Simultaneous photodegradation of VOC mixture by TiO2 powders

Accepted Manuscript Simultaneous photodegradation of VOC mixture by TiO2 powders Marta Stucchi, Federico Galli, Claudia L. Bianchi, Carlo Pirola, Daria C. Boffito, Franco Biasioli, V. Capucci PII:

S0045-6535(17)31763-0

DOI:

10.1016/j.chemosphere.2017.11.003

Reference:

CHEM 20198

To appear in:

ECSN

Received Date: 22 September 2017 Revised Date:

31 October 2017

Accepted Date: 1 November 2017

Please cite this article as: Stucchi, M., Galli, F., Bianchi, C.L., Pirola, C., Boffito, D.C., Biasioli, F., Capucci, V., Simultaneous photodegradation of VOC mixture by TiO2 powders, Chemosphere (2017), doi: 10.1016/j.chemosphere.2017.11.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Simultaneous photodegradation of VOC mixture by TiO2 powders

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Marta Stucchia, Federico Gallia,*, Claudia L. Bianchib, Carlo Pirolab, Daria C. Boffitoa,

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Franco Biasiolic, V. Capuccid

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a

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H3C 3A4 Montrèal (QC), Canada.

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b

Università di Milano, Chemistry Department, Via Golgi 19, 20133 Milano, Italy.

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c

Research & Innovation Centre, Fondazione Edmund Mach, Via E. Mach 1, 38010 San

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Michele a/A, Italy.

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d

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Polytechnique Montréal, Département de Génie Chimique, 2900 Edouard Montpetit Blvd,

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GranitiFiandre SpA, Via Ghiarola Nuova 119, 42014 Castellarano, Italy.

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*corresponding author: [email protected]

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Abstract

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Volatile and semi volatile organic compounds’ concentration have dramatically increased in

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indoor environments in recent years. UV light promotes titanium dioxide, which oxidises

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various molecules; however, most of the studies report the degradation of a single VOC. Here,

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we investigate the photo-oxidation of 17 molecules in mixture to have a realistic test of TiO2

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efficacy. We compare P25, a nanometric catalyst, and 1077, a micrometric sample, that poses

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less health concerns. A proton-transfer-reaction mass spectrometer measured online the

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concentration of all the pollutants simultaneously. Aldehydes compete for the adsorption on

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both the catalyst’s active sites and thus they degrade 70 % and 55 % with P25 and 1077

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respectively. Considering the single pollutant oxidation, instead, aldehydes fully oxidize. Even

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though benzene is recalcitrant to degradation, P25 and 1077 reduced toluene’s concentration

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to 97 % and 96 % in 55 min, respectively. Acetonitrile is refractory to photocatalysis.

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Keywords

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Photocatalysis, PTR-MS, VOCs mix, titanium dioxide, micrometric, indoor pollution

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1. Introduction

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European Environmental Agency estimated that Europeans spend 90 % of their time indoor

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(European Environment Agency, 2013). Americans and Canadians spend 87 % of time

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indoors and an additional 6 % in a vehicle (Klepeis et al., 2001).

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The US Environmental Protection Agency (EPA) found that indoor air is two to five times

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more polluted than outdoor air (Sundell, 2004). Indoor volatile organic compounds (VOCs)

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exposure may originate both human health effects and symptoms including liver damage,

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mucous membrane irritation, nausea, dyspnoea, and dizziness (US Environmental Protection

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Agency) (Branco et al., 2014). Both inorganic and organic species pollute indoor

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environments (Jeleńska et al., 2017). Their concentration depends on emissions rates, room

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dimensions in which these emissions occur, and adsorption capacity of materials (Wallace,

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2001).

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The World Health Organisation (WHO) focused its attention for the first time on indoors

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organic pollutants in 1989 (World Health Organization). Since then, diverse analytical

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techniques were developed (Panagiotras et al., 2014). Minhucd and Zaray detected more than

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500 indoor organic pollutants (Mihucz and Zaray, 2016).

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Aldehydes pollute 99.4 % of the environment (Clobes et al., 1992): acrolein exceeds 1.1 μg/m3

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and in the 5 % of domestic environments, hexaldehyde concentration is greater than 50.2 μg

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m-3 (Duboudin, 2009). Hydrocarbons values range from a concentration of 1.0 μg/m3 for

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ACCEPTED MANUSCRIPT styrene and trichloroethylene to 12.2 μg m-3 for toluene, from 2.7 μg m-3 to 150 μg m-3 in the

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case of 1,4-dichlorobenzene (Kirchner et al., 2007).

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The most abundant VOCs are formaldehyde and benzene (Harrison et al., 2010). Benzene

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concentration range from 8 μg m-3 (Batterman et al., 2007), to 167 μg m-3 (Pandit et al., 2001)

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while formaldehyde exceeds 20 μg m-3 in most of the environments (Chen et al., 2016).

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The International Agency for Research on Cancer (IARC) classifies formaldehyde as human

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carcinogen (Group 1) (Salthamer et al., 2013; World Health Organization, 2010; Dahnke et al.,

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2002). Formaldehyde levels highly increased in polluted urban areas, until it reached the

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same concentration both outdoor and indoor, as reported by WHO (World Health

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Organization, 2010). Indoor concentration levels oscillate depending on the detection site. Jia

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et al. reported an indoor concentration of 390 ± 200 μg m-3 (Jia, 2015), while Liu et al.

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revealed a concentration of 1120 ± 624 μg m-3 (Liu et al., 2006). Prefabricated houses where

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chipboard furniture or carpets are the indoor that are mostly concerned, because these

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materials contain and release formaldehyde (Ryan and Bowles, 2011; Jones, 1999; Vaajasaari

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et al., 2004). Phthalates, pesticides, alkilphenols and aromatic cyclic hydrocarbons (semi-

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volatile organic compounds) are equally important because they adsorb on surfaces and are

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more abundant than typical VOCs.

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Carbonyls are the most stable intermediate species in the oxidation of VOCs (Huang et al.,

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2016). In residential environments, the predominant molecules bearing carbonyl groups are

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aldehydes (Villaneuva et al., 2015 ). Clarisse et al. measured contamination levels in several

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houses in Paris, basing on a multiple linear regression model; they found that

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propionaldehyde and benzaldehyde were less concentrated than formaldehyde, acetaldehyde,

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pentanal, and hexanal (Clarisse et al., 2003). The average concentration value was 34.4 ± 1.9

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μg m-3 (ppb) for formaldehyde and 10.7 ± 1.8 μg m-3 (ppb) for acetaldehyde. However, Pereira

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et al. (Pereira et al., 2004) validated a specific method to detect aldehydes and they compared

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ACCEPTED MANUSCRIPT acetaldehyde and formaldehyde specifically, finding acetaldehyde levels higher than

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formaldehyde, Nevertheless, acetaldehyde concentration strongly depends on human exhaled

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air as reported by Concle et al. (Conkle, Camp, and Welch, 1975).

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Zhang et al. (Zhang, He, and Lioy, 1994) found that indoor formaldehyde and acetaldehyde are

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2-10 times higher than outdoor, bearing their relevance. Catalysts (Rodriguez et al., 2016;

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Karuppiah et al., 2012) or photocatalysts (Hussain et al., 2017) degrade VOCs. TiO2 based

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catalysts photodegrade ethanol (Bianchi et al., 2015b), NOx (Bianchi et al., 2015a),

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formaldehyde (Zhang et al., 2016) and other VOCs (Gunschera et al., 2009).

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UV light absorbed excites electrons of a photocatalyst (which is a semiconductor). These

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electrons transfer to the conductive band of the material and become available for chemical

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reaction if the recombination time is long enough. On the other hand, a positive vacancy is left

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when the electron leaves. This oxidises electron donors, like organic molecules, and

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contributes to the photocatalytic effect. A detailed review on the principles and mechanism of

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photocatalysis was published by Linsebigler et al. (Linsebigler, Lu and Yates, 1995). In the last

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years, research work aimed at making the recombination between photogenerated electron

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and positive hole less probable has been published, in order to increase catalyst’s quantum

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yield. Wang et al. prepared rutile TiO2 nanorod and achieved a longer distance electron

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transfer along it. They were able to improve by one order of magnitude the photodegradation

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of benzene (Wang et al., 2016).

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photocatalyst with carbon nitride and titanium dioxide. They obtained between 78 % and 97

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% formaldehyde conversion depending on the preparation method (Yu et al., 2013). Huang

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degraded a mixture of 59 VOCs with thermally activated persulfate (Huang et al., 2005).

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Except halogenated alkanes, all compounds oxidized, especially if double bonds were present.

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However, persulfate is a stoichiometric catalyst and is active in solution. A photocatalysts

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react VOCs directly in gas phase.

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On the other hand, Yu et al. prepared a Z-scheme

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ACCEPTED MANUSCRIPT Hussain et al. oxidized ethylene and propylene with nanostructured titania-silica catalysts

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(Hussain et al., 2017), and Abbas et al. reported the degradation of ethylene, propylene and

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toluene by nano-TiO2 (Abbas et al., 2011). Zhang et al., reached > 75 % formaldehyde

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degradation with a nano-TiO2/diatomite composite (Zhang et al., 2017). They evaluated the

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influence of catalyst amount, light intensity and relative humidity. The good dispersion of the

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active phase and the strong interaction between the VOC and the catalyst were the reasons for

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the high activity.

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Ao et al. (Ao et al., 2003) reported the simultaneous degradation of BTEX, NOx and VOCs,

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excluding aldehydes. However, aldehydes are preponderant in indoor environment. No one

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studied the photo-catalytic abatement of several (10+) VOCs, including aldehydes.

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Evaluating the activity of TiO2 with a mixture of VOC gives information about titanium dioxide

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reactivity in real condition (Grinshpun et al., 2007; Boyjoo et al., 2017).

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Gas chromatography detects and quantifies single VOCs offline. However, since a GC’s

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response time is much slower compared to most photodegradation reactions, a gas

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chromatograph is not suited to monitor a fast reaction in continuous whereby the sample is a

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mixture that requires adequate peak separation.

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Proton-transfer-reaction mass spectrometry (PTR-MS) is a technique able to monitor the

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photodegradation of a wide range of compounds either in solution (Zou et al., 2017) or in gas

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phase (Hewitt et al., 2003), thus detecting individual VOCs in a mixture. Bianchi et al. (Bianchi

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et al., 2016) detected aldehydes and their oxidation by-products with PTR-MS.

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Therefore, our work is original for several aspects: i) We target the degradation of a gaseous

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mixture of aldehydes, hydrocarbons and chloro-aromatic compounds (17 chemicals in total);

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ii) We selected a micrometric photocatalyst vs. the widely adopted nano-sized powder (e.g.

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TiO2 P25) with the intent to avoid nano-risks; iii) We adopt proton-transfer-reaction mass

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spectrometry (PTR-MS) to detect single components in a mixture.

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2. Material and methods

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We tested Degussa (Evonik) P25 and 1077 by Kronos. The characterization data of P25 (75:25

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Anatase:Rutile) are well known (Ohtani et al., 2010). Bianchi et al. characterized 1077 TiO2

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(Bianchi et al., 2013; Bianchi et al., 2014); P25 and 1077 differ in particle size: the former is

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nanometric while the latter micrometric (see Supporting Information, Table S1).

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P25 is the photocatalysts with the largest production volume, as well as the reference sample

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for photocatalysis (Sangchay, Sikong, and Kooptarnond, 2012) because of its high activity in

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many photocatalytic reactions (Ohtani et al., 2010).

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Ohno et al. reported P25 morphology and its crystallographic composition (Ohno et al., 2001).

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However, P25’s size is a critical issue. Nanoparticles are dangerous for human health because

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they interact with living cells (Warheit, 2013).

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Kronos Company Inc. produces several TiO2 powders as pigments. Among them, 1077

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consists only of anatase and its particles are homogeneous in size. We selected 1077 after

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comparing its photocatalytic activity with other commercial samples (Bianchi et al., 2013).

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IONICON Analytik Gesellschaft m.b.H. supplied the mixture of pollutants (diluent: nitrogen).

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2.1

PTR-MS and photocatalytic tests

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2.1.1 PTR-MS

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Proton-transfer-reaction mass spectrometry (PTR-MS) is a technique developed 1995 almost

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exclusively for the detection of volatile organic compound (VOCs) (Blake, Monks and Ellis,

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2009). Having a response time of 10 ms, it is highly sensitive to small variations in

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concentrations and is regarded as a real time detection technique (De Gouw and Warneke,

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2007). The laboratory of the “Sensory Quality and Traceability” department, at the Edmund

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ACCEPTED MANUSCRIPT Mach foundation (Trento), determined VOCs concentration with a PTR mass spectrometer

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(IONICON Analytic GmBH, Compact IONICON PTR-TOF-MS).

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A pump sends air through a drift tube reactor. VOCs react with hydrogen ions (H+) without

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fragmentations; the mass of the product ion equals the VOC mass plus one. A quadrupole mass

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spectrometer, placed at the end of the drift tube, measures product ions. The signal is

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proportional to the VOCs’ concentration. In addition, the sample does not require any

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treatment (De Gouw and Warneke, 2007). We calibrated the instrument as reported by Blake

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et al. (Blake et al., 2009; Yao and Feilberg, 2015).

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2.1.2 Photocatalytic system

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The reactor is a glass 5 L volume cylinder with three ports. The Gas Calibration Unit (GCU,

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IONICON Analytik GmbH, Austria) sets the VOC concentration by varying air and VOCs

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mixture flowrate (Fig. 1).

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Figure 1. Setup scheme.

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We suspended 50 mg of powder in 10 ml of isopropanol and placed it on the glass. We

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repeated this operation three times. We placed the plate in the center of the reactor. To

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maintain a uniform atmosphere, we placed a magnetic stirrer beneath the plate. Valve opens

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during the reactor loading. When the concentration inside the reactor reached a constant

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value, the valve closed and the reaction starts by turning on the UV lamp. We calculated the

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uncertainty of the experimental data monitoring the concentration after the loading

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procedure (stationary state) before starting the reaction.

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A UV lamp (500 W Jelosil model HG 500, emitting in the 315–400 nm wavelength range UV-A)

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is 40 cm above the reactor and irradiates the sample with an energy of 30 Wm-2 (measured by

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a spectrophotometer).

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The gas mixture bubbles through water and enters the reactor with a relative humidity (RH)

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of 40 %.

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3. Results and discussion

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3.1 Aldehydes

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Formaldehyde concentration decreased over time with both catalysts (Fig. 2).

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Figure 2. Aldehydes concentrations vs. UV irradiation time (power: 30 Wcm-2) by nanometric TiO2

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(top) and micrometric TiO2 (bottom).

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64.1 60.0

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Formaldehyde Acetaldehyde Acrolein Crotonaldehyde

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ppb) in 30 min. The trend is the same for Chrotonaldehyde and Acrolein despite their

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different chemical structures and the higher initial concentrations. P25 and Kronos degraded

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72 % and 55 % acetaldehyde, respectively. We speculate that the slower acetaldehyde

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degradation rate compared to the single pollutant degradation (see Supporting Information)

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is due to a competition between bigger aldehydes to access TiO2 active sites. However, the

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total amount of aldehydes reduced of 88% and 80% with P25 and Kronos, respectively,

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confirming the grater activity of P25 compared with the micrometric sample, as confirmed by

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Jung et al. (Jung, Park, and Ihm, 2002).

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Kinetic studies performed on the mixture of aldehydes compared with single-compound

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photodegradation confirms the competition between aldehydes and catalysts active sites. C.L.

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Bianchi et al. (Bianchi et al., 2016) showed that both P25 and 1077 micro-TiO2 oxidize

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acetaldehyde (starting concentration 400 ppm) after 60 minutes.

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In mixture, the competing presence of other molecules slows down the oxidation, i.e. 70 % of

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acetaldehyde is degraded in 1 h (Fig. 2) at both concentrations tested vs. the uncompleted

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oxidation in the presence of other compounds (Fig. 2). Crotonaldehyde and acrolein

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degradation rates are similar for both the catalysts.

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3.2 Hydrocarbons

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Comparing the trend of hydrocarbons with both the catalysts (Fig 3), results are coherent

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with samples’ particle size.

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Figure 3. Hydrocarbons concentration vs. UV irradiation time (30 W cm-2) by nanometric TiO2 (top)

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and micrometric TiO2 (bottom).

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Benzene Toluene o-xylene a-pinene Isoprene

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Benzene Toluene o-xylene isoprene a-pinene

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Indeed, nanometric TiO2 reached higher hydrocarbon conversion. Considering benzene and

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toluene, their conversions after 10 min are 35.9 % and 57.4 %, respectively, with P25; with

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1077 they are 16.1 % and 39.6 % (Table 1). Toluene degrades more than benzene if they are

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in mixture.

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ACCEPTED MANUSCRIPT Fu et al. investigated the oxidation of benzene over different TiO2 photocatalysts; they

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reached complete degradation of benzene after doping TiO2 with Pt (Fu, Zeltner, and

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Anderson, 1995). After, Jacoby et al. (Jacoby et al., 1996) proved the efficiency of TiO2 for the

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degradation of benzene; moreover, they showed that i) UV light promotes adsorption of

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benzene, ii) water adsorption interferes with benzene one and, iii) the surface reaction is the

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rate-limiting step. In 2011, Xie et al. reported the photodegradation of benzene with TiO2, as

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single molecule (Xie et al., 2011) and showed that concentration of benzene decreases from

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20 (± 2) to 3 (± 1) ppb in 500 minutes, with a final degradation of 85 (± 1) %. Bianchi et al.

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showed toluene is recalcitrant to photo-oxidation (Bianchi et al. 2014); consider the

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photodegradation of toluene as single molecule (starting concentration 400 ppm), both nano-

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and micro-TiO2 reached a maximum degradation of 60 and 46 % respectively (see Supporting

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Information).

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Both the catalysts eliminate α-pinene, isoprene and o-xylene in 55 min.

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Considering the mixture, benzene competes with toluene for the adsorption on the active sites

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of TiO2. This is consistent considering the steric hindrance of each molecule: Toluene fills the

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surface first because its molecular surface area is greater than benzene’s. Photocatalytic

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reactions are generally interpreted with a Langmuir Hinshelwood mechanism (Alberici et al.,

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1997).

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3.3 Chlorinated compounds

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1077 photocatalytic activity is lower than P25 for chlorinated compounds, confirming the

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relation between photocatalytic activity and surface area (Fig 4).

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Figure 4. Chlorinated compounds concentration vs. UV irradiation time (30 Wcm-2) by nanometric

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TiO2 (top) and micrometric TiO2 (bottom).

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2D Graph 4

Chlorobenzene 1,2-dichlorobenzene 1,2,4-trichlorobenzene

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We speculate that the rate-determining step for the degradation of a mixture of VOC is the

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adsorption (external diffusion) on the catalysts active sites, thus the higher surface area the

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higher the degradation.

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3.4 Other VOCs

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ACCEPTED MANUSCRIPT TiO2 transforms methanol and ethanol as single molecules in CO2. Bianchi et al. (Bianchi et al.,

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2015b) obtained a complete photodegradation with both P25 and micro-TiO2 after 60

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minutes.

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Alberici et al. reported the photocatalytic destruction of several VOCs, including methanol,

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with a conversion of 97.9 % (Alberici et al., 1997); Addamo et al. investigated the degradation

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of acetonitrile using commercial TiO2 catalysts, showing that the final degradation depends on

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the acetonitrile starting concentration and P25 did not completely mineralize it (Addamo et

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al., 2005).

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Here, the data collected (Fig. 5) highlight the competition among VOCs for active sites.

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Figure 5. Generic VOCs concentration vs. UV irradiation time (30 W cm-2) by nanometric TiO2 (top) and

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micrometric TiO2 (bottom).

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ACCEPTED MANUSCRIPT 43.6 40.0

2-butanone Methanol Acetonitrile Ethanol

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Photo-degradation rate of acetonitrile is lower in comparison with the other organic

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molecules, and 1077 is not effective for acetonitrile degradation (degradation 0.7 % after 10

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minutes) while P25 reached a conversion of 15.2 % after 20 minutes (Table 1), which is

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consistent with previous investigations that showed its low reactivity towards photo-

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oxidation (Inturi et al., 2014).

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Table 1. VOCs conversion % after 10 and 20 minutes for P25 or 1077 Kronos and dipolar moment of

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VOC.

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ACCEPTED MANUSCRIPT P25 time

1077 KRONOS

10’

20’

10’

Dipolar moment (Rumble, 2017)

(D)

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Formaldehyde 42.7 ±1.9 61.0 ±1.7 15.9 ±2.9 23.6 ±2.8 1.85 57.4 ±0.8 71.6 ±0.8 43.4 ±0.9 54.9 ±0.9 2.70

Benzene

35.9 ±2.0 62.4 ±1.8 16.1 ±1.3 31.8 ±1.2 0.00

Toluene

57.4 ±3.9 84.8 ±3.6 39.6 ±4.4 68.5 ±3.9 0.38

2-Butanone

63.4 ±2.2 88.1 ±2.1 57.1 ±1.6 85.1 ±1.5 2.78

Methanol

61.1 ±1.5 75.9 ±1.4 50.8 ±1.4 70.7 ±1.3 1.60

Ethanol

60.3 ±3.3 83.1 ±3.1 68.9 ±3.1 85.3 ±3.0 1.69

Acetonitrile

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±1.8 10.1 ±1.8 3.92

The lower surface area of 1077 affected formaldehyde and benzene degradation, decreasing

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them of 37 % and 30 %, respectively, compared to P25 (Table 1). For other VOCs, such as 2-

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Butanone, Methanol, Ethanol and Acetonitrile, the difference in activity between the two

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catalysts reduced to maximum 5 %.

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Alberici et al. (Alberici et al., 1997) speculated that in a gas phase reactor the adsorption of

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molecules is the kinetic limit step. According to their results, alcohol adsorbs more than

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ketones and almost ten times more than chlorinated compounds. The least adsorbed

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molecules were hydrocarbons.

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Due to the presence of hydroxyl group on titanium dioxide surface, so it is reasonable to think

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that polar molecules interact more with it compared to non-polar ones, i.e. hydrocarbons. We

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can discuss the behavior of the VOCs degradation looking at the polarity of the molecules and

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their initial concentration. The dipolar moment expresses the polarity of a molecule, while,

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since adsorption is a physical equilibrium, the initial concentration is proportional to the

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ACCEPTED MANUSCRIPT number of molecules adsorbed (with the equilibrium constant being the proportionality

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factor).

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For example, 2-butanone, ethanol and methanol were among the best-degraded molecules,

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with a high initial concentration and a dipole moment > 1.5 D. Formaldehyde and benzene

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degraded less, but for a different reason, formaldehyde initial concentration is 6 ppb, and thus

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little part of it will be adsorbed. Benzene is completely non-polar, so even if its concentration

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is higher, it won’t interact with P25. Toluene is more polar than benzene (dipolar moment of

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0.256 compared to 0) and its initial concentration is high (50 ppb), which explains its greater

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degradation.

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TiO2 degraded more than 90 % of either single formaldehyde or single acetaldehyde, proving

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that the photocatalytic degradation of organics in mixture is more complex and affected by

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micro-kinetics of adsorption (see Supporting Information).

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Thus, all the models usually presented on single molecules do not describe properly the

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behavior of a mixture of VOCs.

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4. Conclusion

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P25 and 1077 TiO2 photocatalytically degrade volatile organic compounds, which are the

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major indoor pollutants. We attained a final degradation of 74 % and 69 % for aldehydes, 86

295

% and 72 % for hydrocarbons, 84 % and 82 % for chlorinated compounds and 78 % and 54 %

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for the rest of VOCs, with P25 and 1077, respectively. VOCs compete for the adsorption on the

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catalyst surface according to their polarity and their initial concentration, thus the reaction

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rate is slower compared to the single molecule case. TiO2 degraded almost 100 % of

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formaldehyde or acetaldehyde at a starting concentration of 400-500 ppb with a relative

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humidity of 40 %, while considering mixture, degradations were 37 % and 17 %, respectively.

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This stresses how the photocatalytic degradation of organic molecules in gas phase

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micro-TiO2. This work proved the photocatalytic efficiency of a micrometric TiO2 on mixing

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VOCs, opening the way for an in-depth analysis of its features, as well as its improvement as

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safer and cheaper material than nano. Both these aspects, i.e. the behavior of organic

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pollutants in mixture and the application of a micro-TiO2 instead of P25, are key factors for

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applying photocatalytic technologies in real life.

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Acknowledgment

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We thank Mr. Nicolas A. Patience for helpful scientific discussions and comments.

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The authors gratefully acknowledge the support of the Natural Sciences and Engineering

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Research Council of Canada (NSERC). This research was undertaken, in part, thanks to

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funding from the Canada Research Chairs program. The authors acknowledge the Ministère

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des Relations internationales et de la Francophonie for the Coopération Québec-Italie 2017-

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2019 (Project code: QU17MO09).

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Simultaneous photodegradation of VOC mixture by TiO2 powders. Franco Biasiolic, V. Capuccid a

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Marta Stucchia, Federico Gallia,*, Claudia L. Bianchib, Carlo Pirolab, Daria C. Boffitoa,

Polytechnique Montréal, Département de Génie Chimique, 2900 Edouard Montpetit

Blvd, H3C 3A4 Montrèal (QC), Canada.

Università di Milano, Chemistry Department, Via Golgi 19, 20133 Milano, Italy.

c

Research & Innovation Centre, Fondazione Edmund Mach, Via E. Mach 1, 38010 San

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Michele a/A, Italy.

GranitiFiandre SpA, Via Ghiarola Nuova 119, 42014 Castellarano, Italy.

*corresponding author: [email protected]

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Highlights

UV-activated titanium dioxide degraded a mixture of 17 volatile organic compounds

•

We compared nano- and micro-sized TiO2 catalysts

•

Proton mass transfer reaction spectrometer followed the pollutants’ concentration

•

Micrometric catalyst is as effective as nanometric and can replace it

•

Volatile organic compounds compete for the adsorption on catalyst’s active sites

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•