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Photocatalytic Antibacterial Performance of Glass Fibers Thin Film Coated with N-Doped SnO2/TiO2

Photocatalytic Antibacterial Performance of Glass Fibers Thin Film Coated with N-Doped SnO2/TiO2 Hindawi Publishing Corporation e Scientific World Journal Volume 2014, Article ID 869706, 9 pages http://dx.doi.org/10.1155/2014/869706 Research Article Photocatalytic Antibacterial Performance of Glass Fibers Thin Film Coated with N-Doped SnO /TiO 2 2 1 1 2 1 Peerawas Kongsong, Lek Sikong, Sutham Niyomwas, and Vishnu Rachpech Department of Mining and Materials Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla 90112, aTh iland Department of Mechanical Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla 90112, ai Th land Correspondence should be addressed to Lek Sikong; [email protected] Received 19 August 2013; Accepted 30 October 2013; Published 12 February 2014 Academic Editors: C. He and G. Ouyang Copyright © 2014 Peerawas Kongsong et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Both N-doped and undoped thin films of 3SnO /TiO composite were prepared, by sol-gel and dip-coating methods, and then 2 2 calcined at 600 C for 2 hours. eTh films were characterized by FTIR, XRD, UV-Vis, SEM, and XPS, and their photocatalytic activities to degrade methylene blue in solution were determined, expecting these activities to correlate with the inactivation of bacteria, which was confirmed. The doped and undoped films were tested for activities against Gram-negative Escherichia coli (E. coli)and Salmonella typhi (S. typhi), and Gram-positive Staphylococcus aureus (S. aureus). eTh eeff cts of doping on these composite films included reduced energy band gap, high crystallinity of anatase phase, and small crystallite size as well as increased photocatalytic activity and water disinfection efficiency. 1. Introduction sulfide (CdS), and silver nanoparticles have been widely studied and are considered promising due to their unique The supply of safe drinking water is an issue of concern, properties including large specific area and high reactivity [ 2]. particularly in developing countries. Although several initia- TiO is the most commonly used semiconductor photo- tiveshavebeensuccessfulinsupplyingsafedrinkingwater catalyst and the most studied of the various nanomaterials. to urban populations, the extent of these efforts still falls Activated by UV-A irradiation, its photocatalytic properties short of the required targets for sustainable development. In have been utilized in various environmental applications to developing countries, water delivery systems are plagued by remove contaminants from both water and air. A wealth of leakages, illegal connections, and vandalism, and precious information on TiO photocatalytic inactivation of bacteria water resources are mismanaged. In Africa, Asia, Latin Amer- has been acquired over the last 20 years. TiO can kill both ica, and the Caribbean, nearly one billion people in rural areas Gram-negative and Gram-positive bacteria, although Gram- have no access to sucffi ient clean water supplies [ 1]. Con- positive bacteria are able to form spores and therefore are taminated water commonly contains dangerous pathogens, less sensitive. eTh exact bactericidal mechanism of reactive and its consumption creates serious health eeff cts and societal oxygen species (ROS) is not yet fully known, but the pho- problems. In the past decade, many innovative disinfection tocatalytic activity of TiO produces them, and they are technologies were developed and adopted as alternatives extremely reactive killing or deactivating microorganisms on to chlorine and ozone associated disinfection processes, contact [3]. including germicide ultraviolet (UV) radiation and photo- eTh re are many techniques to improve photoactivity such catalytic oxidation. eTh traditional disinfection approaches as control of phase morphology, crystallite size, and reducing have potentialrisks,suchascarcinogenicbyproducts(DBPs). band gap energy. Doping TiO with N and combining it with For the alternative technologies, diverse nanophotocatalysts such as titanium dioxide (TiO ), zinc oxide (ZnO), cadmium SnO couldimprove thephotochemical activity [4, 5]. 2 2 2 The Scientific World Journal The aim of this work was to investigate the water dis- The crystallite sizes were estimated from XRD peaks using infection efficiency of N-doped and undoped 3SnO /TiO the Scherrer equation [8]: 2 2 composite films under UV radiation. The quantity of dopants 0.9𝜆 in TiO films was varied. The N-doped and undoped 𝐷= , 2 (1) 𝛽 cos𝜃 3SnO /TiO compositefilmswereformedascoatingson 2 2 glass b fi ers, and the photocatalytic antibacterial eeff cts of where 𝐷 is crystallite size, 𝜆 is the wavelength of X-ray these films against Gram-negative Escherichia coli (E. coli), radiation (Cu-K𝛼 =0.15406nm),𝛽 is the angle width at half Salmonella typhi (S. typhi), and Gram-positive Staphylococcus maximum height, and𝜃 in degrees is the half diffraction aureus (S. aureus) were assessed. The fraction of viable angle of the peak centroid. eTh FTIR transmittance spectra bacteria that survived the treatment was determined with the of the samples were also analyzed in order to confirm spread plate technique. Furthermore, photocatalytic degrada- hydroxyl functional groups (TiO –OH bonds) of the films. tion of methylene blue dye in solution was also investigated, The band gap energies of TiO and TiO composites, in 2 2 to correlate this activity with antibacterial activity. powder form, were measured by UV-Vis-NIR spectrometer with an integrating sphere attachment (Shimadzu ISR-3100 spectrophotometer) by using BaSO as reference. eTh onset 2. Experimental absorbances were determined by the linear extrapolation of 2.1. Materials and Methods. The TiO composite films were thesteep part of theUVabsorptiontowardthe base line. formed on glass b fi ers (E-type) with two coating layers. The specific surface area of the starting glass fiber materials 2.3. Photocatalytic Reaction Test. eTh photocatalytic activities 2 −1 is 2 m g [6]. The first layer was 5SiO /TiO ,and this 2 2 of TiO and of N-doped 3SnO /TiO thin films on glass 2 2 2 film was prepared by adding titanium (IV) isopropoxide fibers were tested by observing the degradation of methylene −5 (TTIP, 99.95%, Fluka Sigma-Aldrich) dropwise under vig- blue (MB). eTh MB solution (50 mL) had 1×10 Minitial orous stirring into a mixture solution containing ethanol concentration, and 1 g [8]ofundoped or dopedTiO coated (99.9%, Merck, Germany) and tetraethylorthosilicate (TEOS, glass b fi ers were provided excitation from a 50 W UV-lamp 98%, Fluka Sigma-Aldrich). The second coating layer was (black light) in the 310–400 nm wavelength range, set at 32 cm (optionally N-doped) 3SnO /TiO composite. The N-doped 2 2 distance from the samples. eTh photocatalytic reaction tests 3SnO /TiO was prepared by mixing 10 mL glacial acetic, 2 2 were done in a dark chamber, with various UV irradiation 0.289 g ammonium carbonate, and 0.315 g Tin (IV) chloride times up to 4 h. The remaining concentration of methylene pentahydrate. For the rfi st coating layer the concentration of blue was determined by UV-VIS spectrophotometer. SiO was xfi ed at 5 mol%, while SnO doped in the second 2 2 layer was xfi ed at 3 mol%. Nitrogen at 20 mol% was used for 2.4. Photocatalytic Antibacterial Measurements. Gram-neg- doping of the 3SnO /TiO composite films, following Qin 2 2 ative (E. coli and S. typhi)and Gram-positive(S. aureus) and coworkers [7]. The N-doped 3SnO /TiO solutions were 2 2 bacteria were obtained from the Microbiology Science Lab- stirred at room temperature for 60 min, and then 2 M HCl oratory, Prince of Songkla University, Songkhla. eTh bacteria wasaddedintothe solution to adjust itspHtoabout 3.5. were grown aerobically in 4 mL of trypticase soy broth, at The glass b fi ers were first kept at 500 C for 1 h in order to 37 C for 24 h. Then the bacterial solution was diluted in remove wax and then carefully cleaned with ethanol. A dip- saline solution (0.85% NaCl) until the count of bacteria coating apparatus was used to coat the fibers. The first coating per milliliter of solution was in the range of 30–300. es Th e with SiO /TiO actedasabueff rlayer on theglass bfi ers, and 2 2 counts were estimated by colony counter. eTh number of N-doped 3SnO /TiO sol was coated on the bueff r layer as viable bacteria in a treated solution is readily quantiefi d by 2 2 the second coating. A dipping speed of 1.0 mm/s into the sols spread plate technique, in which the sample is appropriately gave homogeneous coatings. The coating films were turned diluted and transferred to an agar plate. eTh grown colonies are counted, and each colony represents an initial viable into gels by drying at 60 C for 30 min. Then coated b fi ers were ∘ ∘ bacterium in the plate culture. It is known that the initial bac- heated to 600 C at a heating rate of 10 C/min and held for terial concentration is an important factor aeff cting apparent 2 h. eTh coated glass fibers were cleaned by immersion in an antibacterial ecffi iency [ 9]. The initial bacterial concentration ultrasonic bath of distilled water for 15 min in order to remove was set to about 10 CFU/mL. A 50 mL aliquot of bacterial excess TiO particles. eTh TiO composite film coated glass 2 2 ∘ suspension was treated with a 40 g/L dose of coated glass fibers were dried at 105 C for 24 h. The samples were tested fibers, with exposure to UV irradiation for various durations. immediately aeft r they had cooled in a desiccator to ambient Then, 1 mL of treated suspension was sampled and cultured temperature. on MacConkey agar plates (E. coli and S. typhi)orNutrient agar plates (S. aureus), by incubation at 37 Cfor 24h. Aeft r 2.2. Material Characterization. Surface morphology was incubation, the colony counts were recorded as estimates of investigated by scanning electron microscopy (SEM) and viable bacteria counts. energy-dispersive X-ray spectroscopy (EDS). XPS spectra To assess the antimicrobial mechanisms of the TiO were recorded with an AXIS Ultra DLD (Kratos Analytical composite film coatings on glass b fi ers, the test fibers were Ltd., UK). Phase composition was characterized with an dipped in 10 CFU/mL bacterial solution. After incubation, X-ray diffractometer (XRD) (Phillips E’pert MPD, Cu-K 𝛼 ). bacteria attached to the coatings were xfi ed with 0.05% The Scientific World Journal 3 Si Anatase Al Ca Ca Ti (d) (c) (c) (b) (b) (a) (a) 0 24 6 8 10 10 20 30 40 50 60 70 Energy (keV) 2𝜃 (∘) ∘ Figure 2: EDS spectra for (a) uncoated glass, (b) TiO ,(c) Figure 1: XRD patterns of TiO thin films calcined at 600 C: (a) 3SnO /TiO coating, and (d) 20N/3SnO /TiO coating, all calcined 2 2 2 2 TiO ,(b) 3SnO /TiO , and (c) 20N/3SnO /TiO . 2 2 2 2 2 ∘ at 600 C. Table1:Eeff ct of thin filmtypeonits anatasecrystallite size,energy band gap, and photocatalytic degradation of MB in 4 h. and𝑐 = 0.96917 nm for 20N/3SnO /TiO ). Compared with 2 2 anatase TiO (𝑎 =𝑏 =0.37852nm and𝑐 = 0.95083 nm), the Crystallite Energy band %Degradation 2 Samples lattice parameters𝑎 and𝑏 of 20N/3SnO /TiO were almost size (nm) gap (eV) of MB in 4 h (%) 2 2 unchanged while𝑐 had increased. er Th efore, the doping had TiO 17.2 3.20 71.9 slightly distorted the crystal lattice structure, as expected [10]. 3SnO /TiO 17.2 3.20 80.3 2 2 Both crystallite size and degree of crystallinity are known to 20N/3SnO /TiO 9.8 3.03 89.5 2 2 aeff ct photocatalytic activity. 3.2. EDS Spectra and Morphology of Surface iTh n Films. The glutaraldehyde in phosphate buffer saline and dehydrated EDS spectra taken from TiO and TiO composite films 2 2 sequentially by water-alcohol solutions (50%, 70%, 80%, 90%, are presented in Figure 2. eTh elements Si, Al, Ca, and and100%alcohol,usedinthisorder)for 30minineach Oweremainlyinthe glassfibersubstrates, whileTi, N, solution. Aeft r dehydrating by a series of ethanol solutions, and O elements were in the composite films from TiO specimens were dried in a critical-point dryer. The samples and 20N/3SnO /TiO .Thepeakfor Sn is notobserved, 2 2 were mounted on stubs and coated with gold. The cell wall presumably because of its low dosage in the composite films. characteristics were observed by SEM imaging. The morphologies of the coated surfaces are illustrated in Figure 3,asobservedbySEM.Thenucleationofanatasephase 3. Results and Discussion was homogeneous, and the film surface was smooth. How- ever, some excess TiO had remained randomly deposited on 3.1. XRD Results of TiO Thin Films. Figure 1 shows the XRD 2 the coatings of glass bfi ers. Agglomeration of nanoparticles patterns of the thin films, namely, undoped 3SnO /TiO 2 2 occurred in 3SnO /TiO films, but not in 20N/3SnO /TiO 2 2 2 2 and 20N/3SnO /TiO ,aeft rcalcination at 600 Cfor 2h.By 2 2 films. N-doping hindered anatase crystal growth, in agree- comparison with anatase and rutile ASTM cards (American ment with the XRD spectra shown in Figure 1. Society for Testing and Materials, cards JCPDS 21–1272 and JCPDS 21–1276), the films included anatase phase, and the 3.3. FTIR Analysis. The photogenerated hydroxyl groups various types of thin films did not differ in these observa- on titanium dioxide surface can be characterized using tions. During the high calcinations temperature, TiO had FTIR transmittance spectra especially the peaks at 3200– transformed from amorphous to anatase structure. eTh very −1 3600 cm [11, 12]. Figure 4 shows the FTIR spectra of broad diffraction peak at (1 0 1) plane (2 𝜃 =25.3 )was due TiO ,3SnO /TiO , and 20N/3SnO /TiO calcined at 600 C. to the small crystallite size of TiO .Thecrystallite sizes 2 2 2 2 2 −1 The bands appearing at about 3400–3468 cm in TiO , calculated from Scherrer’s equation are shown in Table 1.The 2 3SnO /TiO , and 20N/3SnO /TiO coatings correspond to calcined 20N/3SnO /TiO composite film had the smallest 2 2 2 2 2 2 stretching vibrations of OH groups linked with titanium 9.8 nm crystallites. Nitrogen doping seems to hinder phase atoms (Ti–OH). This confirms that photocatalytic reactions transformation from amorphous to anatase phase, leading took place on the sample surfaces. eTh broad and strong peaks to a low degree of crystallinity, while 3SnO /TiO had 2 2 −1 at 1630–1640 cm areascribedtothe bendingvibration of thehighest degreeofcrystallinity (Figure 1). A tetragonal OH groups, of free or absorbed water [13, 14]. The peaks at Bravais lattice type was evident, and the lattice constants were −1 calculated from diffraction peaks ( 𝑎 =𝑏 =0.37821nm and 1403 cm in the spectrum of the 20N/3SnO /TiO sample 2 2 𝑐 =0.95402nm for3SnO /TiO ,and𝑎 =𝑏 =0.37852nm areassignedtothe vibrations of N–Hbonds [15]. The peak 2 2 Intensity (counts) Intensity (a.u.) 4 The Scientific World Journal (a) (b) (c) (d) (e) (f) (g) (h) Figure 3: SEM images of glass fibers, some coated and calcined at 600 C: (a) uncoated 1,500x, (b) uncoated 60,000x, (c) TiO 1,500x, (d) TiO 60,000x, (e) 3SnO /TiO 1,500x, (f) 3SnO /TiO 60,000x, (g) 20N/3SnO /TiO 1,500x, and (h) 20N/3SnO /TiO 60,000x. 2 2 2 2 2 2 2 2 2 are shown in Figure 5. eTh absorption edge energies were (c) determined from the following relation: N–H bending (b) 1239.8 (a) (2) 𝐸 = , where𝐸 (eV) is thebandgap energy of thesampleand𝜆 (nm) is the onset wavelength of the spectrum. The dopants O–H stretching O–H bending aeff cted the UV-Vis spectra by inhibiting recombination of Ti–O stretching electron-hole pairs, especially in the case of N-doping. eTh 400 900 1400 1900 2400 2900 3400 3900 band gap energy of N-doped TiO is shifted by 0.17 eV from −1 the 3.20 eV of pure TiO (Table 1), and 3SnO /TiO showed Wavenumber (cm ) 2 2 2 a smaller shift to 3.20 eV. es Th e eeff cts suggest a strategy Figure 4: FTIR spectra of (a) pure TiO ,(b) 3SnO /TiO ,and (c) 2 2 2 for mediating photocatalysis through atomic-level doping of 20N/3SnO /TiO powders calcined at 600 C. 2 2 nanocatalysts. It can be seen that the absorption wavelength of 20N/3SnO /TiO photocatalyst is extended towards visible 2 2 light (𝜆 =409.2nm)relativetoothervaryinglydoped samples −1 at 600 cm is ascribed to absorption bands of Ti–O and [16]orpureTiO . eTh nitrogen doping hinders the growth of O–Ti–O, related to flexion vibration [ 16]. anatase phase (Figure 1) or it can reduce the crystallite size of TiO composite films to be about 10 nm ( Table 1), leading to a 3.4. Energy Gap Measurement. The photon energy versus quantum conn fi ement effect of nanocrystals and the highest curveofpureTiO ,3SnO /TiO , and 20N/3SnO /TiO photocatalytic activity. 2 2 2 2 2 Transmittance (%) The Scientific World Journal 5 485.1 Sn 3d 493.6 480 482 484 486 488 490 492 494 496 498 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Binding energy (eV) Photon energy (eV) Figure 7: XPSspectrumofSn3donthe surface of 20N/3SnO /TiO 20N/3SnO /TiO 2 2 2 2 thin film, calcined at 600 C. 3SnO /TiO 2 2 TiO Figure 5: eTh photon energy versus ( 𝛼 hv) curve of representative pure TiO ,3SnO /TiO , and 20N/3SnO /TiO samples calcined at 399.6 N 1s 2 2 2 2 2 600 C. 397.0 O 1s Sn 3d (b) Ti 2p Ti 2s N 1s 392 394 396 398 400 402 404 406 (a) Binding energy (eV) Figure 8: XPS spectrum of N 1s on the surface of 20N/3SnO /TiO 2 2 thin film, calcined at 600 C. 0 200 400 600 800 1000 1200 Binding energy (eV) Figure 6: XPS spectra of (a) TiO and (b) 20N/3SnO /TiO thin different states of N. The main peak at 399.6 eV binding 2 2 2 films, calcined at 600 C. energy was attributed to the N–Ti–O environment, while the peaks at 397.0 eV were assigned to the substitutional nitrogen in the Ti–N structure [18]. 3.5. XPS Analysis. Figure 6 shows the X-ray photoelectron spectroscopic (XPS) spectra of TiO and 20N/3SnO /TiO 3.6. Photocatalytic Activity Test. The photocatalytic activi- 2 2 2 thin films.TheTi, O, N, andSnelementsweredetectedin ties of TiO and the composite films were determined, by 20N/3SnO /TiO thin films, in the respective percentages measuring degradation of methylene blue in solution (MB) 2 2 −5 7.25, 61.44, 1.35, and 2.39. The XPS peaks indicate that the with an initial concentration of1×10 M, under UV for codoped TiO powders contain Ti, Sn, O, and N elements, various irradiation times. Figure 9 shows the fraction of and the binding energies of Ti 2p, Sn 3d, O 1s, and N 1s are the MB remaining versus irradiation time, which equals 458, 486, 531, and 399 eV, respectively. eTh Sn 3d peak in current concentration relative to initial concentration,𝐶/𝐶 . the spectrum of Sn-TiO ,shown in Figure 7, demonstrates The 3SnO /TiO had better photocatalytic activity than 2−𝑥 2 2 tinonthe surfaceofTiO . eTh 485.1 eV binding energy pure TiO , possibly because photogenerated electrons can 2 2 of tin in Sn-TiO is lower than the reference 486.6 eV accumulate in SnO and photogenerated holes in TiO , 2−𝑥 2 2 energy reported for Sn 3d5/2-binding [17]. To assess the with a heterojunction formed at the SnO -TiO interface. 2 2 chemical state of N in 20N/3SnO /TiO thin films, a high- This would lower the recombination rate of photogenerated 2 2 resolution XPS spectrum of N 1s was measured; see Figure 8. charge carriers, giving higher quantum ecffi iency and better The N 1s binding energy peaks were broad and asymmetric, photocatalytic activity [19]. The N-doped 20N/3SnO /TiO 2 2 demonstrating at least two chemical states of N, with binding thin films had the most photoactivity ( Figure 10). According energies 397.0 and 399.6 eV. Each of these broad peaks was to prior research, factors influencing the photoactivity of decomposed to three peaks, by curve fitting, indicating two TiO photocatalysts include crystalline phase, grain size, 2 2 ( hv) (eV/cm ) Intensity (cps) Intensity (cps) Intensity (cps) 6 The Scientific World Journal 1.0 Table 2: A summary of numerical tfi s of first-order kinetics to the degradation of MB. TiO 3SnO /TiO 2 2 −1 2 0.8 Samples Rate equation Rate constant (𝑘 )(hr ) 𝑅 20N/3SnO /TiO 2 2 −0.34𝑡 TiO 𝐶=𝑒 0.34 0.952 −0.43𝑡 0.6 3SnO /TiO 𝐶=𝑒 0.43 0.975 2 2 −0.60𝑡 20N/3SnO /TiO 𝐶=𝑒 0.60 0.974 2 2 0.4 1.00 0.2 0.0 UV irradiation time (hr) 0.10 Figure 9: Photocatalytic degradation of MB in solution under UV excitation by various thin film coatings on glass fibers. The surface area of thin film available for reaction was held approximately constant, based on weight of glass b fi ers. 0.01 1.000 0 5 10 15 20 25 30 Time (min) Uncoated 3SnO /TiO 2 2 TiO 20N/3SnO /TiO 0.100 2 2 2 Figure 11: Antibacterial eeff cts of glass fibers with various coatings against E. coli under UV irradiation. 0.010 the pathogen, was tested with UV excitation. eTh initial 0.001 bacterial concentration was about 10 CFU/mL, and the 02468 10 12 14 results are shown in Figures 10–13.Thesurvivalrates of Time (min) bacteria were estimated from CFU cultures that determine the number of viable cells. eTh survival curves in Figures Uncoated 3SnO /TiO 2 2 20N/3SnO /TiO TiO 2 2 10–12 show the fraction surviving 𝑁/𝑁 ,where 𝑁 is 2 0 0 the initial and 𝑁 the current viable count, at a given Figure 10: Antibacterial effects of coated glass b fi ers against S. typhi duration of irradiation. The 20N/3SnO /TiO film had the 2 2 under UV irradiation. highest bactericidal activity, better than either pure TiO or 3SnO /TiO with similar UV excitation, and dramatically 2 2 better than UV alone. In the presence of 20N/3SnO /TiO , 2 2 specific surface area, surface morphology, and surface state S. typhi was almost completely inactivated within 10 min (surface OH radicals), and these factors are correlated [20, andcompletelykilledwithin15min.Incomparisonwith 21]. Doping TiO with N shifts its light absorption wavelength control b fi ers, TiO ,and 3SnO /TiO thin films, S. typhi was 2 2 2 to thevisible region,reduces crystallitesize, andnarrows its killed 74%, 97%, and 99.5%, respectively, aer ft 15 min UV energy band gap (3.03 eV) [22]. A well-crystallized anatase irradiation (Figure 10). The results shown in Figure 11 phase facilitates transfer of photo-induced vacancies from for E. coli are qualitatively similar, with almost complete bulk to surface, for degradation of organic composites, inactivation reachedwithin30min andcompletekillwithin and effectively inhibits the recombination between photo- 40 min in the best case, and the different film types had the generated electrons and holes, giving excellent photocatalytic same rank order as above. The rank order remained the same activity. As seen in Figure 1, the 20N/3SnO /TiO thin film 2 2 with S. aureus, which was completely killed within 60 min had the smallest crystallite size, estimated to be about 9.8 nm in the best case (Figure 12). Clearly the 20N/3SnO /TiO 2 2 (Table 1). The reaction rate constant 𝑘 determined is a direct film had the best antibacterial effects against each pathogen quantitative indicator of photocatalytic activity (Table 2), and tested. eTh antibacterial activity of the prepared films −1 𝑘 was highest at 0.6 hr for the 20N/3SnO /TiO composite 2 2 correlates well with the photocatalytic activity, determined film, almost double that of pure TiO . 2 from degradation of methylene blue. eTh inactivation rate constant, 𝑘 of control (uncoated glass b fi ers under UV 3.7. Photocatalytic Disinfection against Bacteria. The photo- irradiation), TiO ,3SnO /TiO , and 20N/3SnO /TiO films 2 2 2 2 2 inactivation of bacteria, in distilled water containing determined from Figures 10–12 illustrated in Table 3,isa N/N 0 C/C N/N 0 The Scientific World Journal 7 Table 3: A summary of numerical tfi s of first-order kinetics to the inactivation of bacteria. −1 2 Bacteria Samples Rate Equation Rate constant (𝑘 ) (min ) 𝑅 −0.050𝑡 Uncoated 𝑁=𝑒 0.050 0.883 −0.240𝑡 TiO 𝑁=𝑒 0.240 0.975 S. typhi −0.350𝑡 3SnO /TiO 𝑁=𝑒 0.350 0.990 2 2 −0.450𝑡 20N/3SnO /TiO 𝑁=𝑒 0.450 0.960 2 2 −0.044𝑡 Uncoated 𝑁=𝑒 0.044 0.935 −0.086𝑡 TiO 𝑁=𝑒 0.086 0.986 E. coli −0.103𝑡 3SnO /TiO 𝑁=𝑒 0.103 0.993 2 2 −0.128𝑡 20N/3SnO /TiO 𝑁=𝑒 0.128 0.975 2 2 −0.036𝑡 Uncoated 𝑁=𝑒 0.036 0.888 −0.058𝑡 TiO 𝑁=𝑒 0.058 0.940 S. aureus −0.070𝑡 3SnO /TiO 𝑁=𝑒 0.070 0.944 2 2 −0.082𝑡 20N/3SnO /TiO 𝑁=𝑒 0.082 0.936 2 2 1.00 100 0.10 0.01 0 1020304050 10 20 30 40 50 60 Time (min) Time (min) Uncoated 3SnO /TiO 2 2 S.typhi TiO 20N/3SnO /TiO 2 2 2 E.coli S.aureus Figure 12: Antibacterial effects of glass b fi ers with various coatings against S. aureus under UV irradiation. Figure 13: Antibacterial effects of 20N/3SnO /TiO coated glass 2 2 fibers against S. typhi, E. coli and, S. aureus under UV irradiation. direct quantitative indicator of antibacterial activity. It is seen that the𝑘 value of 20N/3SnO /TiO film was higher than that The photos in Figure 14 show bacterial cultures on agar 2 2 of othersamples duetoits smallercrystallite size or larger plates, illustrative of viable counts aeft r various treatment −1 surface area. The killing rate, 𝑘 , was the highest at 0.450 min times with 20N/3SnO /TiO under UV irradiation. The 2 2 −1 for S. typhi disinfection compared to 0.128 and 0.082 min damage to cell walls of bacteria can be immediate on for E. coli and S. aureus, respectively. Figure 13 shows the irradiation in the presence of TiO thin films, and is followed antibacterial efficiency of 20N/3SnO /TiO composite thin by further damage to the cell membranes [25]. SEM images 2 2 film under UV irradiation. This thin film has a stronger of bacteria before and aeft r treatment with 20N/3SnO /TiO 2 2 antibacterial effect on Gram-negative than Gram-positive thin films are shown in Figures 15(a), 15(b),and 15(c) and bacteria,because Gram-positivebacteriahavethick cell Figures 15(d), 15(e),and 15(f), respectively. The cell walls walls composed of multilayered peptidoglycan [23], and also of untreated bacteria were normal, and the number of E. coli has thicker cell walls than S. typhi. eTh bactericidal germs was high (Figures 15(a)–15(c)). After 15 min of UV effect of TiO has been started from the damage of bacterial irradiation the cell walls and cell membranes were damaged outer membranes aer ft contact with reactive oxygen species by contact with TiO composite films. The mechanism of ∙ ∙ (ROS), primarily hydroxyl radicals (OH ), which leads to this eeff ct is that the photo-generated hydroxyl (OH )and −∙ phospholipid peroxidation and ultimately cell death. It has super oxygen (O ) radicals react, as powerful oxidizing also been suggested that nanomaterials that can physically agents, with peptidoglycan (poly-𝑁 -acetylglucosamine and attach to a cell could be bactericidal on such contact [24]. 𝑁 -acetylmuramic acid) of bacterialcell wall [26]. N/N Disinfection efficiency (%) 8 The Scientific World Journal 0min 10min 20min 30min 40min 50min 60min S.typhi E.coli S.aureus Figure 14: Growth of bacterial colonies on agar plates, aer ft various treatment times. Glass b fi ers coated with 20N/3SnO /TiO were used to 2 2 treat S. typhi, E. coli, and S. aureus under UV irradiation, and the number of colonies corresponds to remaining viable count of bacteria. (a) (b) (c) (d) (e) (f) Figure 15: SEM images of bacteria observed on surface coated thin films: (a) untreated ( S. typhi), (b) untreated (E. coli), (c) untreated (S. aureus), (d) irradiated for 15 min (S. typhi), (e) irradiated for 40 min (E. coli), and (f) irradiated for 60 min (S. aureus) of 20N/3SnO /TiO 2 2 composite thin films. 4. Conclusion Gram-negative type. The synthesized 20N/3SnO /TiO film 2 2 coated on glass b fi ers is antibacterial photocatalyst that will N-doped and undoped 3SnO /TiO composite films were 2 2 be suitable for water puricfi ation. prepared as coatings on glass b fi ers, by sol-gel and dip- coating methods. eTh films were heated to 600 Catarate of Conflict of Interests 10 C/min and held for 2 h, in order to form anatase phase. eTh 20N/3SnO /TiO composite film had comparatively narrow 2 2 eTh authors declare that there is no conflict of interests re- band gap energy, high crystallinity of anatase phase, and small garding the publication of this paper. crystallitesizeaswellasthe highestphotocatalyticactivity of the films prepared. Its antibacterial activity under UV irradiation was superior to undoped TiO films, correlating Acknowledgments well with photocatalytic activity determined from MB degra- dation. Antibacterial activity was experimentally established The authors gratefully acknowledge support by the Depart- against selected bacteria of both Gram-positive and Gram- ment of Mining and Materials Engineering, Faculty of Engi- negative types, with stronger antibacterial effects against neering, Prince of Songkla University and financial support The Scientific World Journal 9 to Peerawas Kongsong and Lek Sikong by the ai Th land [15] X.Z.Bu, G. K. Zhang, Y. Y. Gao, andY.Q.Yang, “Prepara- tion and photocatalytic properties of visible light responsive Research Fund through the Royal Golden Jubilee Ph.D. N-doped TiO /rectorite composites,” Microporous and Meso- Program (Grant no. PHD/0169/2553). Associate Professor Dr. porous Materials,vol.136,no. 1–3, pp.132–137,2010. SeppoKarrila,fromthe FacultyofScience andTechnology, [16] L. Sikong,M.Masae,K.Kooptarnond,W.Taweepreda, andF. is also acknowledged for comments and suggestions, as is the Saito, “Improvement of hydrophilic property of rubber dipping copyediting service of the Research and Development Office former surface with Ni/B/TiO nano-composite film,” Applied of PSU. Surface Science, vol. 258, no. 10, pp. 4436–4443, 2012. [17] B. Xin, D. Ding, Y. Gao, X. Jin, H. Fu, and P. Wang, “Preparation References of nanocrystalline Sn-TiO -X via a rapid and simple stannous chemical reducing route,” Applied Surface Science,vol.255,no. [1] S. Gelover, L. A. Go´mez,K.Reyes,and M. Teresa Leal,“A 11, pp.5896–5901,2009. practical demonstration of water disinfection using TiO films [18] L. Zhang, F. Lv, W. Zhang et al., “Photo degradation of methyl and sunlight,” Water Research,vol.40, no.17, pp.3274–3280, orange by attapulgite-SnO -TiO nanocomposites,” Journal of 2 2 Hazardous Materials,vol.171,no. 1–3, pp.294–300,2009. [2] P.Gao,J.Liu,T.Zhang,D.D.Sun, andW.Ng, “Hierarchical [19] X. Cheng, X. Yu,Z.Xing, andJ.Wan,“Enhanced photocatalytic TiO /CdS “spindle-like” composite with high photodegrada- activity of nitrogen doped TiO anatase nano-particle under tion and antibacterial capability under visiblelight irradiation,” simulated sunlight irradiation,” in Proceedings of the Interna- Journal of Hazardous Materials, vol. 229-230, pp. 209–216, 2012. tional Conference on Future Energy, Environment, and Materials [3] Q. Li, S. Mahendra, D. Y. Lyon et al., “Antimicrobial nanoma- (FEEM ’12), vol. 16, pp. 598–605, April 2012. terials for water disinfection and microbial control: potential [20] A. J. Zaleska, J. W. Sobczak, E. Grabowska, and J. Hupka, applications and implications,” Water Research,vol.42, no.18, “Preparation and photocatalytic activity of boron-modified pp.4591–4602,2008. TiO under UV and visible light,” Applied Catalysis B,vol.78, [4] N.T.Nolan,D.W.Synnott,M.K.Seery,S.J.Hinder, A. Van no.1-2,pp. 92–100,2008. Wassenhoven, andS.C.Pillai,“Eeff ctofN-dopingonthe [21] X. Zhang and Q. Liu, “Preparation and characterization of photocatalytic activity of sol-gel TiO ,” Journal of Hazardous titania photocatalyst co-doped with boron, nickel, and cerium,” Materials,vol.211-212,pp. 88–94,2012. Materials Letters,vol.62, no.17-18,pp. 2589–2592, 2008. [5] L.C.Chen, F. R. Tsai,S.H.Fang, andY.C.Ho, “Properties [22] J.Yang,H.Bai,Q.Jiang,andJ.Lian,“Visible-lightphotocatalysis of sol-gel SnO /TiO electrodes and their photoelectrocatalytic 2 2 in nitrogen-carbon-doped TiO films obtained by heating TiO 2 2 activities under UV and visible light illumination,” Electrochim- gel-filminanionized N gas,” Thin Solid Films ,vol.516,no. 8, ica Acta,vol.54, no.4,pp. 1304–1311, 2009. pp.1736–1742,2008. [6] L. Kiwi-Minsker, I. Yuranov, B. Siebenhaar, and A. Renken, [23] M. Ramani, S. Ponnusamy, and C. Muthamizhchelvan, “From “Glass fiber catalysts for total oxidation of CO and hydrocar- zinc oxidenanoparticles to microflowers: a study of growth bons in waste gases,” Catalysis Today,vol.54, no.1,pp. 39–46, kinetics and biocidal activity,” Materials Science Engineering C, vol. 32,no. 8, pp.2381–2389,2012. [7] H.L.Qin, G. B. Gu,and S. Liu, “Preparation of nitrogen-doped [24] G. Rajakumara,A.Abdul Rahumana,S.MohanaRoopanb et titania with visible-light activity and its application,” Comptes al., “Fungus-mediatedbiosynthesis and characterization of TiO Rendus Chimie, vol. 11, no. 1-2, pp. 95–100, 2008. 2 nanoparticles and their activity againstpathogenic bacteria,” [8] Z. Liuxue, L. Peng, and S. Zhixing, “Photocatalysis anatase thin Spectrochimica Acta A, vol. 91, pp. 23–29, 2012. film coated PAN fibers prepared at low temperature,” Materials [25] X. Wang and W. 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Photocatalytic Antibacterial Performance of Glass Fibers Thin Film Coated with N-Doped SnO2/TiO2

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Copyright © 2014 Peerawas Kongsong et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Hindawi Publishing Corporation e Scientific World Journal Volume 2014, Article ID 869706, 9 pages http://dx.doi.org/10.1155/2014/869706 Research Article Photocatalytic Antibacterial Performance of Glass Fibers Thin Film Coated with N-Doped SnO /TiO 2 2 1 1 2 1 Peerawas Kongsong, Lek Sikong, Sutham Niyomwas, and Vishnu Rachpech Department of Mining and Materials Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla 90112, aTh iland Department of Mechanical Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla 90112, ai Th land Correspondence should be addressed to Lek Sikong; [email protected] Received 19 August 2013; Accepted 30 October 2013; Published 12 February 2014 Academic Editors: C. He and G. Ouyang Copyright © 2014 Peerawas Kongsong et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Both N-doped and undoped thin films of 3SnO /TiO composite were prepared, by sol-gel and dip-coating methods, and then 2 2 calcined at 600 C for 2 hours. eTh films were characterized by FTIR, XRD, UV-Vis, SEM, and XPS, and their photocatalytic activities to degrade methylene blue in solution were determined, expecting these activities to correlate with the inactivation of bacteria, which was confirmed. The doped and undoped films were tested for activities against Gram-negative Escherichia coli (E. coli)and Salmonella typhi (S. typhi), and Gram-positive Staphylococcus aureus (S. aureus). eTh eeff cts of doping on these composite films included reduced energy band gap, high crystallinity of anatase phase, and small crystallite size as well as increased photocatalytic activity and water disinfection efficiency. 1. Introduction sulfide (CdS), and silver nanoparticles have been widely studied and are considered promising due to their unique The supply of safe drinking water is an issue of concern, properties including large specific area and high reactivity [ 2]. particularly in developing countries. Although several initia- TiO is the most commonly used semiconductor photo- tiveshavebeensuccessfulinsupplyingsafedrinkingwater catalyst and the most studied of the various nanomaterials. to urban populations, the extent of these efforts still falls Activated by UV-A irradiation, its photocatalytic properties short of the required targets for sustainable development. In have been utilized in various environmental applications to developing countries, water delivery systems are plagued by remove contaminants from both water and air. A wealth of leakages, illegal connections, and vandalism, and precious information on TiO photocatalytic inactivation of bacteria water resources are mismanaged. In Africa, Asia, Latin Amer- has been acquired over the last 20 years. TiO can kill both ica, and the Caribbean, nearly one billion people in rural areas Gram-negative and Gram-positive bacteria, although Gram- have no access to sucffi ient clean water supplies [ 1]. Con- positive bacteria are able to form spores and therefore are taminated water commonly contains dangerous pathogens, less sensitive. eTh exact bactericidal mechanism of reactive and its consumption creates serious health eeff cts and societal oxygen species (ROS) is not yet fully known, but the pho- problems. In the past decade, many innovative disinfection tocatalytic activity of TiO produces them, and they are technologies were developed and adopted as alternatives extremely reactive killing or deactivating microorganisms on to chlorine and ozone associated disinfection processes, contact [3]. including germicide ultraviolet (UV) radiation and photo- eTh re are many techniques to improve photoactivity such catalytic oxidation. eTh traditional disinfection approaches as control of phase morphology, crystallite size, and reducing have potentialrisks,suchascarcinogenicbyproducts(DBPs). band gap energy. Doping TiO with N and combining it with For the alternative technologies, diverse nanophotocatalysts such as titanium dioxide (TiO ), zinc oxide (ZnO), cadmium SnO couldimprove thephotochemical activity [4, 5]. 2 2 2 The Scientific World Journal The aim of this work was to investigate the water dis- The crystallite sizes were estimated from XRD peaks using infection efficiency of N-doped and undoped 3SnO /TiO the Scherrer equation [8]: 2 2 composite films under UV radiation. The quantity of dopants 0.9𝜆 in TiO films was varied. The N-doped and undoped 𝐷= , 2 (1) 𝛽 cos𝜃 3SnO /TiO compositefilmswereformedascoatingson 2 2 glass b fi ers, and the photocatalytic antibacterial eeff cts of where 𝐷 is crystallite size, 𝜆 is the wavelength of X-ray these films against Gram-negative Escherichia coli (E. coli), radiation (Cu-K𝛼 =0.15406nm),𝛽 is the angle width at half Salmonella typhi (S. typhi), and Gram-positive Staphylococcus maximum height, and𝜃 in degrees is the half diffraction aureus (S. aureus) were assessed. The fraction of viable angle of the peak centroid. eTh FTIR transmittance spectra bacteria that survived the treatment was determined with the of the samples were also analyzed in order to confirm spread plate technique. Furthermore, photocatalytic degrada- hydroxyl functional groups (TiO –OH bonds) of the films. tion of methylene blue dye in solution was also investigated, The band gap energies of TiO and TiO composites, in 2 2 to correlate this activity with antibacterial activity. powder form, were measured by UV-Vis-NIR spectrometer with an integrating sphere attachment (Shimadzu ISR-3100 spectrophotometer) by using BaSO as reference. eTh onset 2. Experimental absorbances were determined by the linear extrapolation of 2.1. Materials and Methods. The TiO composite films were thesteep part of theUVabsorptiontowardthe base line. formed on glass b fi ers (E-type) with two coating layers. The specific surface area of the starting glass fiber materials 2.3. Photocatalytic Reaction Test. eTh photocatalytic activities 2 −1 is 2 m g [6]. The first layer was 5SiO /TiO ,and this 2 2 of TiO and of N-doped 3SnO /TiO thin films on glass 2 2 2 film was prepared by adding titanium (IV) isopropoxide fibers were tested by observing the degradation of methylene −5 (TTIP, 99.95%, Fluka Sigma-Aldrich) dropwise under vig- blue (MB). eTh MB solution (50 mL) had 1×10 Minitial orous stirring into a mixture solution containing ethanol concentration, and 1 g [8]ofundoped or dopedTiO coated (99.9%, Merck, Germany) and tetraethylorthosilicate (TEOS, glass b fi ers were provided excitation from a 50 W UV-lamp 98%, Fluka Sigma-Aldrich). The second coating layer was (black light) in the 310–400 nm wavelength range, set at 32 cm (optionally N-doped) 3SnO /TiO composite. The N-doped 2 2 distance from the samples. eTh photocatalytic reaction tests 3SnO /TiO was prepared by mixing 10 mL glacial acetic, 2 2 were done in a dark chamber, with various UV irradiation 0.289 g ammonium carbonate, and 0.315 g Tin (IV) chloride times up to 4 h. The remaining concentration of methylene pentahydrate. For the rfi st coating layer the concentration of blue was determined by UV-VIS spectrophotometer. SiO was xfi ed at 5 mol%, while SnO doped in the second 2 2 layer was xfi ed at 3 mol%. Nitrogen at 20 mol% was used for 2.4. Photocatalytic Antibacterial Measurements. Gram-neg- doping of the 3SnO /TiO composite films, following Qin 2 2 ative (E. coli and S. typhi)and Gram-positive(S. aureus) and coworkers [7]. The N-doped 3SnO /TiO solutions were 2 2 bacteria were obtained from the Microbiology Science Lab- stirred at room temperature for 60 min, and then 2 M HCl oratory, Prince of Songkla University, Songkhla. eTh bacteria wasaddedintothe solution to adjust itspHtoabout 3.5. were grown aerobically in 4 mL of trypticase soy broth, at The glass b fi ers were first kept at 500 C for 1 h in order to 37 C for 24 h. Then the bacterial solution was diluted in remove wax and then carefully cleaned with ethanol. A dip- saline solution (0.85% NaCl) until the count of bacteria coating apparatus was used to coat the fibers. The first coating per milliliter of solution was in the range of 30–300. es Th e with SiO /TiO actedasabueff rlayer on theglass bfi ers, and 2 2 counts were estimated by colony counter. eTh number of N-doped 3SnO /TiO sol was coated on the bueff r layer as viable bacteria in a treated solution is readily quantiefi d by 2 2 the second coating. A dipping speed of 1.0 mm/s into the sols spread plate technique, in which the sample is appropriately gave homogeneous coatings. The coating films were turned diluted and transferred to an agar plate. eTh grown colonies are counted, and each colony represents an initial viable into gels by drying at 60 C for 30 min. Then coated b fi ers were ∘ ∘ bacterium in the plate culture. It is known that the initial bac- heated to 600 C at a heating rate of 10 C/min and held for terial concentration is an important factor aeff cting apparent 2 h. eTh coated glass fibers were cleaned by immersion in an antibacterial ecffi iency [ 9]. The initial bacterial concentration ultrasonic bath of distilled water for 15 min in order to remove was set to about 10 CFU/mL. A 50 mL aliquot of bacterial excess TiO particles. eTh TiO composite film coated glass 2 2 ∘ suspension was treated with a 40 g/L dose of coated glass fibers were dried at 105 C for 24 h. The samples were tested fibers, with exposure to UV irradiation for various durations. immediately aeft r they had cooled in a desiccator to ambient Then, 1 mL of treated suspension was sampled and cultured temperature. on MacConkey agar plates (E. coli and S. typhi)orNutrient agar plates (S. aureus), by incubation at 37 Cfor 24h. Aeft r 2.2. Material Characterization. Surface morphology was incubation, the colony counts were recorded as estimates of investigated by scanning electron microscopy (SEM) and viable bacteria counts. energy-dispersive X-ray spectroscopy (EDS). XPS spectra To assess the antimicrobial mechanisms of the TiO were recorded with an AXIS Ultra DLD (Kratos Analytical composite film coatings on glass b fi ers, the test fibers were Ltd., UK). Phase composition was characterized with an dipped in 10 CFU/mL bacterial solution. After incubation, X-ray diffractometer (XRD) (Phillips E’pert MPD, Cu-K 𝛼 ). bacteria attached to the coatings were xfi ed with 0.05% The Scientific World Journal 3 Si Anatase Al Ca Ca Ti (d) (c) (c) (b) (b) (a) (a) 0 24 6 8 10 10 20 30 40 50 60 70 Energy (keV) 2𝜃 (∘) ∘ Figure 2: EDS spectra for (a) uncoated glass, (b) TiO ,(c) Figure 1: XRD patterns of TiO thin films calcined at 600 C: (a) 3SnO /TiO coating, and (d) 20N/3SnO /TiO coating, all calcined 2 2 2 2 TiO ,(b) 3SnO /TiO , and (c) 20N/3SnO /TiO . 2 2 2 2 2 ∘ at 600 C. Table1:Eeff ct of thin filmtypeonits anatasecrystallite size,energy band gap, and photocatalytic degradation of MB in 4 h. and𝑐 = 0.96917 nm for 20N/3SnO /TiO ). Compared with 2 2 anatase TiO (𝑎 =𝑏 =0.37852nm and𝑐 = 0.95083 nm), the Crystallite Energy band %Degradation 2 Samples lattice parameters𝑎 and𝑏 of 20N/3SnO /TiO were almost size (nm) gap (eV) of MB in 4 h (%) 2 2 unchanged while𝑐 had increased. er Th efore, the doping had TiO 17.2 3.20 71.9 slightly distorted the crystal lattice structure, as expected [10]. 3SnO /TiO 17.2 3.20 80.3 2 2 Both crystallite size and degree of crystallinity are known to 20N/3SnO /TiO 9.8 3.03 89.5 2 2 aeff ct photocatalytic activity. 3.2. EDS Spectra and Morphology of Surface iTh n Films. The glutaraldehyde in phosphate buffer saline and dehydrated EDS spectra taken from TiO and TiO composite films 2 2 sequentially by water-alcohol solutions (50%, 70%, 80%, 90%, are presented in Figure 2. eTh elements Si, Al, Ca, and and100%alcohol,usedinthisorder)for 30minineach Oweremainlyinthe glassfibersubstrates, whileTi, N, solution. Aeft r dehydrating by a series of ethanol solutions, and O elements were in the composite films from TiO specimens were dried in a critical-point dryer. The samples and 20N/3SnO /TiO .Thepeakfor Sn is notobserved, 2 2 were mounted on stubs and coated with gold. The cell wall presumably because of its low dosage in the composite films. characteristics were observed by SEM imaging. The morphologies of the coated surfaces are illustrated in Figure 3,asobservedbySEM.Thenucleationofanatasephase 3. Results and Discussion was homogeneous, and the film surface was smooth. How- ever, some excess TiO had remained randomly deposited on 3.1. XRD Results of TiO Thin Films. Figure 1 shows the XRD 2 the coatings of glass bfi ers. Agglomeration of nanoparticles patterns of the thin films, namely, undoped 3SnO /TiO 2 2 occurred in 3SnO /TiO films, but not in 20N/3SnO /TiO 2 2 2 2 and 20N/3SnO /TiO ,aeft rcalcination at 600 Cfor 2h.By 2 2 films. N-doping hindered anatase crystal growth, in agree- comparison with anatase and rutile ASTM cards (American ment with the XRD spectra shown in Figure 1. Society for Testing and Materials, cards JCPDS 21–1272 and JCPDS 21–1276), the films included anatase phase, and the 3.3. FTIR Analysis. The photogenerated hydroxyl groups various types of thin films did not differ in these observa- on titanium dioxide surface can be characterized using tions. During the high calcinations temperature, TiO had FTIR transmittance spectra especially the peaks at 3200– transformed from amorphous to anatase structure. eTh very −1 3600 cm [11, 12]. Figure 4 shows the FTIR spectra of broad diffraction peak at (1 0 1) plane (2 𝜃 =25.3 )was due TiO ,3SnO /TiO , and 20N/3SnO /TiO calcined at 600 C. to the small crystallite size of TiO .Thecrystallite sizes 2 2 2 2 2 −1 The bands appearing at about 3400–3468 cm in TiO , calculated from Scherrer’s equation are shown in Table 1.The 2 3SnO /TiO , and 20N/3SnO /TiO coatings correspond to calcined 20N/3SnO /TiO composite film had the smallest 2 2 2 2 2 2 stretching vibrations of OH groups linked with titanium 9.8 nm crystallites. Nitrogen doping seems to hinder phase atoms (Ti–OH). This confirms that photocatalytic reactions transformation from amorphous to anatase phase, leading took place on the sample surfaces. eTh broad and strong peaks to a low degree of crystallinity, while 3SnO /TiO had 2 2 −1 at 1630–1640 cm areascribedtothe bendingvibration of thehighest degreeofcrystallinity (Figure 1). A tetragonal OH groups, of free or absorbed water [13, 14]. The peaks at Bravais lattice type was evident, and the lattice constants were −1 calculated from diffraction peaks ( 𝑎 =𝑏 =0.37821nm and 1403 cm in the spectrum of the 20N/3SnO /TiO sample 2 2 𝑐 =0.95402nm for3SnO /TiO ,and𝑎 =𝑏 =0.37852nm areassignedtothe vibrations of N–Hbonds [15]. The peak 2 2 Intensity (counts) Intensity (a.u.) 4 The Scientific World Journal (a) (b) (c) (d) (e) (f) (g) (h) Figure 3: SEM images of glass fibers, some coated and calcined at 600 C: (a) uncoated 1,500x, (b) uncoated 60,000x, (c) TiO 1,500x, (d) TiO 60,000x, (e) 3SnO /TiO 1,500x, (f) 3SnO /TiO 60,000x, (g) 20N/3SnO /TiO 1,500x, and (h) 20N/3SnO /TiO 60,000x. 2 2 2 2 2 2 2 2 2 are shown in Figure 5. eTh absorption edge energies were (c) determined from the following relation: N–H bending (b) 1239.8 (a) (2) 𝐸 = , where𝐸 (eV) is thebandgap energy of thesampleand𝜆 (nm) is the onset wavelength of the spectrum. The dopants O–H stretching O–H bending aeff cted the UV-Vis spectra by inhibiting recombination of Ti–O stretching electron-hole pairs, especially in the case of N-doping. eTh 400 900 1400 1900 2400 2900 3400 3900 band gap energy of N-doped TiO is shifted by 0.17 eV from −1 the 3.20 eV of pure TiO (Table 1), and 3SnO /TiO showed Wavenumber (cm ) 2 2 2 a smaller shift to 3.20 eV. es Th e eeff cts suggest a strategy Figure 4: FTIR spectra of (a) pure TiO ,(b) 3SnO /TiO ,and (c) 2 2 2 for mediating photocatalysis through atomic-level doping of 20N/3SnO /TiO powders calcined at 600 C. 2 2 nanocatalysts. It can be seen that the absorption wavelength of 20N/3SnO /TiO photocatalyst is extended towards visible 2 2 light (𝜆 =409.2nm)relativetoothervaryinglydoped samples −1 at 600 cm is ascribed to absorption bands of Ti–O and [16]orpureTiO . eTh nitrogen doping hinders the growth of O–Ti–O, related to flexion vibration [ 16]. anatase phase (Figure 1) or it can reduce the crystallite size of TiO composite films to be about 10 nm ( Table 1), leading to a 3.4. Energy Gap Measurement. The photon energy versus quantum conn fi ement effect of nanocrystals and the highest curveofpureTiO ,3SnO /TiO , and 20N/3SnO /TiO photocatalytic activity. 2 2 2 2 2 Transmittance (%) The Scientific World Journal 5 485.1 Sn 3d 493.6 480 482 484 486 488 490 492 494 496 498 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Binding energy (eV) Photon energy (eV) Figure 7: XPSspectrumofSn3donthe surface of 20N/3SnO /TiO 20N/3SnO /TiO 2 2 2 2 thin film, calcined at 600 C. 3SnO /TiO 2 2 TiO Figure 5: eTh photon energy versus ( 𝛼 hv) curve of representative pure TiO ,3SnO /TiO , and 20N/3SnO /TiO samples calcined at 399.6 N 1s 2 2 2 2 2 600 C. 397.0 O 1s Sn 3d (b) Ti 2p Ti 2s N 1s 392 394 396 398 400 402 404 406 (a) Binding energy (eV) Figure 8: XPS spectrum of N 1s on the surface of 20N/3SnO /TiO 2 2 thin film, calcined at 600 C. 0 200 400 600 800 1000 1200 Binding energy (eV) Figure 6: XPS spectra of (a) TiO and (b) 20N/3SnO /TiO thin different states of N. The main peak at 399.6 eV binding 2 2 2 films, calcined at 600 C. energy was attributed to the N–Ti–O environment, while the peaks at 397.0 eV were assigned to the substitutional nitrogen in the Ti–N structure [18]. 3.5. XPS Analysis. Figure 6 shows the X-ray photoelectron spectroscopic (XPS) spectra of TiO and 20N/3SnO /TiO 3.6. Photocatalytic Activity Test. The photocatalytic activi- 2 2 2 thin films.TheTi, O, N, andSnelementsweredetectedin ties of TiO and the composite films were determined, by 20N/3SnO /TiO thin films, in the respective percentages measuring degradation of methylene blue in solution (MB) 2 2 −5 7.25, 61.44, 1.35, and 2.39. The XPS peaks indicate that the with an initial concentration of1×10 M, under UV for codoped TiO powders contain Ti, Sn, O, and N elements, various irradiation times. Figure 9 shows the fraction of and the binding energies of Ti 2p, Sn 3d, O 1s, and N 1s are the MB remaining versus irradiation time, which equals 458, 486, 531, and 399 eV, respectively. eTh Sn 3d peak in current concentration relative to initial concentration,𝐶/𝐶 . the spectrum of Sn-TiO ,shown in Figure 7, demonstrates The 3SnO /TiO had better photocatalytic activity than 2−𝑥 2 2 tinonthe surfaceofTiO . eTh 485.1 eV binding energy pure TiO , possibly because photogenerated electrons can 2 2 of tin in Sn-TiO is lower than the reference 486.6 eV accumulate in SnO and photogenerated holes in TiO , 2−𝑥 2 2 energy reported for Sn 3d5/2-binding [17]. To assess the with a heterojunction formed at the SnO -TiO interface. 2 2 chemical state of N in 20N/3SnO /TiO thin films, a high- This would lower the recombination rate of photogenerated 2 2 resolution XPS spectrum of N 1s was measured; see Figure 8. charge carriers, giving higher quantum ecffi iency and better The N 1s binding energy peaks were broad and asymmetric, photocatalytic activity [19]. The N-doped 20N/3SnO /TiO 2 2 demonstrating at least two chemical states of N, with binding thin films had the most photoactivity ( Figure 10). According energies 397.0 and 399.6 eV. Each of these broad peaks was to prior research, factors influencing the photoactivity of decomposed to three peaks, by curve fitting, indicating two TiO photocatalysts include crystalline phase, grain size, 2 2 ( hv) (eV/cm ) Intensity (cps) Intensity (cps) Intensity (cps) 6 The Scientific World Journal 1.0 Table 2: A summary of numerical tfi s of first-order kinetics to the degradation of MB. TiO 3SnO /TiO 2 2 −1 2 0.8 Samples Rate equation Rate constant (𝑘 )(hr ) 𝑅 20N/3SnO /TiO 2 2 −0.34𝑡 TiO 𝐶=𝑒 0.34 0.952 −0.43𝑡 0.6 3SnO /TiO 𝐶=𝑒 0.43 0.975 2 2 −0.60𝑡 20N/3SnO /TiO 𝐶=𝑒 0.60 0.974 2 2 0.4 1.00 0.2 0.0 UV irradiation time (hr) 0.10 Figure 9: Photocatalytic degradation of MB in solution under UV excitation by various thin film coatings on glass fibers. The surface area of thin film available for reaction was held approximately constant, based on weight of glass b fi ers. 0.01 1.000 0 5 10 15 20 25 30 Time (min) Uncoated 3SnO /TiO 2 2 TiO 20N/3SnO /TiO 0.100 2 2 2 Figure 11: Antibacterial eeff cts of glass fibers with various coatings against E. coli under UV irradiation. 0.010 the pathogen, was tested with UV excitation. eTh initial 0.001 bacterial concentration was about 10 CFU/mL, and the 02468 10 12 14 results are shown in Figures 10–13.Thesurvivalrates of Time (min) bacteria were estimated from CFU cultures that determine the number of viable cells. eTh survival curves in Figures Uncoated 3SnO /TiO 2 2 20N/3SnO /TiO TiO 2 2 10–12 show the fraction surviving 𝑁/𝑁 ,where 𝑁 is 2 0 0 the initial and 𝑁 the current viable count, at a given Figure 10: Antibacterial effects of coated glass b fi ers against S. typhi duration of irradiation. The 20N/3SnO /TiO film had the 2 2 under UV irradiation. highest bactericidal activity, better than either pure TiO or 3SnO /TiO with similar UV excitation, and dramatically 2 2 better than UV alone. In the presence of 20N/3SnO /TiO , 2 2 specific surface area, surface morphology, and surface state S. typhi was almost completely inactivated within 10 min (surface OH radicals), and these factors are correlated [20, andcompletelykilledwithin15min.Incomparisonwith 21]. Doping TiO with N shifts its light absorption wavelength control b fi ers, TiO ,and 3SnO /TiO thin films, S. typhi was 2 2 2 to thevisible region,reduces crystallitesize, andnarrows its killed 74%, 97%, and 99.5%, respectively, aer ft 15 min UV energy band gap (3.03 eV) [22]. A well-crystallized anatase irradiation (Figure 10). The results shown in Figure 11 phase facilitates transfer of photo-induced vacancies from for E. coli are qualitatively similar, with almost complete bulk to surface, for degradation of organic composites, inactivation reachedwithin30min andcompletekillwithin and effectively inhibits the recombination between photo- 40 min in the best case, and the different film types had the generated electrons and holes, giving excellent photocatalytic same rank order as above. The rank order remained the same activity. As seen in Figure 1, the 20N/3SnO /TiO thin film 2 2 with S. aureus, which was completely killed within 60 min had the smallest crystallite size, estimated to be about 9.8 nm in the best case (Figure 12). Clearly the 20N/3SnO /TiO 2 2 (Table 1). The reaction rate constant 𝑘 determined is a direct film had the best antibacterial effects against each pathogen quantitative indicator of photocatalytic activity (Table 2), and tested. eTh antibacterial activity of the prepared films −1 𝑘 was highest at 0.6 hr for the 20N/3SnO /TiO composite 2 2 correlates well with the photocatalytic activity, determined film, almost double that of pure TiO . 2 from degradation of methylene blue. eTh inactivation rate constant, 𝑘 of control (uncoated glass b fi ers under UV 3.7. Photocatalytic Disinfection against Bacteria. The photo- irradiation), TiO ,3SnO /TiO , and 20N/3SnO /TiO films 2 2 2 2 2 inactivation of bacteria, in distilled water containing determined from Figures 10–12 illustrated in Table 3,isa N/N 0 C/C N/N 0 The Scientific World Journal 7 Table 3: A summary of numerical tfi s of first-order kinetics to the inactivation of bacteria. −1 2 Bacteria Samples Rate Equation Rate constant (𝑘 ) (min ) 𝑅 −0.050𝑡 Uncoated 𝑁=𝑒 0.050 0.883 −0.240𝑡 TiO 𝑁=𝑒 0.240 0.975 S. typhi −0.350𝑡 3SnO /TiO 𝑁=𝑒 0.350 0.990 2 2 −0.450𝑡 20N/3SnO /TiO 𝑁=𝑒 0.450 0.960 2 2 −0.044𝑡 Uncoated 𝑁=𝑒 0.044 0.935 −0.086𝑡 TiO 𝑁=𝑒 0.086 0.986 E. coli −0.103𝑡 3SnO /TiO 𝑁=𝑒 0.103 0.993 2 2 −0.128𝑡 20N/3SnO /TiO 𝑁=𝑒 0.128 0.975 2 2 −0.036𝑡 Uncoated 𝑁=𝑒 0.036 0.888 −0.058𝑡 TiO 𝑁=𝑒 0.058 0.940 S. aureus −0.070𝑡 3SnO /TiO 𝑁=𝑒 0.070 0.944 2 2 −0.082𝑡 20N/3SnO /TiO 𝑁=𝑒 0.082 0.936 2 2 1.00 100 0.10 0.01 0 1020304050 10 20 30 40 50 60 Time (min) Time (min) Uncoated 3SnO /TiO 2 2 S.typhi TiO 20N/3SnO /TiO 2 2 2 E.coli S.aureus Figure 12: Antibacterial effects of glass b fi ers with various coatings against S. aureus under UV irradiation. Figure 13: Antibacterial effects of 20N/3SnO /TiO coated glass 2 2 fibers against S. typhi, E. coli and, S. aureus under UV irradiation. direct quantitative indicator of antibacterial activity. It is seen that the𝑘 value of 20N/3SnO /TiO film was higher than that The photos in Figure 14 show bacterial cultures on agar 2 2 of othersamples duetoits smallercrystallite size or larger plates, illustrative of viable counts aeft r various treatment −1 surface area. The killing rate, 𝑘 , was the highest at 0.450 min times with 20N/3SnO /TiO under UV irradiation. The 2 2 −1 for S. typhi disinfection compared to 0.128 and 0.082 min damage to cell walls of bacteria can be immediate on for E. coli and S. aureus, respectively. Figure 13 shows the irradiation in the presence of TiO thin films, and is followed antibacterial efficiency of 20N/3SnO /TiO composite thin by further damage to the cell membranes [25]. SEM images 2 2 film under UV irradiation. This thin film has a stronger of bacteria before and aeft r treatment with 20N/3SnO /TiO 2 2 antibacterial effect on Gram-negative than Gram-positive thin films are shown in Figures 15(a), 15(b),and 15(c) and bacteria,because Gram-positivebacteriahavethick cell Figures 15(d), 15(e),and 15(f), respectively. The cell walls walls composed of multilayered peptidoglycan [23], and also of untreated bacteria were normal, and the number of E. coli has thicker cell walls than S. typhi. eTh bactericidal germs was high (Figures 15(a)–15(c)). After 15 min of UV effect of TiO has been started from the damage of bacterial irradiation the cell walls and cell membranes were damaged outer membranes aer ft contact with reactive oxygen species by contact with TiO composite films. The mechanism of ∙ ∙ (ROS), primarily hydroxyl radicals (OH ), which leads to this eeff ct is that the photo-generated hydroxyl (OH )and −∙ phospholipid peroxidation and ultimately cell death. It has super oxygen (O ) radicals react, as powerful oxidizing also been suggested that nanomaterials that can physically agents, with peptidoglycan (poly-𝑁 -acetylglucosamine and attach to a cell could be bactericidal on such contact [24]. 𝑁 -acetylmuramic acid) of bacterialcell wall [26]. N/N Disinfection efficiency (%) 8 The Scientific World Journal 0min 10min 20min 30min 40min 50min 60min S.typhi E.coli S.aureus Figure 14: Growth of bacterial colonies on agar plates, aer ft various treatment times. Glass b fi ers coated with 20N/3SnO /TiO were used to 2 2 treat S. typhi, E. coli, and S. aureus under UV irradiation, and the number of colonies corresponds to remaining viable count of bacteria. (a) (b) (c) (d) (e) (f) Figure 15: SEM images of bacteria observed on surface coated thin films: (a) untreated ( S. typhi), (b) untreated (E. coli), (c) untreated (S. aureus), (d) irradiated for 15 min (S. typhi), (e) irradiated for 40 min (E. coli), and (f) irradiated for 60 min (S. aureus) of 20N/3SnO /TiO 2 2 composite thin films. 4. Conclusion Gram-negative type. The synthesized 20N/3SnO /TiO film 2 2 coated on glass b fi ers is antibacterial photocatalyst that will N-doped and undoped 3SnO /TiO composite films were 2 2 be suitable for water puricfi ation. prepared as coatings on glass b fi ers, by sol-gel and dip- coating methods. eTh films were heated to 600 Catarate of Conflict of Interests 10 C/min and held for 2 h, in order to form anatase phase. eTh 20N/3SnO /TiO composite film had comparatively narrow 2 2 eTh authors declare that there is no conflict of interests re- band gap energy, high crystallinity of anatase phase, and small garding the publication of this paper. crystallitesizeaswellasthe highestphotocatalyticactivity of the films prepared. Its antibacterial activity under UV irradiation was superior to undoped TiO films, correlating Acknowledgments well with photocatalytic activity determined from MB degra- dation. Antibacterial activity was experimentally established The authors gratefully acknowledge support by the Depart- against selected bacteria of both Gram-positive and Gram- ment of Mining and Materials Engineering, Faculty of Engi- negative types, with stronger antibacterial effects against neering, Prince of Songkla University and financial support The Scientific World Journal 9 to Peerawas Kongsong and Lek Sikong by the ai Th land [15] X.Z.Bu, G. K. Zhang, Y. Y. Gao, andY.Q.Yang, “Prepara- tion and photocatalytic properties of visible light responsive Research Fund through the Royal Golden Jubilee Ph.D. N-doped TiO /rectorite composites,” Microporous and Meso- Program (Grant no. PHD/0169/2553). Associate Professor Dr. porous Materials,vol.136,no. 1–3, pp.132–137,2010. SeppoKarrila,fromthe FacultyofScience andTechnology, [16] L. 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