**3.1. Phase and structural characterization**

from toxic surfactants but suffers from tendency to agglomerate. However toxic effect of halides cannot be neglected when metal oxide nanoparticles are prepared by reacting metal halides with organic solvents. In order to avoid halide impurities from metal oxide nanoparticles it is wise to use metal alkoxides, acetates or acetylacetonates as metal precursor. In the

Titanium tetra iso-propoxide (TTIP) was used as Titanium precursor and methoxyethanol as organic solvent. 20 ml TTIP is added to 40 ml methoxyethanol and mixed using magnetic stir-

lysis process. The mixing is continued until viscous gel is formed, which is then dried under

is formed after calcining the amorphous powder at 450°C for 1 hour. The chemical reactions

semiconductor and requires UV irradiation for its operation as a photo catalyst. The contribution of UV light in the solar radiation is less than 5%. Therefore, it is required to tune the band

tron and hole) resulting in less photocatalytic efficiency. Metals [10, 47–52] and nonmetals

states between valence band and conduction band. These energy states serve as charge carrier trapping center and therefore reduce the electron hole recombination rate. The reduction in electron hole recombination rate results in remarkable improvement in photocatalytic performance. In addition, noble metals (Ag, Au and Pt), transition metals [59–61] and nonmetals

surface area and consequently boosts up the photocatalytic performance. However, favorable

one transition metal, Zirconium (Zr) and one other alkali metal, sodium (Na) are discussed. Both these metals have higher ionic radii (~0.79 Å for Zr and ~1.02 Å for Na) as compared to titanium (~0.68 Å for Ti). Large ionic radii and low valence ionic metallic dopant in host Ti4+ always results in strain in the crystal structure that favors the formation of oxygen vacancies [62]. These oxygen vacancies are prone to trap electrons and suppress grain growth resulting

by doping is largely affected by synthesis methods.

<sup>4</sup> → TiO<sup>2</sup> + 2 H2 O (Condensation)

to visible range so that no extra source of radiation energy (other than solar light)

<sup>4</sup> + ROR' (Hydrolysis)

? As explained earlier, TiO<sup>2</sup>

suffers from higher recombination rate of charge carriers (elec-

to visible range. Moreover, many doped TiO<sup>2</sup>

IR lamp and pulverized to obtain amorphous powder. The pure anatase TiO<sup>2</sup>

occurring during hydrolysis and condensation in the synthesis are listed below.

<sup>4</sup> + 4 HOR' → Ti [OH]

[53–58] are well known for their ability to reduce the band gap of TiO<sup>2</sup>

nanoparticles are found to have small size as compared to pristine TiO<sup>2</sup>

In current chapter, synthesis and photocatalytic properties of TiO<sup>2</sup>

reduces the band gap of TiO<sup>2</sup>

nanoparticles using halide

, which also catalyzes the hydro-

nanopowder

is wide band gap

by generating energy

, which improves the

nanoparticles doped with

following subsections, synthesis of pristine and metal doped TiO<sup>2</sup>

rer. The pH of solution is adjusted to value 3 using 1 M HNO<sup>3</sup>

*2.2.1. Synthesis of pristine TiO2*

102 Titanium Dioxide - Material for a Sustainable Environment

Ti [OR]

Ti [OH]

*2.2.2. Synthesis of metal doped TiO2*

is required. Also, pristine TiO<sup>2</sup>

change in properties of TiO<sup>2</sup>

gap of TiO<sup>2</sup>

doping in TiO<sup>2</sup>

What is the motivation for metal doping in TiO<sup>2</sup>

free, nonaqueous, solvent controlled sol-gel route [2, 10] is described.

X-ray diffraction (XRD) is an important tool used to determine the phase purity of sample, crystal structure, lattice parameter, average crystallite size and quantitative phase analysis. Generally, as prepared TiO<sup>2</sup> by sol-gel route is amorphous and therefore requires different heat treatment to form crystalline phases. Low (300–500°C), moderate (500–700°C) and high (more than 700°C) calcination temperature results in pure anatase phase, mixture of anatase and rutile, and pure rutile phase respectively [66]. The anatase to rutile (A-R) phase transformation is largely affected by type and amount of metal doping. Choi et al. [67] studied effect of single metal ion doping on A-R phase transformation temperature in TiO<sup>2</sup> prepared by sol-gel route. They observed that many metals such as Pt, Cr, V, Fe, La doping in TiO<sup>2</sup> lowers the A-R transformation temperature, whereas Ru metal shows opposite behavior. Xie et al. [65] and Singh et al. [2] also reported increased A-R transformation temperature in Na doped TiO<sup>2</sup> nanopowder. The presence of rutile structure in anatase phase affects the photocatalytic activity of metal doped TiO<sup>2</sup> .

**Figure 2(A)** and **Figure 2(B)** shows the XRD pattern of Zr doped TiO<sup>2</sup> and Na doped TiO<sup>2</sup> with pristine TiO<sup>2</sup> respectively. Very fine powders of TiO<sup>2</sup> based photocatalysts prepared by nonaqueous solvent controlled sol-gel route [2, 10] are used to perform XRD using Cu Kα radiation (0.154 nm). Clearly, pure anatase phase of TiO<sup>2</sup> is formed for pristine as well as in Zr and Na doped TiO<sup>2</sup> nanopowder and matches with JCPDS card number 841286. In general, there are two types of doping (i) substitutional, and (ii) interstitial. Which one of these two

a nano meter length scale. In addition, grain boundaries, dislocations and structural defects could be easily identified by TEM. In this technique, a well-focused electron beam impinges on an ultrathin specimen in a high vacuum column, with the help of electromagnetic lenses. The impinged electron beam interacts with specimen and gets transmitted. A controlled and sophisticated system of electromagnetic lenses is used to focus the transmitted electron beam on a fluorescent screen. Selected area electron diffraction, diffraction contrast imaging, high resolution imaging and energy dispersive X-ray spectroscopy are some of the most commonly

**Sample TiO2 Ti0.95Zr0.05O2 Ti0.9Zr0.1O2 Ti0.96Na0.04O2 Ti0.92Na0.08O2 Ti0.9Na0.1O2**

**Table 1.** Particle size (calculated by Debye Scherrer formula) of pristine and metal doped TiO<sup>2</sup>

19.0 14.0 11.0 11.0 10.5 11.0

**Figure 3** shows the bright field TEM images, selective area electron diffraction (SAED)

by nonaqueous solvent controlled sol-gel route. Clearly, the particle size reduces with

The SAED ring pattern and HRTEM images confirm the crystalline nature of pristine as

ing with Zr and Na doping indicates large metal ion substitution at Ti site in agreement

**Figure 3.** TEM images (a, b and c with insets shows respective selective area electron diffraction pattern) and HRTEM

images (d, e and f). Figure (b&e) reprinted with permission from Ref. [10]. Copyright 2017, Elsevier.

nanopowder prepared

nanoparticles.

http://dx.doi.org/10.5772/intechopen.74568

105

. The increase in lattice spac-

, which is in agreement with XRD results.

nanoparticles. The SAED diffraction rings could be indexed as

Novel TiO2 Photocatalyst Using Nonaqueous Solvent-Controlled Sol-Gel Route

used TEM techniques for the characterization of materials.

metal doping in comparison to pristine TiO<sup>2</sup>

well as metal doped TiO<sup>2</sup>

with XRD results.

Particle size (nm)

patterns and HRTEM images of pristine and metal doped TiO<sup>2</sup>

(101), (004) and (200) lattice planes of pristine anatase TiO<sup>2</sup>

**Figure 2.** The XRD patterns of Zr (A) and Na (B) doped TiO<sup>2</sup> nano-powder calcined at 450°C for 1 hr.: (a & e) pristine TiO<sup>2</sup> ; (b) Ti0.95Zr0.05O<sup>2</sup> ; (c) Ti0.90Zr0.10O<sup>2</sup> ; (d) Ti0.85Zr0.15O<sup>2</sup> ; (f) Ti0.96Na0.04O<sup>2</sup> ; (g) Ti0.92Na0.08O<sup>2</sup> and (h) Ti0.90Na0.10O<sup>2</sup> . Figure (A) reprinted with permission from Reference [10]. Copyright 2017, Elsevier.

types of doping is favored, depends on size of guest ion as compared to host ion and volume size of interstitial position in the host lattice. Substitutional doping is preferred in case where size of guest ion is comparable or slightly larger than lattice ion, whereas if size of guest ion is much smaller than lattice ion then it occupies interstitial position of host lattice.

XRD peaks of crystal planes of Zr doped TiO<sup>2</sup> (**Figure 2(A)**) shows red shift in 2θ values, which confirms the substitutional doping of Zr4+ at Ti4+ site [10]. The substitutional doping of Zr in TiO<sup>2</sup> results in an increase in cell parameter and cell volume as reported by Yu et al. [68] and Wang et al. [69] Thus, incorporation of large sized Zr results in lattice strain and hence leads to formation of oxygen vacancies and suppresses the grain growth. Similar behavior is observed for Na doped TiO<sup>2</sup> nanopowder (**Figure 2(B)**) [2]. However formation of oxygen vacancies in Na doped TiO<sup>2</sup> can occur not only due to strain induced by Na doping but also due to lower valence state of Na+1 ion. It should be noted that there are contradictory literature reports regarding doping of Na in TiO<sup>2</sup> . Xie et al. [65] who used aqueous sol-gel synthesis, reported that large size Na cannot substitute Ti and therefore migrates to TiO<sup>2</sup> surface forming Na-O bonds as there is no peak shift is observed in XRD patterns. Thus it appears that substitutional doping of Na at Ti in TiO<sup>2</sup> , as indicated by the XRD peak shifts in **Figure 2(B)**, is facilitated by nonaqueous solvent controlled sol-gel route, which was used by Singh et al. [10].

The crystallite size of pristine and doped TiO<sup>2</sup> nanopowder are calculated by well-known Debye Scherrer formula and tabulated in **Table 1**. In both, Zr doped TiO<sup>2</sup> and Na doped TiO<sup>2</sup> , the crystallite size reduces for certain dopant concentration and hence increases the surface area of nanoparticles. Additionally, A-R phase transformation temperature is increased due to doping Zr4+ and Na+1 in TiO<sup>2</sup> matrix [10, 65, 68, 69].

#### **3.2. Microstructural characterization**

XRD gives structural information like lattice constant and crystalline phases averaged over bulk of the material. TEM on the other hand is able to give microstructural information on


**Table 1.** Particle size (calculated by Debye Scherrer formula) of pristine and metal doped TiO<sup>2</sup> nanoparticles.

a nano meter length scale. In addition, grain boundaries, dislocations and structural defects could be easily identified by TEM. In this technique, a well-focused electron beam impinges on an ultrathin specimen in a high vacuum column, with the help of electromagnetic lenses. The impinged electron beam interacts with specimen and gets transmitted. A controlled and sophisticated system of electromagnetic lenses is used to focus the transmitted electron beam on a fluorescent screen. Selected area electron diffraction, diffraction contrast imaging, high resolution imaging and energy dispersive X-ray spectroscopy are some of the most commonly used TEM techniques for the characterization of materials.

**Figure 3** shows the bright field TEM images, selective area electron diffraction (SAED) patterns and HRTEM images of pristine and metal doped TiO<sup>2</sup> nanopowder prepared by nonaqueous solvent controlled sol-gel route. Clearly, the particle size reduces with metal doping in comparison to pristine TiO<sup>2</sup> , which is in agreement with XRD results. The SAED ring pattern and HRTEM images confirm the crystalline nature of pristine as well as metal doped TiO<sup>2</sup> nanoparticles. The SAED diffraction rings could be indexed as (101), (004) and (200) lattice planes of pristine anatase TiO<sup>2</sup> . The increase in lattice spacing with Zr and Na doping indicates large metal ion substitution at Ti site in agreement with XRD results.

types of doping is favored, depends on size of guest ion as compared to host ion and volume size of interstitial position in the host lattice. Substitutional doping is preferred in case where size of guest ion is comparable or slightly larger than lattice ion, whereas if size of guest ion is

; (f) Ti0.96Na0.04O<sup>2</sup>

which confirms the substitutional doping of Zr4+ at Ti4+ site [10]. The substitutional doping of

and Wang et al. [69] Thus, incorporation of large sized Zr results in lattice strain and hence leads to formation of oxygen vacancies and suppresses the grain growth. Similar behavior

due to lower valence state of Na+1 ion. It should be noted that there are contradictory literature

ing Na-O bonds as there is no peak shift is observed in XRD patterns. Thus it appears that

facilitated by nonaqueous solvent controlled sol-gel route, which was used by Singh et al. [10].

the crystallite size reduces for certain dopant concentration and hence increases the surface area of nanoparticles. Additionally, A-R phase transformation temperature is increased due

XRD gives structural information like lattice constant and crystalline phases averaged over bulk of the material. TEM on the other hand is able to give microstructural information on

matrix [10, 65, 68, 69].

results in an increase in cell parameter and cell volume as reported by Yu et al. [68]

(**Figure 2(A)**) shows red shift in 2θ values,

nano-powder calcined at 450°C for 1 hr.: (a & e) pristine

and (h) Ti0.90Na0.10O<sup>2</sup>

nanopowder (**Figure 2(B)**) [2]. However formation of oxygen

. Xie et al. [65] who used aqueous sol-gel synthesis,

, as indicated by the XRD peak shifts in **Figure 2(B)**, is

nanopowder are calculated by well-known

surface form-

. Figure (A)

,

and Na doped TiO<sup>2</sup>

can occur not only due to strain induced by Na doping but also

; (g) Ti0.92Na0.08O<sup>2</sup>

much smaller than lattice ion then it occupies interstitial position of host lattice.

; (d) Ti0.85Zr0.15O<sup>2</sup>

reported that large size Na cannot substitute Ti and therefore migrates to TiO<sup>2</sup>

Debye Scherrer formula and tabulated in **Table 1**. In both, Zr doped TiO<sup>2</sup>

XRD peaks of crystal planes of Zr doped TiO<sup>2</sup>

**Figure 2.** The XRD patterns of Zr (A) and Na (B) doped TiO<sup>2</sup>

reprinted with permission from Reference [10]. Copyright 2017, Elsevier.

; (c) Ti0.90Zr0.10O<sup>2</sup>

104 Titanium Dioxide - Material for a Sustainable Environment

is observed for Na doped TiO<sup>2</sup>

to doping Zr4+ and Na+1 in TiO<sup>2</sup>

**3.2. Microstructural characterization**

reports regarding doping of Na in TiO<sup>2</sup>

substitutional doping of Na at Ti in TiO<sup>2</sup>

The crystallite size of pristine and doped TiO<sup>2</sup>

vacancies in Na doped TiO<sup>2</sup>

Zr in TiO<sup>2</sup>

TiO<sup>2</sup>

; (b) Ti0.95Zr0.05O<sup>2</sup>

**Figure 3.** TEM images (a, b and c with insets shows respective selective area electron diffraction pattern) and HRTEM images (d, e and f). Figure (b&e) reprinted with permission from Ref. [10]. Copyright 2017, Elsevier.

method is based on the degradation of organic dye methylene blue (MB) by photo catalyst under UV irradiation. The degradation results are further confirmed by measuring total organic carbon (TOC) of initial dye aqueous solution and degraded dye aqueous solution by TOC analyzer.

aqueous solution of MB dye under ultraviolet (UV) irradiation. In order to compare photocatalytic activity of photo catalyst prepared by nonaqueous solvent controlled sol-gel route with commercial photo catalyst, the photocatalytic activity of well-known commer-

ous solution is 5 mg/L. About 100 ml of MB dye aqueous solution (pH 5) is taken in 100 ml borosil glass beaker and 60 mg of photo catalyst is added in the solution. The beaker is kept on magnetic stirrer for uniform suspension of photo catalyst in the solution throughout the experiment. The reaction mixture is irradiated by UV light of peak wavelength at 365 nm and the intensity of UV light at the surface of reaction mixture is 10 mW/cm<sup>2</sup>

The distance between reaction mixture and UV light source is 20 cm resulting in light

equilibrium between photo catalyst and dye, the reaction mixture is stirred for 20 minutes in completely dark chamber. After achieving adsorption-desorption equilibrium, the reaction mixture is irradiated with UV light and a small amount of solution is withdrawn at regular time intervals. The withdrawn sample is centrifuged to separate out nanoparticles from the solution and absorbance of supernatant measured using UV-Visible spectrometer. The photocatalytic degradation percentage of dye for different time intervals is plotted

The degradation percentage of dye is calculated using Eq. 1. The rate constant (k) for the pho-

In order to further confirm the degradation results, TOC of irradiated and nonirradiated dye aqueous solution is measured and TOC removal rate percentage is calculated using Eq. 3.

are the TOC values of dye solution before and after time 't' of UV

tocatalytic degradation of dye is determined from pseudo first order law using Eq. 2.

lux over reaction mixture. In order to complete adsorption-desorption

is evaluated by degrading

http://dx.doi.org/10.5772/intechopen.74568

)/C0) × 100 (1)

is dye concentration after t time

) = kt (2)

)/TOC0) × 100 (3)

.

107

is also evaluated. The initial concentration of MB aque-

Novel TiO2 Photocatalyst Using Nonaqueous Solvent-Controlled Sol-Gel Route

The photocatalytic activity of pristine and metal doped TiO<sup>2</sup>

for several photo catalysts and without catalyst (WC).

Degradation % = ((C0 − Ct

is dye concentration before UV irradiation and C<sup>t</sup>

ln (C0 /Ct

TOC % = ((TOC<sup>0</sup> − TOC<sup>t</sup>

and TOC<sup>t</sup>

**4.1. Degradation experiment**

cially available Degussa P25 TiO<sup>2</sup>

intensity of 8 × 104

where C0

where TOC<sup>0</sup>

irradiation respectively.

of UV irradiation.

**Figure 4.** (A) Principle of photoluminescence spectroscopy. (B) PL spectra of pristine and Na doped TiO<sup>2</sup> nanopowder.

#### **3.3. Photoluminescence study**

Photoluminescence (PL) spectroscopy is a versatile and powerful optical method to investigate the energy levels in materials. The material is irradiated with light photons of energy greater than or equal to band gap energy of material. This results in the excitation of electrons from valence band to the excited states (**Figure 4(A)**) of material. These electrons relax to conduction band by losing excess energy via nonradiative process. When these electrons return to their valence band, the energy is released in the form of photons and the process is known as photoluminescence. The energy of emitted photons is determined by the difference in atomic energy levels, while the intensity of emitted light gives us information regarding recombination of electrons and holes.

The energy and intensity of emitted light in PL spectra of particular material is highly affected by doping. **Figure 4(B)** shows the PL spectra of pristine and Na doped TiO<sup>2</sup> nanopowder at excitation wavelength 390 nm. The shape of PL signal remains same while intensity reduces with increase in doping concentration of Na in TiO<sup>2</sup> matrix. This is attributed to the fact that Na doping in TiO<sup>2</sup> matrix results in formation of oxygen vacancies resulting in energy states lying between valence band and conduction band that trap the electrons form conduction band and thereby reduce electron-hole recombination [68]. However, the PL signal intensity increases for Ti0.9Na0.1O<sup>2</sup> sample. This is attributed to fact that excessive formation of oxygen vacancies might act as recombination centers [70].
