Preparation, Antimicrobial Properties under Different Light Sources, Mechanisms and Applications of TiO2: A Review

Abstract

Traditional antimicrobial methods, such as antibiotics and disinfectants, may cause adverse effects, such as bacterial resistance and allergic reactions. Photocatalysts based on titanium dioxide (TiO₂) have shown great potential in the field of antimicrobials because of their high efficiency, lack of pollution, and lack of side effects. This paper focuses on the antimicrobial activity of TiO₂ under different light sources. To improve the photocatalytic efficiency of TiO₂, we can reduce electron-hole recombination and extend the photocatalytic activity to the visible light region by doping with different ions or compounds and compounding with polymers. We can also improve the surface properties of materials, increase the contact area with microorganisms, and further enhance the resistance to microorganisms. In addition, we also reviewed their main synthesis methods, related mechanisms, and main application fields to provide new ideas for the enhancement of photocatalytic microorganism performance and application popularization in the future.

Keywords: TiO2; mechanisms; photocatalyst; photocatalytic antimicrobial.

Figure 2

(A) Steps involved in the sol–gel process to synthesize MONPs [20]; (B) scanning electron microscopy (SEM) (a) and transmission- electron microscopy (TEM) (b) images of antimicrobials synthesized by the sol–gel method and thermally treated at 350 °C for 2 h [25]; (C) illustration of rGO/TiO₂ nanocomposite formation [30]; (D) SEM images of TiO₂-Sm (a) and TiO₂-Ag (b) [31,32]; (E) schematic diagram showing all steps involved in a generic green synthesis mediated by plant extract using the coprecipitation method [35]; (F) SEM images of different TiO₂ samples [39]; (G) illustration of ALD [47]; (H) different PP mesh samples [44].

Figure 9

(A) Photocatalytic antibacterial efficiency toward E. coli with photocatalysts under visible light (a) and antibacterial effect of TiO₂/Ag₂O (1: 4) on E. coli under visible light (b) [85]; (B) antibacterial activity of different samples against E. coli (1–7) and S. aureus (8–14); (C) antibacterial activity of different samples against E. coli (c) and antibacterial activity of pure TiO₂ and xSnSO₄-TiO₂ against S. aureus in the presence/absence of visible light (d) [88].

Figure 1

Statistical analysis of the number of related papers published in Web of Science with the keywords: (A) ‘Photocatalyst’ and (B) ‘Photocatalytic antimicrobial’.

Figure 3

(A) SEM (a) and AFM (b) analyses of different samples; (B) SEM micrographs of biofilms formed on different samples; (C) Colony-forming units (CFUs) on surfaces of different sample after 1 h of UVA light irradiation [48].

Figure 4

(A) SEM images of E. coli before (a,b) and after (c,d) TiO₂@SiO₂ treatment; (B) image of the antibacterial effect of TiO₂@SiO₂ hybrid materials with different TiO₂ contents on E. coli under UVA irradiation; (C) effect of the antimicrobial property of TiO₂@SiO₂ hybrid materials under UVA irradiation [50].

Figure 5

(A) antimicrobial activity in the dark (a) and under visible light (b) (λ > 450 nm) [58]; (B) TEM images of Au–TiO₂ NTs (a) and Pt–TiO₂ NTs (b); (C) photographs of antibacterial S. aureus agar diffusion tests (a) and the results of CFUs per unit volume of S. aureus cultured on different letters with or without 470 nm and 600 nm visible irradiation (b) [59].

Figure 6

(A) TEM image of N, F doped TiO₂ nanoparticles (a); UV−vis absorption spectrum of colloidal nanoparticles (b); evidence of reactive oxygen species (ROS) generation by nanoparticles under visible-light exposure (c); tert-butyl alcohol (TBA) as a ·OH scavenger to prove that ·OH is the dominant ROS component (d); (B) microscopic imaging of Fusarium oxysporum spore germination under different conditions. Red arrows indicate fungal spores. (C) Images of fungal colonies [65].

Figure 7

(A) SEM image of TiO₂ (B) films with various thicknesses before (a–d) and after (e–h) annealing; (B) visible light-induced photolytic killing of pathogenic bacteria [66]; (C) antibacterial properties of C200 NPs against vegetative bacteria of Bacillus species; (D) antibacterial properties of C200 NPs against spores of Bacillus species [67]; (E) % survival of E. coli with TiO₂TiO₂TiO₂different samples as a function of time under visible light; ## p < 0.01, ** p < 0.01, * p < 0.05. (F) photographs of the photoinactivation of E. coli under visible light exposure [69].

Figure 8

(A) Photocatalytic inactivation of E. coli (a) and S. aureus using 13 wt% CMP/TiO₂-I nanocomposites. Growth images of E. coli (b) and S. aureus on agar plates; (B) SEM images of bacteria (incubated with 13 wt% CMP/TiO₂-I nanocomposites under light irradiation and in the dark); (C) DRS of samples [75].

Figure 10

Schematic of photocatalytic antimicrobial mechanism of TiO₂@SiO₂ hybrid materials and bacterial inactivation on Ag decorated TiO2-NTs [50,111].

Figure 11

(A) Proposed mechanism of the antifungal activity of N, F doped TiO₂ nanoparticles [65]; (B) schematic diagram displaying the antibacterial mechanism of SnSO₄-TiO₂ [88].

Figure 12

Schematic diagrams of the effect of metal ions (A [121]) and TiO₂ (B [123]) particles on cells.

Figure 13

(A) Effect of the prepared composite films on the growth of P. viridicatum after 0 h and 6 h of irradiation; (B) effects of TiO₂ content on the inhibition efficiency of KC/KGM/TiO₂ nanocomposite films against P. viridicatum [138]; (C) preservation of red grapes packed in different materials at 37 °C for 6 days [116]; (D) (a) in vivo fungitoxicity and infection control by nanoparticles. (b) Evidence of intact immunity of nanoparticle and visible-light-treated tomato fruit via nitric oxide imaging. Green fluorescence indicates the presence of nitric oxide [65].

Figure 14

(A) Photographs of the antibacterial activity of Zn2+, H-MeIM and ZIF-L@TiO₂/fabrics against E. coli; (B) photographs of bacterial growth on blank nontextile fabric and ZIF-L@TiO₂/fabric under natural light for 1–5 days at 37 °C [143]; (C) nonwetting behavior of modified cotton (a) and paper (b) surface [144] paper; (D) self-cleaning performance of 1% Cu (II)-doped TiO₂ calcined at 25 °C [145].

Figure 15

(A) Epifluorescence images of surface samples after 24 h of the experiment (blue color represent the coating and red to highlight the bacteria) [146]; (B) photocatalytic disinfection performance of sewage samples and the light control tests of (c) HB and (d) HC under simulated solar light at 25 °C; and regrowth test of inactivated bacteria (24 h and 48 h after reaction) in (e) LT and (f) LB [148]; (C) schematic diagram of TiO₂/SrTiO₃ function; (D) bacteriostatic circles of different samples after 24 h [152].