Method for photocatalytic water disinfection

Abstract

FIELD: water treatment.SUBSTANCE: used in domestic drinking water supply systems, in the food and pharmaceutical industries, as well as in medicine for sterilizing liquids and surfaces. Water is irradiated with visible light with a wavelength of 407–550 nm and an illumination level of 1300–60000 lux in the presence of a photocatalyst. A photocatalyst based on mesoporous titanium dioxide with an average particle diameter of 70–253 nm, modified with a vanadium cation, is used. The vanadium cation content is 2.5–20.0 wt.%.EFFECT: reliable disinfection of water from various types of gram-negative and gram-positive bacteria: Pseudomonasfluorescens, Bacillusbrevis, Micrococcusluteus. The degree of disinfection, depending on the type of bacteria and irradiation conditions, reaches 100%.1 cl, 11 ex

Description

[0001] The invention relates to the field of water treatment and can be used in domestic drinking water supply systems, in the food and pharmaceutical industries, as well as in medicine for sterilizing liquids and surfaces.

[0002] Most existing industrial water treatment systems rely on methods using strong oxidizing agents, such as chlorination, ozonation, and ultraviolet (UV) light disinfection using UV lamps. Among promising water disinfection methods, photocatalytic methods based on semiconductor photocatalysts are receiving particular attention. The most common material for these purposes is titanium dioxide (TiO2), which is highly chemically stable, readily available, and non-toxic. TiO2 operates by generating electron-hole pairs under the influence of light, followed by the formation of reactive oxygen species, particularly hydroxyl radicals, which can mineralize organic compounds and inactivate pathogens. However, known photocatalytic purification methods using TiO2 have a significant drawback.The band gap of titanium dioxide (3.2 eV for the anatase phase) determines its photocatalytic activity only under UV radiation with wavelengths shorter than 380-400 nm. In practice, this requires the use of UV light sources, most often mercury vapor lamps, which consume significant amounts of electricity and have a limited lifespan compared to modern light sources. Mercury is a chemically hazardous substance, posing risks if the lamps are damaged and requiring complex and expensive disposal procedures for spent elements. Therefore, there is a need to develop a simple, effective, and environmentally friendly method for photocatalytic water disinfection that would eliminate the need for chlorination, ozonation, or the use of environmentally hazardous mercury vapor lamps and other UV lamps, and instead utilize visible light sources.

[0003] A method for photocatalytic disinfection of water is known (see patent 2414431 of the Russian Federation, IPC C02F 1 / 32, 1 / 36, 103 / 04 (2006.01), 2011), according to which water is treated with ultraviolet radiation in the presence of a catalyst - titanium dioxide particles with a concentration of 0.5 g / l. For water treatment, narrow-band ultraviolet radiation and a catalyst in the form of titanium dioxide nanoparticles with an average diameter of 23.3 nm are used, which are subjected to preliminary ultrasonic treatment at a frequency of 45 kHz and a power of 50 W for 15 minutes.

[0004] This method disinfects water from only one type of gram-negative bacteria: Escherichia coli. Disadvantages of this method include the need for specialized, energy-intensive excilamps with a narrow wavelength range (λ=222, λ=282 nm) in the UV spectrum and, furthermore, the need for preliminary ultrasonic activation of the photocatalysts.

[0005] Also known is a method for photocatalytic disinfection of water, adopted as a prototype (see Belikov M.L., Fokina N.V., Redkina V.V., Safaryan S.A. Photocatalytic inactivation of bacteria in the presence of titanium dioxide modified with tungsten under irradiation with visible light / Kinetics and Catalysis. 2022. Vol. 63. No. 4. Pp. 433-445) by irradiating it with light of the visible spectrum in the presence of a photocatalyst based on titanium dioxide modified with a tungsten cation in an amount of 20-30 wt. %, with a particle size of 24-33 nm, heat-treated at 600 °C. The visible light sources were an incandescent lamp (100 W), an LED lamp (18 W), and sunlight, providing an illumination level of up to 14,500 lux for the suspension. The inactivation sample was a strain of Gram-negative bacteria, Pseudomonas fluorescens.

[0006] A disadvantage of the known method is that it only considers one target for inactivation: Pseudomonas fluorescens bacteria, which are Gram-negative bacteria with a relatively simple cell wall structure. Furthermore, the titanium dioxide-based photocatalyst used is modified with high concentrations of tungsten (20-30 wt%), which is associated with increased costs.

[0007] The present invention is aimed at achieving a technical result consisting in increasing the efficiency of disinfection from bacteria of a wider range of species, including gram-negative (Pseudomonas fluorescens) and gram-positive (Bacillus brevi and Micrococcus luteu) bacteria.

[0008] The technical result is achieved in that in the method of photocatalytic disinfection of water, including its irradiation with light of the visible spectrum in the presence of a photocatalyst based on titanium dioxide modified with a metal cation, according to the invention, light of the visible spectrum with a wavelength of 407-550 nm and a degree of illumination of 1300-60000 lux and a photocatalyst based on mesoporous titanium dioxide with an average particle diameter of 70-253 nm, modified with a vanadium cation are used.

[0009] The technical result is also achieved by the fact that titanium dioxide modified with a vanadium cation in an amount of 2.5-20.0 wt.% is used as a photocatalyst.

[0010] The essential features of the claimed invention, which determine the scope of legal protection and are sufficient to obtain the above-mentioned technical result, perform the functions and relate to the result as follows.

[0011] Using visible light with a wavelength of 407-550 nm and an illumination level of 1300-60000 lux ensures the activation of the photocatalyst in the specified range of visible light, due to the introduction of vanadium, which helps to narrow the band gap to 2.14-2.4 eV, which initiates oxidation-reduction reactions on the surface of mesoporous titanium dioxide TiO2 with the formation of radicals that ensure water disinfection.

[0012] When irradiated with light with a wavelength of less than 407 nm, the photocatalytic activity remains at a high level, but such light is less accessible, for example, under natural light conditions and requires special radiation sources that are impractical for energy-efficient technologies, and at a wavelength of more than 550 nm, the disinfection efficiency decreases, since the photon energy becomes lower, which contributes to a decrease in the generation of electron-hole pairs necessary for photocatalytic disinfection.

[0013] An illumination level of less than 1300 lux does not provide the necessary photon density for the efficient generation of electron-hole pairs in a material with a band gap of 2.14-2.4 eV, as a result of which the rate of the photocatalytic reaction and the formation of active oxygen species decrease below the threshold values ​​required for the inactivation of microorganisms, and an illumination level exceeding 60,000 lux can lead to the saturation of the catalyst surface with charge carriers and an increase in recombination processes, which reduces the quantum yield of the reaction and the efficiency of disinfection.

[0014] The use of a photocatalyst based on mesoporous titanium dioxide with an average particle diameter of 70-253 nm, modified with a vanadium cation, ensures the formation of a developed specific surface area of ​​the photocatalyst and the effective transport of reagent molecules, which, in combination with modification with vanadium, narrowing the band gap to 2.14-2.4 eV, ensures high photocatalytic activity in visible light and effective water disinfection due to the generation of active oxygen species.

[0015] With a particle diameter of less than 70 nm, the specific surface area increases and the migration path of photoinduced charges from the bulk of the photocatalyst to its surface is shortened, which can lead to increased disinfection efficiency. However, as the particle diameter decreases, their volatility increases significantly and their sedimentation ability decreases, which is crucial for subsequent separation of the photocatalyst from the disinfected water. With particle sizes exceeding 253 nm, the specific surface area of ​​the catalyst decreases, and the migration path of electron-hole pairs to the particle surface becomes excessively long. This dramatically increases the likelihood of charge carrier recombination within the particles before they can react with the bacteria, leading to a decrease in disinfection efficiency.

[0016] The combination of the above-mentioned features is necessary and sufficient to achieve the technical result of the invention, which consists in increasing the efficiency of disinfection from a wider range of bacteria.

[0017] The use of titanium dioxide modified with vanadium cation in an amount of 2.5-20.0 wt.%, heat-treated at 600°C, as a photocatalyst makes it possible to shift the photosensitivity region of the material to the visible range of the spectrum (407-550 nm).

[0018] The essence of the invention can be explained by the following Examples.

[0019] Example 1. Into the source water containing 10 5CFU / ml (colony forming units / ml) of Pseudomonas fluorescens, 2 mg / ml of a photocatalyst based on mesoporous titanium dioxide modified with 2.5 wt.% vanadium, with an average particle diameter of 70 nm, are added and irradiated with an incandescent lamp (100 W) and a fluorescent lamp (18 W) emitting light in the visible spectrum with an illumination of 1300 lux. The maximum efficiency of water disinfection is observed with irradiation with light with a wavelength of 407-550 nm. The degree of disinfection after 3 hours of irradiation reaches 21.2%, and after 24 hours of irradiation - 53.2%).

[0020] Example 2. Into the source water containing 10 5CFU / ml of Pseudomonas fluorescens are added to 2 mg / ml of a photocatalyst based on titanium dioxide modified with 2.5 wt % vanadium, with an average particle diameter of 70 nm, and irradiated with an incandescent lamp (100 W) and a fluorescent lamp (18 W) emitting light in the visible spectrum with an illuminance of 2800 lux. The maximum efficiency of water disinfection is observed with irradiation with light with a wavelength of 407-550 nm. The degree of disinfection after 3 hours of irradiation reaches 36.0%, and after 24 hours of irradiation - 84.1%.

[0021] Example 3. Into the source water containing 10 5CFU / ml Pseudomonas fluorescens, 5 mg / ml of a photocatalyst based on titanium dioxide modified with vanadium in an amount of 2.5 wt.%, with an average particle diameter of 70 nm are added and irradiated with an incandescent lamp (100 W) and a fluorescent lamp (18 W), emitting light of the visible spectrum with an illumination of 2800 lux. The maximum efficiency of water disinfection is observed when irradiated with light with a wavelength of 407-550 nm. The degree of disinfection after 3 hours of irradiation reaches 40.0%), and after 24 hours of irradiation - 99.4%.

[0022] Example 4. In the source water containing 10 5CFU / ml of Pseudomonas fluorescens are added to a solution containing 2 mg / ml of a photocatalyst based on titanium dioxide modified with 5 wt.% vanadium, with an average particle diameter of 73.6 nm, and irradiated with an incandescent lamp (100 W) and a fluorescent lamp (18 W) emitting visible light with an illuminance of 2800 lux. Maximum water disinfection efficiency is observed with irradiation with light with a wavelength of 407-550 nm. The degree of disinfection after 3 hours of irradiation reaches 81.9%, and after 24 hours of irradiation - 100%.

[0023] Example 5. Into the source water containing 10 5CFU / ml of Pseudomonas fluorescens are added with 2 mg / ml of a photocatalyst based on titanium dioxide modified with 20 wt.% vanadium, with an average particle diameter of 253 nm, and irradiated with an incandescent lamp (100 W) and a fluorescent lamp (18 W) emitting visible light with an illuminance of 2800 lux. Maximum water disinfection efficiency is observed with irradiation with light with a wavelength of 407-550 nm. The degree of disinfection after 3 hours of irradiation reaches 46%, and after 24 hours of irradiation - 100%.

[0024] Example 6. In the source water containing 10 4CFU / ml of Bacillus brevis are added to a 2.5 wt.% vanadium-modified titanium dioxide photocatalyst with an average particle diameter of 70 nm and irradiated with natural sunlight through glass. The average daily illumination is 30,005 lux. Maximum water disinfection efficiency is observed with light with a wavelength of 407-550 nm. The disinfection rate after 3 hours of irradiation reaches 4.3% at an illumination of 14,000 lux, and after 24 hours of irradiation, it reaches 36.0%.

[0025] Example 7. In the source water containing 10 4CFU / ml of Bacillus brevis are added to a 5 wt.% vanadium-modified titanium dioxide photocatalyst with an average particle diameter of 73.6 nm and irradiated with natural sunlight through glass. The average daily illumination is 30,005 lux. Maximum water disinfection efficiency is observed with light with a wavelength of 407-550 nm. The disinfection rate after 3 hours of irradiation reaches 23.0% at an illumination of 14,000 lux, and after 24 hours of irradiation, it reaches 60.0%.

[0026] Example 8. In the source water containing 10 4CFU / ml of Bacillus brevis is added to a 20% vanadium-modified titanium dioxide photocatalyst with an average particle diameter of 253 nm and irradiated with natural sunlight through glass. The average daily illumination is 30,005 lux. Maximum water disinfection efficiency is achieved with light with a wavelength of 407-550 nm. The disinfection rate after 3 hours of irradiation reaches 2.9% at an illumination of 14,000 lux, and after 24 hours of irradiation, it reaches 67.1%.

[0027] Example 9. In the source water containing 10 4CFU / ml of Bacillus brevis is added to a photocatalyst based on titanium dioxide modified with 5 wt.% vanadium, with an average particle diameter of 73.6 nm, and irradiated with natural sunlight through glass. The average daily illumination was 30,005 lux. Maximum water disinfection efficiency was observed with light with a wavelength of 407-550 nm. The degree of disinfection after 3 hours of irradiation reaches 70.4% at an illumination of 60,000 lux, and after 24 hours of irradiation - 99.8%.

[0028] Example 10. In the source water containing 10 6CFU / ml Micrococcus luteus, 5 mg / ml of a photocatalyst based on titanium dioxide modified with vanadium in an amount of 5 wt.%, with an average particle diameter of 73.6 nm, are added and irradiated with an incandescent lamp (100 W) and a fluorescent lamp (18 W), emitting light in the visible spectrum with an illuminance of 2800 lux. Maximum water disinfection efficiency is observed with irradiation with light with a wavelength of 407-550 nm. The degree of disinfection after 3 hours of irradiation reaches 57.1%, and after 24 hours of irradiation - 89.3%.

[0029] Example 11. In the source water containing 10 6Micrococcus luteus (CFU / ml) was cultured with 5 mg / ml of a photocatalyst based on titanium dioxide modified with 5 wt.% vanadium, with an average particle diameter of 73.6 nm, and irradiated with natural sunlight through glass. The average daily illumination was 30,005 lux. Maximum water disinfection efficiency was observed with light with a wavelength of 407-550 nm. The disinfection rate after 3 hours of irradiation reached 85.7% at an illumination of 52,000 lux, and 100% after 24 hours of irradiation.

[0030] The above examples demonstrate that the proposed method effectively disinfects water from various types of bacteria: Pseudomonas fluorescens, Bacillus brevis, and Micrococcus luteus. The degree of disinfection, depending on the bacteria type and conditions, when irradiated with visible light in the presence of a vanadium-modified titanium dioxide photocatalyst, reaches 100%. The proposed method can be implemented using standard chemical equipment.

Claims

1. A method for photocatalytic disinfection of water, including irradiating it with visible spectrum light in the presence of a photocatalyst based on titanium dioxide modified with a metal cation, characterized in that visible spectrum light with a wavelength of 407-550 nm and an illumination level of 1300-60000 lux and a photocatalyst based on mesoporous titanium dioxide with an average particle diameter of 70-253 nm, modified with a vanadium cation, are used.

2. The method according to paragraph 1, characterized in that the photocatalyst used is titanium dioxide modified with a vanadium cation in an amount of 2.5-20.0 wt.%.