Preparation method and application of biphase molybdenum carbide quantum dot photo-thermal material

Abstract

The invention discloses a biphase molybdenum carbide quantum dot photo-thermal material, a preparation method and application, particularly relates to a high-carrier-concentration biphase quantum dot photo-thermal material composed of alpha-MoC of a cubic structure and beta-Mo2C of a hexagonal structure and a preparation method, and belongs to the field of nano material preparation. According to the method, an MOF confinement pyrolysis strategy is adopted, gradual conversion from alpha-MoC to beta-Mo2C is achieved by regulating and controlling the pyrolysis process, and precise regulation and control of the relative content of two phases can be achieved. According to the preparation method, the problem of serious agglomeration in the high-temperature carbonization process can be avoided, a material with a double-phase structure can be obtained at the same time, and the prepared double-phase molybdenum carbide is uniformly distributed quantum dot particles and has rich active sites, high carrier concentration (1021 cm <-3 > order of magnitude) and good photo-thermal conversion rate (70% or above); good prospects are realized in the field of photocatalysis.

Description

Technical Field

[0001] The invention relates to a preparation method of a dual-phase molybdenum carbide quantum dot photothermal material, which has a high carrier concentration and belongs to the field of nanomaterial preparation. Background Art

[0002] In recent years, transition metal carbides have attracted widespread attention due to their unique physical and chemical properties. This type of material has shown great potential in the fields of new energy and catalysis, especially in battery electrodes, supercapacitors, and catalytic materials. As a typical representative, molybdenum carbide (Mo2C) has excellent performance characteristics in fields such as electrocatalytic water splitting, photocatalytic reactions, gas sensing devices, and energy storage systems due to its electronic structure similar to that of the precious metal platinum. It is worth noting that molybdenum carbide exists in two main crystal forms: α-MoC and β-Mo2C. The difference in their performance is mainly due to the difference in crystal structure, which makes the precise preparation of crystal phases through process control a current research hotspot.

[0003] In terms of preparation technology, three main process systems are currently used: chemical vapor deposition (CVD), temperature-programmed reduction (TPR), and carbon thermal hydrogen reduction (CHR). Although the CVD method can produce thin-film catalysts with high specific surface area, its deposition efficiency is far from meeting the requirements of industrialization. Although the nanocatalysts prepared by the TPR method have excellent activity, their sensitivity to process parameters leads to insufficient product controllability. The CHR method has unique advantages in controlling specific surface area by regulating the precursor ratio and reaction temperature. It is worth noting that the choice of carbon precursor directly affects the structural characteristics of the product. Commonly used carbon sources include gaseous hydrocarbons such as methane and ethane, but they need to be mixed with hydrogen and react at high temperatures (700-900°C). Such harsh conditions can easily cause the material to sinter and agglomerate, resulting in a reduction in active sites.

[0004] The main challenges facing current preparation technologies focus on active site exposure and crystal phase control. While β-Mo2C, a thermodynamically stable phase, is relatively easy to obtain, the synthesis of the metastable α-MoC requires the use of precious metal catalysts (such as Pt and Rh) in a mixed reducing / carbonizing atmosphere. This not only increases process complexity but also poses safety risks and economic pressures. Crucially, the controllable synthesis of dual-phase composites remains a challenge, severely hindering their application in multifunctional devices. Given this current situation, the development of novel crystal phase control technologies has become a key research direction in this field. An ideal preparation method should possess the following characteristics: simple adjustment of reaction parameters allows for the controlled preparation of the desired crystal phase, avoiding the use of precious metal catalysts while simultaneously reducing process temperatures to improve cost-effectiveness and safety. This approach will have a profound impact on the practical application of molybdenum carbide materials. Summary of the Invention

[0005] The present invention overcomes the problem of high synthesis temperature of existing molybdenum carbide leading to serious product agglomeration, and provides a synthesis method and application of high carrier concentration dual-phase molybdenum carbide quantum dot photothermal materials. During the confined pyrolysis process of the precursor, by adjusting the pyrolysis temperature and time, a continuous conversion (10%-90%) from the metastable α-MoC to the stable β-Mo2C phase can be achieved. This method can avoid the serious agglomeration problem of the high-temperature carbonization process and can simultaneously obtain a material with a dual-phase structure. The prepared dual-phase molybdenum carbide is a uniformly distributed quantum dot particle with abundant active sites and a high carrier concentration (10 21 cm -3 orders of magnitude) and good photothermal conversion rate (more than 70%), it has a good prospect in the field of photocatalysis.

[0006] The present invention provides a dual-phase molybdenum carbide quantum dot photothermal material, wherein the photothermal material is a mixed-phase dual-phase quantum dot material composed of cubic α-MoC and hexagonal β-Mo2C.

[0007] The molar ratio of α-MoC and β-Mo2C phases in the dual-phase molybdenum carbide quantum dot photothermal material varies within a wide range (10%-90%), and the change is from pure α-MoC phase to pure β-Mo2C phase.

[0008] The high carrier concentration dual-phase molybdenum carbide quantum dot photothermal material has a size of 2-10 nm and is evenly distributed on a carbon matrix.

[0009] A method for preparing a high-carrier concentration dual-phase molybdenum carbide quantum dot photothermal material adopts a confined pyrolysis method, which includes the following steps: encapsulating a polyoxometalate guest in a MOF skeleton body to obtain POM@MOF, and then rapidly heating the POM@MOF in an Ar atmosphere to perform a confined carburization reaction to achieve a continuous conversion (10%-90%) from the metastable α-MoC to the stable β-Mo2C phase to obtain a dual-phase molybdenum carbide quantum dot photothermal material.

[0010] Preferably, the high carrier concentration dual-phase molybdenum carbide quantum dot photothermal material comprises α-MoC and β-Mo2C, and the molar ratio of the two phases can be continuously changed.

[0011] Preferably, the MOF skeleton body adopts the metal organic framework ZIF-8.

[0012] Preferably, the molybdenum source is phosphomolybdic acid. In the preparation of POM@MOF, zinc nitrate hydrate and phosphomolybdic acid are mixed evenly in a solvent, polyvinyl pyrrolidone is added, and the mixture is further mixed and then added dropwise to a 2-methylimidazole solution. After the reaction, POM@MOF is obtained by precipitation, washing, and drying.

[0013] The molar ratio of phosphomolybdic acid to Zn(NO3)2·6H2O is 1:1-1:5.

[0014] The heating rate is 20~50° / min, and the carburizing reaction is limited at 700-900℃ for 0.2-1h.

[0015] Preferably, in the temperature control process, the slow heating generates metastable α-MoC, and the rapid heating converts the metastable α-MoC into stable β-Mo2C.

[0016] Preferably, the gradient temperature control process is as follows: when the temperature is below 700°C, a metastable α-MoC phase is obtained. When the temperature is greater than or equal to 900°C, a stable β-Mo2C phase is obtained. When the temperature is greater than 700°C and less than 900°C (i.e., 700-900°C), and a rapid temperature increase temperature control process is used, a mixed phase of the metastable α-MoC and stable β-Mo2C phases is obtained.

[0017] The slow heating stage has a heating rate of 1-10°C / min and a holding time of 1-4 hours; the fast heating stage has a heating rate of 20-50°C / min and a holding time of 0.2-1h.

[0018] The carrier concentration of the dual-phase molybdenum carbide quantum dots obtained in the technical solution of the present invention reaches 10 21 cm -3 And above orders of magnitude; the photothermal conversion rate reaches more than 70%.

[0019] Another aspect of the present invention is to use the prepared high carrier concentration dual-phase molybdenum carbide quantum dot photothermal material as a photocatalytic material.

[0020] A photocatalyst is prepared by using dual-phase molybdenum carbide quantum dots.

[0021] The photocatalyst is obtained by mixing cadmium chloride, sodium sulfide and dual-phase molybdenum carbide quantum dots and then subjecting them to a hydrothermal reaction. The hydrothermal reaction temperature is 150-200° C. and the hydrothermal reaction time is 5-20 hours.

[0022] The high carrier concentration dual-phase molybdenum carbide quantum dot photothermal material prepared by the present invention has the following beneficial effects compared with the existing technology: (1) This method can avoid the serious agglomeration problem during the high-temperature carbonization process. The prepared dual-phase molybdenum carbide is a uniformly distributed quantum dot particle with rich interface structure, active sites, high carrier concentration and photothermal conversion capability.

[0023] (2) This method can simultaneously obtain the difficult-to-prepare metastable α-MoC and the stable β-Mo2C crystal phase, or prepare molybdenum carbide materials in any proportion of the two as needed, providing a simple and efficient source for research and production in other fields.

[0024] (3) This method is simple, safe, efficient and low-cost, providing a basis for the widespread application of molybdenum carbide materials in different fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the X-ray diffraction pattern of the high carrier concentration α-MoC quantum dot photothermal material prepared in Example 1.

[0026] Figure 2 This is the X-ray diffraction pattern of the high carrier concentration β-MoC quantum dot photothermal material prepared in Example 2.

[0027] Figure 3 This is a scanning electron microscope image of the high carrier concentration β-MoC quantum dot photothermal material prepared in Example 2.

[0028] Figure 4 This is a high-resolution transmission electron microscopy image of the high-carrier concentration α-MoC / β-Mo2C dual-phase quantum dot photothermal material prepared in Example 3.

[0029] Figure 5 XRD patterns of CdS, CdS / α-MoC, CdS / β-Mo2C and CdS / α-MoC / β-Mo2C composite materials prepared in Examples 1-3.

[0030] Figure 6 The photocatalytic hydrogen production performance of the CdS / α-MoC / β-Mo2C prepared in Example 3 and the CdS / Pt photocatalyst modified with the precious metal Pt.

[0031] Figure 7 The high carrier concentration α-MoC, β-Mo2C and α-MoC / β-Mo2C (Mo in the figure) prepared in Examples 1-3 x C refers to the thermal imaging of α-MoC / β-Mo2C) dual-phase quantum dot photothermal material under visible light.

[0032] Figure 8 The carrier concentrations of the high carrier concentration α-MoC, β-Mo2C and α-MoC / β-Mo2C dual-phase quantum dot photothermal materials prepared in Examples 1-3 under near-infrared light. DETAILED DESCRIPTION

[0033] The present invention is further illustrated below with reference to specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, modifications of various equivalent forms of the present invention made by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0034] Example 1 First, 9.85 g of 2-methylimidazole was dissolved in 180 ml of methanol and stirred for 30 min to obtain solution A.

[0035] Then, 2.94 g of zinc nitrate hexahydrate Zn(NO3)2·6H2O and 2.994 g of phosphomolybdic acid hydrate (POM) were dissolved in another 180 ml of methanol and ultrasonically treated for 10 min. Then, 1.0 g of polyvinylpyrrolidone (PVP) was added and vigorously stirred for 30 min. This was recorded as solution B.

[0036] Finally, Solution B was rapidly added dropwise to Solution A, and the mixture was stirred continuously at room temperature for 24 hours. After the reaction, the mixture was washed several times by centrifugation with methanol and ethanol. The precipitate was then dried in a vacuum oven at 60°C. After drying, the sample (denoted as POM / ZIF-8) was obtained.

[0037] A 1.5 g sample of dried POM / ZIF-8 was placed in a small corundum crucible. The crucible was then transferred to a tube furnace and heated to 700 °C at a rate of 5 °C / min under a high-purity argon atmosphere for 2 h to obtain a black α-MoC powder.

[0038] CdS / α-MoC was prepared using a one-pot hydrothermal method. 5 mmol of CdCl₂·2.5 HO and 5 mmol of Na₂S·9 HO were dissolved in 20 mL of anhydrous ethanol. 72 mg of α-MoC was added and stirred for 30 minutes to uniformly disperse the mixture. The solution was then placed in a 50 mL Teflon autoclave at 180°C for 12 hours. The mixture was collected by centrifugation and rinsed with deionized water and anhydrous ethanol, respectively. Finally, the sample was dried in a vacuum oven at 60°C for 12 hours.

[0039] 20 mg of the photocatalytic composite was dispersed in 80 mL of a solution containing lactic acid (8 mL) and water (72 mL). A xenon lamp (MC-XF300) was used as a visible light source (λ ≥ 420 nm) to illuminate the reactor horizontally. Prior to illumination, the reactor was evacuated and a recirculating cooling system was used to maintain a stable temperature (7°C) during illumination. Hydrogen generated was monitored every hour by gas chromatography using Ar as the carrier gas.

[0040] The XRD diffraction pattern of the obtained α-MoC is shown in Figure 1 As shown in Figure 2, the product is pure face-centered cubic α-MoC. The H2 production of the obtained CdS / α-MoC composite is 4.01 mmol / h / g, which is about 10 times that of pure CdS (0.41 mmol / h / g).

[0041] Example 2 First, 9.85 g of 2-methylimidazole was dissolved in 180 ml of methanol and stirred continuously for 30 min to obtain solution A. Then, 2.94 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 2.994 g of phosphomolybdic acid hydrate (POM) were dissolved in another 180 ml of methanol and sonicated for 10 min. Subsequently, 1.0 g of polyvinylpyrrolidone (PVP) was added and stirred vigorously for 30 min, which was recorded as solution B. Finally, solution B was quickly added dropwise to solution A, and the mixture was stirred continuously at room temperature for 24 h. After the reaction, the mixture was washed several times by centrifugation with methanol and ethanol. Then, the precipitate was dried in a vacuum drying oven at 60°C. After drying, the sample (referred to as POM / ZIF-8) was obtained.

[0042] A 1.5 g sample of dried POM / ZIF-8 was placed in a small corundum crucible. The crucible was then transferred to a tube furnace and heated to 900 °C at a rate of 5 °C / min under a high-purity argon atmosphere for 2 hours to obtain a black β-Mo2C powder.

[0043] CdS / β-Mo2C was prepared using a one-pot hydrothermal method. 5 mmol of CdCl2·2.5 H2O and 5 mmol of Na2S·9H2O were dissolved in 20 mL of anhydrous ethanol. 72 mg of β-Mo2C was added and stirred for 30 minutes to uniformly disperse the mixture. The solution was then placed in a 50 mL Teflon autoclave at 180°C for 12 hours. The sample was collected by centrifugation and rinsed with deionized water and anhydrous ethanol, respectively. Finally, the sample was dried in a vacuum oven at 60°C for 12 hours.

[0044] 20 mg of the photocatalytic composite was dispersed in 80 mL of a solution containing lactic acid (8 mL) and water (72 mL). A xenon lamp (MC-XF300) was used as a visible light source (λ ≥ 420 nm) to illuminate the reactor horizontally. Prior to illumination, the reactor was evacuated and a recirculating cooling system was used to maintain a stable temperature (7°C) during illumination. Hydrogen generation was monitored every hour by gas chromatography using Ar as the carrier gas.

[0045] The XRD diffraction pattern of β-Mo2C is as follows: Figure 2 As shown, the product is pure hexagonal β-Mo2C, and the SEM picture is as follows Figure 3 As shown in the figure, β-Mo2C is a very small quantum dot. The H2 production of the obtained CdS / α-MoC composite material is 13.96 mmol / h / g, which is about 34 times that of pure CdS (0.41 mmol / h / g).

[0046] Example 3 First, 9.85 g of 2-methylimidazole was dissolved in 180 ml of methanol and stirred continuously for 30 min to obtain solution A. Then, 2.94 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 2.994 g of phosphomolybdic acid hydrate (POM) were dissolved in another 180 ml of methanol and sonicated for 10 min. Subsequently, 1.0 g of polyvinylpyrrolidone (PVP) was added and stirred vigorously for 30 min, which was recorded as solution B. Finally, solution B was quickly added dropwise to solution A, and the mixture was stirred continuously at room temperature for 24 h. After the reaction, the mixture was washed several times by centrifugation with methanol and ethanol. The precipitate was then dried in a vacuum drying oven at 60°C. After drying, the sample (referred to as POM / ZIF-8) was obtained.

[0047] A 1.5 g sample of dried POM / ZIF-8 was placed in a small corundum crucible. The crucible was then transferred to a tube furnace and calcined at a rate of 5°C / min to 700°C under a high-purity argon atmosphere for 2 hours. The temperature was then increased to 850°C at a rate of 25°C / min and calcined for 30 minutes to obtain α-MoC / β-Mo2C dual-phase quantum dots.

[0048] A CdS / α-MoC / β-Mo2C photocatalyst was prepared using a one-pot hydrothermal method. 5 mmol of CdCl2·2.5 H2O and 5 mmol of Na2S·9H2O were dissolved in 20 mL of anhydrous ethanol. 72 mg of α-MoC / β-Mo2C dual-phase quantum dots were added and stirred for 30 minutes to uniformly disperse the solution. The solution was then placed in a 50 mL Teflon autoclave at 180°C for 12 hours. The sample was collected by centrifugation and rinsed with deionized water and anhydrous ethanol, respectively. Finally, the sample was dried in a vacuum oven at 60°C for 12 hours.

[0049] 20 mg of the photocatalytic composite was dispersed in 80 mL of a solution containing lactic acid (8 mL) and water (72 mL). A xenon lamp (MC-XF300) was used as a visible light source (λ ≥ 420 nm) to illuminate the reactor horizontally. Prior to illumination, the reactor was evacuated and a recirculating cooling system was used to maintain a stable temperature (7°C) during illumination. Hydrogen generation was monitored every hour by gas chromatography using Ar as the carrier gas.

[0050] The obtained α-MoC / β-Mo2C dual-phase quantum dots were imaged by high-resolution transmission electron microscopy. Figure 4 As shown, the product is a uniformly distributed hexagonal quantum dot structure composed of pure face-centered cubic α-MoC and β-Mo2C. The resulting CdS / α-MoC / β-Mo2C composite has a H2 yield of 27.32 mmol / h / g, approximately 66 times that of pure CdS (0.41 mmol / h / g).

[0051] The obtained α-MoC / β-Mo2C dual-phase quantum dots were tested for temperature under visible light irradiation by infrared thermal imager. The thermal imaging results are shown in the figure. Figure 7 It can be seen that under the same conditions, the temperature of the obtained α-MoC / β-Mo2C dual-phase quantum dots is significantly higher than that of the α-MoC in Example 1 and the β-Mo2C in Example 2, indicating that the α-MoC / β-Mo2C dual-phase quantum dots have a better photothermal effect.

[0052] The Mott-Schottky curve was used to test the concentration of carriers in the sample under near-infrared light. Figure 8 As shown in Figure 2, the carrier concentration of α-MoC / β-Mo2C dual-phase quantum dots under near-infrared light is 9.37×10 21 cm -3 , which is significantly higher than that of α-MoC in Example 1 (6.03×10 21 cm -3 ) and β-Mo2C in Example 2 (7.18×10 21 cm -3), demonstrating that the dual-phase α-MoC / β-Mo2C quantum dots have a higher carrier concentration, which leads to a stronger photothermal effect.

Claims

1. A dual-phase molybdenum carbide quantum dot photothermal material, characterized in that: The photothermal material is a mixed-phase two-phase quantum dot material composed of cubic α-MoC and hexagonal β-Mo2C.

2. The dual-phase molybdenum carbide quantum dot photothermal material according to claim 1, characterized in that: The molar ratio of α-MoC and β-Mo2C phases in the dual-phase molybdenum carbide quantum dot photothermal material varies in the range of 10%-90%, and the change is from pure α-MoC phase to pure β-Mo2C phase.

3. The dual-phase molybdenum carbide quantum dot photothermal material according to claim 1, characterized in that: The high carrier concentration dual-phase molybdenum carbide quantum dot photothermal material has a size of 2-10 nm and is evenly distributed on a carbon matrix.

4. The method for preparing the dual-phase molybdenum carbide quantum dot photothermal material according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: encapsulating a polyoxometalate guest in a MOF skeleton to obtain POM@MOF, and then rapidly heating the POM@MOF in an inert atmosphere to perform a restricted carburizing reaction to obtain a dual-phase molybdenum carbide quantum dot photothermal material.

5. The method for preparing the dual-phase molybdenum carbide quantum dot photothermal material according to claim 4, characterized in that: The polyoxometalate is phosphomolybdic acid, and the MOF is ZIF-8.

6. The method for preparing the dual-phase molybdenum carbide quantum dot photothermal material according to claim 5, characterized in that: Zinc nitrate hydrate and phosphomolybdic acid are mixed evenly in a solvent, polyvinyl pyrrolidone is added, and the mixture is further mixed and then added dropwise to a 2-methylimidazole solution. After the reaction, the mixture is precipitated, washed, and dried to obtain POM@MOF.

7. The method for preparing the dual-phase molybdenum carbide quantum dot photothermal material according to claim 6, characterized in that: The molar ratio of phosphomolybdic acid to Zn(NO3)2·6H2O is 1:1-1:

5.

8. The method for preparing the dual-phase molybdenum carbide quantum dot photothermal material according to claim 4, characterized in that: The heating rate is 20~50℃ / min, and the carburizing reaction is limited at 700-900℃ for 0.2-1h.

9. The dual-phase molybdenum carbide quantum dot photothermal material prepared by the method according to any one of claims 4 to 8, characterized in that: The carrier concentration of dual-phase molybdenum carbide quantum dots reaches 10 21 cm -3 And above orders of magnitude; the photothermal conversion rate reaches more than 70%.

10. Use of the dual-phase molybdenum carbide quantum dot photothermal material prepared according to claims 1-8 as a photocatalytic material.

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