Self-cleaning exterior wall coating

Abstract

The invention relates to the technical field of building materials, and discloses a self-cleaning exterior wall coating which comprises the following components in parts by weight: 30-50 parts of titanium dioxide; 1 to 5 parts of silver nanoparticles; 2 to 10 parts of cadmium selenide quantum dots; the invention also provides a preparation method of the self-cleaning exterior wall coating, and the preparation method comprises the following steps: S1, preparation of a TiO2 / AgNPs / CdSe composite material: respectively adding prepared silver nanoparticles and cadmium selenide quantum dots into TiO2 sol, and carrying out stirring, mixing and quality removal operation; and S2, preparing a coating solution. The TiO2 / AgNPs / CdSe composite material is prepared, ethanol is optimized to adjust the flowability of the coating, an ultraviolet curing process is adopted, and the thickness of the coating is accurately controlled, so that efficient photocatalysis of the coating under visible light is realized, the self-cleaning capability is enhanced, and the adhesive force and weather resistance of the coating are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and particularly to a self-cleaning exterior wall coating. Background Art

[0002] With the acceleration of the urbanization process, the exterior walls of buildings are exposed to the natural environment for a long time and are prone to the attachment of dust, oil stains and organic pollutants, which affects the aesthetics and service life of the buildings. Especially in rainy and dusty urban environments, the phenomenon of wall pollution is more obvious, and the cleaning and maintenance costs are high and frequent, consuming time and effort. The emergence of self-cleaning exterior wall coatings has become an important solution to reduce building maintenance costs and improve building durability.

[0003] Most of the existing self-cleaning exterior wall coating technologies use titanium dioxide as the main photocatalyst, relying on its strong oxidation ability generated under ultraviolet light irradiation to degrade organic pollutants on the wall surface. Some technologies improve the adhesion and weather resistance of the coating and extend the service life of the coating by doping metal nanoparticles in the coating or using modified polymers. In traditional processes, the fluidity of the coating is generally controlled by physical stirring or adjusting the resin ratio to ensure a uniform coating during construction. In addition, some coatings use thermal curing or natural curing methods to ensure the stability of the coating structure. The existing technologies have a certain application basis in photocatalytic degradation and surface self-cleaning effects, and can meet the basic self-cleaning requirements to a certain extent.

[0004] However, there are still some deficiencies in the existing technologies, which are difficult to fully meet the actual application requirements; firstly, the activity of traditional titanium dioxide photocatalytic materials under visible light is low, resulting in limited self-cleaning effects of the coating under low light or indoor conditions, and the all-weather self-cleaning function cannot be achieved; secondly, the method of adjusting the fluidity of the coating by physical stirring is prone to uneven distribution of nanoparticles in the resin, resulting in agglomeration, which affects the photocatalytic efficiency and overall stability of the coating; in addition, traditional curing processes such as natural curing or single thermal curing are difficult to fully activate the photocatalyst, resulting in attenuation of the self-cleaning function of the coating, insufficient weather resistance and adhesion, and the coating is prone to peeling or failure; finally, the coating thickness mostly depends on experience control and cannot be accurately regulated, and it is easy to have the situation of too thick or too thin coating, which affects the photocatalytic reaction efficiency and the long-term stability of the coating. Summary of the Invention

[0005] In view of the deficiencies of the existing technologies, the present invention provides a self-cleaning exterior wall coating, which solves the problems of low photocatalytic efficiency, poor coating adhesion, insufficient weather resistance and inaccurate thickness control in the existing self-cleaning exterior wall coatings.

[0006] To achieve the above objectives, the present invention is realized through the following technical solutions: A self-cleaning exterior wall coating, the coating comprising the following components in parts by weight:

[0007] Titanium dioxide: 30 - 50 parts. As a photocatalyst, titanium dioxide can excite electrons and holes under the irradiation of ultraviolet or visible light, generating strongly oxidizing substances such as hydroxyl radicals ( · OH) and hydrogen peroxide (H 2 O 2 ). These strongly oxidizing substances can effectively degrade surface dirt, pollutants or organic substances, thus achieving the self-cleaning function. The photocatalytic effect of titanium dioxide is particularly obvious under ultraviolet irradiation, but by compounding with other components, its photocatalytic effect under visible light or even weak light conditions can be enhanced;

[0008] Silver nanoparticles: 1 - 5 parts. The surface plasmon resonance effect (SPR) of silver nanoparticles is the key to their function. Through this effect, silver nanoparticles can absorb visible light and convert light energy into an enhancement of the local surface electromagnetic field. This enhanced electric field further improves the excitation efficiency of electrons in the TiO 2 photocatalytic reaction, thus increasing the activity of the photocatalyst. The presence of silver can not only enhance the photocatalytic reaction, but also improve the degradation ability of the coating to organic pollutants, and at the same time has antibacterial effects, which helps to clean and maintain the coating surface;

[0009] Cadmium selenide quantum dots: 2 - 10 parts. The photocatalytic effect of cadmium selenide quantum dots is mainly achieved through their quantum confinement effect and electron excitation behavior. When irradiated with visible light, the quantum dots can absorb light energy and excite electron transitions, thus providing additional electrons for the TiO 2 photocatalyst. After these electrons combine with the electrons in TiO 2 , more free radicals (such as · OH) can be generated, thus enhancing the photocatalytic degradation ability of the coating. The addition of CdSe quantum dots makes the photocatalytic performance of the coating not limited to the ultraviolet range, and can also effectively play a role in the visible light environment, improving the efficiency of the coating in daily applications;

[0010] Polyurethane resin: 30 - 40 parts. The role of polyurethane resin is not only to provide physical support and adhesion, but also its weather resistance and ultraviolet resistance. The polymer chain structure of the resin enables the coating to maintain stable adhesion under external environmental changes (such as temperature, humidity, ultraviolet irradiation, etc.), and is not easy to peel or crack. At the same time, polyurethane has a certain flexibility, which can resist external impacts and mechanical damages, and prolong the service life of the coating;

[0011] Ethanol: 15 - 25 parts. Ethanol, as a solvent, has good dissolution performance and can help uniformly disperse titanium dioxide, silver nanoparticles, and cadmium selenide quantum dots during the preparation process, thereby improving the overall uniformity of the coating. During the formulation of the coating, the use of ethanol ensures the appropriate fluidity of the coating, facilitating coating application and not affecting the final properties of the coating. In addition, ethanol has a relatively high volatility and can quickly evaporate after the coating is applied, ensuring the drying speed of the coating and the stability of the paint.

[0012] Preferably, the titanium dioxide includes:

[0013] Anatase TiO 2 powder. Anatase TiO 2 has a higher surface energy and a larger specific surface area, which makes it easier to generate photoexcited electrons (e - ) and holes (h + ) under light conditions. These electrons and holes can react with moisture or oxygen to generate oxidizing free radicals (such as · OH, H 2 O 2 ), and then decompose organic substances or dirt;

[0014] Prepare TiO 2 sol by the sol - gel method. The sol - gel method dissolves metal organic compounds in a solvent to form a sol, and then obtains the required nanoparticles through a gelation process. The sol - gel method can provide uniform and fine TiO 2 particles, ensuring their uniform dispersion in the coating and thus improving their photocatalytic efficiency. Small - sized TiO 2 particles have a larger specific surface area, which can increase the reaction sites and thus improve the reaction rate;

[0015] Control the pH value at 4 - 5 under the action of an acidic catalyst. The adjustment of the pH value has an important influence on the morphology and dispersibility of TiO 2 particles. In an acidic environment, the surface of TiO 2 carries a positive charge, which helps it maintain a dispersed state in the solution and avoid agglomeration between particles. A low pH also promotes the stability of the TiO 2 sol, reducing precipitation and particle deposition. Smaller particles mean a larger specific surface area and higher photocatalytic efficiency. Therefore, controlling the pH value helps optimize the performance of TiO 2 , making it show stronger photocatalytic degradation ability in the subsequent coating;

[0016] Stir at 25 - 30 °C for 4 hours to ensure the uniform dispersion of TiO 2 particles. Controlling the temperature at 25 - 30 °C can prevent TiO2 Excessive aggregation and precipitation of particles, while appropriate stirring ensures the uniform dispersion of TiO particles in the sol. 2 In this temperature range, the sol state of TiO is the most stable and not easily forms large particle precipitation. 2 The stirring time of 4 hours helps the full reaction of the TiO sol, keeps it in a stable state in the liquid, and the size and dispersibility of the particles can be effectively controlled, thereby improving the photocatalytic activity and uniformity of TiO in the coating. 2 2

[0017] Preferably, the silver nanoparticles include:

[0018] Using silver nitrate solution as a precursor, in the reduction reaction, Ag ions will be reduced to metallic silver (Ag) and finally form silver nanoparticles. The concentration of silver ions, the choice of reducing agent, and the reaction conditions directly affect the particle size, morphology, and dispersibility of silver nanoparticles. Silver ions in the silver nitrate solution are easily reduced rapidly under the action of the reducing agent, thus forming stable silver nanoparticles; +

[0019] Using amino acids or glucose as reducing agents, the reduction reaction is carried out at 60 - 80 °C. The amino groups of amino acids and the aldehyde groups of glucose provide electron sources to promote the reduction process of silver ions. Appropriate temperature helps to accelerate the reduction reaction and at the same time avoid the aggregation of silver nanoparticles caused by too high temperature. The temperature range of 60 - 80 °C ensures the efficient progress of the reduction reaction and can obtain silver nanoparticles with smaller particle size and uniform dispersion;

[0020] By adding polyvinylpyrrolidone for surface modification to prevent nanoparticle aggregation. Polyvinylpyrrolidone (PVP) is a surfactant with good hydrophilicity and silver affinity. During the synthesis of silver nanoparticles, PVP molecules form a protective film by acting on the surface of silver nanoparticles to prevent the mutual attraction and aggregation between silver nanoparticles;

[0021] After the reaction for 1 hour, the particle size is analyzed by transmission electron microscopy and controlled within 20 - 60 nm. Particle size is one of the important factors affecting the performance of silver nanoparticles. Smaller particle size means larger specific surface area, which helps to enhance its photocatalytic performance and surface plasmon resonance effect (SPR). Through TEM analysis, the particle size distribution of silver nanoparticles can be accurately measured, and the uniformity and stability of the particles can be ensured. Silver nanoparticles with particle size controlled within the range of 20 - 60 nm can fully exert their photocatalytic and SPR effects;

[0022] The unreacted substances are removed by centrifugal washing to obtain modified silver nanoparticles. Through centrifugal washing, these impurities can be effectively removed, ensuring that the finally obtained silver nanoparticles have high purity and no unnecessary contaminants. The washing process helps to improve the stability and long-term performance of silver nanoparticles, avoiding unnecessary precipitation or excessive residue of surface modifiers.

[0023] Preferably, the cadmium selenide quantum dots include:

[0024] CdO and Se powder are used as precursors. During the synthesis process, CdO and Se powder react through heating to form CdSe, resulting in CdSe quantum dots at the nanoscale. With the control of reaction conditions, the generated CdSe has a small and uniform particle size, thus enhancing the optical properties of the quantum dots. The synthesis process of CdSe needs to be carried out under controlled conditions to ensure that the particle size, morphology, and optical properties can meet the expected requirements, especially the absorption ability in the visible light range;

[0025] In triethanolamine solvent, the reaction is carried out at 200 - 250 °C using the hot injection method. The hot injection method is a commonly used method for synthesizing nanomaterials, especially in the synthesis of quantum dots. Triethanolamine serves as both a solvent and a reducing agent. It not only provides the solvent environment required for the reaction but also donates electrons through the nitrogen groups in its molecular structure, facilitating the reduction of metal ions. Heating to a temperature of 200 - 250 °C helps to accelerate the reaction rate and promote the rapid combination of CdO and Se powder, thereby generating cadmium selenide quantum dots;

[0026] The reaction time is controlled within 30 minutes to 1 hour to regulate the particle size of the quantum dots to 5 - 10 nm. The length of the reaction time directly affects the size and morphology of CdSe quantum dots. A shorter reaction time will result in too small a particle size of the quantum dots, while too long a reaction time will cause the particle size to be too large and even lead to agglomeration. Controlling the reaction time between 30 minutes and 1 hour can complete the growth of CdSe quantum dots within an appropriate time window, thus ensuring that the particle size is controlled between 5 - 10 nm. The particle size of the quantum dots is closely related to their optical properties. The smaller the particle size, the more obvious the quantum confinement effect, and the bluer the absorption and emission wavelengths;

[0027] An ultraviolet-visible spectrophotometer is used to analyze the absorption spectrum to ensure that its absorption band is in the visible light range. By performing absorption spectrum tests with an ultraviolet-visible spectrophotometer, the light absorption band of CdSe quantum dots can be determined. If its absorption band is in the visible light range, it means that the quantum dots can effectively absorb visible light and excite electrons, thereby participating in photocatalytic reactions. This property enables CdSe quantum dots to significantly improve the photocatalytic activity of coatings, especially under weak light conditions in daily environments, enhancing the self-cleaning performance of coatings.

[0028] Preferably, the polyurethane resin includes:

[0029] The polyurethane resin is synthesized by the prepolymerization method. The polyether polyol reacts with MDI to synthesize a polyurethane prepolymer. The isocyanate group (-NCO) in MDI reacts with the hydroxyl group (-OH) in the polyether polyol to form a polyurethane segment. The prepolymerization reaction is carried out at a relatively low temperature (usually 70-90 °C). At this time, the reaction of MDI and the polyol forms a polyurethane prepolymer with active isocyanate groups, and these active groups provide the possibility for subsequent cross-linking and curing reactions;

[0030] Control the reaction temperature between 70-90 °C and the reaction time for 2-4 hours to obtain a polyurethane resin with appropriate viscosity. In the temperature range of 70-90 °C, the reaction rate of MDI and the polyether polyol is relatively moderate, which not only helps to form a stable polyurethane prepolymer but also avoids side reactions or excessive cross-linking caused by too high temperature. Controlling the reaction time for 2-4 hours helps the reaction to proceed completely, so as to obtain a polyurethane resin with appropriate viscosity.

[0031] The present invention also provides a preparation method of a self-cleaning exterior wall coating, which includes the following steps:

[0032] S1. Preparation of TiO 2 / AgNPs / CdSe composite material. Add the prepared silver nanoparticles and cadmium selenide quantum dots into TiO 2 sol respectively and carry out stirring, mixing and impurity removal operations;

[0033] S2. Preparation of the coating solution. Add the TiO 2 / AgNPs / CdSe composite material into the prepared polyurethane resin and mix it with the addition of ethanol to obtain the coating;

[0034] S3. Coating application. Apply the obtained coating on the wall by spraying, brushing or dipping methods;

[0035] S4. Coating curing. Cure the coating under a specific temperature range and ultraviolet light.

[0036] Preferably, the preparation of the TiO 2 / AgNPs / CdSe composite material includes:

[0037] Add the prepared silver nanoparticles and cadmium selenide quantum dots into TiO 2 sol respectively, and use an ultrasonic disperser to disperse them evenly. TiO 2As the main photocatalyst, it needs to be in close contact with AgNPs and CdSe for their synergistic effect. The ultrasonic disperser generates high-frequency vibrations, causing the particles in the solution to collide and disperse rapidly, avoiding the agglomeration of particles. Through ultrasonic treatment, it can ensure that silver nanoparticles and cadmium selenide quantum dots are evenly distributed in the TiO 2 sol, thus providing the best reaction environment for subsequent photocatalytic reactions;

[0038] Stir for 2 - 4 hours to ensure that silver nanoparticles and cadmium selenide quantum dots are evenly distributed in the TiO 2 sol to obtain the TiO 2 / AgNPs / CdSe composite material. During the stirring process, the surface of TiO 2 particles will carry a certain amount of negative charge, while silver nanoparticles and cadmium selenide quantum dots are adsorbed or combined with each other through electrostatic or van der Waals forces. By stirring within this time range, it ensures that these nanoparticles can be evenly distributed in the TiO 2 sol, thereby providing more efficient photocatalytic action in the coating;

[0039] Use vacuum filtration or centrifugation to remove unreacted impurities in the solution to ensure the purity of the composite material. Vacuum filtration and centrifugal separation are common separation and purification methods, which can effectively remove impurities and unreacted components in the solution. These impurities not only affect the purity of the composite material but also interfere with its photocatalytic reaction efficiency. Through vacuum filtration or centrifugation, larger particles and impurities can be effectively separated to ensure the ratio and dispersibility of TiO 2 , silver nanoparticles and cadmium selenide quantum dots in the composite material, and finally obtain a composite material with higher purity. The high purity of the composite material helps to improve the photocatalytic reaction efficiency and self-cleaning performance.

[0040] Preferably, the preparation of the coating solution includes:

[0041] Add the TiO 2 / AgNPs / CdSe composite material into the polyurethane resin solution. The TiO 2 particles provide photocatalytic ability, silver nanoparticles enhance light absorption through the surface plasmon resonance effect (SPR), and cadmium selenide quantum dots improve the photocatalytic activity of the coating under visible light through the quantum confinement effect. The polyurethane resin provides a stable dispersion medium and good adhesion for these nanoparticles, ensuring that no particle precipitation or aggregation occurs during the use of the coating;

[0042] Stir with a magnetic stirrer for 2 - 4 hours to ensure uniform dispersion of each component. During the mixing process, the magnetic stirrer can provide uniform stirring force, effectively promoting the dispersion of each component in the polyurethane resin solution. Through an appropriate stirring time (2 - 4 hours), it can ensure that each component is fully fused to form a uniform coating solution, and the coating performance will not be unstable due to particle precipitation or agglomeration. During this process, TiO 2 , the surfaces of silver nanoparticles and cadmium selenide quantum dots interact with the resin matrix, thus forming a composite coating with high stability and high performance;

[0043] According to the viscosity requirement, add 15 - 25 parts of ethanol to adjust the fluidity. By adding an appropriate amount of ethanol, the viscosity of the solution can be reduced, making the coating solution flow more easily and evenly cover the surface of the substrate during the application process. The addition of ethanol can also improve the adaptability of the coating, ensuring that the coating is evenly applied on different substrates without bubbles or irregular areas, thereby improving the quality and self-cleaning performance of the coating. In addition, ethanol has strong volatility, which helps the coating dry quickly and avoids uneven precipitation caused by the coating being exposed to air for too long.

[0044] Preferably, the coating application includes:

[0045] Adopt spraying, brushing or dipping methods to evenly apply the coating on the wall surface. Spraying, brushing and dipping are three common coating application methods, each with its unique application scenarios and effects. Among them, spraying atomizes the coating through a spray gun and evenly sprays it on the wall surface, featuring fast and uniform application, suitable for large-area construction, and capable of forming a uniform coating on complex-shaped surfaces. Brushing uses a brush to evenly apply the coating on the wall, suitable for small areas, detailed processing and local repair. Brushing can ensure precise control of the coating thickness but has low efficiency. Dipping immerses part or all of the wall into the coating, suitable for larger-sized substrates, and can ensure the uniformity of the coating and reduce the risk of bubbles and uneven coating;

[0046] The coating thickness is controlled within the range of 50 - 150 μm. Because the photocatalytic reaction requires a certain amount of time and reaction area, a thin coating (below 50 μm) will reduce the contact area between the photocatalyst and pollutants, thus affecting the effect of the photocatalyst. Although a thick coating (above 150 μm) can increase the surface area, it will lead to a reduction in the coating performance, and even problems such as uneven coating, poor adhesion or surface cracks, affecting the long-term stability and photocatalytic effect of the coating. Therefore, the range of 50 - 150 μm can maximize the photocatalytic effect of the coating and ensure that the role of the photocatalyst in the coating is fully exerted.

[0047] Preferably, the coating curing includes:

[0048] Curing is carried out at 40 - 60 °C for 1 - 2 hours. Controlling the curing temperature within the range of 40 - 60 °C helps to promote the reaction between the isocyanate groups in the resin and the polyol, thus completing the polymerization reaction and forming a cross-linked structure. A moderate curing temperature can accelerate the cross-linking of the polyurethane resin without overheating, which may cause degradation or performance decline of the resin. A curing time of 1 - 2 hours is sufficient to ensure the complete cross-linking of the coating, making the resin have high adhesion, weather resistance and stability, thereby improving the durability and long-term performance of the coating;

[0049] Irradiate the coating with a UV lamp of 40 - 80 W for 25 - 35 minutes to enhance the photocatalytic performance. UV irradiation can promote the excitation of TiO 2 and other photocatalytic components in the coating, thereby enhancing its photocatalytic performance. TiO 2 , silver nanoparticles and cadmium selenide quantum dots can excite electrons and holes under UV irradiation to generate oxidative free radicals (such as · OH). These free radicals can effectively degrade pollutants and dirt, achieving a self-cleaning effect. A UV lamp power of 40 - 80 W can provide sufficient light intensity to ensure the excitation reaction of photocatalysts such as TiO 2 in the coating, while avoiding the negative impacts caused by over-irradiation.

[0050] The present invention provides a self-cleaning exterior wall coating, which has the following beneficial effects:

[0051] 1. By introducing the TiO 2 / AgNPs / CdSe composite material, the present invention effectively enhances the photocatalytic reaction efficiency of the coating, especially showing excellent performance under visible light conditions. Compared with the traditional single TiO 2 photocatalytic solution, the multi-component synergistic effect of the composite material significantly improves the photocatalytic activity, solves the problems of slow photocatalytic reaction and low degradation efficiency in the prior art, and greatly improves the self-cleaning performance of the coating.

[0052] 2. By using the technical solution of adjusting the fluidity of the coating with ethanol, it is ensured that the nanocomposite material is uniformly dispersed in the polyurethane resin, forming a stable and dense coating structure. Compared with the traditional solution of controlling the coating uniformity by physical stirring, the present invention avoids the agglomeration of nanoparticles and coating unevenness through ethanol adjustment, significantly enhances the adhesion and stability of the coating, and completely solves the problems of uneven coating thickness and poor adhesion in the existing coatings.

[0053] 3. Through the ultraviolet lamp irradiation curing process, the photocatalytic components in the coating are effectively activated, enhancing the overall photocatalytic reaction rate and long-term weather resistance of the coating. Compared with the traditional solution without ultraviolet irradiation treatment, the photocatalytic persistence and self-cleaning effect of the coating are significantly enhanced, completely overcoming the problems of unstable photocatalytic efficiency and easy aging of the coating in the existing technology, and improving the durability and applicability of the coating.

[0054] 4. The present invention adopts the technical solution of precisely controlling the coating thickness within the range of 50 - 150 μm, optimizing the reaction surface area and structural stability of the coating. Compared with the existing technology with inaccurate thickness control and easy coating peeling, it effectively solves the problems of uneven coating thickness, weak adhesion, and unstable photocatalytic performance, ensuring that the coating always maintains excellent self-cleaning effect during long-term use. Description of the Drawings

[0055] Figure 1 It is a diagram of the preparation method of the present invention. Detailed Embodiments

[0056] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the specification of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0057] Please refer to the attached Figure 1 :

[0058] Example 1

[0059] Material Preparation: Weigh 40 parts of titanium dioxide, 3 parts of silver nanoparticles, and 5 parts of cadmium selenide quantum dots for standby. Take 35 parts of polyurethane resin solution and 20 parts of ethanol.

[0060] Coating Preparation: Add titanium dioxide, silver nanoparticles, and cadmium selenide quantum dots to the polyurethane resin solution in sequence, and stir with a magnetic stirrer at room temperature for 3 hours to ensure that each nanomaterial is fully and uniformly dispersed in the resin. After stirring, slowly add ethanol and continue stirring for 30 minutes to adjust the viscosity and fluidity of the coating to form a stable and uniform coating solution.

[0061] Coating Process: Adopt the spraying method to evenly coat the prepared coating on the surface of the building exterior wall. The coating thickness is strictly controlled at 100 μm to ensure the density and photocatalytic reaction efficiency of the coating.

[0062] Curing process: Place the coated wall in an environment of 40°C for 1.5 hours to fully crosslink the resin matrix and form a stable coating structure. Subsequently, irradiate the surface of the coating with a 60W ultraviolet lamp for 30 minutes to activate the photocatalytic material and further enhance the self-cleaning performance of the coating.

[0063] Example 2

[0064] Material preparation: Weigh 45 parts of titanium dioxide, 2 parts of silver nanoparticles, 8 parts of cadmium selenide quantum dots, 40 parts of polyurethane resin, and 18 parts of ethanol for standby.

[0065] Coating formulation: First, quickly add titanium dioxide, silver nanoparticles, and cadmium selenide quantum dots to the polyurethane resin and stir with a magnetic stirrer at room temperature for 4 hours to ensure complete dispersion of each component. Then, slowly add ethanol in portions and continue stirring for 1 hour to adjust the viscosity and ensure good workability and stability of the coating.

[0066] Coating process: Adopt the brushing method to evenly brush the coating on the surface of the wall, and control the coating thickness at 75μm to ensure a uniform surface without obvious bubbles or defects.

[0067] Curing process: After the coating is left to stand naturally for 30 minutes, place it in a curing oven at 50°C, and set the curing time to 2 hours to ensure complete crosslinking of the coating. Subsequently, irradiate the coating with an 80W ultraviolet lamp for 25 minutes to further activate the photocatalyst and improve the self-cleaning and pollution resistance of the coating.

[0068] Example 3

[0069] Material preparation: Weigh 50 parts of titanium dioxide, 5 parts of silver nanoparticles, 10 parts of cadmium selenide quantum dots, 30 parts of polyurethane resin, and 25 parts of ethanol.

[0070] Coating formulation: Add titanium dioxide, silver nanoparticles, and cadmium selenide quantum dots to the polyurethane resin at one time. First, stir at low speed for 30 minutes, then switch to high speed and stir for 2 hours to ensure uniform dispersion. Subsequently, slowly dropwise add ethanol and continue stirring for 1 hour to adjust the fluidity and viscosity of the coating and ensure the uniformity of the coating.

[0071] Coating process: Select the dip coating method, immerse the small wall sample in the coating, take it out after 3 minutes, and let the coating level off naturally. Control the coating thickness at about 150μm to ensure a complete and smooth surface of the coating.

[0072] Curing process: Carry out curing treatment at 60°C, and set the curing time to 1 hour to ensure the denseness and adhesion of the coating. After curing is completed, immediately irradiate with a 40W ultraviolet lamp for 35 minutes to fully activate the photocatalytic components and enhance the self-cleaning ability and durability of the coating in complex environments.

[0073] Example 4

[0074] Material preparation: Take 35 parts of titanium dioxide, 1 part of silver nanoparticles, 3 parts of cadmium selenide quantum dots, 40 parts of polyurethane resin, and 15 parts of ethanol.

[0075] Coating formulation: Add titanium dioxide, silver nanoparticles, and cadmium selenide quantum dots into the polyurethane resin solution according to the ratio, and stir for 2 hours to ensure full uniformity. Then slowly add ethanol and stir for 20 minutes to ensure that the fluidity of the coating meets the coating requirements.

[0076] Coating process: Use the spraying method for construction, and control the spraying thickness at 50 μm to ensure that the coating is uniform and completely covered.

[0077] Curing process: After spraying, place it in an environment of 45 °C for 2 hours to ensure that the resin is fully cross-linked and the adhesion is improved. After curing, use a 70W ultraviolet lamp to irradiate the coating surface for 25 minutes to enhance the photocatalytic performance and improve the dirt degradation rate.

[0078] Example 5

[0079] Material preparation: Take 38 parts of titanium dioxide, 4 parts of silver nanoparticles, 7 parts of cadmium selenide quantum dots, 32 parts of polyurethane resin, and 22 parts of ethanol.

[0080] Coating formulation: Add titanium dioxide, silver nanoparticles, and cadmium selenide quantum dots into the polyurethane resin in sequence, and stir with a magnetic stirrer for 3 hours. Then add ethanol slowly in two portions and continue to stir for 30 minutes to ensure the fluidity and stability of the coating.

[0081] Coating process: Use the brushing method, and control the coating thickness at 120 μm to ensure that the coating is dense, uniform, and void-free.

[0082] Curing process: After coating, immediately cure it at 55 °C for 1.5 hours. After curing, irradiate it with a 50W ultraviolet lamp for 30 minutes to activate the photocatalytic performance, enhance the self-cleaning function of the coating, and ensure long-term effective degradation of pollutants.

[0083] Comparative Example 1 (corresponding to Example 1)

[0084] Material preparation: Weigh 40 parts of titanium dioxide, 3 parts of silver nanoparticles, 5 parts of cadmium selenide quantum dots, 35 parts of polyurethane resin, and no ethanol is added.

[0085] Coating formulation: Follow the steps of Example 1 to add titanium dioxide, silver nanoparticles, and cadmium selenide quantum dots into the polyurethane resin, and stir for 3 hours without adding ethanol to adjust the viscosity.

[0086] Coating process: The spraying method is adopted and coated on the wall surface, and the coating thickness is controlled at 100 μm.

[0087] Curing process: Cured at 40 °C for 1.5 hours, and no ultraviolet lamp irradiation treatment was carried out.

[0088] Comparative example 2 (corresponding to Example 2)

[0089] Material preparation: Take 45 parts of titanium dioxide, 2 parts of silver nanoparticles, 8 parts of cadmium selenide quantum dots, 40 parts of polyurethane resin, and 18 parts of ethanol.

[0090] Coating formulation: Stir and disperse according to the steps of Example 2, but reduce the stirring time to only 1 hour, and the nano-components cannot be fully dispersed.

[0091] Coating process: The brushing method is adopted, but the coating thickness is not strictly controlled and exceeds 150 μm.

[0092] Curing process: Cured at 50 °C for 2 hours, and no ultraviolet lamp irradiation treatment was carried out.

[0093] Comparative example 3 (corresponding to Example 3)

[0094] Material preparation: Weigh 50 parts of titanium dioxide, 5 parts of silver nanoparticles, 10 parts of cadmium selenide quantum dots, 30 parts of polyurethane resin, and 25 parts of ethanol.

[0095] Coating formulation: Stir and disperse according to the steps of Example 3, but at the stage of adding ethanol, pour ethanol in quickly at one time, without slow and gradual addition, and without extending the stirring time.

[0096] Coating process: The dipping method is adopted, and the coating thickness is not controlled and exceeds 150 μm.

[0097] Curing process:

[0098] The curing temperature is set at 30 °C and cured for 1 hour, and then no ultraviolet lamp irradiation treatment is carried out.

[0099] Comparative example 4 (corresponding to Example 4)

[0100] Material preparation: Take 35 parts of titanium dioxide, 1 part of silver nanoparticles, 3 parts of cadmium selenide quantum dots, 40 parts of polyurethane resin, and 15 parts of ethanol.

[0101] Coating formulation: The stirring time is shortened to 1 hour to ensure the uniform dispersion of nano-materials.

[0102] Coating process: The spraying method is adopted, but the coating thickness is not properly controlled and is less than 50 μm.

[0103] Curing process: Cured at room temperature in the natural environment for 24 hours, without heat curing or ultraviolet lamp irradiation.

[0104] Comparative Example 5 (corresponding to Example 5)

[0105] Material preparation: Take 38 parts of titanium dioxide, 4 parts of silver nanoparticles, 7 parts of cadmium selenide quantum dots, 32 parts of polyurethane resin, and 22 parts of ethanol.

[0106] Coating preparation: Operate according to the process steps of Example 5, but only perform low-speed stirring for 2 hours during the stirring stage without using high-speed stirring.

[0107] Coating process: Use the brushing process, but control the coating thickness at 180 μm, exceeding the design range.

[0108] Curing process: The curing temperature is 70 °C, cured for 1 hour, without using ultraviolet lamp irradiation.

[0109] Comparative experiment:

[0110] Experiment 1: Photocatalytic self-cleaning performance test

[0111] Experimental materials:

[0112] Coated samples (Examples 1-5 and Comparative Examples 1-5);

[0113] Methyl orange solution (concentration 10 mg / L);

[0114] UV-visible spectrophotometer;

[0115] Standard light source (illuminance 5000 Lux);

[0116] Glass slide (substrate).

[0117] Experimental steps:

[0118] Prepare all coated samples (Examples and Comparative Examples) on glass slides of the same specification to ensure the same thickness.

[0119] Uniformly drop methyl orange solution on the surface of the samples and wait for natural drying to form a pollution layer.

[0120] Place the samples under the standard light source and irradiate for 8 hours.

[0121] Every 2 hours, take samples and use a UV-visible spectrophotometer to detect the change in the methyl orange concentration on the surface.

[0122] Record and calculate the degradation rate of the pollutants.

[0123] Experiment 2: Coating adhesion test

[0124] Experimental materials:

[0125] Coated samples (Examples 1-5 and Comparative Examples 1-5);

[0126] Pull-off tester;

[0127] Test head (standard specification);

[0128] Binder.

[0129] Experimental procedure:

[0130] Paste the standard test head on the surface of each sample to ensure good curing of the binder.

[0131] Install the pull-off tester and set the pull-off speed to 10 mm / min.

[0132] Conduct a pull-off test and record the maximum force required during pulling to characterize the adhesion.

[0133] Repeat three times and take the average value to ensure the accuracy of the results.

[0134] Experiment 3: Coating weather resistance test

[0135] Experimental materials:

[0136] Coated samples (Examples 1-5 and Comparative Examples 1-5);

[0137] Artificial accelerated aging test chamber;

[0138] UV irradiation equipment (UV intensity 1200 W / m 2 );

[0139] Thermostatic and humidistatic chamber.

[0140] Experimental procedure:

[0141] Put all the samples into the accelerated aging test chamber.

[0142] Set the cycle: UV irradiation for 8 hours (60 °C), damp and heat cycling for 4 hours (40 °C, relative humidity 90%).

[0143] The total aging cycle is 500 hours. Observe and record the changes on the surface of the samples every 24 hours, including cracks, peeling, and discoloration.

[0144] After 500 hours, further detect the changes on the coating surface using an electron microscope.

[0145] Experiment 4: Coating thickness uniformity test

[0146] Experimental materials:

[0147] Coated samples (Examples 1-5 and Comparative Examples 1-5);

[0148] Electronic coating thickness gauge.

[0149] Experimental procedures:

[0150] Measure the thickness at 5 different positions on the surface of each coating sample. Record the thickness data, calculate the standard deviation, and evaluate the uniformity of the coating.

[0151] Observe the coating surface and record whether there are defects such as cracks, bubbles or depressions.

[0152] Experiment 5: Photocatalytic reaction rate test

[0153] Experimental materials:

[0154] Coating samples (Examples 1 - 5 and Comparative Examples 1 - 5);

[0155] Ultraviolet lamp (60W);

[0156] Methyl orange solution (concentration 10mg / L);

[0157] UV - Visible spectrophotometer.

[0158] Experimental procedures:

[0159] Drop the methyl orange solution evenly onto the sample surface and let it dry naturally.

[0160] Place the sample under the ultraviolet lamp for irradiation and take samples at 5 - minute intervals.

[0161] Detect the methyl orange concentration by the spectrophotometer and calculate the reaction rate.

[0162] Plot the reaction rate curve and compare the reaction rates of different samples.

[0163] Experimental data of comparison between examples and comparative examples

[0164]

[0165]

[0166] Experimental notes:

[0167] In the photocatalytic self - cleaning performance test, the pollutant degradation rate of Example 1 reached 95%, which was significantly higher than 62% of Comparative Example 1. Example 1 used ethanol to adjust the fluidity, making the TiO 2 / AgNPs / CdSe composite material in the coating more evenly dispersed and enhancing the photocatalytic reaction efficiency. While Comparative Example 1 blindly added ethanol, resulting in uneven distribution of nanoparticles in the coating, and some photocatalysts could not be fully exposed to light, significantly reducing the reaction efficiency.

[0168] In the adhesion test, the adhesion of Example 1 was as high as 5.2 MPa, while that of Comparative Example 1 was only 3.8 MPa. The addition of ethanol optimized the resin cross-linking and improved the bonding strength between the coating and the substrate. In Comparative Example 1, the insufficient coating density led to a decrease in adhesion. Thus, it can be seen that the regulating effect of ethanol has a significant effect on improving the overall performance of the coating.

[0169] After 4 hours of sufficient stirring in Example 2, the pollutant degradation rate reached 93%, while in Comparative Example 2, the stirring time was only 1 hour and the degradation rate dropped to 65%. Long-time stirring contributed to the uniform dispersion of nanoparticles, forming a stable photocatalytic network and enhancing the reaction efficiency. In the comparative example, insufficient stirring led to particle agglomeration, a reduction in photocatalytic active sites, and limited reactions.

[0170] In the adhesion and weather resistance tests, Example 2 showed excellent performance, with an adhesion of 5.5 MPa and no surface cracks or peeling observed during weather resistance testing. In Comparative Example 2, insufficient stirring led to uneven coating thickness, with an adhesion of only 3.5 MPa and local blistering occurring during the weather resistance test. This further demonstrated the profound impact of stirring time on the coating quality and stability.

[0171] The photocatalytic reaction rate experiment showed that the reaction rate of Example 3 was 0.30 mg, while that of Comparative Example 3 was 0.16 mg. Example 3 used a curing temperature of 60 °C, which promoted the cross-linking of the resin and the stable combination of the photocatalytic components, forming a denser coating structure and enhancing the photocatalytic efficiency. In contrast, Comparative Example 3 used a curing temperature of 30 °C, resulting in insufficient cross-linking, uneven dispersion of the photocatalyst, and a significant slowdown in the reaction rate.

[0172] In terms of weather resistance, the surface of Example 3 was stable, and no obvious changes were observed after 500 hours of accelerated aging, while obvious surface cracking occurred in Comparative Example 3. Low-temperature curing failed to form a stable coating structure, resulting in a decrease in weather resistance. This result verified the importance of curing temperature for the durability of the coating.

[0173] The coating thickness uniformity test showed that the standard deviation of the thickness of Example 4 was 2.4 μm, indicating good uniformity, while that of Comparative Example 4 was 7.5 μm, with problems such as uneven thickness and local over-thickness. The thickness of Example 4 was strictly controlled at 100 μm to ensure sufficient exposure of the photocatalyst and a dense coating structure. The thickness of the comparative example was too thin, only 50 μm, resulting in insufficient photocatalytic reaction surface area and affecting the reaction efficiency.

[0174] In the adhesion test, the adhesion of Example 4 reached 5.0 MPa, while that of Comparative Example 4 was only 3.6 MPa. Improper thickness control led to a decrease in coating adhesion and obvious local surface cracks. This shows that the coating thickness plays a decisive role in the performance stability of the coating.

[0175] In Example 5, after 30 minutes of ultraviolet lamp irradiation, the photocatalytic reaction rate was as high as 0.29 mg, and the degradation rate was 94%. In Comparative Example 5, without ultraviolet irradiation, the reaction rate decreased to 0.17 mg, and the degradation rate decreased to 61%. Ultraviolet irradiation effectively activates the electron transition on the surface of the photocatalyst, enhances the reaction activity, and promotes the degradation of pollutants.

[0176] In terms of adhesion and weather resistance, Example 5 showed excellent performance, with an adhesion of 5.3 MPa and no change in the middle coating during weather resistance testing. In contrast, in Comparative Example 5, due to the lack of ultraviolet irradiation, the photocatalyst was not fully activated, resulting in a decrease in adhesion to 3.4 MPa and uneven cracks appearing in the middle coating during weather resistance testing. This result clearly verifies the key role of ultraviolet curing in improving the overall performance of the coating.

[0177] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, and the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A self-cleaning exterior wall paint, characterized in that: The coating comprises the following components in parts by weight: Titanium dioxide: 30-50 parts; Silver nanoparticles: 1-5 parts; Cadmium selenide quantum dots: 2-10 parts; Polyurethane resin: 30-40 parts; Ethanol: 15-25 parts.

2. A self-cleaning exterior wall paint according to claim 1, characterized in that: The titanium dioxide comprises: Use anatase TiO2 powder; TiO2 sol was prepared by sol-gel method; The pH value is controlled at 4-5 under the action of acid catalyst; Stir at 25-30°C for 4 hours to ensure that the TiO2 particles are evenly dispersed.

3. A self-cleaning exterior wall paint according to claim 1, characterized in that: The silver nanoparticles include: Silver nitrate solution was used as a precursor; Using amino acids or glucose as reducing agents, the reduction reaction is carried out at 60-80°C; Surface modification was performed by adding polyvinyl pyrrolidone to prevent the nanoparticles from agglomerating; After 1 hour of reaction, the particle size was analyzed by transmission electron microscopy and controlled to be 20-60 nm; The unreacted products were removed by centrifugal washing to obtain modified silver nanoparticles.

4. A self-cleaning exterior wall paint according to claim 1, characterized in that: The cadmium selenide quantum dots include: CdO and Se powders were used as precursors; In triethanolamine solvent, the reaction is carried out at 200-250°C using a hot injection method; The reaction time is controlled between 30 minutes and 1 hour, and the particle size of the quantum dots is regulated to be 5-10 nm; The absorption spectrum was analyzed using a UV-visible spectrophotometer to ensure that its absorption band was in the visible light range.

5. A self-cleaning exterior wall paint according to claim 1, characterized in that: The polyurethane resin comprises: The polyurethane resin is synthesized by the prepolymerization method, and polyether polyol is reacted with MDI to synthesize the polyurethane prepolymer; The reaction temperature is controlled between 70-90° C. and the reaction time is 2-4 hours to obtain a polyurethane resin with a suitable viscosity.

6. A method for preparing a self-cleaning exterior wall coating, characterized in that: Using a self-cleaning exterior wall paint according to any one of claims 1 to 5 comprises the following steps: S1, preparation of TiO2 / AgNPs / CdSe composite material, adding prepared silver nanoparticles and cadmium selenide quantum dots into TiO2 sol respectively and performing stirring, mixing and decontamination operations; S2, preparing a coating solution, adding the TiO2 / AgNPs / CdSe composite material to the prepared polyurethane resin and mixing and adding ethanol to obtain a coating; S3, coating, coating the obtained coating on the wall by spraying, brushing or dipping; S4. Paint curing: Curing the paint within a specific temperature range and under ultraviolet light.

7. The method for preparing a self-cleaning exterior wall paint according to claim 6, characterized in that: The preparation of the TiO2 / AgNPs / CdSe composite material comprises: The prepared silver nanoparticles and cadmium selenide quantum dots were added into the TiO2 sol respectively, and dispersed evenly using an ultrasonic disperser; Stirring for 2-4 hours to ensure that the silver nanoparticles and cadmium selenide quantum dots are evenly distributed in the TiO2 sol to obtain a TiO2 / AgNPs / CdSe composite material; Use vacuum filtration or centrifugation to remove unreacted impurities from the solution to ensure the purity of the composite material.

8. The method for preparing a self-cleaning exterior wall paint according to claim 6, characterized in that: The preparation of the coating solution includes: The TiO2 / AgNPs / CdSe composite material was added into the polyurethane resin solution; Use a magnetic stirrer to stir for 2-4 hours to ensure that all components are evenly dispersed; According to the viscosity requirements, add 15-25 parts of ethanol to adjust the fluidity.

9. The method for preparing a self-cleaning exterior wall paint according to claim 6, characterized in that: The coating application comprises: Use spraying, brushing or dipping methods to evenly apply the paint on the wall surface; The coating thickness is controlled within the range of 50-150 μm.

10. The method for preparing a self-cleaning exterior wall paint according to claim 6, characterized in that: The coating curing comprises: Curing is carried out at 40-60°C for 1-2 hours; The coating was irradiated with a 40-80W UV lamp for 25-35 minutes to enhance the photocatalytic performance.

Images