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Photocatalytic and Antibacterial Activity of Ag-doped
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TiO2 Nanoparticles
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Weerachai Sangchay
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Faculty of Industrial Technology, Songkhla Rajabhat University, Songkhla,
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Thailand, 90000
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E-mail: weerachai.sang@yahoo.com
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Abstract
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The powders of TiO2 and TiO2 doped with Ag were prepared by sol-gel
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method. The prepared powders were calined at the temperature of 400°C for
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2 h with the heating rate of 10°C/min. The microstructures of the fabricated
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powders were characterized by SEM, XRD and EDX techniques, and the
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results show that all samples were the agglomeration and reveal only the
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anatase phase. The photocatalytic activities of the powders were also tested
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via the degradation of methylene blue (MB) solution under UV irradiation.
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Finally, antibacterial activity efficiency was evaluated by the inactivation of
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E.coli. It was observed that higher Ag concentration gives better
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photocatalytic and
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concentration investigated in this experiment (TiO2-5Ag condition) the
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powders show photocatalytic and antibacterial activity are 52.30 and 95.14%,
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respectively.
antibacterial
activity. With
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the highest dopant
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Keyword: TiO2, Ag-doped, Photocatalytic activity, Antibacterial activity,
Sol-gel
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Introduction
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In recent years, semiconductor photocatalyst has been a subject of considerable
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interest. Titanium dioxide (TiO2) activated by near ultraviolet (UV) light is
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probably by far the most widely studied photocatalyst for its water and air
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purification capabilities. Nanometer semiconductor TiO2 powders have excellent
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properties of photocatalytic degeneration. The glass with TiO2 powders have good
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performance of antibacterial, disinfections, antifogging and self-cleaning, etc. So
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it can be widely used in building, car, bathroom, public latrine and so on (Hongfu
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et al., 2008).
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Nowadays, many studies have been devoted to further improve the
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photocatalytic and antibacterial properties of TiO2 powders or thin films, and the
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investigations suggest that those properties can be enhanced by doping with
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transition metal such as Fe3+ (Saowaluk et al., 2011), N (Mingyang et al., 2009),
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Cu (Kaixi et al., 2008), and Ag (Kornkanok et al., 2010; Yuekun et al., 2008)
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which has also been investigated widely aiming at extending photocatalytic and
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antibacterial activity into the UV region.
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Many methods are used to prepare TiO2 powders. The sol-gel method is
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one of the most commonly employed methods due to high purity materials can be
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synthesized at low temperatures (Marcial et al., 2005; Hou et al., 2006). In this
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work, powders of TiO2 and Ag-doped TiO2 were prepared by sol-gel method.
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Based on our previous studies, the amount of Ag in the range of 0 to 5 mol% of
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TiO2 is carried on. The effect of the Ag doping into TiO2 powders on the
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microstructure photocatalytic and antibacterial activity were investigated.
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Experimental and Details
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Raw Materials
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Titanium (IV) isoproxide (TTIP) and silver nitrate (AgNO3) were used as
raw materials. Ethanol (C2H5OH) was used as a solvent.
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Powders Preparation
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TiO2 and TiO2 doped with Ag (TiO2-Ag) powders were prepared via sol-
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gel method. Firstly, AgNO3 to maintain the mole ratio of Ag in the TiO2 at 0, 1, 3,
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and 5 mol% of TiO2 and TTIP with fixed volume at 10 ml were mixed into 150
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ml of C2H5OH and the mixture was then vigorously stirred at room temperature
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for 15 min. The pH of the mixed solution was adjusted to about 3 - 4 by adding 3
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ml of 2 M HNO3. Finally, it was vigorously stirred at room temperature for 45
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min, dried at 100°C for 24 h and calcined at 400°C for 2 h with a heating rate of
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10°C/min.
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Powders Characterizations
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The morphology and particle size of the fabricated powders were
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characterized by Scanning Electron Microscope (SEM-Quanta 400). The phase
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composition was characterized using an x-ray diffractometer (XRD) (Phillips
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X’pert MPD, Cu-K). The crystallite size was calculated by the Scherer equation,
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Equation 1, (Khatamain and Irani, 2009).
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D = 0.9λ/βcosθB
(1)
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where D is the average crystallite size, λ is the wavelength of the Cu Kα line
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(0.15406), θ is the Bragg angle and β is the full-width at half-maximum (FWHM)
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in radians.
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Photocatalytic Activity Test
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The photocatalytic activity was evaluated by the degradation of MB under
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UV irradiation using eleven 50 W of black light lamps. A 10 ml of MB with a
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concentration of 1 × 10-5 M was mixed with 0.0375 g of TiO2 and TiO2-Ag
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powders and kept in a chamber under UV irradiation for 0, 1, 2, 3, 4, 5, and 6 h.
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After photo-treatment for a certain time, the concentration of treated solution was
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measured by UV-vis. The ratio of remained concentration to initial concentration
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of MB calculated by C/C0 was plotted against irradiation time in order to observe
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the photocatalytic degradation and the percentage degradation of the MB
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molecules (%DMB) was calculated by Equation 2, (Sangchay et al., 2012).
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%DMB = 100(C0-C)/C0
(2)
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where C0 is the concentration of MB aqueous solution at the beginning (1×10-5 M)
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and C is the concentration of MB aqueous solution after exposure to a light
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source.
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Antibacterial Activity Test
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Antibacterial activity of TiO2-Ag powders against the bacteria Escherichia
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coli (E.coli) was studied and compared to the TiO2 powder. Aliquots of 100 ml
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E.coli conidial suspension (105 CFU/ml) were mixed with 0.05 g of powder. The
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mixture was then exposed to either UV irradiation for 0, 15, 30, 45, and 60 min.
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Then, 0.1 ml of mixture suspension was sampled and spread on Macconkey Agar
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plate and incubated at 37°C for 24 h. After incubation, the number of viable
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colonies of E.coli on each Macconkey Agar plate was observed (Saowaluk et al.,
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2011) and disinfection efficiency of each test was calculated in comparison to that
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of the control. Percentage bacterial reduction (%BR) was calculated according to
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the following equation, Equation 3, (Deng et al., 2007).
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%BR = 100(N0-N)/N0
(3)
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where N0 and N are the average number of live bacterial cells per milliliter in the
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flask of the control and thin films finishing agent or treated fabrics, respectively.
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Results and Discussion
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Powders Characterizations
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The surface morphology was observed with SEM. Figure 1 shows surface
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morphologies of TiO2 and TiO2-Ag powders. It was seen that for all powders, the
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agglomeration was observed and the particle size decreases with increases Ag
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doping.
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Figure 1. SEM surface morphology images of TiO2 and TiO2-Ag powders
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(magnification 50000X)
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From the XRD study as shown in Figure 2, it was found that TiO2 and
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TiO2-Ag powders reveal that only the anatase phase. Ag-compound phase can’t be
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verified in these XRD peaks due to a very small amount of Ag doping. The
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anatase peaks were observed about at 25.50°, 37.59°, 48.01°, and 54.16°
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(Saowaluk et al., 2011), and all samples have the crystallite sizes of anatase
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phases in the range of 20.7 to 23.6 nm. The presence of Ag and Ti in the TiO2-Ag
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powders was determined by EDX spectra and the result is shown in Figure 3,
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confirming the presence of the Ti and Ag composition in the powders.
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Figure 2. XRD patterns of TiO2 and TiO2-Ag powders
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Figure 3. EDX spectra of TiO2-5Ag powders
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Photocatalytic Activity
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The photocatalytic degradation of MB by using TiO2 and TiO2-Ag
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powders under UV irradiation is show in Figure 4. It was apparent that Ag added
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in TiO2 has significantly effect on photocatalytic reaction under UV irradiation,
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with the photocatalytic activity increases with increases Ag doping. The MB
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degradation percentage of TiO2 and TiO2-Ag powders under UV irradiation is
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shown in Table 1. It was found that e MB degradation percentage of TiO2 and
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TiO2-Ag powders under UV irradiation for 6 h are 43.89, 46.66, 48.60 and
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52.30% for 0, 1, 3, and 5 mol% of Ag doping, respectively. It was found that
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TiO2-5Ag powders show the best photocatalytic activity.
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Figure 4. The photocatalytic activity of TiO2 and TiO2-Ag powders under UV
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irradiation
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Antibacterial Activity
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Figure 5 displays the E.coli survival rate (N/N0) after testing with UV
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illumination on TiO2 and TiO2-Ag powders. The result shows that the E.coli
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survivals decrease with UV irradiation time. It also indicates that the TiO2 doped
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with 5% Ag powders exhibit higher antibacterial activity compared to TiO2 and
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TiO2 doped with 1 and 3% Ag powders, respectively. The E.coli kills rate
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percentage of TiO2 and TiO2-Ag powders under UV irradiation is shown in Table
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2. It is found that the E.coli kill rate percentage of TiO2 and TiO2-Ag powders
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under UV irradiation for 1 h are 51.43, 62.86, 84.00, and 95.14% for TiO2 and
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TiO2 doped with 1, 3, and 5% Ag powders, respectively. The photo of viable
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bacterial colonies (red spots) on fabricated TiO2, TiO2-Ag powders and the
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control treated with UV for 1 h are illustrated in Figure 6.
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Figure 5. The antibacterial activity of TiO2 and TiO2-Ag powders under UV
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irradiation
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Figure 6. Photo of viable E.coli colonies during 1 h UV irradiation of TiO2
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and TiO2-Ag powders compared with control condition
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Conclusions
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In this work, TiO2 and TiO2 doped with Ag powders were fabricated by sol-gel
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method. The effect of Ag doping into TiO2 powders on microstructure,
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photocatalytic and antibacterial activity were investigated and concluded as
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followings,
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1. TiO2 and TiO2-Ag powders reveal only the anatase phase and surface
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morphologies was found that for all powders, the agglomeration was observed and
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the particle size decreases with increases Ag doping.
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2. The photocatalytic and antibacterial activity of TiO2-Ag powders
increases with Ag doping concentration.
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3. It can be noted that TiO2 doped with 5% Ag powders exhibits higher
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photocatalytic and antibacterial activity under UV irradiation are 52.30 and
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95.14%, respectively.
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Acknowledgements
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The authors would like to acknowledge Institute of Research & development,
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Songkhla Rajabhat University, Thailand for financial support of this research.
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Reference
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Deng, H., Cheuk, K., Zheng, W.N., Wen, C., Xiao, C.F. (2007). Low temperature
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preparation of nano TiO2 and its application as antibacterial agents.
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Transactions of Nonferrous Metals Society of China, 17:700-703.
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Hongfu, S., Chengyu, W., Shihong, P., Xiping, L., Ying, T., Huajuan, T., and
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Ming, L. (2008). Photocatalytic TiO2 films prepared by chemical vapor
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deposition at atmosphere pressure. J. Non-Cryst. solids, 354:1440-1443.
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Hou, X., Wu, X., and Liu, A. (2006). Studies on phtocatalytic activity of Ag/TiO2
films. Front. Chem. China, 4:402-407.
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Kaixi, S., Jiahong, Z., Jianchun, B., and Yuying, F. (2008). Photocatalytic
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Activity of (Copper, Nitrogen)-Codoped Titanium Dioxide Nanoparticles.
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Communications of the American Ceramic Society, 91(4):1396-1371.
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Khatamian, M. and Trani, M. (2009). Preparation and Characterization of
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Nanosized ZSM-5 Zeolite Using Kaolin and Investigation of Kaolin
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Content, Crystallization Time and Temperature Changes on the Size and
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Crystallinity of Products. J. Iran. Chem. Soc., 6(1):187-194.
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Kornkanok, U., Lek, S., and Tienchai, T. (2010). Formaldehyde Degradation by
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Photocatalytic Ag-Doped TiO2 Film of Glass Fiber Roving. J. Nanosci.
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Nanotechno., 10:1-4.
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Marcial, Z., Tessy, L., Ricardo, G., Maximiliano, A., and Ruth, M. (2005).
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Acetone gas phase condensation on alkaline metals doped TiO2 sol-gel
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catalysts. Appl. Surf. Sci., 252:828-832.
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Mingyang, X., Jinlong, Z., and Feng, C. (2009). New approaches to prepare
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nitrogen-doped TiO2 photocatalysts and study on their photocatalytic
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activities in visible light. Appl. Catal., B, 89:563-569.
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Sangchay, W., Sikong, L., and Kooptarnond, K. (2012). Comparison of
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photocatalytic reaction of commercial P25 and synthetic TiO2-AgCl
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nanoparticles. Procedia Eng., 32:590-596.
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Saowaluk, B., Weerawan, S., and Lek, S. (2011). Antibacterial Activity of TiO2
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and Fe3+ doped TiO2 Nanoparticles Synthesized at Low Temperature. Adv.
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Mater. Res., 214:197-201.
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Yuekun, L., Yicong, C., Huifang, Z., and Changjian, L. (2008). A facile method
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for synthesis of Ag/TiO2 nanostructures. Meter. Lett., 62:3688-3690.
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Table 1.
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The MB degradation percentage of TiO2 and TiO2-Ag powders
under UV irradiation
UV irradiation time (h)
Sample
0
1
2
3
4
5
6
TiO2
0.00
21.24
24.09
31.33
36.75
39.83
43.89
TiO2-1Ag
0.00
22.56
26.37
33.88
37.55
41.94
46.66
TiO2-3Ag
0.00
24.09
28.94
35.57
39.97
44.81
48.60
TiO2-5Ag
0.00
26.09
35.96
39.08
42.31
36.67
52.30
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Table 2. The E.coli kills rate percentage of TiO2 and TiO2-Ag powders
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under UV irradiation
UV irradiation time (min)
Sample
0
15
30
45
60
TiO2
0.00
14.29
20.00
42.86
51.43
TiO2-1Ag
0.00
20.00
37.14
54.29
62.86
TiO2-3Ag
0.00
48.00
63.71
70.86
84.00
TiO2-5Ag
0.00
80.00
85.71
92.71
95.14
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Figure 1. SEM surface morphology images of TiO2 and TiO2-Ag powders
(magnification 50000X)
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Figure 2. XRD patterns of TiO2 and TiO2-Ag powders
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Figure 3. EDX spectra of TiO2-5Ag powders
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Figure 4. The photocatalytic activity of TiO2 and TiO2-Ag powders under UV
irradiation
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Figure 5. The antibacterial activity of TiO2 and TiO2-Ag powders under UV
irradiation
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Figure 6. Photo of viable E.coli colonies during 1 h UV irradiation of TiO2
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and TiO2-Ag powders compared with control condition
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