**Photocatalytic TiO2: From Airless Jet Spray Technology to Digital Inkjet Printing** Photocatalytic TiO2: From Airless Jet Spray Technology to Digital Inkjet Printing

DOI: 10.5772/intechopen.72790

Claudia L. Bianchi, Carlo Pirola, Marta Stucchi, Giuseppina Cerrato, Federico Galli, Alessandro Di Michele, Serena Biella, Wen-Fan Chen, Pramod Koshy, Charles Sorrell and Valentino Capucci Claudia L. Bianchi, Carlo Pirola, Marta Stucchi, Giuseppina Cerrato, Federico Galli, Alessandro Di Michele, Serena Biella, Wen-Fan Chen, Pramod Koshy, Charles Sorrell and Valentino Capucci

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http://dx.doi.org/10.5772/intechopen.72790

#### Abstract

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TiO2 powders can be employed as both photocatalytic and structural materials, leading to applications in external coatings or in interior furnishing devices, including cement mortar, tiles, floorings, and glass supports. The technology of photocatalytic building materials is connected with the widespread production of photocatalytic active tiles. All the techniques proposed in the study involve the employment of nanosized TiO2: this represents a new problem to be dealt with, as inhaling nanoparticles exposes workers during industrial production and people in everyday locations to their dangerousness. Only very recently the employment of microsized TiO2 has been proposed, and the authors in this manuscript report the use of micrometric titania materials, but employing a new deposition technique, which is digital inkjet printing. It represents an improvement of the classical spray coating methods, as it requires piezoelectric heads to precisely direct the deposition of the suspension with an electrostatic field. The mixture contains aqueous/ organic components containing micrometric TiO2: to form a suspension, which is printed onto the surface of porcelain grès, large slabs using a digital printer. Many advantages are immediately evident, namely rapid and precise deposition, (almost) no waste of raw materials, thereby highlighting the economy, environmental friendliness, and sustainability of the process. All the materials we obtained have been thoroughly characterized by means of several experimental physico-chemical techniques, such as Raman microspectroscopy and scanning electron microscopy coupled with elemental analysis. Two different model VOCs, ethanol and toluene, and NOx have been selected to test the

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

distribution, and eproduction in any medium, provided the original work is properly cited.

photocatalytic performances of the abovementioned tiles. Moreover, the antibacterial properties of the tiles have been determined, using Escherichia coli as example. Life cycle assessments (LCAs) for the two processes were modeled for 1 m2 of tiles produced in Modena, Italy. The impact assessments revealed that jet spraying exhibited uniformly greater impacts than digital inkjet printing and that the principal impacts were in human toxicity, cancer effects, freshwater ecotoxicity, and climate change. Most of the impacts were associated with the energy required for the production processes. Further considerations revealed that jet spraying is projected to generate twice as much CO2 and 30% more NOx than digital inkjet printing.

1.2. Photocatalytic TiO2 and its applications

zation of contamination from the substrate.

gas concentration and residence time [22].

respirability of nanoparticulates [26].

Semiconductor photocatalysis involves the activation of a photocatalytic material, such as titania (TiO2), by the action of light to produce charge carriers that undergo redox reactions with water and oxygen molecules [11]. This property allows these materials to decompose organic contaminants ideally into CO2 and water, thus allowing applications in self-cleaning, anti-fogging, corrosion prevention, and air and water purification [12]. Although there are many scientific and technical requirements for effective photocatalytic performance [13], there are also numerous practical challenges that must be met. One of these is catalyst immobilization [14] because it generally must balance the requirements of achievement of a robust chemical bond to a substrate, the retention of sufficient exposed surface area, and the minimi-

Photocatalytic TiO2: From Airless Jet Spray Technology to Digital Inkjet Printing

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There has been an increase in the sales of TiO2-based products for self-cleaning and air and water purification owing to growing environmental concerns [15]. One of the key product developments was photocatalytic building materials, which appeared on the market at the beginning of the 1990s [16]. TiO2 can be applied either in exterior construction or in interior furnishing materials, including concrete, mortar, tiles, flooring, and glass. In the early 2000s, the sales of photocatalytic building materials accounted for ~60% of the total market for photocatalytic materials [17]. Recent market projections to 2020 foreshadow increasing demand in the construction sector for self-cleaning coatings and other technologies for improving air quality, leading to a global market for photocatalyst-based products of ~\$2.9 billion [18]. At present, TiO2-based photocatalyst products constitute 97.6% of the market, and this dominance is a result of TiO2's low cost, ready availability, and well-documented performance data. Many studies have demonstrated the effectiveness of photocatalytic materials for pollution abatement of the volatile organic compounds (VOCs) and nitrogen oxides (NOx) that represent widespread risks to health. For example, concrete paving blocks with TiO2 added directly to the mix were able to remove 4.01 mg/h/m2 of NO [19]. However, similar work demonstrated that the efficiency of NOx photodegradation varied significantly according to preparation method and resultant microstructure, with some products achieving 40% photodegradation while others showed almost no effect [20]. A comparison between pure TiO2 and TiO2 embedded in neat hydrated cement revealed that the photocatalytic activity was three to 10 times lower for the latter, which was attributed to the agglomeration of the TiO2 powder [21]. TiO2 also has been applied as surface coatings on roofing tiles and corrugated sheet and found to achieve gaseous toluene removal efficiencies as high as 78 2%, although this was limited by

It is clear that the permanence and performance of TiO2-containing construction products depend significantly on the method used to immobilize the photocatalyst, whether in the bulk or on the surface. Other factors of importance include the type of substrate and the method of TiO2 application [23]. Hence, there has been a commensurate focus on the design of such building products and their manufacture in order to obtain maximal lifetimes and efficiencies. An additional consideration is the potential alteration of the photocatalyst by fouling, which can block the active sites and reduce or prevent photocatalysis [24]. Finally, there are also potential health issues associated with the formation of chemical intermediates [25] and the

Keywords: TiO2, titania, digital inkjet printing, jet spraying, VOCs, NOx, E. coli, life cycle assessment, impact assessments
