**3.3. Evaluation of the photocatalyst concentration**

**Figure 9** shows photocatalytic performance in terms of the concentration of the solid (0.5, 1.0, 1.5, and 2 g/L) obtained with the composites. In photocatalysts with surface areas between 50

**Figure 9.** Composite concentration effect at photocatalytic yields.

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Influence of the Synthesis Method on the Preparation Composites Derived... http://dx.doi.org/10.5772/intechopen.72279 297

**Figure 9.** Composite concentration effect at photocatalytic yields.

between Ti and mixed oxides (CLDH) is in direct relation to the photodegradation percentages,

and the mixed oxides (CLDH), causing the impregnated Ti to be diffused to a greater degree inside the composite, with a lesser proportion to be spread over the surface [36]. The opposite

be explained by the CLDH reconstruction process, since, when these are put in contact with an aqueous solution, they form highly hydroxylated species on the surface which can react with the photogenerated holes to promote ●OH radical production, enabling them to attack

The adsorptive capacity of the composites in general is minimal and is unrelated to the surface

T-LDH is 1.8% (0.18 mg/L), and in TiO<sup>2</sup>

Based on the results obtained, it can be assumed that, in general, phenol removal in the composites is attributed to indirect photocatalytic degradation through oxidation by ●OH radicals as opposed to direct degradation by photogenerated holes due to the low adsorption rates of

degree of chemical interaction of the impregnated Ti, which is in direct relation to the proportion of Ti diffused into the composite and the presence of photocatalytically active phases found on the surface of the material leaving the catalyst more exposed to UV irradiation,

**Figure 9** shows photocatalytic performance in terms of the concentration of the solid (0.5, 1.0, 1.5, and 2 g/L) obtained with the composites. In photocatalysts with surface areas between 50

B-LDH sample, reflected in better photocatalytic performance.

I-LDH, where there is a chemical interaction between Ti


mixed with LDH in the composites can

B-LDH is 3.2% (0.32 mg/L).

I-LDH sample, the percentage of phenol adsorbed


as observed for TiO<sup>2</sup>

can be seen in the TiO<sup>2</sup>

the phenol more effectively [13].

is 1.5% (0.15 mg/L), in TiO<sup>2</sup>

these materials [19].

area of the materials; in the case of the TiO<sup>2</sup>

The photocatalytic efficiency in the synthesized TiO<sup>2</sup>

avoiding agglomeration and the screening phenomenon.

**3.3. Evaluation of the photocatalyst concentration**

T-LDH and TiO<sup>2</sup>

**Figure 8.** (a) Adsorption and (b) phenol photodegradation with TiO<sup>2</sup>

296 Titanium Dioxide - Material for a Sustainable Environment

Another possible cooperative effect between the TiO<sup>2</sup>

and 200 m<sup>2</sup> /g, the optimal concentration was found in the 0.5 to 3.0 g/L range depending on the chemical characteristics and techniques of the irradiation system [19].

The results show that the photocatalytic capacity of the materials is maintained without further decreasing the degradation performance. The decline of photocatalytic activity in successive photodegradation cycles, in general, is not significant and is attributed to the gradual deactivation of the catalyst in the composites and, to a lesser extent, the minimum quantity of solid lost after the aliquot is taken and that cannot be recovered at the end of the irradiation

LDHs were obtained by sol-gel synthesis, which are combined following different procedures. The different methodologies used to prepare the photocatalysts and the composites influence the photocatalytic activity of the materials, giving them different characteristics,

properties (anatase and rutile) in a ratio close to that reported as adequate (≈80:20%), the

and 50 nm), which allows an optimal balance between the production and recombination

characteristics were closest to those described to promote greater photocatalytic activity. The composites originate distinct forms of interaction between the components affecting

composites, a bigger chemical interaction and larger crystals are observed, which indicates

the components remain segregated, with less chemical interaction, at the same time allowing minimal agglomeration and screening of the photocatalyst enhancing the photocatalytic mechanism. For the composites obtained, phenol elimination is attributed mainly to the degradation process through oxidation reactions produced by the formation of ●OH radicals, finding a minimal adsorptive capacity in the materials. In the analysis of the different concentrations of material, a dosage of 1 g/L was the most efficient, exposing the maximum amount of the composite to UV irradiation. In addition, the composites can be separated after use in the aqueous solution, allowing them to be reused with minimal loss of photo-

phases without photocatalytic properties, and the particle size (between 15

inside the composite. Meanwhile, in the TiO<sup>2</sup>

\*, Jose L. García-Rivas<sup>1</sup>

,

using three different methodologies, and

http://dx.doi.org/10.5772/intechopen.72279

Influence of the Synthesis Method on the Preparation Composites Derived...

B precursor was the photocatalyst whose

T-LDH and TiO<sup>2</sup>

with photocatalytic

I-LDH

299

B-LDH sample,

cycle [19].

TiO<sup>2</sup>

**4. Conclusions**

absence of TiO<sup>2</sup>

the degree of diffusion of TiO<sup>2</sup>

catalytic activity between each cycle.

**Author details**

Juan C. Contreras-Ruiz<sup>1</sup>

Julio C. González-Juárez<sup>1</sup>


of photogenerated electron-hole pairs. The TiO<sup>2</sup>

being the most significant generation of mixed crystalline phases of TiO<sup>2</sup>

their photoactivity. Based on the characterization results in the TiO<sup>2</sup>

, Sonia Martínez-Gallegos<sup>1</sup>

and Eduardo Ordoñez<sup>2</sup>

2 Department of Chemistry, National Institute of Nuclear Research, Mexico City, México

\*Address all correspondence to: soniazteca@hotmail.com

1 Technological Institute of Toluca, Metepec, México

High or low dosages of the photocatalyst may lead to a decrease in the reaction rate, so it is advisable to use the concentration of the photocatalyst near the point where its steady state is reached, i.e., the optimal concentration will correspond to the minimum quantity for which the maximum reaction is obtained, which is the highest proportion of material that remains exposed during radiation [19]. For all the composites, this state is observed at a concentration of 1 g/L where the highest performance is reached. In all the samples analyzed, it is observed that in quantities of 0.5 g/L a limiting effect occurs between the number of photocatalytic sites available for the reaction and the amount of phenol to degrade resulting in lower degradation rates [42]. When increasing the concentration of the photocatalyst, the radiation screening and dispersal phenomena—due to turbidity by the particles in suspension—gradually start to become significant, preventing the complete illumination of the solid due to the filtering effect of the excess particles, which mask part of the photosensitive surface. In addition, a bigger amount of the photocatalyst can lead to the deactivation of active molecules by particle collision [19], as observed in the composites on increasing the concentration to 2 g/L.

#### **3.4. Phenol photodegradation in cycles with TiO2 -LDH composites**

One advantage of using TiO<sup>2</sup> composites is their easy recovery and reuse over several degradation cycles [43]. The results obtained on reusing a single solid from the synthesized composites over four rounds are shown in **Figure 10**, indicating the percentage of photodegraded phenol in each cycle. This behavior is favorable for the composites, since they can be reused, thereby demonstrating the synergy between mixed oxides derived from CLDH and TiO<sup>2</sup> , which, once they form the composite, cannot be separated and are therefore reusable.

**Figure 10.** Phenol photodegradation using reutilized composites.

The results show that the photocatalytic capacity of the materials is maintained without further decreasing the degradation performance. The decline of photocatalytic activity in successive photodegradation cycles, in general, is not significant and is attributed to the gradual deactivation of the catalyst in the composites and, to a lesser extent, the minimum quantity of solid lost after the aliquot is taken and that cannot be recovered at the end of the irradiation cycle [19].
