Chances and limitations of nanosized titanium dioxide practical application in view of its physicochemical properties

Abstract

Nanotechnology is a field of science that is nowadays developing in a dynamic way. It seems to offer almost endless opportunities of contribution to many areas of economy and human activity, in general. Thanks to nanotechnology, the so-called nanomaterials can be designed. They present structurally altered materials, with their physical, chemical and biological properties entirely differing from properties of the same materials manufactured in microtechnology. Nanotechnology creates a unique opportunity to modify the matter at the level of atoms and particles. Therefore, it has become possible to obtain items displaying new, useful properties, i.e. self-disinfecting and self-cleaning surfaces. Those surfaces are usually covered by a thin layer of a photocatalyst. The role of the photocatalyst is most of the time performed by the nanosized titanium dioxide (nano-TiO2). Excitation of nano-TiO2 by ultraviolet radiation initiates advanced oxidation processes and reactions leading to the creation of oxygen vacancies that bind water particles. As a result, photocatalytic surfaces are given new properties. Those properties can then be applied in a variety of disciplines, such as medicine, food hygiene, environmental protection or building industry. Practically, the applications include inactivation of microorganisms, degradation of toxins, removing pollutants from buildings and manufacturing of fog-free windows or mirrors.

Keywords: Bacteria; Nanotechnology; Photocatalysis; Reactive oxygen species; Self-disinfecting and self-cleaning surfaces; Titanium dioxide.

Figure 1

ROS generation and its effects. Mechanism of reactive oxygen species (ROS) generation on the surface of titanium dioxide nanoparticles (a) and the effects of ROS activity on organic substances and microorganisms (b). On the surface of the nano-TiO₂ particles, exposed to UV radiation, ROS (^•O₂ ⁻, ^•OH, H₂O₂) are formed (a) that have the ability to inactivate microorganisms and to oxidize organic matter (b).

Figure 2

Comparison of contact angle ( α ) on control surface (a) and surface covered by a thin layer of nano-TiO ₂ (b). Both surfaces are exposed to UV radiation. The surface covered by a thin layer of nano-TiO₂ and exposed to UV radiation exhibits superhydrophilic properties; the contact angle is an acute angle, 0° < α < 90° (b).

Figure 3

Comparison of contact angle ( α ) on control surface (a) and surface covered by a thin layer of nano-TiO ₂ (b) in darkness. The surface covered by a thin layer of nano-TiO₂ exhibits in darkness superhydrophobic properties; the contact angle is an obtuse angle, 90° < α < 180° (b).