Photoelectrocatalytic material as well as preparation method and application thereof

Abstract

The invention relates to the field of photoelectrocatalytic materials, and discloses a photoelectrocatalytic material and a preparation method and application thereof.The photoelectrocatalytic material is formed by a bismuth molybdenum oxide and nickel-doped cobalt oxide heterostructure, the surface plasma resonance effect of gold nanoparticles and a conductive network of nitrogen-doped graphene and carbon quantum dots are combined, and a graded micro-nano structure is constructed; according to the present invention, the material has characteristics of high light current density, low charge transfer resistance and excellent catalytic activity and long-term stability in liquid-phase degradation and gas-phase oxidation through the built-in electric field and the optimization of the conductive network, such that the material has characteristics of high light current density and low charge transfer resistance, and can be used in liquid-phase degradation and gas-phase oxidation. The material is widely applicable to the fields of pollutant degradation, gas conversion, water photoelectrolysis and the like, and an efficient solution is provided for innovative development of a photocatalysis technology.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and specifically to a photocatalytic material, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasingly serious environmental pollution problems, photocatalysis technology has received extensive attention because it can efficiently utilize solar energy to degrade organic pollutants and oxidize small molecule gases (such as methane). Currently, the development of photocatalytic materials mainly focuses on semiconductor materials. However, traditional photocatalytic materials, such as TiO 2 (titanium oxide), although having advantages such as high chemical stability and low cost, due to its relatively wide bandgap (about 3.2 eV), it can only absorb ultraviolet light (wavelength < 400 nm), and the proportion of ultraviolet light in sunlight only accounts for about 5%, which greatly limits its light energy utilization efficiency. In addition, traditional single-component semiconductor materials are prone to rapid recombination of photo-generated electrons and holes during the illumination process, resulting in a significant reduction in photocatalytic efficiency.

[0003] To solve the above problems, many optimization schemes have been proposed in the prior art. For example, introducing narrow-bandgap semiconductors (such as Bi 2 MoO 6 ) to expand the spectral response range. Bi 2 MoO 6 has narrow-bandgap characteristics (about 2.5 eV) and can absorb visible light (wavelength 400 - 700 nm). However, single Bi 2 MoO 6 still faces the problem of low separation efficiency of photo-generated carriers, resulting in its photocatalytic performance far from meeting the actual application requirements. In addition, traditional semiconductors usually cannot effectively utilize near-infrared light (wavelength > 700 nm), and this spectral region accounts for nearly 50% of the solar energy. Therefore, how to design photocatalytic materials that can achieve full-spectrum response has become an important direction for the development of photocatalysis technology.

[0004] On the other hand, the construction of heterojunctions is widely regarded as an effective means to improve photocatalytic performance. Through the interfacial coupling between different semiconductors, heterojunctions can form built-in electric fields at the interface, thereby effectively promoting the separation of photo-generated electrons and holes. However, existing heterojunction materials usually only show high activity in the visible light range, and have limited response ability in weak light environments or the near-infrared light region. Moreover, most heterojunction structure designs do not fully consider how to further improve the migration efficiency of carriers. Therefore, in practical applications, the charge transfer resistance is still high, and the recombination phenomenon of photo-generated carriers has not been fundamentally suppressed.

[0005] In order to solve the problem of charge transfer, the prior art has also proposed the introduction of conductive enhancing materials, such as graphene and carbon quantum dots. The high conductivity of these materials provides a channel for the rapid transmission of photogenerated electrons. However, undoped graphene or carbon quantum dots usually have the problem of insufficient charge density and cannot significantly reduce the migration resistance of photogenerated carriers. Moreover, the distribution and structural design of these conductive enhancing materials in the composite process have not been reasonably optimized, resulting in limited improvement in carrier separation efficiency.

[0006] In addition, existing technologies are not good at optimizing light capture efficiency. Although some studies have attempted to increase the specific surface area of ​​materials through nanostructure regulation, thereby increasing the active sites of photoreactions, most of them are limited to single-dimensional nanostructure designs (such as particles, nanorods, etc.). Materials with a single morphology are difficult to achieve efficient light capture in complex light environments, and the specific surface area of ​​the material is not fully utilized, which limits the overall activity of the photocatalytic reaction.

[0007] It is worth noting that the long-term stability of materials also limits the practical application of photocatalysts. During repeated use, the catalytic efficiency of traditional photocatalytic materials usually decreases rapidly due to the recombination of photogenerated electrons and holes and the degradation of active sites. For example, the traditional TiO 2 After multiple degradation experiments, its activity can usually only maintain 50%-70% of the initial level. Although the existing technology attempts to improve stability through methods such as metal doping, excessive doping may cause lattice defects in the material, which in turn reduces the photocatalytic efficiency. Therefore, how to maintain the high stability of the material while improving the photocatalytic efficiency is one of the key issues that the existing technology needs to solve urgently.

[0008] Therefore, the present invention proposes a photoelectrocatalytic material and a preparation method and application thereof to solve the deficiencies of the prior art. Summary of the invention

[0009] In view of the problems of the prior art, such as limited spectral response range, low efficiency of photogenerated carrier separation, high charge transfer resistance, insufficient light capture ability and poor long-term stability, the present invention provides a photoelectrocatalytic material based on multi-component synergistic optimization and its preparation method and application. By introducing innovative designs such as heterojunctions, gold nanoparticles and hierarchical micro-nanostructures, wide spectrum absorption, efficient carrier separation and migration, enhanced light capture ability and significant improvement in long-term stability are achieved.

[0010] To achieve the above objectives, the present invention is implemented through the following technical solutions: a photoelectrocatalytic material, composed of the following components in proportion by mass:

[0011] Bismuth molybdenum oxide: 30-50 parts;

[0012] Nickel-doped cobalt oxide: 15-35 parts;

[0013] Gold nanoparticles: 5 - 15 parts;

[0014] Nitrogen-doped carbon quantum dots: 5 - 10 parts;

[0015] Titanium oxide: 10 - 20 parts;

[0016] Graphene: 2 - 8 parts;

[0017] Polyethylene glycol: 0.5 - 2 parts.

[0018] Preferably, the bismuth molybdenum oxide is a nanosheet structure prepared by a hydrothermal method, and its specific preparation steps are as follows:

[0019] Dissolve bismuth nitrate and sodium molybdate in deionized water at a molar ratio of 2:1, and stir until completely dissolved;

[0020] Adjust the pH value of the solution to 7 - 9 using dilute ammonia water;

[0021] Transfer the obtained solution to a polytetrafluoroethylene-lined reaction kettle, and carry out hydrothermal reaction at 180 - 200 °C for 4 - 8 hours;

[0022] After cooling, wash the product 3 - 5 times with deionized water and ethanol, and vacuum dry at 60 - 80 °C for 12 hours to obtain bismuth molybdenum oxide nanosheets.

[0023] Bismuth molybdenum oxide (Bi 2 MoO 5 ) is a narrow-bandgap semiconductor with excellent visible light response ability. Its energy band structure enables the top of the valence band to form a type-I heterojunction with the conduction band position of nickel-doped cobalt oxide. The nanosheet structure prepared by the hydrothermal method not only has a high specific surface area, which is beneficial to the exposure of more active sites, but also can shorten the migration path of photo-generated electrons and holes, thus significantly improving the photoelectrocatalytic performance.

[0024] Preferably, the molar ratio of cobalt to nickel in the nickel-doped cobalt oxide is 8:1 to 12:1, and it is prepared by a coprecipitation method. The specific preparation steps are as follows:

[0025] Dissolve cobalt nitrate and nickel nitrate in deionized water at a molar ratio of 8:1 to 12:1;

[0026] Under stirring conditions, gradually add sodium hydroxide solution to adjust the pH value of the solution to 10 - 12, and continue stirring for 30 - 60 minutes to form a precipitate;

[0027] Wash the precipitate with deionized water until the filtrate is neutral;

[0028] Calcinate the precipitate at 400 - 600 °C for 2 - 4 hours to obtain nickel-doped cobalt oxide particles.

[0029] Nickel-doped cobalt (Ni-doped Co 3 O 4 ) adjusts the electronic structure of cobalt oxide by doping, optimizes its band gap width, and enables it to exhibit good visible and near-infrared light absorption capabilities. In the material, nickel doping introduces additional energy levels, providing more paths for photo-generated electron transitions. Meanwhile, the built-in electric field formed at the interface between it and bismuth molybdenum oxide further enhances the separation efficiency of photo-generated carriers.

[0030] Preferably, the particle size range of the gold nanoparticles is 5 - 50 nm, and they are prepared by photoreduction method. The specific preparation steps are as follows:

[0031] Prepare a 1 - 5 mmol / L chloroauric acid solution and a 10 - 20 mmol / L sodium citrate solution;

[0032] Under magnetic stirring, mix the chloroauric acid solution and the sodium citrate solution in a volume ratio of 1:1;

[0033] Spray the mixed solution onto the interface of the bismuth molybdenum oxide and nickel-doped cobalt composite material;

[0034] React under 300 - 500 W ultraviolet light irradiation for 20 - 30 minutes to generate gold nanoparticles.

[0035] Gold nanoparticles (AuNPs) generate surface plasmon resonance (SPR) effects under light irradiation, significantly enhancing the local electromagnetic field intensity and expanding the light absorption range of the composite material. At the same time, gold nanoparticles, as an intermediate electron acceptor, can capture the photo-generated electrons generated in bismuth molybdenum oxide and inject them into nickel-doped cobalt, further improving the charge separation efficiency.

[0036] Preferably, the titanium oxide is nanoparticles prepared by the sol-gel method, with a particle size of 10 - 50 nm. The specific preparation steps are as follows:

[0037] Dissolve tetrabutyl titanate in absolute ethanol and stir evenly;

[0038] Slowly drop dilute hydrochloric acid solution while stirring, and control the pH value of the solution to 2 - 4;

[0039] Add deionized water under stirring to form a milky white gel;

[0040] After drying the gel, calcine it at 400 - 600 °C for 2 - 4 hours to obtain titanium oxide nanoparticles.

[0041] Titanium oxide (TiO 2)As a traditional photocatalytic material, it has good ultraviolet light absorption performance. Its introduction in the photo-electrocatalytic material expands the ultraviolet light response range and improves the overall photocatalytic efficiency through synergistic effects with other components.

[0042] Preferably, the graphene is nitrogen-doped graphene, which is prepared from graphite powder as the raw material by high-temperature chemical vapor deposition method. The specific preparation steps are as follows:

[0043] Mix graphite powder and urea in a mass ratio of 5:1 and put them into the CVD reaction chamber;

[0044] Under a nitrogen atmosphere, heat at a high temperature of 800 - 1000 °C and keep the reaction for 30 - 60 minutes;

[0045] After the reaction is completed, cool it to room temperature to obtain nitrogen-doped graphene.

[0046] Nitrogen-doped graphene (N-doped Graphene) improves the conductivity and electron density by introducing nitrogen atoms. It has excellent charge transport ability, and at the same time provides more active sites on the surface, which helps the efficient migration of photo-generated electrons. In addition, graphene also plays a role in stabilizing the material structure and inhibiting the recombination of photo-generated electrons.

[0047] Preferably, a preparation method of a photo-electrocatalytic material includes the following steps:

[0048] S1. Prepare bismuth molybdenum oxide nanosheets by hydrothermal method;

[0049] S2. Prepare nickel-doped cobalt oxide particles by co-precipitation method;

[0050] S3. Prepare titanium oxide particles by sol-gel method;

[0051] S4. Deposit gold nanoparticles at the interface between bismuth molybdenum oxide and nickel-doped cobalt oxide by photoreduction method;

[0052] S5. Modify nitrogen-doped carbon quantum dots on the surface of the obtained material and introduce graphene as a conductive enhancer;

[0053] S6. Control the morphology of the material by adding polyethylene glycol to form a hierarchical micro-nano structure.

[0054] Preferably, the polyethylene glycol is a water-soluble polymer with a molecular weight of 1000 - 6000, and its addition amount is 0.5% - 2% of the total mass of the sample.

[0055] Polyethylene glycol (PEG) is a commonly used templating agent that can control the morphology of materials during the preparation process to form hierarchical micro-nano structures. The hierarchical structure enhances the light scattering and reflection effects, improves the light trapping ability, and at the same time improves the specific surface area of the catalytic material, exposing more active sites.

[0056] Preferably, the nitrogen-doped carbon quantum dots are prepared from sodium citrate and urea as raw materials. The hydrothermal reaction temperature is 150 - 180 °C, and the reaction time is 4 - 6 hours. After the product is centrifuged and separated, it is washed with deionized water and uniformly coated on the material surface by spin coating.

[0057] Nitrogen-doped carbon quantum dots (CQDs) are a wide-bandgap material that can effectively capture short-wavelength light and convert it into long-wavelength light (upconversion effect), thereby improving the overall light utilization efficiency of the material. In addition, its good electrical conductivity provides a transport channel for photo-generated charges.

[0058] Preferably, an application of a photo-electrocatalytic material, wherein the photo-electrocatalytic material is used in photocatalytic water splitting for hydrogen production, pollutant degradation, or carbon dioxide reduction reaction.

[0059] By optimizing the component design and interface regulation, the present invention utilizes the heterojunction structure of bismuth molybdenum oxide and nickel-doped cobalt oxide in combination with the surface plasmon resonance effect of gold nanoparticles, as well as the efficient conductive network of nitrogen-doped graphene and carbon quantum dots, significantly improving the photo-electrocatalytic performance. The design of the material realizes the unity of broad-spectrum absorption, efficient carrier separation, and photocatalytic stability, providing an efficient solution for photocatalytic water splitting for hydrogen production, pollutant degradation, and carbon dioxide reduction.

[0060] The present invention provides a photo-electrocatalytic material, its preparation method, and application. It has the following beneficial effects:

[0061] 1. By constructing a heterojunction of bismuth molybdenum oxide and nickel-doped cobalt oxide and introducing the surface plasmon resonance effect of gold nanoparticles, the present invention realizes the efficient light absorption of the catalyst in the ultraviolet, visible, and near-infrared light regions. Compared with the traditional photocatalysts in the prior art (such as TiO 2 ) which are limited to ultraviolet light absorption, the spectral response range of the material of the present invention is greatly extended to 200 - 900 nm. Especially the utilization of the near-infrared band breaks through the limitation of the low efficiency of traditional materials in low-light environments, providing a new solution for the full-spectrum utilization of sunlight.

[0062] 2. The built-in electric field design at the heterojunction interface of the present invention significantly improves the separation efficiency of photo-generated electrons and holes, while reducing the carrier recombination rate. Further, by combining nitrogen-doped graphene and carbon quantum dots, a hierarchical micro-nano conductive network is constructed, optimizing the carrier migration path, making electron transport more efficient and significantly reducing the resistance. Compared with the prior art without heterojunction construction or unoptimized conductive network, the present invention realizes an increase in photocurrent density (up to 9.2 μA / cm 2 ), and the charge transfer resistance is reduced to 85 Ω, significantly improving the activity of the catalyst in photocatalytic degradation and gas-phase oxidation.

[0063] 3. Through the design of the hierarchical micro-nano structure, porous and highly dispersed active sites are formed on the material surface, while optimizing the multiple reflection paths of light, significantly improving the light capture efficiency. Compared with the materials without hierarchical structure optimization in the prior art, the present invention effectively increases the specific surface area and photocatalytic reaction efficiency of the material. This micro-nano structure also combines the electromagnetic field enhancement effect of metal nanoparticles, enabling more concentrated utilization of light energy.

[0064] 4. The performance decay of the catalyst material of the present invention during recycling is significantly lower than that of the prior art. In multiple liquid-phase degradation and gas-phase oxidation experiments, the material exhibits excellent anti-deactivation ability, and the activity retention rate reaches over 95%, far higher than 50%-70% of traditional single-component catalysts. This stability benefits from the multi-component collaborative design, where the supporting role of gold nanoparticles and the conductive network in carrier migration during long-term reactions effectively inhibits the failure of the catalyst. The present invention provides an innovative solution to the problem of rapid activity decay of traditional photocatalytic materials during multiple uses, demonstrating extremely high application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a flow chart of the preparation method of the photo-electrocatalytic material. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0066] The technical solutions of the present invention will be clearly and completely described below with reference to the drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0067] Please refer to the attached Figure 1 :

[0068] Example 1: Construction of a bismuth molybdate / nickel-doped cobalt oxide heterojunction composite material

[0069] Materials and Reagents

[0070] Sodium bismuthate (NaBiO3 , AR, Aladdin Chemistry)

[0071] Ammonium molybdate ((NH 4 ) 6 Mo 7 O 24 ·4H 2 O, AR, Sinopharm Group)

[0072] Nickel chloride (NiCl 2 ·6H 2 O, AR, Aladdin)

[0073] Cobalt nitrate (Co(NO 3 ) 2 ·6H 2 O, AR, Aladdin)

[0074] Polyethylene glycol (PEG, molecular weight 6000, Macklin)

[0075] Deionized water, dilute hydrochloric acid (1 mol / L).

[0076] Preparation steps

[0077] Preparation of bismuth molybdenum oxide

[0078] Prepare 100 mL of deionized water, dissolve 10 mmol of sodium bismuthate and 5 mmol of ammonium molybdate in it, set the stirring speed to 500 rpm, and control the stirring time for 30 minutes. During the reaction, use a glass rod to test the dissolution situation to ensure no precipitation.

[0079] Adjust the pH of the solution to 7.0, add dilute hydrochloric acid dropwise, and monitor with a precision pH meter. Keep the transparency of the solution during the process.

[0080] Transfer the prepared solution to a 200 mL hydrothermal reaction kettle lined with polytetrafluoroethylene, place it in an incubator, set the temperature to 100 °C, and the reaction time to 12 hours.

[0081] Take it out and cool it to room temperature, wash it 5 times with deionized water by centrifugation (2500 rpm each time, 10 minutes), and dry it in a vacuum drying oven at 50 °C for 12 hours. Obtain light yellow bismuth molybdenum oxide powder.

[0082] Preparation of nickel-doped cobalt oxide

[0083] Prepare a metal salt solution, dissolve 5 mmol of nickel chloride and 10 mmol of cobalt nitrate in 100 mL of deionized water respectively, add 1 g of PEG as a dispersant to ensure the solution is uniformly transparent.

[0084] Add 25 wt% ammonia water solution to the system. The reaction system gradually shows blue turbid precipitation. Control the pH to 10 and continuously react for 2 hours using a magnetic stirrer (set at 600 rpm).

[0085] After standing for 24 hours, filter the precipitate and dry it in a forced-air drying oven at 80 °C for 6 hours. After drying, calcine the powder in a muffle furnace at 500 °C in air for 4 hours. The color of the product changes from blue to black, and nickel-doped cobalt oxide powder is obtained.

[0086] Construction of heterojunction

[0087] Weigh 3 g of bismuth molybdenum oxide and 1 g of nickel-doped cobalt oxide, add 20 mL of absolute ethanol, and grind them in a mortar for 15 minutes to form a uniform slurry.

[0088] Spread the slurry evenly in a ceramic crucible and dry it in a drying oven at 80 °C for 4 hours. After ensuring that the ethanol has completely evaporated, transfer it to a tube furnace. Set the temperature to 400 °C and calcine it in a nitrogen atmosphere for 2 hours with a heating rate of 2 °C / min. After calcination, let it cool naturally.

[0089] Take out the powder after calcination and observe it with an electron microscope. The powder shows an obvious particle accumulation morphology and is evenly distributed among the crystals.

[0090] Example 2: Construction of a plasma-enhanced composite photocatalytic system

[0091] Materials and reagents

[0092] Chloroauric acid (HAuCl 4 ·3H 2 O, AR, Aladdin)

[0093] Sodium citrate (Na 3 C 6 H 5 O 7 ·2H 2 O, AR, Sinopharm Group)

[0094] Deionized water, absolute ethanol

[0095] Bismuth molybdenum oxide / nickel-doped cobalt oxide heterojunction composite material

[0096] Preparation steps

[0097] Preparation of gold nanoparticles

[0098] Prepare 50 mL of 1 mmol / L chloroauric acid solution, put it into a 100 mL three-necked flask, and heat it to boiling with a magnetic stirrer, maintaining the temperature at 100 °C.

[0099] Quickly add 5 mL of 0.1 mol / L sodium citrate solution using a pipette. The color of the reaction solution rapidly changes from light yellow to wine red, indicating the formation of gold nanoparticles.

[0100] After the reaction is completed, stop heating and cool it to room temperature to obtain a stable dispersion of gold nanoparticles. The solution can be stored in a refrigerator at 4 °C for future use.

[0101] Preparation of composite material

[0102] Take 100 mg of bismuth molybdate / nickel-doped cobalt oxide heterojunction powder and add it to 50 mL of the gold nanoparticle dispersion.

[0103] Use an ultrasonic processor to sonicate for 30 minutes, set the power to 100 W, ensure that the material is fully suspended in the dispersion, and promote the adsorption of nanoparticles.

[0104] Transfer the suspension to a constant-temperature stirring device and stir at a speed of 300 rpm for 2 hours to ensure that the gold nanoparticles are evenly deposited on the surface of the heterojunction.

[0105] After centrifugal separation, wash it 3 times with deionized water to remove the unbound gold nanoparticles, and dry it in a vacuum at 50 °C for 12 hours. The powder is light brown and is the final composite material.

[0106] Material characterization

[0107] Use a transmission electron microscope (TEM) to observe the distribution of gold nanoparticles. The results show that the particles are evenly distributed on the surface of the heterojunction material, and the particle size is about 15 nm.

[0108] Through ultraviolet-visible absorption spectroscopy (UV-Vis) analysis, this composite material exhibits enhanced light absorption ability in the 600 - 800 nm wavelength band.

[0109] Example 3: Construction of a hierarchical micro-nano structure conductive network

[0110] Materials and reagents

[0111] Nitrogen-doped carbon quantum dots (purchased from Aladdin)

[0112] Nitrogen-doped graphene (prepared in the laboratory using chemical vapor deposition method with methane and ammonia)

[0113] Heterojunction composite material modified with gold nanoparticles

[0114] Preparation steps

[0115] Modification of carbon quantum dots

[0116] Prepare 100 mL of deionized water, disperse 10 mg of nitrogen-doped carbon quantum dots in it, and sonicate for 15 minutes to form a homogeneous solution.

[0117] 50 mg of gold nanoparticle-modified heterojunction material was added and stirring was continued for 4 hours.

[0118] The solution was allowed to stand for 12 hours, and the stability of the solution was observed, and no sedimentation was observed. After centrifugation, the solution was dried at 50°C for 6 hours to obtain a carbon quantum dot modified material.

[0119] Introduction of nitrogen-doped graphene

[0120] 50 mg of nitrogen-doped graphene was added to 5 mL of anhydrous ethanol and sonicated with a handheld sonicator for 20 min to achieve uniform dispersion.

[0121] Add it to the carbon quantum dot modified material, set the magnetic stirring speed to 400 rpm, and react for 12 hours.

[0122] The dried material was calcined at 400° C. in a nitrogen atmosphere for 2 hours to form a composite material with a hierarchical micro-nano structure.

[0123] Morphology observation and conductivity test

[0124] The surface morphology of the material was observed using a scanning electron microscope (SEM), which showed that the hierarchical micro-nano pores were evenly distributed and had a large specific surface area.

[0125] The conductivity of the material was measured using a Hall effect instrument, and the results showed that the electron mobility was significantly improved.

[0126] Comparative Example:

[0127] Comparative Example 1: Bismuth Molybdenum Oxide / Nickel-doped Cobalt Oxide Heterojunction Not Constructed

[0128] Materials and Reagents

[0129] Sodium Bismuthate (NaBiO 3 , AR, Aladdin)

[0130] Ammonium molybdate (NH 4 ) 6 Mo 7 O 24 ·4H 2 O, AR, Sinopharm Group)

[0131] Nickel chloride (NiCl 2 6H 2 O, AR, Aladdin)

[0132] Cobalt nitrate (Co(NO 3 ) 2 6H 2 O, AR, Aladdin)

[0133] Deionized water, dilute hydrochloric acid (1 mol / L).

[0134] Preparation steps

[0135] Preparation of bismuth molybdenum oxide

[0136] Prepare 100 mL of deionized water, dissolve 10 mmol of sodium bismuthate and 5 mmol of ammonium molybdate, and continuously stir for 30 minutes to ensure that the solution is uniform and transparent.

[0137] Adjust the pH of the solution to 7.0, add dilute hydrochloric acid drop by drop, and precisely control the reaction environment. Use a constant temperature magnetic stirrer throughout the process, and keep the stirring speed at 500 rpm.

[0138] Transfer the solution to a hydrothermal reaction kettle lined with polytetrafluoroethylene, place it in an incubator at 100 °C and react for 12 hours. After cooling, take out the solution and centrifuge (3000 rpm, 10 minutes) and wash 5 times to remove by-products.

[0139] Dry the powder in a vacuum drying oven at 50 °C for 12 hours to obtain bismuth molybdenum oxide powder, which is a pale yellow solid.

[0140] Preparation of nickel-doped cobalt oxide

[0141] Dissolve 5 mmol of nickel chloride and 10 mmol of cobalt nitrate in 100 mL of deionized water, add 1 g of polyethylene glycol (PEG), and stir for 15 minutes to form a stable solution.

[0142] Adjust the pH to 10 with 25 wt% ammonia water solution. During the dropwise addition of ammonia water, blue precipitate gradually forms, ensuring complete reaction.

[0143] Continuously stir for 2 hours, let it stand for 24 hours, then wash 3 times with anhydrous ethanol and deionized water respectively. The obtained precipitate is dried in a blast drying oven at 80 °C for 6 hours.

[0144] Calcine the dried powder in air atmosphere at 500 °C for 4 hours, with a heating rate of 5 °C / min. After cooling, black nickel-doped cobalt oxide powder is obtained.

[0145] Testing materials

[0146] In the photocatalytic performance test, the two materials are not compounded. Directly mix bismuth molybdenum oxide and nickel-doped cobalt oxide in a mass ratio of 1:1.

[0147] The powder is simply mechanically mixed, no heterojunction structure is formed, and there is no further calcination treatment.

[0148] The mixture is directly used for testing to compare the improvement effect of constructing a composite heterojunction on photocatalytic performance.

[0149] Comparative Example 2: No introduction of surface plasmon resonance enhancement of gold nanoparticles

[0150] Materials and Reagents

[0151] Bismuth molybdenum oxide / nickel-doped cobalt oxide heterojunction composite material (prepared according to Example 1)

[0152] Deionized water, anhydrous ethanol

[0153] Preparation steps

[0154] Preparation of heterojunction

[0155] According to the method of Example 1, a bismuth molybdenum oxide / nickel-doped cobalt oxide heterojunction was prepared to obtain a composite material as a subsequent experimental sample.

[0156] Handling of test samples

[0157] No gold nanoparticles were introduced, and no surface modification process was performed. The prepared bismuth molybdenum oxide / nickel-doped cobalt oxide heterojunction material was directly used as a catalytic test material.

[0158] Gold nanoparticles were prepared without using chloroauric acid and sodium citrate, and the plasmon resonance enhancement mechanism was not involved.

[0159] In subsequent tests, this material was used as a sample and directly used in photocatalytic degradation experiments to compare the contribution of the introduction of gold nanoparticles to the wide spectral response and near-infrared enhancement effect.

[0160] Comparative Example 3: No hierarchical micro-nanostructure conductive network was constructed

[0161] Materials and Reagents

[0162] Bismuth molybdenum oxide / nickel-doped cobalt oxide heterojunction composite material (prepared according to Example 1)

[0163] Nitrogen-doped graphene (purchased from Aladdin, no morphology control)

[0164] Nitrogen-doped carbon quantum dots (purchased from Aladdin, no structural design)

[0165] Anhydrous ethanol, deionized water

[0166] Preparation steps

[0167] Simple conductive material composite

[0168] 50 mg of bismuth molybdenum oxide / nickel-doped cobalt oxide heterojunction powder was weighed and dispersed in 20 mL of anhydrous ethanol, and ultrasonicated for 30 minutes using an ultrasonic processor (power 100 W) to form a uniform suspension.

[0169] Another 20 mg of nitrogen-doped graphene and 10 mg of nitrogen-doped carbon quantum dots were added to the suspension at a ratio of 1:1, and stirred for 6 hours using a magnetic stirrer (300 rpm) to obtain a physically mixed suspension.

[0170] The mixed suspension was centrifuged (3000 rpm, 10 minutes), and after separation of the precipitate, it was vacuum dried at 50° C. for 6 hours to obtain a simple composite powder without structural regulation.

[0171] Material properties

[0172] The hierarchical structure was not formed through morphology design, and the distribution and synergistic conductivity of graphene and carbon quantum dots were not optimized.

[0173] No further calcination or high temperature treatment step provides a stable conductive network structure.

[0174] Comparative Example 4: No nitrogen-doped conductive reinforcement material was used

[0175] Materials and Reagents

[0176] Bismuth molybdenum oxide / nickel-doped cobalt oxide heterojunction composite material (prepared according to Example 1)

[0177] Undoped graphene (purchased from Aladdin)

[0178] Undoped carbon quantum dots (purchased from Aladdin)

[0179] Preparation steps

[0180] Composites of undoped conductive materials

[0181] 50 mg of bismuth molybdenum oxide / nickel-doped cobalt oxide heterojunction powder was added to 20 mL of anhydrous ethanol and treated with ultrasound (power 100 W) for 30 minutes.

[0182] 20 mg of undoped graphene and 10 mg of undoped carbon quantum dots were taken respectively, directly added into the suspension, and stirred for 4 hours to form a mixed solution.

[0183] The precipitate was separated by centrifugation (3000 rpm, 10 minutes) and then dried at 50°C to obtain a sample composited with an undoped conductive material.

[0184] Test comparison

[0185] This comparative example does not use nitrogen-doped graphene and carbon quantum dots, and fails to significantly improve the electron migration efficiency of the material. The conductivity enhancement effect depends on the intrinsic properties of graphene and carbon quantum dots, and does not optimize the electron density and migration channel.

[0186] Test experiment:

[0187] Experimental Materials

[0188] Catalyst samples

[0189] Example samples:

[0190] E1: Constructed by a heterostructure of bismuth molybdenum oxide (Bi 2 MoO 5 ) and nickel-doped cobalt oxide (Ni-Co 3 O 4 ), and the heterojunction interface provides a photogenerated carrier separation effect.

[0191] E2: Loaded with gold nanoparticles (AuNPs) on the basis of E1 to enhance the absorption of near-infrared light.

[0192] E3: Further optimized from E2, a hierarchical micro-nano structure is constructed by introducing nitrogen-doped graphene and nitrogen-doped carbon quantum dots to improve the light trapping ability and electron migration efficiency.

[0193] Comparative sample:

[0194] B1: Bismuth molybdenum oxide and nickel-doped cobalt oxide are only simply mixed without a heterojunction structure.

[0195] B2: Heterojunction material without gold nanoparticles.

[0196] B3: Heterojunction material without a nitrogen-doped conductive network.

[0197] B4: Using undoped graphene and carbon quantum dots to replace the nitrogen-doped materials.

[0198] B5: Commercial P25 titanium oxide (widely used for photocatalysis comparison).

[0199] Experimental reagents

[0200] Methyl orange: Target pollutant (C14H14N3NaO3S, AR grade).

[0201] Mixed gas: 100 ppm methane and nitrogen (volume ratio 90:10).

[0202] Electrolyte: 0.5 mol / L Na 2 SO 4 solution (AR grade).

[0203] Experimental equipment

[0204] Light source:

[0205] 300 W xenon lamp equipped with an AM1.5 filter (simulating sunlight).

[0206] Use a far-infrared cut-off filter to test the near-infrared light response.

[0207] Reactor:

[0208] The liquid-phase degradation reactor is a closed-loop quartz container with a water-cooling system (temperature maintained at 25 °C).

[0209] The gas-phase oxidation reactor is a stainless-steel sealed cavity with gas flow regulation and sampling ports.

[0210] Detection instruments:

[0211] UV-Vis spectrophotometer: Shimadzu UV-2600, used to detect the main absorption peak of methyl orange (λ = 465 nm).

[0212] Gas chromatograph: GC-MS, used to analyze the oxidation products of methane.

[0213] Electrochemical workstation: CHI660E, used for photocurrent and electrochemical impedance spectroscopy tests.

[0214] Fluorescence spectrometer: FLS980, used to measure the lifetime of photo-generated electrons.

[0215] Experimental procedures

[0216] Spectral response range test

[0217] Test method

[0218] Use a UV-Vis diffuse reflectance spectrometer (UV-Vis DRS) to test the light absorption performance of each catalyst sample in the range of 200 - 900 nm.

[0219] Uniformly coat the sample on the surface of a quartz sheet, fix it in an optical test sample chamber, and record the absorption spectral curve.

[0220] For samples E2 and E3, additionally test the light absorption ability under far-infrared cut-off conditions (λ > 700 nm) to confirm the gold nanoparticle enhancement effect.

[0221] Before the light absorption test, the sample needs to be dried in a vacuum drying oven (50 °C) for 6 hours to ensure no moisture interference.

[0222] Quartz sheet cleaning: After cleaning with ethanol and deionized water, dry it for standby to avoid surface contamination.

[0223] Liquid-phase photocatalytic performance test

[0224] Test method

[0225] Prepare 100 mL of 50 mg / L methyl orange solution, and the target solution is the photocatalytic reaction matrix.

[0226] Weigh 50 mg of the catalyst sample and add it to a quartz reactor, and stir it using a magnetic stirrer (600 rpm).

[0227] Before illumination, stir for 30 minutes under darkroom conditions to ensure sufficient adsorption equilibrium between the catalyst and methyl orange.

[0228] Turn on the xenon light source (light intensity: 100 mW / cm 2 ), take 3 mL of the sample every 10 minutes, filter it with a 0.22-μm filter membrane, and measure the intensity of the main absorption peak of methyl orange (λ = 465 nm).

[0229] React continuously for 60 minutes and calculate the degradation rate.

[0230] To avoid catalyst agglomeration, the sample needs to be pretreated by ultrasound (100 W, 10 minutes) before being dispersed in the solution.

[0231] After each sampling, the same volume of fresh methyl orange solution needs to be added to keep the liquid level in the reaction system stable.

[0232] Gas-phase photocatalytic performance test

[0233] Test method

[0234] Inject 1 L of mixed gas (100 ppm methane and nitrogen, volume ratio 90:10) into the reaction chamber.

[0235] Add 50 mg of catalyst powder to ensure uniform distribution at the bottom of the reaction chamber.

[0236] Turn on the light source and simulate sunlight irradiation (light intensity: 100 mW / cm 2 ), and the reaction time is 30 minutes.

[0237] Collect gas samples every 5 minutes and analyze the methane concentration and oxidation products (CO 2 , methanol, etc.) by GC-MS.

[0238] The gas sampling tube needs to be evacuated twice in advance to avoid detection errors caused by gas retention.

[0239] When the catalyst surface is evenly spread on the bottom of the chamber, ensure uniform coverage to avoid local effects.

[0240] Photogenerated carrier separation efficiency test

[0241] Test method

[0242] Take 5 mg of the catalyst and disperse it in 1 mL of absolute ethanol, ultrasonicate for 10 minutes, and coat it on the surface of the FTO glass.

[0243] Dry the FTO electrode at 150 °C for 30 minutes and use it as the working electrode after cooling.

[0244] In the electrolyte containing 0.5 mo l / L Na 2 SO 4 , test the transient photocurrent response and record the change in photocurrent density under alternate light / dark irradiation.

[0245] When coating FTO, use a micro syringe to ensure uniform coating and avoid dead zones with uneven conductivity.

[0246] In the electrolytic cell, use a graphite electrode as the counter electrode and Ag / AgCl as the reference electrode.

[0247] Fluorescence spectrum test

[0248] Test method

[0249] Take 50 mg of the catalyst sample and place it in the fluorescence spectrum test chamber.

[0250] Set the excitation wavelength to 365 nm, test the change trend of the fluorescence intensity of the sample over time, and analyze the lifetime of photo-generated electrons.

[0251] Before the sample test, it needs to be stored in the dark to avoid background fluorescence interference caused by surface electron excitation.

[0252] Maintain a dry environment in the test chamber, and control the humidity below 20%.

[0253] Material stability test

[0254] Test method

[0255] In the liquid-phase photocatalytic degradation experiment, after one degradation, use a 0.22 μm filter membrane to filter and recover the catalyst.

[0256] Centrifuge and wash 3 times (alternate between deionized water and absolute ethanol), and dry at 50 °C for standby.

[0257] Repeat the above experiment 5 times, record the degradation rate each time and calculate the activity retention rate.

[0258] Before the washed catalyst is air-dried naturally, it is necessary to detect its dispersibility to ensure that the catalyst particles are not significantly agglomerated.

[0259] Experimental data:

[0260] Table 1: Comprehensive photocatalytic performance test data

[0261]

[0262] In the technical solution of this experiment, all test results not only clearly demonstrate the significant advantages of the present invention in material design and photocatalytic performance, but also verify the independent role and synergy of each inventive point in the overall performance improvement through comparative examples that gradually exclude some key design elements.

[0263] The E3 catalyst of the present invention combines a heterojunction structure, the gold nanoparticle enhancement effect, and a hierarchical micro-nano structure to optimize the conductive network. These characteristics act together through a synergistic effect during the photocatalysis process, significantly enhancing the material's ability to absorb full-spectrum light and simultaneously enhancing the separation and migration efficiency of photo-generated carriers. The wide spectral response range of the E3 sample reaches 200 - 900 nm, demonstrating that the surface plasmon resonance effect of gold nanoparticles significantly improves the light utilization rate in the near-infrared region. Compared with B1 and B2, the synergistic effect of the heterojunction design and gold nanoparticles significantly enhances the ability of gas-phase photocatalytic oxidation of methane. This is not only due to the wide spectral response but also benefits from the local electromagnetic field enhancement effect on the surface of gold nanoparticles, which makes photo-generated electrons easier to separate and quickly migrate to catalytic active sites through the heterojunction interface.

[0264] In addition, the design of the hierarchical micro-nano structure further enhances the light trapping ability and constructs a high-speed electron transport network through nitrogen-doped graphene and carbon quantum dots, greatly reducing the charge transfer resistance (Rct drops to 85 Ω). In the test of photo-generated carrier separation efficiency, the photocurrent density of E3 reaches 9.2 μA / cm 2 , which is more than twice that of B3 without the hierarchical micro-nano structure. This design not only optimizes the lifetime of photo-generated electrons (extended to 12.5 ns) but also effectively improves the catalytic efficiency and stability of the material. By comparing with B4, it can be seen that the undoped conductive enhancement material cannot provide sufficient electron density and migration channels, resulting in a significant decline in overall performance.

[0265] The heterojunction designed in the present invention can not only achieve the efficient utilization of ultraviolet and visible light but also suppress the recombination behavior of photo-generated electrons and holes through reasonable interface engineering regulation. The degradation rate of the E1 sample reaches 89.5% in the liquid-phase photocatalysis experiment, which is significantly better than that of single materials (B1, B5). When gold nanoparticles are further introduced, the photocatalytic activity of E2 in the near-infrared band is significantly enhanced, verifying the key role of metal nanoparticles in a weak light environment. In addition, through long-term stability experiments, it can be seen that the activity retention rate of the catalyst of the present invention is higher than 95% after multiple uses, far higher than that of traditional titanium oxide (B5), which fundamentally overcomes the limitation of the rapid decay of the activity of traditional materials.

[0266] Through comparison, it can be found that the significant performance degradation will occur if the heterojunction is not constructed (B1), the gold nanoparticles are not introduced (B2), or the conductive network is not optimized (B3, B4). Especially in the weak light environment (gas-phase oxidation of methane experiment), the comprehensive performance of E3 is the best, with the gas-phase oxidation rate reaching 82.5%, while that of B2 is only 41.7%, and B5 is even less than 16%. These results fully prove that the present invention has achieved a creative improvement over the prior art through multi-component collaborative design, enabling the material to have broad-spectrum absorption ability, efficient carrier separation performance, and excellent stability, providing a new idea for the further development of photocatalysis technology.

[0267] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A photoelectrocatalytic material, characterized in that: It is composed of the following components in proportion by mass: Bismuth molybdenum oxide: 30-50 parts; Nickel-doped cobalt oxide: 15-35 parts; Gold nanoparticles: 5-15 parts; Nitrogen-doped carbon quantum dots: 5-10 parts; Titanium oxide: 10-20 parts; Graphene: 2-8 parts; Polyethylene glycol: 0.5-2 parts.

2. A photoelectrocatalytic material according to claim 1, characterized in that: The bismuth molybdenum oxide is a nanosheet structure prepared by a hydrothermal method, and the specific preparation steps are as follows: Dissolve bismuth nitrate and sodium molybdate in deionized water at a molar ratio of 2:1 and stir until completely dissolved; Adjust the pH value of the solution to 7-9 using dilute ammonia water; The obtained solution was transferred to a polytetrafluoroethylene-lined reactor and subjected to hydrothermal reaction at 180-200°C for 4-8 hours; After cooling, the product was washed with deionized water and ethanol for 3-5 times, and vacuum dried at 60-80° C. for 12 hours to obtain bismuth molybdenum oxide nanosheets.

3. A photoelectrocatalytic material according to claim 1, characterized in that: The molar ratio of cobalt to nickel in the nickel-doped cobalt oxide is 8:1 to 12:1, and the nickel-doped cobalt oxide is prepared by a coprecipitation method. The specific preparation steps are as follows: Dissolve cobalt nitrate and nickel nitrate in deionized water in a molar ratio of 8:1 to 12:1; Under stirring conditions, sodium hydroxide solution was added dropwise to adjust the pH value of the solution to 10-12, and stirring was continued for 30-60 minutes to form a precipitate; The precipitate was washed with deionized water until the filtrate was neutral; The precipitate is calcined at 400-600° C. for 2-4 hours to obtain nickel-doped cobalt oxide particles.

4. A photoelectrocatalytic material according to claim 1, characterized in that: The gold nanoparticles have a particle size range of 5-50 nm and are prepared by a photoreduction method, and the specific preparation steps are as follows: Prepare 1-5 mmol / L chloroauric acid solution and 10-20 mmol / L sodium citrate solution; Under magnetic stirring, chloroauric acid solution and sodium citrate solution were mixed in a volume ratio of 1:1; spraying the mixed solution onto the interface of the bismuth molybdenum oxide and the nickel-doped cobalt oxide composite material; The reaction was carried out under 300-500W ultraviolet light for 20-30 minutes to generate gold nanoparticles.

5. The photoelectrocatalytic material according to claim 1, characterized in that: The titanium oxide is a nanoparticle prepared by a sol-gel method, and the particle size is 10-50 nm. The specific preparation steps are as follows: Dissolve tetrabutyl titanate in anhydrous ethanol and stir evenly; Slowly add dilute hydrochloric acid solution while stirring to control the pH value of the solution to 2-4; Under stirring, deionized water was added to form a milky white gel; After the gel is dried, it is calcined at 400-600° C. for 2-4 hours to obtain titanium oxide nanoparticles.

6. The photoelectrocatalytic material according to claim 1, characterized in that: The graphene is nitrogen-doped graphene, which is prepared by high-temperature chemical vapor deposition using graphite powder as raw material. The specific preparation steps are as follows: Graphite powder and urea were mixed in a mass ratio of 5:1 and placed in a CVD reaction chamber; In a nitrogen atmosphere, heat at 800-1000°C and keep the reaction for 30-60 minutes; After the reaction is completed, the mixture is cooled to room temperature to obtain nitrogen-doped graphene.

7. A method for preparing a photoelectrocatalytic material according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Preparation of bismuth molybdenum oxide nanosheets by hydrothermal method; S2, preparing nickel-doped cobalt oxide particles by coprecipitation; S3, preparing titanium oxide particles by a sol-gel method; S4, depositing gold nanoparticles at the interface of bismuth molybdenum oxide and nickel-doped cobalt oxide by photoreduction method; S5, modifying the surface of the obtained material with nitrogen-doped carbon quantum dots, and introducing graphene as a conductivity enhancer; S6. The morphology of the material is controlled by adding polyethylene glycol to form a hierarchical micro-nano structure.

8. The method for preparing a photoelectrocatalytic material according to claim 7, characterized in that: The polyethylene glycol is a water-soluble polymer with a molecular weight of 1000-6000, and its addition amount is 0.5%-2% of the total mass of the sample.

9. The method for preparing a photoelectrocatalytic material according to claim 7, characterized in that: The nitrogen-doped carbon quantum dots are prepared from sodium citrate and urea as raw materials, with a hydrothermal reaction temperature of 150-180° C. and a reaction time of 4-6 hours.

10. The use of a photoelectrocatalytic material according to claim 1, characterized in that: The photoelectrocatalytic material is used in photolysis of water to produce hydrogen, degradation of pollutants or carbon dioxide reduction reaction.

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