Self-cleaning type aquatic product detection sealing bag and preparation method and application thereof

Abstract

The application discloses a self-cleaning type aquatic product detection sealing bag and a preparation method and application thereof, and relates to the technical field of food safety detection. The sealing bag is a three-layer composite structure, which is integrally integrated by a food-grade plastic sealing film, a flexible PDMS base and an ABD-MoS2 SERS detection layer through a hot pressing process. The ABD-MoS2 nanosheet is prepared by a CVD one-step method, is stably loaded on the PDMS base by optimizing a wet transfer process, and is hot-pressed with the food-grade plastic sealing film to obtain a finished product. The prepared sealing bag can closely fit the irregular curved surface of aquatic products, realizes in-situ adsorption and detection of target objects, does not need sampling treatment, and is simple to operate. The detection limit of the sealing bag for dye residues such as methylene blue is as low as 10 ‑8 M, which meets the accuracy requirements of aquatic product residue detection, and has self-cleaning and recycling performance. After detection, the sealing bag can degrade the residual target objects under light, and is suitable for detection scenes directly contacting aquatic products.

Description

Technical Field

[0001] This invention relates to the field of food safety testing technology, specifically to a self-cleaning aquatic product testing sealing bag, its preparation method, and its application. Background Technology

[0002] The quality and safety of aquatic products are closely related to consumer health, and the standardized development of the cold chain logistics industry has also placed higher demands on aquatic product testing technology. Current mainstream aquatic product testing methods suffer from problems such as inability to perform in-situ testing, complex operation, long testing cycles, and susceptibility to cross-contamination, making it difficult to meet the needs of large-scale, on-site testing.

[0003] Two-dimensional transition metal dichalcogenides, such as MoS2, have shown great potential in the field of flexible detection due to their excellent layered structure and chemical stability. However, existing MoS2-based detection materials suffer from bottlenecks such as unstable preparation processes, weak anti-interference capabilities during detection, easy cross-contamination caused by residual target substances after detection, and inability to be reused, which limit their commercial application in aquatic product detection. In addition, traditional detection equipment or materials cannot adapt to the irregular curved surfaces of aquatic products, resulting in low detection efficiency, unstable signal acquisition, and increased detection costs.

[0004] Therefore, developing a flexible MoS2SERS detection substrate material that combines high sensitivity, self-cleaning surface, and surface adaptability has become a technical requirement for the commercialization of aquatic product food testing. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a curved-surface adaptable self-cleaning aquatic product testing sealing bag, which enables in-situ, highly sensitive, and pollution-free detection of dye residues on the surface of aquatic products. At the same time, the testing substrate has recyclable characteristics, reducing testing costs.

[0006] To achieve the above objectives, the first aspect of the present invention provides a curved-surface adaptable self-cleaning aquatic product testing sealing bag. The sealing bag has a three-layer composite structure, which is integrally formed by a food-grade plastic sealant, a flexible PDMS (polydimethylsiloxane) substrate, and an ABD-MoS2 SERS detection layer through a hot-pressing process. ABD-MoS2 nanosheets are prepared by a one-step CVD method, and are stably loaded onto the PDMS substrate by an optimized wet transfer process, and then hot-pressed with a food-grade plastic sealant to obtain the finished product.

[0007] The food-grade plastic sealant layer serves as the outer layer to ensure the safety of direct contact with food; the flexible PDMS substrate layer serves as the middle layer to provide good flexibility and surface adaptability, allowing it to closely adhere to the surface of aquatic products; the ABD-MoS2SERS detection layer serves as the inner layer, loaded on the surface of the PDMS substrate, and is responsible for the adsorption of target substances, SERS signal enhancement, and photocatalytic degradation.

[0008] Furthermore, the ABD-MoS2 is a MoS2 nanosheet with orthosulfide defects.

[0009] A second aspect of the present invention provides a method for preparing the above-mentioned curved surface adaptable self-cleaning aquatic product testing sealing bag, comprising the following steps: Step 1: Preparation of ABD-MoS2: A one-step chemical vapor deposition (CVD) method was used, with SiO2 / Si as the substrate. MoO3 powder was mixed with NaCl and placed separately with S powder in quartz boats. The mixture was heated and reacted in a protective atmosphere to grow iodine-defect MoS2 nanosheets on the SiO2 / Si substrate, i.e., ABD-MoS2 nanosheet substrate. The introduction of iodine defects can form shallow defect energy levels, which can effectively promote the separation and migration of photogenerated electron-hole pairs, thereby improving the SERS detection sensitivity and endowing the material with photocatalytic self-cleaning ability.

[0010] Step 2: Wet transfer preparation of ABD-MoS2-PDMS: A polymethyl methacrylate (PMMA) solution was spin-coated onto the surface of an ABD-MoS2 nanosheet substrate. After curing, the SiO2 layer was removed, and a composite film was transferred using a PDMS substrate. After drying, the PMMA was removed, and the substrate was washed with deionized water and dried with nitrogen to obtain the ABD-MoS2-PDMS composite substrate.

[0011] Step 3: Hot-pressing integration: The ABD-MoS2-PDMS composite substrate obtained in step two was hot-pressed into a food-grade plastic sealant, and after cooling, a curved self-cleaning aquatic product testing sealing bag was obtained.

[0012] In step one, the protective atmosphere is nitrogen; the mass of MoO3 powder is 0.02 g, the mass of NaCl is 0.0125 g, and the mass of S powder is 0.2 g. The heating temperature of MoO3 was 720℃, the heating temperature of S powder was 165℃, and the holding time for the reaction was 1 hour.

[0013] Further, in step two, the amount of PMMA solution used is 1-5 μL, the concentration is 1-9 wt%, and the spin-coating speed is 1000-3000 rpm. To achieve stable and complete loading of ABD-MoS2 on the PDMS substrate, the three key parameters of PMMA spin-coating dosage, concentration, and speed were optimized. The optimal process was determined to be: PMMA spin-coating dosage 2.0 μL, spin-coating concentration 5 wt%, and spin-coating speed 2000 rpm. Under these conditions, the transferred ABD-MoS2 film showed no damage or wrinkles, strong bonding with the PDMS substrate interface, and stable SERS signal.

[0014] Furthermore, in step two, the method for removing the SiO2 layer is to immerse the sample in NaOH solution, and the method for removing PMMA is to immerse the sample in acetone solution for 24 hours, and then wash and dry it.

[0015] Furthermore, in step three, the process conditions for hot pressing integration are: hot pressing temperature 80℃, pressure 0.3 MPa, and holding time 10 minutes.

[0016] The third aspect of this invention provides the application of the above-mentioned curved surface adaptable self-cleaning aquatic product testing sealing bag, which is used for in-situ detection of residues on the surface of aquatic products and self-cleaning regeneration of the substrate.

[0017] Furthermore, the application of the aforementioned curved surface-adapted self-cleaning aquatic product testing sealing bag includes the following steps: S1. Detection stage: The ABD-MoS2 detection layer of the sealed bag is attached to the surface of the aquatic product to be tested. After the target substance is adsorbed, the surface enhanced Raman scattering (SERS) signal is collected by a portable Raman spectrometer. Characteristic peaks can be detected, and in-situ qualitative or quantitative detection of the target substance can be achieved. S2. Self-cleaning and regeneration stage: After the test is completed, the sealed bag is treated with light to carry out a photocatalytic reaction, so that the substrate can be regenerated for reuse.

[0018] Furthermore, the light treatment is xenon lamp irradiation, with an irradiation distance of 15cm and an irradiation time of 125 to 150 minutes; Furthermore, the photocatalytic reaction conditions are as follows: hydrogen peroxide and a catalyst are added, with the amount of hydrogen peroxide being 0.6 mL and the catalyst being molybdenum disulfide with ortho-sulfur defects, with the amount of ortho-sulfur defective molybdenum disulfide being 30 mg. By optimizing the photocatalytic reaction parameters and controlling the amount of hydrogen peroxide to 0.6 mL and the light irradiation distance to 15 cm, the degradation efficiency of the target substance reaches 99.64%, ensuring a self-cleaning effect.

[0019] Compared with the prior art, the present invention has achieved the following beneficial technical effects: 1. Curved surface adaptation and in-situ detection: Relying on the flexible properties of the PDMS substrate, the detection sealing bag can closely fit the irregular curved surface of aquatic products, realizing in-situ adsorption and highly sensitive detection of target substances, without the need for sampling and processing, and the operation is simple and quick.

[0020] 2. High sensitivity and wide detection range: The detection limit for dye residues such as methylene blue is as low as 10. 8 M, effective detection range covers 10 -3 M to 10 -8 M meets the accuracy requirements for residue detection in aquatic products.

[0021] 3. Self-cleaning and recyclable: With the photocatalytic performance of ABD-MoS2, residual target substances can be degraded after detection by irradiating the sealed bag with light, realizing substrate regeneration. It still maintains excellent detection performance after six cycles, with a detection recovery rate of 75%-95%, avoiding cross-contamination and reducing detection costs.

[0022] 4. Safe and reliable: Made with food-grade plastic sealing film and non-toxic MoS2 and PDMS materials, it meets food safety requirements and is suitable for testing scenarios that involve direct contact with aquatic products. Attached Figure Description

[0023] Figure 1 This is a structural diagram of the self-cleaning aquatic product testing sealing bag prepared in Example 1 of the present invention.

[0024] Figure 2 The image shows the effect of the self-cleaning aquatic product detector prepared in Example 1 of this invention on the surface detection of fish.

[0025] Figure 3 The graph shows the effect of PMMA dosage of 1, 2, 3, 4, and 5 μL on the intensity of SERS characteristic peaks during ABD-MoS2 wet transfer.

[0026] Figure 4 The graph shows the effect of PMMA mass percentage concentrations of 1%, 3%, 5%, 7%, and 9% on the intensity of SERS characteristic peaks during ABD-MoS2 wet transfer.

[0027] Figure 5 The graph shows the effect of spin-coating speeds of 1000, 1500, 2000, 2500, and 3000 rpm on the intensity of the characteristic peak of SERS during the wet transfer of PMMA in ABD-MoS2.

[0028] Figure 6 Sensitivity detection and cyclic detection plots of MB solutions with different concentration gradients on ABD-MoS2-PDMS SERS substrate.

[0029] Figure 7 ABD-MoS2-PDMS SERS substrate concentration 10 -3 M to 10 -8 Methylene blue was used for SERS cycle detection.

[0030] Figure 8 This is a test chart showing the detection limit of methylene blue molecules at different concentrations for self-cleaning sealed bags.

[0031] Figure 9 For self-cleaning sealed bags with a concentration of 10 -1 M to 10 -10Methylene blue was used for cyclic detection of surface-enhanced Raman scattering (SERS). Detailed Implementation

[0032] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this invention, the technical solution of this invention is described in detail below. This invention is not limited to the specific embodiments listed below. Those skilled in the art can implement this invention using various other specific embodiments based on the content disclosed herein. Any modifications or variations made to the design structure and concept of this invention fall within the protection scope of this invention. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0033] Unless otherwise specified, the experimental methods in the following examples are conventional methods, and the experimental materials used are all commercially available products.

[0034] The present invention will be further described in detail below with reference to the embodiments: Example 1: Preparation of a self-cleaning aquatic product testing sealing bag with curved surface adaptation The preparation of the sealed bag for aquatic product testing in this embodiment includes the following steps: Preparation of S1.ABD-MoS2: 0.02 g of MoO3 powder was mixed with 0.0125 g of ground NaCl and placed in a quartz boat. 0.2 g of S powder was placed in another quartz boat. The two quartz boats, along with a quartz boat containing a SiO2 / Si substrate with a 300 nm SiO2 layer, were placed in a tube furnace. Nitrogen gas was introduced as a protective gas. The MoO3 was heated to 720 °C and the S powder to 165 °C. The reaction was maintained at this temperature for 1 hour. After cooling, ABD-MoS2 nanosheet substrate was obtained.

[0035] S2. Wet transfer preparation of ABD-MoS2-PDMS: 1.0 μL of a 5 wt% PMMA solution was spin-coated onto the ABD-MoS2 surface at 3000 rpm. After curing, the sample was immersed in NaOH solution to remove the SiO2 layer. After the composite film floated, it was retrieved and dried using a PDMS substrate. The sample was then immersed in acetone solution for 24 hours to remove PMMA, washed with deionized water, and dried with nitrogen to obtain the ABD-MoS2-PDMS composite substrate.

[0036] S3. Integration of the Sealed Bag for Testing: The ABD-MoS2-PDMS composite substrate is integrated with a food-grade plastic sealing film through a hot-pressing process. The hot-pressing temperature is 80℃, the pressure is 0.3 MPa, and the holding time is 10 minutes, resulting in a curved, self-cleaning sealed bag for testing aquatic products. Its structure is as follows: Figure 1 As shown.

[0037] Example 2: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that the amount of PMMA solution used in step S2 is 2 μL.

[0038] Example 3: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that the amount of PMMA solution used in step S2 is 3 μL.

[0039] Example 4: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that the amount of PMMA solution used in step S2 is 4 μL.

[0040] Example 5: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that the amount of PMMA solution used in step S2 is 5 μL.

[0041] Example 6: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that in step S2, the mass percentage of PMMA solution is 1%.

[0042] Example 7: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that the mass percentage of PMMA solution in step S2 is 3%.

[0043] Example 8: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that in step S2, the mass percentage of PMMA solution is 7%.

[0044] Example 9: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that in step S2, the mass percentage of PMMA solution is 9%.

[0045] Example 10: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that in step S2, the spin coating speed of the PMMA solution is 1000 rpm.

[0046] Example 11: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that in step S2, the spin coating speed of the PMMA solution is 1500 rpm.

[0047] Example 12: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that in step S2, the spin coating speed of the PMMA solution is 2000 rpm.

[0048] Example 13: The preparation method of the curved surface adaptable self-cleaning aquatic product testing sealing bag in this embodiment is the same as that in embodiment 1, except that in step S2, the spin coating speed of the PMMA solution is 2500 rpm.

[0049] like Figure 3 The figure shows the effect of PMMA dosage of 1, 2, 3, 4, and 5 μL on the intensity of SERS characteristic peaks during ABD-MoS2 wet transfer. The results indicate that when the PMMA dosage is low (1 μL), the PMMA is too thin, leading to V2 during the transfer process. ss -ABD-MoS2 is highly susceptible to breakage, resulting in an incomplete structure that affects adsorption and electronic transitions. When the PMMA dosage is high (3-5 μL), the excessive PMMA thickness prevents acetone from completely removing it over 24 hours. The remaining intermediate layer hinders the transition between the substrate and the molecule, leading to a significant decrease in the characteristic peak intensity of MB. When the dosage is 2 μL, V... ss The phonon vibration peak intensity of -ABD-MoS2 and the SERS characteristic peak intensity of MB are the strongest, so 2 μL is the most suitable PMMA dose.

[0050] like Figure 4 The figure shows the effect of PMMA mass percentage concentrations of 1%, 3%, 5%, 7%, and 9% on the intensity of SERS characteristic peaks during ABD-MoS2 wet transfer. The results show that the transfer effect is best and the SERS characteristic peak intensity is strongest when the mass percentage concentration of PMMA is 5 wt%.

[0051] like Figure 5 The figure shows the effect of spin coating speeds of PMMA (1000, 1500, 2000, 2500, and 3000 rpm) on the intensity of the SERS characteristic peak during the wet transfer of ABD-MoS2. The results show that when the PMMA concentration is below 5% and the spin coating speed is above 2000 rpm, the PMMA is too thin and easily damaged; when the PMMA concentration is above 5% and the spin coating speed is below 2000 rpm, the PMMA is too thick and hinders electron transfer. Therefore, the optimal process is determined to be: PMMA spin coating dose of 2.0 μL, spin coating concentration of 5 wt%, and spin coating speed of 2000 rpm. Under these conditions, the transferred ABD-MoS2 film is undamaged and wrinkled, has a strong interface with the PDMS substrate, and the SERS signal is stable.

[0052] Example 14: Detection of ABD-MoS2-PDMS SERS substrate To evaluate the detection performance of the ABD-MoS2-PDMS SERS substrate, sensitivity detection and cyclic detection were performed on MB solutions with different concentration gradients. Figure 6 As shown, for concentrations from 10 -3 M to 10 -8 The characteristic peak positions of MB can be clearly observed in M, and the peak intensity gradually decreases with decreasing concentration. Therefore, the detection limit of the flexible Vss-ABD-MoS2-PDMS SERS substrate for MB solution is 10. -8 M.

[0053] ABD-MoS2-PDMS SERS substrate concentration 10 -3 M to 10 -8 Methylene blue (MB) was used for SERS cycle detection. For example... Figure 7 As shown, the cyclic detection limit of the substrate for MB is 10. -8 M, and still has detection capability within 6 cycles, demonstrating that the ABD-MoS2-PDMS SERS substrate has good self-cleaning ability.

[0054] Example 15: Practical application and self-cleaning performance verification of sealed bags for aquatic products S1. Detection stage: Fresh freshwater fish were soaked in 50 mL of a solution with a concentration of 1×10⁻⁶. -6 M to 1×10 -5 After soaking in Methylene blue solution for 1 hour, the fish was removed and tightly wrapped in the sealed bag prepared in Example 1. This bag allowed for thorough adhesion and adsorption of residual MB molecules on the freshwater fish surface, achieving enrichment of MB molecules on the substrate surface (e.g., ...). Figure 2 As shown in the figure, after adsorption for 30 minutes, a portable Raman spectrometer (SERS) was used to detect and collect signals from the bonding area. Characteristic peaks were detected, and the results showed that the characteristic SERS signal of methylene blue could be clearly acquired, such as... Figure 8 As shown, this indicates that the plastic wrap can achieve in-situ detection of residues on the surface of fish. In actual aquaculture, the concentration range of MB as a bactericide is 2.67 × 10⁻⁶. -6 M~8.02×10 -6 Within M, the detection range is expanded to 1×10 -6 M~10×10 -6 SERS testing of M showed that the sealed bag can achieve in-situ detection of residues on the surface of the fish.

[0055] S2. Self-cleaning and regeneration stage: After the test is completed, the used sealed bag is irradiated with a xenon lamp for 125 minutes for photocatalytic degradation. The photocatalytic reaction parameters are as follows: 0.6 mL of hydrogen peroxide, 30 mg of molybdenum disulfide with orthosulfide defects, and a light irradiation distance of 15 cm, so that the degradation efficiency of the target substance reaches 99.64% and the self-cleaning effect is guaranteed.

[0056] To further verify the self-cleaning ability of the ABD-MoS2-PDMS SERS substrate integrated in the sealed bag, after the light exposure, the fish were removed from the sealed bag, and SERS cycle detection was performed on the substrate. Raman spectroscopy was then used to detect the same area again. The results showed that the characteristic peaks of methylene blue had essentially disappeared. Figure 9 As shown, the substrate still retains its detection capability after 6 cycles of testing, with a recovery rate of 75%-95%, indicating that the residual methylene blue is completely degraded and the substrate can be regenerated. The ABD-MoS2-PDMS SERS substrate integrated into the sealed bag has excellent self-cleaning function, demonstrating excellent recyclability and reusability, avoiding cross-contamination and reducing testing costs.

Claims

1. A curved surface adaptable self-cleaning aquatic product testing sealing bag, characterized in that, The sealed bag has a three-layer composite structure, which is composed of a food-grade plastic sealing film, a flexible PDMS substrate, and an ABD-MoS2 SERS detection layer integrated by a hot-pressing process. The food-grade plastic sealant layer serves as the outer layer; the flexible PDMS substrate layer serves as the middle layer; and the ABD-MoS2SERS detection layer serves as the inner layer, loaded onto the surface of the PDMS substrate.

2. The curved surface adaptable self-cleaning aquatic product testing sealing bag according to claim 1, characterized in that, The ABD-MoS2 is a MoS2 nanosheet with orthosulfide defects.

3. A method for preparing a curved surface adaptable self-cleaning aquatic product testing sealing bag as described in claim 1 or 2, characterized in that, Includes the following steps: Step 1: Preparation of ABD-MoS2: ABD-MoS2 nanosheet substrates were grown on the SiO2 / Si substrate using a one-step chemical vapor deposition (CVD) method with SiO2 / Si as the substrate. MoO3 powder was mixed with NaCl and placed separately with S powder in quartz boats. The mixture was heated and reacted in a protective atmosphere. Step 2: Wet transfer preparation of ABD-MoS2-PDMS: PMMA solution was spin-coated onto the surface of ABD-MoS2 nanosheet substrate. After curing, the SiO2 layer was removed. The composite film was transferred using a PDMS substrate. After drying, the PMMA was removed. The substrate was then washed with deionized water and dried with nitrogen to obtain the ABD-MoS2-PDMS composite substrate. Step 3: Hot-pressing integration: The ABD-MoS2-PDMS composite substrate obtained in step two was hot-pressed into a food-grade plastic sealant, and after cooling, a curved self-cleaning aquatic product testing sealing bag was obtained.

4. The method for preparing the curved surface adaptable self-cleaning aquatic product testing sealing bag according to claim 3, characterized in that, In step one, the protective atmosphere is nitrogen; the mass of MoO3 powder is 0.02g, the mass of NaCl is 0.0125g, and the mass of S powder is 0.2g. The heating temperature of MoO3 was 720℃, the heating temperature of S powder was 165℃, and the holding time for the reaction was 1 hour.

5. The method for preparing the curved surface adaptable self-cleaning aquatic product testing sealing bag according to claim 3, characterized in that, In step two, the amount of PMMA solution used is 1-5 μL, the concentration is 1-9 wt%, and the spin coating speed is 1000-3000 rpm.

6. The method for preparing the curved surface adaptable self-cleaning aquatic product testing sealing bag according to claim 3, characterized in that, In step two, the method for removing the SiO2 layer is to immerse the sample in NaOH solution, and the method for removing PMMA is to immerse the sample in acetone solution for 24 hours, and then wash and dry it.

7. The method for preparing the curved surface adaptable self-cleaning aquatic product testing sealing bag according to claim 3, characterized in that, In step three, the hot-pressing integration process conditions are: hot-pressing temperature 80℃, pressure 0.3 MPa, and holding time 10 minutes.

8. An application of the curved surface adaptable self-cleaning aquatic product testing sealing bag as described in claim 1 or 2, characterized in that, It is used for in-situ detection of residues on the surface of aquatic products and for self-cleaning regeneration of substrates.

9. The application according to claim 8, characterized in that, Includes the following steps: S1. Detection stage: The ABD-MoS2 detection layer of the sealed bag is attached to the surface of the aquatic product to be tested. After adsorbing the target substance, the SERS signal is collected by a portable Raman spectrometer. Characteristic peaks can be detected, and in-situ qualitative or quantitative detection of the target substance can be achieved. S2. Self-cleaning and regeneration stage: After the test is completed, the sealed bag is treated with light to carry out a photocatalytic reaction, so that the substrate can be regenerated for reuse.

10. The application according to claim 9, characterized in that, The light treatment is xenon lamp irradiation, with an irradiation distance of 15cm and an irradiation time of 125 to 150 minutes; The conditions for the photocatalytic reaction are as follows: hydrogen peroxide and a catalyst are added, wherein the amount of hydrogen peroxide is 0.6 mL, and the catalyst is molybdenum disulfide with ortho-sulfur defects, wherein the amount of molybdenum disulfide with ortho-sulfur defects is 30 mg.

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