**Applications of Mesoporous Ordered Semiconductor Materials — Case Study of TiO2**

Antonio E. H. Machado, Karen A. Borges, Tatiana A. Silva, Lidiaine M. Santos, Mariana F. Borges, Werick A. Machado, Bruno P. Caixeta, Marcela Dias França, Samuel M. Oliveira, Alam G. Trovó and Antonio O.T. Patrocínio

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/59602

**1. Introduction**

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#### **1.1. Titanium dioxide (TiO2)**

TiO2 is a promising material for technological applications for its versatility [1-4], abundance, low toxicity, good chemical stability, photosensitivity and photostability [5-8]. In nature, it is found mainly in the mineral *ilmenite* [9], that can be processed industrially by two different routes [10]: The first, involves the reaction of the concentrate of *ilmenite* with hot sulphuric acid, resulting in the formation of sulphates of titanium, Fe(II) and Fe(III), being these last eliminat‐ edbycentrifugation, after cooling.The final solutionis thenpurifiedandhydrolyzedtoproduce pure TiO2 [11]. The other usual way of obtaining consists in combining the ore with coke and gaseouschlorineunderheating,resultinginCO2 andaspongymaterialrichinTiCl4.Thereaction product is subjected to successive fractional distillation, with the formation of TiCl2 and TiCl3, due to stability of titanium in other degrees of oxidation. The different precursors of titanium are hydrolyzed, forming titanium dioxide [12].

In 1972, [13], obtained, for the first time, success in decomposition of water under irradiation with light and without application of any electric potential. They reported that, in trials where they employed n-type TiO2 as anode and Platinum as cathode, when TiO2 electrode illuminat‐ edunder short-circuit conditions,hydrogenevolvedfromthePlatinumelectrode,whileoxygen evolved from the anode. Since then, studies aimed at discovering and exploring different possibilities of technological application for TiO2 have been given great importance [14-22].

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As technological applications for TiO2 can be cited its use in ultraviolet radiation absorbing filters [3, 23], in chemical sensors for gases [24-26], as a bactericide [27], in biomaterials for bone implants [28], in environmental photocatalysis [8, 24, 29, 30], in the photocatalytic hydrogen evolution [17, 31-36], in dye-sensitized solar cells [21, 37-44], among other.

The photocatalytic efficiency of TiO2 depends on its structural and morphological character‐ istics, which are related to the method of synthesis used in the preparation of nanoparticles [18, 21, 29, 45]. To be photoactive, favoring the photocatalysis process, besides being mainly consisting of anatase crystalline phase, the TiO2 must possess high specific surface area, good porosity, with high sized pores [35, 45, 46]. In this context, the search for TiO2 particles that have differentiated features, with catalytic properties potentiated, constitutes a field of intense activity [19, 20, 47-50].
