*2.4.2. Electrochemical properties determination*

of the dispersion and the type of optical properties (especially the undertone and gloss) are strongly dependent on the degree of particulate dispersion, we can conclude that in controlled

in the formation of free electrons and electron-holes in the crystal lattice. These radicals react easily with neighboring organic molecules and, result in degradation of the medium [36–38].

violet-colored species. For that reason, discoloration (greying) of the exposed area might be

num, silicon and zirconium [39–42]. Silica contributes to durability, while zirconia improves gloss and durability. Alumina is usually used as a final layer to increase dispersion stability. Sometimes, special surface treatment, for example, with aluminum phosphate is required to provide high lightfastness in applications such as decorative papers [43]. Scanning transmis-

The lightfast properties of printing inks can be defined as the amount of resistance to fade or color change of a printed surface when exposed to daylight (or an artificial light source) over

For determination of lightfastness of prints, Blue Wool Scale is utilized. According to this

method, samples are exposed to a standard xenon light in appropriate equipment.

with aluminum phosphate coating.

photocatalytic activity. During weathering, interaction of UV light with TiO<sup>2</sup>

observed. This is usually described in terms of the lightfastness [37].

is a semi-conducting material and show some intrinsic

particles results in the formation of Ti3+ centers that are

, surface treated with aluminum phosphate is

grades are surface-treated with hydrated compounds of alumi-

occurs resulting

surface treatment, we obtained more dispersed particles.

 **applications in paper laminates**

As already mentioned before, TiO<sup>2</sup>

438 Titanium Dioxide - Material for a Sustainable Environment

The interaction of UV light with TiO<sup>2</sup>

sion electron microscopy (STEM) image of TiO<sup>2</sup>

Generally, commercial TiO<sup>2</sup>

presented in **Figure 21**.

*2.4.1. Lightfastness*

a set period of time.

**Figure 21.** STEM image of TiO<sup>2</sup>

**2.4. TiO2**

IEP of pure TiO<sup>2</sup> particles is about pH 4. Modifying the pigment surface with inorganic layers of, for example, Al<sup>2</sup> O3 , SiO<sup>2</sup> , ZrO<sup>2</sup> , phosphates changes the IEPs [2]. Whereas, for example, Al<sup>2</sup> O3 (IEP = 9) and Al(OH)<sup>3</sup> species (IEP is about 6.8) shifts the IEP to higher pH values, other substances normally tend to reduce the IEP to lower pH values (IEP of SiO<sup>2</sup> = 2, IEP of ZrO<sup>2</sup> = 4). Phosphates, used for surface treatment form acidic groups on the surface of particles, which are acidic and becomes a potential determinant [2, 14].

In **Figure 22**, the zeta potential as a function of pH for untreated and surface-treated TiO<sup>2</sup> pigments are presented. IEP of pure TiO<sup>2</sup> particles is about 4 and according to literature [2], IEP of aluminum surface-treated TiO<sup>2</sup> is 8.65, which is close to the values determined for Al<sup>2</sup> O3 . IEP of Si surface-treated TiO<sup>2</sup> shifted to pH 2.5, close to IEP characteristic for SiO<sup>2</sup> . Complete alumina layers contributed to shift IEP to higher pH values (pH 8.6), which proves a successful surface treatment, since the IEP value of surface-treated samples lies close to the IEP value characteristic for alumina. The results are in agreement with literature. Multi-layered surface treatments, alumina in combination with silica and phosphate, shifted IEP to lower pH. IEP values for all samples are presented in **Table 4**. The uniformity and the properties of hydroxide coatings influenced the surface properties of the pigment particles because the coated particles show similar surface characteristic, such as surface charge and surface active sites or groups, as the coating material.

**Figure 22.** Zeta potential as a function of pH.


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TiO2 Applications as a Function of Controlled Surface Treatment

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starting from sodium metaaluminate and the pigmentary

coating layers on the surfaces of rutile TiO<sup>2</sup>

particles in an aqueous process. Industrial and Engineering

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particles during aqueous precipitation. Industrial and Engineering Chemistry

powders and the pigmentary proper-

2− on the heterogeneous precipitation coating

—From process to application. Journal of

and the pigmentary

441

and the

particles,

**Table 4.** IEPs for untreated and surface-treated TiO<sup>2</sup> particles.
