Accepted Manuscript

Passive Photo-catalytic Destruction of Air-borne VOCs in High Traffic Areasusing TiO2-coated Flexible PVC Sheet

Ravi Tejasvi, Mukesh Sharma, Kritika Upadhyay

PII: S1385-8947(14)01372-2DOI: http://dx.doi.org/10.1016/j.cej.2014.10.040Reference: CEJ 12783

To appear in: Chemical Engineering Journal

Received Date: 25 July 2014Revised Date: 19 September 2014Accepted Date: 10 October 2014

Please cite this article as: R. Tejasvi, M. Sharma, K. Upadhyay, Passive Photo-catalytic Destruction of Air-borneVOCs in High Traffic Areas using TiO2-coated Flexible PVC Sheet, Chemical Engineering Journal (2014), doi:http://dx.doi.org/10.1016/j.cej.2014.10.040

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Passive Photo-catalytic Destruction of Air-borne VOCs in High Traffic Areas 1

using TiO2-coated Flexible PVC Sheet 2

Ravi Tejasvi1, Mukesh Sharma

2* and Kritika Upadhyay

2 3

1Department of Chemical Engineering, Indian Institute of Technology Delhi, SW Delhi - 11001616, Delhi, India 4

2Department of Civil Engineering, Centre for Environmental Science and Engineering, Indian Institute of 5

Technology Kanpur, Kanpur - 208016, UP, India 6

Keywords: Photo-catalytic oxidation, TiO2, Reaction rate, VOCs, PVC-sheet 7

Abstract 8

Photo-catalytic oxidation (PCO) of VOCs in high traffic regions can be achieved by providing 9

optimum catalyst coating on large surface areas of advertising boards. Nine different sol-gel 10

preparation techniques were attempted for coating TiO2 on flexible PVC sheet used for 11

advertising boards. These coatings were characterized for structural continuity, surface 12

roughness, surface impurities, strong surface attachment and particle size using AFM, XRD, 13

FESEM, and EDX analyzers and optimum sol preparation technique for coating was adopted. 14

Several sets of experiments were conducted for oxidation of benzene and toluene in a batch 15

reactor (having optimum coating on PVC sheet) and parameters like reaction rate constant, 16

order of reaction and removal efficiency etc. were evaluated. The reactions followed 1st order 17

reaction rate model with rate constants for benzene 1.65x 10-5 min-1cm-2 and toluene 1.07x 10-4 18

min-1cm-2. The oxidation rate achieved on PVC sheet using natural sunlight for benzene and 19

toluene was around 50 and 68 percent of that achieved for artificially controlled UV light. This 20

study proposes a novel method of ambient air VOC destruction using PCO technique under 21

natural sunlight in high traffic areas having large advertisement boards that can provide surface 22

for catalytic coating. 23

*Corresponding author. Present address: Department of Civil Engineering, Indian Institute of Technology 24

Kanpur, Kanpur - 208016, UP, India. Tel.: +91-512-22597759; Fax: +91-512-22597395. 25

E-mail address: mukesh@iitk.ac.in 26

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1. Introduction 1

Any organic compound is considered as volatile organic compound (VOC) if it has vapor 2

pressure of 10 Pa or more at 20°C [1]. Amid various VOCs present in ambient air, benzene, 3

toluene, ethyl benzene and xylene (BTEX) are catalogued as hazardous air pollutants and are 4

also registered in the list of priority pollutants of USEPA [2,3]. Vehicular emission is an 5

important source of these VOCs, with ethylene, toluene and benzene being the most abundant 6

VOCs in exhaust gases [4]. The high traffic areas witness elevated concentration of VOCs, as 7

street canyon conditions inhibit dispersion [5,6]. Being generated in open atmosphere, these 8

emissions are dispersed swiftly but remain in lower troposphere. These diffused VOCs cannot be 9

effectively collected to facilitate ex-situ treatment. Therefore, it is desirable to treat them through 10

in-situ techniques. The traditional VOC control techniques such as condensation, incineration, 11

and adsorption are not feasible as in-situ techniques. Photo catalytic oxidation (PCO) with 12

titanium and other semi-conductor based catalysts has been extensively studied for VOC control 13

[7,8,9]. The PCO using nano size semiconductor photo catalysts and UV as a source of light has 14

been an effective, relatively inexpensive and safe technique [10]. In semiconductor material, an 15

e- of valence band (VB) is excited by photo-irradiation to a vacant conduction band (CB) 16

creating an h+ in VB. The e- coerces reduction and h+ propels oxidation of compounds adsorbed 17

on the surface of a photo catalyst [10]. As a result, the organic compounds adsorbed on the 18

surface are remediated as water vapor (H2O) and carbon dioxide (CO2), along with other minor 19

by products like HCHO [11,12]. 20

Most PCO studies [13,14,15] have used TiO2 nano-particles as the UV radiation excitable 21

catalyst, because of its catalytic activity, chemical stability, non- toxicity, relative 22

inexpensiveness and availability. Amidst the known phases of Titania, its anatase phase is most 23

widely used because this phase absorbs UV light below 380nm wavelength [16]. The energy 24

band gap between CB and VB in anatase phase is 3.2 eV, which can be activated by UV 25

radiation with a wavelength up to 387.5 nm [17]. The oxidative potential of a positively charged 26

hole is more than any other oxidant at ambient conditions, which makes it feasible to photo 27

catalytically oxidize complex organic compounds [18]. The humidity is an important constituent 28

for effective PCO as humidity is the sole supplier for the OH- that is needed during photo-29

catalysis to maintain a reasonable population of OH° [19,20]. VOCs are converted to CO2 and 30

water in photo catalytic reactions with TiO2 as catalyst according to the following reactions [21]: 31

Activation Reaction TiO2 + hν → h+ + e- 32

Oxidation reaction h+ + OH- → OH° 33

Reduction reaction O2 + 2e- +2H2O→ H2O2 + 2OH- 34

H2O2 + e- → OH° + OH- 35

Net Reaction OH° + CnHm + O2 TiO2→ nCO2 + mH2O 36

For coating of catalyst, sol–gel process (described later) is widely used for depositing thin layer 1

of catalyst [22]. Sol-gel is one of the most successful techniques for preparing nano size metallic 2

oxide materials with high photo-catalytic activities [23]. Several studies [24,25] have reported 3

that PCO is more effective at moderate temperatures than at an elevated temperature 4

because sorption of reactants on catalyst surface is difficult at higher temperatures [26]. The 5

optimum temperature range for PCO of benzene and toluene has been reported as 25 - 45°C 6

[26]. 7

The current study focuses on an innovative idea of ambient air VOCs destruction using PCO 8

technique in high traffic areas having large advertising boards that can provide surface for 9

catalytic coating. Sunlight can be the source of UV radiation to promote PCO of VOCs in 10

ambient air. The most preferred material for printing advertising boards is ‘Synthetic Flex’ aka 11

‘Flexi Paper’ or ‘Flexo Paper’, which is made of flexible PVC having good weathering 12

endurance. These flexible sheets can be coated with TiO2 catalyst and placed on the desired 13

location on a busy roadside. It stays there undisturbed from active human interactions and could 14

be used for catalytic oxidation of VOCs on its surface. To contribute in developing such a 15

passive reaction surface to destroy VOCs, specific objectives include: (i) synthesis of TiO2 16

nanoparticles as thin film on flexible PVC sheet by sol-gel coating methods, and optimize 17

coating technique by characterizing the surface; and (ii) demonstration and evaluation of PCO-18

driven degradation of VOCs on coated flexible PVC sheet for use in high traffic areas. 19

2. Materials and methods 20

2.1 Materials 21

Synthetically Polymerized Flex lined Flexible PVC sheet, Labolene (pH neutral, Qualigens), 22

Titanium tetra iso-propoxide (TTIP, 98%, Spectrochem), Tetra n-butyl ortho-titanate (TBOT, 23

98%, Merck), Di ethanol amine (DEA, 98%, Merck), Acetyl acetone (AcAc, 99.55 %, 24

LobaChemie), Ethyl aceto acetate (EAcAc, 99.55 %, LobaChemie), Methanol (HPLC, 25

Qualigens), Ethanol (absolute, Merck), n-Propanol (HPLC, Qualigens), and iso- propanol 26

(HPLC, Qualigens), Hydrochloric Acid (AR, Qualigens), Nitric Acid (AR, Qualigens), 27

Aluminum/ Alumina powder, U1 class Borosilicate Low Iron Solar Glass and Titanium dioxide 28

powder (anatase and rutile phase mixture, Code 634662-25G, Sigma Aldrich) were used in this 29

study. 30

2.2 Nanosol Preparation Techniques 31

Various techniques of nanosol preparations were attempted to obtain an optimum coating on 32

the substrate (flexible PVC sheet). These techniques are briefly described below. 33

Technique-1 (referred to as M1) used TTIP as precursor, DEA as stabilizer, and ethanol as 34

solvent. As a result, a stable sol was formed which turned into gel after 8 days [27]. Technique-2 35

(referred to as M2) used TBOT as precursor while having AcAc as stabilizing agent, water as 36

hydrolyser, and ethanol as solvent. Thus obtained sol was kept still for 24 hours at room 1

temperature for aging before being eligible for coating on substrates [28,29].Technique-3 2

(referred to as M3) used TBOT as precursor and ethanol as solvent while hydrochloric acid and 3

water worked as hydrolyzing agents [28,30]. Technique-4 (referred to as M4) used two sub-4

solutions M4A and M4B. Both sub-solutions had TTIP as precursor and ethanol as solvent. In 5

preparing M4A sub-solution, DEA was the stabilizer and no external hydrolyser was added. 6

In preparing M4B sub-solution, AcAc was stabilizer and water was added as hydrolyser. Equal 7

volumes of M4A and M4B were homogeneously mixed to prepare third solution M4 [31]. 8

Technique-5 (referred to as M5) used TBOT was precursor while EAcAc was stabilizer, water 9

was hydrolyser, and ethanol was solvent. Thus obtained sol was incubated for 24 hours at room 10

temperature before being eligible for coating on substrates [29]. Technique-6 (referred to as M6) 11

was a modified version of the technique originally proposed [32]. It took TTIP as precursor 12

and ethanol as solvent while water was hydrolyser. Technique-7 (referred to as M7) used TTIP 13

as precursor and ethanol as solvent while hydrochloric acid as hydrolyser [32]. 14

2.3 Coating Protocol 15

The substrate was properly cleaned and then submerged slowly and horizontally into a glass 16

tray containing the sol. After keeping it submerged for 1 minute, the substrate was slowly 17

withdrawn from the opposite edge (with speed never more than 6 cm per minute) and was kept 18

at room temperature for 5 minutes and then was heated in hot air oven at 60°C for 15 19

minutes. After applying the coating, substrate was heated for 5 minutes in pre-heated oven at 20

80°C for first time to fix the first layer of coating on substrate and at 70°C for subsequent 21

repetitions. The whole procedure was repeated 4 times before getting appreciable thickness of 22

catalyst without impairing the glossiness of the substrate. 23

2.4 Characterization of TiO2 Coating 24

Preliminary visual colour analysis was done to select only transparent or light colored coating 25

sols. These selected coatings were considered for further characterization studies to obtain 26

information about the thickness, surface roughness, surface morphology, elemental 27

composition, grain size, and surface area and photo-activity. 28

The X-ray diffraction (XRD) analysis of the thin coated samples of size 1 cm × 1 cm was carried 29

out using copper target. From the XRD data, one can determine the average size of the particle 30

using the Scherrer’s Equation: 31

(1) 32

Where, β is full width half maxima (FWHM) value of the peaks of particle; λ is wavelength of x-33

ray diffracted from chromium target (λ = 2.20927Å); Å is unit of diameter (10 Å = 1 nm); θ is 34

half of angle at which significant peak is observed. 35

Field emissive scanning electron microscopy (FESEM) technique was used for studying surface 1

morphology and estimating film thickness. Thin coated samples (1cm × 1cm) were covered with 2

gold (to make them conducting) and then analyzed in the FESEM apparatus, SUPRA 40VP (Carl 3

Zeiss NTS GmbH, Germany). 4

Energy dispersion absorption x-ray spectroscopy (EDX) technique was used for the elemental 5

analysis of prepared gold coated TiO2 using EDX instrument (FEI Quanta 200 HV). The EDX 6

analysis gives the percentage elemental composition of the coating. This knowledge can be used 7

for ascertaining presence of TiO2 and other impurities in the coated surface. 8

In atomic force microscopy (AFM) technique samples were analyzed using GWYDDION 9

software to obtain various parameters like grain size, surface roughness, and topographical 10

surface features. 11

The coating techniques (M1 to M7) were evaluated based on the above characterization studies 12

and best technique was obtained for further experiments (described in results and discussion). 13

2.5 Batch Reactor System 14

An air tight batch reactor system (size 20 cm (L) × 20 cm (W) × 4.8 cm (H), capacity 1920 15

cm3, and total internal surface area 1184 cm2) made of aluminium and covered with glass was 16

used in the experiments. The reactor was installed with thermometer for monitoring the internal 17

temperature. It had provisions to inject known concentrations of benzene and toluene and to 18

withdraw gas samples. A known volume of benzene and toluene vapours were collected at 19

atmospheric pressure from the headspace of their respective bottles and injected into the reactor. 20

A hold time of one minute was given before drawing the first sample from the reactor to 21

account for the diffusive mass transfer phenomena. Gas sample of 1ml (volume at atmospheric 22

pressure and ambient temperature) was taken at every 20 minute interval from the reactor, for 23

a period of 3 hours, and then analyzed using a gas chromatograph (GC; Buck Scientific, USA). 24

The reactor was used to study (i) PCO of benzene and toluene under natural UV irradiance (ii) 25

surface absorption of the benzene and toluene on metal and uncoated substrate surfaces (iii) 26

catalyst-enhanced UV degradation possibilities for benzene and toluene with variation in coated 27

area. 28

2.6 Analysis of Benzene and Toluene 29

The degradation of benzene and toluene inside the batch reactor was examined for varying 30

catalytic area in presence and absence of UV radiation. Gas samples were drawn from the reactor 31

and injected into the GC column using a 5ml gas tight SGE syringe at an injector temperature of 32

130°C. Restek MST volatile column (0.53mm Id, 30mm length and 2µm film thickness) was 33

used to separate the compounds during analysis. High purity helium was used as a carrier gas 34

with flow rate of 14ml/min. Hydrogen with 20ml/min and zero air with 250ml/min were used for 35

operating FID and Methanizer. Total time for one run was 29 minutes. 36

3. Results and Discussion 1

3.1 Characterization of TiO2 Coating 2

Any visual colour on coated surface of advertisement board is not acceptable. The TiO2 coated 3

surface of various techniques (M1, M2, M3, M4, M4A, M4B, M5, M6, and M7) was visibly 4

examined. Only M1, M4A, and M6 techniques produced transparent coatings and were further 5

examined for structure and morphology of the coating to select the optimum technique. 6

Techniques, M2, M3, M4, M4B, M5 and M7 were not considered further because these 7

produced colour on PVC sheet. 8

XRD analysis was performed to identify the phase of TiO2 crystals by comparing atomic 9

arrangement of coated TiO2 with the standard TiO2 (mixture of anatase and rutile phase). The 10

peak pattern of atomic structure obtained for M4A was closest to the pattern obtained for the 11

standard (Fig. 1 (a), (b), (c) and (d)). The average particle sizes obtained using Eq 1 for 12

different sol-gel coating techniques were 41.65nm for M1, 23.21nm for M4A and 53.51nm for 13

M6. 14

FESEM analysis was performed at various magnifications to investigate uniformity of TiO2 15

coating, crack width and width of pieces. Fig. 2 (a), (b) and (c), shows 5000 times magnified 16

images from FESEM for M1, M4A, and M6. The piece width range was: 55 – 90 µm (for M1), 17

12– 15 µm (for M4A) and 0.5 – 28 µm (for M6). The separation between the two pieces was: 18

0.9– 3.2 µm (for M1), 0.8– 2.5 µm (for M4A) and 0.1– 5.0 µm (for M6). Cracks were found in 19

M1 and M6 technique with cracking width of 0.2 – 0.5 µm. No crack formation was seen in the 20

catalyst layer coated by technique M4A, which indicates longer adhesion of the coating on the 21

substrate as well as more wear and tear endurance. 22

EDX was performed on gold-coated samples to assess the ratio of various constituting 23

elements in the coating to ascertain the presence of various compounds, especially that of 24

TiO2. Technique M4A showed highest proportion of Ti and rational proportions of oxygen that 25

suggested a substantial amount of TiO2 on the scanned spot (Fig. 3(a),(b) and (c)) . 26

AFM analysis was carried out to characterize 2-dimensional (2D) and 3-dimensional (3D) 27

surface topography for M1, M4A and M6. The 3D topographical structures (Fig. 4(a), (b) and 28

(c)) depict various surface topographical features (STF) like local maxima, local minima, 29

planes and plateaus. The 2D surface (not shown here) topography showed phase distribution on 30

the scanned area with more than one phases present on the spot. The results of XRD analysis 31

supported the presence of different crystalline phases of Titania (anatase and rutile in 32

particular). 33

From Fig. 4(a), (b) and (c), STF can be summarized as: (i) non-uniform distribution for M1 (ii) 34

uniform distribution for M4A and (iii) large number of pits for M6. The results of surface 35

roughness parameters for three techniques are presented in Table 1; deviations in average 1

thickness and root mean square roughness are smallest for M4A technique. 2

The AFM results reject M6 technique because of pit formation with the average pit bore of 3

159.6±53.09 nm which is about the same size of soot particles emitted by vehicles. These 4

particles may get deposited in the pits and deactivate the surface for further oxidation of VOCs. 5

3.2 Optimization of Sol-gel Preparation Technique 6

As seen from Section 3.1, visible colour examination, EDX, AFM, and XRD analyses clearly 7

suggest that M4A technique was most suitable for coating TiO2. Specifically, FESEM analysis 8

showed formation of clean layered structure of TiO2 coating for M4A solution. Further AFM 9

analysis revealed that M4A technique provided homogeneously distributed surface roughness. 10

M4A technique was also suitable in terms of crystal size, film thickness and adherence to the 11

substrate. Therefore, M4A coating technique was adjudged optimum for conducting experiments 12

for VOC mitigation. 13

3.3 Oxidation of Benzene and Toluene in Batch Reactor 14

Various sets of experiments were conducted repeatedly in the batch reactor assembly (having the 15

coated flexible sheet) and samples were drawn periodically from the reactor and analyzed on 16

GC. Reaction parameters like reaction rate constant, order of reaction, removal efficiency etc. 17

were evaluated for benzene and toluene. 18

UV radiation is of paramount importance in PCO. In this study, natural UV (A+B) radiation 19

intensity was measured at the experiment spot (26.511°N, 80.234°E) using UV light meter 20

(Lutron UV-340, USA). The general pattern of variation of incident UV (A+B) radiation had 21

higher intensity at noon time (1000-2100 µW/ cm2) while the intensity was increasing in the 22

morning session (200-2000 µW/ cm2) and decreasing in afternoon session (2000-100 µW/cm2). 23

Only 88-90% of incident UV (A+B) intensity was transmitted through glass top of the reactor to 24

excite the catalyst. 25

The temperature inside the reactor was measured and it was in the range of 25-35ºC, normally 26

observed in ambient air in Indian conditions in daytime. 27

Relative humidity inside the reactor was equal to that of the ambient air and outside it was 28

always in excess to 50%. No artificial humidifying or dehumidifying attempts were exercised at 29

any point of time. 30

Fig. 5(a) and Fig. 6(a) show un-reacted mole fraction of benzene and toluene with respect to 31

time under varying reaction conditions. These experiments were conducted under noontime solar 32

UV irradiation (11am to 2 pm) on TiO2 coated PVC sheet of size 20cm×20cm. The results were 33

used to calculate net fractional oxidation of benzene and toluene. Fractional oxidation was least 34

in the blank condition when neither catalyst nor UV radiation was available. A minimal PCO is 35

expected under blank conditions. Although it appears that under blank conditions benzene 1

continues to be removed even after 60 minutes, it may be recognized that rate of removal of 2

benzene on TiO2 surface with UV light is 5.78 x 10-3 min-1 whereas it is only 1.59 x 10-3 min-1 3

for blank conditions. The possible reason for small benzene removal under blank conditions 4

could be minor leakage in the reactor. The same explanation for reduction in toluene under blank 5

conditions should be applicable. 6

Net oxidation of benzene and toluene in the presence of catalyst and UV radiation (after 7

excluding the conversion in the blank reactor) was calculated (Fig. 5(b) and Fig. 6(b)) and the 8

reaction appeared to follow 1st order reaction rate model. The estimated 1st order reaction 9

constant for benzene oxidation was 1.51×10-2 min-1 and for toluene oxidation was 2.13×10-2 10

min-1; half-life of benzene was estimated to be about 46 minutes and for toluene it was about 33 11

minutes. The order of reaction is the 1st order and the reaction rate (rA) can be expressed as 12

-rA=kCA (k is rate constant, min-1 and CA is concentration (mol/l) at any given time). 13

Fig. 7(a) and Fig. 8(a) show un-reacted mole fraction of benzene and toluene under varying 14

ratio of coated catalyst surface area (CSA) and irradiation exposed area (IEA, i.e. top area of the 15

reactor, constant at 20cm×20cm). Fig. 7(b) and Fig. 8(b) shows a linear association between 16

the experimentally-estimated reaction rate constants (for benzene and toluene) and size of 17

catalyst coated area. It was observed that the reaction rate constant increases with increasing 18

coated surface. Thus large surface area facilitate reaction of more number of pollutant molecules 19

per unit time and the reaction rates are reported as min-1cm-2 (for benzene 7.65x 10-5 min-1cm-2 20

and for toluene 1.07x 10-4 min-1cm-2). 21

It was observed that the combined presence of UV and TiO2 produces the most efficient 22

remediation for benzene and toluene under given reaction conditions. Table 2 compares reaction 23

rates with previous studies which used artificial germicidal lamp radiation (λ = 254 nm) without 24

attenuation whereas the present study used only natural UV(A+B) radiation (280 nm ≤ λ ≤ 370 25

nm, more fraction of larger wavelength) with 10 to 12% attenuation. It should be noted that the 26

oxidation of benzene and toluene under natural sunlight can achieve rates equal to 50 percent and 27

68 percent of rate of oxidation attained under artificially controlled UV light. 28

4. Conclusions 29

Passive in-situ photo-catalytic oxidation of VOCs has been attempted on TiO2-coated PVC 30

flexible sheets used for advertisement boards in urban areas. Nine different sol-gel preparation 31

techniques were attempted for coating TiO2 on PVC sheet. Various characterization tests were 32

performed on coatings using AFM, XRD, FESEM, and EDX analyzers. The technique having 33

Titanium tetra iso-propoxide as precursor, ethanol as solvent and di-ethanol amine as stabilizer 34

was found suitable in terms of crystal size, homogeneous surface roughness, film thickness, 35

clean layered structure of coating and adherence to the substrate. This technique was adjudged as 36

the optimum coating technique on PVC sheet. It is observed that oxidation of benzene and 37

toluene on TiO2 coated PVC sheet followed 1st order reaction rate. The reaction rate constants 1

(benzene 7.65x 10-5 min-1cm-2 and toluene 1.07x 10-4 min-1cm-2) were linearly related with coated 2

surface area. The oxidation rate attained by benzene and toluene under natural sunlight was 50 3

percent and 68 percent, of the oxidation rate attained under artificially controlled UV light. It is 4

concluded that the technology of TiO2-coated PVC sheet in presence of natural sunlight holds 5

promise for passive oxidation of VOCs in ambient air of high traffic area. 6

Acknowledgement 7

The study was partly funded by Ministry of Environment and Forests, Government of India 8

through project grant 1-14/20009-CT, dated March 30, 2012. 9

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Fig.1 XRD Analyses; Count per second (CPS) versus Incidence Angle

(a) CPS versus 2θ plot for (b) CPS versus 2θ plot for (c) CPS versus 2θ plot

for M6

(c) CPS versus 2θ plot

for M1

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(a) M1 (b) M4 (c) M6

Fig. 2. FESEM analyses of different coating techniques (5000X magnification)

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Fig.3. EDX Analyses

(a) EDX spectrum of Substrate Coated by

M1

(c) EDX spectrum of Substrate Coated by

M6

(b) EDX spectrum of Substrate Coated by

M4A

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Fig. 4. 3-D topographical spectrum: AFM Analyses of different techniques 5

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(a) M1 (b) M4 (c) M6

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(a) Average of three experiments (b) Net Non-oxidized mole fraction (excluding blank)

Fig. 5. Non-oxidized mole fraction of benzene versus time

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(a) Average of three experiments (b) Net Non-oxidized mole fraction (excluding blank)

Fig. 6. Non-oxidized mole fraction of toluene versus time

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Fig. 7(a) Benzene PCO order (on varying sizes of coated area)

CSA is 0% of IEA CSA is 25% of IEA CSA is 50% of IEA

CSA is 100% of IEA

Fig. 7(b) Benzene PCO apparent rate constant varying with coated area size

Ratio of CSA/IA

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Fig. 8(a) Determining Toluene PCO order (on varying sizes of coated area)

CSA is 0% of IEA CSA is 25% of IEA CSA is 50% of IEA CSA is 100% of

IEA

Fig. 8(b) Toluene PCO apparent rate constant varying with coated area size

Ratio of CSA/IA

1

Table 1 2

Summary of AFM results for different techniques 3

4

Technique

Name Average Thickness (Deviation %)

Root Mean Square Roughness

(Deviation %)

Catalyst surface area to volume

ratio (m2/m

3)

M1 3983±58 nm (1.45%) 90±42 nm (45.96%) 3.07×105 m2/m3

M4A 4604±38 nm (0.82%) 32±6 nm (18.58%) 2.20×105 m2/m3

M6 5203±589 nm (11.33%) 229±99 nm (43.23%) 2.24×105 m2/m3

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Table 2 1

Comparison of present study estimated Reaction rate constant for individual pollutant with previous studies 2

3

Reactant Rate Constant (Present Study) Rate Constant (Nagar, 2010) Rate Constant (Mohanan, 2009)

Special Note

Surface Area 196cm2 Surface Area 523.5cm2 Surface Area 411.4cm2

Passive Reduction in Batch Reactor Active Reduction in Continuous Plug Flow Reactor

Active Reduction in Continuous Plug Flow Reactor

τ = 180 minutes τ = 120 minutes τ = 120 minutes

280 nm ≤ λ ≤ 370 nm λ = 254 nm λ = 254 nm

Benzene 7.65x 10-5 min-1 /cm2 1.6x10-4 min -1/cm2 1.6x10-4 min-1/cm2

Toluene 1.07x 10-4 min-1/cm2 1.39x10-4 min-1/cm2 1.7x10-4 min-1/cm2

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Highlights 1

• Innovative photo-catalytic oxidation of VOCs on advertising boards (flexible PVC) in high traffic regions; 2

• Characterization and optimization of TiO2 coating on flexible PVC sheet. 3

• Order of reaction and rate constant for VOC destruction on TiO2 coated flexible PVC sheet. 4

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