**2.2. Solvent controlled nonaqueous sol-gel route**

exceptional biocompatibility, corrosion resistance, high photosensitivity and reactivity, as well as

3.2 eV) [17] allows it to degrade toxic organic compounds into simple hydrocarbons such as

respectively. These electrons and holes result in formation of oxygen active species (OH\*,

fication, soil remediation, surface wettability adjustment, bacteria killing, solar cells, sensors,

ticles with controlled shape, size, good yield and high dispersibility (less agglomeration). The shape and size of nanoparticles greatly affect the photocatalytic performance of the photocatalyst [26, 27]. Highly pure metal oxides can be prepared by conventional solid state route [28], but high processing temperature requirement limits its frequent use for synthesis. The biological synthesis method [11, 29] leads to formation of cost-effective, mono-dispersed nanoparticles but reproducibility needs improvement. To overcome all these difficulties during nanoparticles synthesis, alternative well-known liquid phase synthesis methods such as sol-gel [30, 31], hydrothermal [32, 33], microemulsion [34, 35], reverse microemulsion [36], sonochemical [37, 38] and microwave [39, 40] are employed. Among these synthesis methods,

Sol-gel route can also yield multifold nanostructures such as nanoparticle, nanorods, nanotubes, aerogels and zeolites at a single platform. In addition, good yield and reproducibility

The present chapter will highlight the features of nonaqueous solvent controlled sol-gel route

synthesis strategy on structural and surface properties are correlated with photocatalytic

The sol-gel route [41, 42] involves the mixing of metal precursor into either water or organic solvent followed by formation of 3-dimensional network resulting in viscous gel, which in

photocatalyst.

nanoparticles. Effects of metal doping and

A large number of synthesis methods have been employed for designing of TiO<sup>2</sup>

the sol-gel synthesis route gets special attention because of following reasons:

**1.** Homogeneity of starting precursor at molecular scale.

**2.** Low processing temperature.

are the key features of sol-gel route.

activity of pure and metal doped TiO<sup>2</sup>

for the synthesis of pure and metal doped TiO<sup>2</sup>

**3.** Cost-effective. **4.** Easy doping.

**2. Synthesis**

**2.1. General overview**

O under UV irradiation. Under UV irradiation of energy greater than or equal to

, electrons and holes are produced in valence band and conduction band,

is well known photocatalyst largely utilized for water reclamation, air puri-

, which reacts with toxic organic compounds and decompose

(Band gap of

nanopar-

cost-effective and easy synthesis [13–16]. Semiconducting nature of anatase TiO<sup>2</sup>

CO<sup>2</sup>

H2 O2 , O<sup>2</sup> ¯, 1 O2

and H2

energy gap of TiO<sup>2</sup>

them. Thus, TiO<sup>2</sup>

) at surface of TiO<sup>2</sup>

100 Titanium Dioxide - Material for a Sustainable Environment

self-cleaning and anti-reflective surfaces [18–25].

A good alternative to surfactant assisted nonaqueous sol-gel route [45, 46] is solvent controlled nonaqueous sol-gel route. The solvent in itself plays role of oxygen donor necessary for oxide formation and stabilizing agent to control shape, size and morphology of nanoparticles. This modified sol-gel route also facilitates highly pure nanoparticles completely free

**Figure 1.** Various types of sol–gel synthesis routes.

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 following subsections, synthesis of pristine and metal doped TiO<sup>2</sup> nanoparticles using halide free, nonaqueous, solvent controlled sol-gel route [2, 10] is described.

in reduced charge recombination rate and small crystallite size respectively. There are many

of same dopant under different synthesis routes. Bessekhouad et al. [63] compared the photo

and impregnation technology. They found that photo catalytic efficiency of nanopowder prepared by impregnation technology is higher than nanopowder prepared by aqueous sol-gel

On the other hand, Yang et al. [64] showed higher photocatalytic activity of Na doped TiO<sup>2</sup> nanopowder prepared via solvothermal method. XRD analysis by Yang et al. [64], Xie et al. [65] as well as Bessekhouad et al. [63] could not confirm the doping of large sized Na into TiO<sup>2</sup>

Therefore, it is required to study the effect of synthesis method on doping mechanism and

aqueous sol-gel route. Easily dissolvable zirconium oxy-nitrate and sodium nitrate are used as precursor of Zr and Na respectively. To achieve nominal dopants concentration, calculated amount of precursor is added to solvent prior to addition of Ti precursor. After complete dissolution of dopant precursor, Ti precursor is added to reaction solution and similar steps are

nanopowder.

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,

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

ture, whereas Ru metal shows opposite behavior. Xie et al. [65] and Singh et al. [2] also reported

nonaqueous solvent controlled sol-gel route [2, 10] are used to perform XRD using Cu Kα

there are two types of doping (i) substitutional, and (ii) interstitial. Which one of these two

rutile structure in anatase phase affects the photocatalytic activity of metal doped TiO<sup>2</sup>

by sol-gel route is amorphous and therefore requires different heat treatment

nanopowder and matches with JCPDS card number 841286. In general,

lattice and therefore hinted at the tendency of large sized Na + ions to migrate to TiO<sup>2</sup>

nanopowder prepared via two methods*:* sol-gel route

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

matrix via aqueous sol-gel route decreases the photo-

matrix.

matrix individually by solvent controlled non-

prepared by sol-gel route. They observed that

lowers the A-R transformation tempera-

nanopowder. The presence of

based photocatalysts prepared by

is formed for pristine as well as in Zr

.

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

surface instead of entering in the lattice.

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

after doping

103

surface.

reports which claimed contradictory reports on photocatalytic activity of TiO<sup>2</sup>

catalytic efficiency of Na doped TiO<sup>2</sup>

route. In addition, Na doping in TiO<sup>2</sup>

catalytic efficiency due to migration of Na at TiO<sup>2</sup>

In [2, 10] Zr and Na has been doped in TiO<sup>2</sup>

followed as in preparation of doped TiO<sup>2</sup>

**3.1. Phase and structural characterization**

on A-R phase transformation temperature in TiO<sup>2</sup>

many metals such as Pt, Cr, V, Fe, La doping in TiO<sup>2</sup>

increased A-R transformation temperature in Na doped TiO<sup>2</sup>

radiation (0.154 nm). Clearly, pure anatase phase of TiO<sup>2</sup>

**Figure 2(A)** and **Figure 2(B)** shows the XRD pattern of Zr doped TiO<sup>2</sup>

respectively. Very fine powders of TiO<sup>2</sup>

as prepared TiO<sup>2</sup>

with pristine TiO<sup>2</sup>

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

photocatalytic activity of large sized metal dopants in TiO<sup>2</sup>

**3. Characterization of pristine and metal doped TiO2**
