Limits...
Antibacterial property of Ag nanoparticle-impregnated N-doped titania films under visible light.

Wong MS, Chen CW, Hsieh CC, Hung SC, Sun DS, Chang HH - Sci Rep (2015)

Bottom Line: However, the major limitation of this Ag-TiO2 composite material is its durability; the antibacterial property decreased markedly after repeated use.Here we revealed that the antibacterial durability of these thin films is substantially improved in both the dark and visible light, by which bacteria, such as Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus, and Acinetobacter baumannii, could be efficiently eliminated.This study demonstrated a feasible approach to improve the visible-light responsiveness and durability of antibacterial materials that contain silver nanoparticles impregnated in TiO2(N) films.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Materials Science and Engineering, National Dong Hwa University, Hualien, Taiwan [2] Nanotechnology Research Center, National Dong Hwa University, Hualien, Taiwan.

ABSTRACT
Photocatalysts produce free radicals upon receiving light energy; thus, they possess antibacterial properties. Silver (Ag) is an antibacterial material that disrupts bacterial physiology. Our previous study reported that the high antibacterial property of silver nanoparticles on the surfaces of visible light-responsive nitrogen-doped TiO2 photocatalysts [TiO2(N)] could be further enhanced by visible light illumination. However, the major limitation of this Ag-TiO2 composite material is its durability; the antibacterial property decreased markedly after repeated use. To overcome this limitation, we developed TiO2(N)/Ag/TiO2(N) sandwich films in which the silver is embedded between two TiO2(N) layers. Various characteristics, including silver and nitrogen amounts, were examined in the composite materials. Various analyses, including electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and ultraviolet-visible absorption spectrum and methylene blue degradation rate analyses, were performed. The antibacterial properties of the composite materials were investigated. Here we revealed that the antibacterial durability of these thin films is substantially improved in both the dark and visible light, by which bacteria, such as Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus, and Acinetobacter baumannii, could be efficiently eliminated. This study demonstrated a feasible approach to improve the visible-light responsiveness and durability of antibacterial materials that contain silver nanoparticles impregnated in TiO2(N) films.

No MeSH data available.


Related in: MedlinePlus

Field emission scanning electron microscopy of TiO2(N)/Ag/TiO2(N) films of various nitrogen content.Images of lateral view (A–E) and vertical view (F–J) of TiO2(N)/Ag/TiO2(N) films after annealing were showed.
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f4: Field emission scanning electron microscopy of TiO2(N)/Ag/TiO2(N) films of various nitrogen content.Images of lateral view (A–E) and vertical view (F–J) of TiO2(N)/Ag/TiO2(N) films after annealing were showed.

Mentions: To increase the visible-light responsiveness, N doping is critical6. The nitrogen content in these films was minimal when oxygen flow was high [5 sccm (standard cubic centimeters per minute)] during film deposition. We hypothesized that this was caused by an excess supply of oxygen, rendering N unable to be efficiently integrated into the lattice structure of TiO2. Thus, various low-O2-supplying conditions, including the O2 flow rate of 2, 3, 4, and 5 sccm, were tested (Supplementary Table 1). Consistent with our hypothesis, an X-ray photoelectron spectroscopy analysis revealed that reduced O2 supply improved N levels in composite thin films (Fig. 3A). However, the Ti-to-O ratio was also changed, with the N(4)TA and N(5)TA samples exhibiting a relatively 1:2 ratio, whereas the N(2)TA and N(3)TA samples exhibited a ratio of approximately 1:1 (Fig. 3A; the amount of oxygen supplied was indicated in brackets, e.g., N(4)TA was prepared with 4 sccm O2). These results indicated that 2 and 3 sccm O2 supply were insufficient to oxidize Ti and produce TiO2; instead, TiN or TiON was formed. Consistently, X-ray photoelectron spectroscopy analysis for the 1 s atomic orbital of N indicated a significant increase in the formation of TiN (Fig. 3B). X-ray diffraction analysis further revealed the production of TiN in N(2)TA and N(3)TA samples before and after annealing (Fig. 3C,D). Because TiO2 was not efficiently produced in the N(2)TA and N(3)TA samples, the rutile and anatase TiO2 signals were observed only in the N(4)TA and N(5)TA thin films after annealing (Fig. 3D). The field-emission scanning electron microscopy analysis indicated that the N(2)TA and N(3)TA samples formed thicker films, with less surface-exposed Ag nanoparticles compared with the N(4)TA and N(5)TA samples (Fig. 4A–E). A UV–Vis absorption spectroscopy analysis indicated that reduced O2 supply caused remarkable redshifts in the samples (Fig. 5A,B). The band gaps were calculated using the UV–Vis spectroscopy and Tauc plots19. However, the band gaps for the N(2)TA and N(3)TA were not derived, because the two samples produced under 2 and 3 sccm O2 supply were insufficient to form TiO2; instead, TiN or TiON was formed with high amount of nitrogen of 18.8% and 13.5% and thus, with high absorbance (Fig. 3A,B). These results indicated that the increased N content reduced the band gap of the thin films (Fig. 5C, Supplementary Table S1). Analyses of MB and Hoechst dye degradation rates further revealed that the N(4)TA sample exhibited a superior visible-light-induced photocatalytic ability than did the other samples (Fig. 5D; Supplementary Fig. S3), suggesting that the balance of the N-doping amount and TiO2 production was critical. In accordance with the aforementioned analyses, antibacterial experiments demonstrated that the N(4)TA sample exhibited the highest antibacterial activity among the thin film samples under visible light illumination (Fig. 5E, N(4)TA-N500). In addition, visible light illuminating the N(4)TA sample exerted higher bactericidal activity than did the control groups with the N(4)TA sample in the dark (Fig. 5E, N(4)TA-N500; *P < 0.05).


Antibacterial property of Ag nanoparticle-impregnated N-doped titania films under visible light.

Wong MS, Chen CW, Hsieh CC, Hung SC, Sun DS, Chang HH - Sci Rep (2015)

Field emission scanning electron microscopy of TiO2(N)/Ag/TiO2(N) films of various nitrogen content.Images of lateral view (A–E) and vertical view (F–J) of TiO2(N)/Ag/TiO2(N) films after annealing were showed.
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f4: Field emission scanning electron microscopy of TiO2(N)/Ag/TiO2(N) films of various nitrogen content.Images of lateral view (A–E) and vertical view (F–J) of TiO2(N)/Ag/TiO2(N) films after annealing were showed.
Mentions: To increase the visible-light responsiveness, N doping is critical6. The nitrogen content in these films was minimal when oxygen flow was high [5 sccm (standard cubic centimeters per minute)] during film deposition. We hypothesized that this was caused by an excess supply of oxygen, rendering N unable to be efficiently integrated into the lattice structure of TiO2. Thus, various low-O2-supplying conditions, including the O2 flow rate of 2, 3, 4, and 5 sccm, were tested (Supplementary Table 1). Consistent with our hypothesis, an X-ray photoelectron spectroscopy analysis revealed that reduced O2 supply improved N levels in composite thin films (Fig. 3A). However, the Ti-to-O ratio was also changed, with the N(4)TA and N(5)TA samples exhibiting a relatively 1:2 ratio, whereas the N(2)TA and N(3)TA samples exhibited a ratio of approximately 1:1 (Fig. 3A; the amount of oxygen supplied was indicated in brackets, e.g., N(4)TA was prepared with 4 sccm O2). These results indicated that 2 and 3 sccm O2 supply were insufficient to oxidize Ti and produce TiO2; instead, TiN or TiON was formed. Consistently, X-ray photoelectron spectroscopy analysis for the 1 s atomic orbital of N indicated a significant increase in the formation of TiN (Fig. 3B). X-ray diffraction analysis further revealed the production of TiN in N(2)TA and N(3)TA samples before and after annealing (Fig. 3C,D). Because TiO2 was not efficiently produced in the N(2)TA and N(3)TA samples, the rutile and anatase TiO2 signals were observed only in the N(4)TA and N(5)TA thin films after annealing (Fig. 3D). The field-emission scanning electron microscopy analysis indicated that the N(2)TA and N(3)TA samples formed thicker films, with less surface-exposed Ag nanoparticles compared with the N(4)TA and N(5)TA samples (Fig. 4A–E). A UV–Vis absorption spectroscopy analysis indicated that reduced O2 supply caused remarkable redshifts in the samples (Fig. 5A,B). The band gaps were calculated using the UV–Vis spectroscopy and Tauc plots19. However, the band gaps for the N(2)TA and N(3)TA were not derived, because the two samples produced under 2 and 3 sccm O2 supply were insufficient to form TiO2; instead, TiN or TiON was formed with high amount of nitrogen of 18.8% and 13.5% and thus, with high absorbance (Fig. 3A,B). These results indicated that the increased N content reduced the band gap of the thin films (Fig. 5C, Supplementary Table S1). Analyses of MB and Hoechst dye degradation rates further revealed that the N(4)TA sample exhibited a superior visible-light-induced photocatalytic ability than did the other samples (Fig. 5D; Supplementary Fig. S3), suggesting that the balance of the N-doping amount and TiO2 production was critical. In accordance with the aforementioned analyses, antibacterial experiments demonstrated that the N(4)TA sample exhibited the highest antibacterial activity among the thin film samples under visible light illumination (Fig. 5E, N(4)TA-N500). In addition, visible light illuminating the N(4)TA sample exerted higher bactericidal activity than did the control groups with the N(4)TA sample in the dark (Fig. 5E, N(4)TA-N500; *P < 0.05).

Bottom Line: However, the major limitation of this Ag-TiO2 composite material is its durability; the antibacterial property decreased markedly after repeated use.Here we revealed that the antibacterial durability of these thin films is substantially improved in both the dark and visible light, by which bacteria, such as Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus, and Acinetobacter baumannii, could be efficiently eliminated.This study demonstrated a feasible approach to improve the visible-light responsiveness and durability of antibacterial materials that contain silver nanoparticles impregnated in TiO2(N) films.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Materials Science and Engineering, National Dong Hwa University, Hualien, Taiwan [2] Nanotechnology Research Center, National Dong Hwa University, Hualien, Taiwan.

ABSTRACT
Photocatalysts produce free radicals upon receiving light energy; thus, they possess antibacterial properties. Silver (Ag) is an antibacterial material that disrupts bacterial physiology. Our previous study reported that the high antibacterial property of silver nanoparticles on the surfaces of visible light-responsive nitrogen-doped TiO2 photocatalysts [TiO2(N)] could be further enhanced by visible light illumination. However, the major limitation of this Ag-TiO2 composite material is its durability; the antibacterial property decreased markedly after repeated use. To overcome this limitation, we developed TiO2(N)/Ag/TiO2(N) sandwich films in which the silver is embedded between two TiO2(N) layers. Various characteristics, including silver and nitrogen amounts, were examined in the composite materials. Various analyses, including electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and ultraviolet-visible absorption spectrum and methylene blue degradation rate analyses, were performed. The antibacterial properties of the composite materials were investigated. Here we revealed that the antibacterial durability of these thin films is substantially improved in both the dark and visible light, by which bacteria, such as Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus, and Acinetobacter baumannii, could be efficiently eliminated. This study demonstrated a feasible approach to improve the visible-light responsiveness and durability of antibacterial materials that contain silver nanoparticles impregnated in TiO2(N) films.

No MeSH data available.


Related in: MedlinePlus