Manganese-loaded gallium nitride nanowire photocatalyst, preparation method thereof and seawater photocatalytic conversion method

Abstract

The invention belongs to the technical field of photocatalysis, and particularly relates to a manganese-loaded gallium nitride nanowire photocatalyst, a preparation method of the manganese-loaded gallium nitride nanowire photocatalyst and a seawater photocatalytic conversion method. The gallium nitride nanowires are vertically arranged on the surface of the silicon substrate; the manganese species are uniformly deposited on the surface of the gallium nitride nanowire, and the manganese species are MnOx (OH) y in which a plurality of Mn oxidation states coexist. Compared with the prior art, the invention solves the problems of high cost and low benefit caused by using noble metal as the photocatalyst in the prior art. According to the scheme, manganese (Mn) nano-particles are deposited on gallium nitride (GaN) nano-wires of a silicon wafer substrate, a multifunctional catalytic system is constructed, the oxidation-reduction reaction in the water decomposition process is jointly driven, and therefore the catalytic efficiency and long-term stability of the system are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to a manganese-supported gallium nitride nanowire photocatalyst and its preparation method, and a method for photocatalytic conversion of seawater. Background Technology

[0002] Hydrogen energy is considered the most promising clean energy carrier due to its significant advantages: firstly, its gravimetric energy density reaches 142 MJ / kg (approximately three times that of traditional fossil fuels), giving it a prominent energy storage advantage; secondly, hydrogen production through renewable energy-based water electrolysis can achieve carbon neutrality throughout its entire life cycle, with its combustion product being only water, fundamentally avoiding carbon emissions. However, currently, approximately 96% of global hydrogen production still relies on traditional processes such as steam reforming (SMR) of methane and coal gasification. These technologies not only consume large amounts of fossil fuels but also involve harsh thermodynamic conditions such as high temperature and high pressure, resulting in inherent drawbacks such as low energy efficiency and high carbon emission intensity. Therefore, developing green hydrogen production technologies driven by renewable energy has become a key path to overcome the bottlenecks in energy transition.

[0003] Sunlight and water, as the most abundant, clean, and renewable natural resources on Earth, provide an ideal foundation for sustainable energy development. Among these, solar-driven water splitting technology offers a promising solution for green hydrogen production and intermittent solar energy storage. In this system, the performance of semiconductor materials and cocatalysts directly determines photon absorption efficiency, carrier transport characteristics, and surface reaction kinetics, thus becoming key factors in determining water splitting efficiency. The main challenge in current research lies in exploring semiconductor materials with excellent performance, developing highly efficient cocatalysts, and achieving a reasonable synergistic effect between the two. However, traditional water splitting systems generally suffer from low efficiency due to excessively high photogenerated carrier recombination rates.

[0004] Natural seawater, due to its abundance, provides a promising feedstock for hydrogen production. However, to date, successful attempts at photocatalytic seawater splitting to produce hydrogen have been limited due to the following issues: 1) the competitive anodic chlorine formation reaction (2Cl - 2e = Cl2, with a potential of 1.49V relative to the standard hydrogen electrode); 2) severe corrosion of the photocatalyst caused by seawater impurities; and 3) the indispensable use of sacrificial reagents in all reported photocatalytic seawater splitting processes to date. Furthermore, noble metal-based catalysts are often indispensable for the overall redox reaction of water splitting in order to accelerate the slow kinetic process, which hinders the commercialization of this technology. Therefore, there is a strong desire to overcome these bottlenecks by exploring a suitable photocatalyst to achieve high efficiency, long-term stability, and cost-effectiveness in photocatalytic hydrogen production from seawater.

[0005] In recent years, vertically aligned gallium nitride (GaN) nanowires on silicon substrates, namely GaN / Si nanowire structures, have become a research hotspot in novel semiconductor platforms due to their unique structural features, excellent photoelectric properties, and outstanding catalytic activity. This nanostructure effectively addresses key scientific problems commonly found in traditional photocatalytic materials, such as low light capture efficiency, high carrier recombination rates, and slow surface reaction kinetics, providing an ideal semiconductor material system for solar-driven water splitting technology.

[0006] For example, CN119746906A discloses a palladium-supported gallium nitride nanowire photocatalyst, its preparation method, and its application. The palladium-supported gallium nitride nanowire photocatalyst includes a silicon substrate, gallium nitride nanowires vertically grown on the silicon substrate, and palladium nanoparticles uniformly supported on the surface of the gallium nitride nanowires. However, the photocatalyst proposed in this scheme still uses the noble metal palladium to achieve seawater photocatalytic decomposition. Due to the limited reserves, production volume, and price of palladium, this noble metal-based catalyst is difficult to meet the requirements for large-scale, long-term, sustainable, and highly efficient application in seawater photocatalytic decomposition for hydrogen production. Summary of the Invention

[0007] The purpose of this invention is to address at least one of the aforementioned problems by providing a manganese-supported gallium nitride nanowire photocatalyst and its preparation method, as well as a method for seawater photocatalytic conversion, thereby solving the problems of high cost and low efficiency associated with using noble metals as photocatalysts in existing technologies. This method involves depositing manganese (Mn) nanoparticles onto gallium nitride (GaN) nanowires on a silicon wafer substrate to construct a multifunctional catalytic system that jointly drives the redox reaction in the water splitting process, thus significantly improving the system's catalytic efficiency and long-term stability.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] The first aspect of this invention discloses a manganese-supported gallium nitride nanowire photocatalyst, comprising:

[0010] silicon substrate;

[0011] Gallium nitride nanowires vertically aligned on the surface of a silicon substrate;

[0012] Manganese species uniformly deposited on the surface of gallium nitride nanowires, wherein the manganese species is MnO with multiple Mn oxidation states coexisting. x (OH) y .

[0013] Preferably, the gallium nitride nanowires have a coverage of 0.2-0.4% on the silicon substrate; and / or,

[0014] The average height of the gallium nitride nanowires is 690-720 nm.

[0015] Preferably, the average size of the manganese species is 2-4 nm; and / or,

[0016] The deposition amount of the manganese species does not exceed 0.322 μmol·cm⁻¹. -2 .

[0017] A second aspect of this invention discloses a method for preparing a manganese-supported gallium nitride nanowire photocatalyst as described in any of the preceding embodiments, comprising the following steps:

[0018] S1: Gallium nitride nanowires are grown on a silicon substrate under nitrogen-rich conditions by radio frequency plasma-assisted molecular beam epitaxy.

[0019] S2: Using manganese sulfate aqueous solution as a precursor, manganese species were deposited onto the surface of gallium nitride nanowires by photochemical deposition under full-spectrum xenon lamp irradiation.

[0020] Preferably, in step S1, the silicon substrate is degassed at 800°C for 30 minutes.

[0021] Preferably, in step S1, the radio frequency plasma-assisted molecular beam epitaxy growth is:

[0022] Nitrogen plasma is generated using a 400W radio frequency power supply as the nitrogen source; and / or,

[0023] A dual-filament Knudsen cell is used as the gallium source; and / or,

[0024] The nitrogen flow rate is 1 sccm; and / or,

[0025] The vapor pressure of the gallium source is 5 × 10⁻⁶. -7 To; and / or,

[0026] The elemental ratio of nitrogen to gallium is 0.2; and / or,

[0027] The growth temperature is 600℃; and / or,

[0028] The growth rate of gallium nitride nanowires is 300 nm / h.

[0029] Preferably, in step S2, the photochemical deposition method is:

[0030] The full-spectrum xenon lamp has a power of 300W; and / or,

[0031] A methanol-water mixture with a volume ratio of 1:5 was used as the photodeposition medium; and / or,

[0032] Performed in a saturated argon atmosphere; and / or,

[0033] The deposition time is 30 minutes.

[0034] A third aspect of this invention discloses a method for photocatalytic conversion of seawater, comprising the following steps:

[0035] In an oxygen-free environment and under light conditions, seawater is decomposed to produce hydrogen under the catalytic action of any of the photocatalysts described above.

[0036] Preferably, the radiant intensity of the light under the illumination conditions is 2-6 W·cm. -2 .

[0037] Preferably, at 3.3 W·cm -2 Under illumination: the hydrogen production rate of the decomposition hydrogen production is 15.2 mol·g⁻¹. -1 ·h -1 The photo-hydrogen conversion efficiency of the decomposition hydrogen production is 6.15%.

[0038] The working principle of this invention is as follows:

[0039] In the photocatalytic process, Mn nanoparticles act as highly efficient hole acceptors, promoting the water oxidation reaction to generate key intermediates *OH and *OOH, significantly reducing the energy barrier of the potential-determining steps. Simultaneously, chloride ions (Cl-) in seawater further optimize the photogenerated charge dynamics by forming an interfacial polarized electric field.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] This invention, for the first time, combines Mn nanoparticles with GaN nanowire arrays to construct a highly efficient seawater photocatalytic decomposition system. Through a combination of experiments and theoretical calculations, the mechanism by which Mn nanoparticles act as hole acceptors was revealed, whereby Mn nanoparticles act as oxidation sites to promote the oxidation reaction (i.e., the rate-limiting step of photocatalytic water splitting, the oxygen evolution reaction). This contrasts sharply with the traditional understanding of electron extractors, such as the previous work disclosed in CN119746906A, which often uses co-catalysts as electron acceptors. The invention also discovered and verified the promoting effect of Cl- on photogenerated charge dynamics in the seawater system. Furthermore, it achieved efficient and stable hydrogen production under natural seawater conditions, providing technical support for large-scale green hydrogen production.

[0042] Through outdoor experiments, this invention has demonstrated the feasibility of producing green hydrogen using natural seawater and solar energy, providing a new technological approach for the storage and utilization of renewable energy.

[0043] This invention represents a significant innovation in the field of nanowire photocatalyst preparation technology, particularly in its application in photocatalytic water splitting to produce hydrogen and oxygen, demonstrating unique advantages and potential. The following is a detailed description of the key points of this invention:

[0044] (1) Nanowire structure: By precisely controlling the synthesis process parameters, a one-dimensional nanowire structure with uniform distribution was successfully prepared on a silicon wafer. This structure not only significantly increases the specific surface area of ​​the material and provides abundant catalytic active sites, but also optimizes the light absorption and carrier transport characteristics, thereby greatly improving the efficiency of photocatalytic reaction.

[0045] (2) Manganese nanoparticle loading: Manganese nanoparticles were uniformly loaded onto the surface of gallium nitride nanowires using photodeposition technology to construct a composite photocatalyst with a special interface structure. This special interface structure, which enables spatial separation of electron and hole sites, can achieve effective separation of photogenerated carriers and suppress recombination. This structure effectively promotes the separation of photogenerated electron-hole pairs and significantly enhances the catalytic performance.

[0046] (3) High hydrogen production activity and conversion frequency: Based on the synergistic effect of Mn nanoparticles and GaN nanowires: In the system, manganese nanoparticles act as hole trapping centers, effectively promoting the generation and desorption kinetics of hydroxyl radicals (·OH) and reducing the energy barrier of water oxidation reaction; thus, by optimizing the separation efficiency of photogenerated electrons and holes, efficient redox active sites are provided, promoting the generation and desorption of reaction intermediates, and finally achieving excellent hydrogen production activity and high conversion frequency.

[0047] This invention discloses a method for preparing a highly efficient manganese-supported gallium nitride nanowire photocatalyst. By uniformly loading manganese nanoparticles with controllable particle size onto the surface of gallium nitride nanowires, the photogenerated carrier separation efficiency is significantly improved. This catalyst exhibits excellent hydrogen production performance in natural seawater medium, at 3.3 W·cm⁻¹. -2 Under light intensity, it can achieve 15.2 mol·g. -1 ·h -1 The hydrogen yield and photocatalytic energy conversion efficiency (LTH) reached 6.15% (far exceeding the 4.38% in the existing technology CN119746906A), representing a significant improvement over current advanced photocatalytic water splitting catalysts. The high STH efficiency (photocatalytic energy conversion efficiency, with an AM1.5 filter and simulated illumination) not only reflects the synergistic optimization capabilities of the photocatalytic system in solar energy absorption, carrier separation, and surface reactions, but also represents its potential to efficiently convert solar energy into chemical energy under real-world conditions. Compared to traditional indicators, STH more comprehensively reflects the energy efficiency level of the entire reaction system and is one of the most critical parameters for measuring the performance of photocatalytic water splitting. Its improvement is of great significance for promoting the practical application of solar-driven clean hydrogen energy technology.

[0048] After 6 hours of continuous operation testing, the catalyst maintained more than 95% of its initial activity, with a conversion frequency of 44,278 mol H2 / mol Mn, breaking through the stability bottleneck of the seawater photolysis system.

[0049] This invention employs a low-temperature deposition process, avoiding high-temperature and high-pressure operations, thus reducing energy consumption and providing an economical and feasible technical solution for large-scale green hydrogen production. Attached Figure Description

[0050] Figure 1 These are 45° scanning electron microscope (SEM) side and top views of the gallium nitride nanowires prepared in Example 1 of this invention.

[0051] Figure 2 Transmission electron microscopy (TEM) images and particle size distribution of Mn nanoparticles prepared in Example 2 of this invention.

[0052] Figure 3 The variation trend of the photocatalytic rate of the manganese-supported gallium nitride nanowires in Example 3 of the present invention includes the variation trend of hydrogen production rate and temperature with light intensity.

[0053] Figure 4 To ensure the stability of the manganese-supported gallium nitride nanowires in Example 3 of this invention, the catalytic performance, including the conversion number, showed almost no significant change under continuous light irradiation for 360 minutes.

[0054] Figure 5 This is a comparative analysis of the hydrogen production rate, photo-hydrogen efficiency, and publication year of the advanced seawater or water splitting catalysts in Comparative Example 1.

[0055] Figure 6 For comparative example 4, Mn / Si, GaN / Si and MnO x (OH) y Comparison of GaN / Si structures used as photocatalysts for seawater catalysis.

[0056] Figure 7 The results show the effect of the loading amount of manganese-loaded gallium nitride nanowires on the photohydrogen efficiency in Example 3 of the present invention. Detailed Implementation

[0057] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, but this is by no means a limitation thereof. Any preparation methods, materials, structures, or compositional ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0058] The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0059] The present invention can be practiced using conventional chemical techniques within the art. In the following embodiments, efforts have been made to ensure the accuracy of the figures used (including quantities, temperatures, reaction times, etc.), but some experimental errors and deviations should be taken into account.

[0060] In this embodiment, all reagents used are commercially available.

[0061] This invention constructs a multifunctional catalytic system by integrating manganese (Mn) nanoparticles onto gallium nitride (GaN) nanowires on a silicon wafer substrate, thereby simultaneously driving redox reactions in the water splitting process and significantly improving the system's catalytic efficiency and long-term stability.

[0062] A method for preparing manganese-supported gallium nitride nanowire photocatalysts, the synthesis method comprising the following steps:

[0063] (1) Growth of gallium nitride nanowires: Gallium nitride (GaN) nanowires were grown on a silicon substrate under a nitrogen-rich atmosphere using molecular beam epitaxy (MBE) at a deposition temperature of 600 °C. The resulting nanowires were vertically aligned on the silicon substrate, with a coverage of 0.2-0.4 nm and a height distribution in the range of 690-720 nm.

[0064] (2) Loading of manganese nanoparticles: Using manganese sulfate (MnSO4) aqueous solution as a precursor, manganese (Mn) nanoparticles were loaded onto the surface of gallium nitride nanowires by photodeposition. The specific process was carried out under xenon lamp irradiation, and finally, uniformly distributed Mn nanoparticles were obtained on the surface of the nanowires.

[0065] Furthermore, the gallium nitride nanowires obtained in step (1) are vertically aligned on a silicon substrate, with a nanowire coverage of approximately 0.2-0.4 and a height of 690-720 nm.

[0066] Furthermore, the manganese nanoparticles obtained in step (2) are deposited on the surface of the nanowires with an average size of approximately 2-4 nm.

[0067] This photocatalyst also enhances charge separation:

[0068] The designed nanostructure has a high specific surface area, which can significantly improve light absorption efficiency.

[0069] With the assistance of Mn nanoparticles, the system achieved efficient electron-hole separation, in which Mn nanoparticles, as hole extractors, successfully achieved spatial decoupling of water oxidation sites and hydrogen evolution sites.

[0070] A method for photocatalytic water splitting, wherein the method comprises: at an intensity of 2-6 W·cm -2 Manganese-supported gallium nitride nanowire photocatalysts were exposed to natural seawater under xenon lamp irradiation.

[0071] In the photocatalytic process, photoexcited electrons reduce water molecules to hydrogen, while photoexcited holes oxidize water molecules to oxygen, thus achieving a complete water splitting reaction.

[0072] The system can operate sustainably without the need for external sacrificial agents or additional energy input.

[0073] The technical concept of this invention is as follows:

[0074] To address the shortcomings of existing photocatalytic water splitting systems, such as low photohydrogen efficiency, high carrier recombination rate, slow reaction kinetics, and difficulties in separating the simultaneously generated hydrogen-oxygen mixture, this invention provides an innovative solution. Furthermore, considering the scarcity of freshwater resources, this invention selects seawater, which is abundant on Earth, as the reaction feedstock. This not only effectively solves the feedstock shortage problem but also provides a feasible pathway for large-scale green hydrogen production.

[0075] By constructing a composite structure of a one-dimensional gallium nitride (GaN) nanowire vertical array and manganese (Mn) nanoparticles, highly efficient photocatalytic decomposition of natural seawater is achieved. Specifically, this invention uses epitaxial growth technology to prepare a GaN nanowire array with a wurtzite structure on a silicon wafer. Its unique variable polarity surface characteristics are beneficial for controlling charge transport behavior, reactant adsorption, and intermediate formation. Furthermore, Mn nanoparticles are uniformly loaded onto the surface of the GaN nanowires using photodeposition, forming a nano-hybrid material with synergistic effects.

[0076] In the photocatalytic process, Mn nanoparticles act as highly efficient hole acceptors, promoting the water oxidation reaction to generate key intermediates *OH and *OOH, significantly reducing the energy barrier of the potential-determining steps. Simultaneously, chloride ions (Cl-) in seawater further optimize the photogenerated charge dynamics by forming an interfacial polarized electric field.

[0077] The prepared catalyst exhibits excellent hydrogen production performance, with a hydrogen production rate of 3,000-20,000 mmol·g. -1 ·h -1 .

[0078] The photocatalytic system using this photocatalyst has the ability to operate stably for a long time.

[0079] Experiments show that this catalyst is effective at 3.3 W·cm⁻¹ -2 Under concentrated light irradiation, 15,200 mmol·g can be achieved. -1 ·h -1The hydrogen production rate was achieved, with a solar hydrogen production efficiency of 6.15%. The developed manganese-supported gallium nitride nanowire catalyst maintained excellent stability after 6 hours of continuous operation, achieving a turnover number (TON) of 44,278 moles of H2 per mole of Mn nanoparticles. Furthermore, characterization analysis showed that the catalyst maintained its original structure and composition during long-term use, and its catalytic activity did not show significant decline.

[0080] Example 1

[0081] This application discloses a method for preparing gallium nitride nanowire photocatalysts based on silicon substrates, the method comprising the following steps: preparing gallium nitride nanowire arrays on a silicon substrate:

[0082] (1) Prior to the synthesis of gallium nitride (GaN) nanowires, the silicon (Si)(111) substrate was degassed at 800°C for half an hour to remove residual oxides and surface impurities, thus providing an atomically clean surface for epitaxial growth. Subsequent nanowire growth was carried out at a substrate temperature of 600°C. During deposition, nitrogen plasma was generated using a 400-watt radio frequency power supply while maintaining a constant gas flow rate of 1 standard cubic centimeter per minute (sccm). Simultaneously, the gallium source was maintained at 5 × 10⁻⁶ ppm. -7 The vapor pressure of Torr creates a nitrogen-rich growth environment, which is crucial for obtaining high-quality gallium nitride nanowire structures.

[0083] (2) Gallium nitride nanowires were epitaxially grown on 4-inch silicon (111) wafers using a plasma-assisted selective region molecular beam epitaxy (SAVTAMBE) system under constant nitrogen flow rate and a growth temperature of 600°C. The system was configured with a dual-filament Knudsen cell as the gallium source (Ga purity ≥ 99.99%) and a Vieco single-bubble radio frequency nitrogen plasma source (N2 purity ≥ 99.99%). Under conditions of a constant nitrogen flow rate of 1.0 sccm (standard cubic centimeters per minute) and 400 W radio frequency power, the growth rate of GaN nanowires remained stable at 300 nm / h. All GaN nanowires were grown in a nitrogen-rich environment, strictly maintaining a III / V element ratio of 0.2. Figure 1 As shown.

[0084] Example 2

[0085] This embodiment provides a method for synthesizing a gallium nitride nanowire catalyst supported on manganese (Mn) nanoparticles for high-efficiency photocatalytic seawater splitting to produce hydrogen, specifically including the following steps:

[0086] (1) Using photodeposition technology with a 300W xenon lamp as the light source, Mn metal was deposited on the surface of GaN nanowires (prepared in Example 1) in a quartz reaction chamber. First, the GaN nanowires grown on a bulk silicon wafer were divided into sections with a geometric surface area of ​​0.2-0.5 cm². 2 Small pieces were placed at the bottom of the reaction chamber.

[0087] (2) A methanol-water mixture was used as the photodeposition medium at a volume ratio of 1:5, with a total volume of 60 mL. Subsequently, a manganese sulfate (MnSO4) solution of a specific concentration was added to the reaction chamber as the Mn precursor solution. Dissolved gases in the solution were removed by vacuum treatment, and the reaction chamber was saturated with argon gas. Finally, the mixture was irradiated with a xenon lamp for 30 minutes at a set light intensity to complete the deposition of Mn nanoparticles on GaN nanowires. Figure 2 As shown.

[0088] Example 3

[0089] The photocatalytic reaction was carried out in a custom-designed sealed glass reaction chamber using a 300W xenon lamp as the light source, unless otherwise specified. Before fixing the manganese (Mn) nanoparticle-supported gallium nitride (GaN) nanowire catalyst prepared in Example 2 to the bottom of the reaction chamber, it was thoroughly cleaned with deionized water. A certain amount of natural seawater from the Beibu Gulf of the South China Sea was injected into the reaction chamber, and the pH of the solution was adjusted to approximately 12-13 with sodium hydroxide (NaOH). The reaction chamber was then completely evacuated to remove residual oxygen and purged with argon (Ar). Finally, the reactor was placed under a 300W xenon lamp to carry out the photocatalytic reaction.

[0090] Gas chromatographs equipped with flame ionization detectors (FID) and thermal conductivity detectors (TCD) were used to analyze the gaseous products. The formation of the byproduct hydrogen peroxide (H₂O₂) was detected using a UV-Vis spectrophotometer with 2,2'-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) as an indicator: 2.85 mL of 0.1 mol / L potassium phosphate buffer containing 2 mmol ABTS and 2.5 units of horseradish peroxidase (HRP) was used as the colorimetric reagent, and the absorbance was recorded at 420 nm. The o-toluidine method and UV spectrophotometry confirmed that no byproducts such as chlorine oxides and hydrogen peroxide were formed after the reaction.

[0091] Experimental results show that: by scanning electron microscopy (SEM), Figure 1 ) and transmission electron microscopy (TEM) Figure 2The morphology and structure of Mn-loaded GaN nanowires were characterized. SEM images confirmed that the GaN nanowires were vertically aligned on the silicon wafer, with an average height of 690-720 nm and a coverage of 0.2-0.4. TEM images showed that the one-dimensional structure remained unchanged after the introduction of Mn, and high-resolution TEM further confirmed that Mn nanoparticles with a size of approximately 3 nm were uniformly distributed on the surface of the GaN nanowires. The lattice spacing of 0.24 nm can be attributed to the (202) crystal plane of metallic manganese.

[0092] Based on high-resolution X-ray photoelectron spectroscopy (HR-XPS) characterization, Ga 3d and N1s exhibit characteristic binding energy signals at 20 eV and 397 eV, respectively. Compared with pure GaN, the binding energies of Ga 3d and N1s in Mn-doped GaN nanowires show significant shifts of -0.3 eV and -0.2 eV, respectively, confirming the presence of electronic rearrangement effects at the Mn / GaN interface. This interfacial electronic modulation promotes the migration of photogenerated carriers in the heterojunction and effectively suppresses the aggregation of Mn species through strong electronic coupling. HR-XPS analysis of the Mn 2p orbitals indicates that Mn species are in a variable valence state, which is crucial for charge transfer during redox processes. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) further confirms the coexistence of multiple Mn oxidation states and detects oxygen- and hydroxyl-rich species on the surface, indicating that the deposited Mn species are MnO. x (OH) y This invention introduces manganese, which has multiple valence states, as a co-catalyst, which plays a key role in the photocatalytic hydrogen production reaction from seawater: manganese is often expressed as Mn. 2 + Mn 3+ Mn 4+ Mn exists in multiple oxidation states, and this multivalent characteristic endows it with excellent electron transport capabilities and redox buffering performance. In the photocatalytic process, Mn acts as a temporary reservoir for holes, effectively promoting the separation and transfer of photogenerated carriers and inhibiting carrier recombination, thereby improving the overall reaction efficiency. In addition, multivalent Mn has a strong synergistic catalytic effect in the water oxidation reaction, which can accelerate the oxidation process of water molecules and improve the utilization efficiency of photogenerated holes.

[0093] Further research was conducted on MnO x (OH) y Photoelectric properties of redox integrated components using GaN nanowires. Bader charge analysis indicates that in the optimized structure, MnO... x (OH) y Significant interfacial charge transfer exists between the nanoclusters and GaN nanowires, confirming substantial electronic interactions. The study also found that MnO... x (OH) yThe introduction of [a specific ingredient] effectively suppressed the recombination of photogenerated electron-hole pairs in GaN nanowires. Time-resolved photoluminescence (TRPL) measurements showed that the carrier lifetime decreased from 2.28 ns in pristine GaN to [a specific value] in MnO. x (OH) y The 1.82 ns of GaN nanowires indicates a significant improvement in the spatial separation efficiency of photogenerated carriers. Furthermore, in a seawater environment, MnO... x (OH) y The carrier lifetime of / GaN nanowires was further shortened to 1.82 ns, which is better than 2.55 ns in pure water environment, proving that ions in seawater enhance interfacial charge transfer through charge polarization effect.

[0094] like Figure 3 As shown, this is the result of the photocatalytic reaction in Example 3. With the gradual increase of light intensity (2.7 W / cm²), the photocatalytic reaction... 2 Up to 5.5W / cm 2 The photocatalytic system provided by this invention exhibits significantly enhanced catalytic activity in the photocatalytic seawater splitting for hydrogen production, manifested as a continuous increase in hydrogen production per unit time. This phenomenon demonstrates the system's strong responsiveness to light energy, effectively exciting photogenerated carriers under high-intensity light conditions, thereby promoting the reduction reaction of water molecules. Simultaneously, the system maintains good stability and selectivity under high light intensity, with no obvious side reactions or photocorrosion observed, further validating its adaptability and practical potential under high light flux conditions. Therefore, this invention possesses the technical advantage of efficiently utilizing light energy to directly drive hydrogen production from seawater under natural sunlight or enhanced light-gathering conditions, providing strong support for building a sustainable green energy system.

[0095] like Figure 4 As shown, at a set light intensity of 3.3 W·cm -2 Under these conditions, the photocatalyst provided by this invention exhibits excellent long-term operational stability, maintaining a stable hydrogen production rate throughout continuous reaction for 6 hours without significant performance degradation or catalytic deactivation. This result fully demonstrates that the catalyst possesses good photochemical and structural stability in practical applications, effectively resisting potential influencing factors such as photocorrosion, salt ion interference, and the accumulation of reaction byproducts. Furthermore, this stable hydrogen production performance is consistent in natural seawater systems, further confirming the applicability and sustainable operation capability of the catalyst in complex environments, providing a solid technical guarantee for its application in large-scale, long-term seawater photocatalytic hydrogen production devices.

[0096] In summary, this invention provides a photocatalytic system based on a composite of manganese nanoparticles and gallium nitride nanowires for efficient solar-driven hydrogen production. The preparation method of this system is simple; the deposition amount of Mn nanoparticles can be precisely controlled by adjusting the precursor solution concentration. The deposition amount of Mn nanoparticles significantly affects the catalytic activity, and its deposition effect can be characterized by transmission electron microscopy and inductively coupled plasma spectroscopy. Experimental results show that the photocatalytic water splitting activity is significantly enhanced when the Mn deposition amount is less than 0.322 μmol·cm⁻¹. -2 The range is enhanced with increasing sedimentation amount, such as... Figure 7 As shown (using the experimental conditions of Example 3, only changing the loading of Mn in the catalyst during preparation). The photocatalyst of this invention enhances light-harvesting ability by constructing a high specific surface area gallium nitride nanowire array and utilizes surface-loaded manganese nanoparticles to achieve effective separation of electron-hole pairs. Introducing Mn nanoparticles as a key functional component into the experimental system allows them to function as highly efficient hole extractors, successfully achieving spatial decoupling between water oxidation sites and hydrogen evolution sites.

[0097] The innovation of this invention lies in revealing the mechanism of action of Mn nanoparticles in the photocatalytic process through a combination of in-situ spectroscopic characterization and theoretical calculation. On the one hand, Mn nanoparticles act as highly efficient hole extractors, promoting the separation of photogenerated carriers; on the other hand, they significantly reduce the activation energy of the reaction by forming the key intermediate *OOH. Furthermore, chloride ions in seawater further optimize the transfer efficiency of photogenerated electron-hole pairs by constructing an interfacial polarized electric field, thereby accelerating the redox reaction kinetics. Without sacrificial agents and without external energy input, this photocatalyst achieves a yield of 3.3 W / cm². 2 Under strong light irradiation, it exhibits excellent catalytic performance in natural seawater, with a hydrogen production rate reaching 15,200 mmol·g⁻¹. -1 ·h -1 The photo-to-hydrogen conversion efficiency is 6.15%. Notably, the system exhibits excellent stability, maintaining high activity even after 6 hours of continuous operation, achieving a turnover rate of 44,278 moles of H2 per mole of Mn nanoparticles.

[0098] The photocatalyst was further validated through outdoor testing. This invention employs a Fresnel lens to filter natural sunlight with intensity fluctuations (intensity range of 2-5 W·cm²). -2Effective focusing is achieved to increase the incident light energy density and enhance catalytic driving efficiency. Under continuous operation conditions (March 26, 2025, 10:00 to 16:00, local time), the system exhibited good response performance to changes in solar irradiance intensity, and the measured hydrogen production rate over time showed a high degree of consistency with solar radiation intensity. Specifically, during the lower solar irradiance period from 10:00 to 11:00, the catalyst maintained a yield of 1.78 mol·g⁻¹. -1 ·h -1 The baseline hydrogen production rate was determined. With increasing light intensity between 11:00 and 13:00, the system's hydrogen production rate significantly increased, reaching its maximum during the peak sunlight period from 13:00 to 14:00. This photocatalytic system has significant application potential in solar-driven seawater splitting for the production of green hydrogen.

[0099] Comparative Example 1

[0100] Compared with catalysts disclosed in existing literature, such as Figure 5 As shown, the photocatalyst prepared in this scheme exhibits both high photo-hydrogen efficiency (6.15%) and high hydrogen production rate (15.2 mol·g⁻¹) when applied to the photocatalytic decomposition of seawater for hydrogen production. -1 ·h -1 As can be seen, the manganese-supported gallium nitride nanowire photocatalyst prepared by this method has significant advantages in the photocatalytic decomposition of seawater.

[0101] Comparative Example 2

[0102] Compared with the palladium-supported gallium nitride nanowire photocatalyst disclosed in CN119746906A, although it has a higher hydrogen production rate (24,654 mmol / g (palladium / gallium nitride) / hour), its photo-hydrogen conversion efficiency is 4.38%, which is lower than the 6.15% photo-hydrogen conversion efficiency of the manganese-supported gallium nitride nanowire photocatalyst of this invention (as in Example 3). This indicates that the manganese-supported gallium nitride nanowire photocatalyst of this scheme can utilize light energy to produce hydrogen more efficiently, and its application fields and regions are wider.

[0103] Comparative Example 3

[0104] This comparative example uses deionized water as the photocatalytic reactant, and the specific photocatalytic reaction method is consistent with that in Example 3. Testing revealed that, in this comparative experiment, compared to deionized water conditions, the catalyst system described in this invention exhibits higher photocatalytic hydrogen production activity when using natural seawater as the reaction medium. This is because the various ionic components in seawater can act as external ionic charge regulating factors under illumination, helping to enhance the internal electric field of the system, thereby effectively promoting the separation of photogenerated electrons and holes, reducing carrier recombination, and significantly improving the photocatalytic reaction efficiency. Therefore, under the same conditions, based on the role of seawater in assisting the separation of photogenerated electrons and holes with external ionic charges, the hydrogen production rate measured in the seawater medium is much higher than that in the pure water system, demonstrating the high adaptability of this invention to the seawater environment and its practical application value.

[0105] Comparative Example 4

[0106] Furthermore, to verify the performance advantages of the catalyst system described in this invention, a comparative catalyst was constructed: a Mn / Si catalytic system was formed by directly loading manganese species onto the surface of a silicon wafer using the same photodeposition preparation method as in Example 1 (i.e., according to step (2): manganese sulfate was used as a precursor and loaded onto the silicon substrate by photodeposition), which served as a reference sample for comparative experiments; and GaN / Si was prepared using the same gallium nitride nanowire growth method as in Example 1 (i.e., step (1)), which served as a reference sample for comparative experiments. Under the same reaction conditions, the MnO described in this invention... x (OH) y / GaN composite photocatalyst (MnO x (OH) y GaN / Si exhibits significantly better hydrogen production performance than the comparative example in seawater media, such as... Figure 6 As shown, the hydrogen production rate of the comparative catalyst is significantly lower, indicating limitations in terms of photogenerated carrier separation efficiency and catalytic interfacial reaction activity.

[0107] In summary, this invention discloses a novel photocatalytic system based on manganese-modified gallium nitride nanowires, which can achieve efficient seawater decomposition under natural light conditions, simultaneously producing hydrogen and oxygen. The GaN nanowire array, vertically grown on a silicon substrate using molecular beam epitaxy (MBE), exhibits a unique one-dimensional structure that significantly increases the effective reaction area and improves the photogenerated carrier separation efficiency. The manganese nanoparticles deposited on the nanowire surface serve as hole-trapping centers, and the heterointerface formed between the Mn / GaN and GaN displays excellent catalytic properties. Theoretical calculations confirm that the Mn / GaN interface significantly reduces the activation energy of the key step in water splitting (*H₂O→*H⁺*OH) from 2.22 eV in the original GaN to -2.92 eV, effectively stabilizing the formation of *OH and *OOH intermediates. Notably, naturally occurring ions in seawater accelerate charge transport kinetics, enhancing the overall water splitting efficiency.

[0108] This system can achieve 15,000-20,000 mmol·g under normal temperature and pressure conditions without any external energy input or sacrificial agent assistance. -1 ·h -1 The study demonstrated a sustained hydrogen production rate and maintained stable operation for over 6 hours. The results indicate that this technology, combining abundant Earth-sourced materials with marine resources, successfully overcomes the dual limitations of traditional photocatalysis technology, namely its dependence on pure water sources and high electron-hole recombination rates. It provides a technologically promising industrial-scale approach for building a terawatt-scale, low-cost, sustainable hydrogen production system, and plays a significant role in promoting the innovative development of clean energy systems.

[0109] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A manganese-supported gallium nitride nanowire photocatalyst, characterized in that, include: silicon substrate; Gallium nitride nanowires vertically aligned on the surface of a silicon substrate; Manganese species uniformly deposited on the surface of gallium nitride nanowires, wherein the manganese species is MnO with multiple Mn oxidation states coexisting. x (OH) y .

2. The manganese-supported gallium nitride nanowire photocatalyst according to claim 1, characterized in that, The gallium nitride nanowires have a coverage of 0.2-0.4% on the silicon substrate; and / or, The average height of the gallium nitride nanowires is 690-720 nm.

3. The manganese-supported gallium nitride nanowire photocatalyst according to claim 1, characterized in that, The average size of the manganese species is 2-4 nm; and / or, The deposition amount of the manganese species does not exceed 0.322 μmol·cm⁻¹. -2 .

4. A method for preparing a manganese-supported gallium nitride nanowire photocatalyst as described in any one of claims 1-3, characterized in that, Includes the following steps: S1: Gallium nitride nanowires are grown on a silicon substrate under nitrogen-rich conditions by radio frequency plasma-assisted molecular beam epitaxy. S2: Using manganese sulfate aqueous solution as a precursor, manganese species were deposited onto the surface of gallium nitride nanowires by photochemical deposition under full-spectrum xenon lamp irradiation.

5. The method for preparing a manganese-supported gallium nitride nanowire photocatalyst according to claim 4, characterized in that, In step S1, the silicon substrate is degassed at 800°C for 30 minutes.

6. The method for preparing a manganese-supported gallium nitride nanowire photocatalyst according to claim 4, characterized in that, In step S1, the radio frequency plasma-assisted molecular beam epitaxy growth is described as follows: Nitrogen plasma is generated using a 400W radio frequency power supply as the nitrogen source; and / or, A dual-filament Knudsen cell is used as the gallium source; and / or, The nitrogen flow rate is 1 sccm; and / or, The vapor pressure of the gallium source is 5 × 10⁻⁶. -7 To; and / or, The elemental ratio of nitrogen to gallium is 0.2; and / or, The growth temperature is 600℃; and / or, The growth rate of gallium nitride nanowires is 300 nm / h.

7. The method for preparing a manganese-supported gallium nitride nanowire photocatalyst according to claim 4, characterized in that, In step S2, the photochemical deposition method is described as follows: The full-spectrum xenon lamp has a power of 300W; and / or, A methanol-water mixture with a volume ratio of 1:5 was used as the photodeposition medium; and / or, Performed in a saturated argon atmosphere; and / or, The deposition time is 30 minutes.

8. A method for photocatalytic conversion of seawater, characterized in that, Includes the following steps: In an oxygen-free environment and under light conditions, seawater is decomposed to produce hydrogen under the catalytic action of the photocatalyst described in any one of claims 1-3.

9. A method for photocatalytic conversion of seawater according to claim 8, characterized in that, The radiation intensity of the light under the aforementioned illumination conditions is 2-6 W·cm. -2 .

10. A method for photocatalytic conversion of seawater according to claim 8, characterized in that, At 3.3 W·cm -2 Under illumination: the hydrogen production rate of the decomposition hydrogen production is 15.2 mol·g⁻¹. -1 ·h -1 The photo-hydrogen conversion efficiency of the decomposition hydrogen production is 6.15%.

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