Photocatalytic performance of Fluorine-doped Anatase Titanium dioxide obtained through the Sol-Gel method

Fluorine-doped anatase TiO2 nanoparticles are prepared using a simple sol-gel method in an NH4F-H2O-C2H5OH mixed solution using the precursor TTIP. The prepared samples are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and photocatalytic properties. The anatase phase TiO2 nanoparticles are identified by X-ray diffraction data. The X-ray photoelectron spectroscopy indicated that fluorine is doped effectively and most fluorine dopants might be present in the surface of TiO2 nanoparticles. The photocatalytic activity is evaluated by photocatalytic oxidation decomposition of methylene blue (MB) in atmospheric air under Visible light illumination. 84% photocatalytic efficiency observed for 5W% fluorine-doped TiO2 nanoparticles. The higher photocatalytic activity predicted is due to the formation of photocatalytic reactive radicals.


INTRODUCTION
Titanium dioxide (TiO 2 ) is one of the most popular highefficiency catalysts, due to the advantages of its high catalytic activity, environment-friendly properties, and low cost [1].In order to improve its photocatalytic property, much care has been made in current years to modify TiO 2 with different methods such as doping with metals or nonmetal ions and composite design with porous materials [2].Plenty of methods applicable to the synthesis of TiO 2 , inclusive of chemical deposition, sol-gel process, microemulsion, and hydrothermal process.Of these, the solgel method is extensively used for photocatalytic applications due to their ability to control textural properties and surface oxides.The sol-gel process is based upon the development of a polymeric oxide network [3].The familiar crystalline polymorphs of Titanium dioxide are anatase, rutile, and brookite.Each phase has differed with refractive index, chemical reactivity, photochemical response, and stability.Out of the three polymorphs, anatase phase is broadly applicable for photocatalysis [4].The photocatalytic performance of anatase phase TiO 2 nanoparticles enhanced by doped with non-metal ions.Fluorine ion is one of the nonmetal ions in order to improve the photocatalytic performance of TiO 2 nanoparticles [5].In the current study, we report the preparation and photocatalytic performance of anatase phase fluorine-doped TiO 2 nanoparticles by sol-gel method.

Preparation of fluorine doped TiO 2 nanoparticles
A total of three fluorine-doped TiO 2 nanoparticles is prepared via sol-gel method using the precursor TTIP, deionized water, and Ethanol.In this process, 100 ml of ethanol is mixed with 15 ml of TTIP in a beaker. 2 ml of acetic acid is added to the above solution and stirred for 10 minutes using magnetic stirrer.Consequently, a suitable amount of aqueous ammonium fluoride solution is added dropwise to the above solution for hydrolysis reaction.Now the solution transformed to gel.After aging 24 hours the gel is filtered and dried.Powdered samples are used for further characterization.

Material Characterization and Photocatalytic measurements
The prepared TiO 2 nanoparticles are characterized by Powder XRD using XPERT-PRO diffractometer.XPS spectrum is recorded using MULTILAB 2000 X-Ray photoelectron spectroscopy instrument.The photocatalytic activity of the fluorine-doped TiO 2 nanoparticles is evaluated by the photodegradation of MB aqueous solution with an initial concentration of 12 ppm/L.Two conventional lamps (18W) of fluorescent type is used as the light source.The degradation of the solution is analyzed by UV-Vis absorption spectra of MB recorded every 30 minutes.According to the standard curve between concentration and absorption, the value of ((C 0 -C 1 /C 0 ) x 100%) was calculated, denoted as degradation efficiency.Where D is the average crystallite size, λ is the wavelength of the X-ray radiation (1.54060 Å), β is the band broadening (FWHM) of high intense (101) peak, and θ is the diffraction angle [9,10].The average crystallite sizes are calculated to be 9.9 nm, 14.6 nm, and 16.4 nm for 1, 3 and 5 W% fluorine-doped TiO 2 nanoparticles, respectively.

XPS Analysis
The X-ray photoelectron spectroscopy (XPS) test was performed to determine the chemical composition of the samples for 5W% fluorine-doped TiO

IV. CONCLUSIONS
In summary, the fluorine-doped TiO 2 nanoparticles are prepared by the sol-gel method and investigated by XRD, XPS, and photocatalytic measurements.Anatase phase TiO 2 nanoparticles are confirmed by XRD analysis.Successful doping of fluorine with TiO 2 nanoparticles indicated by XPS spectrum.5W% fluorine-doped TiO 2 nanoparticles demonstrated a higher degradation efficiency under visible light irradiation than that of 1 W% fluorine-doped TiO 2 nanoparticles.This result indicates that our prepared fluorine-doped TiO 2 nanoparticles is a very interesting and promising photocatalytic material and has good potential for application to water purification.

Fig. 1 :
Fig. 1: XRD patterns of fluorine-doped TiO 2 nanoparticles Crystallite size of fluorine-doped TiO 2 nanoparticles are usually estimated using the Scherrer formula, 2 nanoparticles.XPS peaks indicated that the fluorine-doped TiO 2 powder contains the elements Ti, O and F. The peak at 458.11 and 529.3 eV corresponds to Ti 2p and O 1s, respectively [11].Fluorine region of XPS spectrum gone into two regions (See Fig. 3).