A multi-legged nanocrystal for photocatalytic reforming of biomass and its derivatives to produce hydrogen and a preparation method and application thereof

Abstract

The present application relates to the technical field of inorganic nanometer catalyst material manufacturing, and particularly relates to a multi-legged nanocrystal for photocatalytic reforming of biomass and derivatives thereof to produce hydrogen as well as a preparation method and application thereof. The multi-legged nanocrystal takes spherical quantum dots as a core, and grows multiple nanometer arms on the surface of the core under the regulation of a surfactant. The specific surface area of the multi-legged nanocrystal is large, and more surface active sites can be exposed, so as to improve the migration efficiency of photo-generated carriers. Meanwhile, the nanometer arms can effectively solve the problems of electron and hole recombination and electron migration in photocatalysis. As the main light absorption unit, the nanometer arms absorb photons, generate electrons, and make the electrons gather on the nanometer arms, thereby inhibiting the recombination of electrons and holes and accelerating the photocatalytic reaction and improving the photocatalytic efficiency. The size of the multi-legged nanocrystal is adjustable, and the stability is good, so that the problem of photo corrosion in photocatalysis can be effectively alleviated.

Description

Technical Field

[0001] This invention relates to the field of inorganic nanocatalyst material manufacturing technology, specifically to a multi-legged nanocrystal for hydrogen production from biomass and its derivatives via photocatalytic reforming, its preparation method, and its application. Background Technology

[0002] Currently, traditional fossil fuels such as coal, oil, and natural gas suffer from low utilization efficiency, severe environmental pollution, and gradual depletion, making them unsuitable for the future demands of an efficient, clean, economical, and safe energy system. Therefore, energy development faces enormous challenges and pressures. Simultaneously, increased global concern about environmental issues such as climate change and pollution makes future energy production and utilization more focused on environmental and ecological effects. Thus, developing renewable energy has become a crucial issue. Solar energy, as an abundant and clean renewable energy source, converts solar energy into chemical energy, particularly through photocatalytic water splitting into hydrogen (H2), offering an effective way to simultaneously address global energy demand and environmental problems. Consequently, scientists have conducted extensive research on catalysts for photocatalytic water splitting.

[0003] Semiconductor quantum dot (QD) photocatalysts have been extensively studied due to their advantages such as large specific surface area, tunable band structure, and short electron and hole migration distances. In existing technologies, Ba Yang et al. loaded ReS2 nanoparticles onto a CdS / ZnS heterojunction to form a spherical core / shell structure semiconductor quantum dot CdS / ZnS-ReS2. Their results showed that CdS / ZnS-ReS2 achieved the highest hydrogen production rate of 10722 μmol g⁻¹. -1 h -1The hydrogen evolution rate of ReS2 is 178 times that of pure CdS and 5 times that of CdS / ZnS heterojunctions, effectively improving photocatalytic activity and stability and broadening the application range of ReS2 as a cocatalyst [ACS Omega 2023,8,6059-6066]. However, the spherical core / shell structure inhibits the migration ability of photogenerated charges within the core, thereby reducing photocatalytic activity and efficiency. Unlike core-shell materials, Yi Jianjian et al. synthesized CdS nanorods with {100} exposed faces and CdS nanosheets with {001} exposed faces using a simple wet chemical method. In the photocatalytic reaction, the hydrogen evolution rate of the original CdS nanorods (16.99 μmol / h) was higher than that of the original CdS nanosheets (4.97 μmol / h). When using pristine CdS as a catalyst, the {100} crystal facet is more conducive to proton adsorption than the {001} crystal facet, resulting in higher performance of CdS nanorods with the {100} crystal facet as the surface reaction site. This demonstrates the different roles of crystal facets as surface active sites and interfacial charge migration channels [Applied Surface Science 2023, 615, 156402]. Yang Xiaofei et al. successfully synthesized hollow CdS cubes using a template-assisted reverse cation exchange strategy. The designed hollow CdS exhibited significantly improved photocatalytic performance, with a hydrogen production rate of 965 μmol g. -1 h -1 It is 2.8 times larger than that of ordinary CdS nanorods [International Journal of Hydrogen Energy 2023, 48, 26757-26767]. However, CdS has poor stability, and the problem of photocorrosion in photocatalysis remains unsolved. In summary, for semiconductor quantum dot photocatalysts, it is urgent to solve the problems of few active sites, low photocatalytic efficiency, and poor stability. Summary of the Invention

[0004] To overcome the aforementioned problems, this invention provides a multi-legged nanocrystal for hydrogen production from biomass and its derivatives via photocatalytic reforming, along with its preparation method and applications. The multi-legged nanocrystal of this invention has a large specific surface area, exposing more surface active sites, thereby improving the migration efficiency of photogenerated carriers. Simultaneously, the nanoarms effectively address the issues of electron-hole recombination and electron migration in photocatalysis. As the main light-absorbing unit, the nanoarms absorb photons and generate electrons, causing electrons to accumulate on the nanoarms, inhibiting electron-hole recombination, accelerating the photocatalytic reaction, and improving photocatalytic efficiency. The multi-legged nanocrystals have adjustable size and good stability, effectively mitigating the problem of photocorrosion in photocatalysis.

[0005] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a multi-legged nanocrystal for hydrogen production by photocatalytic reforming of biomass and its derivatives, wherein the multi-legged nanocrystal is a spherical quantum dot core on which multiple nanoarms are grown on the surface under the control of a surfactant.

[0007] The spherical quantum dots include one or more of the following: CdSe, CdTe, CdS, ZnSe, ZnTe, and ZnS quantum dots;

[0008] The nanoarms are composed of one of ZnS, CdS, CdSe, ZnSe, and ZnTe.

[0009] The spherical quantum dots and nanoarms may have the same or different compositions.

[0010] A second aspect of the present invention provides a method for preparing the above-mentioned multi-legged nanocrystals for hydrogen production by photocatalytic reforming of biomass and its derivatives, comprising the following steps:

[0011] (1) Under an inert gas atmosphere, ZnO or CdO is dissolved in organic solvent A, then oleic acid and stabilizer are added, and the solution is heated until it is completely dissolved and transparent. The precursor solution of Se, Te or S is quickly injected, and the reaction is heated and stirred. After the reaction is completed, anhydrous ethanol is added to obtain a precipitate. After washing, spherical quantum dots can be obtained.

[0012] (2) Under an inert gas atmosphere, ZnO or CdO is dissolved in organic solvent B, then surfactant and oleic acid are added, and the solution is heated until it is completely dissolved and transparent. The precursor solution of Se, Te or S and the spherical quantum dots obtained in step (1) are quickly injected, and the reaction is heated and stirred. After the reaction is completed, the temperature is quickly lowered to room temperature, and the multi-legged nanocrystals are obtained after purification with methanol and n-hexane.

[0013] The length of the nanoarms of the multi-legged nanocrystal can be controlled by the amount of surfactant and the concentration of the precursor solution in step (2). The number of nanoarms of the multi-legged nanocrystal can be controlled by the reaction temperature in step (2), and can be one or more of the following: monopodial, dipodial, tripodial, tetrapodial, hexapodial, and octpodial. In a specific embodiment of the present invention, the number of nanoarms is four-legged.

[0014] In a third aspect, the present invention provides multi-legged nanocrystals for hydrogen production by photocatalytic reforming of biomass and its derivatives under visible light conditions.

[0015] The beneficial effects of this invention are as follows:

[0016] In the semiconductor quantum dot photocatalytic water splitting system, the following three processes mainly occur: ① Semiconductor quantum dots, acting as the light-absorbing unit of the system, absorb photons to generate photoexcitons; ② Photoexcitons separate to generate photogenerated electrons and holes, which migrate to the semiconductor surface; ③ Photogenerated electrons and holes respectively carry out hydrogen and oxygen production reactions. However, in ordinary semiconductor quantum dot photoexciton separation, the photogenerated electrons and holes recombine, affecting the hydrogen and oxygen production reactions. In this invention, nanoarms can effectively solve the problems of electron and hole recombination and electron migration in photocatalysis. As the main light-absorbing unit, the nanoarms absorb photons and generate electrons, causing electrons to accumulate on the nanoarms, while holes are transferred to the nucleus, inhibiting electron and hole recombination, accelerating the photocatalytic reaction, and improving photocatalytic efficiency. The multi-legged nanocrystals of this invention have a large specific surface area, which can expose more surface active sites, thereby improving the migration efficiency of photogenerated carriers. At the same time, the multi-legged nanocrystals have adjustable size and good stability, which can effectively alleviate the problem of photocorrosion in photocatalysis. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 The images show the ultraviolet absorption spectra of the spherical quantum dots ZnSe and ZnSe / CdS multi-legged nanocrystals prepared in Example 1.

[0019] Figure 2 High-resolution transmission electron microscope image of spherical quantum dots ZnSe prepared in Example 1;

[0020] Figure 3 Here is a high-resolution transmission electron microscope image of the ZnSe / CdS multi-legged nanocrystals prepared in Example 1;

[0021] Figure 4 Transmission electron microscopy (TEM) images of ZnSe / CdS multi-legged nanocrystals prepared in Examples 1 and 2, where a is Example 1 and b is Example 2;

[0022] Figure 5 Transmission electron microscopy image of ZnTe / CdS multi-legged nanocrystals synthesized in Example 3;

[0023] Figure 6 Transmission electron microscopy image of the ZnSe / CdSe multi-legged nanocrystals synthesized in Example 5;

[0024] Figure 7 Figures showing hydrogen production in the triethylamine reforming system of ZnSe / CdS multipod nanocrystals and ZnTe / CdSe multipod nanocrystals;

[0025] Figure 8 Figures showing hydrogen production from ZnTe / CdS multi-legged nanocrystals under different biomass conditions;

[0026] Figure 9 A diagram showing the long-term hydrogen production of the CdTe / CdS multi-legged nanocrystal reformed triethylamine system;

[0027] Figure 10 A comparison diagram of hydrogen production between the thin and thick arms of ZnSe / CdS multi-legged nanocrystals;

[0028] Figure 11 The images show the XRD patterns of the ZnSe / CdS multi-legged nanocrystals in Example 1 and Example 2. Detailed Implementation

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] The first typical embodiment of the present invention provides a multi-legged nanocrystal for hydrogen production by photocatalytic reforming of biomass and its derivatives. The multi-legged nanocrystal is a multi-legged nanocrystal with a spherical quantum dot core, and multiple nanoarms are grown on the surface of the core under the control of a surfactant.

[0032] The spherical quantum dots include one or more of the following: CdSe, CdTe, CdS, ZnSe, ZnTe, and ZnS quantum dots;

[0033] The nanoarms are composed of one of ZnS, CdS, CdSe, ZnSe, and ZnTe.

[0034] The spherical quantum dots and nanoarms may have the same or different compositions.

[0035] A second typical embodiment of the present invention provides a method for preparing the above-mentioned multi-legged nanocrystals for hydrogen production by photocatalytic reforming of biomass and its derivatives, comprising the following steps:

[0036] (1) Under an inert gas atmosphere, ZnO or CdO is dissolved in organic solvent A, then oleic acid and stabilizer are added, and the solution is heated until it is completely dissolved and transparent. The precursor solution of Se, Te or S is quickly injected, and the reaction is heated and stirred. After the reaction is completed, anhydrous ethanol is added to obtain a precipitate. After washing, spherical quantum dots can be obtained.

[0037] (2) Under an inert gas atmosphere, ZnO or CdO is dissolved in organic solvent B, then surfactant and oleic acid are added, and the solution is heated until it is completely dissolved and transparent. The precursor solution of Se, Te or S and the spherical quantum dots obtained in step (1) are quickly injected, and the reaction is heated and stirred. After the reaction is completed, the temperature is quickly lowered to room temperature, and the multi-legged nanocrystals are obtained after purification with methanol and n-hexane.

[0038] In the specific embodiments of the present invention described below, the number of nanoarms is four.

[0039] In one or more embodiments, in step (1), the organic solvent A comprises octadecene or tri-n-octylphosphine.

[0040] In one or more embodiments, in step (1), the stabilizer is octadecylamine.

[0041] In one or more embodiments, in step (1), when the raw material is ZnO, the temperature at which the solution is heated to completely dissolve and become transparent is 245-255°C, preferably 250°C; when the raw material is CdO, the temperature at which the solution is heated to completely dissolve and become transparent is 345-355°C, preferably 350°C.

[0042] In one or more embodiments, in step (1), the method for preparing the precursor solution of Se, Te or S includes: dissolving Se, Te or S in tri-n-octylphosphine.

[0043] In one or more embodiments, in step (1), when the raw material is ZnO, the heating and stirring reaction temperature is 245-255°C, preferably 250°C; the reaction time is 18-22 min, preferably 20 min. When the raw material is CdO, the heating and stirring reaction temperature is 345-355°C, preferably 350°C; the reaction time is 8-12 min, preferably 10 min.

[0044] In one or more embodiments, in step (1), the molar ratio of Se, Te or S in the precursor solution of ZnO or CdO, oleic acid and Se, Te or S is 1:5 to 7:0.5, preferably 1:5:0.5.

[0045] In one or more embodiments, in step (2), the organic solvent B comprises tri-n-octylphosphine oxide.

[0046] In one or more embodiments, in step (2), the surfactant includes any one or more of dodecyl phosphate, tetradecyl phosphate, hexadecyl phosphate, and octadecyl phosphate, preferably octadecyl phosphate.

[0047] In one or more embodiments, in step (2), when the raw material is ZnO, the temperature at which the solution is heated to completely dissolve and become transparent is 245-255°C, preferably 250°C; when the raw material is CdO, the temperature at which the solution is heated to completely dissolve and become transparent is 345-355°C, preferably 350°C.

[0048] In one or more embodiments, in step (2), the method for preparing the precursor solution of Se, Te or S includes: dissolving Se, Te or S in tri-n-octylphosphine.

[0049] In one or more embodiments, in step (2), when the raw material is ZnO, the heating and stirring reaction temperature is 245-255°C, preferably 250°C; the reaction time is 18-22 min, preferably 20 min. When the raw material is CdO, the heating and stirring reaction temperature is 345-355°C, preferably 350°C; the reaction time is 8-12 min, preferably 10 min.

[0050] In one or more embodiments, in step (2), the molar ratio of Se, Te, or S in the precursor solution of ZnO or CdO, surfactant, oleic acid, Se, Te, or S, and the spherical quantum dots obtained in step (1) is: 4:4:15~17:2:2~3×10 -6 The preferred ratio is 4:4:16:2:2.5×10. -6 .

[0051] In one or more embodiments, in step (2), the volume ratio of methanol to n-hexane is 1 to 3:1, preferably 2:1. The synthesized multi-legged body solution is first precipitated with methanol, then the supernatant is removed by centrifugation, and n-hexane is added for dispersion. This process is repeated twice to obtain highly uniform nano-multi-legged crystals.

[0052] The mechanism for synthesizing multi-legged nanocrystals is as follows: Step (1) of this invention is to prepare spherical quantum dots containing oleic acid ligands. This is because spherical quantum dots themselves are oleophobic. However, organic solvents are required in the process of synthesizing nanoarms in the second step. The presence of oleic acid ligands in step (1) is to ensure that the spherical quantum dots containing oleic acid ligands can dissolve in organic solvents, which lays the foundation for the growth of nanoarms in step (2). In step (2), the reaction temperature needs to be controlled. The lattice matching degree between nanoarms of different materials and spherical quantum dots is different. At a suitable temperature, the organic ligands on the crystal faces of the spherical quantum dots with higher activity will preferentially fall off, thereby promoting the growth of arms. In addition, in step (2), oleic acid, as a weak ligand, can make the nanoarms more inclined to grow radially. Therefore, changing the concentration of oleic acid will lead to a change in the diameter of the multi-legged nanoarms. Long-chain alkylphosphonic acid, as a strong ligand, can make the nanoarms grow axially. Therefore, long-chain alkylphosphonic acid can be used to control the length of the nanoarms. Oleic acid and long-chain alkylphosphonic acid together regulate the size of the nanoarms.

[0053] A third typical embodiment of the present invention provides the above-mentioned multi-legged nanocrystals for photocatalytic reforming of biomass and its derivatives to produce hydrogen under visible light conditions.

[0054] In one or more embodiments, the biomass and its derivatives include one or more of triethylamine, triethanolamine, diisopropylamine, diethylamine, L-cysteine, lactic acid, mercaptopropionic acid, mercaptoacetic acid, mercaptoethylamine, p-methylthiophenol, p-methoxythiophenol, p-trifluoromethylthiophenol, n-butanethiol, n-hexanethiol, methanol, ethanol, isopropanol, lignocellulose, and 5-hydroxymethylfurfural.

[0055] In one or more embodiments, a co-catalyst is also required to be added during the photocatalytic reforming of biomass and its derivatives to produce hydrogen under visible light conditions. The co-catalyst includes: divalent nickel salt, divalent cobalt salt, divalent iron salt, trivalent iron salt and divalent platinum salt.

[0056] Preferably, the divalent nickel salt includes nickel acetate, nickel nitrate, nickel sulfate, or nickel halide;

[0057] Preferably, the divalent cobalt salt includes cobalt acetate, cobalt nitrate, cobalt sulfate, or cobalt halide;

[0058] Preferably, the ferrous salt includes ferrous acetate, ferrous nitrate, ferrous sulfate, or ferrous halide;

[0059] Preferably, the trivalent ferric salt includes ferric acetate, ferric nitrate, ferric sulfate, or ferric halide;

[0060] Preferably, the divalent platinum salt includes platinum acetate, platinum nitrate, platinum sulfate, or platinum halide.

[0061] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0062] Example 1: Preparation of ZnSe / CdS multi-legged nanocrystals

[0063] Preparation of spherical quantum dots ZnSe: A clean magnetic dot was placed in a 100 mL three-necked round-bottom flask, and 32.6 mg ZnO (0.4 mmol), 15 mL 1-octadecene, 760 μL oleic acid (2.4 mmol), and 5 mL octadecylamine were added sequentially. Argon gas was introduced to create a vacuum (repeated 3 times for 1 min) to ensure the entire reaction was carried out in an argon atmosphere. The temperature was then raised to 250 °C to completely dissolve the solution until it became transparent. The prepared Se precursor (0.2 mmol Se was dissolved by sonication in 1 mL tri-n-octylphosphine) was rapidly injected, and the reaction was carried out at 250 °C for 20 min, followed by rapid cooling to room temperature. The precipitate was transferred to two separate 50 mL centrifuge tubes. Three to four times the volume of anhydrous ethanol were added to make the solution cloudy. The tubes were then centrifuged at 10,000 rpm for five minutes to remove the supernatant. Next, 5 mL of n-hexane was added to disperse the precipitate, followed by the addition of anhydrous ethanol (4:1 ratio to n-hexane). The tubes were then centrifuged at 10,000 rpm for five minutes to remove the supernatant. The purified ZnSe was colorless and transparent when dispersed in 10 mL of n-hexane.

[0064] Preparation of ZnSe / CdS multi-legged nanocrystals: A clean magnetic ball was placed in a 100 mL three-necked flask, and 0.4 mmol of cadmium oxide, 2.65 g of tri-n-octylphosphine oxide, 0.4 mmol of octadecylphosphonic acid, and 0.5 mL of oleic acid were added sequentially. Argon gas was introduced to create a vacuum (repeated 3 times for 1 min) to ensure the entire reaction occurred under an argon atmosphere. The temperature was then raised to 350 °C to completely dissolve and clarify the solution. 1.8 mL of tri-n-octylphosphine was then injected. While maintaining the temperature at 350 °C, the pre-prepared S precursor (0.2 mmol of S added to 0.6 mL of tri-n-octylphosphine and dissolved by sonication) and the ZnSe QDs (2.5 × 10⁻⁶) prepared in Example 1 were rapidly injected. -9 A mixture of mol (mol) was reacted at 350℃ for 10 min, then rapidly cooled to room temperature. The mixture was purified twice with methanol and n-hexane in a 2:1 ratio. Finally, it was dispersed in 10 mL of n-hexane. The purified ZnSe / CdS multi-legged nanocrystals were orange-yellow.

[0065] The ultraviolet absorption spectra of the spherical quantum dots ZnSe and ZnSe / CdS multi-legged nanocrystals prepared in this embodiment are shown below. Figure 1 As shown. From Figure 1As can be seen, the first absorption peak of ZnSe quantum dots is located at 389 nm, and the first absorption peak of CdSe / ZnS multi-legged nanocrystals is located at 468 nm.

[0066] High-resolution transmission electron microscopy (TEM) images of the spherical quantum dots ZnSe and ZnSe / CdS multi-legged nanocrystals prepared in this embodiment are shown below. Figure 2 and 3 As shown. Figure 2 As shown, ZnSe quantum dots have a spherical structure with a diameter of approximately 4 nm. Calculations show that the lattice spacing of the (111) crystal plane of ZnSe is 0.327 nm. Figure 3 As shown, the lattice spacing of the (002) crystal plane of CdS is 0.359 nm. The lattice heights of ZnSe and CdS are highly matched, so ZnSe and CdS can form a multi-legged heterostructure.

[0067] Example 2: Preparation of coarse-armed ZnSe / CdS multi-legged nanocrystals

[0068] The preparation of spherical quantum dots ZnSe is the same as in Example 1.

[0069] Preparation of coarse-armed ZnSe / CdS multi-legged nanocrystals: A clean magnetic ball was placed in a 100 mL three-necked flask, and 0.4 mmol of cadmium oxide, 2.65 g of tri-n-octylphosphine oxide, 0.2 mmol of octadecylphosphonic acid, and 1.0 mL of oleic acid were added sequentially. Argon gas was introduced to create a vacuum (repeated 3 times for 1 min) to ensure the entire reaction occurred under an argon atmosphere. The temperature was then raised to 350 °C to completely dissolve and clarify the solution. 1.8 mL of tri-n-octylphosphine was then injected. While maintaining the temperature at 350 °C, the pre-prepared S precursor (0.2 mmol of S added to 0.6 mL of tri-n-octylphosphine and dissolved by sonication) and the ZnSe QDs (2.5 × 10⁻⁶) prepared in Example 1 were rapidly injected. - 9 A mixture of mol (mol) was reacted at 350℃ for 10 min, then rapidly cooled to room temperature. The mixture was purified twice with methanol and n-hexane in a 2:1 ratio. Finally, it was dispersed in 10 mL of n-hexane. The purified ZnSe / CdS multi-legged nanocrystals were orange-yellow.

[0070] Transmission electron microscopy images of the ZnSe / CdS multi-legged nanocrystals prepared in Examples 1 and 2 are shown below. Figure 4 As shown, Figure 4As shown, the ZnSe / CdS multi-legged nanocrystals prepared in Example 1 have thin and long nanoarms, but the ZnSe / CdS multi-legged nanocrystals in Example 2 have thick and short nanoarms. This is because the amounts of oleic acid and the surfactant octadecylphosphonic acid were changed. It can be seen that changing the concentration of oleic acid will lead to a change in the diameter of the multi-legged nanoarms. As a strong ligand, long-chain alkylphosphonic acid can make the nanoarms grow along the axial direction, so the length of the nanoarms can be controlled by long-chain alkylphosphonic acid.

[0071] Example 3: Preparation of ZnTe / CdS multi-legged nanocrystals

[0072] Preparation of spherical quantum dots ZnTe: A clean magnetic dot was placed in a 100 mL three-necked round-bottom flask, and 32.6 mg ZnO (0.4 mmol), 15 mL 1-octadecene, 760 μL oleic acid (2.4 mmol), and 5 mL octadecylamine were added sequentially. Argon gas was introduced to create a vacuum (repeated 3 times for 1 min) to ensure the entire reaction was carried out in an argon atmosphere. The temperature was then raised to 260 °C to completely dissolve the solution until it became transparent. The prepared Te precursor (0.2 mmol Te was dissolved by sonication in 1 mL tri-n-octylphosphine) was rapidly injected, and the reaction was carried out at 260 °C for 20 min, followed by rapid cooling to room temperature. Transfer the solution to two 50 mL centrifuge tubes, add 3 to 4 times the volume of anhydrous ethanol to make the solution cloudy, then centrifuge at 10,000 rpm for 5 minutes to remove the supernatant; add 5 mL of n-hexane to disperse the precipitate, then add anhydrous ethanol in a ratio of 4:1, centrifuge at 10,000 rpm for 5 minutes to remove the supernatant.

[0073] Preparation of ZnTe / CdS multi-legged nanocrystals: A clean magnetic ball was placed in a 100 mL three-necked flask, and 0.4 mmol of cadmium oxide, 2.65 g of tri-n-octylphosphine oxide, 0.2 mmol of octadecylphosphonic acid, and 1.0 mL of oleic acid were added sequentially. Argon gas was introduced to create a vacuum (repeated 3 times for 1 min) to ensure the entire reaction occurred under an argon atmosphere. The temperature was then raised to 350 °C until the solution was completely dissolved and transparent. 1.8 mL of tri-n-octylphosphine was then injected, and the temperature was maintained at 350 °C. The pre-prepared S precursor (0.2 mmol of S added to 0.6 mL of tri-n-octylphosphine and dissolved by sonication) and ZnTe QDs (2.5 × 10⁻⁶) were then rapidly injected. -9 A mixture of mol (mol) was reacted at 370°C for 10 min, then rapidly cooled to room temperature. The mixture was purified twice with methanol and n-hexane in a 2:1 ratio. Finally, it was dispersed in 10 mL of n-hexane. The purified ZnTe / CdS multi-legged nanocrystals were orange-yellow, and slightly darker in color than the ZnSe / CdS multi-legged nanocrystals in Example 2. Figure 5This is a transmission electron microscope (TEM) image of the ZnTe / CdS multi-legged nanocrystals synthesized in this embodiment.

[0074] Example 4: Preparation of ZnTe / CdSe multi-legged nanocrystals

[0075] The preparation of spherical quantum dots ZnTe is the same as in Example 2.

[0076] Preparation of ZnTe / CdSe multi-legged nanocrystals: A clean magnetic ball was placed in a 100 mL three-necked flask, and 0.4 mmol of cadmium oxide, 2.65 g of tri-n-octylphosphine oxide, 0.2 mmol of octadecylphosphonic acid, and 0.5 mL of oleic acid were added sequentially. Argon gas was introduced to create a vacuum (repeated 3 times for 1 min) to ensure the entire reaction occurred under an argon atmosphere. The temperature was then raised to 350 °C until the solution was completely dissolved and transparent. 1.8 mL of tri-n-octylphosphine was then injected, and the temperature was maintained at 360 °C. The pre-prepared Se precursor (0.2 mmol of Se added to 0.6 mL of tri-n-octylphosphine and dissolved by sonication) and ZnTe QDs (2.5 × 10⁻⁶) were then rapidly injected. -9 A mixture of [amount] mol was reacted at 360℃ for 10 min, then rapidly cooled to room temperature. The mixture was purified twice with methanol and n-hexane in a 2:1 ratio. Finally, it was dispersed in 10 mL of n-hexane to obtain purified ZnTe / CdSe multi-legged nanocrystals.

[0077] Example 5: Preparation of ZnSe / CdSe multi-legged nanocrystals

[0078] The preparation of spherical quantum dots ZnSe is the same as in Example 1.

[0079] Preparation of ZnSe / CdSe multi-legged nanocrystals: A clean magnetic ball was placed in a 100 mL three-necked flask. 0.4 mmol of cadmium oxide, 2.65 g of tri-n-octylphosphine oxide, 0.2 mmol of octadecylphosphonic acid, and 0.5 mL of oleic acid were added sequentially. Argon gas was introduced to create a vacuum (repeated 3 times for 1 min) to ensure the entire reaction occurred under an argon atmosphere. The temperature was then raised to 340 °C until the solution was completely dissolved and transparent. 1.8 mL of tri-n-octylphosphine was then injected, and the temperature was maintained at 360 °C. The pre-prepared Se precursor (0.2 mmol of Se added to 0.6 mL of tri-n-octylphosphine and dissolved by sonication) and ZnSe QDs (2.5 × 10⁻⁶) were then rapidly injected. -9 A mixture of [amount] mol was reacted at 340 °C for 10 min, then rapidly cooled to room temperature. The mixture was purified twice with methanol and n-hexane in a 2:1 ratio. Finally, it was dispersed in 10 mL of n-hexane to obtain purified ZnTe / CdSe multi-legged nanocrystals. Figure 6 This is a transmission electron microscope (TEM) image of the ZnSe / CdSe multi-legged nanocrystals synthesized in this embodiment.

[0080] Example 6: Preparation of CdTe / CdSe multi-legged nanocrystals

[0081] Preparation of spherical quantum dots CdTe: A clean magnetic dot was placed in a 100 mL three-necked round-bottom flask. CdO (0.4 mmol), 15 mL of 1-octadecene, 760 μL of oleic acid (2.4 mmol), and 5 mL of octadecylamine were added sequentially. Argon gas was introduced to create a vacuum (repeated 3 times for 1 min) to ensure the entire reaction was carried out in an argon atmosphere. The temperature was then raised to 260 °C to completely dissolve the solution until it became transparent. The prepared Te precursor (0.2 mmol of Te was added to 1 mL of tri-n-octylphosphine and dissolved by sonication) was quickly injected. The reaction was carried out at 280 °C for 10 min, and then rapidly cooled to room temperature. Transfer the solution to two 50 mL centrifuge tubes, add 3 to 4 times the volume of anhydrous ethanol to make the solution cloudy, then centrifuge at 10,000 rpm for 5 minutes to remove the supernatant; add 5 mL of n-hexane to disperse the precipitate, then add anhydrous ethanol in a ratio of 4:1, centrifuge at 10,000 rpm for 5 minutes to remove the supernatant.

[0082] Preparation of CdTe / CdSe multi-legged nanocrystals

[0083] Place a clean magnetic flask in a 100 mL three-necked flask, and add 0.4 mmol of cadmium oxide, 2.65 g of tri-n-octylphosphine oxide, 0.2 mmol of octadecylphosphonic acid, and 0.5 mL of oleic acid sequentially. Purge with argon gas to create a vacuum (repeated 3 times for 1 min) to ensure the entire reaction occurs under an argon atmosphere. Then, heat to 340 °C until the solution is completely dissolved and transparent. Next, inject 1.8 mL of tri-n-octylphosphine and maintain the temperature at 360 °C. Quickly inject the pre-prepared Se precursor (0.2 mmol of Se added to 0.6 mL of tri-n-octylphosphine and dissolved by sonication) and CdTe QDs (2.5 × 10⁻⁶). -9 A mixture of mol (mol) was reacted at 380 °C for 10 min, then rapidly cooled to room temperature. The mixture was purified twice with methanol and n-hexane in a 2:1 ratio. Finally, it was dispersed in 10 mL of n-hexane to obtain purified CdTe / CdSe multipodial nanocrystals.

[0084] Example 7: Preparation of CdTe / CdS multi-legged nanocrystals

[0085] The preparation of spherical quantum dots CdTe is the same as in Example 6.

[0086] Preparation of CdTe / CdS multi-legged nanocrystals

[0087] Place a clean magnetic flask in a 100 mL three-necked flask, and add 0.4 mmol of cadmium oxide, 2.65 g of tri-n-octylphosphine oxide, 0.2 mmol of octadecylphosphonic acid, and 0.5 mL of oleic acid sequentially. Purge with argon gas to create a vacuum (repeated 3 times for 1 min) to ensure the entire reaction occurs under an argon atmosphere. Then, heat to 340 °C until the solution is completely dissolved and transparent. Next, inject 1.8 mL of tri-n-octylphosphine and maintain the temperature at 360 °C. Quickly inject the pre-prepared S precursor (0.2 mmol of S added to 0.6 mL of tri-n-octylphosphine and dissolved by sonication) and CdTe QDs (2.5 × 10⁻⁶). -9 A mixture of mol (mol) was reacted at 360℃ for 10 min, then rapidly cooled to room temperature. The mixture was purified twice with methanol and n-hexane in a 2:1 ratio. Finally, it was dispersed in 10 mL of n-hexane to obtain purified CdTe / CdS multipod nanocrystals.

[0088] Example 8

[0089] This embodiment provides a method for preparing multi-legged nanocrystals by controlling the surface ligand strategy of nanomaterials. The multi-legged nanocrystals prepared in Examples 1 to 7 are hydrophobic and cannot react with water, so it is necessary to replace the hydrophobic ligands with hydrophilic ligands. The method includes the following steps:

[0090] (2) The multi-legged nanocrystals prepared in Examples 1-7 were dispersed in 10 mL of n-hexane, 0.4 mL of 3-mercaptopropionic acid and a small amount of NaOH particles were added, and the mixture was stirred vigorously for 20 minutes at a speed of 8000 rpm / min for 5 minutes. After centrifugation, the prepared multi-legged nanocrystals were washed with 10 mL of n-hexane to remove excess 3-mercaptopropionic acid and other impurities.

[0091] (3) Disperse the multi-legged nanocrystals in 10 mL of water, add 40 mL of acetone, set the rotation speed to 8000 rpm / min, and centrifuge for 5 min. After centrifugation, disperse the multi-legged nanocrystals in 10 mL of water. The dispersions of the multi-legged nanocrystals prepared in Examples 1 to 7 are respectively a, b, c, d, e, f, and g.

[0092] Experimental Example 1

[0093] This experimental example provides a method for reforming biomass and producing hydrogen using a multi-legged nanocrystal photocatalytic system, specifically including the following steps:

[0094] Take 0.4 mL of the a (ZnSe / CdS) multi-legged nanocrystal dispersion prepared in Example 9 and the d (ZnTe / CdSe) multi-legged nanocrystal dispersion prepared in Example 9 and add them to a 15 mL Pyrex test tube, respectively. Add 4.6 mL of water for dispersion, add 1.0 mL of triethylamine as biomass, add 0.2 mg of nickel acetate as a co-catalyst, seal the tube, remove the air in the test tube with nitrogen, inject 1 mL of methane as an internal standard, then seal with wax, irradiate the Pyrex test tube with a 460 nm LED lamp, and detect the generated hydrogen gas with a gas chromatograph.

[0095] Figure 7 The graphs show the hydrogen production in the triethylamine reforming system using ZnSe / CdS multi-legged nanocrystals and ZnTe / CdSe multi-legged nanocrystals. It can be seen that the ZnSe / CdS multi-legged nanocrystals exhibit excellent photocatalytic hydrogen production activity. After 2 hours of reaction, the ZnSe / CdS multi-legged nanocrystals produced 54.96 μmol of hydrogen, while the ZnTe / CdSe multi-legged nanocrystals produced 67.32 μmol. After 4 hours of reaction, the ZnSe / CdS multi-legged nanocrystal photocatalyst produced 39.52 μmol of hydrogen per hour. -1 mg -1 Hydrogen gas is produced at a rate of 40.28 μmol / h⁻¹ from ZnTe / CdSe multi-legged nanocrystals. -1 mg -1 Hydrogen gas is produced at a rate of [missing information].

[0096] Experiment Example 2

[0097] Take 0.4 mL of the c (ZnTe / CdS in Example 3) multi-legged nanocrystal dispersion prepared in Example 9, add it to a 15 mL Pyrex test tube, and add 4.6 mL of water for dispersion. Add 1.0 mL of triethylamine, isopropanol, triethanolamine, L-ascorbic acid sodium, and anhydrous ethanol as biomass to the system, and 0.2 mg of nickel acetate as a co-catalyst. Seal the tube, remove air from the test tube with nitrogen, inject 1 mL of methane as an internal standard, and then seal with wax. Irradiate the Pyrex test tube with a 460 nm LED lamp, and detect the generated hydrogen gas using a gas chromatograph. The results are as follows: Figure 8 As shown. From Figure 8 As can be seen from the data, when using isopropanol, the amount of hydrogen produced after 2 hours of light irradiation was 29.46 μmol; when using triethanolamine, the amount of hydrogen produced after 2 hours of light irradiation was 14.61 μmol; when using sodium L-ascorbate, the amount of hydrogen produced after 2 hours of light irradiation was 54.2 μmol; when using anhydrous ethanol, the amount of hydrogen produced after 2 hours of light irradiation was 21.13 μmol; and when using triethylamine, the amount of hydrogen produced after 2 hours of light irradiation was 54.96 μmol.

[0098] Experimental Example 3

[0099] Take 0.4 mL of the CdTe / CdS multi-legged nanocrystal dispersion prepared in Example 9 (Example 7) and add it to a 15 mL Pyrex test tube. Add 4.6 mL of water for dispersion, add 1.0 mL of triethylamine as biomass, add 0.2 mg of nickel acetate as a co-catalyst, seal the tube, remove the air in the test tube with nitrogen, inject 1 mL of methane as an internal standard, then seal with wax, irradiate the Pyrex test tube with a 460 nm LED lamp, and detect the generated hydrogen gas using a gas chromatograph.

[0100] Figure 9 The image shows the long-term hydrogen production of the CdTe / CdS multi-legged nanocrystal reforming triethylamine system. It can be seen that the CdTe / CdS multi-legged nanocrystals exhibit excellent photocatalytic hydrogen production activity and stability. After 8 hours of reaction, the CdTe / CdS multi-legged nanocrystal photocatalyst achieved a hydrogen production rate of 38.28 μmol / h⁻¹. -1 mg -1 Hydrogen gas is produced at a rate of [missing information].

[0101] Experiment Example 4

[0102] Take 0.4 mL of the multi-legged nanocrystal dispersion a (ZnSe / CdS in Example 1) prepared in Example 9 and the multi-legged nanocrystal dispersion b (ZnSe / CdS in Example 2) prepared in Example 9 and add them to a 15 mL Pyrex test tube, respectively. Add 4.6 mL of water for dispersion, add 1.0 mL of triethylamine as biomass, add 0.2 mg of nickel acetate as a co-catalyst, seal the tube, remove the air in the test tube with nitrogen, inject 1 mL of methane as an internal standard, then seal with wax, irradiate the Pyrex test tube with a 460 nm LED lamp, and detect the generated hydrogen gas with a gas chromatograph.

[0103] from Figure 10 It can be seen that within 4 hours, the thin arm of the ZnSe / CdS multi-legged nanocrystal prepared in Example 1 produced 376.15 μmol of hydrogen, while the thick arm of the ZnSe / CdS multi-legged nanocrystal prepared in Example 2 produced 51.11 μmol of hydrogen. The hydrogen production performance of the thin arm of the ZnSe / CdS multi-legged nanocrystal is significantly higher than that of the thick arm. Because the diameter of the thin arm is smaller than that of the thick arm, the distance for electrons to migrate to the surface of the thin arm multi-legged body is shorter, resulting in a much better photocatalytic hydrogen production effect for the thin arm multi-legged body. The XRD patterns of the ZnSe / CdS multi-legged nanocrystals in Example 1 and Example 2 are shown below. Figure 11 As shown.

Claims

1. A method for preparing multi-legged nanocrystals for hydrogen production from biomass and its derivatives via photocatalytic reforming, characterized in that, The multi-legged nanocrystals are made with spherical quantum dots as the core, and multiple nanoarms are grown on the surface of the core under the control of long-chain alkylphosphonic acid. The spherical quantum dots include one or more of CdSe, CdTe, CdS, ZnSe, ZnTe, and ZnS quantum dots; the nanoarms include one of ZnS, CdS, CdSe, ZnSe, and ZnTe. Includes the following steps: (1) In an inert gas atmosphere, ZnO or CdO is dissolved in organic solvent A, then oleic acid and stabilizer are added, and the solution is heated until it is completely dissolved and transparent. The precursor solution of Se, Te or S is quickly injected, and the reaction is heated and stirred. After the reaction is completed, anhydrous ethanol is added to obtain a precipitate. After washing, spherical quantum dots can be obtained. (2) In an inert gas atmosphere, ZnO or CdO is dissolved in organic solvent B, then long-chain alkylphosphonic acid and oleic acid are added, and the solution is heated until it is completely dissolved and transparent. The precursor solution of Se, Te or S and the spherical quantum dots obtained in step (1) are quickly injected, and the reaction is heated and stirred. After the reaction is completed, the temperature is quickly lowered to room temperature, and the multi-legged nanocrystals are obtained after purification with methanol and n-hexane. In step (2), oleic acid, as a weak ligand, makes the nanoarms more inclined to grow radially. Therefore, changing the concentration of oleic acid will lead to a change in the diameter of the multi-legged nanoarms. Long-chain alkylphosphonic acid, as a strong ligand, makes the nanoarms grow axially. Therefore, long-chain alkylphosphonic acid is used to control the length of the nanoarms. Oleic acid and long-chain alkylphosphonic acid together regulate the size of the nanoarms. In step (2), the long-chain alkylphosphonic acid includes any one or more of dodecyl phosphate, tetradecyl phosphate, hexadecyl phosphate, and octadecyl phosphate.

2. The method for preparing multi-legged nanocrystals as described in claim 1, characterized in that, In step (1), the organic solvent A includes octadecene or tri-n-octylphosphine oxide; Alternatively, in step (1), the stabilizer is octadecylamine.

3. The method for preparing multi-legged nanocrystals as described in claim 1, characterized in that, In step (1), when the raw material is ZnO, the temperature at which the solution is heated to completely dissolve and become transparent is 245~255 ℃; when the raw material is CdO, the temperature at which the solution is heated to completely dissolve and become transparent is 345~355 ℃. Alternatively, in step (1), when the raw material is ZnO, the heating and stirring reaction temperature is 245~255 ℃; the reaction time is 18~22 min; when the raw material is CdO, the heating and stirring reaction temperature is 345~355 ℃; the reaction time is 8~12 min. Alternatively, in step (1), the molar ratio of Se, Te or S in the precursor solution of ZnO or CdO, oleic acid and Se, Te or S is 1:5~7:0.

5.

4. The method for preparing multi-legged nanocrystals as described in claim 3, characterized in that, In step (1), when the raw material is ZnO, the temperature at which the solution is heated to completely dissolve and become transparent is 250 °C; when the raw material is CdO, the temperature at which the solution is heated to completely dissolve and become transparent is 350 °C.

5. The method for preparing multi-legged nanocrystals as described in claim 3, characterized in that, In step (1), when the raw material is ZnO, the heating and stirring reaction temperature is 250 ℃; the reaction time is 20 min; when the raw material is CdO, the heating and stirring reaction temperature is 350 ℃; the reaction time is 10 min.

6. The method for preparing multi-legged nanocrystals as described in claim 3, characterized in that, In step (1), the molar ratio of Se, Te or S in the precursor solution of ZnO or CdO, oleic acid and Se, Te or S is 1:5:0.

5.

7. The method for preparing multi-legged nanocrystals as described in claim 1, characterized in that, The method for preparing the precursor solution of Se, Te or S includes: dissolving Se, Te or S in tri-n-octylphosphine.

8. The method for preparing multi-legged nanocrystals as described in claim 1, characterized in that, In step (2), the organic solvent B includes tri-n-octylphosphine oxide.

9. The method for preparing multi-legged nanocrystals as described in claim 1, characterized in that, In step (2), the long-chain alkylphosphonic acid is octadecyl phosphate.

10. The method for preparing multi-legged nanocrystals as described in claim 1, characterized in that, In step (2), when the raw material is ZnO, the temperature at which the solution is heated to completely dissolve and become transparent is 245~255 ℃; when the raw material is CdO, the temperature at which the solution is heated to completely dissolve and become transparent is 345~355 ℃. Alternatively, in step (2), when the raw material is ZnO, the heating and stirring reaction temperature is 245~255 ℃; the reaction time is 18~22 min; when the raw material is CdO, the heating and stirring reaction temperature is 345~355 ℃; the reaction time is 8~12 min. Alternatively, in step (2), the molar ratio of Se, Te, or S in the precursor solution of ZnO or CdO, long-chain alkylphosphonic acid, oleic acid, Se, Te, or S, and the spherical quantum dots obtained in step (1) is: 4:4:15~17:2:2~3×10 -6 .

11. The method for preparing multi-legged nanocrystals as described in claim 10, characterized in that, In step (2), when the raw material is ZnO, the temperature at which the solution is heated to completely dissolve and become transparent is 250 °C; when the raw material is CdO, the temperature at which the solution is heated to completely dissolve and become transparent is 350 °C.

12. The method for preparing multi-legged nanocrystals as described in claim 10, characterized in that, In step (2), when the raw material is ZnO, the heating and stirring reaction temperature is 250 ℃; the reaction time is 20 min; when the raw material is CdO, the heating and stirring reaction temperature is 350 ℃; the reaction time is 10 min.

13. The method for preparing multi-legged nanocrystals as described in claim 10, characterized in that, In step (2), the molar ratio of Se, Te, or S in the precursor solution of ZnO or CdO, long-chain alkylphosphonic acid, oleic acid, Se, Te, or S, and the spherical quantum dots obtained in step (1) is 4:4:16:2:2.5×10⁻⁶. -6 .

14. The application of the multi-legged nanocrystals obtained by the preparation method of any one of claims 1-13 in the photocatalytic reforming of biomass and its derivatives for hydrogen production under visible light conditions.

15. The application as described in claim 14, characterized in that, The biomass and its derivatives include one or more of the following: triethylamine, triethanolamine, diisopropylamine, diethylamine, L-cysteine, lactic acid, mercaptopropionic acid, mercaptoacetic acid, mercaptoethylamine, p-methylthiophenol, p-methoxythiophenol, p-trifluoromethylthiophenol, n-butanethiol, n-hexanethiol, methanol, ethanol, isopropanol, lignocellulose, and 5-hydroxymethylfurfural.

16. The application as described in claim 14, characterized in that, In the process of photocatalytic reforming of biomass and its derivatives to produce hydrogen under visible light conditions, a co-catalyst is also required. The co-catalyst includes: divalent nickel salt, divalent cobalt salt, divalent iron salt, trivalent iron salt and divalent platinum salt.

17. The application as described in claim 16, characterized in that, The divalent nickel salts include nickel acetate, nickel nitrate, nickel sulfate, or nickel halides.

18. The application as described in claim 16, characterized in that, The divalent cobalt salts include cobalt acetate, cobalt nitrate, cobalt sulfate, or cobalt halide.

19. The application as described in claim 16, characterized in that, The divalent ferric salts include ferrous acetate, ferrous nitrate, ferrous sulfate, or ferrous halide.

20. The application as described in claim 16, characterized in that, The trivalent ferric salts include ferric acetate, ferric nitrate, ferric sulfate, or ferric halide.

21. The application as described in claim 16, characterized in that, The divalent platinum salts include platinum acetate, platinum nitrate, platinum sulfate, or platinum halide.

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