**2.5. Other methods**

There are several other methods for TiO2 -AgNP preparation, including graphene oxidation [57], radiolitic reduction by using γ-ray [61], electrolytic oxidation-reduction [62], and mirror reaction [65].

#### **3. Characterization of TiO2 -AgNP photocatalyst**

#### **3.1. The existence of the silver species in TiO2 -AgNP**

The content of Ag incorporated in the TiO2 crystal structure prepared by sol-gel, precipitation and photodeposition can be determined by elemental analyses by X-Ray Fluorescence (XRF) [68, 75], ICP-MS [35] and atomic absorption spectrophotometry (AAS) [83]. In general, the content of Ag formed in TiO2 -AgNP is proportional to the initial concentration of precursors of the AgNO3 solution.

is found to be more than 0.80 moles% [66], but 0.25 moles% or higher is also reported [68].

/Ag-0.05%, (c) TiO2

or metallic silver Ag0

can be distinguished by XPS. The XPS spectrum shows the characteristic Ag 3d peak that has a binding energy of 368 eV with a 6.0 eV splitting of the 3d doublet of low spin 3d1/2 and high

ferent from the XRD data that can only provide the metallic silver in high level; the XPS gives

calcined at 350°C [72] shows reduction peak at around 135°C, which suggests a reduction of Ag+

spectra peak at around 350 and 500°C, probably due to Ag reduction with support material [72].

is meant to allow the TiO2

energy (Eg) or absorption in visible light. The band gap energy (Eg) can be determined based

spin 3d5/2 [33]. It confirms that the presence of metallic silver deposits on the TiO<sup>2</sup>

metallic without interacting with the support. Also, TiO2

reduction (TPR) spectrometry technique. The profile of the TPR spectra of sol-gel TiO<sup>2</sup>


/Ag-0.10%, (d) TiO2

Silver Nanoparticle Incorporated Titanium Oxide for Bacterial Inactivation and Dye Degradation


**-AgNP**

*-AgNP on the absorption shift into visible light*

photocatalyst under visible is assigned by the lower band gap

, in the TiO2

/g-0.15%,(e) TiO2

http://dx.doi.org/10.5772/intechopen.75918

335


/Ag-0.25%, and (f)




to be active under visible light. The

[33]. It is dif-


Depending on the concentration, the detectable metallic silver in TiO2

, (b) TiO2

ing step causes Ag particles to form large aggregate [31].

additional proof that the metallic silvers are formed in TiO2

**3.2. Band gap energy (Eg) and absorption edge (λ) of TiO<sup>2</sup>**

in the XRD pattern when TiO<sup>2</sup>

**Figure 1.** XRD patterns of (a) TiO<sup>2</sup>

/Ag-0.50% [71].

The existence of Ag in TiO2

*3.2.1. Mechanism and role of Ag in TiO2*

The incorporation of Ag on TiO2

photocatalytic ability of TiO2

into Ag0

TiO2

The valence state of silver, as ionic Ag+

The presence of Ag in the TiO2 -AgNP can be detected by XRD method. It can be carried out by detecting X-ray diffraction pattern evolution with the reference of native TiO<sup>2</sup> . The XRD pattern of TiO<sup>2</sup> recorded by using a CuKα source of XRD machine gives several characteristics peaks of 2θ values at 25.091, 37.651, 48.021, 53.891, 55.071, 62.381, 68.701, 70.041 and 75.001. These peaks are confirmed with JCPD Card No. (21-1272) and are attributed to the diffraction of TiO2 anatase. They correspond to the lattice planes (101), (004), (200), (105), (211), (204), (220), (220), and (215), respectively [67, 68, 77, 82]. In many instances, Ag is not detected in the XRD pattern. It is probably located in bulk (inside the TiO<sup>2</sup> crystals) [77], and/or Ag clusters smaller than 0.3 nm [66], or diffused in the TiO<sup>2</sup> crystal lattice [68], or well dispersed throughout the TiO2 surface [31] (**Figure 1**).

High Ag content (more than 0.25 mol%) in TiO2 -AgNP prepared by precipitation assisted with microwave [68] and that of by photocatalytic reduction [67] have additional diffraction peaks at 2θ values of 38.011, 44.261, 64.021 and 77.361. The appearance of the peaks can be assigned to the face centered cubic lattice planes of metallic silver of (111), (200), (200) and (311) planes, respectively [67, 68]. It is evident that TiO2 -AgNP photocatalyst with low metallic Ag content is undetectable by the XRD technique [82]. The detectable metallic Ag level

Silver Nanoparticle Incorporated Titanium Oxide for Bacterial Inactivation and Dye Degradation http://dx.doi.org/10.5772/intechopen.75918 335

**2.4. Photocatalytic deposition**

334 Titanium Dioxide - Material for a Sustainable Environment

or sonicating for about 15 min to form titania sol. The AgNO3

300–400°C [31, 33, 67, 69–71, 73, 79, 81]. In this method, when TiO2

coming from AgNO3

metallic particles. The small particle of Ag0

[67] and/or deposited onto TiO2

There are several other methods for TiO2

**3.1. The existence of the silver species in TiO2**

XRD pattern. It is probably located in bulk (inside the TiO<sup>2</sup>

smaller than 0.3 nm [66], or diffused in the TiO<sup>2</sup>

surface [31] (**Figure 1**).

High Ag content (more than 0.25 mol%) in TiO2

(311) planes, respectively [67, 68]. It is evident that TiO2

The content of Ag incorporated in the TiO2

**3. Characterization of TiO2**

content of Ag formed in TiO2

The presence of Ag in the TiO2

solution.

powder is dispersed into ethanol and water, followed by stirring

surface to form a small cluster.

resulting in the reduction reaction of the Ag+


crystal structure prepared by sol-gel, precipitation



can be inserted into the crystal lattices

The mixture is irradiated with UV lamp for a certain period of time along with constant stirring. After a certain time, the solid was separated by filtration and dried at around

to UV light, electrons are revealed along with the formation of OH radicals. The electrons

[57], radiolitic reduction by using γ-ray [61], electrolytic oxidation-reduction [62], and mirror

**-AgNP photocatalyst**

and photodeposition can be determined by elemental analyses by X-Ray Fluorescence (XRF) [68, 75], ICP-MS [35] and atomic absorption spectrophotometry (AAS) [83]. In general, the

peaks of 2θ values at 25.091, 37.651, 48.021, 53.891, 55.071, 62.381, 68.701, 70.041 and 75.001. These peaks are confirmed with JCPD Card No. (21-1272) and are attributed to the diffraction

(220), (220), and (215), respectively [67, 68, 77, 82]. In many instances, Ag is not detected in the

with microwave [68] and that of by photocatalytic reduction [67] have additional diffraction peaks at 2θ values of 38.011, 44.261, 64.021 and 77.361. The appearance of the peaks can be assigned to the face centered cubic lattice planes of metallic silver of (111), (200), (200) and

lic Ag content is undetectable by the XRD technique [82]. The detectable metallic Ag level

anatase. They correspond to the lattice planes (101), (004), (200), (105), (211), (204),

by detecting X-ray diffraction pattern evolution with the reference of native TiO<sup>2</sup>

**-AgNP**

recorded by using a CuKα source of XRD machine gives several characteristics

solution is added to the sol.

photocatalyst is exposed

to

. The XRD

crystals) [77], and/or Ag clusters

crystal lattice [68], or well dispersed through-



In this method, the TiO2

will interact with Ag+

**2.5. Other methods**

reaction [65].

of the AgNO3

pattern of TiO<sup>2</sup>

of TiO2

out the TiO2

form Ag0

of TiO2

**Figure 1.** XRD patterns of (a) TiO<sup>2</sup> , (b) TiO2 /Ag-0.05%, (c) TiO2 /Ag-0.10%, (d) TiO2 /g-0.15%,(e) TiO2 /Ag-0.25%, and (f) TiO2 /Ag-0.50% [71].

is found to be more than 0.80 moles% [66], but 0.25 moles% or higher is also reported [68]. Depending on the concentration, the detectable metallic silver in TiO2 -AgNP is also observed in the XRD pattern when TiO<sup>2</sup> -AgNP is calcined at a higher temperature (700°C) since sintering step causes Ag particles to form large aggregate [31].

The valence state of silver, as ionic Ag+ or metallic silver Ag0 , in the TiO2 -AgNP photocatalyst can be distinguished by XPS. The XPS spectrum shows the characteristic Ag 3d peak that has a binding energy of 368 eV with a 6.0 eV splitting of the 3d doublet of low spin 3d1/2 and high spin 3d5/2 [33]. It confirms that the presence of metallic silver deposits on the TiO<sup>2</sup> [33]. It is different from the XRD data that can only provide the metallic silver in high level; the XPS gives additional proof that the metallic silvers are formed in TiO2 -AgNP at all concentration levels.

The existence of Ag in TiO2 -AgNP can also be distinguished by temperature-programmed reduction (TPR) spectrometry technique. The profile of the TPR spectra of sol-gel TiO<sup>2</sup> -AgNP calcined at 350°C [72] shows reduction peak at around 135°C, which suggests a reduction of Ag+ into Ag0 metallic without interacting with the support. Also, TiO2 -AgNP calcined at 500°C give spectra peak at around 350 and 500°C, probably due to Ag reduction with support material [72].

#### **3.2. Band gap energy (Eg) and absorption edge (λ) of TiO<sup>2</sup> -AgNP**

#### *3.2.1. Mechanism and role of Ag in TiO2 -AgNP on the absorption shift into visible light*

The incorporation of Ag on TiO2 is meant to allow the TiO2 to be active under visible light. The photocatalytic ability of TiO2 photocatalyst under visible is assigned by the lower band gap energy (Eg) or absorption in visible light. The band gap energy (Eg) can be determined based on the data of the maximum absorption wavelength (λ) according to the equation Eg = 1239/λ, where the maximum absorption wavelength is obtained from the diffuse reflectance (DR) data [67].

process is calcination at a higher temperature that is about 350–500°C. The high calcination

ger Ag metallic cluster, which prevents it from entering the gap. The significant shift of the absorption wavelength is expected because this should promote higher photocatalyst activity

confirmed by their basal spacing obtained from the XRD patterns. It is found that the presence

the 2θ angle position is getting lower as the Ag content increases. The 2θ angle value is related

nλ = 2 d sin θ (3)

The equation describes the smaller sin θ value, the larger the d spacing. It is known that the value of d increases gradually with increase in Ag contents. The enlargement of the XRD

tents increasing from 0 to 0.25 mol%, the peak broadening of [101] planes gradually increases, which indicates the smaller crystallite size of Ag. The smaller size facilitates them to diffuse

or disturb the chemical bonds of Ti-O in the solid. To better understand the effect of the Ag as a

photocatalyst illustrating several absorptions appear at various wavelengths [68, 77, 81]. A broad peak at 3448 cm−1 represents O-H stretching of Ti-O-H. Also, a peak seen at 1635 cm−1 is due to

540 and 678 cm−1 are also observed due to Ti-O-Ti stretching and Ti-O-Ti bending, respectively

decreases after Ag loading. The intensity decreases imply the alteration of the crystallinity

size and surface area. The particle size determines its surface area, where the smaller the

ticles with an average particle size of 2–4 nm. At high silver level, the formation of large Ag


basal spacing (d) implies that more silver diffuses into the lattice of TiO<sup>2</sup>

doping agent, the spectrometer data of IR is used. The FTIR spectra of both TiO2

respectively. The shifts may be affected by the interaction between Ag and TiO<sup>2</sup>

and TiO2

**-AgNP**

grain size, the larger the surface area. TEM can trace the particle size of Ag in TiO2

TEM image displays that the size varied with the Ag content in the TiO2

the OH bending mode of water adsorbed on the surface of TiO2

composite and/or the insertion of Ag into host lattice of TiO<sup>2</sup>

The XRD patterns confirm the distortion of the TiO<sup>2</sup>

due to the insertion of Ag into the lattice of the TiO<sup>2</sup>

ture [72]. With a high temperature, the silver sintering on TiO2

The diffusion of Ag into the crystal lattice of TiO<sup>2</sup>

The insertion of the metallic silver into the TiO2


Silver Nanoparticle Incorporated Titanium Oxide for Bacterial Inactivation and Dye Degradation

crystal as represented by Bragg's equation [68]:

may be occurred to form big-

337

http://dx.doi.org/10.5772/intechopen.75918

shifts to a low 2θ angle. Further,

[68]. As the Ag con-

and TiO2

to form Ti-O-Ag


par-


. The peaks at the wavelength of

structure after doping with metallic Ag.



may enlarge its basal spacing (d) that can be

crystal lattice may distort the structure of TiO<sup>2</sup>

, the peaks at 540 and 679 cm−1 shifts to 556 and 694 cm−1,

may affect several important properties including particle

[68].

crystal [67].


temperature of TiO2

in the visible region.

of Ag in the TiO2

to the basal spacing (d) of TiO2

into the crystal lattice easily.

[68, 75]. After loading Ag on TiO2

The XRD peaks belonged to both TiO2

**3.3. Particle size of the silver on TiO2**

The Ag incorporation into the TiO2

the two atomic% Ag in TiO2

The DR-spectra at 200–800 nm of TiO<sup>2</sup> displays that the maximum absorption is seen at around 400–390 nm corresponding to 3.15–3.20 eV of the band gap energy of anatase [1–3]. Furthermore, the metallic silver loading on TiO2 is observed to shift the maximum absorption to a longer wavelength that is about 430–574 nm [31, 66, 67, 72, 75, 81]. The DR spectra give respective band gap energy as much as 2.88–2.16 eV. The absorption wavelength or the band gap energy values allow the TiO2 -AgNP photocatalyst to be active in the visible region. The absorption shift may be resulted by the diffusion of the metallic silver into the crystal lattice of the TiO2 structure that the silver to be dispersed or inserted between the conduction and valence bands of the host material [31, 67, 75] (**Figure 2**).

The absorption shift is found to be affected by Ag content in TiO<sup>2</sup> -AgNP [67, 68, 75, 81], the preparation method of TiO2 -AgNP, and calcination temperature [72]. The shift increases with the increasing Ag amount in TiO2 because more Ag inserted into the gap so that the gap becomes narrower than that of bare TiO2 , shifting in the absorption wavelength to increase. Based on the preparation method, TiO<sup>2</sup> -AgNP photocatalyst prepared by sol-gel has a more substantial shift in the wavelength than the ones produced by the impregnation method [72]. In the sol-gel process, the silver ion (Ag+ ) having a small size interacts with the titania sol, allowing the ion to disperse into the crystal lattice of TiO<sup>2</sup> . Meanwhile, in the impregnation the silver introduced into the titania sol present as AgNO3 salt is difficult to penetrate the lattice [75], giving less effect on the band gap. The final step in the TiO<sup>2</sup> -AgNP preparation

**Figure 2.** DR spectra, from the top in order representing TiO2 , TiO2 /Ag-0.05%, TiO2 /Ag-0.25%, and TiO2 /Ag-0.50% [71].

process is calcination at a higher temperature that is about 350–500°C. The high calcination temperature of TiO2 -AgNP gives smaller absorption shift than the low calcination temperature [72]. With a high temperature, the silver sintering on TiO2 may be occurred to form bigger Ag metallic cluster, which prevents it from entering the gap. The significant shift of the absorption wavelength is expected because this should promote higher photocatalyst activity in the visible region.

The diffusion of Ag into the crystal lattice of TiO<sup>2</sup> may enlarge its basal spacing (d) that can be confirmed by their basal spacing obtained from the XRD patterns. It is found that the presence of Ag in the TiO2 -AgNP causes the XRD peak position of TiO2 shifts to a low 2θ angle. Further, the 2θ angle position is getting lower as the Ag content increases. The 2θ angle value is related to the basal spacing (d) of TiO2 crystal as represented by Bragg's equation [68]:

$$\mathbf{n}\lambda = \mathbf{2} \,\mathrm{d}\sin\Theta\tag{3}$$

The equation describes the smaller sin θ value, the larger the d spacing. It is known that the value of d increases gradually with increase in Ag contents. The enlargement of the XRD basal spacing (d) implies that more silver diffuses into the lattice of TiO<sup>2</sup> [68]. As the Ag contents increasing from 0 to 0.25 mol%, the peak broadening of [101] planes gradually increases, which indicates the smaller crystallite size of Ag. The smaller size facilitates them to diffuse into the crystal lattice easily.

The insertion of the metallic silver into the TiO2 crystal lattice may distort the structure of TiO<sup>2</sup> or disturb the chemical bonds of Ti-O in the solid. To better understand the effect of the Ag as a doping agent, the spectrometer data of IR is used. The FTIR spectra of both TiO2 and TiO2 -AgNP photocatalyst illustrating several absorptions appear at various wavelengths [68, 77, 81]. A broad peak at 3448 cm−1 represents O-H stretching of Ti-O-H. Also, a peak seen at 1635 cm−1 is due to the OH bending mode of water adsorbed on the surface of TiO2 . The peaks at the wavelength of 540 and 678 cm−1 are also observed due to Ti-O-Ti stretching and Ti-O-Ti bending, respectively [68, 75]. After loading Ag on TiO2 , the peaks at 540 and 679 cm−1 shifts to 556 and 694 cm−1, respectively. The shifts may be affected by the interaction between Ag and TiO<sup>2</sup> to form Ti-O-Ag composite and/or the insertion of Ag into host lattice of TiO<sup>2</sup> [68].

The XRD patterns confirm the distortion of the TiO<sup>2</sup> structure after doping with metallic Ag. The XRD peaks belonged to both TiO2 and TiO2 -AgNP seemed similar, but the peak intensity decreases after Ag loading. The intensity decreases imply the alteration of the crystallinity due to the insertion of Ag into the lattice of the TiO<sup>2</sup> crystal [67].

#### **3.3. Particle size of the silver on TiO2 -AgNP**

on the data of the maximum absorption wavelength (λ) according to the equation Eg = 1239/λ, where the maximum absorption wavelength is obtained from the diffuse reflectance (DR)

around 400–390 nm corresponding to 3.15–3.20 eV of the band gap energy of anatase [1–3].

to a longer wavelength that is about 430–574 nm [31, 66, 67, 72, 75, 81]. The DR spectra give respective band gap energy as much as 2.88–2.16 eV. The absorption wavelength or the band

absorption shift may be resulted by the diffusion of the metallic silver into the crystal lattice

substantial shift in the wavelength than the ones produced by the impregnation method [72].

, TiO2

/Ag-0.05%, TiO2

/Ag-0.25%, and TiO2

/Ag-0.50% [71].

structure that the silver to be dispersed or inserted between the conduction and

displays that the maximum absorption is seen at



because more Ag inserted into the gap so that the gap

, shifting in the absorption wavelength to increase.

) having a small size interacts with the titania sol,


is observed to shift the maximum absorption


. Meanwhile, in the impregnation

salt is difficult to penetrate the


data [67].

of the TiO2

The DR-spectra at 200–800 nm of TiO<sup>2</sup>

336 Titanium Dioxide - Material for a Sustainable Environment

gap energy values allow the TiO2

preparation method of TiO2

the increasing Ag amount in TiO2

becomes narrower than that of bare TiO2

In the sol-gel process, the silver ion (Ag+

**Figure 2.** DR spectra, from the top in order representing TiO2

Based on the preparation method, TiO<sup>2</sup>

Furthermore, the metallic silver loading on TiO2

valence bands of the host material [31, 67, 75] (**Figure 2**).

allowing the ion to disperse into the crystal lattice of TiO<sup>2</sup>

the silver introduced into the titania sol present as AgNO3

lattice [75], giving less effect on the band gap. The final step in the TiO<sup>2</sup>

The absorption shift is found to be affected by Ag content in TiO<sup>2</sup>

The Ag incorporation into the TiO2 may affect several important properties including particle size and surface area. The particle size determines its surface area, where the smaller the grain size, the larger the surface area. TEM can trace the particle size of Ag in TiO2 -AgNP. The TEM image displays that the size varied with the Ag content in the TiO2 -AgNP [33, 67]. For the two atomic% Ag in TiO2 -AgNP sample, Ag deposits are well dispersed on the TiO2 particles with an average particle size of 2–4 nm. At high silver level, the formation of large Ag particles (>100 nm) is observed in the TEM images [33, 67]. The particle size of Ag-doped TiO2 is also directed by the preparation methods [33]. In TiO2 -AgNP prepared by the impregnation method, Ag is detected to have a larger size than that of sol-gel. In the impregnation process, AgNO3 salt and TiO2 are suspended in water in the TiO2 -AgNP preparation [33]. Consequently, the Ag particle is not limited by the TiO2 structure that enables them to form a large agglomerate. Meanwhile, in the sol-gel method, TiO2 -AgNP is prepared from titania sol and Ag+ solution that allows them to have mutual interaction and inhibit their particle growth. As a result, it forms the small grain size (**Figure 3**).

size of the TiO2

surface area of the TiO2

**4. Activity of TiO2**

**4.1. Bacterial inactivation**

The antibacterial performance of TiO2

and TiO2

under visible light. Addition of Ag to TiO2

bacterial wall [10, 11]. Under visible light, TiO2

The doping TiO2

The doping TiO2

sure. The TiO2

. Both TiO<sup>2</sup>

is a synergic effect of TiO<sup>2</sup>

The role of Ag in TiO2

bacterial inactivation.

The Ag content in TiO2

tent can block the TiO2

TiO2

TiO2

powder.

**-AgNP photocatalyst**

ible light both for bacterial inactivation and dye photodegradation.

with metallic silver to produce TiO2

with metallic Ag is intended to activate TiO2

TiO2

can be calculated by using the Scherrer's Equation [31]. It is observed that the

Silver Nanoparticle Incorporated Titanium Oxide for Bacterial Inactivation and Dye Degradation


http://dx.doi.org/10.5772/intechopen.75918

339

provides OH radicals during




is less active




and Ag in inhibiting bacteria [63–65, 78, 79]. The activity of Ag in



surface and prevent the light absorption, producing a lower amount of

also gives the excellent antibacterial agent, that is

 crystallite has an average size of 15 nm, and it decreases up to 10 nm for 0.25 mol% of Ag loading [68]. It is also confirmed that the decreasing the crystallite size increases the specific

tial antibacterial agent in inactivating *Escherichia coli* [63–65, 78, 79] under visible light expo-


to its high band gap energy (Eg), which is in the same order as UV light, TiO2

the bacteria inactivation process is examined by applying TiO2

decline in bacterial inactivation [34, 63–65, 78, 79]. Increasing Ag in TiO2

The depletion of OH radicals leads to the inactivation declined [64].

UV or visible irradiation at a suitable wavelength. The OH radicals attack and destroy the

a low band gap energy (Eg) that matches with the visible region wavelength. Meanwhile, due

by penetrating the metallic Ag nanoparticles into the cell membrane of the bacteria [84]. There

It has been postulated that silver disrupts the cell wall and affects the rapid penetration of the metallic ions into the cell where irreversible precipitation of the bacteria's DNA occurs [84].

ability as a center of the separation of photoinduced electron and OH radicals that delay the recombination of electron and hole [34, 63–65, 78, 79]. The other role of Ag in the improving the bacterial inactivation corresponds to the electron capture that can prevent the recombination. The inhibition of the recombination creates more OH radicals, which improves the

the electron capture, forming anion Ag, which allows more OH radical available. The more OH radicals available, the better bacterial inactivation. However, a further increase in Ag con-

OH radicals. The other possible reason is the attachment of OH radical with excess Ag anion.



#### **3.4. Surface area of TiO2 -AgNP**

The surface area is determined by surface area analyzer based on the BET method. In general, the surface area of TiO2 -AgNP is controlled by the Ag content in TiO2 -AgNP, preparation method, and the calcination temperature [33, 68, 72]. The surface area of TiO2 -AgNP prepared by impregnation method is observed to decrease with increase in the Ag-doped TiO2 [72]. By impregnation method, the metallic silver is formed as large agglomerate that may block the surface of the TiO2 particle. Such surface blocking leads to the surface area to decline. In contrast, by a sol-gel method, the surface area increases with the enlargement of Ag content in TiO2 -AgNP. The particle size of the metallic Ag is small due to the limitation of particle growth.

By the photo-deposition method, the addition of Ag at only 0.25 mol%, an appreciable increase in the specific surface area is observed [33, 68]. The surface area of TiO2 -AgNP with Ag content smaller than 0.25 mol% is not significantly different from that of the pure TiO<sup>2</sup> due to the vast and thin dispersion of the Ag particles on the TiO2 structure. Ag in TiO2 -AgNP as much as 0.25 mol% seems to be well dispersed on the surface of the TiO2 grain that contributes to a large surface area. The Ag loading higher than 0.25 mol% leads to the decrease in surface area that is resulted from by large silver aggregate.

The other reasons for the surface area improvement are proposed as follows [31, 68, 76]. The Ag doping with a suitable amount (ca. 2–6 mol%) promotes the phase transformation of TiO2 from anatase to rutile since the surface area of rutile is larger than that of the anatase. The Ag-doped TiO2 also has a depressing effect on the anatase grain growth. The average crystallite

**Figure 3.** The TEM images of (a) TiO2 /Ag-0.05%, (b) TiO2 /Ag-0.25%, and (c) TiO2 /Ag-0.50% [71].

size of the TiO2 can be calculated by using the Scherrer's Equation [31]. It is observed that the TiO2 crystallite has an average size of 15 nm, and it decreases up to 10 nm for 0.25 mol% of Ag loading [68]. It is also confirmed that the decreasing the crystallite size increases the specific surface area of the TiO2 powder.

#### **4. Activity of TiO2 -AgNP photocatalyst**

The doping TiO2 with metallic Ag is intended to activate TiO2 -AgNP photocatalyst under visible light both for bacterial inactivation and dye photodegradation.
