2.3. Characterization

Mineralogical analyses were done by laser Raman microspectroscopy (Raman; inVia Raman Microscope, green laser, 514 nm, 20, 1.5-μm beam diameter, Renishaw, Wotton-under-Edge, Gloucestershire, UK). Microstructural analyses were done by field emission gun scanning electron microscopy (Field emission gun scanning electron microscopy (FEG-SEM); LEO 1525, 15, or 20 kV accelerating voltage, LEO Electron Microscopy Inc., Thornwood, NY, USA). Elemental analyses were done by paired energy dispersive spectroscopy (EDS; Bruker Quantax, Bruker Italia S.r.l., Milan, Italy).

2.5. Antibacterial effects

of >85% in the range of 340–380 nm.

3. Results and discussion

3.1.1. Field emission gun scanning electron microscopy

3.1. Characterization

The photocatalytic tiles were tested using Escherichia coli (E. coli, ATCC 8739) according to ISO 27447:2009 Fine Ceramics—Test Method for Antibacterial Activity of Semiconducting Photocatalytic Materials. Each strain was inoculated into a nutrient agar slant, incubated for 16–24 h at 37 1C, and then transferred to a new nutrient agar slant and again held at 37 1C for 16–24 h. An appropriate quantity of bacteria was dispersed in 1/500 nutrient broth (NB) to obtain a count of 6.7 <sup>10</sup><sup>5</sup> to 2.6 <sup>10</sup><sup>6</sup> cells/mL. Tile samples of dimensions 50 50 mm were rinsed with distilled water and autoclaved at 121C for 30 min prior to testing in order to remove any organic residue on the surfaces. For each strain, six tile samples without (controls) and six with photocatalytic coating were investigated. A volume of 0.15 mL of bacterium suspension was placed on each specimen and covered with an inert and non-water adsorbent film of dimensions 40 40 mm; the film transmitted >85% of radiation in the range of 340–380 nm. Each specimen was placed in a 100-mm diameter Pyrex Petri dish containing a moistened paper filter to prevent drying of the suspension and covered with a 1-mm thickness borosilicate glass slide, also with radiation transmission

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

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

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A fluorescent UV lamp (18 W, Royal Philips, Amsterdam, Netherlands) was used for the testing at an intensity of 0.25 mW/cm2 for 8 h. A viability count was performed by dilution and plating

The FEG-SEM images shown in Figure 2 reveal a relatively widespread, homogeneous, and thick deposition of TiO2 on the digital inkjet-printed tile surface in comparison to the jetsprayed tile surface, which shows that voids are present. The EDS data confirmed a greater areal extent of coverage by TiO2 for digital inkjet printing. However, it is significant that the digital inkjet-printed coating exhibits a considerably lower degree of agglomeration than does the jet-sprayed coating. The former can be expected to provide a greater surface area and associated density of photocatalytically active sites. The reason for this difference is the superior dispersion of the TiO2 powder by the inclusion of a dispersant in the ink, which reduced the formation of soft agglomerates. Further, it is likely that the included organic phases played a key role in the development of this microstructure through separation of the particles and consequent surface exposure during pyrolysis. Consequently, digital inkjet printing can be expected to exhibit a superior photocatalytic performance owing to the greater volume of

deposited TiO2, the extent of areal coverage of the tile, and exposed surface area.

on nutrient agar incubated at 37C for 48 h. More details are reported elsewhere [37].
