SARS-CoV-2 Inactivation and Photocatalytic Degradation by TiO2 Photocatalyst Coatings

Characterizations and photocatalytic activity of TiO2/Ti on Al photocatalyst coating2O3 balls

The appearance of the photographs of the Al2O3 beads (2 mm in diameter), and samples of Ti and TiO2/Ti. Ti and TiO coatings2/ Ti coatings are shown in Fig. S1. Ti and TiO coatings2 coatings have formed on the surface of the Al2O3 balls, due to the change in color and appearance, which is similar to those of 1mm Al2O3 balls so date21. Surface and cross-sectional SEM images of Ti, TiO samples2/Ti and TiO2/Ti–O are shown in Fig. 1. He could find that the Ti coatings formed are bulge-like structure (Fig. 1a-1) and uneven (Fig. 1a-4), compared to that of Al2O3 balls (Fig. S2). Then the TiO2 the coatings formed on the surface of the Ti coatings exhibit a grainy-textured surface structure (Fig. 1b-2). Interesting, the uneven part of the Ti coatings was filled with TiO2 coatings (Fig. 1b-4), which make the surface smooth (Fig. 1b-1). Moreover, the thicknesses of Ti and TiO2 the coatings are about 97 μm and 3 μm, respectively, according to abbreviated calculations from SEM photographs. However, with the comparison of samples of TiO2/Ti and TiO2/Ti–O, the influence of oxidation followed in air at 500°C for 5 h on the surface structure and cross-sections is insignificant. Figure 2a shows the XRD patterns of the samples of Ti, TiO2/Ti and TiO2/Ti–O. In general, the peaks of Ti and TiO2 the peaks mean that the Ti and TiO coatings2 coatings successfully form on Al2O3 balls. After air oxidation, the Al2O3 peaks disappear and Ti and anatase TiO2 the peaks increase significantly, indicating that the crystallinity of anatase TiO2 has been greatly improved.

Figure 1

SEM microstructures of sample surfaces and cross-sections. (a) Ti, (b) TiO2/Ti, and (vs) TiO2/Ti–O.

Figure 2
Figure 2

XRD patterns of the samples. (a) XRD diagrams, (b) XPS O 1s spectra, (vs) Ti 2p XPS spectra, (D) XPS C 1s spectra, and (e) the photocatalytic activity with respect to the degradation of the MB solution.

XPS spectra were used to study the chemical bond change on the surface of the samples, as shown in Fig. 2b–d. For comparison, Figure 2b shows the O 1 s peak at around 529.4 eV of the samples, which could correspond to the Ti–O bond of anatase TiO224.25. Although the displacement of O 1 s could hardly be found from the samples of TiO2/Ti and TiO2/ Ti–O, but the peak at about 530.8 eV of TiO2/Decrease in sample Ti–O, compared to that of TiO2/ Ti–O sample, which suggests that the crystallinity of TiO anatase2 has been greatly improved, matching the XRD results. Figure 2e reveals that samples of TiO2/Ti and TiO2/Ti–O exhibit excellent photocatalytic activity, compared to that of Ti coatings. In general, TiO2 the coatings clearly show the photocatalytic activity, and the photocatalytic activity could be further enhanced with increased crystallinity of TiO anatase2.

TiO environmental purification function2/Ti–O on Al sample2O3 balls

Figure 3 shows the decomposition and removal performance of TiO2/Ti–O sample for C2H4O. Setting up the decomposition performance for C2H4O and a layer of TiO2/ Ti–O samples are shown in Fig. 3a. The concentration of C2H4O increases from the start of the test and reaches 5 ppm, as shown in Figure 3b. When the UV light turns on, the concentration of C2H4O decreases rapidly and remains at around 1.3 ppm due to decomposition by TiO2/Ti–O on Al sample2O3 balls. Additionally, the CO2 concentration generated by the decomposition of C2H4O26,27,28, and increases with the progress of decomposition. As the UV irradiation fades, the concentration of C2H4O returns to nearly 5 ppm of feed concentration, and CO2 the concentration drops back to 0 ppm. The results mean that the decay function of TiO2/Ti–O sample for C2H4O is significant and efficient. In general, when TiO2 has been illuminated with photons having an energy greater than its band gap, electrons and holes will be simultaneously generated and then separated into conduction band and valence band respectively. Charge carriers can migrate to the surface of the photocatalyst and react with O2H2O or hydroxyl groups, with generation of OH and O2. During decomposition, C2H4O was first adsorbed on the surface of TiO2 photocatalyst. So a part of C2H4O could be oxidized to CO2 and H2O by O2 or Oh directly. The remainder could first be oxidized to acetic acid by OHthen oxidized to CO2 and H2O by O227.28.

picture 3
picture 3

The decomposition test of C2H4O and CH2O with TiO2/Ti–O sample. (a) The installation, (b) the concentration changes of C2H4O and CO2(vs) changes in CH concentration2O.

Additionally, Figure 3c shows the decomposition and removal performance of TiO2/Ti–O sample for CH2O. When the UV light turns on, the concentration of CH2O decreases rapidly from 1 ppm, then remains at about 0.43 ppm. It was believed that the hydroxyl radicals formed transferred to the surface of TiO2 can not only react directly with CH2O molecules, but also can suppress electron-hole recombination during the transfer process to further enhance photocatalytic activity29,30,31. When the UV light stops, the concentration of CH2O quickly returns to 1 ppm of the supplied concentration. These results also reveal the high decomposition capacity of TiO2/Ti–O sample for CH2O. In the case of the degradation process of CH2O, the generated OH and O2 will first attack the C–H bonds in CH2O, then react with the released hydrogen atoms to form new free radicals29.30. In general, the initial stage of the degradation process will produce formic acid and then eventually decompose CH2O molecules to H2O and CO2.

Inactivation of the virus by TiO2/Ti–O on Al sample2O3 balls

Fig. 4 shows the configuration of the inactivation test for H3N2 influenza virus, according to JIS R 1706:2020. Table 1 shows the infectious value and the antiviral activity value of the samples under UV irradiation and in the dark. Antiviral activity values ​​are calculated by the following equations of (1) and (2).

$${text{Antiviral activity value}}left( {text{bright spot}} right){:};{text{ V}}_{{text{L}}} = {text{ Log}}left( {{text{B}}_{{text{L}}} }right),-{text{Log}}left( {{text {C} }_{{text{L}}} } right)$$

(1)

$${text{Antiviral activity value}}left( {{text{dark}}} right){:};{text{ V}}_{{text{D}}} = { text{ Diary}}left( {{text{B}}_{{text{D}}} } right) , – {text{ Diary}}left( {{text {C }}_{{text{D}}} } right)$$

(2)

where B is the virus solution infection titer only, C is the sample infection titer, L is with UV irradiation, and D is in the dark. According to ISO 18184 Annex G, an antiviral activity value of 3.0 or more is considered effective antiviral activity, therefore, an average value of V0.25= 3.4 of TiO2/ Ti–O sample is sufficient for antiviral efficacy. The virus inactivation rate calculated from the average infectious value of 87 pfu/ml under 0.25 mW/cm2 reached 99.96%, indicating that the TiO2/ The Ti–O sample has a very high inactivation function for influenza virus.

Figure 4
number 4

The implementation of an antiviral test using the influenza virus under UV irradiation and in the dark.

Table 1 The infectious value and the antiviral activity value of the samples, under UV irradiation (0.25 mW/cm2) and in the dark.

Figure 5 shows the TiO inactivation test2/Ti–O on Al sample2 O3bullets for SARS-CoV-2. Figure 5a clearly shows the knockout assay setup. The infectious titer of the control under UV irradiation tends to decrease, whereas the infectious titer of TiO2/ The Ti–O sample decreases significantly, with an infectious value below the detection limit after 6 h, as shown in Fig. 5b. Additionally, the rate of virus decline was calculated and shown in Figure 5c. The TiO inactivation function2/ The Ti–O sample is satisfactory under UV irradiation, and the decrease in virus rate rapidly increases to 96% in a short time, reaching 99.99% in 6 h. These results mean that the TiO2/ Ti–O samples have high inactivation function against SARS-CoV-2.

Figure 5
number 5

The TiO SARS-CoV-2 Inactivation Test2 /Ti–O sample. (a) The installation, (b) the change in infectious value of SARS-CoV-2, (vs) the rate of decline of SARS-CoV-2.

It is well known that TiO2 is a metal oxide semiconductor photocatalyst with a wide band gap of 3.2 eV (anatase type)32. TiO2when exposed to UV light of energy equal to or greater than its bandgap, there is excitation of electrons from the valence band (VB) to the conduction band (CB) of TiO2. These charge carriers move on the surface of TiO2then interact with ambient oxygen (O2) and water (H2O) molecules. H oxide holes2 O molecules into highly reactive hydroxyl radicals (superoxide radical anion (O2), which is then reduced to OH. Since these radicals are highly reactive, hence they are known as reactive oxygen species (ROS). These formed ROS on the surface of TiO2 react with viruses and lead to their degradation into CO2and H2O33, as shown in the proposed block diagram of FIG. 6. Photocatalysis is a surface phenomenon that oxidizes/reduces or degrades organic pollutants. Therefore, the TiO2/ Ti photocatalyst coating beads with large specific surface area are easy to operate, exhibiting high functions of environmental purification and virus inactivation.

Figure 6
number 6

Proposed mechanisms of TiO-induced viral inactivation2/Ti photocatalyst coatings.

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