Antimicrobial effect of nano titanium dioxide on surfaces

Antimicrobial effect of nano titanium dioxide on surfaces

Nano TiO2 was introduced in the late 1980s and is an inorganic material with a wide range of uses. Due to its unique UV shielding, photocatalysis, color effects and other properties, it has broad application prospects in advanced coatings, chemical products, wastewater treatment, air purification, sterilization and high-efficiency solar cells. As a photocatalytic semiconductor inorganic antibacterial agent, nano titanium dioxide (TiO2) has a broad-spectrum antibacterial function, can inhibit and kill microorganisms, and has the functions of deodorization, mildew proofing, and sterilization, and is inherently chemically stable and harmless to the human body and the environment. The photocatalytic effect is long-lasting, and it is increasingly favored by the world.

There are two crystalline states of nanocrystalline TiO2: rutile and anatase. In general, rutile titanium dioxide has poor photocatalytic activity, and anatase titanium dioxide has strong photocatalytic activity. The anatase nano-TiO2 undergoes a photocatalytic reaction in H2O and O2 systems. The resulting hydroxyl radicals (HO·) react with a variety of bacteria and odors, effectively sterilizing and eliminating odors, and can thus be made. Nano-TiO2 antibacterial agent. The nano-TiO2 antibacterial agent has the ability to kill bacteria and their remains together, while also breaking down the toxins secreted by the bacteria. And nano-TiO2 as a fungicide also has the following characteristics: First, good effect, such as silver series of antibacterial agent effect occurs in about 24h, and nano-TiO2 only about 1h; Second, TiO2 is a semi-permanent maintenance of antibacterial The effect of antibacterial agents, unlike other antibacterial agents will gradually decline with the dissolution of antibacterial agents; Third, there is a good safety, and no adverse effects on skin contact.

In this experiment, four new types of nanometer TiO2 spray liquids (stock solution, compound solution 1#, compound solution 2æ–¡, and compound solution 3#) were sprayed on tiles and paper sheets, and applied to tiles and paper sheets. The bactericidal effect was tested and observed. At the same time, we observed the sterilizing effect of some ceramic tiles coated with nano-TiO2 spray liquid after high-temperature pretreatment.

1 Materials and Methods

1.1 source of bacteria

E. coli Laboratory, School of Food Science and Engineering, South China University of Technology.

1.2 Materials

1.2.1 Medium

Nutrient broth (g/100 mL): casein quinone 1.0, beef extract 1.0, NaCl 0.5.

MR-VP medium (g/100 mL) : (month ) 胨 0.7 , glucose 0.5 , K2HPO4 0.5, pH 6.9.

1.2.2 Tiles and Paper

Tile: 3cm×3cm clean tiles.

Paper sheet: Coniferous wood pulp with a whiteness of 85 (%, ISO) was converted to a sheet of paper with a basis weight of 60 g/m2 without any chemicals.

Nanometer TiO2: Beautiful Nano-Net, Yellow Transparent Liquid provided by Fantry Science (Shenzhen) Co., Ltd.

1.3 Preparation and Determination of E. coli Bacteria

1.3.1 Preparation of E. coli

50mL nutrient broth was placed in a 250mL flask and inoculated with 0.4mL of E. coli. After shaking at 28°C for 30 minutes, a THZ-C rotating bed was shaken for 24h. The cultured E. coli was diluted 10 times and used (14500 cells/mL).

1.3.2 E.coli detection method

In this experiment, the MP-VP method was used to colorimetrically determine the E. coli MPN value in each microliter of bacterial solution.

1.4 Antibacterial experiment

Apply 0.4mL of nano-TiO2 spray liquid to clean tiles and paper sheets of 3cm×3cm. After drying, put them into an sterilizing pot and sterilize them, and then cool them for use. Some of the coated tiles were subjected to a high temperature of 600°C and used after cooling. Take 0.6mL of spare E. coli solution on the tiles and paper. After 2 hours of light irradiation, colonies were cultured and cultured at 36°C for 96 hours. The control sample was a bacterial suspension without nano-TiO2 spray. Diluted samples in the experimental and control groups were counted using the MR-VP method and the bactericidal rate was calculated: bactericidal rate (%) = (viable concentration in the control group - viable concentration in the test group) / viable concentration in the control group × 100% .

2 Antibacterial test results

The bactericidal effect of E. coli broth on four different nano- TiO2 spray samples is shown in Tables 1, 2, 3, and 4. The nano TiO2 spray liquid has strong antibacterial and antibacterial ability under visible light and normal temperature.

Table 1 Determination of the bactericidal effect of nano-TiO2 liquid spray (ceramic tile)

Note: The number of blank colonies in the tiles is 6250/mL. Composite 1#, composite 2#, composite 3# are silver nano-TiO2 composites; the concentration of nano-TiO2 coated on the ceramic tile is 2%.

We observed that the nano- TiO2 spray liquid coating on the ceramic tile experiment found that most of the nano-TiO2 spray liquid samples have a strong antibacterial effect, and the nano-TiO2 spray liquid has a kill rate of more than 95% for E. coli. The bactericidal rate of the original liquid reached 100%, which is a very good antibacterial agent, and the effect of the compound nanometer liquid spray is slightly poor. This may be due to the addition of silver salt in the nano titanium dioxide spray solution. The silver salt is added to the original hope. Improve the antibacterial effect of nano-TiO2, especially in the natural light environment. However, the addition of silver salt may promote the agglomeration of nano-TiO2 and reduce the dispersion uniformity of nano-TiO2 on ceramics, affecting the adsorption of nano-TiO2 on the solid surface, and reducing the photocatalytic reaction in H2O and O2 systems. The bactericidal effect is lower than that of nano-TiO2 spray liquid.

Table 2 Determination of the bactericidal effect of nano-TiO2 liquid spray (paper sheet)

Note: The number of blank colonies in the tiles is 6250/mL. Composite 1#, 2#, and 3# are silver nano-TiO2 composites; the concentration of nano-TiO2 coated on the paper is 2%.

We performed antibacterial experiments on nano- TiO2 sprays on paper. The results show that the four nano-TiO2 sprays have strong antibacterial and antibacterial activities under visible light and at room temperature. The killing rate of E. coli by nano-TiO2 sprays is More than 93%, of which the sterilizing rate of raw liquid and compound 3# reached 100%, and the composite 3# bactericidal effect was better than that applied on the ceramic tile. The results need to be further studied. Therefore, this nano-TiO2 is a very good bactericidal, antibacterial agent, can be used for paper products on the surface of the antibacterial, especially for high-grade paper packaging materials.

In order to imitate the production of ceramic sanitary ware, the tiles used were coated with nano- TiO2 and processed at high temperature. From Table 3, it can be seen that after the application of nano-TiO2, the high-temperature treated tiles also have a very good bactericidal effect. The sterilizing rates of the coated sizing, composite 1#, composite 2#, and composite 3# samples all reached 100%. This may be due to the fact that silver-based nano-TiO 2 is better covered on the tiles after high-temperature treatment and the antibacterial effect is improved. . From Table 4, it can be seen that the sterilizing rate of ceramics coated with dilute stock solutions (1#, 2#, and 3#) is low, which may be caused by too small amount of coated nano-TiO2, while the sprayed amount of nano-TiO2 increases, and the solids The antibacterial ability of the surface increases, and at the same time, the high temperature treatment may change the crystalline state of the nano-TiO2 on the surface of the ceramic tile to a certain extent, and affect the photocatalysis.

Table 3 Determination of bactericidal effect of nano-TiO2 spray (ceramic tile)

Note: The sample is a ceramic tile coated with nano- TiO2 and treated at a high temperature of 600°C. The number of blank colonies of the tile is 6250/mL. The concentration of the coating solution, composite 1#, 2#, and 3# nano-TiO2 on the tile was all 2%.

Table 4 Determination of the bactericidal effect of nano-TiO2 liquid spray (ceramic tile)

Note: The sample is a ceramic tile coated with nano- TiO2 and treated at a high temperature of 600°C. The number of blank colonies of the tile is 6250/mL. The concentration of nano-TiO2 in the coating liquid on the tile is 2%; the diluted stock solution 1#, the diluted stock solution 2#, and the diluted stock solution 3# are the concentrations of the nano-TiO2 coated on the ceramic stock diluted to 0.1% and 0.5 respectively. %,1%.

3 Discussion

Nano-TiO2 is an ultra-fine TiO2 which is based on the photocatalytic reaction to decompose organic matter and has antibacterial, anti-virus and purification effects. In water and air systems, under the irradiation of sunlight, especially ultraviolet light, a series of reactions are initiated to generate negatively charged electrons (e-) and positively charged holes (h+) to form hole-electron pairs. These hole-electron pairs interact with H2O or OH- and O2 adsorbed on their surface to generate hydroxyl radical OH· and superoxide anion radical O2-. The newly generated free radicals have strong chemical activity, especially atomic oxygen can react (oxidize) with most organics, and thus can effectively decompose and destroy various toxic gases in the air. When bacteria are encountered, they can directly attack the bacterial cell wall, Cell membrane or intracellular components. In addition, these reactive oxygen species also cause breakage of the phosphodiester bond between the bases in the DNA strand, destroying the DNA double helix structure, thereby destroying the DNA replication of microbial cells and metabolizing the disordered cells.

The test nano-TiO2 spray liquid and silver salt and nano-TiO2 composite spray coating on the solid surface, the killing rate of E. coli in visible light and room temperature is very high, in which the sterilization rate of the raw liquid sample reaches 100%. The good sterilizing effect of nanometer TiO2 spray on tiles shows that the nano TiO2 spray can be sprayed onto the walls of the house to eliminate and suppress bacteria and purify the air. The nano TiO2 spray is applied on the tiles and is exposed to high temperatures. After treatment, it has a bactericidal effect, so this nano material will play an important role in antibacterial of sanitary wares; at the same time, we have also done a wash test, washed ceramic tiles coated with nanometer TiO2 spray 1000 times, and found porcelain Tablets still have a good bactericidal effect. The paper coated with nano-TiO2 spray liquid also has a sterilizing effect. Because TiO2 itself is chemically stable and harmless to the human body and the environment, it can be applied to commodity packaging, especially for chemical products and food packaging. Effectively inhibits and kills microorganisms, and has the functions of deodorization, mildew prevention, and disinfection, and prevents products from being corroded due to contamination.