Core-shell structure photocatalyst SiO2 (at) SrSiO3 / TiO2, preparation method and application

Abstract

The core-shell structure photocatalyst SiO2 (at) SrSiO3 / TiO2 is characterized in that the catalyst is of a core-shell structure composed of a core layer and a shell layer, the core layer is SiO2 of an amorphous structure, and the shell layer is composed of heterojunctions formed by SrSiO3 and TiO2.

Description

Technical Field

[0001] The present application belongs to the technical field of photocatalytic materials and wastewater treatment, and specifically relates to a core-shell structure photocatalyst SiO2@SrSiO3 / TiO2, a preparation method and an application thereof. Background Art

[0002] In recent decades, with the rapid development of the global economy and the continuous progress of society, environmental problems, especially water pollution, have become increasingly serious. Widely distributed pollutants in the water environment pose a major threat to human health. As an efficient advanced oxidation technology, photocatalysis has been widely studied in wastewater treatment due to its mild reaction conditions, strong oxidation ability, and wide range of applications. The preparation of efficient photocatalytic materials is of great significance.

[0003] TiO2 is considered to be an excellent catalytic material because of its non-toxic, corrosion-resistant, thermally stable, and high photocatalytic activity. In order to improve its reduction efficiency, the use of other metal oxide semiconductor materials and TiO2 to form a heterojunction has become a research hotspot for photocatalytic reduction of nitrates in recent years. In addition, light capture ability is an important indicator for evaluating photocatalysts. Light scattering materials (LSM, such as SiO2, Al2O3, etc.) are widely used in dye-sensitized cells to improve light capture. Light scattering materials can trap scattered light in the lattice to confine light and increase the light absorption path by scattering. When an LSM with a large refractive index difference from the substrate material is used, the effect will be further enhanced at the doping interface. Since the refractive index of SiO2 (n=1.55) is much lower than that of TiO2 (n=2.49), it is expected that the photocatalyst with SiO2 as the core and TiO2 as the shell will enhance light absorption and strengthen the photocatalytic performance of the material. Summary of the invention

[0004] The present application aims to solve the problems mentioned in the above background technology.

[0005] The present invention discloses a core-shell structure photocatalyst SiO2@SrSiO3 / TiO2, wherein the catalyst has a core-shell structure consisting of a core layer and a shell layer, wherein the core layer is SiO2 with an amorphous structure, and the shell layer is composed of a heterojunction formed by SrSiO3 and TiO2.

[0006] In a specific embodiment, the SiO2 core is a spherical structure, and the SrSiO3 / TiO2 shell is a hollow spherical structure formed by particle accumulation wrapped on the SiO2 core, wherein TiO2 is in the outer region of the shell and SrSiO3 is in the inner region of the shell.

[0007] The method for preparing a core-shell structured photocatalyst SiO2@SrSiO3 / TiO2 of the present invention comprises the following steps: S1, preparation of SiO2 core, ethanol, ammonia and water were mixed and stirred at room temperature for 10 minutes; then tetraethyl silicate ethanol solution was continuously added, maintained for 2-2.5 hours, white powder was separated and washed with ethanol, and then dried in an oven to obtain SiO2 nanospheres; S2, preparation of SiO2@TiO2, the SiO2 nanospheres obtained in S1 are fully mixed with ethanol and ammonia water, and an ester compound containing Ti is added during stirring, and the mixture is maintained at 40-60°C for 24-48 hours, and then a white powder is separated and dried, and the dried powder is calcined at high temperature to obtain SiO2@TiO2; S3, preparation of SiO2@SrSiO3 / TiO2, the SiO2@TiO2 obtained in S2 is fully stirred and mixed with deionized water, Sr-containing compounds and alkaline compounds, and then transferred to a hydrothermal kettle, maintained at 160-200°C for 16-30h, and then the white powder is separated and dried; the above operation of S3 is repeated to obtain a SiO2@SrSiO3 / TiO2 photocatalyst with a core-shell structure.

[0008] In a specific embodiment, in said S1: The ethanol solution of tetraethyl silicate is tetraethyl silicate dissolved in anhydrous ethanol, and the concentration of tetraethyl silicate is 50-200 g / L; Wherein, the amount of ethanol solution of tetraethyl silicate added is 6-20 ml / h; Wherein, the ethanol concentration is not less than 95%, and the amount of ethanol used is 10-20 times the amount of ethanol solution of tetraethyl silicate added per hour; The concentration of ammonia water is 25-28%, and the amount of ammonia water used is 0.5-2 times the amount of tetraethyl silicate ethanol solution added per hour; Among them, the diameter of SiO2 spheres is 200-500 nm.

[0009] In a specific embodiment, in said S2: The Ti-containing ester compounds are isopropyl titanate and tetrabutyl titanate; The amount of Ti ester compound added is 0.5-2 times the molar amount of the material obtained in S1; Wherein, the concentration of ethanol is not less than 95%, and the amount of ethanol used is 50-100 times the mass of the material obtained in S1; The concentration of ammonia water is 25-28%, and the amount of ammonia water used is 1-2 times the mass of the material obtained containing S1; Wherein, the calcination temperature is 500-800°C.

[0010] In a specific embodiment, in said S3: The Sr-containing compounds are SrCl2, Sr(OH)2 and their corresponding hydrates; The alkaline compounds are NaOH and Ca(OH)2; The amount of Sr-containing compound added in each hydrothermal reaction is 10%-20% of the molar amount of SiO2@TiO2; The amount of the alkaline compound added in each hydrothermal reaction is 1-2 times the molar amount of the Sr-containing compound; Wherein, step S3 is repeated 5-10 times; Among them, the hydrothermal temperature is 160-200°C, and the hydrothermal time is 16-30h; The present invention discloses an application of a core-shell structure photocatalyst SiO2@SrSiO3 / TiO2, wherein the SiO2@SrSiO3 / TiO2 photocatalyst, an additive and a light source are placed in wastewater to be treated, and the light source is turned on to perform photocatalytic wastewater treatment.

[0011] In a specific embodiment, the wastewater to be treated contains nitrates and / or organic pollutants.

[0012] In a specific embodiment, when the wastewater to be treated contains nitrate, the additive is formic acid or oxalic acid; when the wastewater to be treated contains organic pollutants, the additive is hydrogen peroxide, ozone or persulfate.

[0013] In a specific embodiment, the dosage of SiO2@SrSiO3 / TiO2 is 0.1‰~0.5‰ of the mass of the wastewater solution to be treated; the dosage of formic acid or oxalic acid is 0-60 mmol / L; the dosage of hydrogen peroxide, ozone or persulfate is 50-200 mmol / L. Beneficial Effects

[0014] Compared with the prior art, the present application has the following beneficial effects: 1. The light scattering material SiO2 is used as the core. The incident light forms backscattered light after passing through the shell material. SiO2 can trap the backscattered light in the lattice to produce a light confinement effect, and extend the light absorption path through forward scattering, promote further absorption of the shell material, and enhance the photocatalytic performance of the material.

[0015] 2. In order to avoid excessive dissolution of SiO2 under alkaline conditions, which may lead to the collapse of the core-shell structure, SrSiO3 is synthesized in batches under weak alkaline conditions. A small amount of precursor material is added to each batch to promote the generation of SrSiO3 on the surface of the SiO2 core; and under S3 conditions, part of the shell TiO2 will dissolve into TiO3 2- However, due to the dissolution product of SiO2, SiO3 2- More active, TiO3 2-It will not react further, but will gradually recrystallize into TiO2. During the recrystallization process, the TiO2 inside the shell will combine with SrSiO3 to form a heterojunction. This material preparation method can maintain the core-shell structure morphology and form a relatively independent SiO2 core and SrSiO3 / TiO2 shell, ensuring that each component can effectively exert its own photocatalytic activity in the reaction.

[0016] 3. The material is a dual-functional material that can utilize the reducing property of SrSiO3 to carry out denitrification reaction, and can also utilize the oxidizing property of TiO2 to degrade organic pollutants. At the same time, since most of the SrSiO3 is in the inner area of ​​the shell, in the process of treating nitrate wastewater, the outer TiO2 can play a protective role, reduce the loss of the active component SrSiO3, and extend the service life of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a SEM image of SiO2 / SrSiO3 / TiO2 in the present invention; Figure 2 The NO3 of the simulated nitrate wastewater degraded by the photocatalytic material in Example 2 of the present invention and Comparative Example 1 - Removal situation map; Figure 3 It is a diagram of TOC removal of phenol simulated wastewater degraded by photocatalytic materials in Example 3 of the present invention and Comparative Example 2. DETAILED DESCRIPTION

[0018] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0019] In the description of the present invention, it should be understood that the terms "center", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "counterclockwise", "clockwise", "axial", "radial", "circumferential" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0020] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection, it can be a direct connection, it can be an indirect connection through an intermediate medium, and it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. Example 1

[0021] This embodiment provides a core-shell structure photocatalyst SiO2@SrSiO3 / TiO2, wherein the catalyst has a core-shell structure consisting of a core layer and a shell layer, wherein the core layer is SiO2 with an amorphous structure, and the shell layer is composed of a heterojunction formed by SrSiO3 and TiO2, and the preparation method thereof comprises the following steps: S1: Preparation of SiO2 core: 250 ml ethanol, 20 ml ammonia and 15 ml water were mixed and stirred at room temperature for 10 min. Then 100 g / L tetraethyl silicate ethanol solution was added at a rate of 12 ml / h and the reaction was continued for 3 h. Then the white powder was separated and washed with ethanol, and finally dried in an oven at 60 °C to obtain SiO2 nanospheres.

[0022] S2: Preparation of SiO2@TiO2: 0.5 g SiO2 nanospheres were fully mixed with 120 ml ethanol and 0.5 ml ammonia water, and 2 ml tetrabutyl titanate was added while stirring. The mixture was maintained at 45°C for 30 h, and then the white powder was separated and dried. The dried powder was calcined at 550°C for 4 h to obtain SiO2@TiO2.

[0023] S3: Preparation of SiO2@SrSiO3 / TiO2: 0.5 g SiO2@TiO2 was thoroughly mixed with 80 ml deionized water, 0.08 g Sr(Cl)2·6H2O, and 0.05 g NaOH, and then transferred to a hydrothermal reactor and maintained at 160°C for 20 min. Then, a white powder was separated and dried. The above operation of S3 was repeated 5 times to obtain a core-shell structured SiO2@SrSiO3 / TiO2 photocatalyst.

[0024] Result analysis: The SiO2@SrSiO3 / TiO2 powder obtained above was characterized by SEM. Figure 1 As shown, the material is a core-shell structured nanosphere. Example 2

[0025] This embodiment provides a photocatalytic process for degrading nitrate simulated wastewater.

[0026] Prepare 1L of sodium nitrate simulated wastewater, NO3- The concentration was 100 mg / L. After ultrasonic mixing with 2.5 g of the catalytic material obtained in Example 1, the mixture was transferred to a photocatalytic device, 1 ml of formic acid was added, the UV light power was set to 500 W, and the total reaction time was 1.5 h. During the process, samples were taken every 15 min and NO3 was tested. - The results are as follows Figure 2 shown. Example 3

[0027] This embodiment provides a photocatalytic process for degrading phenol simulated wastewater.

[0028] 1L of phenol simulated wastewater was prepared, with a TOC concentration of 200mg / L. After ultrasonic mixing with 5g of the catalytic material obtained in Example 1, it was transferred to a photocatalytic device, 5ml of hydrogen peroxide was added, and the ultraviolet light power was set to 100W. The total reaction time was 2h. Samples were taken every 30min during the process and the TOC content was tested. The results are as follows: Figure 3 shown.

[0029] Comparative Example 1

[0030] This comparative example provides a photocatalytic process for degrading nitrate simulated wastewater.

[0031] The photocatalytic process was carried out in accordance with Example 2, except that the catalytic material used was commercial TiO2 (P25). Figure 2 It is shown that the material obtained in Example 1 has better nitrate reduction ability.

[0032] Comparative Example 2

[0033] This comparative example provides a photocatalytic process for degrading phenol simulated wastewater.

[0034] The photocatalytic process was carried out in accordance with Example 3, except that the catalytic material used was commercial TiO2 (P25). Figure 3 As shown, it is shown that the material obtained by implementation 1 has better phenol mineralization ability.

Claims

1. A core-shell structured photocatalyst SiO2@SrSiO3 / TiO2, characterized in that: The catalyst has a core-shell structure consisting of a core layer and a shell layer, wherein the core layer is SiO2 with an amorphous structure, and the shell layer is composed of a heterojunction formed by SrSiO3 and TiO2.

2. The core-shell structure photocatalyst SiO2@SrSiO3 / TiO2 according to claim 1, characterized in that: The core layer SiO2 is a nano-spherical structure, and the shell layer SrSiO3 / TiO2 is a hollow spherical structure wrapped on SiO2 and formed by the accumulation of nanoparticles, wherein TiO2 is located in the outer region of the shell layer and SrSiO3 is located in the inner region of the shell layer.

3. A method for preparing a core-shell structure photocatalyst SiO2@SrSiO3 / TiO2 as claimed in claim 1 or 2, characterized in that: The following steps are involved: S1, preparation of SiO2 core, ethanol, ammonia and water were mixed and stirred at room temperature for 10 minutes; then tetraethyl silicate ethanol solution was continuously added, maintained for 2-2.5 hours, white powder was separated and washed with ethanol, and then dried in an oven to obtain SiO2 nanospheres; S2, preparation of SiO2@TiO2, the SiO2 nanospheres obtained in S1 are fully mixed with ethanol and ammonia water, and an ester compound containing Ti is added during stirring, and the mixture is maintained at 40-60°C for 24-48 hours, and then a white powder is separated and dried, and the dried powder is calcined at high temperature to obtain SiO2@TiO2; S3, preparation of SiO2@SrSiO3 / TiO2, the SiO2@TiO2 obtained in S2 is fully stirred and mixed with deionized water, Sr-containing compounds and alkaline compounds, and then transferred to a hydrothermal kettle, maintained at 160-200°C for 16-30h, and then the white powder is separated and dried; the above operation of S3 is repeated to obtain a SiO2@SrSiO3 / TiO2 photocatalyst with a core-shell structure.

4. The method for preparing a core-shell structured photocatalyst SiO2@SrSiO3 / TiO2 according to claim 3, characterized in that: In said S1: The ethanol solution of tetraethyl silicate is tetraethyl silicate dissolved in anhydrous ethanol, and the concentration of tetraethyl silicate is 50-200g / L; Wherein, the amount of ethanol solution of tetraethyl silicate added is 6-20 ml / h; Wherein, the ethanol concentration is not less than 95%, and the amount of ethanol used is 10-20 times the amount of ethanol solution of tetraethyl silicate added per hour; The concentration of ammonia water is 25-28%, and the amount of ammonia water used is 0.5-2 times the amount of tetraethyl silicate ethanol solution added per hour; Among them, the diameter of SiO2 spheres is 200-500 nm.

5. The method for preparing a core-shell structured photocatalyst SiO2@SrSiO3 / TiO2 according to claim 3, characterized in that: In said S2: The Ti-containing ester compounds are isopropyl titanate and tetrabutyl titanate; The amount of Ti ester compound added is 0.5-2 times the molar amount of the material obtained in S1; Wherein, the concentration of ethanol is not less than 95%, and the amount of ethanol used is 50-100 times the mass of the material obtained in S1; The concentration of ammonia water is 25-28%, and the amount of ammonia water used is 1-2 times the mass of the material obtained containing S1; Wherein, the calcination temperature is 500-800°C.

6. The method for preparing a core-shell structured photocatalyst SiO2@SrSiO3 / TiO2 according to claim 3, characterized in that: In the S3: The Sr-containing compounds are SrCl2, Sr(OH)2 and their corresponding hydrates; The alkaline compounds are NaOH and Ca(OH)2; The amount of Sr-containing compound added in each hydrothermal reaction is 10%-20% of the molar amount of SiO2@TiO2; The amount of the alkaline compound added in each hydrothermal reaction is 1-2 times the molar amount of the Sr-containing compound; Wherein, step S3 is repeated 5-10 times; Among them, the hydrothermal temperature is 160-200°C, and the hydrothermal time is 16-30h.

7. Application of a core-shell structured photocatalyst SiO2@SrSiO3 / TiO2, characterized in that: The SiO2@SrSiO3 / TiO2 photocatalyst, additives and light source are placed in the wastewater to be treated, and the light source is turned on to carry out photocatalytic wastewater treatment.

8. The use of a core-shell structure photocatalyst SiO2@SrSiO3 / TiO2 according to claim 7, characterized in that: The wastewater to be treated contains nitrates and / or organic pollutants.

9. The use of a core-shell structure photocatalyst SiO2@SrSiO3 / TiO2 according to claim 8, characterized in that: When the wastewater to be treated contains nitrate, the additive is formic acid or oxalic acid; when the wastewater to be treated contains organic pollutants, the additive is hydrogen peroxide, ozone or persulfate.

10. The use of a core-shell structured photocatalyst SiO2@SrSiO3 / TiO2 according to claim 9, characterized in that: The dosage of SiO2@SrSiO3 / TiO2 is 0.1‰~0.5‰ of the mass of the wastewater solution to be treated; the dosage of formic acid or oxalic acid is 0-60 mmol / L; the dosage of hydrogen peroxide, ozone or persulfate is 50-200 mmol / L.

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