**1. Introduction**

Synthetic organic composites like phenol are widely used in a great variety of industries including paper, wood, paint, and fertilizers [1]. Wastewater from such industrial processes contains this kind of composite and poses a threat to aquatic life and the environment. It is therefore important to remove or degrade such composites before discharging the wastewater into the environment. Among the technologies used for the degradation of organic pollutants in aqueous media are advanced oxidation processes (AOPs), specifically heterogeneous photocatalysis, which promotes the degradation of several pollutants by broadband semiconductor excitation [2–5]. Photon adsorption by the semiconductor with higher bandgap energy leads to the formation of an electron-hole pair (e− BC-h<sup>+</sup> BV). The photogenerated holes in the valence band are powerful oxidants, while the conduction band electrons are good reducers. The formation of other highly oxidant species (mainly ●OH radicals) can also occur; these redox-type reactions occur when the electron-hole recombination is minimized [6]. The use of TiO<sup>2</sup> as photocatalyst has caused great interest due to its high activity, resistance to mild chemical corrosion, low toxicity, and efficiency [7]. The anatase crystalline phase of TiO<sup>2</sup> is more effective than the rutile phase for the photodegradation of several contaminants [5]; however, photoactivity has been found to increase in mixed anatase-rutile phases [8]. One difficulty with the use of TiO<sup>2</sup> is its separation and recovery for possible reuse; the addition of a support material or coadsorbent to immobilize TiO<sup>2</sup> particles to facilitate recycling has been the subject of various investigations [9, 10].

**2. Materials and methods**

The photocatalysts were synthesized using three methods. (i) First, following the sol–gel pro-

(Sigma-Aldrich) in 47 mL of ethanol (Civeq); the mixture was agitated for 3 hours after which 12.25 mL of deionized water were added. Agitation continued at 78°C for 20 hours. The solid was washed with deionized water by centrifugation and dried at 80°C during 1 hour. The

The mixture was aged during 24 hours at constant agitation and temperature. The resulting solid was recovered and washed by centrifugation using ethanol, dried during 24 hours at

nation of TTIP by placing 10 mL in mechanical agitation in air for 30 minutes, before being

LDHs were synthesized by the sol–gel method [17], mixing 5.72 g of magnesium ethoxide

of HCl (Fermont); the mixture was maintained at 80°C with reflux and agitation. The second

in 80 mL of ethanol and added dropwise to the first solution maintaining pH 10 with a 3:1

by centrifugation and dried at 100°C for 24 hours (LDH). It was then calcined at 550°C for

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

catalyst screening phenomenon. In this work according to previous tests, three methodolo-

on their photocatalytic efficiency, which are representative for the three different synthesized

continuing with the methodology described in the previous paragraph. Finally, the solid was

I-LDH).

solution was prepared by dissolving 5.4 g of aluminum acetylacetonate C15H21AlO<sup>6</sup>

CH<sup>2</sup>

OH in water. The mixture was aged for 20 hours. The solid was separated

T). In all cases, calcination took place at 550°C for 3.5 hours.

H10O (Sigma-Aldrich) were mixed with 120 mL of deionized water; both reagents were heated at 70°C in a water bath with continuous agitation and reflux system. Subsequently,

B). (iii) The third method of obtaining TiO<sup>2</sup>

)2 ]4

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

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

I). (ii) In the second method, 90 mL of 1-buta-

Ti 97% (Sigma-Aldrich) were added by dripping.

OH (99.5%) (Civeq) and adding 8.8 mL

composites [15], the use of anionic

and sol-gel HDL based

particles on the surface of material minimizing the photo-

I catalyst were mixed with the gel during LDH synthesis,

were added to 97%

283

was direct calci-

(Aldrich)

cedure [16], 5.25 mL of titanium isopropoxide (TTIP) Ti[OCH(CH<sup>3</sup>

resulting powder was ground and calcined (TiO<sup>2</sup>

(Aldrich) in 100 mL of ethanol CH<sup>3</sup>

**-LDH composites**

gies were chosen in the preparation of composites derived from TiO<sup>2</sup>

As previously reported, in the preparation of HDL-TiO<sup>2</sup>

45 mL of titanium butoxide (TOBT) C16H36O<sup>4</sup>

100°C, and finally calcined (TiO<sup>2</sup>

 **synthesis**

**2.1. TiO2**

nol C<sup>4</sup>

calcined (TiO<sup>2</sup>

H10MgO<sup>2</sup>

solution of NH<sup>4</sup>

3.5 hours (CLDH).

photocatalysts:

**2.3. Synthesis of TiO2**

offers a bigger dispersion of TiO<sup>2</sup>

(i) In the first method, 2.0 g of TiO<sup>2</sup>

calcined at 550°C for 3.5 hours (TiO<sup>2</sup>

C4

**2.2. LDH synthesis**

Layered double hydroxides (LDHs) are synthetic composites belonging to the anionic clay family, having a hexagonal or octahedral crystalline structure. They consist of layers of positively charged metal cations, where the surface of the layers is occupied by hydroxyl groups, anions, and water molecules. LDHs are the result of isomorphic variations of brucite-type layers (Mg(OH)<sup>2</sup> ) when Mg2+ cations are substituted by Al3+ cations, thereby generating a positive charge residue which is offset by the presence of intercalated anions, carbonate (CO<sup>3</sup> 2−) being the predominant anion [11]. Hydrotalcite is an LDH-type layered material, with the chemical formula [M2+ 1−xM3+ x (OH)<sup>2</sup> ] x (An−) x/n•mH<sup>2</sup> O, where M2+ and M3+ are di- and trivalent cations (Mg2+ and Al3+) and An− is the intercalated anion. LDH and its calcined products are porous materials with large surface area, have the capacity to adsorb pollutants, and have proven suitable for immobilizing TiO<sup>2</sup> particles for the photodegradation of organic pollutants [12, 13].

The aim of this work is to synthesize composites derived from the TiO<sup>2</sup> photocatalyst and the LDH anionic clays to study the influence of the preparation method on the photocatalytic capacity of those composites in a phenol solution. Two groups of synthesis methods were used: the first one is to obtain the TiO<sup>2</sup> photocatalyst, and the second one is in the preparation of the TiO<sup>2</sup> -LDH composites. The LDH was prepared by the sol-gel method, according to previously optimized procedures [14, 15] in relation to its photoactivity evaluated with the degradation of phenol. The synthesized composites in this work were also tested for phenol photodegradation in aqueous solution. These materials also showed advantages in their reusability and were able to be used in four photocatalytic cycles with a minimum loss in the photocatalytic activity at the end of the test.
