A type s titanium dioxide-palladium oxide-cuprous oxide composite material, a preparation method and application thereof

Abstract

The application belongs to the technical field of photocatalytic materials, and discloses a S-type titanium dioxide-palladium oxide-cuprous oxide composite material and a preparation method and application thereof. First, a titanium source is added into ethylene glycol, and a titanium dioxide precursor is prepared through a reflux reaction; second, the titanium dioxide precursor, a palladium salt solution and water are mixed, and a titanium dioxide-palladium oxide composite material is prepared through calcination; finally, the titanium dioxide-palladium oxide composite material, a copper salt solution and water are mixed and subjected to oil bath stirring, and then a sodium hydroxide solution and an ascorbic acid solution are added in sequence and subjected to stirring reaction, so that the S-type titanium dioxide-palladium oxide-cuprous oxide composite material is finally obtained. In the application, cuprous oxide nanoparticles and palladium oxide nanoparticles are loaded on the surface of titanium dioxide microrods, and an S-type heterojunction is successfully constructed between TiO2 and Cu2O, so that the obtained composite material exhibits good photocatalytic performance under light, and is suitable for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to an S-type titanium dioxide-palladium oxide-cuprous oxide composite material, its preparation method, and its application. Background Technology

[0002] With the large-scale exploitation of fossil fuels, the energy crisis has become a major problem that urgently needs to be solved by the world today. Solar energy, with its advantages of being clean, harmless, and pollution-free, has become a hot topic in contemporary new energy research. Among these methods, photocatalytic semiconductor water splitting can convert solar energy into hydrogen energy. This is one way to maximize the utilization of solar energy. The basic principle of photocatalysis is: when light with a band gap greater than the semiconductor surface shines on it, electrons will jump from the valence band to the conduction band, creating holes in the valence band; these electron-hole pairs have strong redox capabilities, H... + Accepting electrons, a reduction reaction occurs, producing H2; other sacrificial agents or water combine with holes, resulting in an oxidation reaction. Among photocatalytic materials, the most common N-type semiconductor TiO2 has become a research hotspot due to its advantages of being non-toxic, harmless, inexpensive, and stable. However, it also suffers from a wide band gap, easy recombination of photogenerated carriers, and insufficient kinetic energy for surface catalytic reactions.

[0003] To address the issue of easy recombination of photogenerated carriers in TiO2, heterojunctions can be constructed for improvement. The construction of heterojunctions can adjust charge separation and transfer, thereby enhancing photocatalytic activity. Cu2O, as a narrow-bandgap p-type semiconductor material, shows significantly improved photocatalytic activity when combined with TiO2 to form heterojunctions. Titanium dioxide / cuprous oxide composite photocatalysts have been extensively studied. Lv et al. designed and constructed an oxygen vacancy-excited direct Z-scheme Cu2O / TiO2 hybrid photocatalyst. Its oxygen vacancy-excited Z-scheme electron transfer mechanism consumes holes, exhibiting significantly enhanced activity and stability in both water and seawater, with hydrogen production rates reaching 11 mmol in both environments. -1 h -1 and 5.1 mmol g -1 h -1 Qiu et al. designed a novel ternary Cu@TiO2-Cu2O hybrid photocatalyst with multiple charge transfer channels, and achieved efficient solar hydrogen production by combining Schottky and pn junctions.

[0004] Currently studied heterojunctions formed between Cu₂O / TiO₂ are mostly type II or Z-type heterojunctions. However, in type II heterojunctions, the efficiency of photogenerated electron-hole separation comes at the cost of reduced oxidation capacity of the two semiconductor photocatalysts. Furthermore, due to electrostatic interactions, the presence of photogenerated electrons and holes in the original photocatalyst inhibits the interfacial transfer of electrons and holes in the other catalyst. In Z-type heterojunctions, the larger potential difference interferes with the charge transfer process. Therefore, there are still some problems in improving catalytic performance by constructing heterojunctions, affecting their effectiveness and applications. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing an S-type titanium dioxide-palladium oxide-cuprous oxide composite material, its preparation method and application. Cuprous oxide nanoparticles and palladium oxide nanoparticles are loaded on the surface of titanium dioxide microrods, and an S-type heterojunction is successfully constructed between TiO2 and Cu2O. The resulting composite material exhibits good photocatalytic performance under light irradiation and is suitable for widespread application.

[0006] To address the technical problem proposed in this invention, this invention provides a method for preparing an S-type titanium dioxide-palladium oxide-cuprous oxide composite material, comprising the following steps:

[0007] 1) Add the titanium source to ethylene glycol and disperse it by ultrasonication, then reflux the reaction, wash and dry the product to obtain the titanium dioxide precursor.

[0008] 2) Add titanium dioxide precursor, palladium salt solution and water to a crucible, disperse by ultrasonication, and then calcine to obtain titanium dioxide-palladium oxide composite material;

[0009] 3) Add the titanium dioxide-palladium oxide composite material, copper salt solution and water to a flask, disperse by ultrasonication, stir in an oil bath once, add sodium hydroxide solution and ascorbic acid solution in sequence, stir in an oil bath a second time, and then centrifuge, wash and dry to obtain the titanium dioxide-palladium oxide-cuprous oxide composite material.

[0010] In the above scheme, the titanium source is tetrabutyl titanate.

[0011] In the above scheme, the molar ratio of the titanium source to ethylene glycol is (0.004~0.008):1.

[0012] In the above scheme, the ultrasonic dispersion time in step 1) is 5 to 10 minutes.

[0013] In the above scheme, the reflux reaction temperature is 110-150℃ and the reaction time is 0.5-2h.

[0014] In the above scheme, the palladium salt solution is an aqueous solution of palladium nitrate with a concentration of 0.1–0.2 mol / L.

[0015] In the above scheme, the molar ratio of the palladium salt solution to the titanium source is 1:(0.1~1.8).

[0016] In the above scheme, the volume ratio of water to palladium salt solution in step 2) is 1:(0.005~0.05).

[0017] In the above scheme, the ultrasonic dispersion time in step 2) is 5 to 10 minutes.

[0018] In the above scheme, the calcination temperature is 500-550℃ and the calcination time is 90-120min.

[0019] In the above scheme, the copper salt solution is an aqueous solution of copper nitrate with a concentration of 0.1 to 0.2 mol / L.

[0020] In the above scheme, the volume ratio of water to copper salt solution in step 3) is 1:(0.02~0.2).

[0021] In the above scheme, the ultrasonic dispersion time in step 3) is 5 to 10 minutes.

[0022] In the above scheme, the concentration of the sodium hydroxide solution is 0.5 to 1 mol / L.

[0023] In the above scheme, the concentration of the ascorbic acid solution is 0.1-0.3 mol / L.

[0024] In the above scheme, the oil bath temperature for oil bath stirring is 55-70℃, the time for the first oil bath stirring is 5-20 minutes, and the time for the second oil bath stirring is 5-10 minutes.

[0025] In the above scheme, the molar ratio of the titanium source, copper salt solution, sodium hydroxide solution and ascorbic acid solution is (0.02~0.25):(0.04~2):(0.2~5):1.

[0026] In the above scheme, the centrifugal washing speed is 7000-8000 rpm.

[0027] The present invention also provides an S-type titanium dioxide-palladium oxide-cuprous oxide composite material, which is prepared by the above method and includes titanium dioxide microrods and cuprous oxide nanoparticles and palladium oxide nanoparticles loaded on their surface, wherein the length of the titanium dioxide microrods is 3.5-7 μm, the particle size of the cuprous oxide nanoparticles is 15-50 nm, and the particle size of the palladium oxide nanoparticles is 16-50 nm.

[0028] This invention also provides an application of an S-type titanium dioxide-palladium oxide-cuprous oxide composite material as a photocatalyst, specifically for photocatalytic methanol-to-hydrogen production.

[0029] The principle of the synthesis method of this invention is as follows:

[0030] Palladium nitrate was introduced into an aqueous solution containing a titanium dioxide precursor. Palladium oxide was loaded onto the surface of rod-shaped titanium dioxide under ultrasonic and high-temperature calcination conditions. Then, copper nitrate was introduced into the aqueous solution containing titanium dioxide-palladium oxide microrods. Under ultrasonic and stirring conditions, Cu... 2+ The Cu is adsorbed on the TiO2 surface and further stabilized by the complexation effect of sodium hydroxide. Then, ascorbic acid is introduced as a reducing agent under oil bath conditions to reduce Cu. 2+ Reduced to Cu + The reaction further results in Cu2O nanoparticles being uniformly loaded onto the surface of titanium dioxide microrods, achieving in-situ synthesis and loading of Cu2O onto titanium dioxide microrods.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1) The construction of S-type heterojunctions mainly faces the following challenges. S-type heterojunctions are constructed by staggering reduced semiconductor photocatalysts (RP) with a small work function and a high Fermi level, and oxidized semiconductor photocatalysts (OP) with a large work function and a low Fermi level. This places high demands on the band structure and construction method of the photocatalyst materials. This invention successfully synthesized an S-type titanium dioxide-palladium oxide-cuprous oxide composite material using an in-situ growth method. The S-type heterojunction was verified by probe molecular PL testing and conduction band and valence band position testing. The chemical formula of the composite material is PdO@TiO2-Cu2O. Cuprous oxide and palladium oxide nanoparticles are loaded on the surface of porous titanium dioxide microrods, forming effective contact and exhibiting good stability.

[0033] 2) In the composite material obtained by this invention, the matched band positions and effective contact between TiO2 and Cu2O constitute an S-type heterojunction. Before they come into contact, the Fermi level of TiO2 is lower than that of Cu2O. However, under the tight coupling of TiO2 and Cu2O, electrons spontaneously transfer from TiO2 to Cu2O, forming an equivalent Fermi level, which causes band bending. Negatively charged ions accumulate on the TiO2 side of the interface, while positively charged ions accumulate on the Cu2O side. This redistribution of charge leads to the formation of an interfacial electric field (IEF) from Cu2O to TiO2. The tight interface between TiO2 and Cu2O further promotes charge transfer. Under visible light irradiation, photo-excited electrons and holes are generated in the corresponding CB and VB of TiO2 and Cu2O. IEF and band bending make it easier for photogenerated electrons from TiO2 CB and holes from Cu2O VB to recombine. At the same time, photogenerated electrons in Cu2O CB and holes in TiO2 VB are repelled from the interface and gather on both sides of the interface. Photogenerated electrons and holes are spatially separated, so their recombination is greatly reduced. Moreover, electrons on Cu2OCB and holes on TiO2 VB exhibit stronger redox capabilities, thereby improving the photocatalytic hydrogen production rate. In addition, the introduction of palladium oxide is beneficial to the consumption of holes, realizing the separation of photogenerated carriers. It also forms a multi-channel charge transfer mechanism in combination with the S-type heterojunction. The combination of the two makes the composite material have both high redox performance and efficient charge separation capability, realizing efficient photocatalytic hydrogen production.

[0034] 3) The preparation process of the present invention is simple, the reaction conditions are mild, and the operation is convenient. The synthesized catalyst has cuprous oxide and palladium oxide nanoparticles loaded on the surface of titanium dioxide microrods, which has high stability, meets the actual production needs, and has great application potential. Attached Figure Description

[0035] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the PdO@TiO2-Cu2O composite material obtained in Example 1.

[0036] Figure 2 The X-ray photoelectron spectroscopy (XPS) images show the full spectrum and the fine spectra of Ti 2p, Cu 2p and Pd 3d of the PdO@TiO2-Cu2O composite material obtained in Example 1.

[0037] Figure 3 The images show scanning electron microscope (SEM) images and EDX mapping images of the PdO@TiO2-Cu2O composite material obtained in Example 1.

[0038] Figure 4The images show the photocatalytic hydrogen production activity and average hydrogen production bar charts for the PdO@TiO2-Cu2O composite material obtained in Example 1 and Comparative Examples 1, 2, 3, and 4.

[0039] Figure 5 The band gap diagrams are for Cu2O in Comparative Example 1 and TiO2 in Comparative Example 2 (the inset is the valence band diagram).

[0040] Figure 6 The liquid fluorescence spectra of the PdO@TiO2-Cu2O composite material obtained in Example 1 and other comparative materials are shown in (a) and the PL spectra of the PdO@TiO2-Cu2O composite material obtained in Example 1 and other comparative materials obtained by probe molecule PL testing are shown in (b).

[0041] Figure 7 The XPS valence band spectrum and fine spectrum of Cu2O in Comparative Example 1, the XPS valence band spectrum and fine spectrum of TiO2 in Comparative Example 2, and the XPS fine spectrum of TiO2-Cu2O in Comparative Example 3 are shown.

[0042] Figure 8 The diagram shows the band structure of TiO2 and Cu2O (a), the reaction mechanism diagram of the type II heterojunction system (b), and the reaction mechanism diagram of the type S heterojunction system (c). Detailed Implementation

[0043] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0044] Example 1

[0045] A method for preparing an S-type titanium dioxide-palladium oxide-cuprous oxide composite material includes the following steps:

[0046] 1) Add 3 mmol of ethylene glycol to a round-bottom flask, then add 0.015 mmol of tetrabutyl titanate, sonicate for 5 min, then heat to 120 °C and reflux for 2 h. Wash and dry the product to obtain the titanium dioxide precursor.

[0047] 2) Prepare a 0.1 mol / L palladium nitrate solution by preparing palladium nitrate dihydrate. Add all the titanium dioxide precursor obtained in step 1), 0.625 mL of palladium nitrate solution and 20 mL of deionized water to a crucible. After ultrasonic dispersion for 5 min, calcine at 500 °C for 120 min to obtain titanium dioxide-palladium oxide composite material.

[0048] 3) Prepare a 0.1 mol / L copper nitrate solution by dissolving copper nitrate trihydrate. Add all the titanium dioxide-palladium oxide composite material obtained in step 2), 0.625 mL of copper nitrate solution and 10 mL of deionized water to a round-bottom flask. After ultrasonic dispersion for 5 min, stir in an oil bath at 60 °C for 10 min. Then add 500 μL of 1 mol / L sodium hydroxide solution and 500 μL of 0.2 mol / L ascorbic acid solution in sequence. Continue stirring in an oil bath for 5 min. Then centrifuge at 7000 rpm, wash and dry to obtain the titanium dioxide-palladium oxide-cuprous oxide composite material, denoted as PdO@TiO2-Cu2O composite material.

[0049] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the PdO@TiO2-Cu2O composite material obtained in this embodiment. As can be seen from the figure, the diffraction peaks of the composite material PdO@TiO2-Cu2O correspond to TiO2 (4-477), Cu2O (1-1142) and PdO (6-515), respectively, indicating the successful synthesis of the composite material.

[0050] Figure 2 The images show the full spectrum and fine spectra of Ti 2p, Cu 2p, and Pd 3d of the PdO@TiO2-Cu2O composite material obtained in this embodiment, obtained via X-ray photoelectron spectroscopy (XPS). The XPS spectrum reveals that the composite material synthesized in this embodiment is composed of five elements: Ti, Cu, O, Pd, and C. C is the carbon element introduced during the testing, further confirming the elemental composition of the composite material. Single-element valence state analysis shows that Ti exists in a +4 valence state, Pd in ​​a +2 valence state, and Cu in a +1 valence state. The XPS results further confirm the synthesis of the PdO@TiO2-Cu2O composite material.

[0051] Figure 3 The images show scanning electron microscope (SEM) and EDX mapping images of the PdO@TiO2-Cu2O composite material obtained in this embodiment. It can be seen that TiO2 has a rod-like structure with a length of 3.5-7 μm. The morphology did not change after calcination. Cuprous oxide and palladium oxide nanoparticles are loaded on the TiO2 surface. The particle size of the cuprous oxide nanoparticles is 15-50 nm, and the particle size of the palladium oxide nanoparticles is 16-50 nm.

[0052] Comparative Example 1

[0053] The material in Comparative Example 1 is Cu2O with a particle size of 15–50 nm.

[0054] Comparative Example 2

[0055] The material in Comparative Example 2 is TiO2 with a particle size of 3.5–7 μm.

[0056] Comparative Example 3

[0057] The material in Comparative Example 3 is TiO2-Cu2O, and its preparation method is as follows:

[0058] 1) Add 180 mL of ethylene glycol to a 250 mL round-bottom flask, add 5 mL of tetrabutyl titanate solution to the ethylene glycol, mix thoroughly by ultrasonication, reflux and stir for 1 h in an oil bath at 120 °C, wash with water and alcohol, centrifuge and dry to obtain titanium dioxide precursor; take 0.4 g of titanium dioxide precursor and place it in a crucible, add 20 mL of deionized water, mix thoroughly by ultrasonication, and calcine in a muffle furnace at 500 °C for 2 h to obtain TiO2;

[0059] 2) Take 0.24g TiO2 and add it to a round-bottom flask. Add 10mL of deionized water and sonicate until homogeneous. Then add 1.25mL of 0.1mol / L Cu(NO3)2·3H2O solution and sonicate until homogeneous. Stir in an oil bath at 60℃ for 10min. First add 500μL of 1mol / L NaOH solution, then add 500μL of 0.2mol / L ascorbic acid solution and continue stirring in an oil bath for 5min. Finally, wash with water and alcohol, centrifuge to collect the product, and dry in a vacuum drying oven for 12h to obtain the titanium dioxide-cuprous oxide composite material, denoted as TiO2-Cu2O.

[0060] Comparative Example 4

[0061] The material in Comparative Example 4 is the titanium dioxide-palladium oxide composite material prepared in step 2) of Example 1, denoted as PdO@TiO2.

[0062] Application Example 1

[0063] The PdO@TiO2-Cu2O composite material obtained in this embodiment was applied to photocatalytic methanol-to-hydrogen production. A 100 mL quartz reactor was used as the photoreactor. 25 mg of PdO@TiO2-Cu2O composite material and 50 mL of 20% (v / v) methanol aqueous solution were added, and a condenser circulating water device was added to maintain the temperature at 10°C. Nitrogen gas was introduced to purge the air from the reactor before illumination. Then, a 300 W xenon lamp was used as the light source to irradiate the photoreactor. The amount of hydrogen produced was analyzed every 30 minutes using a gas chromatography system with a thermal conductivity detector. The total photocatalytic hydrogen production time was 4 hours. In addition, the materials in each Comparative Example 2 were also applied to photocatalytic methanol-to-hydrogen production according to the above method. The test results are shown in [Figure 1]. Figure 4 The results show that the PdO@TiO2-Cu2O composite material of the present invention has the most efficient photocatalytic hydrogen evolution activity.

[0064] To further demonstrate the band structure of the composite material in Example 1, DRS and XPS-VB analyses were performed on Cu2O in Comparative Example 1 and TiO2 in Comparative Example 2. Figure 5 As shown, the band gaps of TiO2 and Cu2O are 3.03 eV and 2.17 eV, respectively, according to the Kubelka-Munk transform function formula. However, the valence band potentials of TiO2 and Cu2O are 2.59 eV and 1.37 eV, respectively, according to E... CB =E VB -E g The conduction band potential, E, can be calculated. CB (TiO2) = -0.44 eV, E CB (Cu2O) = -0.80 eV.

[0065] To investigate the formation of its heterostructure, probe molecular PL testing was performed on the composite material. First, Figure 6 (a) shows the liquid fluorescence spectra of the PdO@TiO2-Cu2O composite material and other comparative materials. The fluorescence intensity is Cu2O > TiO2 > TiO2-Cu2O > PdO@TiO2 > PdO@TiO2-Cu2O. The lower the fluorescence intensity, the better the photogenerated electron-hole separation efficiency, indicating that the PdO@TiO2-Cu2O composite material has a higher photogenerated electron-hole separation efficiency. Secondly, using terephthalic acid as a probe molecule, the ability of the material to generate hydroxyl radicals was studied. The principle is that non-fluorescent terephthalic acid molecules react with ·OH to generate 2-hydroxy-terebenzoic acid with high fluorescence intensity, which can be detected by a PL spectrometer. Figure 6 (b) shows the PL spectrum changes of the probe molecule terephthalic acid solution under irradiation for 90 min in the PdO@TiO2-Cu2O composite material and other comparative materials. It can be seen that the generation rate of hydroxyl radicals is Cu2O < TiO2-Cu2O < PdO@TiO2-Cu2O < PdO@TiO2 < TiO2. The high fluorescence intensity of TiO2 (k = 61.39) is due to the fact that TiO2 itself has a higher VB (2.59 eV) than ·OH / H2O (2.38 eV), so it can oxidize water to produce ·OH and has a higher fluorescence intensity. Cu2O (k = 0.056), as a narrow bandgap semiconductor, cannot oxidize water to produce ·OH with its VB (1.37 eV), so its fluorescence intensity is weaker. The reduced activity of PdO@TiO2-Cu2O compared to TiO2 may be due to the recombination of some holes, which prevents the holes from being fully used to produce ·OH. To further investigate the mechanism, the band structure of semiconductors TiO2 and Cu2O was further confirmed based on the band gap and valence band diagrams, such as... Figure 7 As shown, the core energy level E of a single material CL The energy difference ΔE between the maximum valence band and the maximum valence bandVBO The energy difference between the core energy levels at the heterojunction interface Described by the following formula:

[0066]

[0067]

[0068]

[0069] The ΔE of TiO2-Cu2O was calculated. VBO =0.36eV, ΔE CBO = 1.22 eV. Based on the above results, the band structures of TiO2 and Cu2O and their band shift difference can be obtained as follows: Figure 8 As shown in (a), the possible electron transfer mechanisms between TiO2 and Cu2O are as follows: Figure 8 (b) and Figure 8 As shown in (c), the first type is the type II charge transfer mechanism, where electrons on the CB of TiO2 are transferred to the CB of Cu2O, and holes on the VB of TiO2 are transferred to the VB of Cu2O. However, in this transfer mechanism, the final oxidation potential is lower than the generation potential of ·OH, meaning no fluorescence is generated, which contradicts the above measurement results. Therefore, TiO2 and Cu2O should form an S-type charge transfer mechanism, where electrons on the CB of TiO2 recombine with holes on the VB of Cu2O. Electrons on the CB of Cu2O are used to produce hydrogen, while holes in the VB of TiO2 are used to oxidize water to produce ·OH. The loading of palladium oxide improves the separation efficiency of photogenerated carriers, which is consistent with the results of the fluorescent probe experiment.

[0070] Example 2

[0071] A method for preparing an S-type titanium dioxide-palladium oxide-cuprous oxide composite material includes the following steps:

[0072] 1) Add 3 mmol of ethylene glycol to a round-bottom flask, then add 0.012 mmol of tetrabutyl titanate, sonicate for 6 min, then heat to 110 °C and reflux for 1.5 h. Wash and dry the product to obtain the titanium dioxide precursor.

[0073] 2) Prepare a 0.12 mol / L palladium nitrate solution by preparing palladium nitrate dihydrate. Add all the titanium dioxide precursor obtained in step 1), 0.25 mL of palladium nitrate solution and 20 mL of deionized water to a crucible. After ultrasonic dispersion for 8 min, calcine at 510 °C for 100 min to obtain titanium dioxide-palladium oxide composite material.

[0074] 3) Prepare a 0.1 mol / L copper nitrate solution by dissolving copper nitrate trihydrate. Add all the titanium dioxide-palladium oxide composite material obtained in step 2), 1 mL of copper nitrate solution and 10 mL of deionized water to a round-bottom flask. After ultrasonic dispersion for 6 min, stir in an oil bath at 55 °C for 15 min. Then add 500 μL of 0.5 mol / L sodium hydroxide solution and 500 μL of 0.1 mol / L ascorbic acid solution in sequence. Continue stirring in an oil bath for 8 min. Then centrifuge at 7500 rpm, wash and dry to obtain the titanium dioxide-palladium oxide-cuprous oxide composite material.

[0075] Example 3

[0076] A method for preparing an S-type titanium dioxide-palladium oxide-cuprous oxide composite material includes the following steps:

[0077] 1) Add 3 mmol of ethylene glycol to a round-bottom flask, then add 0.018 mmol of tetrabutyl titanate, sonicate for 7 min, then heat to 130 °C and reflux for 1 h. Wash and dry the product to obtain the titanium dioxide precursor.

[0078] 2) Prepare a 0.14 mol / L palladium nitrate solution by preparing palladium nitrate dihydrate. Add all the titanium dioxide precursor obtained in step 1), 0.9 mL of palladium nitrate solution and 20 mL of deionized water to a crucible. After ultrasonic dispersion for 6 min, calcine at 520 °C for 100 min to obtain titanium dioxide-palladium oxide composite material.

[0079] 3) Prepare a 0.1 mol / L copper nitrate solution by dissolving copper nitrate trihydrate. Add all the titanium dioxide-palladium oxide composite material obtained in step 2), 0.35 mL of copper nitrate solution and 15 mL of deionized water to a round-bottom flask. After ultrasonic dispersion for 9 min, stir in an oil bath at 65 °C for 7 min. Then add 800 μL of 0.2 mol / L sodium hydroxide solution and 800 μL of 0.12 mol / L ascorbic acid solution in sequence. Continue stirring in an oil bath for 9 min. Then centrifuge at 7800 rpm, wash and dry to obtain the titanium dioxide-palladium oxide-cuprous oxide composite material.

[0080] Example 4

[0081] A method for preparing an S-type titanium dioxide-palladium oxide-cuprous oxide composite material includes the following steps:

[0082] 1) Add 3 mmol of ethylene glycol to a round-bottom flask, then add 0.021 mmol of tetrabutyl titanate, sonicate for 10 min, then heat to 130 °C and reflux for 1.5 h. Wash and dry the product to obtain the titanium dioxide precursor.

[0083] 2) Prepare a 0.1 mol / L palladium nitrate solution by preparing palladium nitrate dihydrate. Add all the titanium dioxide precursor obtained in step 1), 0.125 mL of palladium nitrate solution and 20 mL of deionized water to a crucible. After ultrasonic dispersion for 10 min, calcine at 550 °C for 90 min to obtain titanium dioxide-palladium oxide composite material.

[0084] 3) Prepare a 0.1 mol / L copper nitrate solution by dissolving copper nitrate trihydrate. Add all the titanium dioxide-palladium oxide composite material obtained in step 2), 1.125 mL of copper nitrate solution and 10 mL of deionized water to a round-bottom flask. After ultrasonic dispersion for 8 min, stir in an oil bath at 70 °C for 20 min. Then add 500 μL of 0.5 mol / L sodium hydroxide solution and 500 μL of 0.3 mol / L ascorbic acid solution in sequence. Continue stirring in an oil bath for 8 min. Then centrifuge at 8000 rpm, wash and dry to obtain the titanium dioxide-palladium oxide-cuprous oxide composite material.

[0085] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing an S-type titanium dioxide-palladium oxide-cuprous oxide composite material, characterized in that, Includes the following steps: 1) Add the titanium source to ethylene glycol and disperse it by ultrasonication, then reflux the reaction, wash and dry the product to obtain the titanium dioxide precursor. 2) Add titanium dioxide precursor, palladium salt solution and water to a crucible, disperse by ultrasonication, and then calcine to obtain titanium dioxide-palladium oxide composite material; 3) Add the titanium dioxide-palladium oxide composite material, copper salt solution and water to a flask, disperse by ultrasonication, stir in an oil bath once, add sodium hydroxide solution and ascorbic acid solution in sequence, stir in an oil bath a second time, and then centrifuge, wash and dry to obtain the titanium dioxide-palladium oxide-cuprous oxide composite material.

2. The method for preparing the S-type titanium dioxide-palladium oxide-cuprous oxide composite material according to claim 1, characterized in that, The titanium source is tetrabutyl titanate, and the molar ratio of the titanium source to ethylene glycol is (0.004~0.008):1; the reflux reaction temperature is 110~150℃, and the reaction time is 0.5~2h.

3. The method for preparing the S-type titanium dioxide-palladium oxide-cuprous oxide composite material according to claim 1, characterized in that, The palladium salt solution is an aqueous solution of palladium nitrate with a concentration of 0.1–0.2 mol / L; the molar ratio of the palladium salt solution to the titanium source is 1:(0.1–1.8); the volume ratio of water to palladium salt solution in step 2) is 1:(0.005–0.05).

4. The method for preparing the S-type titanium dioxide-palladium oxide-cuprous oxide composite material according to claim 1, characterized in that, The calcination temperature is 500–550℃, and the calcination time is 90–120 min.

5. The method for preparing the S-type titanium dioxide-palladium oxide-cuprous oxide composite material according to claim 1, characterized in that, The copper salt solution is an aqueous solution of copper nitrate with a concentration of 0.1–0.2 mol / L; the sodium hydroxide solution has a concentration of 0.5–1 mol / L; and the ascorbic acid solution has a concentration of 0.1–0.3 mol / L.

6. The method for preparing the S-type titanium dioxide-palladium oxide-cuprous oxide composite material according to claim 1, characterized in that, The oil bath temperature for the oil bath stirring is 55-70℃, the time for the first oil bath stirring is 5-20 minutes, and the time for the second oil bath stirring is 5-10 minutes.

7. The method for preparing the S-type titanium dioxide-palladium oxide-cuprous oxide composite material according to claim 1, characterized in that, In step 3), the volume ratio of water to copper salt solution is 1:(0.02-0.2); the molar ratio of titanium source, copper salt solution, sodium hydroxide solution and ascorbic acid solution is (0.02-0.25):(0.04-2):(0.2-5):

1.

8. The method for preparing the S-type titanium dioxide-palladium oxide-cuprous oxide composite material according to claim 1, characterized in that, The ultrasonic dispersion time in steps 1), 2), and 3) is 5 to 10 minutes; the centrifugal washing speed is 7000 to 8000 rpm.

9. The S-type titanium dioxide-palladium oxide-cuprous oxide composite material prepared by the method according to any one of claims 1 to 8, characterized in that, It includes titanium dioxide microrods and cuprous oxide nanoparticles and palladium oxide nanoparticles loaded on their surfaces. The length of the titanium dioxide microrods is 3.5 to 7 μm, the particle size of the cuprous oxide nanoparticles is 15 to 50 nm, and the particle size of the palladium oxide nanoparticles is 16 to 50 nm.

10. The application of the S-type titanium dioxide-palladium oxide-cuprous oxide composite material as described in claim 9 in photocatalytic methanol-to-hydrogen production.

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