WO2023131819A1

WO2023131819A1 - A composition for disinfection and a method of preparing a disinfectant

Info

Publication number: WO2023131819A1
Application number: PCT/IB2022/050148
Authority: WO
Inventors: Jianping Lu; Jianying Ouyang; Bassel AKACHE; Zhiyi Zhang; Ye Tao; Gerard AGBAYANI; Daniel Poitras
Original assignee: National Research Council Of Canada
Priority date: 2022-01-10
Filing date: 2022-01-10
Publication date: 2023-07-13

Abstract

TiO2 is a wide bandgap material, which means that ultraviolet (UV) radiation is required for the photoactivation. Since UV light poses a hazard to human health, the applications of TiO2 as a photocatalyst are limited. Therefore, the present specification is directed to a composition of TiO2 which is reactive under blue light. To achieve this, TiO2 is doped to red-shift its absorption spectrum. The present specification further provides a method of preparing a disinfectant which contains a titanium dioxide nanoparticle and a dopant.

Description

A COMPOSITION FOR DISINFECTION AND A METHOD OF PREPARING A DISINFECTANT

FIELD

[0001] The present specification is directed to disinfection using photocatalytic oxidation and more particularly, the photocatalytic oxidation of titanium dioxide under visible light.

BACKGROUND

[0002] Due to its high photostability (i.e. resistance to photocorrosion), low cost, and nontoxicity, titanium dioxide (TiO₂) has been widely used in photocatalytic applications, including the degradation of organic pollutants in aqueous and gaseous phases, removal of heavy metals from contaminated waters, hydrogen gas generation from photocatalytic water splitting, etc. Upon bandgap illumination, electrons are raised into the conduction band (CB) and holes are left in the valence band (VB) of titanium dioxide. Then, a portion of the electrons and holes successfully reach the surface where the subsequent chemical reactions can take place.

[0003] The primary cause for the photocatalytic activity of titanium dioxide is believed to be the formation of hydroxyl ("OH) radicals by rapid conversion of photogenerated holes upon contact with the adsorbed water molecules on titanium dioxide. The highly active "OH radicals are capable of mineralizing most organic pollutant molecules and killing bacteria and viruses. The photogenerated charge carriers can easily reach the surface before they recombine, so that a high quantum yield can also be expected.

SUMMARY

[0004] It is an aspect of the present specification to provide a titanium dioxide composition for catalyzing a synthesis of hydroxyl radicals when exposed to visible light.

[0005] The above aspects can be attained by a composition that contains a nanocomposite of titanium dioxide and a dopant. The dopant red-shifts the absorption of the nanocomposite into the visible spectrum, allowing the nanocomposite to perform photocatalysis in the presence of visible light.

[0006] In some implementations, the dopant comprises a metal. The metal may be selected from a group consisting of chromium, iron, copper, manganese, vanadium, cobalt, nickel, magnesium, bismuth, gold, and platinum. [0007] In further implementations, the dopant comprises iron and gold.

[0008] In yet further implementations, the visible light has a peak wavelength selected to excite an electron from the dopant to the conduction band of the titanium dioxide.

[0009] In other implementations, the visible light has a peak wavelength between 380 and 500 nanometers.

[0010] In further implementations, the composition includes a solute.

[0011] In other implementations, the composition includes a ligand to suspend the nanocomposite in the solute.

[0012] In other implementations, the atomic ratio between the dopant and the titanium dioxide is approximately 0.1.

[0013] In other implementations, the titanium dioxide includes a nanotube.

[0014] It is a further aspect of the present specification to provide a method of preparing a disinfectant containing titanium dioxide which catalyzes a synthesis of hydroxyl radicals when exposed to visible light.

[0015] The above aspects can be attained by doping the titanium dioxide to red-shift its absorption into the visible spectrum, allowing the nanocomposite to perform photocatalysis in the presence of visible light.

[0016] In some implementations, the doping is achieved by a hydrothermal doping process.

[0017] In some implementations, the nanocomposite is applied onto a substrate.

[0018] In some implementations, the nanocomposite is suspended in a solution before the nanocomposite is applied to the substrate. The nanocomposite is applied to the surface by casting the solution onto the substrate and drying the substrate.

[0019] In some implementations, a plurality of layers of the nanocomposite are applied to the substrate.

[0020] It is a further aspect of the present specification to provide the use of chromium-doped titanium dioxide for disinfection under visible light.

[0021] It is a further aspect of the present specification to provide the use of gold- and iron- doped titanium dioxide for disinfection under visible light. [0022] These together with other aspects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a diagram showing the photocatalytic synthesis of hydroxyl radicals.

[0024] Figure 2 is a flowchart showing a method disinfecting a substrate.

[0025] Figure 3 is a graph showing the absorption spectrum of various transition metal-doped titanium dioxide nanocrystals.

[0026] Figure 4 is a graph showing the absorption spectrum of gold-Fe³⁺ doped titanium dioxide nanocrystals.

[0027] Figure 5 is a graph showing the evaluation of the anti-microbial efficiency of the composition and method.

[0028] Figure 6 is another graph showing the evaluation of the anti-microbial efficiency of the composition and method.

DETAILED DESCRIPTION

[0029] The present disclosure is described with respect to a composition for disinfection using photocatalytic oxidation of titanium dioxide under visible light.

[0030] “Nanoparticle” herein refers to a particle having at least one dimension measuring less than 100 nanometres.

[0031] “Rutile phase” herein refers to a polymorph of titanium dioxide characterized by a bandgap of approximately 3.0 eV.

[0032] “Anatase phase” herein refers to a polymorph of titanium dioxide characterized by a bandgap of approximately 3.2 eV.

[0033] “Bandgap” herein refers to the minimum amount of energy required for an electron to be excited from the valence band to the conduction band of an atom. [0034] “Blue light” herein refers to electromagnetic radiation having a wavelength of about 380 nanometers to about 500 nanometers.

[0035] “Visible light” herein refers to electromagnetic radiation having a wavelength of about 380 nanometers to about 750 nanometers.

[0036] “Hydroxyl radical” or “•OH) herein refers to the oxidizing species comprising oxygen and hydrogen.

[0037] “Absorption spectrum” herein refers to the fraction of incident radiation absorbed by a material over a range of frequencies of electromagnetic radiation.

[0038] “Red-shift” herein refers to an increase in wavelength in the light.

[0039] “rpm” herein refers to revolutions per minute.

[0040] The present disclosure provides a composition and method for disinfection using photocatalytic oxidation of titanium dioxide under visible light.

[0041] Titanium dioxide can catalyze a synthesis of hydroxyl radicals when exposed to light, as represented in Figure 1. When a particle of TiO₂ 104 is excited with bandgap illumination, electrons 108 may be raised into the conduction band (CB), leaving holes 112 in the valence band (VB) of the TiO₂. A portion of the electrons 108 and holes 112 may reach the surface of the TiO₂104 where the formation of -'OH (hydroxyl) radicals 116 may occur. -OH radicals 116 may be formed by the conversion of photogenerated holes 112 upon contact with the adsorbed H₂O molecules on TiO₂. The -OH radicals 116 may mineralize organic pollutant molecules and destroy bacteria and viruses 120. One mechanism by which the -'OH radicals may destroy bacteria and viruses is through the photocatalytic oxidation of methanol to formaldehyde.

[0042] TiO₂ is a wide bandgap material (3.0 eV for the rutile phase and 3.2 eV for the anatase Phase), which means ultraviolet (UV) radiation is required for the photoactivation. Unfortunately, the UV light poses a hazard to human health, which limits its applications. Therefore, the present specification is directed to a composition of TiO₂ which is reactive under visible light. To achieve this, TiO₂ is doped to red-shift its absorption spectrum.

[0043] The composition for disinfection comprises a nanocomposite of titanium dioxide and a dopant. When exposed to visible light, the nanocomposite is configured to catalyze a synthesis of hydroxyl radicals.

[0044] The titanium dioxide may comprise titanium dioxide in rutile phase or anatase phase or a combination of the rutile and anatase phase. The titanium dioxide may comprise a nanoparticle such as a nanocrystal or a nanotube. In some implementations, the titanium dioxide may comprise a Ti0₂-carbon nanostructure.

[0045] The dopant may comprise a metal, and in particular, a transition metal. Examples of suitable metals for the dopant include chromium (Cr), iron (Fe), lutetium (Lu), manganese (Mn), vanadium (V), cobalt (Co), nickel (Ni), magnesium (Mg), bismuth (Bi), gold (Au), and platinum (Pt), however the dopant is not particularly limited. The dopant may comprise a single metal or a combination of two or more metals. In certain implementations, the dopant comprises iron and gold. In other implementations, the dopant comprises chromium (Cr³⁺). The absorption spectrum for the nanocomposite may depend in part on which dopant is selected. In order to shift the absorption spectrum of the nanocomposite into the visible portion of the electromagnetic spectrum, a dopant that causes red-shift may be selected.

[0046] The relative amounts of dopant and TiO₂ may be selected to achieve an atomic ratio between the dopant and the TiO₂ of approximately 0.1 to 1 percent.

[0047] Since the dopant causes a red-shift in the absorption spectrum of the nanocomposite, the atomic ratio of dopant to TiO₂ may be correlated to the peak wavelength absorbed by the nanocomposite. At higher concentrations of the dopant, the nanocomposite may exhibit an absorption spectrum with a higher energy wavelength. At lower concentrations of the dopant, the nanocomposite may exhibit an absorption spectrum with a lower energy wavelength. For this reason, the dopant and the atomic ratio of dopant to TiO₂ may be selected such that the absorption spectrum of the nanocomposite has a peak wavelength that is visible to the human eye. In certain implementations, the dopant and the atomic ratio of dopant to TiO₂ may be selected such that the absorption spectrum of the nanocomposite has a peak wavelength that corresponds to blue light, green light, or a combination of blue and green light. In other implementations, the dopant and the atomic ratio of dopant to TiO₂ may be selected such that the absorption spectrum of the nanocomposite has a peak wavelength between 380 and 500 nanometers.

[0048] The composition may comprise a solvent with the nanocomposite suspended in said solvent. The dispersion may comprise any solvent in which the nanocomposite is dispersed. Some examples of a suitable solvent include polar solutes such as water, an alcohol, or a combination thereof. In some implementations, the solvent comprises ethanol. The relative amounts of the nanocomposite and the solvent may be selected to achieve a desired concentration. In some implementations, the concentration of the nanocomposite in the dispersion is approximately 1% by weight.

[0049] In implementations where the composition comprises a solute, the composition may further include a ligand for suspending the nanocomposite in the solute. It is appreciated that the selected ligand will not interfere with the photocatalytic properties of the nanocomposite.

[0050] A disinfectant comprising titanium dioxide and a dopant may be prepared according to the method described in Figure 2.

[0051] At block 204, the method comprises synthesizing a nanocomposite by doping a titanium dioxide nanoparticle with a dopant. As described above, the dopant may comprise a metal. The nanocomposite may be synthesized using a variety of methods known in the art including, but not limited to, hydrothermal doping, ion implantation, and metal organic chemical vapour deposition.

[0052] In embodiments where the doping method is hydrothermal doping, the doping may include preparing an aqueous solution of the dopant in water. Then, the dopant solution may be combined with water, an alcohol, and a suitable amount of TiO₂ powder. The resulting solution may be charged into a pressure vessel and heated at a temperature of approximately 180-220 °C for approximately 8 hours. The resulting powders may be collected by centrifugation at a suitable speed, for example 8,000 to 10,000 rpm. The powders may be rinsed at least once. In some implementations, the powders may be rinsed with a rinsing solution, for example an acid or an alcohol or a combination of an acid and an alcohol. The resulting mixture may be dried. In some implementations, the mixture may be dried at approximately 70-90 °C for approximately 1 day. It may be desirable to ground the resulting powder to produce a finer powder.

[0053] In order to sanitize a substrate, the powder comprising the nanocomposite may be suspended in a solvent, as indicated at block 208. The dispersion may comprise any solvents in which the nanocomposite is dispersed. Some examples of a suitable solvent include polar solutes such as water, an alcohol, or a combination thereof. In some implementations, the solvent comprises ethanol. The relative amounts of the nanocomposite and the solvent may be selected to achieve a desired concentration. In some implementations, the concentration of the nanocomposite in the solute is approximately 1 % by weight.

[0054] At block 212, the dispersion comprising the nanocomposite may be applied on a substrate. In some implementations, the dispersion may be applied so as to coat the substrate entirely. In other implementations, the dispersion may be applied so as to coat a portion of the substrate. Suitable substrates may include metal, glass, plastic, and cloth, but the substrate is not particularly limited. Examples of substrates include as door handles, handrails, elevator buttons, light switches, faucet handles, tables, countertops, and electronics; personal protective equipment (PPE) such as facial masks, respirators, face shields, gloves, gowns, safety glasses, goggles, foot covers, and hair bonnets; and medical equipment. However, the substrate is not particularly limited.

[0055] To eliminate the solvent, the substrate may be dried, as represented at block 216. Drying may be performed by heating, air drying, vacuum drying, drum drying, dielectric drying, or a combination thereof, but the drying method is not particularly limited. As a result of the drying, the nanocomposite may be deposited on the substrate in a film, coating, or layer. In some implementations, the film, coating, or layer may be long-lasting. In other implementations, the film, coating, or layer may be permanent.

[0056] To achieve a desired thickness of nanocomposite on the substrate, blocks 212 and 216 may be repeated. The repetition of blocks 212 and 216 may deposit a plurality of layers of the nanocomposite onto the substrate.

[0057] Substrates on which the nanocomposite have been deposited may be sanitized by illuminating the surface with visible light. Any suitable light source that emits visible light may be used including, but not limited to, sunlight, a flame, an LED lamp, an incandescent lamp, and a fluorescent lamp. The light source may emit light that includes the peak wavelength of the absorption spectrum for the nanocomposite. In some implementations, the peak wavelength of the light source is approximately the same as the peak wavelength of the absorption spectrum for the nanocomposite. The intensity of the light is not particularly limited, however the time required for disinfection may depend on the intensity of light. At a higher light intensity, disinfection may be achieved in a shorter duration of time, whereas at a lower light intensity, disinfection may be achieved in a longer duration of time.

[0058] The nanoparticle may be particularly beneficial for medical equipment such as PPE, which is typically considered to be a single-use item. By exposing the PPE to visible light, the PPE may be sanitized and re-used, which has a number of environmental and financial benefits. Sanitizing PPE can reduce healthcare costs, reduce waste, and avoid shortages of PPE.

[0059] Example 1 [0060] Synthesis of the nanocomposite using hydrothermal doping will now be explained. Example 1 describes the synthesis of the nanocomposite with Cr³⁺ as the dopant, however the dopant is not particularly limited.

[0061] In this method, titanium dioxide nanoparticles were doped with Cr³⁺ ions. First, an aqueous solution including Cr³⁺ ions was prepared by dissolving 50 mg of Cr(NO₃)3'9H₂O (Millipore Sigma®; Oakville Canada) in 10 ml of deionized water to obtain a 2.0 mg/ml solution of Cr(NO₃)3. Then, 0.2 g of TiO₂ particle, the Cr(NO₃)3 solution (1 .5 to 2.5 ml), DI water (2.5 mL), and isopropanol (25 mL) were charged into a pressure vessel. Suitable examples of TiO₂ particles include p25 from Degussa Corp.® (Essen, Germany), or Ti-nanoxide™ T600/SC from Solaronix® (Aubonne, Switzerland). The pressure vessel was heated to 200 °C at a rate of 5 “C/minute and kept at 200 °C for 8 hours. After cooling, the resulting powders were collected by centrifugation at 10,000 rpm and washed twice with isopropanol (MilliporeSigma; Oakville, Canada). The resulting mixture is then rinsed with nitric acid (0.01 M in isopropanol) (MilliporeSigma, Oakville Canada ) and isopropanol repeatedly, and dried at 80 °C for 24 hours and ground with an alumina mortar and pestle for further characterization.

[0062] About 0.19 g of yellow-gray fine powder was obtained. For the TiO₂ particles doped by this hydrothermal method, there existed a high-to-low dopant concentration gradient from exterior to interior of the respective particle. The obtained TiO₂ particles were Cr³⁺ rich on the surface, improving their efficacy in disinfection.

[0063] The doped TiO₂ made from Ti-nanoxide™ T600/SC will be referred to herein as “Cr³⁺- doped TiO₂-1 ”, and the one made from p25 will be referred to herein as “Cr³⁺-doped TiO₂-2”. The atomic ratio of chromium to titanium in each of the samples is approximately 0.5%.

[0064] Example 2

[0065] Fe³⁺-doped TiO₂ particles were synthesized according to a modified literature procedure. 0.5 grams of FeCI₃-6H₂O (Millipore Sigma®; Oakville Canada), 0.15 grams of terephthalic acid (Millipore Sigma®; Oakville Canada), and 12 millilitres of dimethylformamide (DMF) (Millipore Sigma®; Oakville Canada), were added into a 20-mL glass vial, which was sonicated in a water bath for 0.5 hours. The resulting clear brown solution was transferred to a Teflon® liner and heated in an autoclave (Parr® Instrument Company; Moline, Illinois) at 130 °C for 24 hours. The products were collected by centrifugation at 8,000 rpm for 20 minutes, washed three times with DMF-ethanol mixtures in 1 :1 , 1 :2, 0:1 volume ratios, respectively. Finally, the synthesized compound, referred to herein as “MIL-101 (Fe)”, was dried two days at 60 °C.

[0066] 15.3 grams of MIL-101 (Fe) was dissolved in 10 ml of ethanol, followed by the addition of tetrabutyl titanate (150 pL). After the mixture was stirred for 20 minutes at room temperature, 2.1 mL of deionized water and 60 pL of HF were added and the stirring continued for 10 min. The mixture was transferred into a 45 mL Teflon®-lined stainless steel autoclave together with 10 mL ethanol washings and heated in an autoclave (Parr® Instrument Company; Moline, Illinois) for 20 hrs at 170 °C. The sample was centrifuged at 8,500 rpm for 40 min, washed with deionized water once and absolute ethanol twice, and then dried in a vacuum oven at 60 °C for 24 hours. The obtained powder was calcined at 400 °C in air for 4 hours, the resultant product will be referred to herein as “Fe³⁺ doped TiO₂”, which was provided for disinfection evaluation. Fe³⁺- doped TiO₂ prepared by this method was shown to have Fe³⁺ dopants reside on the interior of the particles. This kind of dopant distribution pattern may not be ideal for the antimicrobial property. An energy dispersive X-ray spectroscopy (EDS) measurement showed that the atomic ratio of Fe to Ti in Fe³⁺-doped TiO₂ was 1 :9.4.

[0067] Example 3

[0068] Gold and iron (Fe³⁺) co-doped TiO2 nanoparticles were synthesized in two steps according to the following two-step procedure.

[0069] In the first step, Fe³⁺ doped TiO₂ nanoparticles were synthesized. Two solutions were prepared: (i) 6 mL tetrabutyl titanate was dissolved into 34 mL anhydrous ethanol; (ii) 41 .4 mg Fe(NO₃)3, 0.585 g nitric acid, 1 .6 mL deionized water and 17 mL anhydrous ethanol were mixed. Then solution (i) in an addition funnel was added drop-wise to the solution (ii) in a conical flask with stirring. The resultant mixture was stirred at room temperature for one week. The resulted mixture, which was pale yellow and cloudy, was then transferred into a 100-mL Teflon®-inner- liner stainless steel autoclave (Parr® Instrument Company; Moline, Illinois) and heated for 12 hours under 190 °C for crystallization. Afterwards, the mixture was centrifuged at 7500 rpm for 15 minutes. The precipitates were washed with anhydrous ethanol and centrifuged for three times, followed by drying at 60 °C overnight. The resulting product weighed 1.4 grams.

[0070] In the second step, gold(lll) chloride trihydrate (0.944 g), urea (2.546 g), Fe³⁺-doped TiO₂ (1 .000 g), and deionized water (100 mL) were loaded into a 250-mL conical flask, which was then heated in an oil bath at 80 °C with stirring for 4 hours. To avoid light, the flask was covered with aluminum foil. The product obtained after centrifugation was washed with deionized water four times, and then dried overnight in an oven (Thermo Fisher Scientific®; Mississauga, Canada) at 40 °C. The powder was then calcined at 400 °C for 4 hours under a flow of dry air at 0.4 L/minute. The resultant product was named Au-Fe³⁺-doped TiO₂, which was provided for disinfecting evaluation. EDS analysis revealed that the atomic ratio between Fe, Au, and Ti was 1 :8.5:120.

[0071] Example 4

[0072] In one example, the absorption spectra for various nanoparticles were measured and compared.

[0073] UV-vis diffuse reflectance spectra (DRS) were recorded on a PerkinElmer® Lambda900 UV/Vis/NIR spectrophotometer (PerkinElmer® Health Sciences Canada, Inc.; Woodbridge, Canada) equipped with an integrating sphere (150 mm in diameter). In order to successfully conduct optical characterization of powders, especially via DRS, highly diffusely reflecting and opaque samples were used. The samples were prepared using methods generally known in the art, such as Torrent et al. (J. Torrent, V. Barron, “Diffuse Reflectance Spectroscopy”, Chapter 13 in Methods of Soil Analysis Part 5-Mineralogical Methods; Number 5 in the Soil Science Society of America Book Series; Ulery, A.L., Drees, L.R., Eds.; Soil Science Society of America Inc.: Madison, Wl, USA, 2008; Volume 5, pp. 367-385) and Brock et al. (S. Bock, C. Kijatkin, D. Berben and M. Imlau, “Absorption and Remission Characterization of Pure, Dielectric (Nano-)Powders Using Diffuse Reflectance Spectroscopy: An End-To-End Instruction”, Appl. Sc/. 2019, 9, 493. doi:10.3390/app9224933). A powdered form of each sample was pressed into a pellet in a mortar and pestle system. The pellets were approximately 1 centimeter in diameter and non-translucent, with a near Lambertian scattering behavior. The reflectance of each pellet was measured with the pellet still in the mortar, using a 1 -centimeter diameter aperture accessory to expose only the surface of the pellet to the incident light beam. With the light beam cross-section being larger than the aperture, the reflectance of the aperture without samples (l₀) was subtracted from all measurements, and the samples measurements (l_s) were compared to a white standard (I o). In this example, the white standard used was Spectralon® Diffuse Reflectance Material (Distribution Labsphere Inc.; Brossard, Canada). The diffuse reflectance of each pellet was calculated according to Equation 1 below:

Equation 1

Rd = (ls-lo)/(lioo-lo) [0074] To compare the pellets, the diffuse reflectance electronic absorption spectra was derived from R_d using the Kubelka-Munk (K-M) function shown in Equation 2 below:

Equation 2

F(R) = (1 -Rd)²/(2R_d)

[0075] The Kubelka-Munk function absorption for each pellet is plotted against the wavelength in nanometers in Figures 3 and 4.

[0076] Figure 3 is a graph showing the absorption spectrum of TiO₂ nanoparticles. 404 represents the absorption spectrum of P25 commercial TiO₂. 408 represents the absorption spectrum of Cr³⁺-doped TiO₂-1 , which was prepared according to methods explained in Example 1. 412 represents the absorption spectrum of Cr³⁺-doped TiO₂-2, which prepared according to methods explained in Example 2. 416 represents the absorption spectrum of Fe³⁺-doped TiO₂.

[0077] As shown in Figure 3, doping TiO₂ with either Cr³⁺ or Fe³⁺ ions can extend the absorption of TiO₂ into the visible region. For Cr³⁺-doped TiO₂, a broad, weak absorption peak in the region from 560-800 nanometers was observed owning to ⁴A_2g ⁴T_2g d-d transitions of Cr³⁺.

[0078] Figure 4 is a graph showing the absorption spectrum of Au-Fe³⁺-doped TiO₂. 504 represents the absorption spectrum of Au-Fe³⁺-doped TiO₂. This pellet was dark brown in colour. As shown in Figure 4, when TiO₂ was co-doped with both Fe³⁺ and Au, the absorption in the visible region was strong, with an absorption peak around 510 nanometers

[0079] Example 5

[0080] In another example, TiO₂ particles were formulated in an ink for film deposition on a substrate. First, doped TiO₂ nanoparticles were mixed with ethanol at a concentration of 0.7 wt% and dispersed with an ultrasonic probe for 30 minutes. Next, the dispersion solution was cast on a glass slide and heated at 120 °C for 20 minutes to obtain a first layer of nanoparticle coating. This process was repeated seven times for a total of eight layers. The glass slide was completely covered by the nanoparticles.

[0081] Example 6

[0082] Bioburden testing of Ti0₂-coated substrates was performed with Escherichia coli (E co//)(Thermo Fisher Scientific®; Mississauga, Canada). First, E. coli from frozen stock was grown through overnight incubation in BBL™ Trypticase™ soy broth (BD®; Mississauga, Canada) at 37 °C on a shaker (Thermo Fisher Scientific®; Mississauga, Canada) at 200 rpm. The bacterial culture was resuspended in a saline solution of 0.9% sodium chloride (Brenntag®; Toronto, Canada) at 1/100 of the original volume, resulting in a suspension of approximately 10¹⁰ to 10¹¹ bacterial colony-forming units (CFUs)/mL.

[0083] Next, glass slides were prepared according to the methods described above with respect to Examples 4 and 5. Ten glass slides were prepared with the coatings indicated below in Table 1.

Table 1

[0084] The uncoated slides were used as controls. The slides were baked at 100 °C for 30 minutes prior to applying the bacterial suspension as 5-10 pL drops for a total of 50 pL onto each slide. The estimated bacterial load was 1 .9x10⁹ CFUs per slide. Slides were left to dry for approximately 1 hour in a biological safety cabinet (Thermo Fisher Scientific®; Mississauga, Canada). One slide of each coating type was then exposed for 4 hours to either a 5.2 watt blue LED light (herein referred to as “+Blue Light”) or ambient light (herein referred to as “-Blue Light”).

[0085] Loaded bacteria were recovered by transferring each slide into a 50-mL Falcon® conical centrifuge tube (Thermo Fisher Scientific®; Mississauga, Canada) containing 10-mL saline solution and sonicating for 2 minutes in an ultrasonic water bath (VWR®; Mississauga, Canada). The bacterial suspension in each tube was then pipetted up and down 20 times to increase bacterial recovery from the slide. Each slide was removed from the tube, and bacteria in solution were quantified by plating serial dilutions onto Tryptone Bile X-glucuronide or “TBX” (Thermo Fisher Scientific®; Mississauga, Canada) agar plates and counting the resulting blue- green CFUs after 24 hours of incubation at 37 °C. All bacterial loading, drying and recovery procedures were performed in a biological safety cabinet to limit external sources of contamination.

[0086] Figure 5 is a graph showing the results of bioburden testing on glass slides coated with Au-Fe³⁺-doped TiO₂ as compared with an uncoated slide. 604 represents the number of CFUs recovered from a glass slide coated with Au-Fe³⁺-doped TiO₂ and exposed to blue light. 608 represents the number of CFUs recovered from a glass slide coated with Au-Fe³⁺-doped TiO₂ and exposed to ambient light. 612 represents the number of CFUs recovered from a glass slide coated with Au-Fe³⁺-doped TiO₂ and exposed to blue light. The dotted line indicated at 616 represents the limit of detection.

[0087] Figure 6 is a graph showing the results of bioburden testing on glass slides coated with Fe³⁺-doped TiO₂ and Cr³⁺-doped TiO₂ as compared with uncoated slides. The white columns 704, 712, 720, 732 indicate slides that were exposed to ambient light for four hours. The filled columns 708, 716, 724, 728 indicate slides that were exposed to blue light for four hours. 704 represents the number of CFUs recovered from a glass slide coated with Fe³⁺-doped TiO₂ and exposed to ambient light. 708 represents the number of CFUs recovered from a glass slide coated with Fe³⁺-doped TiO₂ and exposed to blue light. 712 represents the number of CFUs recovered from a glass slide coated with Cr³⁺-doped TiO₂-1 and exposed to ambient light. 716 represents the number of CFUs recovered from a glass slide coated with Cr³⁺-doped TiO₂-1 and exposed to blue light. 720 represents the number of CFUs recovered from a glass slide coated with Cr³⁺-doped TiO₂-2 and exposed to ambient light. 724 represents the number of CFUs recovered from a glass slide coated with Cr³⁺-doped TiO₂-2 and exposed to blue light. 728 represents the number of CFUs recovered from an uncoated glass slide exposed to blue light. The dotted line indicated at 732 represents the limit of detection.

[0088] As shown in Figure 5, The Au-Fe³⁺-doped TiO₂ slide exhibited an approximately 5-fold decrease in CFUs after 4h of +Blue Light exposure 604 relative to the -Blue Light 608 and uncoated +Blue Light slides 612. As shown in Figure 6, the Cr³⁺-doped TiO₂ -1 716 and Cr³⁺- doped TiO₂ -2 724 slides showed approximately 3-log and 5-log decreases in CFUs, respectively, post-exposure to blue light when compared to their counterparts incubated with ambient light 712, 720. CFUs recovered from the Cr³⁺-doped TiO₂ -1 716 and Cr³⁺-doped TiO₂ - 2 724 slides were also ~4 logs lower relative to the uncoated slide 728 after +Blue Light exposure. [0089] No anti-microbial effect was observed with the Fe³⁺-doped TiO₂ slide 708 after exposure to blue light. The poor performance from Fe³⁺-doped TiO₂ may be explained by the fact that the Fe³⁺ dopants reside inside the nanoparticles. As a result, the photo-generated holes in the valence band may not reach the particle surface to kill bacteria. This result suggests that the dopant distribution pattern in the particles played an important role in determining the antimicrobial property of TiO₂ particles.

[0090] Overall, the reduction in bacterial numbers on the Au-Fe³⁺- doped TiO₂ slide 604 and Cr³⁺-doped TiO₂ slides 716, 724 may be attributed to the anti-microbial effects of specific surface coating types when activated under blue light and are not solely due to exposure to either the slide coating or blue light alone. Although Au-Fe³⁺-doped TiO₂ particles demonstrated strong absorption in the visible region (Figure 4), this didn’t translate into high photocatalytic activity as the valence band was raised up too much by the Au doping. As a result, the photo oxidation activity was not high.

[0091] The presently described method offers several advantages over other sanitization methods. Typically, a diluted bleach or alcohol solution is used to kill bacteria and viruses including coronaviruses, but alcohol and bleach disinfectant solutions must be applied frequently and every time after the surface is touched by a person. This is inconvenient, wasteful, and not practical. Moreover, sometimes spraying alcohol over a large area is a fire hazard while bleach is corrosive. The presently described TiO₂ nanocomposite may be applied as a permanent coat to a targeted surface. As long as the coatings are exposed to a visible light source such as a blue-light LED lamp, the nanocomposite may sanitize in a continuous fashion. The nanocomposite can be applied onto the outside surface of face masks as well. After each usage, the mask can be easily disinfected under visible light and thus can be reused.

[0092] The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Claims

CLAIMS We claim:

1 . A composition for disinfection comprising a nanocomposite of titanium dioxide and a dopant, the nanocomposite to catalyze a synthesis of hydroxyl radicals when exposed to visible light.

2. The composition of claim 1 wherein the dopant comprises a metal.

3. The composition of claim 2 wherein the metal is selected from a group consisting of chromium, iron, copper, manganese, vanadium, cobalt, nickel, magnesium, bismuth, gold, and platinum.

4. The composition of claim 2 wherein the dopant comprises iron and gold.

5. The composition of any one of claims 1 to 4 wherein the visible light has a peak wavelength selected to excite an electron from the dopant to the conduction band of the titanium dioxide.

6. The composition of claim 5 wherein the visible light has a peak wavelength between 380 and 500 nanometers.

7. The composition of any one of claims 1 to 6 further comprising a solvent.

8. The composition of claim 7 further comprising a ligand to suspend the nanocomposite in the solvent.

9. The composition of any one of claims 1 to 8 wherein the atomic ratio between the dopant and the titanium dioxide in the nanocomposite is between 0.1 % and 10%.

10. The composition of any one of claims 1 to 9 wherein the titanium dioxide comprises a nanotube.

11. A method of preparing a disinfectant, the method comprising doping a titanium dioxide nanoparticle with a dopant to synthesize a nanocomposite, the nanocomposite to catalyze a synthesis of hydroxyl radicals when exposed to visible light.

12. The method of claim 11 , the doping further comprising hydrothermal doping.

13. The method of claim 11 or 12 further comprising applying the nanocomposite onto a substrate.

14. The method of claim 13 further comprising suspending the nanocomposite in a solution prior to applying the nanocomposite onto the substrate, wherein applying the nanocomposite onto the substrate comprises casting the solution on the substrate and drying the substrate. The method of claim 13 or 14 further comprising applying a plurality of layers of the nanocomposite onto the substrate. The use of chromium-doped titanium dioxide for disinfection under visible light. The use of gold- and iron-doped titanium dioxide for disinfection under visible light.