Preparation, testing and performance of a TiO 2 /polyester photocatalyst for the degradation of gaseous methanol M.I. Mejı ´ a a , J.M. Marı ´n a , G. Restrepo a , L.A. Rios a , C. Pulgarı ´n b , J. Kiwi b, * a Applied Physicochemical Processes Group, Chemical Engineering Department, Antioquia University, Engineering College, Street 67 53-108, AA 1226, Medellı ´n, Colombia b EPFL-SB-ISIC-GGEC, Station 6, Ecole Polytechnique Fe ´de ´rale de Lausanne, 1015 Lausanne, VD, Switzerland 1. Introduction TiO 2 has become a widely used photocata lyst employe d in degradation of gaseous and liquid pollutants due to its low price, chemical stability and lack of toxicity [1,2]. Furthermore, TiO 2 is used in the preparation of many composites [3,4], self-cleaning [5,6] and bactericide [7,8] materials. Heterogeneo us photocataly sis is a promising technology for the removal of VOCs like gaseous methanol. TiO 2 photocatalysts are commonly used in processes to degrade in the gas phase [9,10]. Volat ile orga nic comp oun ds (VOC s) con stitu te an impo rtant group of pollutants due to their toxicity and adverse biological eff ects. Methanol is used wid ely as the solvent in indus tryandalso as raw material to prepare formaldehyde, anti-freezing solvents, fuels, in inks and in the preparation of dyes, resins and adhesives [11–15] . Methanol at 20 C achieves quickly a harmful concentra- tion in the air leading to irritation of the eyes, skin and respiratory prob lems. A prol onge d expo sure to meth ano l caus es dizz iness, nausea, lack of coordination and drowsiness. Higher doses lead to unconsciousness and death [16]. A variation on the commonly used dip-coating method for the depo sitionof TiO 2 is pre sen tedin thi s stu dy.Our app roa chfocuseson th e immersion time of th e po lyest er in th e TiO 2 suspensions. Subsequently these photocatalysts were tested during the degrada- tion of methanol. Two immersion methods were used during the catalyst preparation [17–18]. Th e fir stmethodused sil ica sol–gelas a TiO 2 bin deronthe tex til e toavoidthecorr osi onof thepoly est erby the h + holesproduce d by TiO 2 unde r lightirradiatio n. Thesecond method used silicon as a binding agent to protect the polyester textile. Polyester is one of the most resistant low cost fabrics that have been coated for different uses by TiO 2 [1–4]. This textile presents a large surface area making it suitable as a substrate for photo- catlytic application s [5–7]. The poly este r fabr ics hav e been cho sen bec aus e the y are flexi ble andstablemater ialsprodu cedin larg e qua ntities. In rec entyears , the mod ific ation of tex tile s by TiO 2 aimi ng at poll utant degrada tio n and self-cle aning processes has been reported [19–21]. This tex tile presents a large surface area making it suitable as a substrate for photocatlytic applications [5–7]. This study reports the preparative conditions of TiO 2 /polyes ter used at low temp eratures for degrada - tion of gaseous methanol. Applied Catalysis B: Environmental 94 (2010) 166–172 A R T I C L E I N F O Article history: Receiv ed 1 Augus t 2009 Recei ved in revised form 4 November 2009 Accepted 7 November 2009 Available online 11 November 2009 Keywords: Sol–gel Photocatalysis Polyester-TiO2 Methanol photodegradation A B S T R A C T TiO 2 modified polyester photocatalysts were prepared by immersion, drying and curing of the polyester in TiO 2 containing suspensions under different experimental conditions. The structure of TiO 2 layers on the pol yester var ied accord ing to the time of immersi on and type of pol yes ter used . The optical microscopy (OM) and scanning electron microscopy (SEM) show a more uniform distribution of TiO 2 on the polyester prepared by sol–gel as comp ared to the silicone as a binder. Energy diffuse spectrosco py (EDS) and infrared (ATR-FTIR) spectroscopy confirmed that TiO 2 bonded to the polyester textile. BET analysis showed that TiO 2 –SiO 2 applied by sol– gel on polyest er led to a higher surface area comp ared to silicon. Photodegradation of gaseous methanol mediated by the TiO 2 –polyester was followed by gas chromatography (GC) and ATR-FTIR spectroscopy. The TiO 2 –polyester sample prepared by sol–gel with an immersion time of 11 h exhibited the most favorab le photocatalyti c perfor mance during methanol degradatio n in the gasphase.The bestperformance dur ing met hanol photodegr adat ionwas obs erved for the smallest agglomerate TiO 2 size. The structure–reactivity relationship for different photocatalysts was systematically explored. Quantitative evaluation of the cluster size, immersion time and catalyst loading prov ided the evidence for the best perfor mance for methanol degradatio n by the catalyst prepare d at 11 h immersi on time. The photoc atal ytic activi ty of the TiO 2 –polyes ter catalyst was observed to remain stable during methanol over several degradat ion cycles. 2009 Elsevier B.V. All rights reserved. * Corr espon ding author . Tel.: +0041 21 534 8261; fax: +0041 21 693 4111. E-mail address: john.kiwi@epfl.ch(J. Kiwi). Contents lists available at ScienceDirect Appli ed Cataly sis B: Environmental journal homepage: www.elsevier.com/locate/apcatb 0926-3373/$ – see front matter2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2009.11.005
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Preparation, Testing and Performance of a TiO2polyester Photocatalyst for the Degradation of Gaseous Methanol
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8/11/2019 Preparation, Testing and Performance of a TiO2polyester Photocatalyst for the Degradation of Gaseous Methanol
Preparation, testing and performance of a TiO2/polyester photocatalyst for thedegradation of gaseous methanol
M.I. Mejıa a, J.M. Marın a, G. Restrepo a, L.A. Rios a, C. Pulgarın b, J. Kiwi b,*a Applied Physicochemical Processes Group, Chemical Engineering Department, Antioquia University, Engineering College, Street 67 53-108, AA 1226, Medellı n, ColombiabEPFL-SB-ISIC-GGEC, Station 6, Ecole Polytechnique Fe de rale de Lausanne, 1015 Lausanne, VD, Switzerland
1. Introduction
TiO2 has become a widely used photocatalyst employed in
degradation of gaseous and liquid pollutants due to its low price,
chemical stability and lack of toxicity [1,2]. Furthermore, TiO2 is
used in the preparation of many composites [3,4], self-cleaning
[5,6] and bactericide[7,8] materials. Heterogeneous photocatalysis
is a promising technology for the removal of VOCs like gaseous
methanol. TiO2 photocatalysts are commonly used in processes to
degrade in the gas phase [9,10].
Volatile organic compounds (VOCs) constitute an important
group of pollutants due to their toxicity and adverse biological
effects. Methanol is used widely as the solvent in industry and also
as raw material to prepare formaldehyde, anti-freezing solvents,
fuels, in inks and in the preparation of dyes, resins and adhesives
[11–15]. Methanol at 20 8C achieves quickly a harmful concentra-
tion in the air leading to irritation of the eyes, skin and respiratory
problems. A prolonged exposure to methanol causes dizziness,
nausea, lack of coordination and drowsiness. Higher doses lead to
unconsciousness and death [16].
A variation on the commonly used dip-coating method for the
depositionof TiO2 is presentedin this study.Our approachfocuses on
the immersion time of the polyester in the TiO2 suspensions.
Subsequently these photocatalysts were tested during the degrada-
tion of methanol. Two immersion methods were used during the
catalyst preparation [17–18]. The firstmethodused silica sol–gelas a
TiO2binderonthe textile toavoidthecorrosionof thepolyesterby the
h+holesproduced by TiO2under lightirradiation. Thesecondmethod
used silicon as a binding agent to protect the polyester textile.
Polyester is one of the most resistant low cost fabrics that have
been coated for different uses by TiO2 [1–4]. This textile presents a
large surface area making it suitable as a substrate for photo-
catlytic applications [5–7].
The polyester fabrics have been chosen because they are flexible
andstablematerialsproducedin large quantities. In recentyears, the
modification of textiles by TiO2 aiming at pollutant degradation and
self-cleaning processes has been reported [19–21]. This textile
presents a large surface area making it suitable as a substrate for
photocatlytic applications [5–7]. This study reports the preparative
conditions of TiO2/polyester used at low temperatures for degrada-
uniform and smaller size agglomerates were observed at 11 h.
After 11 h immersion(Fig. 6d and e), the sizeof the TiO2 aggregates
increases again showing some inter-particulate cracks. These
cracks were observed to disappear during the methanol photo-
degradation described in Section 3.7 below. In order to gain a more
detailed and quantitative information of the TiO2 size agglomer-ates we carried out SEM and the results are presented next in
Section 3.2.
3.2. Scanning electron microscopy (SEM)
The scanning electron microscopy for several SiO2–TiO2–PT
polyestersamples with differentimmersions is shown in Fig.7. The
micrographs show widespread aggregation of TiO2 particles
covering the polyester surfaces. The information obtained con-
sidered more than 100 TiO2 aggregates and show that the size of
TiO2 aggregates decrease with longer immersion times. The TiO2
after 11 h immersion presented the more uniform TiO2-agglom-
erate distribution. At longer immersion times, the TiO2 film
thickness increased and the crack density was also observed to
increase on the polyester surface. Due to the type of preparation, it
is probably the SiO2 film thickness that increases and not the TiO2
film as seen in Fig. 7(c).
Fig. 8 presents in more detail way the average size of
agglomerates found on SiO2–TiO2–PT polyester samples impreg-
nated at different times by sol–gel. It is noted that the size of agglomerates decreaseswith increasedimmersion time,reaching a
minimum at 11 h. At 11 h, the agglomerates present a small size,
revealing a slightly higher amount of SiO2 than TiO2. At higher
immersion times up to 24 h, the size of the agglomerates was
observed to increase again.
3.3. Energy dispersive spectroscopy (EDS) analysis
The EDS results for SiO2–TiO2–PT polyester samples with 11 h
immersion time show the presence of TiO2 12.8%, C 22.1%, O 51.6%
and Si 13.55%. These results indicate that TiO2 was deposited on
the polyester, the presence of C and O was due to the polyester
surface. The signal due to Si (from tetraethyl ortosilicate TEOS)was
also observed.
Fig. 6. Optical with 10 for TiO2–SiO2–polyester fabric prepared by sol–gel at immersion times of (a) 2 h, (b) 6.5 h, (c) 11 h, (d) 15.5 h and (e) 20 h.
M.I. Mejı a et al./ Applied Catalysis B: Environmental 94 (2010) 166–172 169
8/11/2019 Preparation, Testing and Performance of a TiO2polyester Photocatalyst for the Degradation of Gaseous Methanol
There is a small loss of TiO2 during the methanol degradation
confirming the stability of this catalyst.
Table shows the methanol degradation percentage for the two
types of fabrics PT and PM by sol–gel (the first two rows) and
binding agent method (the last two rows). Methanol degradation
percentages of the fabrics with immersion of 11 and 24 h are
shown in Table 3.
The PT sol–gel based photocatalyst lead to a higher degradation
of methanoldue to a more homogeneous TiO2 film and a lower film
delamination.
The effect of the different immersion times on the methanol
degradation is presented in detail in Fig. 13. The conversion rate
was calculated for the methanol concentration reaching a plateau
at 200 min. The increase of immersion time up to 11 h causes a
greater amount of methanol to be degraded due to the increased
TiO2 presence on the polyester surface relative to immersiontimes
of 2 and 6.5 h. At 11 h immersion time, the TiO2 agglomerates
attain a small size (Fig. 8). Concomitantly, Fig. 9 shows that the
TiO2 loading on the polyester for this sample is relatively high. At
longer immersion times, the size of the agglomerated increases
(Fig. 8) astheTiO2 deposited increases,but the catalyticactivity for
methanol decomposition decreases (Fig. 13). This means that a
TiO2–SiO2–PT sol–gel sample immersed for 11 h presents the
highest amount of TiO2 sites held in exposed positions available tointeract with methanol in the photoreactor. At 11 h immersion
time, there was an optimal ratio of TiO2/cluster size effective in
methanol decomposition. At longer immersion times, the TiO2
dispersion decreases due to the agglomeration of TiO2 on the
polyester fabric.
4. Conclusions
A strong dependence between the time of immersion and the
structure of the TiO2 surface agglomerates on the polyester
surface was observed.The polyester immersed for11 h in sol–gel
presented the most uniform distribution, smaller aggregate size
and highest photocatlytic activity. Longer immersion times lead
to bigger agglomerates decreasing the reactivity towardsmethanol degradation in spite of a slight increase in the TiO2
loading on the polyester.
Similar methanol photodegradation kinetics was reached up to
six successive cycles by using a TiO2–SiO2–PT polyester sample
obtained by sol–gel. The TiO2–polyester coated using silicone binder lead to less
effective methanol degradation.
Acknowledgements
The authors thank COLCIENCIASand the University of Antioquia
for financing the project. We thank for the help of J-M Lavanchy,
IMG-Centre d’Analyse Minerale, Bat Anthropole, Univ-Lausanne,
CH-1025, Lausanne, Switzerland with the X-ray fluorescence and
to S. Arroyave and C. Sanchez, PFA group, Medellın, Colombia for
the help with the BET measurements.
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