This paper study the synthesis of the TiO2 nanoparticles using the sol-gel method and TiCl4 as raw material (TiO2 sol-gel) and characterize it and TiO2 pure by Powder X-Ray Diffraction (XRD), both samples show they are anatase phase with high crystallinity and purity. Fourier transform infrared spectrum (FTIR) both samples it showed in the graph that TiO2 pure, TiO2 sol-gel various frequency vibrations which are shown by different peaks formed, The specific surface area and porosity of the TiO2 pure (46.962 m²/g) and TiO2 sol-gel (38.264 m²/g) were evaluated by using the nitrogen adsorption and desorption isotherms by using Brunauer-Emmett-Teller (BET) method. Using Ocean Optio USB- 2000 spectrometer for optical properties which are related to the absorption spectrum but using diffuse reflectance spectrum in the state of the Kubelka-Munk remission function replaces the Lambert-Beer law.
Nanotechnology is a broad and intense area of res-earch and development that has been growing world-wide in the past decade. Nano-materials are subs-tances whose dimension is less than approximately 100 nanometers (Hayle, 2014). Nanocrystalline semi- conductors have achieved great importance in the industrial world today (Wang, 2010; Qu, 2013) which include metal oxides (ZnO, V2O5, Fe2O3, SnO2, CdO, and TiO2) and metal sulphide (CdS and ZnS) (Karunakaran, 2004). Titanium dioxide is an important semiconductor material due to its proper-ties such as cheap, nontoxic, photo-chemical and chemical stability, high refractive index, wide band gap (Cassano, 2000; Wang, 2010). Soit was applied in environmental protection, paint, toothpaste, UV protection, photo-catalysis, photo-voltaics, electro-chromics, gas sensing, dye-sensitized solar cells, photo-induced hyrophilicity, and soon (Liu, 2007; Chen, 2006; 2012; Ohenoja, 2013). Titanium di-oxide crystallized in four natural phases: brookite (orthorhombic), anatase (tetragonal), rutile (tetraga-nol) and TiO2 (B) (monoclinic). The three crystal structures of TiO2 are shown in Fig. 1. Besides these polymorphs two additional high- pressure forms have been synthesized from rutile; the first form is TiO2 (ӀӀ) with a PdO2 structure (Simons, 1967) and the second form is TiO2 (H) with a hollandite struc-ture (Latroche, 1989; Yousif and Ali, 2021).
Among the titanium dioxide forms rutile phase is the most thermodynamically stable whereas brookite are transformed to rutile on heating (Ohenoja, 2013). Various investigations have established that TiO2 is much more effective as a photo-catalyst in the form of nanoparticles than in bulk powder. During the past two decades, several synthetic methods have been used to prepare TiO2 nanoparticles (Su, 2006).
Fig. 1: Crystal structures of (a) TiO2anatase, (b) brookite, and (c) rutile.
Generally, the methods of preparing nano-TiO2 are gas methods (chemical vapor deposition CVD, phy-sical vapor deposition PVD and spray pyrolysis) and liquid methods (co-precipitation, solvothermal, microemulsion, combustion synthesis, electroche-mical synthesis, sol-gel methods) (Carp, 2004).
Liquid methods are often used because they do not need any special equipment in comparison with gas methods (Chen, 2006). Properties of nano-TiO2 particles are dependent on synthesis method which is responsible for their chemical purity and its crys-tal form (anatase or rutile) also on various particle features (specific surface area and particle size), crystallinity and surface chemistry (Carp, 2004). Among these methods, sol-gel method is regarded as good method for synthesis ultra-fine metallic oxide and has been widely employed for preparing tita-nium dioxide nanoparticles (Su, 2006).
The sol-gel method has many advantages such as purity, stoichiometry control, ease of processing, and control over composition (Carp, 2004). The us-ually sol-gel procedure includes three steps; hydro-lysis, drying, and calculation. There are two types of titanium sources for preparation of nano-TiO2 par-ticles which include organic titanium alkoxide (tita-nium iso-propoxide Ti(i-OP)4, Titanium ethoxide Ti(OE)4, etc.) and inorganic titanate (titanium tetra-chloride TiCl4, titanium trichloride TiCl3 or Tita-nium sulphate TiO(SO4)2) (Carp, 2004). When using Titanium alkoxide expensive chemicals must be used and the hydrolysis process is difficult to control; otherwise, tetrachloride TiCl4 is cheap, easy control of hydrolysis (Zhu, 2000; Chen, 2006). Titanium dioxide has been prepared in different morphologies powder, thin film, annotates and nanorods (Burda, 2005; Banu et al., 2021).
The sol-gel method was used for the syn-thesis titanium dioxide nano particle with using titanium tetrachloride as a precursor. And study its and tita-nium dioxide pure properties by using X-Ray Dif-fraction (XRD), micrometric gas adsorption analyzer by using Brunauer-Emmett-Teller (BET) method, Ocean Optic-USB-2000 spectrometer.
Pure Titanium dioxide from Aldrich, Titanium tetra-chloride TiCl4 (Mwt 189.87gmol-1, 99.9%), absolute Ethanol, Ammonium hydroxide (Mwt 17.03gmol-1, 25%), di-ionized water, silver nitrate (Mwt 169.87 gmol-1, 98.4%).
Preparation catalyst
A sample of titanium dioxide nanoparticles was synthesized by using the Sol-gel method, 30cm3 of titanium tetra chloride was added to 500 cm3 di-ionized water in an ice bath under fume-hood followed by the addition 350 cm3 of ethanol with vigorous stirring for half of the hour at room temperature. Justified the pH to 8 by adding am-monia solution 25% drop by drop and precipitate was obtained.
After stirring vigorously then the solution was made to settle for 24 hours. Then the precipitate was separated by using a centrifuge and washed to re-move chloride ions using silver nitrate to detect that then the precipitate was dried at 200oC for two hours and an amorphous TiO2 was obtained. At last obtain-ned the powder of titanium di-oxide nanoparticles (Uddin et al., 2021; Hayle, 2014)
Methods of Characterization of TiO2 Nanoma-terials
There are many methods to characterize TiO2 nano-material. In this study used X-ray powder diffraction (XRD) was performed using PAN-alyticals X-ray diffract meter (Cu X-ray λ = 1.540598Å) over a range (10-60)° 2θ the powdered sample was packed on the sample holder by back pressure technique and mounted on the sample stage of the machine then determination the particles structure crystal size from the XRD pattern.
The crystallite sizes of the TiO2 nano-materials were estimated using Scherer equation (1) (Han, 2012; Hayle, 2014).
Where d is the crystallite size in nanometer, K is the shape factor constant, which is 0.89, β is the full width at half maximum (FWHM) in radian, λ is the wave length of the X-ray which is 0.1540598nm for Cutarge tKα radiation and is the Bragg angle, Micrometric gas adsorption analyzer.
The specific surface area and porosity of the two samples were evaluated by using the nitrogen pres-sure sata constant temperature (typically liquid N2, 77K) the sample loaded (0.1036g of sample 1, 0.60 98g of sample 2) (Analysis Time is 281.6 min for sample 1,571.2 min for sample 2) then nitrogen adsorption isotherm of both samples were analyzed for the specific surface area using the BET equation (3) which required a linear plot of1/[W(P/P0)-1] against P/P0.
Ocean optio USB2000 Spectrometer stat up by connect it to desktop PC via USB port or serial port, Ocean Optics OOI Base32 software application installed and configured for use with the USB 2000 OOIBase32 can use to get spectroscopic measurements (such as absor-bance, reflectance, and emission) .
At first stored reference and dark measurements then the light transmits through an optical fiber to the sample. There is another optical fiber collects and transmits the result of the interaction to the spectro-meter, then OOIBase32 compares the sample to the reference measurement and displays the spectral infor-mation. In reflectance spectroscopy, the Kubelka-Munk remission function F(R) replaces the Lambert-Beer law (Sikorska, 2003).
Sol-gel TiO2 catalyst
Where W = weight of gas adsorbed, P/P0 =relative pressure, Wm = weight of adsorbate as monolayer, C = BET constant. Using FTIR-8400S Fourier transform infrared spectroscopy to analyzed the both samples.
The samples were grind down with KBr and press to make disk and insert into the sample holder then take the FTIR spectra in range (400 – 3000cm-1).
When TiCl4 solution was added to two of di-ionized water under fume hood, an exothermic reaction was observed. Then, a white precipitate was obtained after adding a drop of ammonium hydroxide (NH4OH) wisely; and the yellow gel rose this indicates the form-ation of Ti(OH)4.
After stirring the solution settling and centrifuging and drying the precipitate which leads to the formation of white amorphous TiO2; then cooling, grinding and calcination lead to the form-ation of white powder TiO2 nanoparticles. The Weight of precipitate before calcimined is 19.2005g. The weight of precipitate after calcinated is 14.4458g.
Characterization of the catalysts
As can be observed from Fig. (1 and 2), the XRD peaks in the angle range of 20°˂ 2θ° ˂ 60° for TiO2 (pure) which are 25.4039°, 36.9877°, 37.8628°, 38.6280°, 48.0839°, 53.9365° and 55.1030°an for TiO2(sol-gel) which are 25.3275°, 37.8174°, 48. 0607°, 53.8852°, and 55.0714° among the XRD peaks. The width of 25.4039° for TiO2 (pure) and 25.3275° for TiO2 (sol-gel) are useful peak since they have a high intensity which in turn are used to determine crystals size. According to (Hayle, 2014) the peaks values correspond to the tetragonal ana-tase phase. Using equation (1) the estimated crys-talline size is explored in the following table.
Table 1: Crystallite size (d) of pure TiO2 & sol-gel TiO2nano-materials.
Fig. 1: The XRD pattern of TiO2 (pure).
A sharp increase in adsorption volume of N2was observed and located in the P/Po range of (0.067 - 0.88), (0.36 – 0.89) for TiO2 pure and TiO2 sol-gel respectively. The specific surface area value of the TiO2 pure is 46.962 m²/g and the specific surface area value of the TiO2 sol-gel is 38.264 m²/g (Govin-daraj, 2015).
Fig. 2: The XRD pattern of TiO2 (sol- gel).
Micrometric gas adsorption analyzer
Fig. (3a, b) is shown the nitrogen adsorption and desorption isotherm which exhibits a type IV pat-tern with hysteresis loop characteristic of meso-porous material according to the classification of IUPAC.
Fig. 3: a. Nitrogen Adsorption-Desorption isotherm of pure TiO2 b. Nitrogen Adsorption-Desorption isotherm of TiO2sol-gel.
Fourier transforms infrared (FTIR) spectroscopy
In this graph different peaks formed at different wave numbers (400-3000cm-1). It is noticed that TiO2 pure, TiO2 sol-gel various frequency vibrations which are shown by different peaks formed. The peak in the range (400 – 800cm-1) was characteristic Ti-O. The peak in range 1426-1696cm-1 was charac-teristic of the O-Ti-O bond and Ti= =O bending region. In Fig. 4b there is the peak in the range (2000-3000) is characteristic O-H (Grujić, 2006).
Fig. 4: (a). The FTIR spectra of TiO2 pure; (b). The FTIR spectra of TiO2 sol-gel.
Optical properties using USB 2000 spectrometer
Fig. 5 displays the reflectance spectra of TiO2 pure which has a maximum value at region (371-408nm), (483- 506nm) and above 650nm. We noticed the reflectance spectrum is decreased in region (410-629). The reflectance spectra of TiO2 sol-gel it. Has a maximum value at region (373-694nm) the curve s reachs saturation above 669nm.We noticed the ref-lectance spectra are decreased in the region (520-540nm),(576 - 584) and (657- 690nm).
The optical absorption coefficient, α, which is the relative rate of decrease in light intensity along its path of propagation, was calculated using equation (5) from the transmittance and reflectance data in the wavelength range 300-800nm. The nature of the optically induced transitions was determined from these data (Baydogan, 2013; and Rabeh, 2014).
Fig. 5: The reflectance spectra of (TiO2pure) and TiO2sol-gel.
Fig. 6: Diffuse reflectance spectrum of TiO2 pure and TiO2 sol-gel with Kubelka-Monk conversion.
Fig. 7: The optical absorption coefficient of TiO2 pure and TiO2sol-gel.
Where T is the transmittance, R is the reflectance, and d is the sample thickness. The optical absorp-tion coefficient was found to be exponentially dep-endent on the photon energy. However, when the particle size decreases the optical absorption coeffi-cient will increase Fig.7 show that TiO2 sol-gel has a high value of 0.99 at 384nm and TiO2 pure has 0.92 at 379nm.
Fig. 8: The extinction coefficient TiO2 pure and TiO2sol-gel.
The extinction coefficient which is shown in Fig. 8 was calculated using equation (6)
Where k is the extinction coefficient, α is the absorp-tion co-efficient and λ is the wavelength. The differ-ence in values of extinction coefficient for two samples TiO2 pure (0.32), and TiO2 sol-gel due to that TiO2 sol-gel has a small particle size. The refractive index deter- mined using transmittance and reflectance measure-ments from Fig. 9 is noticed that there refractive index has a maximum value of 11 at wavelength 415 nm for TiO2 pure and 16.3 at wavelength 384 nm for TiO2 sol-gel which is due to interactions takes place between photons and electrons. The refractive index changes with the variety of the wavelength of the incident light beam due to these interactions, i.e. the optical loss caused by absorption and scattering (Baydogan, 2013).
Fig. 9: The refractive index of TiO2 pure and TiO2sol-gel.
The energy band gap of these materials is deter-mined using the reflection spectra. According to the Tauccrelation, the absorption coefficient is given by Sharma equation (7) (Rabeh, 2014).
Where Eg is the energy gap, B constant is different for different transitions, (hν) is the energy of photon and n is an index which expects the values 1/2, 3/2, 2, and 3 depending on the nature of the electronic transition responsible for the reflection. The exponent r = 1/2, 3/2 for indirect transition is allowed or forbidden in the quantum mechanical sense, and r=2, 3 for allowed and forbidden direct transition, respectively. From Fig. 10 the energy band gap is 3.07 eV for TiO2 pure and 3.23 for TiO2 sol-gel (Baydogan, 2013; Rabeh, 2014).
Fig. 10: The optical energy gab spectrum for TiO2 pure and TiO2sol-gel.
TiO2 nanomaterial was prepared by using the most convenient ways of synthesizing method known as sol gel synthesis. Sol-gel is and easy method due to low cost and is done at low temperature. XRD re-sults exhibited the interesting peak value are (25. 4039°, 25.3275°) which is anatase TiO2 nano- mate-rial due to (49.11070, 22.08194nm) for TiO2 pure and TiO2 sol-gel respectively. The specific surface area and porosity of theTiO2 pure and TiO2 sol-gel were evaluated by using the nitrogen adsorption and desorption isotherms, the specific surface area of the TiO2 pure are 46.962 m²/g and The specific surface area of the TiO2 sol-gel are38.264 m²/g. The isotherm exhibits a type IV pattern with a hysteresis loop. From the FTIR spectrum both samples obser-ved that TiO2 pure, TiO2 sol-gel various frequency vibrations which are shown by different peaks formed. Optical properties are studied by using the Diffuse reflectance spectrum in which the Kubelka - Munk remission function replaces the Lambert-Beer law. TiO2sol-gel has an optical absorption co-efficient (0.99), extinction coefficient (1), a refra-ctive index 16.3 and the energy band gap of 3.23eV while TiO2 pure has optical absorption coefficient of 0.92, extincttion coefficient (0.32), there refr-active index 11 and the energy band gap 3.03eV.
Express gratitude to all who encouragement and helping. Thank Industrial Research and Consulting Center and especially thank Dr. Abd Elsakhi for his help.
The authors declare that the manuscript has no com-peting interests to the publication.
Academic Editor
Dr. Toansakul Tony Santiboon, Professor, Curtin University of Technology, Bentley, Australia.
College of Science, Dept. of Chemistry, Sudan University of Science & Technology, Sudan
Elrazeg YA, Badiruzzaman M, Islam M, Morshed MM, and Elmugdad AA. (2022). Synthesis of titanium dioxide by sol-gel method and comparison with titanium dioxide pure, Int. J. Mat. Math. Sci., 4(3), 75-82. https://doi.org/10.34104/ijmms.022.075082