**2.2. LDH synthesis**

LDHs were synthesized by the sol–gel method [17], mixing 5.72 g of magnesium ethoxide C4 H10MgO<sup>2</sup> (Aldrich) in 100 mL of ethanol CH<sup>3</sup> CH<sup>2</sup> OH (99.5%) (Civeq) and adding 8.8 mL of HCl (Fermont); the mixture was maintained at 80°C with reflux and agitation. The second solution was prepared by dissolving 5.4 g of aluminum acetylacetonate C15H21AlO<sup>6</sup> (Aldrich) in 80 mL of ethanol and added dropwise to the first solution maintaining pH 10 with a 3:1 solution of NH<sup>4</sup> OH in water. The mixture was aged for 20 hours. The solid was separated by centrifugation and dried at 100°C for 24 hours (LDH). It was then calcined at 550°C for 3.5 hours (CLDH).

#### **2.3. Synthesis of TiO2 -LDH composites**

As previously reported, in the preparation of HDL-TiO<sup>2</sup> composites [15], the use of anionic clays synthesized by the sol-gel method has advantages over those prepared by the conventional coprecipitation method, because the sol-gel HDL possesses smaller crystal size, which offers a bigger dispersion of TiO<sup>2</sup> particles on the surface of material minimizing the photocatalyst screening phenomenon. In this work according to previous tests, three methodologies were chosen in the preparation of composites derived from TiO<sup>2</sup> and sol-gel HDL based on their photocatalytic efficiency, which are representative for the three different synthesized photocatalysts:

(i) In the first method, 2.0 g of TiO<sup>2</sup> I catalyst were mixed with the gel during LDH synthesis, continuing with the methodology described in the previous paragraph. Finally, the solid was calcined at 550°C for 3.5 hours (TiO<sup>2</sup> I-LDH).

(ii) In the second method, 2.0 g of the TiO<sup>2</sup> B catalyst and 0.2 g of the CLDH solid were mixed in 20 mL of ethanol with mechanical agitation for 3 hours; the resulting paste was dried at 100°C for 20 hours (TiO<sup>2</sup> B-LDH).

the experiments. The phenol concentration was determined by UV-Vis spectrophotometry using the 4-aminoantipyrine method [18]. In order to determine the reuse capacity of the synthesized composites, photodegradation tests were conducted with UV irradiation using the same solid in consecutive rounds. At the end of a photodegradation cycle, the material was recovered from the solution by sedimentation and reused with a new phenol solution until

precursors along with

anatase phase, presenting peaks at

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

2θ (JCPDS 01-089-4921), in addition to a peak related to the

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

2θ of TiO with monoclinic structure (JCPDS 01-072-0020) and one

BV) and a lesser affinity for the adsorption of organic com-

rutile phase with tetragonal coordination at 27.6 o

2θ (JCPDS 00-029-1360). The diffractogram for the TiO<sup>2</sup>

shows a bigger variety in the different crystalline structures that this photocatalyst possesses,

phase with rhombohedral structure are observed in 32.9, 35.7, and 40.8 o

B sample shows peaks referring to the TiO<sup>2</sup>

orthorhombic crystalline formation (JCPDS 00-029-1360), as well as peaks related to the TiO<sup>2</sup>

In a photocatalyst, the pure anatase phase is considered photocatalytically superior to the rutile phase, which, although more heat stable, at the same time has a higher rate of elec-

anatase-rutile material at an optimal ratio of about 80:20%, which has lower recombination

part causing oxidation and reducing reactions, which are carried out separately, maximizing the photocatalytic mechanism [8]. The composition of the precursor photocatalysts in the anatase-rutile phases was determined by the Spurrs and Myers equation [20], finding that the

catalyst; only the anatase and brookite phases were present. These results occasionally influence the performance of these materials and the composites used in the photocatalytic tests,

BV) due to the interconnection of the electronic bands, in which the rutile phase

BC collector. In the meanwhile, the anatase phase is the photocatalytically active

2θ (JCPDS 01-089-4921) and a signal at 30.9 o

2ϴ (JCPDS 01-089-4920).

optimal anatase-rutile phase ratio (80:20%) was close to be found in samples TiO<sup>2</sup>

2θ and smaller peaks at 37.9, 48.1, 54.0, and 55.2 o

anatase phase (JCPDS 01-089-4921). In smaller proportion characteristic, reflections of

I sample is com-

2θ referring to the

anatase phase at 25.4, 37.9,

2θ of the TiO<sup>2</sup>

was not observed in the TiO<sup>2</sup>

T sample

285

2θ (JCPDS

2θ (JCPDS

brookite with

is to obtain a mixed

T (82:18%)

I photo-

**Figure 2** shows the X-ray diffraction patterns for the synthesized TiO<sup>2</sup>

posed mostly of the crystalline structure related to the TiO<sup>2</sup>

BC-h<sup>+</sup>

B (89:11%). Meanwhile, the rutile phase of TiO<sup>2</sup>

pounds like phenol [19]. A key factor in the photocatalytic activity of TiO<sup>2</sup>

the LDH and its calcined product CLDH. For the photocatalysts, the TiO<sup>2</sup>

four cycles were completed.

**3. Results and discussion**

25.4, 37.9, 48.1, 54.1, 55.2, and 62.6 o

brookite phase at 30.9 o

with a main peak at 25.4 o

01-071-0146), a peak at 43.7 o

rutile phase at 27.6 and 36.2 o

tron–hole recombination (e−

01-089-4920). The TiO<sup>2</sup>

48.1, 54.0, and 55.2 o

BC-h<sup>+</sup>

lower peak associated with TiO<sup>2</sup>

**3.1. Characterization**

TiO<sup>2</sup>

TiO<sup>2</sup>

the TiO<sup>2</sup>

rates (e−

acts as e−

and TiO<sup>2</sup>

as discussed later.

(iii) In the preparation of the third composite, 9 mL of TTIP were mixed with 0.5 g of CLDH, and the mixture agitated for 30 minutes in the air. The samples were then calcined at 550°C for 3.5 hours (TiO<sup>2</sup> T-LDH). **Figure 1** illustrates the processes described above in the preparation of TiO<sup>2</sup> -LDH composites.
