A covalently linked graphene oxide-molybdenum disulfide quantum dot composite and its preparation and application

Abstract

The present invention relates to a covalently linked graphene oxide-molybdenum disulfide quantum dot complex, its preparation, and application. Graphene oxide is covalently modified with thiophenol via diazo chemistry, and the sulfur defects in the molybdenum disulfide quantum dots are passivated using the modified thiol groups on the graphene oxide. This composite is thus prepared. Compared to the prior art, the graphene oxide and molybdenum disulfide quantum dots are connected by a covalent bond, resulting in excellent stability. Furthermore, effective interfacial charge interactions and synergistic effects enable the composite to exhibit enhanced anti-saturation absorption properties relative to the raw materials and physical mixtures.

Description

Technical Field

[0001] The invention belongs to the field of inorganic functional composite materials and high-intensity laser protection materials, and relates to a covalently linked graphene oxide-molybdenum disulfide quantum dot composite and its preparation and application. Background Art

[0002] Materials exhibiting nonlinear optical absorption under laser light have potential applications in optical switching, optical pulse generation, optical limiting, data storage, and other fields, and are a key research direction in modern optics. Low-dimensional materials exhibit excellent nonlinear optical properties due to their strong quantum confinement and light-matter interactions. Complexes composed of low-dimensional materials often exhibit superior nonlinear responses compared to single low-dimensional materials due to effective interfacial charge interactions and synergistic effects, making them a popular new type of nonlinear optical material. Among them, the most widely studied are complexes based on transition metal dichalcogenides, graphene, metals, and metal oxides, such as MoS2 / WS2 complexes and MoS2 / ZnO complexes. Although these complexes exhibit excellent nonlinear optical properties, weak van der Waals forces mean that the interfacial electronic interactions of the complexes are difficult to effectively control. Furthermore, the stability of these complexes stacked with van der Waals forces during solution processing is also an urgent issue.

[0003] In addition to van der Waals forces, different low-dimensional materials can also be linked by covalent bonds through chemical reactions. This connection method gives the resulting composites high stability and tunable interfacial interactions between the components. Among various low-dimensional materials, graphene oxide (GO) has shown great potential for constructing composites due to its large, flexible planar structure, good solubility, and unique electronic properties. Furthermore, GO possesses numerous oxygen-containing groups, such as carboxyl, hydroxyl, carbonyl, and epoxy groups, which are capable of undergoing a variety of chemical reactions, such as amidation, esterification, and cycloaddition. MoS2 is a layered material with a tunable band gap and diverse crystalline forms. Due to quantum limiting effects and a unique electronic structure, low-dimensional MoS2 exhibits strong light-matter interactions and nonlinear optical absorption responses. Covalently linking GO to MoS2 through chemical reactions may yield covalent composites with enhanced nonlinear optical absorption responses and stability. However, the chemical activity of MoS2 is low because the molybdenum atoms are encapsulated within the sulfur atomic layer, which is in a saturated and stable state. The preparation of covalently linked GO-MoS2 composites remains a challenge. Summary of the Invention

[0004] The purpose of the present invention is to provide a covalently linked graphene oxide-molybdenum disulfide quantum dot composite and its preparation and application. The prepared composite is simple to prepare, low in cost, short in time and has strong anti-saturation absorption in the field of femtosecond visible and near-infrared lasers.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] One of the technical solutions of the present invention provides a method for preparing a covalently linked graphene oxide-molybdenum disulfide quantum dot composite, specifically comprising: covalently modifying thiophenol onto graphene oxide by a diazo chemical method to obtain GO-SH;

[0007] MoS2 quantum dots were prepared by hydrothermal synthesis;

[0008] The thiophenol-modified graphene oxide is reacted with MoS2 quantum dots to obtain a GO-MoS2 complex, which is the covalently linked graphene oxide-MoS2 quantum dot complex.

[0009] More specifically, the following steps are included:

[0010] (1) adding 4-mercaptophenyl diazonium tetrafluoroborate to a dispersion of graphene oxide under a nitrogen atmosphere, stirring and reacting to prepare GO-SH;

[0011] (2) Sodium molybdate dihydrate is used as a metal source and L-cysteine ​​is used as a sulfur source, and a MoS2 quantum dot dispersion is prepared by hydrothermal treatment;

[0012] (3) GO-SH and MoS2 quantum dot dispersion are heated and stirred to react. After the reaction is completed, the unreacted MoS2 quantum dots are removed, separated, and dried to obtain the target product.

[0013] Furthermore, in step (1), the mass ratio of 4-mercaptophenyl diazonium tetrafluoroborate to graphene oxide is 2: 1. In addition, the solvent used in the graphene oxide dispersion is DMF.

[0014] Furthermore, in step (1), the graphene oxide dispersion is bubbled with nitrogen gas before the reaction to remove the influence of oxygen in the solvent. After the stirring reaction is completed, the residual diazonium salt and impurities are washed with solvents such as DMF, dichloromethane and ethanol.

[0015] Furthermore, in step (1), the stirring reaction temperature is room temperature and the reaction time is 24 hours.

[0016] Furthermore, in step (1), the 4-mercaptophenyl diazonium tetrafluoroborate is prepared by the following method:

[0017] HBF4 solution was added to an anhydrous ethanol solution of 4-aminothiophenol cooled to 0°C in an ice bath, and then tert-butyl nitrite was added dropwise. The reaction was stirred at room temperature. The obtained reaction product was filtered and dried to obtain 4-mercaptophenyl tetrafluoroborate diazonium salt as a light yellow solid.

[0018] Furthermore, the molar ratio of 4-aminothiophenol, HBF4 and tert-butyl nitrite is 1:2:2.

[0019] Furthermore, in step (2), the molar ratio of the sulfur source to the metal source is 3:1. Specifically, before the hydrothermal treatment,

[0020] Furthermore, in step (2), the temperature of the hydrothermal treatment is 200° C. and the time is 36 h.

[0021] Furthermore, in step (3), the concentration of the GO-SH DMF dispersion was 1 mg / mL, the concentration of the MoS2 quantum dot solution was 0.2 mg / mL, and the mass ratio of GO-SH to MoS2 quantum dots was 10:3.

[0022] Furthermore, in step (3), the temperature of the heating and stirring reaction is 50° C. and the time is 3 days.

[0023] Furthermore, in step (3), after the reaction, the unreacted quantum dots were removed by centrifugation at 10,000 rpm, and the centrifuged precipitate was ultrasonically dispersed in DMF and centrifuged again. The ultrasonic-centrifugation cycle was repeated 5 times to wash away the adsorbed MoS2 quantum dots.

[0024] A second technical solution of the present invention provides a covalently linked graphene oxide-molybdenum disulfide quantum dot composite, which is prepared using any of the preparation methods described above. Specifically, it is composed of graphene oxide, thiophenol as a covalent linking bridge, and MoS2 quantum dots.

[0025] The composite has no characteristic absorption peaks in the visible and near-infrared bands, exhibiting a broad-band absorption pattern with gradually decreasing absorbance as wavelength increases. Specifically, the composite exhibits excitation-light-dependent fluorescence, with a peak at 458 nm and maximum fluorescence intensity under 370 nm excitation. Compared to its component MoS2 quantum dots, the fluorescence intensity decreases and the fluorescence lifetime shortens. Exemplarily, the composite exhibits stronger anti-saturation absorption under 800 and 515 nm femtosecond laser pulses than graphene oxide, MoS2 quantum dots, and their physical mixtures.

[0026] The third technical solution of the present invention provides the application of covalently linked graphene oxide-molybdenum disulfide quantum dot complexes in the field of femtosecond visible and near-infrared lasers.

[0027] The present invention provides a covalently linked graphene oxide-MoS2 quantum dot complex. This complex lacks characteristic absorption peaks in the visible and near-infrared bands, exhibiting a broad-band absorption pattern with gradually decreasing absorbance as wavelength increases. The complex also exhibits excitation-light-dependent fluorescence and significant fluorescence quenching relative to MoS2 quantum dots. Under 800 and 515 nm femtosecond laser pulse excitation, the graphene oxide-MoS2 quantum dot complex exhibits stronger anti-saturation absorption than graphene oxide, MoS2 quantum dots, or their physical mixtures due to interfacial charge interactions and synergistic effects.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The covalently linked GO-MoS2 complex has good stability.

[0030] 2. The GO-MoS2 complex has interfacial charge / energy interaction, which causes fluorescence quenching of the MoS2 quantum dot component.

[0031] 3. Under 800 and 515 nm femtosecond laser irradiation, the GO-MoS2 composite has enhanced anti-saturation absorption compared with single components graphene oxide and MoS2 quantum dots, as well as their physical mixture. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the synthesis route of the covalently linked GO-MoS2 complex prepared in the present invention;

[0033] Figure 2 Raman spectra of the GO-MoS2 composite and raw materials prepared in Example 1 of the present invention;

[0034] Figure 3 The infrared spectra of the GO-MoS2 composite and raw materials prepared in Example 1 of the present invention;

[0035] Figure 4 Transmission electron microscopy (TEM) image of the GO-MoS2 composite prepared in Example 1 of the present invention;

[0036] Figure 5 Absorption spectra of the GO-MoS2 composite and raw materials prepared in Example 1 of the present invention;

[0037] Figure 6 Fluorescence spectrum of the GO-MoS2 composite prepared in Example 1 of the present invention (a), and the fluorescence spectrum of the comparative material (b);

[0038] Figure 7 The fluorescence lifetime spectra of the GO-MoS2 composite and raw materials prepared in Example 1 of the present invention;

[0039] Figure 8 Nonlinear optical absorption spectra of the GO-MoS2 composite and raw materials prepared in Example 1 of the present invention under 800nm ​​(a) and 515nm (b) femtosecond pulses;

[0040] Figure 9 This is a photo of the GO-MoS2 composite prepared in Example 1 of the present invention after being placed in air at room temperature for 30 days. DETAILED DESCRIPTION

[0041] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0042] In the following examples, sodium molybdate dihydrate, L-cysteine, 4-aminothiophenol, and solvents used in the present invention are all commercial products of Anaiji Chemical Reagent Co., Ltd.

[0043] Example 1:

[0044] Preparation of GO-MoS2 composite (see Figure 1 ):

[0045] First, graphene oxide (GO) was prepared by adding 3g of graphite to 120mL of concentrated sulfuric acid and stirring. 1.5g of potassium permanganate was slowly added in portions under an ice bath, maintaining the reaction temperature low. After stirring at 35°C for 3 hours, 100mL of deionized water was added to the reaction solution and stirring continued for 15 minutes. The reaction solution was then poured into a large beaker containing 500mL of water, and a 25mL aqueous solution of 30% H2O2 was slowly added. The reaction solution was washed until the pH of the supernatant reached approximately 5. The washed dispersion was then freeze-dried to yield 4g of GO.

[0046] Next, the 4-mercaptophenyl diazonium salt used for modification was prepared. To a solution of 4-aminothiophenol (1250 mg, 10 mmol) in anhydrous ethanol cooled to 0°C in an ice bath, 2.5 mL of HBF4 solution (50% by mass, 20 mmol) was slowly added. Tert-butyl nitrite (2.7 mL, 20 mmol) was then added dropwise to the mixture. After the addition was complete, the reaction solution was further stirred at room temperature for 30 minutes. The resulting suspension was filtered and thoroughly rinsed with methyl tert-butyl ether. Finally, the filter cake was dried in vacuo to obtain 4-mercaptophenyl tetrafluoroborate diazonium salt (1350 mg, yield: 60%) as a pale yellow solid. The resulting diazonium salt was stored at -18°C.

[0047] Next, GO-SH was prepared. 50 mg of GO was mixed with 50 mL of DMF and sonicated for 30 minutes to form a uniform dispersion. The GO dispersion was degassed in a reaction flask by bubbling N2 for 30 minutes. Then, 4-mercaptophenyl diazonium tetrafluoroborate (100 mg, 0.45 mmol) dissolved in 5 mL of DMF was added dropwise at 0°C. After the addition was complete, the reaction solution was stirred at room temperature under a N2 atmosphere for 24 hours. Finally, the reaction solution was filtered through a nylon membrane (0.45 μm pore size) and thoroughly rinsed with DMF, dichloromethane, and ethanol. After drying under vacuum, 39 mg of GO-SH was obtained.

[0048] Then came the preparation of MoS2 quantum dots. Sodium molybdate dihydrate (600 mg, 2.47 mmol) was dissolved in 55 mL of deionized water, and the solution was stirred at room temperature for 15 min. The pH of the solution was adjusted to 6.5 by adding 0.1 M hydrochloric acid. After that, L-cysteine ​​(1346 mg, 7.42 mmol) dissolved in 55 mL of deionized water was added, and the resulting solution was transferred to a 150 mL Teflon-lined stainless steel autoclave and then heated at 200 ° C for 36 h. After hydrothermal treatment, the supernatant containing MoS2 quantum dots was filtered through a nylon membrane (0.1 μm pore size) and dialyzed in deionized water for 3 days to remove unreacted reagents and impurities. The obtained MoS2 quantum dot aqueous solution was freeze-dried and dispersed in DMF at a concentration of 0.2 mg / mL and stored at 0 ° C.

[0049] Finally, the GO-MoS2 composite was prepared. 20 mg of GO-SH was dispersed in 20 mL of DMF and ultrasonically treated for 30 minutes to make it a uniform dispersion. Then 30 mL of MoS2 quantum dot solution was added and stirred at 50°C for 3 days. To remove unreacted MoS2 quantum dots, the mixture was centrifuged at 10,000 rpm for 9 minutes, and then the centrifugal precipitate was redispersed in DMF by ultrasonic treatment. The above procedure was repeated five times. Finally, 16 mg of GO-MoS2 composite was obtained after drying under vacuum. After multiple ultrasonic washings, the MoS2 quantum dot component on the prepared GO-MoS2 composite did not detach, confirming its stability during liquid phase processing.

[0050] Figure 2 The Raman spectra of GO-MoS2 composite, GO, MoS2 quantum dots, etc. are shown. Both GO-SH and GO show characteristic corresponding sp 3 The disordered vibration modes of carbon atoms and sp 2 The D band (1300-1500 cm) of the tangential vibration mode of carbon atoms -1 ) and G belt (1500-1700cm -1 ), its intensity ratio ID / I G The ratio increases from 0.79 for GO to 0.91 for GO-SH, which is consistent with the fact that the double bonds on graphene can be broken by free radical addition reaction, sp 3 This is consistent with the fact that the number of carbon atoms increases accordingly. MoS2 quantum dots show E2 1 g and A 1g The vibration mode peaks come from the in-plane and out-of-plane vibrations of the Mo-S bond, respectively, while the GO-MoS2 composite shows Raman signals of MoS2 quantum dots and GO, confirming the successful composite of the two.

[0051] Figure 3 The infrared spectra of GO-MoS2 composites, GO, and MoS2 quantum dots are shown. In the infrared spectrum of GO, around 3200 cm -1 The broad peak at 1715 cm can be attributed to OH stretching vibration. -1 The absorption peak at about 1372 cm -1 The signal peak at 2516 cm is consistent with the C-OH stretching vibration. -1 A new absorption peak is shown at 2270 cm, which can be attributed to SH stretching vibration, indicating that thiophenol has been modified onto GO. -1 The N≡N stretching vibration at 30 nm was not observed, indicating that physical adsorption of the diazonium salt hardly occurred. However, in the spectrum of the GO-MoS2 composite, the absorption band corresponding to the SH stretching vibration disappeared, which means that the thiol group chemically reacted with the sulfur defect in the MoS2 quantum dots.

[0052] Figure 4 The TEM image of the GO-MoS2 composite is shown, which appears as many two-dimensional curled nanosheets decorated with quantum dots, consistent with the modification of MoS2 quantum dots on the surface of GO nanosheets.

[0053] Figure 5 The UV-visible absorption spectrum of the GO-MoS2 complex is shown. GO exhibits a broad, featureless absorption band from 370 to 900 nm. MoS2 quantum dots also lack an absorption peak, with their absorbance decreasing rapidly from 370 to ~420 nm and then slowly from ~420 to ~700 nm. Compared to GO-SH, the increased absorption below 500 nm of the GO-MoS2 complex can be attributed to the modified MoS2 quantum dots, indicating successful assembly between GO and MoS2 quantum dots.

[0054] Figure 6The fluorescence of the GO-MoS2 complex (a) and the fluorescence intensity comparison (b) are shown. As the excitation wavelength shifts from 320 nm to 450 nm, the fluorescence peak position of the GO-MoS2 complex also red-shifts from 418 nm to 500 nm. Since GO does not fluoresce, the fluorescence naturally comes from the attached MoS2 quantum dots. To make a fair comparison of fluorescence intensity, all samples were dispersed in DMF and the absorbance at 370 nm was adjusted to be the same. Under excitation at 370 nm, the GO-MoS2 complex exhibits a broad fluorescence peak at approximately 458 nm, but its intensity is much lower than the fluorescence of the MoS2 quantum dots, and the degree of fluorescence quenching is estimated to be 81%. In addition, a physical mixture GO / MoS2 was prepared as a reference. GO / MoS2 showed a lower degree of fluorescence quenching (60%), indicating that there is a stronger excited-state electron interaction in the covalently linked GO-MoS2 complex than in the physical mixture.

[0055] Transient fluorescence measurements further provide evidence of excited-state electronic interactions. Figure 7 As shown in Figure 3, under excitation at 370 nm, the average fluorescence lifetime at 458 nm decreases from 7.0 ns for MoS2 quantum dots to 5.0 ns for GO / MoS2 mixture, and then to 3.1 ns for GO-MoS2 composite. The GO-MoS2 composite shows a shorter fluorescence lifetime, which is caused by the effective excited-state electron interaction in the covalently linked GO-MoS2 composite.

[0056] Figure 8 The nonlinear optical absorption spectra of GO-MoS2 composites and raw materials under 800nm ​​(a) and 515nm (b) femtosecond pulses are shown. Under 800nm ​​femtosecond pulses, all samples show symmetrical valley-shaped curves, with the lowest transmittance at the focus, indicating anti-saturation absorption. The normalized transmittance at the focus (linear transmittance is defined as 1) decreases from 1 to 0.92 for GO, 0.91 for GO-SH, 0.87 for MoS2 quantum dots, 0.83 for GO / MoS2, and 0.74 for GO-MoS2 composites. Nonlinear coefficient β eff The value was extracted from the Z-scan curve and was 0.027 cm GW for GO -1 , GO-SH is 0.030 cm GW -1 , MoS2 quantum dots are 0.037cm GW -1 , GO / MoS2 is 0.063cm GW -1 , 0.142 cm GW for GO-MoS2 composite -1Under 515 nm femtosecond pulse laser irradiation, all samples showed anti-saturation absorption behavior, similar to the results measured at 800 nm, with the normalized transmittance decreasing from 1 to 0.80 for GO, 0.75 for GO-SH, 0.78 for MoS2 QDs, 0.62 for GO / MoS2, and 0.54 for GO-MoS2 composite. eff The values ​​are: GO is 0.091cm GW -1 , GO-SH is 0.130cm GW -1 , MoS2 quantum dots are 0.072cm GW -1 , GO / MoS2 is 0.246cm GW -1 , 0.372 cm GW for the GO-MoS2 composite -1 The GO-MoS2 composite exhibits the strongest anti-saturation absorption at both 800 and 515 nm, which can be attributed to the effective charge interaction and synergistic effect between GO and MoS2 quantum dots.

[0057] Figure 9 The photo shows the GO-MoS2 composite after being placed in air at room temperature for 30 days. GO-MoS2 did not precipitate in the solvent DMF and the color did not change, indicating the excellent stability of the GO-MoS2 dispersion.

[0058] Based on the above results, it can be confirmed that the nonlinear optical absorption performance of the material can be effectively enhanced by covalently bonding GO and MoS2 quantum dots, which provides a reference for the future design of nonlinear optical materials based on low-dimensional material composites.

[0059] Comparative Example 1:

[0060] Compared with Example 1, the synthesis method is similar, GO and MoS2 quantum dots are directly mixed, and the washing process is more gentle to avoid removing the physically adsorbed MoS2 quantum dots, thereby obtaining a GO / MoS2 complex. Under similar absorbance conditions, the covalently linked GO-MoS2 complex has a more significant fluorescence quenching phenomenon than the physically mixed GO / MoS2 complex ( Figure 6 , Figure 7 ), indicating a more effective charge interaction. Accordingly, under 800 and 515 nm femtosecond lasers, the GO-MoS2 composite exhibits better anti-saturation absorption performance than GO / MoS2 ( Figure 8 ).

[0061] Comparative Example 2:

[0062] A physical composite of MoS2 nanosheets and graphene was prepared by means of mixed filtration (see He, M.; Quan, C.; He, C.; Huang, Y.; Zhu, L.; Yao, Z.; Zhang, S.; Bai, J.; Xu, X., Enhanced Nonlinear Saturable Absorption of MoS2 / Graphene Nanocomposite Films. J. Phys. Chem. C 2017, 121 (48), 27147-27153). Due to its larger size, the composite exhibits a distinct absorption spectrum, and therefore exhibits saturated absorption under 800nm ​​femtosecond laser. In the present invention, MoS2 quantum dots and graphene oxide are used, which have better chemical activity, facilitate covalent bonding, and have a significant difference in absorption spectrum, thus exhibiting an anti-saturated absorption response.

[0063] Comparative Example 3

[0064] MoS2 nanosheets and graphene heterojunctions were prepared by chemical vapor deposition (Xu, Y.; Yan, L.; Si, J.; Li, M.; Ma, Y.; Li, J.; Hou, X., Nonlinear absorption properties and carrier dynamics in MoS2 / Graphene van der Waals heterostructures. Carbon 2020, 165, 421-427.), which showed saturation absorption under 800nm ​​femtosecond laser. Similar to the case of Comparative Example 2, the present invention uses different materials and exhibits opposite nonlinear optical properties.

[0065] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a covalently linked graphene oxide-molybdenum disulfide quantum dot composite, characterized in that: The following steps are involved: (1) Adding 4-mercaptophenyl diazonium tetrafluoroborate to a dispersion of graphene oxide under a nitrogen atmosphere, stirring and reacting to prepare GO-SH; (2) Sodium molybdate dihydrate was used as a metal source and L-cysteine ​​was used as a sulfur source, and a MoS2 quantum dot dispersion was prepared by hydrothermal treatment; (3) GO-SH and MoS2 quantum dot dispersion are heated and stirred to react. After the reaction is completed, the unreacted MoS2 quantum dots are removed, separated, and dried to obtain the target product.

2. The method for preparing a covalently linked graphene oxide-molybdenum disulfide quantum dot composite according to claim 1, wherein: In step (1), the mass ratio of 4-mercaptophenyl diazonium tetrafluoroborate to graphene oxide is 2:

1.

3. The method for preparing a covalently linked graphene oxide-molybdenum disulfide quantum dot composite according to claim 1, wherein: In step (1), the stirring reaction temperature is room temperature and the reaction time is 24 hours.

4. The method for preparing a covalently linked graphene oxide-molybdenum disulfide quantum dot composite according to claim 1, wherein: In step (1), the 4-mercaptophenyl diazonium tetrafluoroborate is prepared by the following method: HBF4 solution was added to an anhydrous ethanol solution of 4-aminothiophenol cooled to 0°C in an ice bath, and then tert-butyl nitrite was added dropwise. The reaction was stirred at room temperature. The obtained reaction product was filtered and dried to obtain 4-mercaptophenyl tetrafluoroborate diazonium salt as a light yellow solid.

5. The method for preparing a covalently linked graphene oxide-molybdenum disulfide quantum dot composite according to claim 4, wherein: The molar ratio of 4-aminothiophenol, HBF4 and tert-butyl nitrite is 1:2:

2.

6. The method for preparing a covalently linked graphene oxide-molybdenum disulfide quantum dot composite according to claim 1, wherein: In step (2), the molar ratio of the sulfur source to the metal source is 3:

1.

7. The method for preparing a covalently linked graphene oxide-molybdenum disulfide quantum dot composite according to claim 1, wherein: In step (2), the temperature of the hydrothermal treatment is 200°C and the time is 36 hours.

8. The method for preparing a covalently linked graphene oxide-molybdenum disulfide quantum dot composite according to claim 1, wherein: In step (3), The reaction temperature was 50°C and the stirring time was 3 days.

9. A covalently linked graphene oxide-molybdenum disulfide quantum dot composite, prepared by the preparation method according to any one of claims 1 to 8.

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