Synthesis and study the concentration effect on the photocatalytic activity of titania nanoparticles as anti-bactria using reactive magnetron sputtering technique

In this work, the dc reactive magnetron sputtering technique was used to prepare and deposit nanostructured titanium dioxide (TiO2) thin films on glass substrates. Titanium dioxide thin films of mixed phase (anatase+rutile) and single phase (anatase) were prepared using different gas mixing ratios, and for both of the two phases, they were diagnosed via x-ray diffraction (XRD). It was found that the contents of rutile in mixed phase dependent on the deposition time increased from the ratio of 40 to 46% and 50% as the deposition time increased from 3 h to 3.30 and 4 h. The photocatalytic activity of the mixed and single phase TiO2 was measured by kill the bacteria Escherichia coli (E.Coli) under exposure to UV-radiation. It was proven that the photocatalytic activity in the mixed phase (TiO2) gave better results weight fraction is 40% as an antibacterial activity. Based on the obtained results anti-bacterial activity of dioxide titanium nanoparticles was dependent on the concentration and phase of TiO2 and weight fraction of mixed-phase.


Introduction
The research interest in nanostructured titanium dioxide (TiO 2 ) thin films is rapidly rising due to its numerous and potential applications, such as photocatalysis, photonics, optoelectronics, electrochemistry, and photoelectrochemistry (Jin et al. 2001). These applications are used for the optical, electrical, chemical and mechanical characteristics of TiO 2 thin films and nanoparticles (Karabay et al. 2012).Because of its outstanding properties, such as nontoxicity, high photocatalytic activity, chemical stability, ability to be coated as a thin film on a substrate, and Friendly to the environment, TiO 2 is being hailed as a potential photocatalyst among all semiconductor photocatalysts. (Wang et al. 2009). the average nanocrystalline size, crystallinity, specific surface area, and phases involved are all known to affect the photocatalytic activity of pure-TiO 2 (Baiju et al. 2007;MehranRiazian 2017). TiO 2 exists as three different polymorphs: anatase, rutile, and brookite. The main source and the most stable form of TiO 2 is rutile, In terms of photocatalytic activity, anatase TiO 2 is more active than rutile TiO 2 . (Fasciani et al. 2017).
The mixed TiO 2 phase anatase/rutile, which is more popular than the single anatase or rutile phase, has greater photocatalytic activity than the single anatase or rutile phase, which is attributed to a synergistic effect between the two phases. (Firas 2019). The copresence of anatase and rutile crystallites induces a high level of photocatalytic activity; the transfer of photoexcited electrons and positive holes between interconnecting anatase and rutile particles may enhance charge separation and hence improve the efficiency of utilization of electron-hole pairs (Hurum et al. 2003). Additional characterizations confirmed electron transport between the two phases, suggesting that phase composition is a fundamentally important factor in high photocatalytic activity (Hurum et al. 2005).
The function of the Titania photocatalyst can be divided into these major categories: Purifying water, Preventing contamination, Deodorizing, Purifying the air self-cleaning, and Anti-bacteria (Kaneko and Okura 2002). Titania nanoparticles have a broad spectrum of activity against microorganisms, including Gram-negative and positive bacteria, as well as fungus, which is especially important for drug-resistant strains. Furthermore, prior research has shown that TiO 2 may not only kill a complex cellular congregation with major implications in pathogenicity (fungal) as concentration increases, but it can also prevent fungus development at lower concentrations (Haghighi 2013;Berridge et al. 1996;Dunne 2002).
Synthesizing TiO 2 can be done in a variety of ways. TiO 2 films may be made using a variety of physical vapor deposition (PVD) and chemical vapor deposition (CVD) processes and techniques, including sol-gel, pulsed-laser deposition, ion beam, and dc magnetron sputtering (Habibi and Talebian 2007;Stoller et al. 2007;Vijayalakshmi 2012). The dc closed-field unbalanced reactive magnetron sputtering technique offers several advantages over other techniques, particularly when it comes to producing very pure and homogenous thin films on vast areas of substrates at low processing temperatures. Changes in operating parameters such as total gas pressure, working gas pressures, inter-electrode distance, gas mixing ratio, electrical discharge power, substrate temperature, cooling rate, and sputtering time can alter the characteristics of sputtered TiO 2 films (Hussain and Wahab 2014;Yang et al. 2012;Mi et al. 2009).
In the present work, the anti-bacterial effect of TiO 2 nanoparticles was investigated as a function of concentration under light irradiation.

Experimental part
In the present work, Titanium Dioxide nanostructures were synthesized as thin films using reactive magnetron plasma sputtering deposition method. To produce TiO 2 thin coatings on glass substrates, the electric power for glow discharge which in turn generating plasma in the system was provided by a dc power supply, connected to the electrodes. The highest electrical power was 150 W, with a discharge voltage of 3 kV with a discharge current of 50 mA, and a selected distance of 4 cm between the target and the substrate. More information about the system's working conditions and parameters tuning may be obtained elsewhere (Hammadi et al. 2014;Firas 2018).
The sputtered target was a titanium sheet with a purity of 99.99%. A two-stage rotary pump (Edward 8 m 3 /h) was run at a base pressure of around 3 × 10 -2 mbar to prevent contamination of the chamber during the deposition process.To produce the discharge plasma, a glass substrate was exposed to pure argon gas at the start of the thin-film preparation process. All samples were reactively sputtered in a combination of Argon gas (99.99%) as precursor gas and Oxygen gas (99.99%) as reactive gas. The film samples were prepared as a function of different deposition time (3, 3.30, and 4 h) and three different mixing ratios of Ar:O 2 gases (50:50, 67:33, and 80:20). Before pumping the gas mixture to the deposition chamber, a stainless steel mixer was employed to control the mixing ratios. Conjunctional freezing-assisted ultrasonic extraction was used to extract nanopowder from thin-film samples (Hammadi 2018). Figure 1 shows a photo of TiO 2 sample, synthesized in the present work, as thin film and as extracted powder.
The bacteria Escherichia coli (E. coli) samples have been selected and prepared for testing in the application of photocatalytic activity. For 24 h, Escherichia coli have been cultured in nutrient broth at 37 °C. Before overnight growth, a small swab of the E. coli sample by using a sterile swab has been taken and distributed evenly on the surface of nutrient agar. TiO 2 nanopowder (extracted from the prepared films) of different concentrations 0.25, 0.5, and 1 g have been dissolved in sterilized deionized water by using an ultrasonic bath, homogenized by a vortex mixer, added to the plates, and then the dishes have been exposed to UV irradiation (200-400 nm) for 90 min. The UV source is placed at a distance of 10 cm from the Petri dish. Finally, incubated at 37 °C for 24 h and then the formation of growth inhibitory zones have been examined, as shown in the Fig. 2.

Results and discussion
The crystalline structure of the samples synthesized under various processing parameters was investigated using X-ray Shimadzu diffractometer with Cu Kα radiation (λ = 1.54060 Å) at 40.0 kV and 30 mA, Fig. 3 include x-ray diffraction patterns. The first one (A) represents the mixing phase structure (anatase /rutile) of one of the prepared TiO 2

A (101) A (004) A (200) A (105) A (211) A (118) A (116) A (220) A (125)
making a heat sink under the substrate. The weight fraction (f) of the rutile phase in an anatase-rutile combination may be calculated using the equation (Firas 2019): here ƒ is the weight fraction of rutile in mixed-phase (anatase + rutile) and I A /I R is the ratio of the intensity of anatase (I A ) phase to that of rutile (I R ) phase that is determined from the x-ray intensities. For samples prepared following deposition times of 3, 3:30, and 4 h, the relative quantities of rutile in mixed-phase (anatase-rutile) samples were 40, 46 and 50%, respectively.
On the other side, the crystallite size of the particles was calculated from Deby-Scherrer's equation using the XRD line broadening (Firas and Kadhim*, Esraa A. Al-Oubidy, 2018).
here D is the crystallite size, θ is the diffraction angle, λ is the x-ray radiation wavelength (0.15406 nm) for CuK, K is a constant typically chosen as 0.89, and β is the full-width at half-maximum (FWHM) (Balachandran et al. 2010). At gas mixing ratios of Ar: O 2 equal to 0:50, 67:33 and 80:20, the average crystallite size determined to be 18.3, 19.9 and 17.5 nm respectively for mixing phases (anatase+rutile).
In order to infer the structural properties of forming TiO 2 via sputtering method, Fourier-transform infrared (FTIR) spectroscopy in the range of 400-4000 cm − 1 (using Shimadzu 8400S FTIR) has been employed as shown in the Fig. 4. The IR absorption bands appeared at around 3454, 1637 cm −1 corresponds to the symmetric/asymmetric stretching and bending modes of vibration of a hydroxyl group (O − H bond) present in the structure, which indicate the presence of traces of water molecules due to humidity (Wei et al. 2008;Kathiravan and Renganathan 2009). The peak at 420 cm −1 is attributed to Ti-O-Ti bonds in the TiO 2 network, whereas the band assigned to Ti-O stretching vibration is at 444 and 653 cm −1 . As a result, the prepared samples, via sputtering method, may be described as extremely pure in which no peaks reflect the existence of any impurities.
AFM (Atomic force microscopy) was used to study the surface morphology. Figure  with an Ar: O 2 mixing ratio of 50:50 and a 3 h deposition time with an average roughness of 3.47 nm and a root mean square (R r.m.s. ) value of 4.33 nm, a significantly homogeneous distribution of TiO 2 nanoparticles was generated. The large surface area to volume ratio of produced TiO 2 nanoparticles may provide an advantage for using such surfaces in photonic and optoelectronic devices that use TiO 2 nanostructures. Photocatalysts are another major application of TiO 2 nanostructures with a high surface area to volume ratio. The UV-visible spectroscopy was studied in the spectral region of 300-800 nm by recording the absorption spectra of mixed-phase nanocrystalline TiO 2 film samples containing various quantities of rutile as illustrates in Fig. 6. For a sample with a 40 wt% rutile phase, an absorption edge was found at around 339 nm, whereas this edge was shifted to approximately 351 and 437 nm for samples with 46 and 50 wt% rutile phase, respectively.
The optical energy band gap (E g ) of nanocrystalline TiO 2 films can be calculated from their absorption spectra using the following equation (Zachariah et al. 2008a;Zhao et al. 2007): Photon energy(ev)

ev
where h is Planck's constant, υ is the frequency of incident photon., A is constant,, α is the linear absorption coefficient, and r is a fixed value that depends on the type of the optical transition. The value of r is choose to be 0.5 indicates direct allowed transitions. The band gap of mixed-phase nanocrystalline TiO 2 with rutile 40 wt% was estimated to be 3.43 eV, as shown in Fig. 7. While it becomes 3.39 and 3.35 eV, as the quantity of rutile is increased to 46 and 50 wt.%, respectively. This decrease in energy band gap is ascribed to the charge-separation mechanism (CSM) (Zachariah et al. 2008b). Figure 8 shows the absorption spectrum of single-phase (anatase) TiO 2 nanostructures after 3 h time deposition with a heat sink under the substrate using a 50:50 gas-mixing ratio. Figure 9 depicts the energy of this directly allowed band gap, which was determined to be 3.21 eV in as-deposited Nanostructured TiO 2 thin films with an Ar: O 2 mixing ratio50:50. Figure 10 depicts the antibacterial effectiveness of TiO 2 nanoparticles at different concentrations (0.25, 0.5 and 1) g for (single and mixed) phase against E. coli before and after photocatalytic treatment. The TiO 2 nanoparticles' activity is associated with the lightinduced generation of free radicals, which causes peroxidation when the radical reacts with the bacterial cell membrane. The extremely active oxygen species produced can oxidize organic compounds resulting in the disassembly and elimination of bacterial. The results showed that a concentration of 1 g of mixing phases of dioxide titanium nanoparticles has good antibacterial effects more than other concentrations. Based on the attained results anti-bacterial activity of dioxide titanium nanoparticles was depended on the concentration, phase of TiO 2 , and weight fraction of mixed-phase.

Conclusion
In this study, it was shown that the weight fraction of the rutile phase in the mixing phase structure rutile /anatase depends on the deposition time. On the same path, the synthesis of anatase TiO 2 can be successfully achieved without any thermal treatment via this configuration of sputtering. On the other side, it was observed that the single phase and mixing phase of TiO 2 have anti-bacterial activity with slightly preference for anatase phase. Also the anti-bacterial activity of mixing phase TiO 2 change with the rutile content, where 40% rutile content shows more activity than other contents.