**2.2. Impregnation method**

The titania has been employed as a photocatalyst in several photocatalytic reactions due to its high photoactivity, low cost, low toxicity and good chemical and thermal stability [1–3]. However, its large energy band gap inhibits it from being active under UV light [31–35]. The solar spectrum consists of only 4–5% UV light and around 40% visible light [31].

to improve the photocatalytic efficiency of TiO<sup>2</sup>

has been attempted. The metal doping agents introduced for TiO2

irradiation is necessary. The modification by non-metal [36–51] and metal [52–83] doping

metals (Fe, Cu, Cr, Co, and Ni) [52–56] and noble metals (Ag, Au, Pd, and Pt) [57–83]. Among the noble metals, silver has received considerable interest due to its additional potential as an antibacterial agent [84]. The importance of medical applications of metal-

manufacturing silver-doped titania. There are ongoing works related with the use of Ag for possible medical devices [79], dental implants [78, 79], food packagings [80], air conditioning filters, and so on [79]. Some works focus on bacterial inactivation [34, 63] and dye waste treatment under visible light irradiation [66, 67, 81–83]. Hence, the preparation and

The sol-gel method involves the interaction of titania sol with silver ion the solution, which forms a gel. The gel is heated at a low temperature to evaporate the solvent followed by calcination at high temperature [31, 35, 72, 73, 78, 80, 82, 83]. The main precursor of titania is com-

Titania sol is prepared by mixing TTip solution in ethanol and water accompanied by stirring vigorously at room temperature for about 15 min. During the dissolution of TTip in the ethanol medium, an exchange of propyl group from TTip with ethyl group from the ethanol to yield titania tetra ethoxides takes places by the release of propanol. Titanium tetra ethoxide

sol of silver. Finally, the silver sol is added dropwise to the titania sol with stirring, where transparent titania sol changes its viscous yellow solution. The reaction between titania sol

<sup>4</sup> + C2 H5 O − AgTi (OH)

is frequently employed [31, 72, 75, 77, 80, 82, 83]; however, silver acetylacetonate

solution is mixed with ethanol and stirred [31, 72, 75, 77, 80, 82, 83], giving the

monly liquid titanium(IV) isopropoxide (TTiP) with a chemical formula of Ti(OC3

H9 ) 4


as a photocatalyst under sunlight irradiation is limited.

under sunlight visible

H7 ) 4 [31, 35,

[6–11] attracts researchers to think of

[82, 83] is also potential. For silver starting mate-

<sup>3</sup> − Ag + C2 H5 OH (1)

.

are transition

Therefore, the efficiency of TiO<sup>2</sup>

332 Titanium Dioxide - Material for a Sustainable Environment

characterization of the TiO2

**2. Preparation of TiO2**

72, 75], but titanium n-butoxide (Ti(OC4

and silver sol is commonly written as follows:

is also chosen sometime [35].

Ti (OH)

**2.1. Sol-gel**

rial, AgNO3

The AgNO3

lic silver [85, 86] and antibacterial activity of TiO2

**-AgNP**

is hydrolyzed in acidic medium to form sol titanol of Ti(OH)4

Modification of TiO<sup>2</sup>

on TiO2

The synthesis of TiO2 -AgNP by impregnation method is carried out by stirring the solution of AgNO3 mixed with the suspension of TiO2 in water for 24 h. The solvent is later removed by drying at 150°C followed with calcination of the product at 500°C [68]. Some modifications in the impregnation method such as the use of capping agent [74] and combustion method [63, 64] are also possible.

The modification starts with silver nanoparticles preparation in polyvinylpyrrolidone (PVP) as a capping agent. For this purpose, the AgNO3 solution is added to methanol and is mixed with PVP. The mixture is refluxed for 3 h at 110°C to give a yellow-orange color solution. The solvent was evaporated at 55°C, and the obtained Ag nanoparticles were dispersed into ethanol and thoroughly washed with hexane and ethanol. The Ag nanoparticles are redispersed into the ethanol under sonication, and TiO2 powder is added to the solution. This mixture is sonicated for 3 h and is dried at 60°C to remove the solvent followed temperature rise to 90°C [74].

The combustion method is carried out by heating a mixture of AgNO3 , titanyl nitrate and glycine as fuel in the muffle furnace at 150°C for 2 h [63, 64]. The remaining solid from the combustion is supposed to be TiO2 -AgNP.
