At present, the preparation technology of nanometer titanium dioxide (TiO2) in China is quite mature. There are many methods for preparing titanium dioxide, mainly including sulfuric acid method, chlorination method, titanium tetrachloride liquid phase hydrolysis method, titanium tetrachloride oxyhydrogen flame method (flame vapor deposition method) and titanium alkoxide hydrolysis method. Among them, the sulfuric acid method and the chlorination method are commonly used in industry.
Most of the research on TiO2 is focused on the weather resistance, photocatalytic performance, composite materials, etc., and the research on nano-TiO2 on special paper is relatively scarce. In addition, nano-TiO2 is not easy to disperse in non-polar media, and easy aggregation in polar media directly affects the performance of nano-titania itself. Therefore, there is an urgent need to solve the problem of nano titanium dioxide dispersion.
1.Characteristics of 1 nanometer TiO2
- 1.1 Sterilization function
Nano-scale titanium dioxide has high light activity and uses strong light sterilization technology [1-3]. Experiments show that anatase nano-TiO2 at a concentration of 0.1mg / cm3 can completely kill malignant Hella cells, and as the amount of superoxide dismutase (SOD) added increases, the efficiency of TiO2 photocatalysis to kill cancer cells Also improved . The killing rate of Bacillus subtilis var. Spores, Pseudomonas aeruginosa, E. coli, Salmonella, Rhizoctonia, and Aspergillus all reached more than 98%.
- 1.2 UV protection function
Nano-TiO2 can absorb ultraviolet rays, reflect and scatter ultraviolet rays, and can also transmit visible light. It is a physical shielding ultraviolet protective agent with excellent performance and great development prospect. Because of its small particle size and high activity, nano-sized titanium dioxide can reflect and scatter ultraviolet rays, and absorb ultraviolet rays, so as to have a stronger barrier to ultraviolet rays. Compared with some organic UV protective agents at the same dose, nano-TiO2 has a higher absorption peak in the ultraviolet region. Unlike organic UV protective agents, it only absorbs UVA or UVB only. More importantly, it is a broad-spectrum shielding agent [ 5]. Titanium dioxide can absorb ultraviolet energy with an energy higher than 420nm to stimulate the transition of inner electrons in the crystal structure of titanium dioxide. The transparency and ultraviolet absorption capacity of nano-TiO2 can also be used as food packaging films, inks, coatings, textile products and plastic fillers. It can replace organic ultraviolet absorption agents and can be used in coatings to improve the aging resistance of coatings.
- 1.3 Self-cleaning function
Nano-TiO2 has strong “super-hydrophilicity”, it is not easy to form water beads on its surface, and nano-TiO2 can act on hydrocarbons under visible light irradiation. Using such an effect, a thin layer of nano-TiO2 can be coated on the surface of glass, ceramics and ceramic tiles. The photocatalytic reaction of titanium oxide can decompose the organic pollutants adsorbed on the surface of titanium oxide into CO2 and O2. The inorganic substances can be washed away by rain water together, thereby realizing the self-cleaning function. Japan has successfully developed self-cleaning tiles in the laboratory. This new product has a thin layer of nano-TiO2 film on the surface. Any substance that adheres to the surface, including oil stains and bacteria. Under the irradiation of light, due to the catalysis of nano-TiO2 Effect, these hydrocarbons can be further oxidized into a gas or a substance that is easily wiped off. Nano-TiO2 photocatalysis makes it easy to clean the glass of high-rise buildings, ceramic tiles that are easy to get oily in the kitchen, car rearview mirrors and front window glass.
2 nanometer TiO2 dispersion properties
- 2.1 Nano-TiO2 dispersion mechanism
Hu Jie et al  found that in the nano-titania water dispersion system, mainly van der Waals force, electrostatic repulsive force, steric hindrance effect due to the adsorption layer, etc. In addition, the dispersion mechanism of nano-TiO2 can also be explained from the theory of double electron layer. The theory of double-electron layer means that the inside of the particle is called a particle nucleus, which is generally negatively charged to form a negative ion layer, and the outside of it forms a positive ion layer due to electrical attraction (the counter ion layer includes an inactive ion layer and a diffusion layer). Called the electric double layer. The theory generally relies on adjusting the PH value or adding an electrolyte to generate charges on the surface of the particles to increase the thickness of the electric double layer and the potential value on the surface of the particles, so that repulsive forces are generated between the particles, thereby achieving the dispersion of the particles.
- 2.2 The effect of pH on the dispersion of nano-TiO2
Titanium dioxide can be positively charged, negatively charged or electrically neutral due to the different pH values in the aqueous solution. When the pH value is low, TiO2-OH2 + is formed on the surface of the nano-TiO2, resulting in a positive charge on the particle surface; when the pH value is at an intermediate value, the particle surface forms a Ti-OH bond, and the particles are electrically neutral The dispersion performance is the worst; when the pH value is high, the OH-O- bond is formed on the surface of the particle, which makes the particle surface negatively charged. Thick, the greater the repulsive potential energy between particles, the better the particle dispersion effect . Guo Wenlu et al.  believed that in the study of the stability of nano-titania water dispersion system, the dispersion effect was the best state when pH = 10.
- 2.3 The effect of electrolyte on the dispersion of nano-TiO2
Nano-titanium dioxide dispersion is related to electrolyte. When pure water is used as a dispersant, the uneven distribution of nano titanium dioxide is caused by electrostatic attraction between particles. Studies have shown that when organic solvents are used as dispersants in aqueous solutions, nano-TiO2 has better dispersibility. Ren Xijuan et al  proved through experiments that the higher the electrolyte ion price, the stronger the agglomeration effect, and a small amount of electrolyte will also cause the dispersion to agglomerate. Therefore, mixing and adhesion of inorganic salts should be avoided during normal use and storage.
- 2.4 Effect of surfactant on the dispersion of nano-TiO2
Polymer surfactants can be adsorbed by nano-titanium dioxide through hydrogen bonding, van der Waals force, and electrostatic attraction. For example, those with longer molecular chains (polyacrylamide PAM, polymethacrylic acid PMAA, etc.) can provide steric hindrance shielding, thereby preventing the agglomeration of nano-titania particles. However, the amount of polymer surfactant added needs to be strictly controlled, otherwise it will be counterproductive.
The compound surfactant has a good effect on the dispersibility of titanium dioxide. Ionic surfactants and nonionic surfactants are mixed in solution to form micelles. After the nonionic surfactant molecules are inserted into the micelles, the electrical properties between the original “ionic head” of the ionic surfactants The repulsive force weakens, causing the CMC in the mixed solution to drop .
- 2.5 The effect of dispersing equipment on the dispersion of nano-TiO2
Nano titanium dioxide has semiconductor properties, and has excellent characteristics such as high stability, high transparency, and high activity. Nano-titanium dioxide will be widely used in industrial research applications at present. As an emerging nano-material, it is very necessary to mention its dispersibility. Different decentralized equipment will show different degrees of effect on its decentralization. At present, the commonly used dispersing equipment are: ultrasonic oscillation dispersing instrument, electric agitator, vertical stirring mill .
3 nanometer TiO2 in pulp and paper
- 3.1 Application in the preparation of functional paper
Japan has developed a functional paper with nano-titanium dioxide. This product has a photocatalytic function and can be used for packaging paper and wallpaper for interior decoration. This type of functional paper can effectively absorb formaldehyde, benzene, ammonia and other harmful gases. Hebei Maisen Titanium Dioxide Co., Ltd. has developed high-weather resistance and wear-resistant decorative base paper, and improved the filler used for decorative base paper. The improved filler products also have an organic / inorganic three-dimensional interpenetrating network structure, which has inorganic rigid It is very wear-resistant and greatly improves the overall performance of the paper. Nano-titanium dioxide used in general paper products, such as toilet paper, food packaging paper, etc. also has a bactericidal effect [12-13].
- 3.2 Application in papermaking wet end
The chemical nature of the wet end of papermaking is a surface and colloidal chemistry. The structure of many components in the papermaking wet end ingredients is very small, so the introduction of special nano-scale components can greatly improve the papermaking effect .
Nano-titanium dioxide is used as retention aid and filter aid in the wet end of papermaking, and has good retention aid and filter aid effect. Secondly, due to its excellent performance, it can also effectively suppress the pollution and damage of DCS harmful substances to white water.
- 3.3 Application of waste paper deinking
In the paper industry, the ink particles in the secondary fiber have a great influence on the paper. There are two methods of deinking, flotation and washing, and the former is often used in industry because it is more effective for the removal of large particle inks. Because nanometer titanium dioxide has a positive charge and a large specific surface area, it has an efficient flotation effect on the ink particles in the secondary fiber. Adding nano titanium dioxide in the flotation process can also remove stickies in waste paper pulp to a certain extent.
- 3.4 Application of papermaking wastewater treatment
Pulp and paper wastewater mainly includes cooking waste liquid, pulp washing wastewater, papermaking wastewater, etc. These waste liquids mainly contain large amounts of lignin and various phenolic organic compounds. Photocatalytic oxidation can treat papermaking wastewater, and it can also degrade lignin and phenols, completely eliminating toxicity. At the same time, it has a good degradation effect on the toxic and difficult to be degraded organic matter in the papermaking wastewater. The use of nano-titanium dioxide to treat papermaking wastewater can make it reach the standard discharge, and greatly reduce the pollution to the environment.
Nano titanium dioxide is an excellent inorganic fine chemical material. There are many factors that affect the dispersibility of nano-titanium dioxide, such as surfactants, pH value, electrolyte, etc., we need to do further exploration to optimize the utilization rate of nano-titanium dioxide. At present, China vigorously advocates green and sustainable development. Nano-TiO2 has broad prospects in the application and development of pulp and paper and functional paper with its functions of sterilization, high efficiency self-cleaning, photocatalytic energy, and wastewater treatment.