TIO2 PHOTOCATALYSIS FOR IMPROVING THE AIR QUALITY: FROM MOLECULES, TO BUILDING MATERIALS DEVELOPMENT
Tesi di Dottorato
Data di Pubblicazione:
2017
Citazione:
TIO2 PHOTOCATALYSIS FOR IMPROVING THE AIR QUALITY: FROM MOLECULES, TO BUILDING MATERIALS DEVELOPMENT / M. Stucchi ; tutor: C. L.M. Bianchi ; co-tutor: C. Argirusis. DIPARTIMENTO DI CHIMICA, 2017 Mar 16. 29. ciclo, Anno Accademico 2016. [10.13130/stucchi-marta_phd2017-03-16].
Abstract:
General abstract
1. Introduction
During these last years, the innovation and development processes lead pollution to its highest level; the air pollution is one the most prominent and dangerous form of it. Causes are several, from fuel combustion to factories activity, which increase the level of organic molecules and nitrogen or sulfur oxides in atmosphere (WHO Global Urban Ambient Air Pollution Database, update 2016).
Unfortunately, effects are more than evident: from the global warming, to the acid rains, from the sudden climate changes, to the increase of diseases such as asthma and lung cancer (Ambient (outdoor) air quality and health, WHO).
Outdoor air pollution is the major environmental health problem affecting everyone in developed and developing countries alike, however, unlike one might usually think, indoor levels of organic pollutants are often higher than outdoor (Viegi et al., 2004). The problem is even more important because people live mainly indoors, constantly exposed to all the pollutants present in these close environments (Chen et al., 2016; Allen et al., 2016).
For this reason, demands to improve the air quality situation have been largely extended, finding new strategies for waste reduction or for the oxidation and degradation of pollutants (Ambient (outdoor) air quality and health, WHO).
Among several processes, considering that very important factors are saving energy and reducing emissions, photocatalysis has been exploited as very suitable technique to reduce pollution.
In a photocatalytic reaction (eq. 1), a semiconductor material, the photocatalyst, is activated by light and, thanks to the formation of some electron-hole couples between his valence and conduction bands, it is able to reduce or oxidize molecules that adsorb on his surface (J.M. Herrmann, 2005).
In heterogeneous photocatalysis, the reaction implies the previous formation of an interface between the semiconductor and the reactants of the reaction (K. Demeestere et al., 2007; M. Schiavello, 1997).
(Ox1)ads + (Red2)ads Red1 + Ox2 (1)
Among a large variety of semiconductor materials, which are mainly metal oxides, only few of them are considered to be applicable photocatalysts, in relation with their specific photocatalytic properties. Titanium dioxide (TiO2) induced photocatalysis is an example of AOP processes and it has been demonstrated its efficiency in the decomposition of various organic contaminants. TiO2 is a very well known and well-researched material due to the stability of its chemical structure, biocompatibility, physical, optical, and electrical properties (M. Serpone et al., 1989).
The crystalline forms of TiO2 are anatase, rutile and brookite (A. Linsebigler et al., 1995). In general, TiO2 is preferred in anatase form because of its high photocatalytic activity, however the major drawbacks of TiO2-based photocatalysts is related to the rapid charge recombination of the electron−hole pairs, and the wide band gap, which restricts light absorption to only ultraviolet region (wavelength <390 nm), restraining the practical applications of TiO2-based photocatalysts under solar light or visible light.
TiO2-based photocatalysts are used for a variety of applications such as degradation of volatile organic compounds (VOCs) and decomposition of nitrogen pollutants (NOx) or also organic dyes, like Methylene Blue (K. Demeestere et al., 2007; P.K.J. Robertson et al., 2005).
When TiO2 is irradiated with energies equal to or higher than its band gap (>3.0 eV), electrons are excited from the valence band into the conduction band, leading to excited electrons in the conduction band and positive holes in the valence band. This fundamental process can be expressed by the
Tipologia IRIS:
Tesi di dottorato
Keywords:
TiO2; photocatalysis; photocatalytic materials; visible light activity; pollution; air quality
Elenco autori:
M. Stucchi
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