Silicon / apatite-type lanthanum silicate composite and method of preparation

Abstract

The application discloses a kind of silicon / apatite type lanthanum silicate composite and preparation method;The preparation method of the application is mainly that lanthanum nitrate hexahydrate and uniform benzenetricarboxylic acid solution are mixed uniformly at room temperature, continue to be stirred to obtain lanthanum-based coordination polymer;Lanthanum-based coordination polymer and silicon dioxide are ground and mixed uniformly, and then high-temperature calcination is carried out to obtain silicon / apatite type lanthanum silicate composite.The silicon / apatite type lanthanum silicate composite prepared by the method of the application is composed of irregular microspheres with a particle size of about 200 nm.The synthesis method avoids the risk of explosion by magnesium reduction method, has the advantages of green environmental protection, simple operation, no reduction atmosphere, etc.The silicon / apatite type lanthanum silicate composite can be applied to photoelectric catalysis.

Description

Technical Field

[0001] This invention relates to the preparation of composite materials, specifically to a silica / apatite-type lanthanum silicate composite and its preparation method. Background Technology

[0002] Silicon is one of the most abundant elements on Earth and a fundamental material for modern industrial development. Silicon possesses a suitable band gap and band structure, exhibiting a conduction band approximately -0.5V different from the standard hydrogen electrode and a band gap of 1.12 eV. This classifies silicon as a promising material for assembling photoelectrodes. Unfortunately, because Si readily forms an insulating silicon dioxide (SiO₂) under aqueous or aerobic conditions... x (The layer becomes inactive.)

[0003] Rare earth silicates possess high-temperature stability, excellent oxidation resistance, and corrosion resistance. Constructing composites of rare earth silicates with silicon holds promise for adjusting the electronic structure of Si, ensuring the stability of elemental silicon in aqueous systems. Among them, lanthanum silicate of the apatite type exhibits excellent performance and advantages in photoelectrocatalysis, including high ionic conductivity, low activation energy, a wide spectral response range, high chemical stability, and environmental friendliness. Firstly, the crystal structure of lanthanum silicate of the apatite type contributes to its high ionic conductivity and low activation energy. Furthermore, it exhibits good chemical stability, maintaining stability in high-temperature and acidic media, and is not prone to corrosion or deactivation. Secondly, the synthesis conditions for lanthanum silicate of the apatite type are relatively mild, allowing for the preparation of materials with different morphologies and structures by adjusting synthesis parameters, which helps improve its photoelectrocatalytic performance. Simultaneously, lanthanum silicate of the apatite type has a broad spectral response range, absorbing visible and near-infrared light, making it a promising candidate for applications in photoelectrocatalysis. Therefore, constructing a composite structure of elemental silicon and apatite-type lanthanum silicate to alter electronic properties, improve stability, and expose active sites to enhance catalytic performance is an important research direction at present.

[0004] Metal coordination polymers have attracted widespread attention as precursors or templates for constructing functional materials due to their tunable composition, controllable morphology, porosity, and variable structure. Using lanthanum-based coordination polymers (LaCPs) as precursors and reducing agents, silicon elemental was anchored in apatite-type lanthanum silicate through in-situ reduction of silica at high temperature, serving as a photoanode for efficient photoelectrocatalytic water splitting.

[0005] There are currently no reports on the in-situ preparation of silicon / rare earth silicate composites. Summary of the Invention

[0006] This invention employs a simple sol-gel method to obtain SiO2 microspheres, which are then thoroughly ground with a lanthanum-based coordination polymer. The mixed powder is then directly calcined at high temperature under an inert atmosphere. The carbon in the lanthanum-based coordination polymer acts as a reducing agent to reduce SiO2 to elemental silicon in situ, thus obtaining an elemental silicon / lanthanum silicate composite (Si / La) in a one-step process. 10 (SiO4)6O3). This method has the advantages of simple operation, no need for a reducing atmosphere, and good dispersion of the obtained silicon in lanthanum silicate.

[0007] This invention provides a method for preparing a silica / apatite-type lanthanum silicate composite, the specific steps of which are as follows:

[0008] (1) Dissolve lanthanum nitrate hexahydrate in deionized water and label it solution A;

[0009] (2) Dissolve pyromellitic acid in a mixed solvent of deionized water and anhydrous ethanol, and denote it as solution B;

[0010] (3) After transferring solution A to solution B under magnetic stirring, stirring was continued to obtain a white precipitate;

[0011] (4) The white precipitate obtained in step 3 was washed repeatedly with deionized water and ethanol, the sample was collected, and vacuum dried at 60°C for 20-30 h to obtain white powder, namely lanthanum-based coordination polymers (LaCPs).

[0012] (5) Grind LaCPs and SiO2 microspheres in a mortar to mix them evenly; transfer the powder to a crucible and calcine it at high temperature in a tube furnace to obtain the target product, lanthanum silicate / apatite type composite.

[0013] Furthermore, in step (1), the amount of lanthanum nitrate hexahydrate added is 1-5 mmol, and the volume of deionized water is 5-10 mL.

[0014] Furthermore, in step (2), the amount of pyromellitic acid is 1-5 mmol, the volume of deionized water is 20-50 mL, and the volume of anhydrous ethanol is 20-50 mL.

[0015] Furthermore, in step (3), the stirring time is 0.5 to 3 hours after the addition of solution A to solution B is completed; preferably, the stirring time is 2 hours.

[0016] Furthermore, in step (4), the drying conditions are drying at 60°C for 20–30 h.

[0017] Further, in step (5), the mass of LaCPs added is 200-400 mg; the mass of SiO2 microspheres is 50-150 mg; preferably, the mass of SiO2 microspheres is 100 mg.

[0018] Furthermore, in step (5), the calcination temperature is 900-1300℃; preferably, the calcination temperature is 1000℃ or 1200℃.

[0019] Further, in step (5), the calcination time in a nitrogen atmosphere is 1 to 4 hours; preferably, the calcination time is 2 hours. The heating rate is 2 to 5 °C / min.

[0020] This invention provides a method for preparing a silicon / apatite-type lanthanum silicate composite material based on the above steps. The silicon / lanthanum-based silicate composite is composed of irregularly shaped microspheres with a diameter of approximately 200 nm bonded together, and can be applied in photoelectrocatalysis.

[0021] The beneficial effects of this invention are:

[0022] The preparation process provided by this invention uses SiO2 as the silicon source and reactants, while LaCPs are calcined at high temperature under a protective atmosphere. The carbon in the ligands acts as a reducing agent to reduce elemental silicon in situ from SiO2 and precipitate it onto the surface of lanthanum silicate. This synthesis method avoids the explosion risk associated with magnesium reduction methods and has advantages such as being green and environmentally friendly, simple to operate, and requiring no reducing atmosphere. Attached Figure Description

[0023] Figure 1 This is a SEM image of SiO2 prepared in Example 1 of the present invention.

[0024] Figure 2 This is a SEM image of the LaCPs prepared in Example 1 of the present invention.

[0025] Figure 3 This is a SEM image of the silica / apatite-type lanthanum silicate composite prepared in Example 1 of the present invention.

[0026] Figure 4 The images show the XRD patterns of the silica / apatite-type lanthanum silicate composites prepared in Examples 1, 2, 3 and 4 of this invention.

[0027] Figure 5 The images show the XRD patterns of the silica / apatite-type lanthanum silicate composites prepared in Examples 5, 6, 7 and 8 of this invention. Detailed Implementation

[0028] The beneficial effects of this invention will be described in detail below with reference to the accompanying drawings and specific embodiments, aiming to help readers better understand the essence of this invention, but should not be construed as limiting the implementation and scope of protection of this invention. It should be noted that the preparation of SiO2 microspheres in this invention is still under development and will not be described in detail here.

[0029] Example 1

[0030] A method for preparing a silica / apatite-type lanthanum silicate composite:

[0031] Preparation of SiO2 microspheres: Tetraethyl orthosilicate was slowly added dropwise to a mixed solution containing 20 mL anhydrous ethanol, 6 mL deionized water, and 6 mL 25-28% ammonia. After the solution turned milky white, stirring was continued for 2 hours. The mixture was then centrifuged and washed repeatedly with deionized water and anhydrous ethanol alternately. The sample was collected and vacuum dried at 60 °C for 12 hours to obtain SiO2 microspheres.

[0032] Preparation of lanthanum silicate / apatite-type lanthanum silicate composite: 1–5 mmol of lanthanum nitrate hexahydrate was dissolved in 5–10 mL of deionized water, denoted as solution A; 1–5 mmol of trimesic acid was dissolved in a mixed solution of 20–50 mL of deionized water and 20–50 mL of anhydrous ethanol, denoted as solution B; solution A was added to solution B under magnetic stirring, and stirring was continued for 2 h to obtain a white precipitate. The white precipitate was washed repeatedly with deionized water and anhydrous ethanol, the sample was collected, and vacuum dried at 60 °C for 24 h to obtain lanthanum-based coordination polymers LaCPs. 200–400 mg of dried LaCPs and 100 mg of SiO2 microspheres were weighed and ground thoroughly in a mortar for 30 min, then transferred to a crucible and calcined at 1000 °C for 2 h in a tube furnace under N2 atmosphere to obtain the target product, the lanthanum silicate / apatite-type lanthanum silicate composite.

[0033] like Figure 1 The image shown is a SEM image of the prepared SiO2 microspheres, which shows that the average particle size is about 200 nm.

[0034] like Figure 2 The image shown is a SEM image of a lanthanide coordination polymer, which has an irregular rod-like morphology with a particle size of 1-2 μm.

[0035] like Figure 3 The image shows a SEM image of a silica / apatite-type lanthanum silicate composite. As can be seen from the image, it is composed of irregular microspheres with a particle size of about 200 nm, which is basically the same as the particle size of SiO2 microspheres. This indicates that SiO2 and LaCPs are thoroughly ground and calcined, with SiO2 as the template and maintaining a spherical morphology.

[0036] like Figure 4 The image shows the XRD patterns of silica / apatite-type lanthanum silicate composites prepared by calcination of SiO2 and LaCPs at 1000℃ under a nitrogen atmosphere with different mass ratios. When SiO2 / LaCPs = 50:250, the calcination product is apatite-type lanthanum silicate (La... 10 (SiO4)6O3), with continued increase in the amount of SiO2 added, diffraction peaks of Si appeared in the calcined product. The diffraction peaks of Si were strongest when the amount of SiO2 added was 100 mg. When the amount of SiO2 added was increased to 125 mg, the product was still Si / La.10 The (SiO4)6O3 composite material exhibits significantly weaker Si diffraction peaks. Therefore, the optimal SiO2 dosage is 100 mg.

[0037] like Figure 5 The image shows the XRD patterns of silica / apatite-type lanthanum silicate composites prepared by calcination of SiO2 and LaCPs at 1200℃ under a nitrogen atmosphere with different mass ratios. At 1200℃, all samples showed diffraction peaks for Si with no significant change in intensity, while the lanthanum silicate was apatite-type lanthanum silicate (La). 10 The composite phase of (SiO4)6O3 and lanthanum silicate (La2Si2O7) is not a pure phase, therefore the optimal calcination temperature is 1000℃.

[0038] Example 2

[0039] A method for preparing a silica / apatite-type lanthanum silicate composite, wherein the mass of SiO2 microspheres added in Example 1 is changed to 50 mg:

[0040] Preparation of SiO2 microspheres: Tetraethyl orthosilicate was slowly added dropwise to a mixed solution containing 20 mL anhydrous ethanol, 6 mL deionized water, and 6 mL 25-28% ammonia. After the solution turned milky white, stirring was continued for 2 hours. The mixture was then centrifuged and washed repeatedly with deionized water and anhydrous ethanol alternately. The sample was collected and vacuum dried at 60 °C for 12 hours to obtain SiO2 microspheres.

[0041] Preparation of lanthanum silicate / apatite-type lanthanum silicate composite: 1–5 mmol of lanthanum nitrate hexahydrate was dissolved in 5–10 mL of deionized water, denoted as solution A; 1–5 mmol of trimesic acid was dissolved in a mixed solution of 20–50 mL of deionized water and 20–50 mL of anhydrous ethanol, denoted as solution B; solution A was added to solution B under magnetic stirring, and stirring was continued for 2 h, resulting in a white precipitate. The white precipitate was washed repeatedly with deionized water and anhydrous ethanol, and the sample was collected and vacuum dried at 60 °C for 24 h to obtain lanthanum-based coordination polymers LaCPs. 200–400 mg of dried LaCPs and 50 mg of SiO2 microspheres were weighed and ground thoroughly in a mortar for 30 min, then transferred to a crucible and calcined at 1000 °C for 2 h in a tube furnace under N2 atmosphere to obtain the target product, the lanthanum silicate / apatite-type lanthanum silicate composite.

[0042] Example 3

[0043] A method for preparing a silica / apatite-type lanthanum silicate composite, wherein the mass of SiO2 microspheres added in Example 1 is changed to 75 mg:

[0044] Preparation of SiO2 microspheres: Tetraethyl orthosilicate was slowly added dropwise to a mixed solution containing 20 mL anhydrous ethanol, 6 mL deionized water, and 6 mL 25-28% ammonia. After the solution turned milky white, stirring was continued for 2 hours. The mixture was then centrifuged and washed repeatedly with deionized water and anhydrous ethanol alternately. The sample was collected and vacuum dried at 60 °C for 12 hours to obtain SiO2 microspheres.

[0045] Preparation of lanthanum silicate / apatite-type lanthanum silicate composite: 1–5 mmol of lanthanum nitrate hexahydrate was dissolved in 5–10 mL of deionized water, denoted as solution A; 1–5 mmol of trimesic acid was dissolved in a mixed solution of 20–50 mL of deionized water and 20–50 mL of anhydrous ethanol, denoted as solution B; solution A was added to solution B under magnetic stirring, and stirring was continued for 2 h, resulting in a white precipitate. The white precipitate was washed repeatedly with deionized water and anhydrous ethanol, and the sample was collected and vacuum dried at 60 °C for 24 h to obtain lanthanum-based coordination polymers LaCPs. 200–400 mg of dried LaCPs and 75 mg of SiO2 microspheres were weighed and thoroughly ground in a mortar for 30 min, then transferred to a crucible and calcined at 1000 °C for 2 h in a tube furnace under N2 atmosphere to obtain the target product, the lanthanum silicate / apatite-type lanthanum silicate composite.

[0046] Example 4

[0047] A method for preparing a silica / apatite-type lanthanum silicate composite, wherein the mass of SiO2 microspheres added in Example 1 is changed to 125 mg:

[0048] Preparation of SiO2 microspheres: Tetraethyl orthosilicate was slowly added dropwise to a mixed solution containing 20 mL anhydrous ethanol, 6 mL deionized water, and 6 mL 25-28% ammonia. After the solution turned milky white, stirring was continued for 2 hours. The mixture was then centrifuged and washed repeatedly with deionized water and anhydrous ethanol alternately. The sample was collected and vacuum dried at 60 °C for 12 hours to obtain SiO2 microspheres.

[0049] Preparation of lanthanum silicate / apatite-type lanthanum silicate composite: 1–5 mmol of lanthanum nitrate hexahydrate was dissolved in 5–10 mL of deionized water, denoted as solution A; 1–5 mmol of trimesic acid was dissolved in a mixed solution of 20–50 mL of deionized water and 20–50 mL of anhydrous ethanol, denoted as solution B; solution A was added to solution B under magnetic stirring, and stirring was continued for 2 h, resulting in a white precipitate. The white precipitate was washed repeatedly with deionized water and anhydrous ethanol, and the sample was collected and vacuum dried at 60 °C for 24 h to obtain lanthanum-based coordination polymers LaCPs. 200–400 mg of dried LaCPs and 125 mg of SiO2 microspheres were weighed and ground thoroughly in a mortar for 30 min, then transferred to a crucible and calcined at 1000 °C for 2 h in a tube furnace under N2 atmosphere to obtain the target product, the lanthanum silicate / apatite-type lanthanum silicate composite.

[0050] Example 5

[0051] A method for preparing a silica / apatite-type lanthanum silicate composite, wherein the calcination temperature in a tube furnace in Example 1 is changed to 1200℃:

[0052] Preparation of SiO2 microspheres: Tetraethyl orthosilicate was slowly added dropwise to a mixed solution containing 20 mL anhydrous ethanol, 6 mL deionized water, and 6 mL 25-28% ammonia. After the solution turned milky white, stirring was continued for 2 hours. The mixture was then centrifuged and washed repeatedly with deionized water and anhydrous ethanol alternately. The sample was collected and vacuum dried at 60 °C for 12 hours to obtain SiO2 microspheres.

[0053] Preparation of lanthanum silicate / apatite-type lanthanum silicate composite: 1–5 mmol of lanthanum nitrate hexahydrate was dissolved in 5–10 mL of deionized water, denoted as solution A; 1–5 mmol of trimesic acid was dissolved in a mixed solution of 20–50 mL of deionized water and 20–50 mL of anhydrous ethanol, denoted as solution B; solution A was added to solution B under magnetic stirring, and stirring was continued for 2 h, resulting in a white precipitate. The white precipitate was washed repeatedly with deionized water and anhydrous ethanol, and the sample was collected and vacuum dried at 60 °C for 24 h to obtain lanthanum-based coordination polymers LaCPs. 200–400 mg of dried LaCPs and 100 mg of SiO2 microspheres were weighed and ground thoroughly in a mortar for 30 min, then transferred to a crucible and calcined at 1200 °C for 2 h in a tube furnace under N2 atmosphere to obtain the target product, the lanthanum silicate / apatite-type lanthanum silicate composite.

[0054] Example 6

[0055] A method for preparing a silica / apatite-type lanthanum silicate composite, wherein the calcination temperature in a tube furnace in Example 2 is changed to 1200℃:

[0056] Preparation of SiO2 microspheres: Tetraethyl orthosilicate was slowly added dropwise to a mixed solution containing 20 mL anhydrous ethanol, 6 mL deionized water, and 6 mL 25-28% ammonia. After the solution turned milky white, stirring was continued for 2 hours. The mixture was then centrifuged and washed repeatedly with deionized water and anhydrous ethanol alternately. The sample was collected and vacuum dried at 60 °C for 12 hours to obtain SiO2 microspheres.

[0057] Preparation of lanthanum silicate / apatite-type lanthanum silicate composite: 1–5 mmol of lanthanum nitrate hexahydrate was dissolved in 5–10 mL of deionized water, denoted as solution A; 1–5 mmol of trimesic acid was dissolved in a mixed solution of 20–50 mL of deionized water and 20–50 mL of anhydrous ethanol, denoted as solution B; solution A was added to solution B under magnetic stirring, and stirring was continued for 2 h, resulting in a white precipitate. The white precipitate was washed repeatedly with deionized water and anhydrous ethanol, and the sample was collected and vacuum dried at 60 °C for 24 h to obtain lanthanum-based coordination polymers LaCPs. 200–400 mg of dried LaCPs and 50 mg of SiO2 microspheres were weighed and ground thoroughly in a mortar for 30 min, then transferred to a crucible and calcined at 1200 °C for 2 h in a tube furnace under N2 atmosphere to obtain the target product, the lanthanum silicate / apatite-type lanthanum silicate composite.

[0058] Example 7

[0059] A method for preparing a silica / apatite-type lanthanum silicate composite, wherein the calcination temperature in a tube furnace in Example 3 is changed to 1200℃:

[0060] Preparation of SiO2 microspheres: Tetraethyl orthosilicate was slowly added dropwise to a mixed solution containing 20 mL anhydrous ethanol, 6 mL deionized water, and 6 mL 25-28% ammonia. After the solution turned milky white, stirring was continued for 2 hours. The mixture was then centrifuged and washed repeatedly with deionized water and anhydrous ethanol alternately. The sample was collected and vacuum dried at 60 °C for 12 hours to obtain SiO2 microspheres.

[0061] Preparation of lanthanum silicate / apatite-type lanthanum silicate composite: 1–5 mmol of lanthanum nitrate hexahydrate was dissolved in 5–10 mL of deionized water, denoted as solution A; 1–5 mmol of trimesic acid was dissolved in a mixed solution of 20–50 mL of deionized water and 20–50 mL of anhydrous ethanol, denoted as solution B; solution A was added to solution B under magnetic stirring, and stirring was continued for 2 h, resulting in a white precipitate. The white precipitate was washed repeatedly with deionized water and anhydrous ethanol, and the sample was collected and vacuum dried at 60 °C for 24 h to obtain lanthanum-based coordination polymers LaCPs. 200–400 mg of dried LaCPs and 75 mg of SiO2 microspheres were weighed and ground thoroughly in a mortar for 30 min, then transferred to a crucible and calcined at 1200 °C for 2 h in a tube furnace under N2 atmosphere to obtain the target product, the lanthanum silicate / apatite-type lanthanum silicate composite.

[0062] Example 8

[0063] A method for preparing a silica / apatite-type lanthanum silicate composite, wherein the calcination temperature in a tube furnace in Example 4 is changed to 1200℃:

[0064] Preparation of SiO2 microspheres: Tetraethyl orthosilicate was slowly added dropwise to a mixed solution containing 20 mL anhydrous ethanol, 6 mL deionized water, and 6 mL 25-28% ammonia. After the solution turned milky white, stirring was continued for 2 hours. The mixture was then centrifuged and washed repeatedly with deionized water and anhydrous ethanol alternately. The sample was collected and vacuum dried at 60 °C for 12 hours to obtain SiO2 microspheres.

[0065] Preparation of lanthanum silicate / apatite-type lanthanum silicate composite: 1–5 mmol of lanthanum nitrate hexahydrate was dissolved in 5–10 mL of deionized water, denoted as solution A; 1–5 mmol of trimesic acid was dissolved in a mixed solution of 20–50 mL of deionized water and 20–50 mL of anhydrous ethanol, denoted as solution B; solution A was added to solution B under magnetic stirring, and stirring was continued for 2 h, resulting in a white precipitate. The white precipitate was washed repeatedly with deionized water and anhydrous ethanol, and the sample was collected and vacuum dried at 60 °C for 24 h to obtain lanthanum-based coordination polymers LaCPs. 200–400 mg of dried LaCPs and 125 mg of SiO2 microspheres were weighed and thoroughly ground in a mortar for 30 min, then transferred to a crucible and calcined at 1200 °C for 2 h in a tube furnace under N2 atmosphere to obtain the target product, the lanthanum silicate / apatite-type lanthanum silicate composite.

[0066] This invention provides a silica / apatite-type lanthanum silicate composite and its preparation method. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing a silica / apatite-type lanthanum silicate composite, characterized in that, The steps include the following: (1) Dissolve lanthanum nitrate hexahydrate in deionized water and mix well to obtain mixed solution A; (2) Mix pyromellitic acid, deionized water and anhydrous ethanol evenly to obtain mixed solution B; (3) Add mixed solution A to mixed solution B in step (2) and continue stirring to obtain a white precipitate; (4) The white precipitate obtained in step (3) is washed and then vacuum dried to obtain lanthanum-based coordination polymers (LaCPs); (5) Grind the LaCPs obtained in step (4) with silica microspheres, mix them evenly, and then calcine them at high temperature under an inert atmosphere to obtain a silica / apatite type lanthanum silicate composite. In step (5), the calcination conditions are calcination at 900~1300℃ for 1~4h, with a heating rate of 2~5℃ / min; in step (5), the mass of the LaCPs added is 200~400mg, and the mass of the silicon dioxide added is 50~150mg.

2. The preparation method according to claim 1, characterized in that, In step (1), the amount of lanthanum nitrate hexahydrate is 1~5 mmol, and the volume of deionized water is 5~10 mL.

3. The preparation method according to claim 1, characterized in that, In step (2), the amount of pyromellitic acid used is 1~5 mmol, the volume of deionized water is 20~50 mL, and the volume of anhydrous ethanol is 20~50 mL.

4. The preparation method according to claim 1, characterized in that, In step (3), the stirring time is 0.5 to 3 hours.

5. The preparation method according to claim 1, characterized in that, In step (4), the drying conditions are drying at 60°C for 20-30 hours.

6. The preparation method according to claim 1, characterized in that, In step (5), the inert atmosphere is a nitrogen atmosphere.

7. The silica / apatite type lanthanum silicate composite obtained by any one of the methods described in claims 1 to 6.

8. The silicon / lanthanum-based silicate composite according to claim 7, characterized in that, The silicon / lanthanum-based silicate composite is composed of irregularly shaped microspheres with a particle size of approximately 200 nm bonded together.

9. The application of the silica / apatite-type lanthanum silicate composite according to claim 7, characterized in that, The silicon / apatite type lanthanum silicate composite is used in photoelectrocatalysis.

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