**3. Results and discussion**

#### **3.1. Profiles of ζ =** *f* **(pH) of TiO2 and different stabilizing agents**

The zeta potential is a parameter by electrochemical nature that allows to study and predict the interactions occurring at the molecular level between the colloidal particles TiO2 and the different stabilizing agents, also it indicates the degree of stability of dispersion in an aqueous medium from the point electrically. The aim is to employ ζ measurements to know and understand the behavior of the type of stabilizing agents in the EPD process performance.

In **Figure 3**, the behavior of the surface charge density of TiO2 particles and stabilizing agents is shown. TiO2 has an anionic character, according to the zeta potential = −7.8 mV, which remains constant at pH 4–11. This implies that by electrostatic interactions, the TiO<sup>2</sup> can interact with the stabilizing agents of opposite charge. Chitosan presents its isoelectric point (ζ = 0) at pH = 6.5, at pH lower than the IEP, shows a cationic character and at pH > IEP, the chitosan becomes an insoluble material and precipitates.

negative surface charge density. Additionally, this implies that we can perform an anodic or

Innovation in the Electrophoretic Deposition of TiO2 Using Different Stabilizing Agents and Zeta…

moves farther from ζ = 0 mV, that is, becomes more negative or very positive. This allows the

however, as mentioned above, there are a series of options to perform the coatings using different stabilizing agents and evaluate their physicochemical properties based on their

which could be expected since they are negatively charged density compounds and would

On the other hand, the addition of the cationic stabilizing agents, CTAB and Ch, caused an

CTAB, a ζ = 9.0 mV was reached, while with Ch, a ζ = 6.0 mV, this difference is attributed to

(ζ = −7.8 mV)

183

0.1 wt. % are

particles,

electrodeposits with chitosan are discussed,

http://dx.doi.org/10.5772/intechopen.73210

particles with a dose of 4 mg. With the

particles. The addition of Triton X-100 caused a decrease

0.1 wt. %.

The addition of a stabilizing agent seeks that the zeta potential value of TiO2

particles to be more stable and avoid the sedimentation phenomenon.

In **Figure 4**, the profiles of ζ = f (stabilizing agent dose) of the dispersion of TiO<sup>2</sup>

The addition of SDS and betaine did not significantly increase the stability of TiO<sup>2</sup>

at ζ = −3.0 mV, at a dose of 11 mg Triton X-100.

cathodic electrodeposit, depending on the application.

In this work, only the characteristics of the TiO2

inversion of the surface charge density of the TiO2

the CTAB having a higher surface charge density.

**Figure 4.** Profiles of ζ = f (stabilizing agent dose) of the dispersion of TiO<sup>2</sup>

increase the repulsion forces of TiO2

TiO2

application.

of ζ = −7.8 mV TiO<sup>2</sup>

shown.

The CTAB presents a cationic character at a pH of 3–11 (ζ = 12.0 mV), this is attributed to the functional group of the surfactant that maintains its positive charge in this pH range. Similarly, the SDS presents a constant charge density, ζ = −12.0 mV at pH 3–11, but of anionic character due to the functional group, it has in its structure. As expected, the Triton X-100 showed a nonionic character (ζ = −3.0 mV), according to the zeta potential value very close to zero, throughout the pH range.

Betaine, being an amphiphilic compound, presented an isoelectric point at pH = 3.0 and another at pH = 12.0, corresponding to the two types of functional groups it has in its structure.

It is well known that an excess or lack of ions on the surface of a material such as TiO2 causes low mobility and therefore, deficiency of fixation on the surface of the metal electrode to be coated. For this reason, a better understanding of the surface properties of a dispersion, such as the profiles ζ = f (pH), may lead to improved surface performance of the material.

#### **3.2. Colloidal titration of TiO2 dispersions**

Considering the profiles of ζ = f (pH) of the stabilizing agents and of TiO<sup>2</sup> , various formulations can be developed in which the TiO2 can have a greater stability and a positive or

**Figure 3.** Profiles of ζ = f (pH) of TiO<sup>2</sup> and different stabilizing agents.

negative surface charge density. Additionally, this implies that we can perform an anodic or cathodic electrodeposit, depending on the application.

In **Figure 3**, the behavior of the surface charge density of TiO2

becomes an insoluble material and precipitates.

182 Titanium Dioxide - Material for a Sustainable Environment

zero, throughout the pH range.

**3.2. Colloidal titration of TiO2**

**Figure 3.** Profiles of ζ = f (pH) of TiO<sup>2</sup>

lations can be developed in which the TiO2

remains constant at pH 4–11. This implies that by electrostatic interactions, the TiO<sup>2</sup>

act with the stabilizing agents of opposite charge. Chitosan presents its isoelectric point (ζ = 0) at pH = 6.5, at pH lower than the IEP, shows a cationic character and at pH > IEP, the chitosan

The CTAB presents a cationic character at a pH of 3–11 (ζ = 12.0 mV), this is attributed to the functional group of the surfactant that maintains its positive charge in this pH range. Similarly, the SDS presents a constant charge density, ζ = −12.0 mV at pH 3–11, but of anionic character due to the functional group, it has in its structure. As expected, the Triton X-100 showed a nonionic character (ζ = −3.0 mV), according to the zeta potential value very close to

Betaine, being an amphiphilic compound, presented an isoelectric point at pH = 3.0 and another at pH = 12.0, corresponding to the two types of functional groups it has in its structure.

It is well known that an excess or lack of ions on the surface of a material such as TiO2 causes low mobility and therefore, deficiency of fixation on the surface of the metal electrode to be coated. For this reason, a better understanding of the surface properties of a dispersion, such as the profiles ζ = f (pH), may lead to improved surface performance of

 **dispersions**

Considering the profiles of ζ = f (pH) of the stabilizing agents and of TiO<sup>2</sup>

and different stabilizing agents.

is shown. TiO2

the material.

particles and stabilizing agents

can inter-

, various formu-

can have a greater stability and a positive or

has an anionic character, according to the zeta potential = −7.8 mV, which

The addition of a stabilizing agent seeks that the zeta potential value of TiO2 (ζ = −7.8 mV) moves farther from ζ = 0 mV, that is, becomes more negative or very positive. This allows the TiO2 particles to be more stable and avoid the sedimentation phenomenon.

In this work, only the characteristics of the TiO2 electrodeposits with chitosan are discussed, however, as mentioned above, there are a series of options to perform the coatings using different stabilizing agents and evaluate their physicochemical properties based on their application.

In **Figure 4**, the profiles of ζ = f (stabilizing agent dose) of the dispersion of TiO<sup>2</sup> 0.1 wt. % are shown.

The addition of SDS and betaine did not significantly increase the stability of TiO<sup>2</sup> particles, which could be expected since they are negatively charged density compounds and would increase the repulsion forces of TiO2 particles. The addition of Triton X-100 caused a decrease of ζ = −7.8 mV TiO<sup>2</sup> at ζ = −3.0 mV, at a dose of 11 mg Triton X-100.

On the other hand, the addition of the cationic stabilizing agents, CTAB and Ch, caused an inversion of the surface charge density of the TiO2 particles with a dose of 4 mg. With the CTAB, a ζ = 9.0 mV was reached, while with Ch, a ζ = 6.0 mV, this difference is attributed to the CTAB having a higher surface charge density.

**Figure 4.** Profiles of ζ = f (stabilizing agent dose) of the dispersion of TiO<sup>2</sup> 0.1 wt. %.

For the present research, it is desired zeta potential values that guarantee stability to achieve a more homogeneous deposit (in terms of grain size and roughness). This indicates that controlling the doses of dispersing agent in such a way as to obtain values of zeta potential farthest from zero will cause the attraction force between the particles to decrease and, in turn, increase the force of attraction toward one of the poles of the electrophoretic cell. This effect is also reflected in a lower voltage demand in the electrophoretic cell and therefore the elimination of electrolysis reactions at the electrodes.

### **3.3. EPD process**

In **Figure 5**, the effect of the electrodeposition time on the deposited TiO<sup>2</sup> -Ch mass is shown. It is observed that 6 mg are deposited in the first 30 min, in a longer time the amount of deposit shows an exponential behavior (**Figure 6**).

**Figure 6.** Schematic representation of the interface model for the EPO process of TiO2

**Figure 7.** Micrographies of the EPD deposits with the dispersions of (a) TiO2

using chitosan.

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185

Innovation in the Electrophoretic Deposition of TiO2 Using Different Stabilizing Agents and Zeta…



#### **3.4. Evaluation of the Ti/TiO2 -CTAB and Ti/TiO2 -chitosan coating**

The SEM images and the corresponding chemical microanalysis of the Ti/TiO2 coating prepared by electrophoresis are presented in **Figure 7**. In the images of **Figure 7a**, the ceramic type structure of TiO2 -CTAB is observed, morphologically very different from the plastic type structure obtained by impregnation of the chitosan in the layer shown in **Figure 7b**.

EDX elemental analysis indicates the presence of titanium and oxygen (TiO<sup>2</sup> ) on the surface of the electrodes. In addition, carbon signals suggest the presence of CTAB and chitosan from the dispersions. **Figure 8** shows the EDX spectra corresponding to Ti/TiO<sup>2</sup> -CTAB and Ti/TiO<sup>2</sup> chitosan electrodes obtained by 10 V electrodeposits.

**Figure 5.** Influence of the electrodeposition time on the coating mass of TiO<sup>2</sup> .

Innovation in the Electrophoretic Deposition of TiO2 Using Different Stabilizing Agents and Zeta… http://dx.doi.org/10.5772/intechopen.73210 185

**Figure 6.** Schematic representation of the interface model for the EPO process of TiO2 using chitosan.

For the present research, it is desired zeta potential values that guarantee stability to achieve a more homogeneous deposit (in terms of grain size and roughness). This indicates that controlling the doses of dispersing agent in such a way as to obtain values of zeta potential farthest from zero will cause the attraction force between the particles to decrease and, in turn, increase the force of attraction toward one of the poles of the electrophoretic cell. This effect is also reflected in a lower voltage demand in the electrophoretic cell and therefore the elimina-

is observed that 6 mg are deposited in the first 30 min, in a longer time the amount of deposit

pared by electrophoresis are presented in **Figure 7**. In the images of **Figure 7a**, the ceramic

of the electrodes. In addition, carbon signals suggest the presence of CTAB and chitosan from

type structure obtained by impregnation of the chitosan in the layer shown in **Figure 7b**.

**-chitosan coating**


.


coating pre-

) on the surface



tion of electrolysis reactions at the electrodes.

184 Titanium Dioxide - Material for a Sustainable Environment

shows an exponential behavior (**Figure 6**).

**3.4. Evaluation of the Ti/TiO2**

type structure of TiO2

In **Figure 5**, the effect of the electrodeposition time on the deposited TiO<sup>2</sup>

**-CTAB and Ti/TiO2**

The SEM images and the corresponding chemical microanalysis of the Ti/TiO2

EDX elemental analysis indicates the presence of titanium and oxygen (TiO<sup>2</sup>

the dispersions. **Figure 8** shows the EDX spectra corresponding to Ti/TiO<sup>2</sup>

chitosan electrodes obtained by 10 V electrodeposits.

**Figure 5.** Influence of the electrodeposition time on the coating mass of TiO<sup>2</sup>

**3.3. EPD process**

**Figure 7.** Micrographies of the EPD deposits with the dispersions of (a) TiO2 -CTAB and (b) TiO<sup>2</sup> -chitosan.

hydrogen bonds between the polysaccharide chains. The band at 1650 cm−1 is assigned to the amine group of stretching vibration C=O (amine I) located in the acetylated chitosan units. The band at 1600 cm−1 is the result of the signal corresponding to amine II and the bending vibration NH (amine II). These signals confirm the presence of the chitosan chains with the

Innovation in the Electrophoretic Deposition of TiO2 Using Different Stabilizing Agents and Zeta…




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187

TiO2

particles in the Ti substrate.

**Figure 10.** Polarization curves of the TiO2

**Figure 9.** Micrographies of the EPD deposits with the dispersions of (a) TiO2

**Figure 8.** Spectrum of surface chemical analysis by EDX of the coatings with the dispersions of (a) TiO<sup>2</sup> -CTAB and (b) TiO2 -Chitosan.

The analysis of the chemical composition of the electrodes showing a higher percentage by weight of carbon by the coating TiO2 -chitosan, this is attributed to the molecular weight of the chitosan that is above the CTAB.

In **Figure 9**, the FTIR spectra of the TiO2 -Ch/Ti coating are shown using EPD (time = 5 min, 10 V) and the chitosan, the coating spectrum shows a wide absorption between 3350 and 3270 cm−1 to a combination of ways to stretch the OH and NH bonds in the chitosan and

Innovation in the Electrophoretic Deposition of TiO2 Using Different Stabilizing Agents and Zeta… http://dx.doi.org/10.5772/intechopen.73210 187

**Figure 9.** Micrographies of the EPD deposits with the dispersions of (a) TiO2 -CTAB and (b) TiO<sup>2</sup> -chitosan.

hydrogen bonds between the polysaccharide chains. The band at 1650 cm−1 is assigned to the amine group of stretching vibration C=O (amine I) located in the acetylated chitosan units. The band at 1600 cm−1 is the result of the signal corresponding to amine II and the bending vibration NH (amine II). These signals confirm the presence of the chitosan chains with the TiO2 particles in the Ti substrate.

**Figure 10.** Polarization curves of the TiO2 -Ch electrodes in 0.5 M sulfuric acid.

The analysis of the chemical composition of the electrodes showing a higher percentage by

**Figure 8.** Spectrum of surface chemical analysis by EDX of the coatings with the dispersions of (a) TiO<sup>2</sup>

10 V) and the chitosan, the coating spectrum shows a wide absorption between 3350 and 3270 cm−1 to a combination of ways to stretch the OH and NH bonds in the chitosan and




weight of carbon by the coating TiO2

In **Figure 9**, the FTIR spectra of the TiO2

186 Titanium Dioxide - Material for a Sustainable Environment

chitosan that is above the CTAB.

(b) TiO2


In **Figure 10**, it can be seen that all TiO2 -chitosan coatings show a lower voltage compared to the Ti electrode, which means that TiO2 -chitosan composite coatings tend to oxidize more easily, because the more negative the difference of the slower the oxidation reaction of the species to the coating, and the faster the reduction reaction of the species to the coating, therefore, higher protective properties are obtained than the Ti electrode (**Figure 6**).

**References**

Society. 1940;**36**:279-283

Publications; 1990. pp. 255-283

pmatsci.2006.07.001

2219(96)00113-6

[1] Hamaker HC. Formation of deposition by electrophoresis. Transactions of the Faraday

Innovation in the Electrophoretic Deposition of TiO2 Using Different Stabilizing Agents and Zeta…

http://dx.doi.org/10.5772/intechopen.73210

189

[2] Sarkar P, Nicholson PS. Electrophoretic deposition (EPD): Mechanism, kinetics and application to ceramics. Journal of the American Ceramic Society. 1996;**79**:1987-2002

[3] Gani MSJ. Electrophoretic deposition. A review. Industrial Ceramics. 1994;**14**:163-174

[4] Heavens N. Electrophoretic deposition as a processing route for ceramics. In: G.P. Binner, editor. Advanced ceramic processing and technology. Vol. 1. Park Ridge, NJ; Noyes

[5] Zhitomirsky I, Boccaccini AR. Application of electrophoretic and electrolytic deposition techniques in ceramics processing. Current Opinion in Solid State and Materials Science.

[6] Besra L, Liu M. A review on fundamentals and applications of electrophoretic deposition (EPD). Progress in Materials Science. 2007;**52**:1-61. DOI: https://doi.org/10.1016/j.

[7] Il C, Ryan MP, Boccaccini AR. Electrophoretic deposition: From traditional ceramics to nanotechnology. Journal of the European Ceramic Society. 2008;**28**:1353-1367. DOI:

[8] Ferrari B, Moreno R. Electrophoretic deposition of aqueous alumina slips, Journal of the European Ceramic Society. 1997;**17**:549-556. DOI: https://doi.org/10.1016/S0955-

[9] Ferrari B, Moreno R. EPD kinetics: A review. Journal of the European Ceramic Society.

[10] Hasegawa K, Kunugi S, Tatsumisago M, Minami T. Preparation of thick films by electrophoretic deposition using modified silica particles derived by sol–gel method. Journal of

[11] Shana W, Zhang Y, Yang W, Ke C, Gao Z, Ye Y, Tang Y. Electrophoretic deposition of nanosized zeolites in non-aqueous medium and its application in fabricating thin zeolite membranes. Microporous and Mesoporous Materials. 2004;**69**:35-42. DOI: https://doi.

[12] Yum JH, Seo SY, Lee S, Sung YE. Y3Al5O12: Ce0.05 phosphor coating on gallium nitride for white light emitting diodes. Journal of the Electrochemical Society. 2003;**150**:47-52

[13] Shane MJ, Talbot JB, Schreiber RG, Ross CL, Sluzky E, Hesse KR. Electrophoretic deposition of phosphors: I conductivity and zeta potential measurements. Journal of Colloid

2010;**30**:1069-1078. DOI: https://doi.org/10.1016/j.jeurceramsoc.2009.08.022

2002;**6**: 251-260. DOI: https://doi.org/10.1016/S1359-0286(02)00080-3

https://doi.org/10.1016/j.jeurceramsoc.2007.12.011

Sol-Gel Science and Technology. 1999;**15**:243-249

org/10.1016/j.micromeso.2004.01.003

and Interface Science. 1994;**165**:325-333

However, the growth of the TiO<sup>2</sup> -chitosan layer appears to displace the overpotentials more negatively. The fact that the chitosan layer does not reduce the corrosion potential may be due to its reaction with the medium, due to the degradation effects of chitosan.
