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Method of photocatalytic disinfection of surfaces
Abstract
The invention relates to the field of disinfection of surfaces by ultraviolet radiation and can be used to disinfect the premises of public institutions, transport, furniture, equipment. The method involves pre-spraying an aqueous suspension of titanium dioxide nanoparticles with an average diameter of 23.3 nm at a concentration of 0.5 g / l for 15 minutes on the surface being treated with ultrasound and then irradiating the surface with narrow-band bactericidal ultraviolet radiation. The invention allows to reduce the time of irradiation of surfaces and improve the efficiency of disinfection. 1 tab.
Description
The invention relates to the field of disinfection of surfaces of objects and internal surfaces of premises for various purposes from pathogenic microflora using ultraviolet (UV) radiation in the presence of a photocatalyst titanium dioxide (TiO 2 ). It can be used for express disinfection of public premises (for example, the internal walls of medical, educational, cultural, sports, preschool institutions), transport, furniture, equipment without the use of disinfectant solutions.
The main oxidizing agents in photocatalytic reactions, as is known, are hydroxyl, peroxide and hydroperoxide radicals, of which the hydroxyl radical ОН ° is considered the most important oxidizing agent, providing inactivation of the cell [1].
Known methods of photocatalytic disinfection of surfaces in the presence of TiO 2 nanoparticles consist mainly in obtaining various antimicrobial films (coatings) based on TiO 2 , applying them to the surface with subsequent irradiation with light in the UV and / or visible range. The methods differ in the chemical composition of the films, the conditions for their preparation and application to the surface to be disinfected.
A known method for disinfecting surfaces, consisting in spraying TiO 2 nanoparticles heated in an induction plasma to 750 ° C on the surface with subsequent moistening and UV irradiation (Patent US 6235351 B1 of 05.22.2001).
The disadvantages of this method are:
a) The need to pre-heat a suspension of nanoparticles in an induction plasma, entailing significant energy costs.
b) The use of alcohol to obtain a suspension of nanoparticles.
c) The use of expensive equipment to obtain a high-temperature plasma discharge.
There is a method of self-disinfecting the surface using a reflective coating (Patent US 7288232 B2 of 10.30.2007), which consists in applying a primer to the surface, then a reflective layer, followed by the deposition of TiO 2 nanoparticles and heat treatment. The disinfecting effect is achieved by irradiation with UV light in the presence of water vapor.
The disadvantages of this method are:
a) strict surface requirements (hard, smooth, chemically inert, heat resistant);
b) multi-stage preliminary preparation of the surface (cleaning with acids, liquid carbon dioxide, organic solvents, applying a primer layer, barium sulfate, silica gel), which requires significant time-consuming;
c) the application of expensive primer and reflective layers;
d) the need for thermal treatment of the photocatalytic coating of the surface at temperatures up to 350 ° C;
e) The need for additional production and introduction of water vapor to initiate photocatalytic reactions that provide a disinfecting effect.
There are also known methods for cleaning the surface from pathogenic microflora and toxic chemicals by coating a surface consisting of an organic polymer base and TiO 2 nanoparticles (Patents US 2004/0224145 A1 of 11.11.2004, WO 2008/097778 A1 of 08/14/2008). The disinfecting effect is also achieved by irradiating with UV light after wetting this coating.
The disadvantages of this method are:
a) The need for preliminary preparation of a coating based on a polymer composition (polyacrylate, fluoropolymers, polyurethane, liquid crystal polymers, latex, etc.) or low-volatile organic solvents containing TiO 2 nanoparticles, as well as pigments, plasticizers, thickeners, thixotropic agents;
b) Special requirements for the surface to be disinfected (hard, cleaned, polished, degreased, and also etched in the case of a metal surface);
c) periodic updating of the polymer coating due to damages, scratches, etc .;
d) the need for additional wetting of the surface coating before UV treatment.
Also known is a method of cleaning and disinfecting surfaces using film-forming aqueous and / or alcohol dispersions of TiO 2 nanoparticles, as well as polymer-containing dispersions of TiO 2 (Patent US 6905814 B1 dated June 4, 2005).
The disadvantages of this method include the above paragraphs. a) and b), as well as:
c) the need to bring the pH of the dispersion of TiO 2 to a certain value depending on its chemical composition and its drying after application to the surface;
d) Use of long-wave UV-radiation at 365 nm for inactivation of aqueous suspensions of Pseudomonas aeruginosa on a film of TiO 2 (5 × 10 7 CFU / ml) and a longer duration of exposure to achieve 99.9% inactivation effect - 6 hours (Example 7 implementation of the method).
A known method of photocatalytic inactivation of Escherichia coli cells on the surface of membrane filters in the presence of immobilized Ti 105 nanoparticles PC 105 [2]. The disadvantages of this method are the high cost of membrane filters and the use of fluorescent lamps emitting in a wide UV range of 290-400 nm and further in the visible range of 400-700 nm. The accepted bactericidal range of wavelengths (205-315 nm) accounts for only 6% of the total radiation of such lamps. Therefore, due to their low bactericidal efficacy, a disadvantage of this method is also the long duration of cell irradiation to achieve 99.9% inactivation effect (2 hours).
The closest analogues of the present invention are a method of disinfecting the surface by UV radiation in the presence of TiO 2 nanoparticles [3] and patent WO 2007/051996 A1 of 05/10/2007, taken as prototypes. In the article [3], the source of UV radiation was a Philips lamp with a power of 2 × 15 W, emitting "white light" ("white light" or visible range) and ultraviolet light at 365 nm. The surface to be disinfected (plexiglass) was coated with a nanoscale TiO 2 Degussa P25 photocatalyst. Next, aqueous suspensions of E. coli were applied and irradiated.
The disadvantages of this method are:
a) low bactericidal efficiency of lamps with low radiation intensity at 365 nm, not included in the accepted bactericidal range (205-315 nm). All radiation intensity falls within the visible range;
b) the limited practical application of the method, since in real conditions microorganisms are on surrounding surfaces, mainly in the form of biofilms, and not in the form of aqueous suspensions;
c) long duration of irradiation of bacterial suspensions on the surface to achieve its complete disinfection (60 min).
In example 1 of the method for producing a TiO 2 -based nanocomposite film and its application for antibacterial purposes (WO 2007/051996 A1), a VL-208BLB UV lamp manufactured by Vilber Lourmat (VWR Ltd.) with a power of 2 × 8 W was used as the radiation source. emitting "black light" at 365 nm with an intensity of 1.3 mW / cm 2 , without visible radiation ("black light blue"). This method has all the above disadvantages. In addition, the method is characterized by a multi-stage sol-gel method for producing a nanocomposite film, which includes expensive silver oxide (chemical synthesis, immersion of a glass slide into a sol to produce a film, doping a film with silver, high-temperature annealing of the finished film).
The task of the invention is to reduce the time of photocatalytic disinfection of surfaces by UV radiation with high efficiency inactivation of microorganisms.
The technical result achieved through the implementation of the invention is to significantly reduce the time of surface treatment to achieve complete inactivation of microorganisms (up to 45 seconds at an initial concentration of E. coli 10 8 CFU / ml).
The technical result is achieved by spraying an aqueous suspension of TiO 2 nanoparticles with an average diameter of 23.3 nm (Start Scientific Production Company, Perm, an analogue of Degussa P25) at a concentration of 0.5 g / l and irradiating the disinfected surface narrow-band ultraviolet radiation in the bactericidal range.
The proposed method does not require the preparation of a special multicomponent coating, applying it to the surface at high temperature and is not limited by the type of surface to be disinfected. Almost any surface located in industrial and medical premises, offices, private houses and apartments, transport (for example, walls, ceilings, floors (with any coating), curtains, curtains, plastic, glass, metal surfaces) can serve as a disinfectable surface. This method is implemented for surfaces infected with pathogenic microorganisms located on them in the form of biofilms, and not only in the form of aqueous suspensions.
The advantages of the proposed method are a significant reduction in the exposure time to achieve a 100% effect of disinfection and the simplicity of the disinfection technology. This provides the possibility of its use in emergency situations when immediate disinfection of contaminated surfaces is required. Titanium dioxide with nanoscale particles is an affordable, non-toxic, highly stable and relatively inexpensive material. As shown by the results of the study [4], TiO 2 nanoparticles (up to 100 nm in diameter) have a higher bactericidal activity than larger particles. The optimum concentration of catalyst in water is 0.5 g / l. For dispersion and activation of TiO 2 in water, we recommend its ultrasonic treatment.
Instead of fluorescent lamps with low bactericidal efficiency, we propose to use modern sources of UV radiation — excilamps and excimer lasers emitting on transitions of excimer and exciplex molecules. Their main advantage is a narrow emission spectrum, more than 80% of the total power of which is concentrated in a narrow (up to several nm at half-height) spectral band of the corresponding molecule. For example, a barrier discharge excilamp on KrCl molecules emits all energy in the bactericidal range with a maximum at a wavelength of 222 nm, and thus has a maximum efficiency in the bactericidal range (up to 30%). In addition, excilamps and excimer lasers do not contain mercury, are distinguished by high photon energy (3.5-10 eV), service life (1000-10000 hour), are simpler and safer for the operator.
Below are examples of the implementation of the claimed method.
Example 1
20 μl of water containing 10 8 CFU / ml of E. coli was applied to the initial sterile surface (glass) and dried at 37 ° C for 15 min to obtain a biofilm. Then, an aqueous suspension of titanium dioxide nanoparticles at a concentration of 0.5 g / l was sprayed onto the surface of the glass and irradiated at room temperature under an UV KrCl excilamp exit window emitting at 222 nm with a radiation intensity of 3.2 mW / cm 2 . Pre-suspension of TiO 2 nanoparticles was subjected to ultrasonic treatment in an ultrasonic bath at a frequency of 45 kHz and power of 50 W for 15 minutes. After irradiation, the cells were washed off the glass, suspended in distilled water, sown on agar medium, and incubated at 37 ° C for 24 hours to count the surviving cells.
The surface dose of UV radiation required to inactivate 99.9% of the cells at 10 8 CFU / ml is 33 mJ / cm 2 and is reached in 10 seconds.
The test results are shown in the table.
Example 2
The disinfection process was carried out analogously to example 1, but using a UV XeBr excilamp emitting at 282 nm with a radiation intensity of 1.0 mW / cm 2 . The surface UV dose, which inactivates 99.9% of the cells at 10 8 CFU / ml, is 9 mJ / cm 2 and is achieved in 9 seconds. The test results are shown in the table.
As an object of comparison, the method of water disinfection [2] and patent WO 2007/051996 A1 were used.
The initial concentration of E. coli cells, CFU / ml UV source, wavelength The time required to inactivate 100% of E. coli cells
Example 1 10 8 KrCl excilamp, 222 nm 45 seconds
Example 2 10 8 HeVG excilamp, 282 nm 25 sec
Kühn et al., 2003 1.2 × 10 7 Philips lamp, 365 nm + "white light" 60 min
Patent WO 2007/051996 A1 1.6 × 10 7 Lamp Vilber Lourmat VL-208 BLB, 365 nm ("black light") 6 hours, efficiency 69%
The results indicate a high bactericidal efficiency of the proposed method.
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