Preparation method of a photocatalytic functional coating for concrete surface and construction process of the coating

Abstract

The present invention belongs to the technical field of building materials, and particularly relates to a preparation method of a photocatalytic functional coating on the surface of concrete and a construction process of the coating. Bismuth oxybromide nanosheets BiOBr are prepared by a solvothermal method, and the solution is transferred to a reaction kettle. Silica coating is carried out on BiOBr by the Stöber method to form a BiOBr@SiO₂ core-shell structure. BiOBr@SiO₂ is dispersed in a mixed solution of ethanol and water to form a photocatalytic suspension. The photocatalytic suspension is sprayed on the surface of the concrete, and after curing, a photocatalytic functional coating on the surface of the concrete is obtained. The present invention solves the problems of ultraviolet dependence and poor bonding strength of the existing photocatalytic coatings through the core-shell structure, graphene oxide doping and layered spraying process. The test data show that the coating is significantly superior to the traditional technology in terms of visible light photocatalytic efficiency, interfacial bonding strength and erosion resistance, and is applicable to actual engineering scenarios such as bridges and tunnels.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a preparation method of a photocatalytic functional coating on the surface of concrete and a construction process of the coating. Background Art

[0002] The application in the field of building materials has become an important direction for the development of green building technologies. Its characteristics of decomposing pollutants and antibacterial and bacteriostatic properties through photocatalytic reactions have significantly improved the comprehensive performance of concrete structures. Currently, the mainstream photocatalytic materials on the market are mainly nano-titanium dioxide. For example, the ST-K01 type TiO2 photocatalyst produced by Toshiba Corporation in Japan has a specific surface area of 45-55 m² / g, and it realizes the degradation of organic substances by generating electron-hole pairs through ultraviolet light excitation. However, such materials have three major defects: strong dependence on ultraviolet light, which only accounts for 3%-5% of the solar spectrum, resulting in low catalytic efficiency under natural light conditions; weak bonding force with the concrete matrix, and the shedding rate is as high as 60% after being washed by rain; the recombination rate of photo-generated carriers of titanium dioxide exceeds 80%, leading to low quantum efficiency.

[0003] In the prior art, Chinese Patent CN111036234A proposes to prepare a photocatalytic composite coating by using metal injection molding technology, but the process requires preheating at 200-400 °C and laser sintering, and the energy consumption exceeds 15 kW·h / m², and the construction cost is too high.

[0004] The prior art generally has the following problems: insufficient visible light response of photocatalytic materials leads to low utilization rate in the actual environment; poor bonding force at the interface between the coating and the matrix leads to insufficient durability; complex preparation processes lead to high costs and difficulty in industrial application; the photocatalytic active components are easily covered or lost, resulting in poor long-term effectiveness. These problems seriously restrict the application of photocatalytic coatings in actual scenarios such as bridges, tunnels, and building facades. Summary of the Invention

[0005] In order to overcome the defects in the prior art, the present invention provides a preparation method of a photocatalytic functional coating on the surface of concrete, and the method includes the following steps:

[0006] Step S1: Prepare bismuth oxybromide nanosheets BiOBr by a solvothermal method. Dissolve bismuth nitrate pentahydrate and sodium bromide in a mixed solvent of ethylene glycol and water according to a molar ratio of 1:1-1:1.5, and the volume ratio of ethylene glycol to water is 3:2-5:2. The reaction temperature is 165-175 °C, and the reaction time is 12-13 hours;

[0007] Step S2: Transfer the solution in Step S1 to a reaction kettle, react at 160-180 °C for 10-14 hours, cool, centrifuge, wash, and dry. The number of centrifugal washing times is 5-8 times, and the drying temperature is 60-80 °C to obtain bismuth oxybromide nanosheets;

[0008] Step S3: Coat BiOBr with silica by the Stöber method to form a SiO2 coating layer. Disperse BiOBr in water, add ethanol and tetraethyl orthosilicate, and stir for 12 - 24 hours to form a BiOBr@SiO2 core - shell structure, where the mass ratio of BiOBr to SiO2 is 1:0.2 - 1:0.5;

[0009] Step S4: Disperse BiOBr@SiO2 in a mixed solution of ethanol and water to prepare a photocatalytic suspension with a concentration of 5 - 15 wt%. Spray the photocatalytic suspension on the concrete surface, and a photocatalytic functional coating on the concrete surface is obtained after curing.

[0010] The following are further optimizations of the above - mentioned technical solutions of the present invention:

[0011] In step S3, the thickness of the SiO2 coating layer is 5 - 50 nm, and 0.5 - 2 wt% of graphene oxide is doped in the SiO2 coating layer.

[0012] Further optimization: The volume ratio of ethanol to tetraethyl orthosilicate is 5:1 - 10:1.

[0013] Further optimization: Add ammonia water as a catalyst in step S3, and the concentration of the ammonia water is 0.1 - 0.5 mol / L.

[0014] Further optimization: Add polyethylene glycol as a dispersant in step S4, and the addition amount of the polyethylene glycol is 0.1% - 1% of the total mass of the suspension.

[0015] Further optimization: In step S4, the suspension further contains sodium dodecyl sulfate with a mass fraction of 0.05 - 0.2%.

[0016] Further optimization: In step S4, 0.1 - 0.5 wt% of epoxy resin is compounded in the spraying of the photocatalytic suspension on the concrete surface.

[0017] The present invention also discloses a construction process for a photocatalytic functional coating on the concrete surface, and this process includes the following steps:

[0018] Step T1: Pretreat the concrete surface, including sandblasting to a surface roughness Ra of 10 - 50 μm, and removing oil stains and loose particles;

[0019] Step T2: Spray the photocatalytic suspension in 2 - 3 layers, with an interval of 10 - 30 minutes between each layer;

[0020] Step T3: Use an ultraviolet lamp for auxiliary curing, with a curing time of 1 - 3 hours, a curing temperature of 20 - 35 °C, and an ultraviolet wavelength of 365 - 405 nm.

[0021] Further optimization: After step T3, the coating is subjected to a hydrophobic treatment by spraying an ethanol solution containing fluorosilane, and the hydrophobic angle is ≥ 120°.

[0022] Further optimization: In step T2, the spraying thickness of each layer is 3 - 8 μm, the spraying pressure is 0.3 - 0.6 MPa, and the distance between the nozzle and the concrete surface is 30 - 50 cm.

[0023] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0024] 1. The present invention uses BiOBr nanosheets as the photocatalytic core. Its narrow bandgap characteristic enables the light absorption range to cover the visible light band, the utilization rate of sunlight is increased to more than 45%, and the visible light response ability is significantly improved. Through the optical waveguide effect of the SiO2 coating layer in the present invention, the incident light forms multiple reflections within the core-shell structure, and the light energy capture efficiency is increased by 30%.

[0025] 2. The present invention dopes graphene oxide and promotes the transport of photo-generated electrons by using its π-π conjugation effect, reducing the carrier recombination rate from 80% of traditional TiO2 to below 35%, and the quantum efficiency is increased to 2.3 times that of the traditional coating. This improvement enables the coating to still maintain high catalytic activity under natural light conditions, breaking through the dependence limitation of traditional materials on ultraviolet light.

[0026] 3. The SiO2 coating layer of the present invention forms a chemical bond with calcium hydroxide on the concrete surface through hydroxyl groups, with high bonding strength, improved compared to the physical adsorption coating, and the interfacial bonding strength and durability are significantly enhanced. After compounding with epoxy resin, a three-dimensional cross-linked network is formed under ultraviolet-assisted curing, and the peeling rate is far better than that of ordinary coatings.

[0027] 4. The addition of sodium dodecyl sulfate in the present invention enables the penetration depth of the suspension to reach the pore area on the surface layer of the concrete, forming a mechanical interlocking effect. In addition, the hydrophobic treatment with fluorosilane makes the contact angle greater than 120°, which not only prevents the loss of active components caused by rainwater scouring.

[0028] 5. By using the solvothermal method combined with the Stöber method, the low-temperature controllable synthesis of the BiOBr@SiO2 core-shell structure is realized, avoiding the high energy consumption problem of the traditional mechanical-thermal coupling process.

[0029] 6. The photocatalytic suspension spraying process is implemented in 2 - 3 layers to form a uniformly covered coating. Compared with the process of the Japanese Toshiba ST-K01 type TiO2 coating that requires high-temperature sintering, the energy consumption of this method is reduced by more than 70%, and the curing temperature is controlled at 20 - 35 °C, significantly reducing the construction cost.

[0030] 7. The synergistic effect of the ammonia water catalytic system and the polyethylene glycol dispersant ensures that the stability of the suspension exceeds 72 hours, meeting the requirements of industrial continuous spraying.

[0031] 8. Through the physical isolation of BiOBr by the SiO2 coating layer, the chemical corrosion of the active components with the cement hydration products is prevented. Compared with the hybrid materials of Ningbo Institute of Materials Technology and Engineering, the coating of the present invention is significantly more excellent in terms of environmental adaptability and long-term effectiveness.

[0032] 9. The coating of the present invention is compounded by doping graphene oxide and epoxy resin. The coating has both conductivity and antistatic properties, and the surface resistivity is reduced, which can be applied to bridges and tunnels with lightning protection requirements.

[0033] The present invention will be further described below in conjunction with the drawings and embodiments. Description of the Drawings

[0034] Figure 1 It is the scanning electron microscope image (a) of BiOBr and the transmission electron microscope image (b) of BiOBr@SiO2 in Example 1 of the present invention;

[0035] Figure 2 It is the XPS spectrum of the product after the reaction of BiOBr@SiO2 with the cement hydration product Ca(OH)2 in Example 1 of the present invention;

[0036] Figure 3 It is the cross-sectional scanning electron microscope image (a) and EDX images (b, c, d) of the photocatalytic functional coating on the concrete surface in Example 1 of the present invention;

[0037] Figure 4 It is the surface scanning electron microscope image (a) and EDX images (b, c, d, e) of the photocatalytic functional coating on the concrete surface in Example 1 of the present invention. Detailed Embodiments

[0038] In the present invention, the sources of various raw materials are briefly described as follows:

[0039] Bismuth nitrate pentahydrate: Purchased from Sigma-Aldrich, USA, CAS No. 10035-06-0, purity ≥99.9%; Sodium bromide: Sinopharm Chemical Reagent Co., Ltd., analytical reagent grade, CAS No. 7647-15-6; Ethylene glycol: Sinopharm Chemical Reagent Co., Ltd., purity ≥99.5%, industrial grade; Tetraethyl orthosilicate (TEOS): Alfa Aesar, USA, CAS No. 78-10-4, purity ≥98%; Graphene oxide: Changzhou Sixth Element Materials Technology Co., Ltd., model SE2430, sheet thickness 1-5 nm; Polyethylene glycol (PEG-400): Dow Chemical Company, USA, molecular weight 380-420, viscosity 70-100 mPa·s; Sodium dodecyl sulfate (SDS): Sinopharm Chemical Reagent Co., Ltd., biological reagent grade, CAS No. 151-21-3; Epoxy resin (E-44): Nan Ya Plastics Corporation, epoxy value 0.41-0.47 eq / 100 g; Ammonia water: Sinopharm Chemical Reagent Co., Ltd., concentration 25%-28%, analytical pure; Fluorosilane (hydrophobic agent): Shin-Etsu Chemical Co., Ltd., Japan, model KF-115, CAS No. 101947-16-4; Ultraviolet lamp: Foshan Lighting Co., Ltd., model FS-ZW30D, wavelength 365-405 nm, power 30 W; Hydroxypropyl methylcellulose (HPMC): Dow Chemical Company, USA, model K4M, viscosity 4000-6000 mPa·s; Sodium hyaluronate: Shiseido Company, Ltd., Japan, molecular weight 80-1.5 million Da, CAS No. 9067-32-7; Carboxymethyl chitosan: Zhejiang Jinke Pharmaceutical Co., Ltd., deacetylation degree ≥85%, viscosity 50-200 mPa·s; Polyglycerol-10 laurate: Hubei Zhenbo Chemical Co., Ltd., CAS No. 34406-66-1, purity ≥99%.

[0040] A preparation method of a photocatalytic functional coating for concrete surface, the method comprising the following steps:

[0041] Step S1: Prepare bismuth oxybromide nanosheets BiOBr by solvothermal method. Dissolve bismuth nitrate pentahydrate and sodium bromide in a mixed solvent of ethylene glycol and water according to a molar ratio of 1:1 - 1:1.5, the volume ratio of ethylene glycol to water is 3:2 - 5:2, the reaction temperature is 165-175 °C, and the reaction time is 12-13 hours;

[0042] Step S2: Transfer the solution of Step S1 to a reaction kettle, react at 160-180 °C for 10-14 hours, cool, centrifuge, wash and dry. The number of centrifugation and washing times is 5-8 times, and the drying temperature is 60-80 °C to obtain bismuth oxybromide nanosheets;

[0043] Step S3: Coating BiOBr with silica by the Stöber method. Disperse BiOBr in water, add ethanol and tetraethyl orthosilicate, and stir for 12 - 24 hours to form a BiOBr@SiO2 core-shell structure, where the mass ratio of BiOBr to SiO2 is 1:0.2 - 1:0.5;

[0044] Step S4: Disperse BiOBr@SiO2 in a mixed solution of ethanol and water to prepare a photocatalytic suspension with a concentration of 5 - 15 wt%. Spray the photocatalytic suspension on the surface of the concrete, and a photocatalytic functional coating on the concrete surface is obtained after curing.

[0045] In step S3, the thickness of the SiO2 coating layer is 5 - 50 nm, and 0.5 - 2 wt% of graphene oxide is doped in the SiO2 coating layer.

[0046] The volume ratio of ethanol to tetraethyl orthosilicate is 5:1 - 10:1.

[0047] In step S3, ammonia water is added as a catalyst, and the concentration of the ammonia water is 0.1 - 0.5 mol / L.

[0048] In step S4, polyethylene glycol is added as a dispersant, and the addition amount of the polyethylene glycol is 0.1% - 1% of the total mass of the suspension.

[0049] In step S4, the suspension also contains 0.05 - 0.2% by mass of sodium dodecyl sulfate.

[0050] In step S4, 0.1 - 0.5 wt% of epoxy resin can be compounded in the spraying of the photocatalytic suspension on the concrete surface.

[0051] A construction process for a photocatalytic functional coating on the concrete surface, the process comprising the following steps:

[0052] Step T1: Pretreatment of the concrete surface, including sandblasting to a surface roughness Ra of 10 - 50 μm, and removing oil stains and loose particles;

[0053] Step T2: Spraying the photocatalytic suspension, spraying in 2 - 3 layers, with an interval of 10 - 30 minutes between each layer;

[0054] Step T3: Curing assisted by an ultraviolet lamp, with a curing time of 1 - 3 hours, a curing temperature of 20 - 35 °C, and an ultraviolet wavelength of 365 - 405 nm.

[0055] After step T3, hydrophobic treatment is carried out on the coating, spraying an ethanol solution containing fluorosilane, and the hydrophobic angle ≥ 120°.

[0056] In step T2, the spraying thickness of each layer is 3-8 μm, the spraying pressure is 0.3-0.6 MPa, and the distance between the nozzle and the concrete surface is 30-50 cm.

[0057] The technical solutions of the present invention will be further described below through examples and comparative examples, but the protection scope of the present invention is not limited thereto. Example 1

[0058] Bismuth oxybromide nanosheets BiOBr were prepared by the solvothermal method. The molar ratio of bismuth nitrate pentahydrate to sodium bromide was 1:1.5, the volume ratio of ethylene glycol to water was 5:2, the reaction temperature was 175 °C, and the reaction time was 12 hours.

[0059] The solution of step S1 was transferred to a reaction kettle, the reaction kettle temperature was 180 °C, the reaction time was 14 hours, centrifugal washing was carried out 5 times, and the drying temperature was 70 °C.

[0060] Silica coating was carried out on BiOBr by the Stöber method. The mass ratio of BiOBr to SiO2 was 1:0.5, the volume ratio of ethanol to tetraethyl orthosilicate was 5:1, the ammonia concentration was 0.3 mol / L, 2% of graphene oxide was doped, and the coating layer thickness was 25 nm.

[0061] BiOBr@SiO2 was dispersed in a mixed solution of ethanol and water to prepare a photocatalytic suspension. The photocatalytic suspension was sprayed on the concrete surface, and a photocatalytic functional coating on the concrete surface was obtained after curing.

[0062] The concentrations of the components in the prepared photocatalytic suspension were: BiOBr@SiO2 15 wt%, polyethylene glycol 0.1 wt%, sodium dodecyl sulfate 0.1 wt%, epoxy resin 0.1 wt%, and the balance was a mixed solution of ethanol and water (V / V: 95:5).

[0063] The concrete surface was pretreated, including sandblasting treatment and removal of oil stains and loose particles; the photocatalytic suspension was sprayed, and ultraviolet lamp-assisted curing was adopted. The sandblasting roughness was 50 μm, the spraying pressure was 0.45 MPa, the ultraviolet curing was 1 hour, and the hydrophobic angle was 122°. Example 2

[0064] In this example, the same parts as in Example 1 will not be described in detail, and the differences are as follows:

[0065] Bismuth oxybromide nanosheets BiOBr were prepared by the solvothermal method. The molar ratio of bismuth nitrate pentahydrate to sodium bromide was 1:1, the volume ratio of ethylene glycol to water was 3:2, the reaction temperature was 165 °C, and the reaction time was 12.5 hours.

[0066] The solution of step S1 was transferred to a reaction kettle, the reaction kettle temperature was 160 °C, the reaction time was 10 hours, centrifugal washing was carried out 8 times, and the drying temperature was 60 °C.

[0067] The mass ratio of BiOBr to SiO2 is 1:0.2, the volume ratio of ethanol to tetraethyl orthosilicate is 10:1, the concentration of ammonia water is 0.1 mol / L, the doped graphene oxide is 0.5%, and the thickness of the coating layer is 5 nm.

[0068] The concentrations of the components in the prepared photocatalytic suspension are as follows: BiOBr@SiO2 5 wt%, polyethylene glycol 1 wt%, sodium dodecyl sulfate 0.05 wt%, epoxy resin 0.5 wt%, and the balance is a mixed solution of ethanol and water (V / V: 95:5).

[0069] The sandblasting roughness is 10 μm, the spraying pressure is 0.3 MPa, the ultraviolet curing is 3 hours, and the hydrophobic angle is 120°. Example 3

[0070] In this example, the same parts as in Example 1 will not be described in detail, and the differences are as follows:

[0071] Bismuth oxybromide nanosheets BiOBr are prepared by a solvothermal method. The molar ratio of bismuth nitrate pentahydrate to sodium bromide is 1:1.25, the volume ratio of ethylene glycol to water is 4:2, the reaction temperature is 170 °C, and the reaction time is 13 hours.

[0072] The solution in step S1 is transferred to a reaction kettle. The temperature of the reaction kettle is 170 °C, the reaction time is 12 hours, centrifugal cleaning is carried out 6 times, and the drying temperature is 70 °C.

[0073] The mass ratio of BiOBr to SiO2 is 1:0.35, the volume ratio of ethanol to tetraethyl orthosilicate is 7:1, the concentration of ammonia water is 0.5 mol / L, the doped graphene oxide is 1.2%, and the thickness of the coating layer is 50 nm.

[0074] The concentrations of the components in the prepared photocatalytic suspension are as follows: BiOBr@SiO2 10 wt%, polyethylene glycol 0.5 wt%, sodium dodecyl sulfate 0.2 wt%, epoxy resin 0.3 wt%, and the balance is a mixed solution of ethanol and water (V / V: 95:5).

[0075] The sandblasting roughness is 30 μm, the spraying pressure is 0.6 MPa, the ultraviolet curing is 2 hours, and the hydrophobic angle is 125°.

[0076] Comparative Example 1

[0077] In this comparative example, the same parts as in Example 1 will not be described in detail, and the differences are as follows: TiO2 coating without BiOBr coating.

[0078] Comparative Example 2

[0079] In this comparative example, the same parts as in Example 1 will not be described in detail, and the differences are as follows: BiOBr coating without doped graphene oxide.

[0080] Material Characterization and Performance Test Analysis

[0081] Bismuth oxybromide (BiOBr), as a new type of photocatalyst, is one of the Bi-based semiconductors. Due to its unique atomic arrangement and electronic configuration, it has high photocatalytic activity under visible light irradiation.

[0082] As Figure 1 shown, the BiOBr@SiO2 core-shell structure was synthesized in this invention.

[0083] As Figure 2 shown, the binding property between the photocatalytic material and the matrix was improved by nano-SiO2, and the pozzolanic reaction occurred between SiO2 and the hydration products of the matrix.

[0084] As Figure 3 and 4 shown, the compatibility between the photocatalyst and the cement-based matrix was improved, and the long-term photocatalytic performance was increased.

[0085] The coatings prepared from 3 examples and 2 comparative examples were subjected to performance tests according to the general method. The test results are shown in Table 1. Among them, the visible-light photocatalytic efficiency was sampled as the NO degradation rate under simulated solar light (AM1.5G); the interfacial bonding strength was determined by the pull-out test for the adhesive force between the coating and the concrete; the erosion and shedding rate was the shedding rate after simulating rainfall (25 mm / h) for 100 times; the quantum efficiency was the carrier separation efficiency tested by photoelectrochemistry.

[0086] Table 1 Performance Test Results

[0087] Group Visible light catalytic efficiency (%) Interface bonding strength (MPa) Wash-off rate (%) Quantum efficiency (%) Example 1 45.3 4.8 4.2 38.5 Example 2 37.8 4.1 5.7 32.1 Example 3 41.6 4.5 4.8 35.4 Comparative Example 1 8.0 1.5 62.0 12.0 Comparative Example 2 29.5 2.1 58.0 24.3

[0088] As can be seen from Table 1, the BiOBr@SiO2 core-shell structures of Examples 1-3 extended the light absorption range to the visible light band through the narrow bandgap property (2.6 - 2.8 eV) and the optical waveguide effect of the SiO2 coating layer, and the catalytic efficiency was significantly increased to 37.8% - 45.3%. In contrast, Comparative Example 1 (traditional TiO2) relied on ultraviolet light and the efficiency was only 8%, and Comparative Example 2 had increased light reflection loss due to no SiO2 coating and the efficiency was reduced to 29.5%.

[0089] The chemical bonding (Si-O-Ca) between the SiO2 coating layer and Ca(OH)2 in the concrete enabled the bonding strengths of Examples 1-3 to reach 4.1 - 4.8 MPa, while Comparative Example 1 (physical adsorption) and Comparative Example 2 (no SiO2) were reduced to 1.5 MPa and 2.1 MPa respectively. The compounding of epoxy resin further formed a three-dimensional cross-linked network to enhance the mechanical interlock between the coating and the matrix.

[0090] The fluorosilane hydrophobic treatment effectively reduces the shedding caused by rainwater scouring. The shedding rates of Examples 1-3 are all lower than 6%, while those of Comparative Examples 1 and 2 are as high as 58%-62% due to loose structure or lack of hydrophobic treatment.

[0091] The π-π conjugation effect of graphene oxide promotes the transfer of photo-generated electrons. The quantum efficiency of Example 1 reaches 38.5%, while that of Comparative Example 2 without doping is only 24.3%.

[0092] In addition, the SiO2 coating layer isolates the chemical corrosion between BiOBr and the hydration products of cement, making the efficiency decay of the coating less than 8% after 1000 hours of aging.

[0093] The present invention comprehensively solves the problems of ultraviolet dependence, poor bonding strength and insufficient long-term effectiveness of existing photocatalytic coatings through the BiOBr@SiO2 core-shell structure, graphene oxide doping and layered spraying process. The test data show that the coating is significantly superior to the traditional technology in terms of visible light photocatalytic efficiency, interfacial bonding strength and erosion resistance, and is applicable to practical engineering scenarios such as bridges and tunnels.

[0094] For those of ordinary skill in the art, according to the teachings of the present invention, without departing from the principles and spirit of the present invention, the changes, modifications, substitutions and variations made to the embodiments still fall within the protection scope of the present invention.

Claims

1. A preparation method of a photocatalytic functional coating on the concrete surface, characterized in that The method includes the following steps: Step S1: Prepare bismuth oxybromide nanosheets BiOBr by solvothermal method. Dissolve bismuth nitrate pentahydrate and sodium bromide in a mixed solvent of ethylene glycol and water at a molar ratio of 1:1 - 1:1.5, where the volume ratio of ethylene glycol to water is 3:2 - 5:2, the reaction temperature is 165 - 175 °C, and the reaction time is 12 - 13 hours. Step S2: Transfer the solution of Step S1 to a reaction kettle, react at 160 - 180 °C for 10 - 14 hours, cool, then centrifuge, wash, and dry. The number of times of centrifugal washing is 5 - 8 times, and the drying temperature is 60 - 80 °C to obtain bismuth oxybromide nanosheets. Step S3: Coating BiOBr with silica by Stöber method to form a SiO2 coating layer. Disperse BiOBr in water, add ethanol and tetraethyl orthosilicate, and stir for 12 - 24 hours to form a BiOBr@SiO2 core - shell structure, where the mass ratio of BiOBr to SiO2 is 1:0.2 - 1:0.

5. Step S4: Disperse BiOBr@SiO2 in a mixed solution of ethanol and water to prepare a photocatalytic suspension with a concentration of 5 - 15 wt%. Spray the photocatalytic suspension on the concrete surface, and after curing, a photocatalytic functional coating on the concrete surface is obtained. In Step S3, the thickness of the SiO2 coating layer is 5 - 50 nm, and 0.5 - 2 wt% of graphene oxide is doped in the SiO2 coating layer.

2. The preparation method of a photocatalytic functional coating on the concrete surface according to claim 1, characterized in that: The volume ratio of ethanol to tetraethyl orthosilicate is 5:1 - 10:

1.

3. The preparation method of a photocatalytic functional coating on the concrete surface according to claim 1, characterized in that: In Step S3, ammonia water is added as a catalyst, and the concentration of the ammonia water is 0.1 - 0.5 mol / L.

4. The preparation method of a photocatalytic functional coating on the concrete surface according to claim 1, characterized in that: In Step S4, polyethylene glycol is added as a dispersant, and the addition amount of the polyethylene glycol is 0.1% - 1% of the total mass of the suspension.

5. The preparation method of a photocatalytic functional coating on the concrete surface according to claim 1, characterized in that: In Step S4, the suspension also contains sodium dodecyl sulfate with a mass fraction of 0.05 - 0.2%.

6. The preparation method of a photocatalytic functional coating on the concrete surface according to claim 1, characterized in that: In Step S4, 0.1 - 0.5 wt% of epoxy resin can be compounded in the spraying of the photocatalytic suspension on the concrete surface.

7. A construction process of a photocatalytic functional coating on the concrete surface prepared by the method according to any one of claims 1-6, characterized in that, This process includes the following steps: Step T1: Pretreatment of the concrete surface, including sandblasting to a surface roughness Ra of 10 - 50 μm, and removing oil stains and loose particles. Step T2: Spray the photocatalytic suspension described in any one of claims 1 - 6, spray in 2 - 3 layers, and the interval between each layer is 10 - 30 minutes. Step T3: Use an ultraviolet lamp for auxiliary curing, the curing time is 1 - 3 hours, the curing temperature is 20 - 35 °C, and the ultraviolet wavelength is 365 - 405 nm.

8. The construction process of a photocatalytic functional coating on the concrete surface according to claim 7, characterized in that: After Step T3, perform hydrophobic treatment on the coating, spray an ethanol solution containing fluorosilane, and the hydrophobic angle ≥ 120°.

9. The construction process of a photocatalytic functional coating on the concrete surface according to claim 7, characterized in that: In Step T2, the spraying thickness of each layer is 3 - 8 μm, the spraying pressure is 0.3 - 0.6 MPa, and the distance between the nozzle and the concrete surface is 30 - 50 cm.

Images