2.5. Antibacterial effects

2.3. Characterization

266 Titanium Dioxide - Material for a Sustainable Environment

Italia S.r.l., Milan, Italy).

2.4. Photocatalysis testing

2.4.2. Nitrogen oxides

for Europe (range 100–200 ppb).

2.4.1. Volatile organic compounds

GC System, Agilent Technologies Italia S.p.A, Milan, Italy).

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

VOC photodegradation reactions were conducted in a Pyrex glass cylindrical reactor with a diameter of 200 mm and an effective volume of 5 L [38]. A 100-cm<sup>2</sup> digital inkjet-printed sample or jet-sprayed sample was placed at the bottom of the reactor and exposed to a 500-W iron halogen lamp (HG 500, 315–400 nm, UV-A, Jelosil, Milan, Italy). The reactor had two entrances, one for VOC loading and the other for sampling by a gas chromatograph (490 Micro

Ethanol and toluene were selected as model pollutants, and the initial concentration for both

Two different setups were used—one under static conditions [39] and the other under flowing conditions [40]. A chemiluminescence NOx monitor (Teledyne API, Model 200E, San Diego, CA, USA) provided online detection of NO and NO2 concentrations. The batch reactor consisted of a Pyrex glass cylinder of volume of 25 L; this is described elsewhere [39]. The tile (2 20 cm) was located at the bottom of the cylinder and an overhead 500-W iron halogenide lamp (HG 500, 315–400 nm, UV-A, Jelosil, Milan, Italy) provided irradiation of 20 W/m2

inlet gas consisted of NO2 (0.6% in N2) mixed with air of relative humidity (RH) 40%, which allowed equilibration between NO and NO2 to be reached quickly. The NO2 concentration was set at 1000 ppb (static) or 250 ppb (flowing) and tests lasted 6 h each. The continuous flow reactor allowed testing of larger tiles (60 60 cm) [40]. A Thermo-Hygro Meter (HT-3006A, Metravi, Calcutta, India) measured both temperature and relative humidity, which ranged between 40 and 50%. Two iron halogen lamps (Jelosil, model HG 500), at 770-mm center-tocenter distance, which was designed to irradiate the sample surface with the same 20 W/m<sup>2</sup> light intensity, were used. The total NOx gas flow was in the range of 140–180 NL/h, which is in accordance with the standard concentration based on the limiting values specified in Directive 2008/50/EC of the European Parliament and of the Council on Ambient Air Quality and Cleaner Air

was 400 ppm for each test. The photodegradation tests were conducted for 6 h.

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 of >85% in the range of 340–380 nm.

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