Preparation method of palladium quantum dot loaded barium titanate composite material

Abstract

The invention discloses a preparation method of a palladium quantum dot loaded barium titanate composite material. The piezoelectric catalytic performance is improved through morphology regulation and interface engineering cooperation. The BTO nanowire is converted from a cubic phase to a strong ferroelectric tetragonal phase by adopting an electrostatic spinning technology and cooperating with a 700 DEG C precise annealing strategy, so that the built-in electric field and piezoelectric response are enhanced, the brittle fracture of the nanowire caused by high temperature is avoided, and the integrity and flexibility of a one-dimensional structure are guaranteed. In the active site loading stage, a synchronous process of ultrasonic dispersion and violent stirring in an ice bath environment is adopted, local concentration polarization is eliminated, nanowire agglomeration is disassembled, and palladium quantum dots are driven to uniformly form a Pd (111) / BTO (110) epitaxial matching heterojunction in situ on a BTO (110) crystal face. According to the high-quality Schottky interface, the charge transfer efficiency is enhanced, the catalytic reduction kinetics is improved, and the hydrogen evolution rate reaches 3464.28 [mu] molgh and is increased by 2.8 times compared with pure BTO under the condition that only 0.75 wt.% of palladium is loaded. Technological parameters are easy to control, the cost is low, and a feasible technical scheme is provided for industrialization of piezoelectric catalytic hydrogen production.

Description

Technical Field

[0001] This application belongs to the field of piezoelectric catalysis technology, specifically relating to a method for preparing barium titanate composite materials. Background Technology

[0002] The global energy crisis continues to escalate, and environmental challenges are becoming increasingly urgent, necessitating the development of clean and renewable energy alternatives. Hydrogen energy, with its outstanding advantages of high energy density and zero carbon emissions, is a highly promising energy carrier for the future; therefore, developing efficient and low-cost hydrogen production technologies is particularly crucial.

[0003] Traditional hydrogen production methods largely rely on fossil fuel reforming or energy-intensive water electrolysis, resulting in high carbon emissions and energy consumption, failing to meet the demands for clean and sustainable energy development. In recent years, piezoelectric catalysis has emerged as an innovative and sustainable hydrogen production method. This technology utilizes mechanical energy such as ultrasound and fluid flow vibration to drive chemical reactions like water splitting, providing a new technological pathway for hydrogen production. Its core mechanism is as follows: when a piezoelectric material with a non-centrosymmetric crystal structure is deformed by mechanical force, it generates a spontaneous built-in electric field. This built-in electric field effectively separates charge carriers, allowing electrons to migrate to the catalyst surface to participate in hydrogen ion reduction, while holes participate in oxidation reactions such as organic degradation, thereby achieving highly efficient catalytic reactions.

[0004] Barium titanate (BaTiO3, BTO) is a lead-free ferroelectric material that has become a key research material in the field of piezoelectric catalysis due to its excellent piezoelectric response, good chemical stability, and environmental friendliness. However, pure-phase BTO has significant limitations when used as a piezoelectric catalyst. The electron-hole pairs it generates tend to recombine rapidly before participating in surface catalytic reactions, resulting in low quantum efficiency and catalytic performance that fails to meet the requirements of practical applications.

[0005] To improve the catalytic performance of piezoelectric catalysts, various modification methods have been developed in existing technologies. One approach involves developing piezoelectric catalysts with low-dimensional nanostructures such as nanowires and nanosheets. These one-dimensional or two-dimensional structures not only provide a larger specific surface area for the catalytic reaction but also allow the piezoelectric catalyst to undergo greater elastic deformation under ultrasonic vibration, thereby enhancing the surface reaction process and inducing a strong polarization effect, thus improving catalytic performance. Another approach involves constructing semiconductor / ferroelectric heterojunctions to regulate the charge transfer process on the material surface, such as TiO2 / BTO heterojunctions. The built-in electric field formed at the heterojunction can serve as a highly efficient electron trapping center, effectively promoting charge separation and migration to catalytically active sites, thereby improving piezoelectric catalytic activity. However, the hydrogen evolution rates of the aforementioned BTO-based piezoelectric composite materials reported so far still fall short of the requirements for practical applications, making large-scale application difficult.

[0006] Noble metals such as silver (Au), platinum (Pt), and palladium (Pd) are widely used as ideal co-catalysts for electrocatalytic water splitting because their adsorption energy for hydrogen and Gibbs free energy for the hydrogen evolution reaction (HER) are close to their optimal values, which can effectively accelerate the rate-determining step of the HER reaction. However, the high cost of raw materials for noble metal co-catalysts further limits their commercialization and practical application.

[0007] In summary, while existing modification methods for BTO-based piezoelectric catalysts can improve their piezoelectric catalytic performance to some extent, they generally suffer from low hydrogen evolution rates and high costs associated with using precious metal co-catalysts, making it difficult to simultaneously achieve the dual goals of high-voltage electrocatalytic performance and low preparation costs. Therefore, developing BTO-based piezoelectric catalysts that combine high-voltage electrocatalytic hydrogen evolution performance with low precious metal loading has become a pressing technical problem in this field. Summary of the Invention

[0008] Based on this, this study proposes a method for preparing barium titanate composite materials. The core design strategy of morphology control and interface engineering synergistic optimization is adopted. BTO nanowires are prepared by electrospinning to enhance mechanical energy harvesting and active surface area. Then, palladium quantum dots are uniformly anchored by NaBH4 reduction, and a high-performance Pd / BTO composite piezoelectric catalyst is successfully prepared. A Pd(111) / BTO(110) heterojunction with specific crystal plane matching is precisely constructed, realizing the precise control of interface engineering.

[0009] A method for preparing palladium quantum dot-supported barium titanate composite material includes the following steps:

[0010] (1) Take the calcined barium titanate nanowires and disperse them in a mixed solvent composed of deionized water and ethylene glycol to obtain a dispersion;

[0011] (2) Place the dispersion obtained in step (1) in an ice bath environment and simultaneously perform ultrasonic dispersion and vigorous stirring to obtain a suspension;

[0012] (3) Add sodium tetrachloropalladium to the suspension described in step (2) and continue stirring to ensure that palladium ions are uniformly adsorbed on the surface of barium titanate nanowires to obtain a composite dispersion.

[0013] (4) Add sodium hydroxide solution to the composite dispersion described in step (3) to obtain an alkaline system;

[0014] (5) Under the conditions of ice bath and vigorous stirring, sodium borohydride solution is added dropwise to the alkaline system. The reduction reaction is completed while maintaining the ice bath environment, so as to ensure that palladium quantum dots grow uniformly in situ on the surface of barium titanate to obtain the reaction product.

[0015] (6) The reaction product was washed repeatedly with deionized water and ethanol and then dried.

[0016] In step (1), the weight ratio of deionized water to ethylene glycol is 25:1.

[0017] In step (2), the ice bath temperature is 0-4℃, and the ultrasonic dispersion and stirring time is 1h.

[0018] The stirring time in step (3) is 0.5h.

[0019] In step (4), the pH of the alkaline system is adjusted to 10.

[0020] The drying temperature in step (5) is 70℃.

[0021] The preparation method of the barium titanate nanowires in step (1) is as follows:

[0022] Mix 4-5 parts ethanol, 1 part deionized water, and 3-4 parts acetic acid by weight, then add 5 wt.% polyvinylpyrrolidone and stir to obtain the base solution;

[0023] After the above base solution is stirred until transparent, barium acetate is added and stirred continuously. Then, tetrabutyl titanate is added dropwise. The molar ratio of barium to titanium is set to 1:1 according to the stoichiometric ratio. The final mixed solution is stirred for 2 hours to obtain a stable precursor sol.

[0024] The prepared precursor sol was electrospun with the following parameters: feed rate 3 mL / h and applied electric field strength 1.5 kV / cm.

[0025] Two-step annealing: The sample collected by electrospinning is placed in an air atmosphere and annealed using a specific two-step heating program: Step 1: Heat to 350℃ to remove the polymer; Step 2: Heat to the target temperature of 550-850℃ to crystallize and obtain the sample.

[0026] The sample was calcined and held at the target crystallization temperature, and then naturally cooled to obtain barium titanate nanowires.

[0027] Preferably, the heating rate in the first heating step is 5℃ / min, and the heating rate in the second heating step is 2℃ / min.

[0028] The advantages and effects of this invention are as follows:

[0029] In an ice bath environment, compared to the situation without ultrasonic cavitation, where newly generated Pd quantum dots tend to grow rapidly in localized high-concentration areas or physically aggregate due to collisions, the process design employing simultaneous ultrasonic dispersion and vigorous stirring achieves a dual optimization effect: on the one hand, it allows barium titanate (BTO) nanowires to fully depolymerize and uniformly disperse in the mixed solvent, avoiding the obstruction of active sites caused by nanowire aggregation; on the other hand, it promotes the full contact and uniform adsorption of Pd²⁺ ions dissociated from sodium tetrachloropalladate onto the surface of BTO nanowires, laying the foundation for subsequent reduction reactions. After reduction with sodium borohydride, palladium quantum dots can be in situ and uniformly anchored on the surface of BTO nanowires, precisely forming a Pd(111) / BTO(110) crystal plane-matched heterojunction, effectively enhancing the interfacial charge transfer efficiency, while significantly reducing the loading of the noble metal palladium (optimally only 0.75 wt.%). This significantly controls the material preparation cost while ensuring high-voltage electrocatalytic performance, solving the pain points of uneven noble metal loading, large dosage, and high cost in existing technologies.

[0030] By optimizing the annealing process, 700℃ was selected as the optimal annealing temperature for BTO nanowires. This temperature can precisely drive the phase transformation of BTO nanomaterials, completely transforming them from a cubic (paraelectric) phase to a tetragonal (ferroelectric) phase. This significantly improves the piezoelectric response performance and built-in electric field strength of the material, effectively promoting electron-hole pair separation and solving the problem of low quantum efficiency in pure BTO. Simultaneously, annealing at 700℃ avoids morphological defects such as brittle fracture and shortening of BTO nanowires caused by high temperatures (above 700℃), ensuring the integrity and flexibility of the nanowires' one-dimensional structure. It retains the advantages of high specific surface area and strong elastic deformation of low-dimensional structures while possessing a stable ferroelectric phase structure. This allows the piezoelectric catalytic hydrogen evolution rate of the composite material to reach 3464.28 μmol・g⁻¹・h⁻¹, approximately 2.8 times higher than that of pure BTO, breaking through the technical bottleneck of low hydrogen evolution rate in existing BTO-based composite materials.

[0031] Employing a synergistic strategy of morphology control and interface engineering, the overall process is based on mature technologies such as electrospinning and chemical reduction. The operation steps are clear, and parameters are easily controlled (e.g., annealing rate, pH value, and reaction temperature can all be precisely adjusted), requiring no complex equipment or harsh reaction conditions. The various process steps exhibit strong adaptability; the 700℃ annealing and palladium quantum dot loading processes are synergistically optimized, enabling stable mass production of Pd / BTO composite materials that combine high-voltage electrocatalytic performance, low noble metal loading, and high cycle stability. This not only meets the practical application requirements for catalytic activity and stability but also reduces the difficulty of large-scale production, providing a feasible path for the industrialization and promotion of piezoelectric catalytic hydrogen production technology. Attached Figure Description

[0032] Figure 1 XRD patterns of BTO at different calcination temperatures.

[0033] Figure 2 Scanning electron microscope (SEM) images of BTO (a) and 0.75%Pd-BTO (c), and fiber diameter distribution maps of the corresponding samples as insets; transmission electron microscope (TEM) images of BTO (b) and 0.75%Pd-BTO (f); high-resolution transmission electron microscope (HRTEM) images of BTO (c) and 0.75%Pd-BTO (g); selected area electron diffraction (SAED) patterns of BTO (d) and 0.75%Pd-BTO (h); energy dispersive spectroscopy (EDS) plots of Ba, Ti, O and Pd elements.

[0034] Figure 3 The image shows the elemental energy spectrum of the BTO sample and its scanning electron microscope (SEM) images after calcination at 650℃, 700℃, 750℃, 800℃, and 850℃, respectively.

[0035] Figure 4 (a) Hydrogen production rate of BTO subjected to ultrasonic treatment at different calcination temperatures; (b) Hydrogen production rate of Pd-BTO with different palladium loading ratios; (c) Cycling performance of 0.75% Pd-BTO under ultrasonic treatment; (d) Comparison with recently reported piezoelectric catalysts.

[0036] Figure 5 This is a schematic diagram of the piezoelectric catalytic mechanism and atomic structure of the material. Detailed Implementation

[0037] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0038] Example 1

[0039] This invention discloses a method for preparing a palladium quantum dot-supported barium titanate composite material, comprising the following steps:

[0040] (1) Substrate dispersion treatment: Barium titanate nanowires calcined at 700℃ were dispersed in a mixed solvent consisting of 25 mL of deionized water and 1 mL of ethylene glycol to obtain a suspension; the suspension was placed in an ice bath environment and simultaneously subjected to ultrasonic dispersion and vigorous stirring for 1 h.

[0041] (2) Palladium ion adsorption: Add a measured amount of sodium tetrachloropalladium (Na2PdCl4) to the above suspension and continue stirring for 0.5 h to ensure that palladium ions (Pd²⁺) are uniformly adsorbed on the surface of barium titanate nanowires.

[0042] (3) pH adjustment of the system: Add sodium hydroxide (NaOH) solution to the adsorbed suspension to adjust the pH value of the system to about 10;

[0043] (4) In-situ reduction growth of palladium quantum dots: Under the conditions of ice bath and vigorous stirring, sodium borohydride (NaBH4) solution was added dropwise to the system to complete the reduction reaction while maintaining the ice bath environment, so as to ensure that palladium quantum dots (Pd-QDs) grow uniformly in situ on the BTO surface;

[0044] (5) Product purification and drying: The Pd / BTO obtained from the reaction was repeatedly washed with deionized water and ethanol, and finally dried at 70°C; a series of samples 0.25%Pd-BTO-2.0%Pd-BTO with palladium quantum dot loading of 0.2-2wt.% were prepared.

[0045] The preparation method of the barium titanate nanowires in step (1) is as follows:

[0046] Preparation of mixed solvent and polyvinylpyrrolidone (PVP) solution: Mix ethanol, deionized water and acetic acid in a weight ratio of 5:1:4, add 5 wt.% PVP to the mixed solution and dissolve to obtain the base solution;

[0047] Preparation of precursor sol: After the above basic solution is stirred until transparent, barium acetate is added and stirred continuously. Then, tetrabutyl titanate (TBT) is added dropwise. The molar ratio of barium (Ba) to titanium (Ti) is set to 1:1 according to the stoichiometric ratio. The final mixed solution is stirred for 2 hours to obtain a stable precursor sol.

[0048] Electrospinning treatment: The prepared precursor sol was electrospinned. The spinning process parameters were: feed rate 3 mL / h, applied electric field strength 1.5 kV / cm.

[0049] Two-step annealing: The sample collected by electrospinning is placed in an air atmosphere and annealed using a specific two-step heating program: (1) First step depolymerization: Heat to 350°C at a heating rate of 5°C / min to remove the polymer; (2) Second step crystallization: Heat to different target temperatures (550-850°C) at a heating rate of 2°C / min to crystallize.

[0050] Post-processing: The sample was calcined at the target crystallization temperature and held for 1 hour, followed by natural cooling to obtain barium titanate nanowires.

[0051] The following experiments were conducted to verify the effectiveness of the invention:

[0052] The crystal phase structure of structured barium titanate (BTO) nanomaterials calcined at different temperatures (500℃-850℃) was characterized by X-ray powder diffraction (XRD). Figure 1 The XRD patterns of BTO nanomaterials after calcination within this temperature range are shown in the figure. The diffraction peaks of all samples correspond completely to the barium titanate standard card (PDF#05-0626).

[0053] like Figure 1 As shown, a fine scanning and fitting analysis was performed on the 2θ=44°-46° range in the XRD pattern. The results showed that as the annealing temperature increased, the diffraction peaks in this range shifted significantly, and the degree of splitting of the diffraction peaks corresponding to the BTO (002) and (200) crystal planes gradually increased. This characteristic evolution indicates that when the annealing temperature is higher than 600℃, the BTO nanomaterial undergoes a phase transformation, changing from a cubic phase (paraelectric phase) to a tetragonal phase (ferroelectric phase). The higher the temperature, the more complete the phase transformation and the more stable the tetragonal phase structure.

[0054] Using scanning electron microscopy (SEM) Figure 2 a, 2e) and transmission electron microscopy (TEM). Figure 2 (b) and (2f) characterize the microstructure of the BTO nanomaterials. The results show that the prepared BTO nanomaterials exhibit a one-dimensional nanowire structure with an average diameter of 350-360 nm and a length reaching several micrometers, exhibiting regular morphology and good continuity. Further research revealed that when the annealing temperature exceeds 700℃, the BTO nanowires exhibit significant brittle fracture, and their length is significantly shortened. Figure 3 (b-3f) This morphological defect can severely affect the performance and stability of the material in flexible piezoelectric catalysis applications.

[0055] Combining the integrity of the crystal structure and the stability of the microstructure, 700℃ was determined to be the optimal annealing temperature for BTO nanomaterials. Subsequent experiments used BTO nanomaterials calcined at this temperature as the substrate.

[0056] The hydrogen evolution activity of BTO calcined at different temperatures was tested using 40kHz ultrasonic vibration as the mechanical excitation source. Figure 4 As shown in Figure a, BTO prepared by calcination at 700℃ exhibits the highest hydrogen evolution rate, reaching 1222.77 μmol・g⁻¹・h⁻¹. This result is consistent with the conclusion determined by XRD characterization in the previous paper that BTO calcined at 700℃ possesses a complete ferroelectric phase and an optimized microstructure. Figure 1 , Figure 3 a) The match is perfect, confirming the key regulatory role of crystal phase structure and morphological integrity in the piezoelectric catalytic performance of BTO.

[0057] Figure 4b shows the effect of Pd quantum dot (Pd-QDs) loading on the hydrogen evolution rate of Pd-BTO composites: with the increase of Pd-QDs loading, the hydrogen evolution rate of Pd-BTO exhibits a volcano-like trend. When the Pd-QDs loading is 0.75 wt.%, the hydrogen evolution rate reaches its peak, achieving the optimal piezoelectric catalytic hydrogen evolution performance of 3464.28 μmol・g⁻¹・h⁻¹, which is about 2.8 times higher than that of pure BTO. The hydrogen evolution performance of the 0.75 wt.% Pd-BTO composite is significantly superior: not only does it achieve a substantial improvement compared to pure BTO, but its catalytic activity is also better than most piezoelectric catalytic materials reported in the prior art. Figure 4 c), demonstrating the superior performance of the composite material prepared by this invention in the field of piezoelectric catalytic hydrogen production.

[0058] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a palladium quantum dot-supported barium titanate composite material, characterized in that, Includes the following steps: (1) Take the calcined barium titanate nanowires and disperse them in a mixed solvent composed of deionized water and ethylene glycol to obtain a dispersion; (2) Place the dispersion obtained in step (1) in an ice bath environment and simultaneously perform ultrasonic dispersion and vigorous stirring to obtain a suspension; (3) Add sodium tetrachloropalladium to the suspension described in step (2) and continue stirring to ensure that palladium ions are uniformly adsorbed on the surface of barium titanate nanowires to obtain a composite dispersion. (4) Add sodium hydroxide solution to the composite dispersion described in step (3) to obtain an alkaline system; (5) Under the conditions of ice bath and vigorous stirring, sodium borohydride solution is added dropwise to the alkaline system. The reduction reaction is completed while maintaining the ice bath environment, so as to ensure that palladium quantum dots grow uniformly in situ on the surface of barium titanate to obtain the reaction product. (6) The reaction product is washed repeatedly with deionized water and ethanol and then dried.

2. The method for preparing palladium quantum dot-supported barium titanate composite material according to claim 1, characterized in that: In step (1), the weight ratio of deionized water to ethylene glycol is 25:

1.

3. The method for preparing palladium quantum dot-supported barium titanate composite material according to claim 1, characterized in that: In step (2), the ice bath temperature is 0-4℃, and the ultrasonic dispersion and stirring time is 1h.

4. The method for preparing palladium quantum dot-supported barium titanate composite material according to claim 1, characterized in that: The stirring time in step (3) is 0.5h.

5. The method for preparing palladium quantum dot-supported barium titanate composite material according to claim 1, characterized in that: In step (4), the pH of the alkaline system is adjusted to 10.

6. The method for preparing palladium quantum dot-supported barium titanate composite material according to claim 1, characterized in that: The drying temperature in step (5) is 70℃.

7. The method for preparing palladium quantum dot-supported barium titanate composite material according to claim 1, characterized in that, The preparation method of barium titanate nanowires is as follows: Mix 4-5 parts ethanol, 1 part deionized water, and 3-4 parts acetic acid by weight, then add 5 wt.% polyvinylpyrrolidone and stir to obtain the base solution; After the above base solution is stirred until transparent, barium acetate is added and stirred continuously. Then, tetrabutyl titanate is added dropwise. The molar ratio of barium to titanium is set to 1:1 according to the stoichiometric ratio. The final mixed solution is stirred for 2 hours to obtain a stable precursor sol. The prepared precursor sol was electrospun with the following parameters: feed rate 3 mL / h and applied electric field strength 1.5 kV / cm. Two-step annealing: The sample collected by electrospinning is placed in an air atmosphere and annealed using a specific two-step heating program: Step 1: Heat to 350℃ to remove the polymer; Step 2: Reheat to the target temperature of 550-850℃ and perform crystallization treatment to obtain the sample; The sample was calcined and held at the target crystallization temperature, and then naturally cooled to obtain barium titanate nanowires.

8. The method for preparing palladium quantum dot-supported barium titanate composite material according to claim 7, characterized in that, The heating rate in the first heating step is 5℃ / min, and the heating rate in the second heating step is 2℃ / min.

Images