition-hydrothermal process. As a result, few-layer MoS\u003csub\u003e2\u003c/sub\u003e nanosheets coupled with BiOBr heterojunctions MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr were successfully fabricated. The visible-light absorption capacity was enhanced and the separation or transfer efficiency of excited charge carriers was remarkably promoted. The photocatalytic performance of as-synthesized MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr microflowers was evaluated by degradation of tetracycline and levofloxacin antibiotics. The detailed relationship between the unique structure and the excellent catalytic performance of MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr microflowers was explored. The possible enhanced photocatalytic mechanism was also proposed based on various experimental investigations. Furthermore, this fabrication method could be extended into a general strategy for the formation of other 2D few-layered heterojunctions.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eSodium molybdate [Na\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e], thiourea [CH\u003csub\u003e4\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003eS], bismuth nitrate pentahydrate [Bi(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;5H\u003csub\u003e2\u003c/sub\u003eO], cetyltrimethylammonium bromide (CTAB), anhydrous ethanol (EtOH), tetracycline and levofloxacin were used without further purification.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of MoS\u003csub\u003e2\u003c/sub\u003e nanosheets\u003c/h2\u003e \u003cp\u003e0.6 g of Na\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e was dissolved in deionized water with continuous ultrasonication for 10 min to obtain the transparent Na\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e solution, followed by the addition of CH\u003csub\u003e4\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003eS (0.5 g). The as-obtained mixture solution was migrated into a 50 mL Teflon-lined stainless steel autoclave and kept at 190\u0026deg;C for 24 h to get MoS\u003csub\u003e2\u003c/sub\u003e suspension. After centrifuge at 10,000 rpm for 10 min, the supernatant was transferred to dialysis bag and kept on dialysis for 2 days. Finally, MoS\u003csub\u003e2\u003c/sub\u003e nanosheets dispersion was obtained for the following step.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Preparation of MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions\u003c/h2\u003e \u003cp\u003eThe MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions were prepared \u003cem\u003evia\u003c/em\u003e a simple deposition-hydrothermal method. Typically, 0.729 g of CTAB was dissolved in a specified amount of anhydrous ethanol, followed by the addition of bismuth nitrate pentahydrate (0.9702 g). After ultrasonication for 30 min, 4 mL of MoS\u003csub\u003e2\u003c/sub\u003e nanosheets dispersion was added. The obtained suspension was added into a 100 mL Teflon-lined stainless-steel autoclave and heated for 17 h at 160 \u0026deg;C. The product was cooled down to 25 \u0026deg;C and separated by filtration. The obtained precipitate was swilled with anhydrous ethanol and dried at 60 \u0026deg;C to obtain MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr samples, marked as 4-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr. Pure BiOBr was also synthesized using the similar procedure to MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr without the addition of MoS\u003csub\u003e2\u003c/sub\u003e nanosheets dispersion. By changing the volume amounts of MoS\u003csub\u003e2\u003c/sub\u003e nanosheets dispersion, 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr, 8-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr, 10-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr samples were also prepared with other parameters unchanged for comparison.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Characterization of the prepared samples\u003c/h2\u003e \u003cp\u003eCrystal structure was studied by X-ray diffractometer (D8 ADVANCE A25, Cu Kα, λ\u0026thinsp;=\u0026thinsp;1.54056\u0026Aring;). The morphology was investigated by scanning electron microscopy (S-3000N) and field emission transmission electron microscopy (G2F30). The surface chemical state was detected using X-ray photoelectron spectroscope (AXIS ULtrabld), operating at 3.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e mbar. The optical absorption property was investigated by Lambd 950 UV-visible diffuse reflectance spectrophotometer. The photoluminescence spectra were measured by using RF-6000 Fluorescence spectrophotometer.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Photocatalytic experiment\u003c/h2\u003e \u003cp\u003ePhotocatalytic capability of the samples was evaluated by elimination of tetracycline and levofloxacin antibiotics. The detailed process was described in our previous work (Ma et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019a\u003c/span\u003e). In a typical process, under the dark condition, 10 mg of the samples were applied to degrade 40 mL tetracycline (20 mg/L) or levofloxacin (20 mg/L) solution with vigorous stirring for 20 min to obtain the equilibrium of adsorption/desorption. Then the dispersion was continuously irradiated with a 250 W Xe lamp. 4 mL suspension was sequentially collected at each 10 min interval and centrifuged through membrane filters (0.22 \u0026micro;m) to take away the solid photocatalyst. The obtained filtrate was transferred into a quartz cuvette to investigate the absorption spectra (200\u0026ndash;750 nm) by using a UV-3200 spectrophotometer.\u003c/p\u003e \u003cp\u003eThe long-term stability was studied as follows. 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions were recycled through centrifugation after the degradation of tetracycline and levofloxacin, respectively, then rinsed with deionized water and recycled to another run.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results And Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Crystal phase structure analysis\u003c/h2\u003e \u003cp\u003eThe XRD patterns of BiOBr, MoS\u003csub\u003e2\u003c/sub\u003e and MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites (4-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr, 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr, 8-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr, 10-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr) were displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. For BiOBr sample, the main detected peaks could be well indexed to (001), (002), (101), (102), (110), (112), (200) and (212) planes of tetragonal phase structure (JCPDS No. 09-0393). The diffraction signals of MoS\u003csub\u003e2\u003c/sub\u003e were assigned to (002), (100) and (110) planes of the hexagonal phase (Chandrabose et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). While for MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites, all detected peaks were well matched to tetragonal BiOBr and no distinct diffraction peaks of MoS\u003csub\u003e2\u003c/sub\u003e were observed because the content of MoS\u003csub\u003e2\u003c/sub\u003e was too low to detect.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Morphology analysis\u003c/h2\u003e \u003cp\u003eThe morphology, size and lattice were characterized by SEM, TEM and HRTEM techniques. Results were showed in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. From Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, it was clearly observed that MoS\u003csub\u003e2\u003c/sub\u003e showed accumulated states of thin nano-plates with the smooth surface. The TEM in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb displayed that MoS\u003csub\u003e2\u003c/sub\u003e exhibited a string of nano-sheets with wrinkled layer outlook and sufficient exposed edges, further confirming the thin size and smooth surface of MoS\u003csub\u003e2\u003c/sub\u003e nano-sheet. The 0.947 nm lattice spacing in the The SEM image in the HRTEM of MoS\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec) could be indexed to its (002) facet (Hu et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed indicated that 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites had a micro-flowers morphology, with the diameter of 2\u0026thinsp;~\u0026thinsp;3 \u0026micro;m, fabricated by some interlaced nano-sheets with thickness of 35 nm. The enlarged SEM (inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed) further indicated that 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr micro-flowers were self-assembled by numerous BiOBr nano-sheets and MoS\u003csub\u003e2\u003c/sub\u003e nano-plates (marked by yellow arrow) were attached on the surface of BiOBr. The TEM images as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee confirmed the as-prepared 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr were sheet-packed 3D hierarchical structures. To confirm the formation of heterojunction between MoS\u003csub\u003e2\u003c/sub\u003e and BiOBr in 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites, HRTEM technique was employed and results were showed in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef. An obvious tight contact boundary (marked by a yellow line) between MoS\u003csub\u003e2\u003c/sub\u003e and BiOBr was evidently observed, which proved that MoS\u003csub\u003e2\u003c/sub\u003e was closely attached to the BiOBr microstructure, which was helpful for the charge separation in the electron-hole transfer process for photocatalytic tetracycline degradation (Liu et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Notably, clear lattice fringes with a spacing of 0.278 and 0.282 nm were obvious, which could be ascribed to (102) and (110) facet of BiOBr.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e was the elemental mapping results of 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites. The Bi, Br, O, Mo and S elements were distributed in the selected district and had a good synergistic correspondence with the whole scanning region, indicating that MoS\u003csub\u003e2\u003c/sub\u003e were attached or immersed well into BiOBr microstructure. This result further proved that MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites were successfully prepared.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 XPS analysis\u003c/h2\u003e \u003cp\u003eTo further prove the interaction between MoS\u003csub\u003e2\u003c/sub\u003e and BiOBr in the heterojunctions and explore the chemical states of 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr, X-ray photoelectron spectroscopies (XPS) were carried out and results were showed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea showed the full spectra of BiOBr and 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr. Bi, O and Br elements could be observed in the spectrum of BiOBr. From the spectrum of 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr, Mo and S elements were detected in addition to Bi, O, Br, implying the successful synthesis of 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb-f was the XPS high resolution spectra of Mo 3d, S 2p, Bi 4f, O 1s and Br 3d. From Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, the two strong Mo 3d signals at 235.53 and 232.29 eV could be ascribed to Mo 3d\u003csub\u003e3/2\u003c/sub\u003e and Mo 3d\u003csub\u003e5/2\u003c/sub\u003e, respectively, demonstrating the valence of molybdenum in 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr sample was +\u0026thinsp;4. The XPS peaks at 164.56 and 159.2 eV shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec could be attributed to S 2p\u003csub\u003e1/2\u003c/sub\u003e and S 2p\u003csub\u003e3/2\u003c/sub\u003e (Li et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). From Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed, two peaks at 164.4 and 159.1 eV for BiOBr sample corresponding to Bi 4f\u003csub\u003e5/2\u003c/sub\u003e and Bi 4f\u003csub\u003e7/2\u003c/sub\u003e were shifted to higher binding energies by 0.1 and 0.16 eV for 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr sample, respectively. The O 1s signal at 529.9 eV of BiOBr in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee could be ascribed to Bi-O bond (Li et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), which was shifted to 530.1 eV with apparent decreased intensity owning to the coupling of MoS\u003csub\u003e2\u003c/sub\u003e in 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr sample. Two signals with binding energies at 69.13 and 68.24 eV presented for pure BiOBr belonging to Br 3d\u003csub\u003e3/2\u003c/sub\u003e and Br 3d\u003csub\u003e5/2\u003c/sub\u003e were shifted to 69.31 and 68. 4 eV for 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions. All these distinct shifts of Bi 4f, O 1s and Br 3d orbits further proved the formation of heterojunction between MoS\u003csub\u003e2\u003c/sub\u003e and BiOBr in 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Photocatalytic degradation of tetracycline and levofloxacin\u003c/h2\u003e \u003cp\u003eThe photocatalytic capabilities of BiOBr and MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterostructures were investigated by photocatalytic removal of antibiotics tetracycline and levofloxacin aqueous solution and the results were given in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. As seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, the degradation efficiency of tetracycline and levofloxacin in the existence of BiOBr was only about 69.99% and 66.08%, respectively. Remarkable enhancement of photocatalytic performance was obtained by the MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions. As shown, the photocatalytic activity of the clearly depended on the coupling amount of MoS\u003csub\u003e2\u003c/sub\u003e and 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr exhibited the best photoactivity, 92.96% for tetracycline and 90.31% for levofloxacin after 70 min Xe lamp illumination. With the increase of MoS\u003csub\u003e2\u003c/sub\u003e coupling amount, excess MoS\u003csub\u003e2\u003c/sub\u003e particles were aggregated and increase the recombination rate of photo-generated charge carriers (Zarezadeh et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), thus leading to the lower photocatalytic activity. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed showed the dependence of UV-vis absorbance for tetracycline and levofloxacin in the absence and presence of heterojunctions. The intensity of major absorption peak for both tetracycline at 370 nm and levofloxacin at 287 nm gradually diminished with prolonging the illumination time and almost disappeared after 70 min, indicating the broken of molecular structure and the conjugated π system in the tetracycline and levofloxacin molecules. This result is very important for the practical antibiotics wastewater decontamination, since the 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions displayed remarkable photocatalytic performance in degradation of tetracycline and levofloxacin, the major effluents from therapeutic medicine, feed supplements and pharmaceutical factory.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eLong-term stability of the photocatalysts is significant for the actual applications. To evaluate the durability of 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions, the recycling degradation experiments for both tetracycline and levofloxacin were examined. The detailed process was based on our reported reference (Ma et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019a\u003c/span\u003e). Typically, 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr composites were collected by centrifugation after each run and washed with deionized water and recycled to another run. The experimental results were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. It was clear that the degradation efficiency of 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr exhibited high stability and potential applications for eliminating antibiotics pollutants, since 85% of tetracycline and 81% of levofloxacin could still be efficiently degraded after 3 runs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo investigate the migration, transfer and separation properties of photo-generated electron/hole (e\u003csup\u003e\u0026minus;\u003c/sup\u003e/h\u003csup\u003e+\u003c/sup\u003e) pairs during the photocatalytic process in the presence of BiOBr and 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr, the UV-vis diffuse reflectance spectra (DRS), photoluminescence (PL) spectroscopy, electrochemical impedance Nyquist (EIS) and transient photocurrent were employed. As evidenced in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, the incorporation of MoS\u003csub\u003e2\u003c/sub\u003e displayed a synergistic effect with significantly improved visible light harvesting in the region of 400\u0026minus;600 nm for 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr, in comparison with that of BiOBr. Furthermore, the PL intensity (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb) and the EIS Nyquist radius (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec) of 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr dramatically decreased compared with that of BiOBr, implying that the recombination of e\u003csup\u003e\u0026minus;\u003c/sup\u003e/h\u003csup\u003e+\u003c/sup\u003e pairs in 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr was strongly inhibited (Wu et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The transient photocurrent shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed displayed that BiOBr had weak response signal while the heterojunction 6-MoS\u003csub\u003e2\u003c/sub\u003e-BiOBr exhibited stronger photocurrent than BiOBr, further proving that the efficient separation of photocarriers in 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr was promoted. The above PL, EIS and photocurrent results were in accordance with the previous photocatalytic performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Detection of reactive species\u003c/h2\u003e \u003cp\u003eTo specify the main reactive species involved in tetracycline and levofloxacin photo-degradation by 6-MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr, reactive radical capture experiments were conducted and ethylene di-ammine tetra acetic acid disodium (Na\u003csub\u003e2\u003c/sub\u003eEDTA), isopropanol (IPA), benzoquinone (BQ) were employed to capture h\u003csup\u003e+\u003c/sup\u003e, \u0026bull;OH, and \u0026bull;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e, respectively. From Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea, it could be seen that the degradation efficiency of tetracycline was dramatically suppressed from 92.96\u0026ndash;54.78% and 63.23% with the addition of Na\u003csub\u003e2\u003c/sub\u003eEDTA and IPA in tetracycline degradation process. However, the addition of BQ had a negligible effect on tetracycline degradation. This phenomenon depicted that h\u003csup\u003e+\u003c/sup\u003e and \u0026bull;OH were the main reactive reagents in tetracycline degradation and the same results were observed in levofloxacin degradation (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Mechanism of enhanced photocatalytic performance\u003c/h2\u003e \u003cp\u003eA plausible enhanced photocatalytic mechanism for tetracycline and levofloxacin degradation over MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions was proposed and illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. As irradiated by the visible-light, both MoS\u003csub\u003e2\u003c/sub\u003e and BiOBr could be inspired and produce electron/hole (e\u003csup\u003e\u0026minus;\u003c/sup\u003e/h\u003csup\u003e+\u003c/sup\u003e) pairs. Based on our previous work, the conduction band potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e) and valence band potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eVB\u003c/sub\u003e) for MoS\u003csub\u003e2\u003c/sub\u003e is 0.33 eV, 1.33 eV (Ma et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019b\u003c/span\u003e), whereas it is 0.19 eV, 3.17 eV for BiOBr (Ma et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019a\u003c/span\u003e). Thus, the heterojunciton structure formed in MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr system could be classified in type-I (Marschall \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Since \u003cem\u003eE\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e value of MoS\u003csub\u003e2\u003c/sub\u003e was larger than that of BiOBr, the photo-induced electrons were partly migrated from the CB of BiOBr to that of MoS\u003csub\u003e2\u003c/sub\u003e. The CB of both MoS\u003csub\u003e2\u003c/sub\u003e and BiOBr were more positive than the oxidation potential of O\u003csub\u003e2\u003c/sub\u003e/\u0026bull;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e (-0.33 eV \u003cem\u003evs\u003c/em\u003e NHE (Liu et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Liu 2017). So \u0026bull;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e radicals cannot be produced by both MoS\u003csub\u003e2\u003c/sub\u003e and BiOBr, which had been confirmed by the radical capturing experiments (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). The \u003cem\u003eE\u003c/em\u003e\u003csub\u003eVB\u003c/sub\u003e of MoS\u003csub\u003e2\u003c/sub\u003e was lower than that of the reduction potential of \u0026middot;OH/OH\u003csup\u003e\u0026minus;\u003c/sup\u003e (1.99 eV \u003cem\u003evs\u003c/em\u003e NHE and \u0026middot;OH/H\u003csub\u003e2\u003c/sub\u003eO (2.27 V \u003cem\u003evs\u003c/em\u003e NHE (Li et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). While the BiOBr had a more positive \u003cem\u003eE\u003c/em\u003e\u003csub\u003eVB\u003c/sub\u003e value than 1.99 and 2.27 eV, so the OH\u003csup\u003e\u0026minus;\u003c/sup\u003e or H\u003csub\u003e2\u003c/sub\u003eO could be oxidized to \u0026middot;OH radicals by BiOBr but not by MoS\u003csub\u003e2\u003c/sub\u003e. The \u0026middot;OH radicals possess strong oxidation ability and could degrade organic molecules to small molecules. The participation of \u0026middot;OH radicals in the degradation process had been approved by radical capturing experiments (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn a word, the fabrication of type-I heterojunction structure at the interface of MoS\u003csub\u003e2\u003c/sub\u003e and BiOBr facilitated the transfer and separation of photo-generated e\u003csup\u003e\u0026minus;\u003c/sup\u003e/h\u003csup\u003e+\u003c/sup\u003e pairs, which could be confirmed by the diminished PL intensity, the decreased EIS Nyquist radius and increased photocurrent signal shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The reaction procedure involved in photo-degradation of tetracycline and levofloxacin was depicted with the following equations:\u003c/p\u003e \u003cp\u003eMoS\u003csub\u003e2\u003c/sub\u003e/BiOBr\u0026thinsp;+\u0026thinsp;\u003cem\u003ehv\u003c/em\u003e \u0026rarr; MoS\u003csub\u003e2\u003c/sub\u003e (e\u003csup\u003e\u0026minus;\u003c/sup\u003e)\u0026thinsp;+\u0026thinsp;Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (h\u003csup\u003e+\u003c/sup\u003e)\u0026thinsp;+\u0026thinsp;MoS\u003csub\u003e2\u003c/sub\u003e (h\u003csup\u003e+\u003c/sup\u003e)\u0026thinsp;+\u0026thinsp;BiOBr (h\u003csup\u003e+\u003c/sup\u003e) (1)\u003c/p\u003e \u003cp\u003eh\u003csup\u003e+\u003c/sup\u003e (BiOBr)\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO \u0026rarr; \u0026bull;OH\u0026thinsp;+\u0026thinsp;H\u003csup\u003e+\u003c/sup\u003e (2)\u003c/p\u003e \u003cp\u003eh\u003csup\u003e+\u003c/sup\u003e (BiOBr)\u0026thinsp;+\u0026thinsp;OH\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026rarr; \u0026bull;OH (3)\u003c/p\u003e \u003cp\u003e\u0026bull;OH\u0026thinsp;+\u0026thinsp;tetracycline or levofloxacin \u0026rarr; intermediates \u0026rarr; CO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO (4)\u003c/p\u003e \u003cp\u003eh\u003csup\u003e+\u003c/sup\u003e + tetracycline or levofloxacin \u0026rarr; intermediates \u0026rarr; CO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO (5)\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this paper, 3D sheet-packed hierarchical MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr type-I scheme heterojunctions were fabricated \u003cem\u003evia\u003c/em\u003e a simple deposition-hydrothermal method. In comparison with pure BiOBr, the MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunctions demonstrated enhanced photocatalytic capability in removal of tetracycline and levofloxacin. The enhanced photocatalytic ability could be accredited to the synergistic effect of stronger photo-absorption and the fabrication of type-I heterojunction at the interface of MoS\u003csub\u003e2\u003c/sub\u003e and BiOBr, which was facilitated the separation and migration of photo-induced e\u003csup\u003e\u0026minus;\u003c/sup\u003e/h\u003csup\u003e+\u003c/sup\u003e pairs. Photo-generated holes and \u0026middot;OH radicals acted as a key role in the whole degradation process. This MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojunction was a promising photocatalysts suitable for eliminating antibiotics in wastewater.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Natural Science Foundation of Shaanxi Province (2019JQ-221)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eZhanying Ma: Visualization, Investigation. Yangqing He: Conceptualization, Methodology, Writing - Original Draft, Writing - Review \u0026amp; Editing, Supervision. Xiaobo Li, Guang Fan and Lingjuan Deng: Formal analysis. All the authors reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets and materials used in study are available from authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval and Consent to Participate\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e All authors agree to publish the paper upon acceptance.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e The authors declare that they have no conflict of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBenavente E, Dur\u0026aacute;n F, Sotomayor-Torres C, Gonz\u0026aacute;lez G (2018) Heterostructured layered hybrid ZnO/MoS\u003csub\u003e2\u003c/sub\u003e nanosheets with enhanced visible light photocatalytic activity. 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Appl Surf Sci 583: 152544. https://doi.org/10.1016/j.apsusc.2022.152544\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"MoS2/BiOBr, Photocatalysis, Antibiotic residues removal, Heterojunctions","lastPublishedDoi":"10.21203/rs.3.rs-2186761/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2186761/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this paper, MoS\u003csub\u003e2\u003c/sub\u003e nanosheets were prepared and deposited on BiOBr microflowers to fabricate MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterojuncitons through deposition-hydrothermal strategy. The SEM and TEM images evidenced that few-layer MoS\u003csub\u003e2\u003c/sub\u003e were grafted on BiOBr surface to yield 3D sheet-packed MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr heterostructures. The obtained MoS\u003csub\u003e2\u003c/sub\u003e/BiOBr samples exhibited tremendous enhanced catalytic activity in comparison with pure BiOBr and the degradation rate reached 92.96% and 90.31% for tetracycline and levofloxacin degradation, respectively. The remarkably enhanced performance could be attributed to the synergistic effect of strong visible-light harvesting ability and the formation of heterojunction between MoS\u003csub\u003e2\u003c/sub\u003e and BiOBr. The reactive species capturing experiments evidenced that photo-generated holes and \u0026sdot;OH radicals played the dominant roles in the whole photocatalytic decomposition process. A plausible mechanism for the enhanced photocatalytic capability was also proposed.\u003c/p\u003e","manuscriptTitle":"Construction of 3D sheet-packed hierarchical MoS2/BiOBr heterostructures with remarkably enhanced photocatalytic performance for tetracycline and levofloxacin degradation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-12-06 15:23:46","doi":"10.21203/rs.3.rs-2186761/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revision","date":"2023-01-06T07:04:56+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2022-12-03T11:37:53+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2022-12-02T20:41:30+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Environmental Science and Pollution Research","date":"2022-11-14T18:54:38+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2022-10-28T04:16:00+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2022-10-24T09:44:01+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"30e98f65-5a38-4cb4-82a6-830d390adbc3","owner":[],"postedDate":"December 6th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-10-16T20:26:58+00:00","versionOfRecord":{"articleIdentity":"rs-2186761","link":"https://doi.org/10.1007/s11356-023-26740-9","journal":{"identity":"environmental-science-and-pollution-research","isVorOnly":false,"title":"Environmental Science and Pollution Research"},"publishedOn":"2023-04-04 20:23:03","publishedOnDateReadable":"April 4th, 2023"},"versionCreatedAt":"2022-12-06 15:23:46","video":"","vorDoi":"10.1007/s11356-023-26740-9","vorDoiUrl":"https://doi.org/10.1007/s11356-023-26740-9","workflowStages":[]},"version":"v1","identity":"rs-2186761","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2186761","identity":"rs-2186761","version":["v1"]},"buildId":"_2-kVJe1T_tPrBINL-cwx","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}