Preparation method of quantum dot homogeneous photocatalytic material and application of quantum dot homogeneous photocatalytic material in photocatalytic methane to methanol

Abstract

The application relates to the technical field of methane photocatalytic materials, in particular to a preparation method of a quantum dot homogeneous photocatalytic material and application of the quantum dot homogeneous photocatalytic material in photocatalytic methane-to-methanol. The preparation method of the quantum dot homogeneous photocatalytic material comprises the following steps: S1, precursor solution preparation: S101, dissolving a cadmium source, a nickel source and mercaptopropionic acid in deionized water to obtain a mixed solution; S102, adjusting the pH value of the mixed solution to 10 by using lye to complete the preparation of the precursor solution; S2, modified quantum dot preparation: S3, post-treatment. The application provides a preparation method of a quantum dot homogeneous photocatalytic material and application of the quantum dot homogeneous photocatalytic material in photocatalytic methane-to-methanol, so as to solve the problems of high energy consumption under the condition of a homogeneous system and peroxidation of photocatalytic methane conversion in the related art.

Description

Technical Field

[0001] This application relates to the field of methane photocatalytic materials technology, and in particular to a method for preparing a quantum dot homogeneous photocatalytic material and its application in the photocatalytic production of methanol from methane. Background Technology

[0002] Methane, a major component of natural gas, shale gas, and combustible ice, is one of the most abundant hydrocarbon resources on Earth. However, its highly symmetrical tetrahedral molecular structure and extremely high CH bond energy (~439 kJ / mol) make it one of the most challenging activated molecules in the chemical industry. Achieving the directed conversion of methane under mild conditions for the direct synthesis of high-value chemicals is considered a major challenge in the field of catalytic chemistry.

[0003] Currently, among existing methane conversion technologies, traditional heterogeneous catalytic systems, such as the widely used industrial methane steam reforming and partial oxidation processes, while technically mature, require high temperatures (>800℃) and high pressures, resulting in huge energy consumption, demanding equipment requirements, and unavoidable deep oxidation problems. They also exhibit low selectivity for the target product and easily generate large amounts of CO2 byproducts. Emerging heterogeneous photocatalytic technologies, such as those using wide-bandgap semiconductors like TiO2, offer the possibility of utilizing solar energy, but their inherent narrow light absorption range, rapid photogenerated electron-hole recombination rate, and excessive adsorption of reaction intermediates on the surface all contribute to low reaction efficiency and uncontrolled product selectivity. Homogeneous molecular catalytic systems, especially those based on noble metal complexes, while exhibiting potentially high selectivity due to their uniform active sites and tunable ligand environments, still face fundamental drawbacks such as photosensitizer dependence, poor stability, and susceptibility to deactivation under strong light irradiation and oxidative environments. Although unmodified photocatalytic nanomaterials such as colloidal quantum dots have size-tunable band structures and excellent visible light absorption capabilities, their surface active sites are nonspecific, their charge separation efficiency is insufficient, and most importantly, they cannot suppress excessive oxidation pathways, resulting in a selectivity of less than 60% for target oxygen-containing chemicals. Summary of the Invention

[0004] This application provides a method for preparing a homogeneous quantum dot photocatalytic material and its application in the photocatalytic conversion of methane to methanol, in order to solve the problems of excessive energy consumption under homogeneous system conditions and peroxidation in the photocatalytic conversion of methane in related technologies.

[0005] In a first aspect, a method for preparing a homogeneous quantum dot photocatalytic material is provided, comprising the following steps:

[0006] S1. Preparation of precursor solution:

[0007] S101. Under an inert atmosphere, cadmium source, nickel source and mercaptopropionic acid are dissolved together in deionized water to obtain a mixed solution;

[0008] S102. Adjust the pH of the mixed solution to 10 using alkaline solution, and continue stirring for 25-30 minutes to complete the preparation of the precursor solution;

[0009] S2, Preparation of modified quantum dots:

[0010] S201. Under vigorous stirring, an aqueous solution of sulfur source is rapidly injected into the precursor solution at 80°C, and then reacted at a constant temperature of 88~90°C for 30 minutes to obtain a quantum dot solution.

[0011] S202. Lower the temperature to 60℃, add 0.003~0.005mol / L thioctic acid solution to the quantum dot solution, and stir for 50~60min. The volume ratio of the thioctic acid solution to the quantum dot solution is 1:(20~25).

[0012] S203. Continue to add modifier and ultrasonically disperse for 30 min to complete the preparation of modified quantum dot solution. The mass-volume ratio of modifier to quantum dot solution is (0.8~1) g: 1 L.

[0013] S3, Post-processing:

[0014] The silica aerogel was dispersed in the modified quantum dot solution at a mass-volume ratio of (1~1.2) g:1 L, and ultrasonically treated for 30~40 min. A dispersant was added, and then the mixture was stirred at 45~50℃ for 1.5~2 h. After centrifugation, the mixture was washed and dried to obtain the homogeneous quantum dot photocatalytic material.

[0015] Preferably, in S101, the cadmium source is selected from CdCl2, and the nickel source is selected from NiCl2·6H2O;

[0016] The amount of CdCl2 added is 0.01 mol / L, the amount of NiCl2·6H2O added is 0.002~0.005 mol / L, and the amount of mercaptopropionic acid added is 0.03 mol / L.

[0017] Preferably, in S102, the alkaline solution is selected from a 1 mol / L NaOH solution.

[0018] Preferably, in S201, the concentration of the aqueous solution of the sulfur source is 0.015 mol / L, and the sulfur source is selected from Na2S·9H2O;

[0019] The volume ratio of the aqueous solution of the sulfur source to the precursor solution is 1:(2~5).

[0020] Preferably, in step S201, the condition for vigorous stirring is a rotation speed of 500~600 r / min;

[0021] The condition for rapidly injecting the aqueous solution of the sulfur source is that the injection time does not exceed 30 seconds.

[0022] Preferably, in S203, the modifier includes polypyrrole and molybdenum disulfide in a mass ratio of 5:(2~3).

[0023] Preferably, step S3 further includes, before adding the dispersant:

[0024] Add zinc ferrite powder and ultrasonically disperse for 20-25 minutes;

[0025] The amount of zinc ferrite added is 0.001 mol / L.

[0026] Preferably, in step S3, the specific surface area of ​​the silica aerogel is ≥800 m². 2 / g.

[0027] Preferably, in step S3, the dispersant is selected from polyethylene glycol, and the concentration of the dispersant in the modified quantum dot solution is 0.2 g / L.

[0028] Secondly, an application of a quantum dot homogeneous photocatalytic material in methane catalysis is provided, wherein the quantum dot homogeneous photocatalytic material is prepared by any of the preparation methods of quantum dot homogeneous photocatalytic materials described above.

[0029] The beneficial effects of the technical solution provided in this application include:

[0030] This application provides a method for preparing a homogeneous quantum dot photocatalytic material and its application in the photocatalytic conversion of methane to methanol. By modifying water-soluble quantum dots with transition metals, not only is the efficient conversion and utilization of methane achieved, but also, as a homogeneous catalyst, the catalytic reaction can be carried out under homogeneous system conditions and room temperature conditions with water as the solvent and solar energy as the energy source, thereby improving the methanol yield and selectivity.

[0031] Lattice doping of cadmium sulfide (CdS) quantum dots with specific transition metal nickel (Ni) and the use of mercaptopropionic acid (MPA) as a surface-modifying ligand can creatively produce a water-soluble quantum dot that combines broad-spectrum absorption, efficient charge separation, and specific catalytic activity. 2+Doping into the CdS lattice creates defect levels in the band gap, acting as efficient electron traps to promote photogenerated charge separation. Simultaneously, Ni sites and MPA ligands synergistically regulate the catalytic microenvironment, moderately weakening the adsorption energy of the CH3O intermediate, causing it to desorb as methanol rather than continuing to dehydrogenate to CO. This kinetically blocks the excessive oxidation pathway, achieving high methanol selectivity and avoiding the generation of byproducts CO and CO2. Surface modification with lipoic acid constructs specific active sites, directionally guiding the breaking of CH bonds in low-carbon alkanes to generate target oxygen-containing chemicals. Combined with modifiers to improve charge separation efficiency, and silica aerogel synergistically enhancing material dispersion stability, this technology can be widely used in clean energy fields such as natural gas conversion and solar fuel production. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a flowchart of the preparation method of the quantum dot homogeneous photocatalytic material provided in this application;

[0034] Figure 2 XRD patterns of CdS QDs provided in this application and Ni:CdS QDs prepared in Example 1;

[0035] Figure 3 TEM images of CdS QDs provided in this application and Ni:CdS QDs prepared in Example 1, wherein... Figure 3 (a) is a TEM image of CdS QDs. Figure 3 (b) is a TEM image of Ni:CdS QDs;

[0036] Figure 4 UV-vis DRS images of CdS QDs provided in this application and Ni:CdS QDs prepared in Example 1;

[0037] Figure 5 Steady-state PL spectra of CdS QDs provided in this application and Ni:CdS QDs prepared in Example 1;

[0038] Figure 6 TRPL spectra of CdS QDs provided in this application and Ni:CdS QDs prepared in Example 1. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0040] See Figures 1-6 As shown, this application provides a method for preparing a homogeneous quantum dot photocatalytic material and its application in the photocatalytic production of methanol from methane.

[0041] Example 1

[0042] The preparation method of the quantum dot homogeneous photocatalytic material provided in this embodiment includes the following steps:

[0043] S1. Preparation of precursor solution:

[0044] S101. Under Ar atmosphere protection, 1.833g CdCl2, 0.8g NiCl2·6H2O and 3.3g mercaptopropionic acid (MPA) are dissolved together in 1L of deionized water to obtain a mixed solution;

[0045] S102. Adjust the pH of the mixed solution to 10 using a 1 mol / L NaOH solution (monitor the pH in real time with a pH meter), and continue stirring for 30 min to complete the preparation of the precursor solution. Under these conditions, MPA forms a stable water-soluble complex with metal ions, and MPA is partially deprotonated, preparing it for subsequent reaction with the sulfur source.

[0046] S2, Preparation of modified quantum dots:

[0047] S201. Under vigorous stirring (550 r / min), 350 mL of a 0.015 mol / L Na2S·9H2O aqueous solution was rapidly injected into the above precursor solution at 80 °C within 30 s. Then, the solution was reacted at 90 °C for 30 min to obtain a quantum dot solution. At this time, the solution rapidly changed from clear to turbid and then back to clear, indicating that the quantum dot nucleation and growth process was completed.

[0048] S202. Lower the temperature to 60℃, add 60mL of 0.003mol / L thioctic acid solution to the quantum dot solution, and stir for 60min;

[0049] S203, continue to add 1.25g of modifier, ultrasonically disperse for 30min, and complete the preparation of modified quantum dot solution; wherein the modifier is a mixture of 1g polypyrrole and 0.4g molybdenum disulfide;

[0050] It should be noted that the polypyrrole is selected from conductive linear polypyrrole (industrial grade, doped), with conductivity (conductivity ≥10 S / cm), molecular weight 30000 Da, and purity ≥99.5%; the molybdenum disulfide is selected from few-layer molybdenum disulfide nanosheets (industrial grade, liquid phase exfoliation type), with purity ≥99%. The following examples and comparative examples will not be repeated.

[0051] S3, Post-processing:

[0052] 1.6g of silica aerogel (specific surface area 800m²) was added. 2 / g) was dispersed in the above modified quantum dot solution, ultrasonicated for 30 min, 0.34g zinc ferrite powder was added and ultrasonically dispersed for 20 min, 0.282g polyethylene glycol-6000 was added, and then stirred at 45℃ for 2 h. After centrifugation, the mixture was washed and dried to obtain the homogeneous quantum dot photocatalytic material.

[0053] Example 2

[0054] The difference from Example 1 is that in this example, the amount of Na2S·9H2O aqueous solution injected in step S201 is 500mL, and zinc ferrate is not added in step S3.

[0055] Example 3

[0056] The preparation method of the quantum dot homogeneous photocatalytic material provided in this embodiment includes the following steps:

[0057] S1. Preparation of precursor solution:

[0058] S101. Under a nitrogen atmosphere, 1.833 g CdCl2, 0.433 g NiCl2·6H2O and 3.3 g mercaptopropionic acid (MPA) were dissolved together in 1 L of deionized water to obtain a mixed solution.

[0059] S102. Adjust the pH of the mixed solution to 10 using 1 mol / L NaOH solution, and continue stirring for 25 min to complete the preparation of the precursor solution;

[0060] S2, Preparation of modified quantum dots:

[0061] S201. Under vigorous stirring (600 r / min), 200 mL of an aqueous solution of Na2S·9H2O with a concentration of 0.015 mol / L was rapidly injected into the above precursor solution within 30 s at 80 °C. Then, the solution was reacted at a constant temperature of 88 °C for 30 min to obtain a quantum dot solution.

[0062] S202. Lower the temperature to 60℃, add 60mL of 0.005mol / L thioctic acid solution to the quantum dot solution, and stir for 50min.

[0063] S203, continue adding 0.96g of modifier, ultrasonically disperse for 30min to complete the preparation of modified quantum dot solution; wherein the modifier is a mixture of 1g polypyrrole and 0.6g molybdenum disulfide;

[0064] S3, Post-processing:

[0065] 1.26g of silica aerogel (specific surface area 900m²) was added. 2 The modified quantum dot material was dispersed in the above modified quantum dot solution, ultrasonically treated for 40 min, 0.252 g of polyethylene glycol-6000 was added, and then stirred at 50 °C for 1.5 h. After centrifugation, the mixture was washed and dried to obtain the homogeneous quantum dot photocatalytic material.

[0066] Example 4

[0067] The preparation method of the quantum dot homogeneous photocatalytic material provided in this embodiment includes the following steps:

[0068] S1. Preparation of precursor solution:

[0069] S101. Under Ar atmosphere protection, 1.833g CdCl2, 1.188g NiCl2·6H2O and 3.3g mercaptopropionic acid (MPA) are dissolved together in 1L of deionized water to obtain a mixed solution;

[0070] S102. Adjust the pH of the mixed solution to 10 using 1 mol / L NaOH solution, and continue stirring for 30 min to complete the preparation of the precursor solution;

[0071] S2, Preparation of modified quantum dots:

[0072] S201. Under vigorous stirring (500 r / min), 400 mL of an aqueous solution of Na2S·9H2O with a concentration of 0.015 mol / L was rapidly injected into the above precursor solution at 80 °C within 30 s. Then, the solution was reacted at a constant temperature of 90 °C for 30 min to obtain a quantum dot solution.

[0073] S202. Lower the temperature to 60℃, add 56mL of 0.004mol / L thioctic acid solution to the quantum dot solution, and stir for 55min.

[0074] S203, continue to add 1.4g of modifier, ultrasonically disperse for 30min, and complete the preparation of modified quantum dot solution; wherein the modifier is a mixture of 1g polypyrrole and 0.4g molybdenum disulfide;

[0075] S3, Post-processing:

[0076] 2.352g of silica aerogel (specific surface area 800m²)2 / g) was dispersed in the above modified quantum dot solution, ultrasonicated for 30 min, 0.472g zinc ferrite powder was added and ultrasonically dispersed for 20 min, 0.392g polyethylene glycol-6000 was added, and then stirred at 50℃ for 2 h. After centrifugation, the mixture was washed and dried to obtain the homogeneous quantum dot photocatalytic material.

[0077] Example 5

[0078] The difference from Example 1 is that the amount of NiCl2·6H2O added in S101 of this application is 0.95g, and zinc ferrite is not added in step S3.

[0079] Comparative Example 1

[0080] The difference between this comparative example and Example 1 is that steps S202 and S203 are not performed, and zinc ferrite is not added in step S3.

[0081] Comparative Example 2

[0082] The difference between this comparative example and Example 1 is that steps S202 and S203 are not performed, and silica aerogel is not added in step S3.

[0083] Comparative Example 3

[0084] The difference between this comparative example and Example 1 is that step S203 is not performed, and silica aerogel is not added in step S3.

[0085] Comparative Example 4

[0086] The difference between this comparative example and Example 1 is that step S203 is not performed, and zinc ferrite is not added in step S3.

[0087] This application also provides an application of a quantum dot homogeneous photocatalytic material, specifically for the photocatalytic production of methanol from methane, and further for the photocatalytic conversion of methane into high-value chemicals:

[0088] The generation was carried out in a 400 mL glass reactor (PQ-256, Beijing Pofilai Technology Co., Ltd., Beijing, China) with a quartz window for light irradiation. A 300 W xenon lamp (full-spectrum light, 600 mW / cm²) was used. 2 The CEL-HXF300 (CEAULIGHT Technology Co., Ltd., Beijing, China) was used as the light source. A cooling water bath was used to control the reaction system temperature at 60±1℃.

[0089] First, 0.02 g of quantum dot homogeneous photocatalytic material was dispersed in 200 mL of deionized water and magnetically stirred before being added to the reactor. Nitrogen gas (50 mL / min) was introduced into the reactor and continuously purged for 10 min. Then, methane gas (99.99% purity, 10 mL / min) was introduced to bring the initial methane concentration in the reactor to 10% (volume fraction). The reactor was then sealed and the xenon lamp light source and the 25°C constant temperature water bath were turned on.

[0090] Start the energy consumption monitor to start the timer. The reaction lasts for 1 hour, and the energy consumption data is recorded every 15 minutes. After 1 hour, turn off all devices and read the total value of the energy consumption monitor as the reaction energy consumption (kWh / h).

[0091] Table 1. Reaction energy consumption of Examples 1-5 and Comparative Examples 1-4

[0092]

[0093] The photocatalytic system does not require high temperature and pressure to maintain the reaction. Water solubility and dispersion stability are achieved through modification with mercaptopropionic acid (MPA) ligands. Nickel doping creates specific defect energy levels in the CdS lattice, which act as efficient electron traps, significantly promoting the separation of photogenerated electron-hole pairs. At the same time, the nickel active sites and MPA ligands synergistically construct a unique catalytic microenvironment, which can precisely control the adsorption energy of reaction intermediates, causing the CH3O* intermediate to desorb as methanol rather than continue to dehydrogenate to CO, thus effectively blocking the over-oxidation pathway kinetically. The thiol group (-SH) of lipoic acid coordinates with metal ions on the quantum dot surface, while the carboxyl group (-COOH) is exposed on the surface, forming specific active sites that inhibit over-oxidation caused by non-specific adsorption. Meanwhile, its hydrophobic chain further improves the dispersion stability of quantum dots in a homogeneous system.

[0094] Aerogels possess high specific surface area and a porous structure that uniformly supports quantum dots, ensuring homogeneous catalytic properties by not hindering the contact between reactants and the active sites of quantum dots. Zinc ferrite, as a secondary dopant in a narrow-bandgap semiconductor, broadens the visible light absorption range. Its Fe... 3+ It can capture photogenerated holes, further improving charge separation efficiency and enhancing catalytic activity. The synergistic effect of multiple technological features improves energy utilization efficiency and alleviates the excessive energy consumption of traditional processes.

[0095] Furthermore, the target product (methanol) and byproducts (formaldehyde, CO2, CO, and unreacted methane) in the gas after the reaction were detected. Specific results are shown in Table 2.

[0096] Table 2. Product yields of Examples 1-5 and Comparative Examples 1-4

[0097]

[0098] Lipoic acid modification optimizes the specificity of active sites, polypyrrole and molybdenum disulfide heterojunction in the modifier improve charge separation efficiency, zinc ferrite captures photogenerated holes, and silica aerogel ensures quantum dot dispersion. The four work synergistically to enhance catalytic activity, improve methane conversion, and thus promote increased gas production.

[0099] From Examples 1 and 3, as the amount of nickel doping increases (0.8 g of NiCl2·6H2O in Example 1 and 0.433 g of NiCl2·6H2O in Example 3), the total gas yield and the yield of the target product show an upward trend. This is because appropriate nickel doping optimizes the quantum dot band structure, improves the visible light absorption efficiency and charge transfer rate, thereby promoting methane conversion. However, when the doping amount is too high (1.188 g of NiCl2·6H2O in Example 4), the agglomeration of excessive nickel elements leads to a slight decrease in the dispersion of quantum dots, and the total gas yield is slightly lower than that in Example 1.

[0100] Meanwhile, the total gas production in the examples was higher than that in the comparative example, which reflects the high activity of the catalytic material and the high methane conversion rate in the examples. The by-product production was ≤6.7mL / h, while the comparative example generated CO2 due to excessive oxidation and had a low methane conversion rate.

[0101] The homogeneous quantum dot photocatalytic material prepared in Example 1 is designated as Ni:CdS QDs, and it is characterized simultaneously with CdS QDs. The preparation method of CdS QDs follows the same steps S1-S201 as in Example 1, except that a nickel source is not added.

[0102] See Figure 2 The image shows the XRD patterns of CdS QDs and Ni:CdS QDs. It can be seen that both exhibit characteristic diffraction peaks at 26.3°, 44.0°, and 51.4°, corresponding to the (111), (220), and (311) cubic cadmium sulfide crystal planes (JCPDS NO.75-0581), respectively. This confirms that both the original Ni:CdS QDs and the original CdS QDs are cubic structures with no significant difference in long-range structural order. Ni doping does not alter the basic crystal structure of CdS QDs; it enters the CdS lattice as a dopant rather than forming an independent nickel-based phase. The introduced lattice defects significantly increase the number of active sites on the quantum dot surface. Furthermore, Ni, as a dopant atom, can regulate the surface electronic structure of the quantum dots, and combined with subsequent lipoic acid modification, can enhance the specific adsorption of reactants by the active sites.

[0103] See Figure 3 As shown, Figure 3 (a) is a TEM image of CdS QDs. Figure 3(b) is a TEM image of Ni:CdS QDs. CdS QDs and Ni:CdS QDs are similar in particle size and shape, and the lattice fringes are clear.

[0104] Figure 4 The UV-vis DRS plots of CdS QDs and Ni:CdS QDs show a significant redshift in the absorption edge of the Ni:CdS QDs sample, indicating a narrower bandgap and enhanced visible light response. This means that Ni:CdS QDs can more effectively capture the lower-energy but higher-proportion visible light in the solar spectrum, thereby exciting more photogenerated electron-hole pairs per unit time and providing a more sufficient driving force for photocatalytic reactions.

[0105] Figure 5 The steady-state PL spectra of CdS QDs and Ni:CdS QDs are shown. The PL intensity of Ni:CdS QDs is significantly higher than that of CdS QDs, indicating that the nonradiative recombination of photogenerated carriers is suppressed after doping, and the lifetime of electron-hole pairs is extended, which is conducive to their migration to the quantum dot surface to participate in catalytic reactions.

[0106] Figure 6 The TRPL spectra of CdS QDs and Ni:CdS QDs are shown. The average carrier lifetime of the Ni:CdS QDs sample is significantly increased to 232 ns, which is much higher than that of CdS QDs (20 ns). This phenomenon may be due to the defect states introduced by moderate Ni doping, which act as electron trapping centers and effectively delay the recombination of electron-hole pairs.

[0107] Figure 2 and Figure 3 This indicates that nickel doping has little effect on the crystal structure or morphology of cadmium sulfide quantum dots. Figure 4 , Figure 5 , Figure 6 This demonstrates that Ni doping and modification effectively modulate the optical properties of the original CdS QDs, not only broadening their photoresponse range but also significantly improving the separation and migration efficiency of photogenerated carriers.

[0108] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a homogeneous quantum dot photocatalytic material, characterized in that, It includes the following steps: S1. Preparation of precursor solution: S101. Under an inert atmosphere, cadmium source, nickel source and mercaptopropionic acid are dissolved together in deionized water to obtain a mixed solution; S102. Adjust the pH of the mixed solution to 10 using alkaline solution, and continue stirring for 25-30 minutes to complete the preparation of the precursor solution; S2, Preparation of modified quantum dots: S201. Under vigorous stirring, an aqueous solution of sulfur source is rapidly injected into the precursor solution at 80°C, and then reacted at a constant temperature of 88~90°C for 30 minutes to obtain a quantum dot solution. S202. Lower the temperature to 60℃, add 0.003~0.005mol / L thioctic acid solution to the quantum dot solution, and stir for 50~60min. The volume ratio of the thioctic acid solution to the quantum dot solution is 1:(20~25). S203. Continue to add modifier and ultrasonically disperse for 30 min to complete the preparation of modified quantum dot solution. The mass-volume ratio of the modifier to the quantum dot solution is (0.8~1) g:1 L. The modifier includes polypyrrole and molybdenum disulfide in a mass ratio of 5:(2~3). S3, Post-processing: The silica aerogel was dispersed in the modified quantum dot solution at a mass-volume ratio of (1~1.2) g:1 L, and ultrasonically treated for 30~40 min. A dispersant was added, and then the mixture was stirred at 45~50℃ for 1.5~2 h. After centrifugation, the mixture was washed and dried to obtain the homogeneous quantum dot photocatalytic material.

2. The method for preparing the quantum dot homogeneous photocatalytic material as described in claim 1, characterized in that: In S101, the cadmium source is selected from CdCl2, and the nickel source is selected from NiCl2·6H2O; The amount of CdCl2 added is 0.01 mol / L, the amount of NiCl2·6H2O added is 0.002~0.005 mol / L, and the amount of mercaptopropionic acid added is 0.03 mol / L.

3. The method for preparing the quantum dot homogeneous photocatalytic material as described in claim 1, characterized in that: In S102, the alkaline solution is selected from a 1 mol / L NaOH solution.

4. The method for preparing the quantum dot homogeneous photocatalytic material as described in claim 1, characterized in that: In S201, the concentration of the aqueous solution of the sulfur source is 0.015 mol / L, and the sulfur source is selected from Na2S·9H2O; The volume ratio of the aqueous solution of the sulfur source to the precursor solution is 1:(2~5).

5. The method for preparing the homogeneous quantum dot photocatalytic material as described in claim 1, characterized in that: In step S201, the condition for vigorous stirring is a rotation speed of 500~600 r / min; The condition for rapidly injecting the aqueous solution of the sulfur source is that the injection time does not exceed 30 seconds.

6. The method for preparing the quantum dot homogeneous photocatalytic material as described in claim 1, characterized in that: S3 further includes the following steps before adding the dispersant: Add zinc ferrite powder and ultrasonically disperse for 20-25 minutes; The amount of zinc ferrite added is 0.001 mol / L.

7. The method for preparing the quantum dot homogeneous photocatalytic material as described in claim 1, characterized in that: In S3, the specific surface area of ​​the silica aerogel is ≥800 m². 2 / g.

8. The method for preparing the homogeneous quantum dot photocatalytic material as described in claim 1, characterized in that: In step S3, the dispersant is selected from polyethylene glycol, and the concentration of the dispersant in the modified quantum dot solution is 0.2 g / L.

9. The application of a quantum dot homogeneous photocatalytic material prepared by a method according to any one of claims 1 to 8 in the photocatalytic production of methanol from methane.

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