Degradation of Pollutant and Antibacterial Activity of ... - Springer Link

Journal of Wuhan University of Technology-Mater. Sci. Ed. www.jwutms.net June 2015

447

DOI 10.1007/s11595-015-1169-7

Degradation of Pollutant and Antibacterial Activity of Waterborne Polyurethane/Doped TiO2 Nanoparticle Hybrid Films QIU Shan1,2, DENG Fengxia1, XU Shanwen1, LIU Peng3, MIN Xinmin3, MA Fang1,2*

(1. School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150006, China; 2. State Laboratory of Urban Water Resources and Environment, Harbin Institute of Technology, Harbin 150006, China; 3. School of Chemistry, Chemical Engineering and Life Science, Wuhan University of Technology,Wuhan 430070, China) Abstract: The waterborne polyurethane/doped TiO2 nanoparticle hybrid films were prepared. Nd, I doped TiO2 was prepared with a 50 nm particle size firstly. The hybrid film was prepared by mixing doped TiO2 with waterborne polyurethane, followed by heat treatment. The presence and nanometric distribution of doped TiO2 nanoparticles in prepared membranes is evident according to SEM images. The photocatalytic activities of doped TiO2 were significantly enhanced compared with pure TiO2 powders. After the hybrid film fabrication, the photocatalytic activities were almost the same as the pure catalysts with kMB of 0.046. In the antibacterial testing, the hybrid films can inhibit E. coli growth. A significant decrease in membrane fluidity and increase of permeability of E. coli were observed. Key words: doped TiO2; polyurethane; hybrid film; photocatalytic activity; antibacterial

1 Introduction Titania is expected to be applied to the field of water treatment plant due to the photo-catalytic activity[1-4]. The mechanism for its bactericidal property is based on the active substances produced during the photo-catalytic reaction. The reaction energy of OH, O 2, and HO 2 formed during the process is higher than many organic bond energies, such as C-C, C-H, C-N, C-O, and H-O. Thus nano-TiO2 can efficiently decompose the materials that form the bacteria and the organic nutrition indispensable for bacterial survival. Moreover, when using UV light as the catalyst, its UV absorption influences most of the photo-catalytic properties[5,6]. In recent years, in order to increase the photocatalysis efficiency, many methods have been

©Wuhan University of Technology and SpringerVerlag Berlin Heidelberg 2015 (Received: Oct. 19, 2014; Accepted: Jan. 17, 2015) QIU Shan(䛡⧺): Assoc. Prof.; Ph D; E-mail: qiushanh@sohu. com *Corresponding author: MA Fang (傜᭮): Prof.; Ph D; E-mail: [email protected] Funded by the National Natural Science Foundation of China (No.51208141 ) and Open Project of State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology(No.QA201206)

attempted to improve the band gap energy, such as metal doping. These methods created intra-band-gap states close to the conduction or valence band edges and hence induce visible light absorption at the subband-gap energies[7,8]. However, how to fix TiO2 is a key question for the application of the photo-catalytic composites. The materials with cellular structures were used to carry the photo-catalytic composites due to their mechanical properties and large surface area, like ceramic foams and fly ash. But the stability of photo-catalytic composites on the cellular materials is a problem in the application and photo-catalytic composites is easy to fall off. Polyurethane (PU) is a polymer composed of a chain of organic units joined by carbamate (urethane) links. PU is commonly used as biomaterials due to its excellent physical and mechanical properties and relatively good biocompatibility. Modified PU nanocomposites due to their superior physical and mechanical properties, good bacterial biocompatibility, less cytotoxicity and low inflammatory responses have emerged as promising materials for the applications[9,10]. In this study, the waterborne polyurethane/doped TiO 2 nanoparticle hybrid films were prepared. The photocatalytic efficiencies of TiO2 powder, the hybrid material and doped TiO 2 were compared with each

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other. The antibacterial activites of the hybrid material were also studied on the E. coli. The results with the unprecedented detail gave us insight into the molecular basis for the waterborne polyurethane/doped TiO 2 Nanoparticle film.

2 Experimental 2.1 Materials Tetrabutyl titanate, potassium iodate, neodymium nitrate, ethanol, MB, BSA, sodium chloride, phosphate buffer solution (PBS), and other routine chemicals were purchased from Shenshi Chem; E. coli (HB101) were provided by the Chinese Center for Type Culture Collections. All chemicals were analytical grade. Deionized and doubly distilled water was used in all experiments. The polyurethane scaffolds were prepared by phase inversion method described in previous works. The used materials were: polyurethane polymer, deionized water as a nonsolvent. 2.2 Preparation of photocatalysts Neodymium nitrate was dissolved in ethanol, followed by the addition of tetrabutyl titanate. After stirring for about 30 minutes, the solution was added dropwise into potassium iodate with vigorous stirring. Then the solution was evaporated in a vacuum oven before being calcined for 2 h. The samples were washed and dried again in the vacuum oven[11]. 2.3 Preparation of polyurethane/doped TiO2 nanoparticle hybrid Films 1 g of Photocatalyst and 1 g of polyurethane scaffold, were added into a three-neck bottle. To lower the viscosity, some water was added. Then copper nanoparticle ink was successfully prepared by sintering the mixture at 70 ºC. The polyurethane/doped TiO2 nanoparticle hybrid films were fabricated by casting onto a glass substrate and then annealed at 120 ºC for 2 hours. 2.4 Characterization of photocatalyst and hybrid films The size and shape of the synthesized photocatalyst were observed by a transmission electron microscope (TEM, H-600, JAPAN HITACHI). The hybrid films were observed by a scanning electron microscope(SEM, JSM-5610LV, Japan). X-ray diffraction (XRD) patterns were obtained on a D8 Advance X-ray diffractometer (Bruker). 2.4 The kinetics for degradation of pollutant The photocatalytic activities of the catalysts were

evaluated by using methylene blue (MB) as the test molecule in a glass container. Four catalysts were used in this test: TiO2 powder; Nd and I doped TiO2 powder; TiO2/Polyurethane hybrid film; Nd and I doped TiO2/ Polyurethane hybrid film. All other conditions are the same. The light source was a iodine tungsten lamp (150 W, FoShan lighting, main wavelength ≥ 760 nm) and the distance between the lamp and the reaction liquid was 15 cm. The reaction temperature was maintained at 31±1 ć. For MB, the reaction liquid was prepared by mixing 0.05 g catalysts and 100 mL MB aqueous solution (10 mg/L). Then the suspensions were stirred in the dark for 30 min to reach adsorption equilibrium before irradiation. Then the mixture was irradiated by the light. After 30 min, 5 mL of suspension was taken from the mixture and centrifuged at 4 000 r/min to separate the photocatalyst particles. Then the supernatants were analyzed by UVvis spectrophotometer (724, Shanghai 3rd Analytical Instrument Ltd.). Subsequently, readings were taken in 30 min intervals. 2.5 Antibacterial activity test 2.5.1 Microcalorimetry Microcalorimetric experiments were performed on a TAM air isothermal microcalorimeter (Thermometric AB, Sweden), which was equipped with eight twin calorimetric channels, of which one side was used for the sample and the other for a static reference. The hybrid films were cut into pieces. E. coli was inoculated in the prepared LB cultures containing different amounts of the hybrid films. Then the solution was put into the calorimeter to monitor the growth of E. coli cells in the presence of the complex. The metabolic thermogenic curves were recorded in real time. 2.5.2 Fluorescence polarization measurement When E. coli was grown to primary-log phase at 37 ć in a culture, the bacteria suspensions were centrifuged at 4 000 r/min for 5 minutes. Then the precipitate was resuspended in PBS buffer. The bacteria were washed 2 times to thoroughly remove the culture medium and then resuspended in PBS. After that, the composite was added into one of the cell suspensions with 0.2 cm2/mL contact area. The cell suspensions were incubated in the culture mediums at 37 ć for some time with continuous shaking. The alteration of E. coli membrane fluidity was studied with the fluorescence polarization technique (Shimadzu, RF-5301), in which 1, 6-diphenyl-1, 3, 5-hexatriene (DPH) was used as a fluorescence probe.


DPH was dissolved and then diluted to 0.004 m mol/L in PBS. After vigorous shaking for 15 min, this solution was mixed sufficiently. The cells were incubated in DPH solution at 25 ć for 30 min, then washed twice by PBS, and resuspended in PBS (vide supra) for measuring FL polarization. The excitation and emission wavelengths were 362 nm and 432 nm, respectively.

3 Results and discussion 3.1 Synthesis of photocatalysts

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TiO 2 nanoparticles into a mixture of waterborne polyurethane with vigorous stirring, and then the mixture was drop cast onto a glass substrate to form hybrid film. The presence and distribution of doped TiO2 nanoparticles in the polyurethane films has been studied by SEM. Fig.3 shows the SEM micrographs of the prepared polyurethane-silica hybrid films. As it is shown, the presence and nanometric distribution of doped TiO2 nanoparticles in the prepared membranes is evident. In this procedure, enough stirring is very important for the dispersity of TiO2 in PU. Otherwise TiO2 nanoparticles would aggregate in PU.

10 mm

1 mm

Fig.3 SEM images of the hybrid films

3.3 Kinetics for degradation of pollutant

Fig.2 TEM image of Nd and I doped TiO2

Fig.1 and Fig.2 show the XRD pattern and TEM image of the Nd, I doped TiO2 (Nd:I:TiO2=5:10;100), respectively. The peaks at 2θ values showed that all products were anatase crystal. TiO2 and I doped TiO2 were calcined at 600 ć or higher temperature, the rutile structure can be observed. The result shows that the doped Nd can postpone the transformation of TiO2 from anatase to rutile. The average size of crystallites is about 50 nm, calculated by the TEM image. Nd3+ ion (diameter: 0.99 Å) was slightly larger than Ti4+ ion (diameter:0.68 Å), so Nd 3+ has difficulty in entering into the lattice of TiO2 to replace the Ti4+ ion abundantly. The majority of Nd3+ (Nd2O3) existed on the surface of TiO2. Meanwhile, iodine was in the form of I7+/I species covering the surface of particles. 3.2 Preparation of the hybrid films The hybrid films were prepared by adding doped

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The photo bleaching and degradation of MB under visible-light irradiation follows apparent first-order kinetics. The observed reaction rate constants (kMB) of the various samples are listed in Table 1. Under visiblelight irradiation at λ400 nm, kMB for direct photolysis with undoped TiO2 particles was 0.003 min1. As for Nd and I doped TiO2, the photocatalytic activities were significantly enhanced with an order of magnitude (kMB =0.045 min1) as shown in Fig.4 (a). After TiO2 was fixed by PU, the photocatalytic activities were enhanced slightly with kMB of 0.006 5 as shown in Fig.4 (b). After Nd and I doped TiO2 was fixed by PU, the photocatalytic activities were almost the same as that of the pure catalysts with kMB of 0.046 as shown in Fig.4(c). 3.4 Determination of antibacterial activity

All biological processes are companied by heat released or absorbed, e g, the metabolism of bacteria.

Microcalorimetry can monitor the bacteria growth by measuring very small heat flow as a non-destructive and non-invasive technique. Fig.5 has shown the growth process of E. coli in the presence of the composites, respectively. From Fig.5, it can be seen the composites showed strong inhibitory effect on E. coli growth. The growth rate of E. coli in the presence of the composites decreased significantly and the generation time prolonged accordingly. With increasing amount of the composites in culture, the heat output power of E. coli cells decreased gradually. When the concentration increased to 0.5 cm2/mL, the growth of bacteria was inhibited completely and no heat released from metabolism was detected. In Fig.6, the fluorescence polarization of native cells was 3.2. The fluorescence polarization increased after treatment with the composites, suggesting that the membrane fluidity of E. coli increased. The decrease in membrane fluidity will cause the increase of cell membrane permeability. Consequently, the composites could cause the increase of cell permeability of E. coli. Membrane fluidity is an important physical character of cell membrane. Many cell functions, including energy transformation, nutrients transportation and transferring signals, are all tightly relevant with cell membrane fluidity[12]. Therefore, the stability of membrane fluidity plays an important role in keeping normal cell functions and resisting various environmental stresses[13,14]. In cells, DPH is distributed within the hydrophobic region of lipid membranes and DPH polarization reflects the average fluidity of all cellular membrane lipids[15]. And an inverse relationship exists between the membrane fluidity and polarization.

4 Conclusions In this paper, the composites were prepared for Polyurethane/Doped TiO 2 nanoparticle hybrid films. The polyurethane scaffolds and Doped TiO 2 were synthesized individually. The composites were prepared by depositing Polyurethane/Doped TiO 2 mixture dispersion on the substrate and then the solvent was evaporated at room temperature. The degradation of MB and antibacterial properties of the composites were studied, respectively. The photocatalytic activities of the hybrid films were significantly enhanced compared to pure TiO2 powder. In the bactericidal activity testing, in the presence of the hybrid films, E. coli growth was inhibited. A significant decrease in membrane fluidity and


increase of permeability of E. coli were observed. The composites prepared in this study are potentially used as biomedical material and water treatment material.

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