Abstract: Inorganic coating on the surface of Titanium Dioxide is an indispensable process in the post-treatment of titanium dioxide. Analyzing the mechanism, structure-activity relationship, and application performance improvement mechanism of inorganic coating of titanium dioxide has important theoretical significance and application value for designing and preparing titanium dioxide coating products with excellent application performance.
Based on the inorganic coating of surface units of titanium dioxide (such as alumina, silica, zirconia, aluminum phosphate, etc.), this paper reviews the research status of microstructure control of inorganic coating layer on titanium dioxide surface, the structure-activity relationship between coating layer microstructure and application performance, and the mechanism for improving application performance. The development trend of theoretical basis research on inorganic coating on the surface of titanium dioxide is discussed.
preface
Since the discovery of titanium in the late 18th century and the use of sulfuric ACID method to prepare commercial titanium dioxide in the early 20th century, there has been over 100 years of history in the preparation and commercialization of titanium dioxide.
Titanium dioxide, as the best white pigment, has advantages such as chemical stability, high whiteness, and high coverage, and is widely used in fields such as coatings, plastics, papermaking, inks, cosmetics, and rubber.
Due to the inherent lattice defects of uncoated titanium dioxide, it has strong photocatalytic activity and is prone to generate active groups with high oxidation ability under sunlight irradiation, leading to oxidative degradation of organic resins in the surrounding environment and reducing the service life of the product.
Meanwhile, the surface energy of uncoated titanium dioxide particles is relatively high, leading to severe self aggregation, resulting in lower dispersion and stability performance, which reduces the stability performance of the product in practical applications.
In addition, when uncoated titanium dioxide is exposed to the external environment, temperature changes and acid rain erosion cause titanium dioxide to pulverize, reducing the service life of the product.
In the application of coatings and cosmetics industry, titanium dioxide needs to have excellent dispersion stability and light resistance; In the plastic, paper, and rubber industries, titanium dioxide needs to have excellent weather and light resistance properties; In the application of ink industry, titanium dioxide needs to have excellent dispersion and stability performance.
To meet the requirements of titanium dioxide in practical industrial applications, it is necessary to treat titanium dioxide with inorganic coatings (such as alumina, silica, zirconia, aluminum phosphate, etc.) to improve its dispersion stability, light resistance, and weather resistance.
Compared with developed countries, China's titanium dioxide industry started relatively late, and there is a certain gap in the application performance and stability of titanium dioxide products compared to developed countries.
Faced with the blockade of developed countries on the inorganic coating process and mechanism of titanium dioxide, it is of great significance to develop titanium dioxide products with excellent application performance and stability, and analyze the mechanism of inorganic coating of titanium dioxide.
For titanium dioxide inorganic coating products, their application performance largely depends on the microstructure of the coating layer. The precise control of the microstructure of the inorganic coating layer on the surface of titanium dioxide is an important technical foundation for optimizing the application performance of titanium dioxide products.
In addition, elucidating the mechanism by which inorganic coating on the surface of titanium dioxide improves dispersion stability, light resistance, and weather resistance is of great theoretical significance for the design and preparation of titanium dioxide coated products with excellent application performance.
In recent years, the author and his research group have used liquid-phase chemical precipitation method and advanced characterization methods of material interface structure and properties to deeply study the precise control law of coating process on the microstructure of coating layer and the formation process of nano coating layer.
The optimized coating process conditions for aluminum oxide, silicon dioxide, zirconia, and aluminum phosphate coated titanium dioxide were obtained, and the structure-activity relationship between the microstructure, physicochemical properties, and application performance of the coating layer was constructed, revealing the mechanism of improving the application performance of titanium dioxide by the coating layer.
Based on the above work and combined with the current research status at home and abroad, the author reviewed the research progress and development trends of nano inorganic material coated modified titanium dioxide from the perspectives of microstructure and regulation of the coating layer, structure-activity relationship, and application performance improvement mechanism.
1. Aluminum oxide coated titanium dioxide
Coating aluminum oxide on the surface of titanium dioxide is one of the common methods in industry to improve the dispersion and stability of aqueous titanium dioxide systems, and is an indispensable process in the post-treatment of titanium dioxide.
Among them, the microstructure of the aluminum oxide coating on the surface of titanium dioxide directly affects its surface properties such as hydroxyl density, surface free energy, surface potential, and spatial hindrance, thereby affecting its dispersion and stability performance in aqueous systems. By adjusting the coating process factors, the microstructure of the aluminum oxide coating can be controlled and optimized.
1.1 Microstructure and Control of Coating Layer
During the process of coating aluminum oxide on the surface of titanium dioxide, the phase structure of hydrated aluminum oxide primary particles and their film-forming process on the surface of titanium dioxide particles jointly determine the microstructure of the coating layer.
Therefore, studying the influence and mechanism of coating process factors (such as reaction pH, reaction temperature, slurry concentration, alumina coating amount, reaction time, maturation time, salt solution type and content, pre dispersant type and content, etc.) on the phase structure and growth process of hydrated alumina primary particles is the key to achieving precise control of the microstructure of the coating layer.
The regulation rules of various coating process parameters on the microstructure of alumina coating layer are summarized as follows.
1) Adjusting the reaction pH can, on the one hand, regulate the generation rate, surface potential, and migration and heterogeneous nucleation rate towards the surface of hydrated alumina primary or polymeric particles, thereby controlling the continuity and aggregation state of the coating layer;
On the other hand, the phase structure of the coating layer (boehmite, Bayerite, and amorphous hydrated alumina) can be regulated, thereby regulating the pore structure characteristics of the coating layer. The porosity of different phase alumina coating layers is ranked from large to small as boehmite, Bayerite, and amorphous hydrated alumina.
2) Adjusting the reaction temperature can regulate the crystallinity and grain size of the coating layer of boehmite, thereby regulating the porosity of the coating layer;
The second is to regulate the dehydration and condensation rate of primary particles and their collision probability with titanium dioxide particles, thereby regulating the aggregation state and porosity of the coating layer.
3) The primary particles of hydrated alumina first undergo heterogeneous nucleation on the surface of titanium dioxide particles to form a continuous dense coating layer, followed by homogeneous nucleation to form a loose flocculent porous coating layer.
Adjusting the amount of aluminum oxide coating can achieve precise control of the continuous dense (inner layer) - loose flocculent porous (outer layer) boehmite coating layer on the surface of titanium dioxide particles.
4) Adjusting the reaction time can regulate the generation rate and concentration of hydrated alumina primary particles in the suspension, change the nucleation state of primary particles (homogeneous or heterogeneous nucleation), and regulate the continuity of the coating layer.
5) Adjusting the maturation time can regulate the hydrolysis and coating process of hydrated alumina primary particles, adjust the ratio of alumina between the surface of titanium dioxide particles and the free alumina between particles, and change the porosity and continuity of the alumina coating layer on the surface of titanium dioxide particles.
6) Adjusting the slurry concentration can regulate the concentration of primary particles of hydrated alumina in the suspension, change the nucleation form of hydrated alumina (heterogeneous or homogeneous nucleation), and thereby regulate the continuity of the alumina coating layer on the surface of titanium dioxide particles.
7) The initial product of titanium dioxide oxidation is obtained by sulfuric acid or chlorination methods, and chloride ions or sulfate ions can enter the coating process with the initial product slurry.
The research results indicate that NaCl can reduce the concentration of hydrated alumina primary particles in the suspension and improve the porosity and continuity of the alumina coating layer by forming [AlCl4] coordination compounds during the process of coating titanium dioxide with alumina;
On the other hand, it can change the viscosity of the initial slurry of titanium dioxide, regulate the nucleation form of primary particles of hydrated alumina (heterogeneous or homogeneous nucleation), and reduce the continuity of the alumina coating layer. However, Na2SO4 has no significant effect on the structure of the coating layer during the process of alumina coating with rutile type titanium dioxide.
8) The influence of different dispersant types on the microstructure and dispersion stability of the coating layer of alumina coated titanium dioxide samples is inconsistent with its influence on the surface potential of titanium dioxide particles.
Among them, dispersants with longer carbon chain lengths can easily induce the growth of boehmite crystal nuclei and form a fibrous coating layer. By adjusting the dispersant, the growth of boehmite crystal nuclei can be induced, and the formation of a high porosity fibrous alumina coating layer can be regulated to improve the spatial hindrance between titanium dioxide particles.
1.2 Structure Activity Relationship
When the aluminum oxide coating layer has a boehmite structure, and its continuity and porosity are higher, the flocculent structure is more significant, and the dispersion and stability performance of titanium dioxide coated aluminum oxide samples in aqueous systems is better.
When the reaction pH is 9, the reaction temperature is 70 ℃, the mass ratio of alumina to titanium dioxide is 3.2%, the reaction time is 60 minutes, the curing time is 120 minutes, the slurry concentration (solid phase mass fraction) is 25%, the NaCl addition amount is 2.5% (mass fraction), and the pre dispersant amount is 0.3% (mass fraction), a flocculent and highly continuous boehmite coating layer is formed on the surface of the prepared alumina coated rutile type titanium dioxide sample, Has excellent dispersion and stability performance in aqueous systems.
1.3 Performance improvement mechanism
The mechanism by which the aluminum oxide coating significantly enhances the dispersion and stability of titanium dioxide samples in aqueous systems:
1) The formation of flocculent or fibrous hydrated alumina coating on the surface of titanium dioxide particles hinders the collision and agglomeration between titanium dioxide particles, maintaining the spatial stability of titanium dioxide particles in aqueous systems;
2) The formation of continuous flocculent hydrated alumina on the surface of titanium dioxide particles significantly increases the hydroxyl content on the particle surface, increases the wettability of the particle surface, and accelerates its dispersion in aqueous systems;
3) The formation of a continuous flocculent coating layer on the surface of titanium dioxide particles increases the zeta potential of the titanium dioxide particle surface, enhances the electrostatic repulsion between particles, and hinders particle aggregation.
2. Silicon dioxide coated titanium dioxide
The silica coating on the surface of titanium dioxide can hinder its direct contact with surrounding media and the external environment, improving the weather resistance of titanium dioxide.
The microstructure of the silica coating on the surface of titanium dioxide directly determines the area of titanium dioxide particles exposed to the external environment or surrounding media, which in turn affects their weather resistance performance.
In recent years, the research progress on the microstructure and regulation, structure-activity relationship, and performance improvement mechanism of silica coated titanium dioxide coating layer [25-35] is summarized as follows.
2.1 Microstructure and Control of Coating Layer
The phase structure of the silica coating layer on the surface of titanium dioxide is amorphous hydrated silica, and its microstructure mainly depends on the adsorption, film formation, and polymerization process of hydrated silica primary particles on the surface of titanium dioxide particles. The regulation law of the microstructure of the silica coating layer by various coating process parameters is as follows.
1) Adjusting reaction pH: ① It can regulate the hydrolysis rate of sodium silicate and control the continuity of the silica coating layer; ② It can regulate the polymerization form of orthosilicate and control the density of the coating layer; ③ It can regulate the degree of hydrolysis of sodium silicate and control the thickness of the coating layer.
2) Adjusting reaction temperature: Firstly, it can regulate the rate of silica generation and the Brownian motion rate of silica particles, change the nucleation mode of silica particles (homogeneous or heterogeneous), and thereby regulate the continuity of the silica coating layer; Secondly, it can regulate the rate of silica gel polymerization, thereby regulating the density of the coating layer.
3) Amorphous hydrated silica first dehydrates and condenses with hydroxyl groups on the surface of titanium dioxide particles to form Si-O-Ti bonds, forming a continuous, dense and thin coating layer. Then, through electrostatic adsorption, a continuous and uniform coating layer structure is formed on the surface of titanium dioxide particles.
Adjusting the amount of silica coating can regulate the thickness of the coating layer, but it has no significant effect on the continuity and density of the coating layer.
4) Adjusting the reaction time can change the nucleation form of silica particles (homogeneous or heterogeneous nucleation), thereby regulating the continuity of the film layer.
5) Adjusting the maturation time can change the progress of silica gel polymerization and adsorption film formation on the surface of titanium dioxide particles, thereby regulating the continuity and thickness of the coating layer.
6) Adjusting the slurry concentration can change the concentration of silica particles in the suspension, causing silica particles to tend towards homogeneous nucleation and adsorb on the surface of titanium dioxide particles, thereby regulating the continuity and thickness of the coating layer.
7) The effect of NaCl on the microstructure of the coating layer is not significant. Adjusting the concentration of Na2SO4 in the initial slurry can adjust the viscosity of the titanium dioxide initial slurry, thereby changing the nucleation mode of silica particles and significantly altering the continuity of the silica coating layer.
8) Similar to the coating of aluminum oxide on the surface of titanium dioxide, the influence of different dispersants on the continuous density and weather resistance of the coating layer of silica coated titanium dioxide samples is inconsistent with its influence on the surface potential of titanium dioxide particles. Pre dispersants may regulate the continuous density of the coating layer by adjusting the rate of silica gel polymerization.
2.2 Structure Activity Relationship
The acid solubility stability performance is used as the evaluation index for weather resistance. The higher the continuity and density of the coating layer of the silica coated titanium dioxide sample, the better the weather resistance of the coated sample. The thicker the coating layer, the better the weather resistance of the coated sample.
When the reaction pH is 9, the reaction temperature is 85 ℃, the mass ratio of silica to titanium dioxide is 2.5%, the reaction time is 90 minutes, the curing time is 120 minutes, the slurry concentration (solid phase mass fraction) is 25%, and the pre dispersant dosage is 0.5% (mass fraction), a highly continuous, dense, and thick coating layer is formed on the surface of the silica coated titanium dioxide sample, which has excellent weather resistance.
2.3 Performance improvement mechanism
The mechanism by which the silica coating significantly improves the weather resistance of titanium dioxide samples:
1) The silica coating can effectively hinder the direct erosion of acidic species on the titanium dioxide core, and slow down the weathering of the titanium dioxide core caused by external environmental changes;
2) The silicon dioxide coating layer can inhibit the transformation of the crystal structure of titanium dioxide, improve the structure and thermal stability of titanium dioxide.
3. Zirconia coated titanium dioxide powder
Titanium dioxide has certain photocatalytic activity and can absorb ultraviolet light to produce reactive groups, causing degradation of surrounding organic media and reducing the service life of the product.
Zirconia has a high refractive index (2.170) and extremely weak absorption capacity for ultraviolet light. Therefore, coating continuous dense zirconia on the surface of titanium dioxide particles can not only reduce the absorption of ultraviolet light, but also hinder direct contact between active groups and surrounding media and the external environment, improving the light resistance performance of titanium dioxide.
3.1 Microstructure and Control of Coating Layer
The phase of the zirconia coating layer on the surface of titanium dioxide is amorphous hydrated zirconia, and the microstructure of the coating layer mainly depends on the adsorption, film-forming, and polymerization process of hydrated zirconia primary particles on the surface of titanium dioxide particles.
The regulation rules of various coating process parameters on the microstructure of zirconia coating layer are summarized as follows: During the zirconia coating process, Zr4+is prone to form hydrated zirconium ions, mainly in the form of [Zr (OH) 2,4H2O] 48+tetramers. Each zirconium atom is coordinated with four bridging hydroxyl groups and four water molecules around its periphery.
During the hydrolysis precipitation process, the tetramer combines with water and undergoes re polymerization by losing protons, forming a network structured polymer through hydroxyl bridging.
1) Adjusting the reaction pH can, on the one hand, alter the process of deprotonation of zirconium tetramer monomer bound to water (forming zirconium tetramer monomer sol or polymerizing to form porous hydroxylated hydrated zirconia), thereby regulating the density of the coating layer;
On the other hand, it can change the surface electrical properties between tetramer monomers and titanium dioxide particles, regulate the nucleation mode of tetramer monomers (heterogeneous or homogeneous nucleation), and thereby regulate the continuity of the coating layer.
2) Adjusting the reaction temperature can, on the one hand, regulate the deprotonation polymerization rate of tetramer particles and the network structure of pre coated particles, and on the other hand, regulate the Brownian motion rate and collision probability to change the nucleation mode. The above two aspects work together to regulate the continuity of the coating layer.
3) Zirconia is continuously coated layer by layer on the surface of titanium dioxide particles, and adjusting the amount of zirconia coating can adjust the thickness of the coating layer.
4) Adjusting the reaction time, i.e. adjusting the rate of precursor addition, can change the concentration of zirconium tetramer monomer particles in the suspension, alter the nucleation form of tetramer monomers, and thereby regulate the continuity of the coating layer.
5) Adjusting the maturation time can regulate the hydrolysis and coating process of zirconia tetramer monomer particles, and change the continuity and thickness of the zirconia coating layer; At the same time, it can regulate the degree of dehydration polymerization of the zirconia coating layer and change the density of the zirconia coating layer.
6) Adjusting the slurry concentration can change the nucleation form of zirconia tetramer monomers (heterogeneous or homogeneous nucleation) and regulate the continuity of the zirconia coating layer.
7) Adjusting the amount of NaCl added can, on the one hand, change the surface charge characteristics of [Zr (OH) 2,4H2O] 48+tetramer monomers, promote the process of monomer particle binding to water deprotonation, and regulate the density of the zirconia coating layer on the surface of titanium dioxide particles;
On the other hand, it can change the initial viscosity of titanium dioxide slurry, regulate the nucleation form of tetramer monomer particles (heterogeneous or homogeneous nucleation), and thereby regulate the continuity of the coating layer.
8) Adjusting the type and dosage of the pre dispersant can change the rate of deprotonation of zirconium tetramer monomers bound to water, and regulate the continuity and density of the zirconia coating layer.
3.2 Structure Activity Relationship
Based on the evaluation index of light resistance, the better the continuity and uniformity of the surface coating layer of zirconia coated titanium dioxide samples, the higher the density, and the better the light resistance of the coated samples.
When the reaction pH is 5, the reaction temperature is 55 ℃, the mass ratio of zirconia to titanium dioxide is 5%, the reaction time is 60 minutes, the curing time is 120 minutes, the slurry concentration (solid phase mass fraction) is 20%, and the pre dispersant dosage is 0.3% (mass fraction), the prepared zirconia coated titanium dioxide sample shows a continuous and dense coating layer structure, with excellent light resistance.
3.3 Performance improvement mechanism
Mechanism of zirconia coating layer improving the light resistance of titanium dioxide samples:
1) The continuous and uniform dense zirconia coating layer hinders the contact between active groups at the interface of titanium dioxide powder and organic matter;
2) Reduce the probability of generation and separation of photo generated electron hole pairs, hinder the migration of photo generated electrons to the particle surface, and accelerate the recombination of photo generated electron hole pairs;
3) Reduce the hydroxyl content on the surface of particles, thereby reducing the rate of generation of active groups on the surface of zirconia coated titanium dioxide, and slowing down its oxidative degradation of surrounding organic matter.
4. Aluminum phosphate coated titanium dioxide
When titanium dioxide is applied in industries such as papermaking and exterior wall coatings, it needs to have both high light resistance and excellent dispersion stability. At present, the practical application requirements are mainly achieved through inorganic organic composite coating of titanium dioxide.
Developing a product that can meet both light resistance and dispersion stability requirements through a single inorganic coating can significantly reduce the cost of organic coating in the later stage.
Aluminum based materials, as good electron acceptors, can annihilate the photogenerated electrons generated by titanium dioxide absorbing ultraviolet light excitation, inhibit the generation of active groups, and improve light resistance performance;
The introduction of phosphate ions can regulate the surface potential of titanium dioxide particles and improve their dispersion stability. Therefore, coating aluminum phosphate on the surface of titanium dioxide can simultaneously improve its light resistance and dispersion stability.
In recent years, domestic and foreign enterprises have designed and developed aluminum phosphate coated titanium dioxide products with excellent application performance, and optimized the relevant coating process parameters.
The following is a summary of the research progress on the microstructure and regulation, structure-activity relationship, and performance improvement mechanism of aluminum phosphate coated titanium dioxide, based on the basic theoretical research work of the author and his research group.
4.1 Microstructure and Control of Coating Layer
The microstructure of the aluminum phosphate coating on the surface of titanium dioxide determines the absorption performance of titanium dioxide particles towards ultraviolet light and the surface potential of titanium dioxide particles.
Improving the continuity of the aluminum phosphate coating can significantly reduce the absorption performance of titanium dioxide particles towards ultraviolet light and their exposed area in the external environment or surrounding media, thereby improving the light resistance of the sample; At the same time, it promotes the surface potential of titanium dioxide particles to shift towards aluminum phosphate, improving the dispersion and stability of the sample.
The regulation law of various coating process parameters on the microstructure of aluminum phosphate coating layer is as follows:
1) Adjusting the reaction pH can regulate the hydrolysis rate of Sodium Hexametaphosphate and the generation rate and concentration of primary aluminum phosphate particles in the suspension, thereby regulating the continuity, crystal structure, and crystallinity of the coating layer;
2) Adjusting the reaction temperature can, on the one hand, change the Brownian motion rate of primary aluminum phosphate particles and titanium dioxide particles in the suspension, adjust the probability of collision adsorption and film formation between the two, and thus regulate the uniformity of the coating layer;
On the other hand, the hydrolysis rate of sodium hexametaphosphate can be adjusted, and the concentration of aluminum phosphate primary particles generated by the reaction in the suspension can be controlled, thereby regulating the degree of aggregation of the coating layer;
3) Adjusting the maturation time can regulate the progress of the gradual adsorption of aluminum phosphate particles free from the slurry onto the surface of titanium dioxide particles, changing the uniformity and continuity of the coating layer.
4.2 Structure Activity Relationship
The light resistance performance is the main evaluation index, and the dispersion stability performance in aqueous systems is the auxiliary evaluation index. The higher the continuity and density of the aluminum phosphate coating layer, the better the light resistance performance and dispersion stability performance of the aluminum phosphate sample coated with titanium dioxide in aqueous systems.
When the reaction pH is 9, the reaction temperature is 50 ℃, the mass ratio of aluminum phosphate to titanium dioxide is 3.0%, the reaction time is 60 minutes, the curing time is 120 minutes, the slurry concentration (solid phase mass fraction) is 25%, and the pre dispersant dosage is 0.2% (mass fraction), a continuous and dense coating layer is formed on the surface of the aluminum phosphate coated titanium dioxide sample, which has excellent light resistance and water-based system dispersion stability.
4.3 Performance improvement mechanism
1) The mechanism of improving the light resistance of titanium dioxide by aluminum phosphate coating: ① Continuous dense aluminum phosphate coating hinders the contact between active groups at the interface of titanium dioxide and organic matter; ② Reduce the rate of generation and separation of photo generated electron hole pairs, accelerate electron annihilation, hinder the migration of photo generated electrons to the particle surface, thereby reducing the rate of generation of surface active groups (hydroxyl radicals, superoxide radicals, etc.) in composite samples, and slowing down their degradation of surrounding organic matter.
2) The mechanism of improving the dispersion and stability of aqueous systems by coating titanium dioxide with aluminum phosphate: ① The continuous aluminum phosphate coating layer increases the surface wettability of titanium dioxide particles by reducing their surface energy, promoting their dispersion in aqueous systems; ② Enhance the electronegativity of titanium dioxide surface, increase the electrostatic repulsion between particles, and hinder the agglomeration between particles.
5 Others
In response to the demand for the application performance of titanium dioxide coating products in different industrial fields, researchers at home and abroad have not only optimized the structure and performance of existing coating products, but also designed, explored, and developed new inorganic coating products on the surface of different types of titanium dioxide (such as cerium dioxide, tin dioxide, etc.).
5.1 Cerium dioxide coated titanium dioxide
Coating cerium dioxide on the surface of titanium dioxide is an important means to improve its light resistance performance. Although there are literature materials related to ceria coated titanium dioxide both domestically and internationally, there are few reports on the microstructure control of ceria coated layers.
Based on existing research both domestically and internationally, a summary was made on the coating process conditions and performance improvement mechanisms.
Optimization process conditions for coating cerium dioxide on the surface of titanium dioxide [57]: reaction temperature is 65-70 ℃, stirring speed is 500r/min, pre dispersant sodium hexametaphosphate dosage is 0.3% (mass fraction), slurry concentration (solid phase mass fraction) is 23%, and the mass ratio of cerium dioxide to titanium dioxide is 3%.
The mechanism of improving the light resistance of titanium dioxide by cerium dioxide coating layer: 1) hinders the contact between rutile type titanium dioxide and surrounding oxygen and water molecules; 2) Block and cover the lattice defects of rutile type titanium dioxide, capture electrons and holes, and reduce the number of active free radicals.
5.2 Tin dioxide coated titanium dioxide
Coating tin dioxide on the surface of titanium dioxide is a relatively mature industrial grade method for preparing conductive titanium dioxide. Although there are literature materials related to tin dioxide coated titanium dioxide both domestically and internationally, there is relatively little work on the microstructure control of tin dioxide coated layers.
Based on reported research both domestically and internationally, the optimization process conditions for tin dioxide coated titanium dioxide were summarized.
Optimization process conditions for coating tin dioxide on the surface of titanium dioxide [57]: reaction pH is 2.0, reaction temperature is 50 ℃, reaction time is 180 minutes, tin chloride addition amount is 25% (mass fraction), tin chloride to antimony chloride mass ratio is 12:1, calcination temperature is 600 ℃, calcination time is 150-180 minutes.
6 Conclusion and Outlook
In recent years, China has made significant progress in the field of inorganic coating technology and product application performance optimization of titanium dioxide. However, there is still insufficient basic theoretical research on the microstructure control of inorganic coating layer on the surface of titanium dioxide, the relationship between coating layer microstructure and application performance, and the improvement mechanism of various application performance.
Deepening the basic research on surface inorganic coating modification of titanium dioxide can provide theoretical and technical support for optimizing the application performance of titanium dioxide products and promoting high-quality industrial development.
In the future, it is necessary to deepen the basic theoretical research on inorganic coating on the surface of titanium dioxide from the following three aspects, based on existing research results and advanced research methods such as modern model prediction and theoretical calculation, in order to provide theoretical guidance for the innovative development of high-end titanium dioxide products:
1) On the basis of existing theoretical research on unit inorganic coating, a layer by layer analysis strategy is adopted to conduct in-depth research on the basic theory of multi-component inorganic coating systems;
2) Based on the microstructure control laws and mechanisms of inorganic coating layers, theoretical models for the growth of each inorganic coating layer on the surface of titanium dioxide were constructed to achieve accurate prediction and controllable preparation of thickness, density, continuity, etc. of each coating layer;
3) Design and optimize inorganic coated titanium dioxide products based on density functional theory (DFT) calculations and performance requirements in different fields.
