Keywords Titanium dioxide · Nanomaterials · Photocatalysis · Water-splitting ·
Water remediation · Environmental chemistry
7.1 Introduction
Since the discovery of water-splitting photocatalysis on a titanium oxide electrode
under UV light in 1972, a wide variety of materials have been investigated as
photocatalysts. However, titanium oxide-based materials are the most widely used
heterogeneous catalysts because of their optical and electronic properties, stability,
low cost, and low toxicity (Liao et al. 2012; Bahruji et al. 2011; Liu et al. 2008). A
lot of effort has been put into their development and implementation in hydrogen and
energy production from solar energy.
Titanium oxide, especially in nanosize form, has an ample field of applications,
among them, the most important are generally associated with the ceramic industry
and its use as cosmetic products and white pigments in paintings. Other more
specific applications of this material include, for example, water purification by
degradation of organic molecules, gas sensors, gas mixture cleaners, antireflective
coatings, antimicrobial photoinduced coating, electrodes for lithium batteries, selfcleaning glasses, and UV absorbers in sun creams. In addition, it has had an
important role in bone implants due to its very high biocompatibility which has
been studied over the last 20 years (Janczarek et al. 2007; Diebold 2003;
Mohammadi et al. 2008). Very recently, titanium oxide has also been used as an
angiogenic promoter and may be useful in the future for the treatment of cardiovascular diseases (Nethi et al. 2017).
7.2 Titanium Oxide: Structure and Properties
Titanium dioxide, TiO 2 , belongs to the family of transition metal oxides. Usually
known as “titania” is a type n semiconductor with sensitivity to light. It presents
three main crystalline phases: rutile (tetragonal structure), anatase (octahedral structure), and brookite (orthorrombic structure) (Pizarro 2005, Gupta and Tripathi 2011)
(Fig. 7.1).
Comparing all the three main phases, rutile is the most thermodinamically stable,
and both anatase and brookite phases can be transformed to rutile when they reach a
particle size larger than 14 nm, especially at high temperatures. Brookite is a
metastable phase, it is a very complex structure with a high cell volume and with a
very low density (the lowest of the three main phases), and due to its very low
density and subsequent mechanical factor, it is not used in experimental research.
However, for nanotechnological approaches anatase is the most suitable phase, due
to its low size (usually below 20 nm). In addition, anatase phase is preferred in
nanotechnology due to its low dielectric constant, high electronic mobility, and low
density. It has also been observed that the (001) face has a higher reactivity than the
(101) face in anatase crystals, so that enrichment of the particles in the dimension of
216
A. Boudjemaa and S. Gómez-Ruiz
Water remediation · Environmental chemistry
7.1 Introduction
Since the discovery of water-splitting photocatalysis on a titanium oxide electrode
under UV light in 1972, a wide variety of materials have been investigated as
photocatalysts. However, titanium oxide-based materials are the most widely used
heterogeneous catalysts because of their optical and electronic properties, stability,
low cost, and low toxicity (Liao et al. 2012; Bahruji et al. 2011; Liu et al. 2008). A
lot of effort has been put into their development and implementation in hydrogen and
energy production from solar energy.
Titanium oxide, especially in nanosize form, has an ample field of applications,
among them, the most important are generally associated with the ceramic industry
and its use as cosmetic products and white pigments in paintings. Other more
specific applications of this material include, for example, water purification by
degradation of organic molecules, gas sensors, gas mixture cleaners, antireflective
coatings, antimicrobial photoinduced coating, electrodes for lithium batteries, selfcleaning glasses, and UV absorbers in sun creams. In addition, it has had an
important role in bone implants due to its very high biocompatibility which has
been studied over the last 20 years (Janczarek et al. 2007; Diebold 2003;
Mohammadi et al. 2008). Very recently, titanium oxide has also been used as an
angiogenic promoter and may be useful in the future for the treatment of cardiovascular diseases (Nethi et al. 2017).
7.2 Titanium Oxide: Structure and Properties
Titanium dioxide, TiO 2 , belongs to the family of transition metal oxides. Usually
known as “titania” is a type n semiconductor with sensitivity to light. It presents
three main crystalline phases: rutile (tetragonal structure), anatase (octahedral structure), and brookite (orthorrombic structure) (Pizarro 2005, Gupta and Tripathi 2011)
(Fig. 7.1).
Comparing all the three main phases, rutile is the most thermodinamically stable,
and both anatase and brookite phases can be transformed to rutile when they reach a
particle size larger than 14 nm, especially at high temperatures. Brookite is a
metastable phase, it is a very complex structure with a high cell volume and with a
very low density (the lowest of the three main phases), and due to its very low
density and subsequent mechanical factor, it is not used in experimental research.
However, for nanotechnological approaches anatase is the most suitable phase, due
to its low size (usually below 20 nm). In addition, anatase phase is preferred in
nanotechnology due to its low dielectric constant, high electronic mobility, and low
density. It has also been observed that the (001) face has a higher reactivity than the
(101) face in anatase crystals, so that enrichment of the particles in the dimension of
216
A. Boudjemaa and S. Gómez-Ruiz