Palladium-loaded gallium nitride nanowire photocatalyst as well as preparation method and application thereof

Abstract

The invention belongs to a photocatalysis technology, and particularly relates to a palladium-loaded gallium nitride nanowire photocatalyst as well as a preparation method and application thereof, and the palladium-loaded gallium nitride nanowire photocatalyst comprises a silicon substrate, a gallium nitride nanowire vertically grown on the silicon substrate and palladium nanoparticles uniformly loaded on the surface of the gallium nitride nanowire. Compared with the prior art, the problem that in the prior art, natural seawater cannot be used for photocatalytic decomposition for hydrogen and hydrogen peroxide is solved. According to the scheme, the limitation is solved by introducing the palladium-modified gallium nitride nanowire: the palladium nanoparticles serve as an efficient hole extractor, so that the adsorption of hydroxyl (* OH) is reduced, and the generation of hydrogen and hydrogen peroxide is accelerated; chloride ions in seawater further improve the catalytic performance by improving charge kinetics and reducing the energy barrier of the reaction.

Description

Technical Field

[0001] The present invention belongs to the photocatalytic technology, and specifically relates to a palladium-loaded gallium nitride nanowire photocatalyst and a preparation method and application thereof. Background Art

[0002] Over the past two and a half centuries, the development of fossil fuels has promoted unprecedented progress in human civilization, but it has also brought about some huge problems, such as energy crisis, environmental pollution and climate change. Therefore, it is very necessary to develop green energy as a substitute for fossil fuels to support the growing population and the growing economy. Hydrogen is recognized as the energy carrier of the future. First, the calorific value of hydrogen is as high as 14230kJ / kg, which is nearly 100 times that of gasoline, coal and lithium-ion batteries. At the same time, hydrogen is a basically carbon-neutral energy carrier because water is the only product of its combustion. But currently hydrogen is mainly derived from methane steam reforming and coal coking or gasification. These routes involve high temperature or high pressure, large amount of heat energy input and non-renewable fossil fuel consumption, which are unsustainable. Therefore, it is crucial to explore green ways to use renewable resources to produce hydrogen on a large scale.

[0003] Sunlight and water are two of the most abundant, cleanest, and most renewable resources on Earth. Solar water splitting provides a green method for hydrogen production and storage of intermittent solar energy. Semiconductors and co-catalysts that determine photon absorption, charge behavior, and surface chemical reactions are crucial for water splitting. Exploring suitable semiconductor materials and efficient co-catalysts and combining them rationally are the top priorities for research in this field.

[0004] Photocatalytic water splitting provides an ideal solution for intermittent solar energy storage, which converts energy into storable green hydrogen and has attracted global attention in the past few decades. Although some remarkable achievements have been made in the efficiency of solar-to-hydrogen conversion, approaching commercial requirements, most reported photocatalytic systems focus on studying the low light-to-hydrogen efficiency (attributed to low optical efficiency) to fast e / h recombination and slow kinetics. More importantly, the oxygen generated synchronously from photocatalytic water splitting (2H2O→2H2+O2) is not an industrially friendly product and requires additional separation costs to handle the hydrogen and oxygen mixture. In addition, it is worth noting that fresh water is one of the most precious resources on earth, and using it as a raw material for hydrogen production may further aggravate resource shortages. In sharp contrast, the abundant seawater on earth can provide an attractive option for large-scale production of green hydrogen; however, the diverse ions contained in natural seawater and the strong corrosiveness of natural seawater pose severe challenges to efficient and stable hydrogen production; and there is currently a lack of basic understanding of the mechanism of photocatalytic reactions in natural seawater.

[0005] Hydrogen peroxide is a versatile and valuable chemical with a wide range of applications. For example, environmental remediation, disinfection and energy carrier applications. Currently, hydrogen peroxide is industrially produced using conventional anthraquinone oxidation methods, but its production is strictly limited due to its high heat input intensity, complex process and severe environmental pollution. Therefore, it is of great significance to explore a green method for hydrogen peroxide preparation, especially powered by almost unlimited solar energy. In recent years, many efforts have been devoted to exploring various photocatalysts such as graphene and organic semiconductors for the production of hydrogen peroxide, which mainly focus on the oxidation of water with oxygen. Despite a series of progress, the photocatalytic production of hydrogen peroxide from water is still unsatisfactory due to the photoelectric performance and the existence of reaction thermodynamic and kinetic barriers. Compared with 2H2O+O2→2H2O2, 2H2O→H2+H2O2 can simultaneously produce green hydrogen and value-added chemicals, while eliminating the need for expensive redox separation of hydrogen and oxygen mixtures. Therefore, the pursuit of multifunctional photocatalysts is highly desirable, which has aroused certain research interests. However, due to the rapid recombination of photoexcited carriers, traditional systems are usually inefficient, resulting in a lack of industrial, large-scale production possibilities. In addition, the simultaneous generation of oxygen in traditional water splitting poses separation and safety issues.

[0006] Therefore, the present invention provides a photocatalyst suitable for photocatalytic decomposition of seawater to produce hydrogen and hydrogen peroxide. Summary of the invention

[0007] The purpose of the present invention is to provide a palladium-loaded gallium nitride nanowire photocatalyst and its preparation method and application in order to solve at least one of the above problems, so as to solve the problem that the existing technology cannot use natural seawater for photocatalytic decomposition to produce hydrogen and hydrogen peroxide. This solution solves these limitations by introducing palladium-modified gallium nitride nanowires: palladium nanoparticles act as efficient hole extractors, reduce hydroxyl (*OH) adsorption, and accelerate the production of hydrogen and hydrogen peroxide; chloride ions in seawater further improve catalytic performance by improving charge dynamics and reducing the energy barrier of the reaction.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] In recent years, vertically aligned GaN nanowires on silicon substrates, namely GaN / Si nanostructures, have become an emerging semiconductor platform due to their unique structural, optoelectronic and catalytic properties. GaN / Si nanostructures provide a suitable semiconductor platform for solar water splitting by addressing the great challenges of low light capture, fierce charge carrier recombination and sluggish reaction kinetics.

[0010] The first aspect of the present invention discloses a palladium-loaded gallium nitride nanowire photocatalyst, comprising a silicon substrate, gallium nitride nanowires vertically grown on the silicon substrate, and palladium nanoparticles uniformly loaded on the surface of the gallium nitride nanowires.

[0011] Preferably, the gallium nitride nanowire has a diameter of 30-60 nm and a length of 150-350 nm.

[0012] Preferably, the average particle size of the palladium nanoparticles is 6-10 nm.

[0013] The second aspect of the present invention discloses a method for preparing a palladium-supported gallium nitride nanowire photocatalyst as described above, comprising the following steps:

[0014] S1: Growth of GaN nanowires on silicon substrates by plasma-assisted molecular beam epitaxy under nitrogen-rich conditions;

[0015] S2: Using palladium precursor, palladium nanoparticles are loaded onto the surface of gallium nitride nanowires by photodeposition.

[0016] Preferably, the silicon substrate is pretreated by: a degassing treatment at 800-1000° C. for 20-50 minutes, and / or a surface nitridation treatment at 700-900° C. for 40-100 seconds.

[0017] Preferably, the temperature of the plasma-assisted molecular beam epitaxial growth is 680-750°C; more preferably, the temperature is 700°C.

[0018] Preferably, the palladium precursor includes palladium chloride, potassium tetrachloropalladate, potassium hexachloropalladate and palladium nitrate, and the photodeposition method uses xenon lamp irradiation.

[0019] The third aspect of the present invention discloses the use of a palladium-supported gallium nitride nanowire photocatalyst as described above in photocatalytic conversion of water.

[0020] Preferably, the photocatalyst is added to seawater and heated to a temperature of 1-3 W·cm -2 Photocatalytic conversion of water under the irradiation of a xenon lamp.

[0021] Preferably, the pH of the seawater is adjusted to 11-13 by an alkaline solution.

[0022] One-dimensional nanostructured gallium nitride is vertically distributed on a silicon wafer. As a new generation semiconductor platform for storing intermittent solar energy into chemicals, gallium nitride is promising for the behavior of mediating charges due to its special optical and electronic properties, especially the wurtzite structure with a polarity-variable surface in the epilayer. In addition, as known, industrially Pd is widely used as an efficient catalyst for the production of hydrogen peroxide by anthraquinone oxidation. Therefore, in this scheme, palladium nanoparticles (NPs) are integrated with GaN nanowires to split seawater with light.

[0023] In situ spectral characterization and isotope labeling experiments combined with theoretical calculations have shown that in this nanohybrid material, the Pd nanoparticles function as effective hole receptors, promoting the oxidation of water to *OH (H2O+h→H + +*OH). This finding is different from previous studies that Pd is an effective electron extractor for the superior co-catalyst of hydrogen evolution reaction. More interestingly, Pd nanoparticles supported by 1D GaN help to alleviate the adsorption of the key intermediate *OH, thereby reducing the energy barrier of the potential-determining step of 2*OH→H2O2 on Pd. In addition, chloride ions in seawater are beneficial to the photogenerated charge dynamics. In summary, in seawater, Pd-supported GaN nanowires accelerate the simultaneous production of hydrogen and hydrogen peroxide, thus showing promise for the simultaneous production of green hydrogen and value-added chemical hydrogen peroxide by using two earth-abundant resources, namely natural seawater and sunlight.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The invention's innovation in the field of nanowire photocatalyst preparation technology, especially its application in photocatalytic water decomposition to produce hydrogen and hydrogen peroxide, shows unique advantages and potential. The photocatalyst of the invention can decompose natural seawater into hydrogen and hydrogen peroxide using sunlight as the only energy source. The system integrates palladium nanoparticles onto gallium nitride nanowires grown on silicon wafers to drive two redox reactions, thereby improving catalytic efficiency and stability.

[0026] The following is a detailed description of the key points of the present invention:

[0027] (1) Nanowire structure: By carefully controlling the synthesis conditions, a uniformly distributed nanowire structure is prepared on a silicon wafer. This vertically grown nanowire structure increases the specific surface area of ​​the material, providing more catalytic active sites, thereby improving the efficiency of the photocatalytic reaction.

[0028] (2) Palladium nanoparticle loading: Palladium nanoparticles are loaded onto gallium nitride nanowires by photodeposition to synthesize a photocatalyst with a special structure (vertically arranged one-dimensional nanowires), which further promotes the separation of photogenerated electrons and holes and improves the catalytic performance.

[0029] (3) High hydrogen production activity and conversion frequency: The gallium nitride nanowire structure loaded with palladium nanoparticles is used to improve the separation efficiency, provide redox sites, promote the desorption of free radicals, and achieve high hydrogen production activity and conversion frequency.

[0030] (4) Co-production of hydrogen and hydrogen peroxide: The present invention combines palladium nanoparticles with gallium nitride nanowire structures to propose a novel photocatalytic water splitting co-production of hydrogen and hydrogen peroxide strategy. Palladium nanoparticles act as hole sites to promote the synthesis and desorption of hydroxyl radicals, thereby achieving the synthesis of hydrogen peroxide.

[0031] The preparation method of the present invention is simple, the manufacturing cost is low, and it exhibits excellent catalytic performance in photocatalytic water decomposition. By loading palladium nanoparticles onto gallium nitride nanowires, the present invention effectively promotes the separation of photogenerated electrons and holes, and significantly improves the co-production efficiency of hydrogen and hydrogen peroxide.

[0032] Compared with the prior art, the photocatalyst of the present invention achieves a photocatalytic activity of up to 24,654 mmol·g- 1 ·h- 1 The hydrogen generation rate is 3W·cm- 2 Under concentrated light irradiation, the photoconversion efficiency of hydrogen is 4.38%. In addition, palladium nanoparticles, as hole acceptors, promote the synthesis and desorption of hydroxyl radicals, further improving the yield of hydrogen peroxide. Stability tests show that the catalyst of the present invention maintains excellent catalytic performance during a reaction process of up to 60 hours, showing good durability and high conversion frequency, and showing broad application prospects in the field of sustainable energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a 45° side view of the gallium nitride nanowire prepared in Example 1 of the present invention, taken through a scanning electron microscope (SEM).

[0034] Figure 2 This is a scanning electron microscope (SEM) top view of the gallium nitride nanowires prepared in Example 1 of the present invention.

[0035] Figure 3 This is a transmission electron microscope (TEM) image of the palladium-supported gallium nitride nanowires prepared in Example 2 of the present invention.

[0036] Figure 4 The photocatalytic rate in Example 3 of the present invention, including the hydrogen production rate and the conversion frequency, varies with the light intensity.

[0037] Figure 5The stability of the palladium-supported gallium nitride in Example 3 of the present invention shows that under 60 hours of continuous illumination, the catalytic performance, including hydrogen production and conversion number, has almost no significant attenuation. DETAILED DESCRIPTION

[0038] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is by no means limited thereto.

[0039] The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several modifications and improvements may be made without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0040] In the following description, unless otherwise specified, the reagents used are conventional commercially available products, and the methods used are well known in the art.

[0041] A method for preparing a palladium-supported gallium nitride nanowire photocatalyst, the synthesis method comprising the following steps:

[0042] (1) GaN nanowires were grown on silicon substrates using plasma-assisted molecular beam epitaxy (MBE) at 700°C under nitrogen-rich conditions.

[0043] (2) Using one or more of palladium chloride, potassium tetrachloropalladate, potassium hexachloropalladate and palladium nitrate as precursors, palladium nanoparticles are loaded onto gallium nitride nanowires by photodeposition. The deposition is performed under the irradiation of a xenon lamp to form evenly distributed palladium nanoparticles on the surface of the nanowires.

[0044] Furthermore, the gallium nitride nanowires obtained in step (1) are vertically arranged on the silicon substrate, with a diameter ranging from 30 to 60 nm and a height ranging from 150 to 350 nm.

[0045] Furthermore, the palladium nanoparticles obtained in step (2) are deposited on the surface of the nanowires, with an average size of about 6-10 nm.

[0046] A method for photocatalytically decomposing water, the method comprising: 2 The palladium-supported gallium nitride nanowire photocatalyst was exposed to natural seawater under irradiation of a xenon lamp.

[0047] Furthermore, the photoexcited electrons reduce water to hydrogen, and the photoexcited holes oxidize water to hydrogen peroxide.

[0048] Furthermore, the system operates without the need for external sacrificial agents or additional energy input.

[0049] Furthermore, the hydrogen production rate reaches 23000-25000mmol·g- 1 ·h- 1 , the efficiency of solar hydrogen production is 4.38%.

[0050] Furthermore, hydrogen peroxide with a concentration of 250-300 μmol / L was produced within 2 hours, and the photochemical efficiency was 0.53%.

[0051] The photocatalyst can generate 3W·cm -2 Under concentrated light irradiation, the hydrogen production rate was 24,654mmol·g -1 ·h -1 , the hydrogen (LTH) efficiency is 4.38%, without the need for any sacrificial agent or external energy. At the same time, hydrogen peroxide is produced at a yield of 300 μmol within a reaction time of 2 hours, and the conversion rate of the photo-chemical reaction (LTC) reaches 0.53%. In addition, the catalyst shows excellent photocatalytic performance. It can stably produce hydrogen within 60 hours, with a turnover number (TON) of up to 1,42,03125 mol of hydrogen per mol of palladium.

[0052] The photocatalyst has the following characteristics: high specific surface area and better light absorption; efficient electron-hole separation efficiency. With the assistance of Pd nanoparticles, the Pd nanoparticles act as hole extractors, decoupling water oxidation and hydrogen evolution sites; the palladium-loaded gallium nitride nanowire catalyst can maintain stability after 60 hours of continuous operation, achieving a turnover number of 1,420,3125 moles of hydrogen per mole of palladium nanoparticles; the structure and composition of the catalyst remain unchanged during long-term use, and the catalytic activity does not decrease significantly.

[0053] In the following examples, efforts have been made to ensure accuracy with respect to numbers used (including amounts, temperatures, reaction times, etc.) but some experimental errors and deviations should be accounted for.

[0054] Example 1

[0055] This embodiment provides a method for synthesizing gallium nitride nanowires, specifically a gallium nitride nanowire semiconductor platform grown on a silicon wafer, the synthesis method comprising the following steps:

[0056] (1) Prior to growth, the silicon wafer is degassed at 900°C for 30 minutes and surface nitrided at 800°C for 60 seconds in the growth chamber to create favorable conditions for the nucleation of the subsequent gallium nitride layer.

[0057] (2) GaN nanowires were grown epitaxially on 4-inch silicon (111) wafers using a plasma-assisted selective area molecular beam epitaxy (SAVTA MBE) system at a constant nitrogen flow rate and a temperature of 700°C. The system was equipped with a dual-filament Knudsen cell for the gallium source (gallium purity was 99.99%) and a Veeco single-bubble RF nitrogen plasma source (nitrogen purity was 99.99%). The nitrogen plasma was operated at a constant nitrogen flow rate of 1.0 standard cubic centimeters per minute and an RF power of 400 watts, which resulted in a growth rate of 300 nanometers per hour for the GaN nanowires. All GaN nanowires were grown under nitrogen-rich conditions, maintaining a III / V group element ratio of 0.2.

[0058] Example 2

[0059] This embodiment provides a method for synthesizing palladium-loaded gallium nitride nanowires for photocatalytic decomposition of seawater to produce hydrogen and hydrogen peroxide, specifically a gallium nitride nanowire semiconductor platform loaded with palladium nanoparticles, using the gallium nitride nanowire semiconductor platform synthesized in Example 1, and the synthesis method comprises the following steps:

[0060] Using photodeposition technology, a 300-watt xenon lamp is used as the light source to deposit palladium metal onto gallium nitride nanowires in a quartz reaction chamber:

[0061] (1) The GaN nanowires on the bulk silicon wafer are cut into small fragments with a geometric surface area of ​​0.2-0.5 square centimeters. The samples are then placed at the bottom of a reaction chamber.

[0062] (2) Photodeposition is performed using a solution of 60 ml of methanol and water in a volume ratio of 1:5. Next, a certain concentration of palladium precursor solution, namely potassium hexachloropalladate solution, is added to the reaction chamber. Subsequently, the air in the solution is removed by vacuum. In addition, argon gas is filled into the reaction chamber to saturate it, and then it is placed under a xenon lamp with a specific light intensity for 30 minutes. This process deposits palladium onto the gallium nitride nanowires.

[0063] Example 3

[0064] The photocatalytic reaction is carried out in a sealed glass reaction chamber. Unless otherwise specified, the reaction chamber is illuminated by a 300-watt xenon lamp. Before the palladium nanoparticle-loaded gallium nitride nanowire semiconductor platform catalyst prepared in Example 2 is fixed to the bottom of the reaction chamber, it is thoroughly cleaned with deionized water. A certain amount of natural seawater taken from the Beibu Gulf of the South China Sea is injected into the reaction chamber. The pH value of the solution is maintained at 12 using an aqueous sodium hydroxide solution. The reaction chamber is then completely evacuated to remove residual oxygen in the system. Argon is then filled into the reaction chamber. The reactor is placed under a 300-watt xenon lamp for a photocatalytic reaction.

[0065] The gaseous products were analyzed by a gas chromatograph equipped with a flame ionization detector and a thermal conductivity detector. Hydrogen peroxide was determined by potassium permanganate titration and using colorimetric test paper purchased from Guangzhou Rohande Company. In addition, a UV-visible spectrophotometer was used to detect the concentration of hydrogen peroxide using ABTS. 2.85 ml of 0.1 mol potassium phosphate buffer containing 2 mmol ABTS and 2.5 units of horseradish peroxidase was used as a colorimetric reagent, and the absorbance was recorded at 420 nm.

[0066] Scanning electron microscopy ( Figure 1 , 2 ) and transmission electron microscopy ( Figure 3 ) characterized the morphology and structure of palladium-loaded gallium nitride nanowires. Scanning electron microscope images confirmed that the gallium nitride nanowires were vertically aligned on the silicon wafer, with an average height of 250-350 nanometers. The lateral diameter of the top of the nanowire ranged from 30 to 60 nanometers. Subsequently, palladium nanoparticles were deposited onto the surface of the gallium nitride nanowires using a photodeposition process, such as Figure 3 As shown. After the introduction of palladium, the one-dimensional structure of the GaN nanowires remains unchanged. In addition, high-resolution transmission electron microscopy images provide valuable insights into the nanowire structure. The surface of the GaN nanowires is uniformly distributed with palladium nanoparticles with a size of 6-10 nanometers. The lattice spacing of 0.22 nanometers can be attributed to the (111) crystal plane of metallic palladium. In summary, Figure 1-3 As shown, gallium nitride nanowires are vertically arranged on a silicon substrate with a diameter ranging from 30-60nm and a height of 150-350nm, and palladium nanoparticles are deposited on the surface of the nanowires with an average size of 6-10nm.

[0067] The hydrogen production activity increases with the increase of light intensity, such as Figure 4 As shown. With the increase of light intensity, 3W·cm -2 Up to 24,654g Pd / GaN -1 ·h -1 The one-dimensional nanostructure has a high atomic efficiency, capable of achieving a conversion efficiency of up to 2,55,066 mol of hydrogen per mol of palladium per hour. The stability of the structure was also evaluated, such as Figure 5 As shown in the figure, the average hydrogen production rate was 24,500 mmol·g in the 60-hour long-term test. Pd / GaN -1 ·h -1 , with a turnover number (TON) as high as 1,42,03125 mol of hydrogen per mol of palladium.

[0068] The chemical composition and bonding interactions of the palladium / gallium nitride nanowires were characterized by X-ray photoelectron spectroscopy. The 3d peak of gallium and the 1s peak of nitrogen were observed at about 19 electron volts and 399 electron volts, respectively. High-resolution X-ray photoelectron spectroscopy analysis showed that the binding energy of gallium and nitrogen was positively shifted. The peaks at 335.3 electron volts and 340.5 electron volts correspond to the 3d peaks of the palladium metal valence. 5 / 2 and 3D 3 / 2 The two peaks with lower intensity, namely, those at 336.5 eV and 341.9 eV, can be attributed to divalent palladium, which confirms that palladium is mainly in the metallic state.

[0069] Diffuse reflectance UV-visible spectroscopy measurements showed that the introduction of palladium nanoparticles did not significantly change the light absorption of GaN nanowires. However, the modification of GaN nanowires with palladium significantly increased the photocurrent density. Electrochemical impedance spectroscopy analysis showed that the Pd / GaN nanowires had a lower charge transfer resistance than pure GaN.

[0070] In addition, transient absorption spectroscopy studies revealed that the Pd / GaN nanowires had a characteristic photobleaching peak at about 479 nm, which was attributed to ground-state bleaching caused by excited-state relaxation. By tracking the ground-state bleaching signal at 479 nm within 1000 ps, ​​it was found that Pd / GaN exhibited a stronger signal intensity compared to GaN, indicating that there was an accumulation of photoexcited electrons in the Pd / GaN system. By modifying with Pd nanoparticles, the decay time of GaN was significantly reduced from 2216 ps to 236 ps, indicating that the charge carrier dynamics were improved. The above results indicate that the deposited Pd nanoparticles are electronically beneficial for achieving high photocatalytic yields of hydrogen and hydrogen peroxide.

[0071] Example 4

[0072] This embodiment is basically the same as the embodiment 1, except that in step (1): the silicon wafer is subjected to a degassing treatment at 800° C. for 50 minutes and a surface nitriding treatment at 900° C. for 40 seconds in the growth chamber. The product is basically the same as the embodiment 1.

[0073] Example 5

[0074] This embodiment is basically the same as the embodiment 1, except that in step (1): the silicon wafer is subjected to a degassing treatment at 1000° C. for 20 minutes and a surface nitriding treatment at 700° C. for 100 seconds in the growth chamber. The product is basically the same as the embodiment 1.

[0075] Example 6

[0076] This embodiment is basically the same as embodiment 2, except that in step (2): the palladium precursor solution is palladium chloride, and the xenon lamp irradiation time is 40 minutes. The product is basically the same as embodiment 2.

[0077] Example 7

[0078] This example is basically the same as Example 2, except that in step (2): the palladium precursor solution is palladium nitrate, and the xenon lamp irradiation time is 35 minutes. The product is basically the same as Example 2.

[0079] In summary, the present invention provides a composite photocatalytic system based on palladium nanoparticles and gallium nitride nanowires for efficient synergistic generation of hydrogen and hydrogen peroxide under illumination. During the synthesis process, the deposition amount of palladium nanoparticles can be regulated by regulating the concentration of the precursor solution, which can be reflected by transmission electron microscopy and inductively coupled plasma spectroscopy. The preparation method of the present invention is simple, and the catalytic performance of photocatalytic seawater co-production of hydrogen and hydrogen peroxide is excellent. The method combining in-situ spectral characterization with computational research reveals that in this nano-hybrid material, palladium nanoparticles play the role of efficient hole extractors and hydroxyl scavengers in the photocatalytic process. At the same time, DFT calculations show that chloride ions in seawater promote the conversion of H2O→H2+H2O2 by improving charge dynamics and reducing the energy barrier of the key hydroxyl self-coupling step on the palladium site in the catalytic system. Thus, in the absence of sacrificial agents and without external energy input, the photocatalyst achieved a respectable hydrogen production rate of 24,654 mmol / g (palladium / gallium nitride) per hour in natural seawater under strong light irradiation of 3 W / cm2, with a light-to-hydrogen conversion efficiency of 4.38%. Notably, the water oxidation reaction produced valuable hydrogen peroxide at a concentration of 300 micromol per liter within two hours, with a photo-chemical conversion efficiency of 0.53%. The photocatalyst exhibited excellent stability for up to 60 hours, with a hydrogen conversion number of up to 1,42,03125 mol per mol of palladium. Outdoor tests further demonstrated its great potential in solar-driven seawater decomposition to produce green fuels and chemicals.

[0080] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A palladium-supported gallium nitride nanowire photocatalyst, characterized in that: The invention comprises a silicon substrate, gallium nitride nanowires vertically grown on the silicon substrate and palladium nanoparticles uniformly loaded on the surface of the gallium nitride nanowires.

2. The palladium-supported gallium nitride nanowire photocatalyst according to claim 1, characterized in that: The gallium nitride nanowire has a diameter of 30-60nm and a length of 150-350nm.

3. The palladium-supported gallium nitride nanowire photocatalyst according to claim 1, characterized in that: The average particle size of the palladium nanoparticles is 6-10 nm.

4. A method for preparing a palladium-supported gallium nitride nanowire photocatalyst according to any one of claims 1 to 3, characterized in that: The steps include: S1: Growth of GaN nanowires on silicon substrates by plasma-assisted molecular beam epitaxy under nitrogen-rich conditions; S2: Using palladium precursor, palladium nanoparticles are loaded onto the surface of gallium nitride nanowires by photodeposition.

5. The method for preparing a palladium-supported gallium nitride nanowire photocatalyst according to claim 4, characterized in that: The silicon substrate is pretreated by: degassing treatment at 800-1000° C. for 20-50 minutes, and / or surface nitriding treatment at 700-900° C. for 40-100 seconds.

6. The method for preparing a palladium-supported gallium nitride nanowire photocatalyst according to claim 4, characterized in that: The temperature of the plasma-assisted molecular beam epitaxial growth is 680-750°C.

7. The method for preparing a palladium-supported gallium nitride nanowire photocatalyst according to claim 4, characterized in that: The palladium precursor comprises palladium chloride, potassium tetrachloropalladate, potassium hexachloropalladate and palladium nitrate, and the photodeposition method adopts xenon lamp irradiation.

8. Use of the palladium-supported gallium nitride nanowire photocatalyst as claimed in any one of claims 1 to 3 in photocatalytic conversion of water.

9. The use according to claim 8, characterized in that: The photocatalyst is added to seawater and heated at an intensity of 1-3 W·cm -2 Photocatalytic conversion of water under the irradiation of a xenon lamp.

10. The use according to claim 8, characterized in that: The pH of the seawater is adjusted to 11-13 by an alkaline solution.

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