Photocatalytic oxidation of phenolic pollutants and hydrophobic organic compounds in industrial wastewater using modified nonosize Titanium Silicate-1 thin film technology

Article abstract of DOI:10.1166/jnn.2014.9237

Nanocrystalline Titanium Silicate-1 (TS-1) with attractive physical and chemical properties is being explored for the degradation of phenol. A fully dispersible nanocrystalline zeolite TS-1 was prepared. The catalyst was characterized by DLS. XRD. TEM and BET analyses. XRD analysis confirmed that the diffraction pattern of the NPs (CP-0) was very similar to that of amorphous silica and the aged concentrated precursor sample CP-48 showed peaks characteristic of MFI. TEM analysis confirmed that the size of the crystal is about 30 nm. The photocatalytic oxidation of phenol was studied over nanocrystalline Titanium silicate-1 thin film flow reactor. The experimental parameters such as aeration, flow rate, solution pH and phenol concentration were optimized. The degradation efficiency of chore-substituted phenols are compared at optimum conditions. In addition, photocatalytic degradation efficiency of simulated phenolic waste water was studied. The results are significant, as the method adopted here can be extended for the treatment and purification of waste water and air using nanocrystalline Titanium silicate-1 thin film flow reactor. Copyright

Full text of DOI:10.1166/jnn.2014.9237

Article
Journal of
Nanoscience and Nanotechnology
Vol. 14, 7345–7350, 2014
Copyright © 2014 American Scientific Publishers
All rights reserved
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Printed in the United States of America
Photocatalytic Oxidation of Phenolic Pollutants and
Hydrophobic Organic Compounds in Industrial
Wastewater Using Modified Nonosize
Titanium Silicate-1 Thin Film Technology
Suzan A. Khayyat1ꢀ∗, Rosilda Selvin1, L. Selva Roselin2, and Ahmad Umar3ꢀ4
1Faculty of Science for Girls, Chemistry Department, King Abdulaziz University,
P.O. Box: 55075, 21534, Jeddah, Saudi Arabia
2Department of Chemistry, Periyar Maniammai University, Vallam, Tanjore 613005, India
3Faculty of Science and Arts, Department of Chemistry, Najran University, Najran-11001,
Kingdom of Saudi Arabia
4Promising Centre for Sensors and Electronic Devices (PCSED), Najran University,
Najran-11001, Kingdom of Saudi Arabia
Nanocrystalline Titanium Silicate-1 (TS-1) with attractive physical and chemical properties is being
explored for the degradation of phenol. A fully dispersible nanocrystalline zeolite TS-1 was prepared.
Delivered by Publishing Technology to: University of Waterloo
IP: 222.175.36.19 On: Wed, 28 Oct 2015 09:49:29
The catalyst was characterized by DLS, XRD, TEM and BET analyses. XRD analysis confirmed that
Copyright: American Scientific Publishers
the diffraction pattern of the NPs (CP-0) was very similar to that of amorphous silica and the aged
concentrated precursor sample CP-48 showed peaks characteristic of MFI. TEM analysis confirmed
that the size of the crystal is about 30 nm. The photocatalytic oxidation of phenol was studied over
nanocrystalline Titanium silicate-1 thin film flow reactor. The experimental parameters such as aer-
ation, flow rate, solution pH and phenol concentration were optimized. The degradation efficiency of
choro-substituted phenols are compared at optimum conditions. In addition, photocatalytic degra-
dation efficiency of simulated phenolic waste water was studied. The results are significant, as the
method adopted here can be extended for the treatment and purification of waste water and air
using nanocrystalline Titanium silicate-1 thin film flow reactor.
Keywords: Photocatalysis, Nanocrstalline Titanium Silicate-1, Phenol, Thin Film Photocatalyst,
Phenolic Wastewater.
1. INTRODUCTION
decade. Nano photocatalysis technology has great potential
for low-cost, environmentally friendly applications like
splitting water for producing hydrogen as fuel, organic
synthesis, and air and water purification. Especially in the
last ten years, great progress has been made in prepar-
ing various nanopaticles. Nanostructured materials are
preferred over dense structures, because of their larger
active surface. Most of the reports dealt with photocat-
alytic reactions induced by irradiation of semiconductor
nanoparticles suspended in aqueous solution. The pow-
der nanocatalysts, however, suffer from several drawbacks,
including: (i) turbidity created by the catalyst when kept
as a suspension will considerably decrease the amount
of light interacting with the catalyst; (ii) Nanoparticles
aggregation due to the highly acidic or basic waste water;
Photocatalysis is a growing field of research because of
its application in various fields, especially in environ-
mental cleanup.1–8 It is a catalytic reaction initiated by
light energy. Several semiconductor oxides and sulfides
have been reported, which have bandgap energies suitable
to absorb light under visible and/or near UV and excite
electrons by photoexcitation and further promote a cat-
alytic reaction. Among these semiconductors, TiO2 has
proven to be the most suitable for widespread environ-
mental applications due to its exceptional optical, elec-
tronic properties. The photochemistry of nanoparticles and
nanomaterials has attracted much attention over the past
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2014, Vol. 14, No. 9
1533-4880/2014/14/7345/006
doi:10.1166/jnn.2014.9237
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Photocatalytic Oxidation of Phenolic Pollutants and Hydrophobic Organic Compounds in Industrial Wastewater
Khayyat et al.
and finally (iii) separation of nano-sized photocatalyst par-
ticles from the treated water. The immobilized photocata-
lysts can be applied in various reactors; they are especially
recommended for those working in a continuous mode.
Thus, the use of immobilized photocatalysts is gaining
importance in the elimination of pollutants from water.9
The growing interest in the development of newer
photocatalyst has led to the development of zeolite
photocatalyst.10–12 Zeolites are microporous crystalline
materials, routinely used as catalysts, ion-exchangers, and
adsorbents. Significant attention is now being directed
towards designing zeolite photocatalysts owing to their
photocatalytic ability in the degradation of various envi-
ronmental pollutants.13–15 Zeolites offer high surface area,
unique nanoscale pore structure and ion exchange proper-
ties for utilization in the design of efficient photocatalytic
systems. Titanium silicate (TS-1) which has a structure
similar to the zeolite ZSM-5 has been shown to degrade
a number of pollutants under mild condition. Most of the
work reported in the literature used zeolite as a support
material but very few reports used zeolite as a photo-
catalyst. Literature reports reveal that titanium contain-
ing zeolite TS-1 is active for the photo degradation of
pollutants.12ꢀ13 The photocatalytic activity per weight of
photocatalyst was lower for TS-1 than TiO2, but the intrin-
sic activity per Ti atom in TS-1 is higher than that in TiO2,
which reflects the benefits of site isolation in TS-1 and
the sieving properties of this porous zeolite. The ability to
to prepare a nano thin film coating which is easy to make
and reproducible method of making photocatalytic thin
film. The aim of this paper is to investigate the efficacy of
nanosize titanium silicate-1 thin film for the photo oxida-
tion of phenolic compounds in aqueous solution.
2. EXPERIMENTAL DETAILS
2.1. Chemicals
Tetraethoxysilane (TEOS), tetrabutylorthotitanat (TBOT),
tetrapropylammonium hydroxide (TPAOH, 40% aq), and
phenol were commercial samples from Merck and were
used without further purification.
2.2. Synthesis of Fully-Dispersible Nanocrystalline
TS-1 Photocatalyst
In order to synthesize fully-dispersible nanocrystalline
TS-1 a RT-hydrolyzed clear sols of TPAOH- TiO2–
SiO2–H2O was prepared. Tetraethylorthosilicate (10.4 g)
and tetrabutylorthotitanate (12.6 g) were transferred to
a polypropylene bottle and stirred (10 min) at 25 ꢀC
until a homogeneous mixture was formed. In a beaker,
tetrapropylammonium hydroxide solution (6.4 g, 40 wt%
aq) was thoroughly mixed with 8.5 g of water. The
diluted organic base solution was then carefully added
to the ester mixture at the rate of about 1.5 ml/min.
The resultant mixture was stirred for about 2 h until a
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clear solution was formed. The remaining water (8.5 g)
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was added at this point to give the final molar compo-
control the zeolite properties through synthetic efforts will
continue to be of great importance. At present, the con-
trol of zeolite properties mainly involves molecular level
manipulations of structural features, e.g., pore size, par-
ticle size and location of active sites. Numerous original
research articles and several reviews deal with the synthe-
sis, modification, and characterization of zeolites.16–20 The
presence of heteroatoms (Ti, V and other transition met-
als) in the zeolite framework can make the structure as a
whole act as a photocatalyst. Many of the reported exam-
ples of photo catalytic reactions using zeolites are relevant
to powder catalysts in batch mode rather than thin film
catalysis in continous mode. The challenge of making a
TiO2 thin film is crucial and our previous studies indicated
the possibility of using nano zeolite sol to improve the
adhesion of TiO2 in any substrate.
Copyright: American Scientific Publishers
sition: 0.25TPAOH:0.06TiO2:1.00SiO2:20H2O. The pH of
the final solution was 11.6. The clear sol was concen-
ꢀ
trated in a rotary evaporator at 80 C as described in the
literature.26 One-tenth of the concentrated precursor sol
kept aside aꢀt RT and the rest was poured to PP vial and
aged at 80 C for 48 h. The product of aged treatment
was translucent. The aged sol was mixed with the un-aged
sol and mixed with 0.5 g tween-20. The transparent sol
was mixed with ethanol to get 0.5 wt% SiO2 and used for
making a thin film.
2.3. Characterization
Powder X-ray diffraction patterns were recorded on a
Regaku 2000 diffractometer using Cu-Kꢁ radiation from
ꢀ
2ꢂ = 5 to 30ꢀ at a scan rate of 2 /min with a step size of
0.04ꢀ. The particle size of the nanocrystals are measured
by nano ZS (Malvern). Morphology and particle size of
the zeolite nanocrystals were examined with TEM (JEM-
2010, 200 kV). For TEM analysis, a drop of the diluted
solution (0.0005 wt% g/water) was placed (placed a drop
of ethanol and dried before placing sample) on carbon
coated copper grid for TEM examination.
Phenol and phenolic derivatives are major contami-
nant in industrial waste water and these materials were
listed by The Agency for Toxic Substances and Disease
Registry-USA (ATSDR) as one of the year 2007 prior-
ity contaminants that have significant potential threat to
human health.21 Owing to increasing environmental pres-
sure and the subsequent increase in environmental legis-
lation, effective effluent treatment are crucial. Numerous
research article deals with the photodegradation of phenols
using various photocatalysts in a batch mode.22–25 Only
very few reports are available on thin film photocatalysis
on photocatalytic degradation of phenol. Still it is needed
2.4. Photocatalytic Reactor Setup
The photocatalytic reaction was carried out using a
photoreactor setup which has been described in detail
elsewhere.1 The photocatalytic reactor setup is shown in
7346
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Khayyat et al.
Photocatalytic Oxidation of Phenolic Pollutants and Hydrophobic Organic Compounds in Industrial Wastewater
CP-48
CP-0
5
10
15
20
25
30
2 Theta (degrees)
Figure 2. XRD patterns of the concentrated NPs and aged NPs.
to subtract the dissolved CO2. From, this amount of CO2
liberated during the reaction was estimated and hence the
extent of photocatalytic degradation of phenol was calcu-
lated and compared with the theoretical values calculated
on the basis of the known stoichiometry of the reaction.
The reusability of the thin film nanocrystalline TS-1
photocatalyst was studied by conducting the photocatalytic
reaction with same thin film TS-1 catalyst for subsequent
runs for phenol degradation under similar conditions.
Before each run, the catalyst was rinsed with distilled
Figure 1. Schematic diagram of TS-1 coated thin film flow photo
reactor.
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Figure 1. The photoreactor consisted of a low pressure
ꢀ
water followed by drying at 100 C.
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Copyright: American Scientific Publishers
mercury lamp (253.7 nm, 6 W) enclosed in a quartz tube
fitted tightly into an outer glass tube. The outer glass tube
was provided with an inlet and outlet for aeration. The
inner wall of the glass tube was coated with nanocrytalline
TS-1 by dip coating method. The glass tube was dried in
3. RESULTS AND DISCUSSION
3.1. XRD
The XRD patterns of the concentrated NPs and aged NPs
are shown in Figure 2. The diffraction pattern of the NPs
(CP-0) was very similar to that of amorphous silica. The
aged concentrated precursor sample CP-48 shows, peaks
characteristic of MFI. Compared to the standard diffraction
patterns of micrometer-sized zeolite MFI, the diffraction
peaks of nanocrystal samples are broadened.
ꢀ
an air oven at 120 C for one hour.
2.5. Photocatalytic Reaction Procedure
The typical procedure for the degradation of phenol using
the thin film tubular photoreactor consisted of irradiation
of 100 mL of a known concentration of the phenol solu-
tion and was pumped into the reactor tube at a desired
speed using peristaltic pump. The progress of the reac-
tion was followed by withdrawing 3 ml of the photolysed
phenol solution from the receiving flask after each cycle
and the amount of phenol was estimated spectrophotomet-
rically using 4-aminoantipyrine method.27
3.2. TEM
The TEM micrographs of the aged precursor sample is pre-
sented in Figure 3. The size of the crystal is about 30 nm.
Total organic carbon was estimated by quantitative anal-
ysis of CO2 formed in the photocatalytic process. For
this, 25 ml of known concentration of phenol solution
was taken in the tubular photoreactor and irradiated with
UV light. The carbon dioxide formed during the reaction
was flushed-out continuously by a stream of air and was
trapped in an aqueous KOH solution of known concentra-
tion. The excess unreacted KOH was estimated by titration
with known concentration of HCl.1ꢀ28 Blank experiment
was carried out with water through the same procedure
Figure 3. TEM image of the concentrated NPs.
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Photocatalytic Oxidation of Phenolic Pollutants and Hydrophobic Organic Compounds in Industrial Wastewater
Khayyat et al.
Table I. The DLS result of TS-1.
Without aeration
With aeration
50
40
30
20
10
0
Sample code
K counts
Z Ave (nm)
Poly index
NPs
454
4ꢃ3
42ꢃ5
0.49
0.04
48NPs
243ꢃ6
3.3. Dynamic Light Scattering (DLS) Measurements
The concentrated precursor sol (CP-0) and 48 h aged pre-
cursor sol (CP-48) were subjected to DLS analysis. The
results shown in Table I represents that the particle size
increases with the aging period due to the aggregation pro-
cess during ageing.26
0
20
40
60
80
100 120 140 160 180
Time (min)
3.4. Photocatalytic Degradability of Phenol
Over Nanocrystalline TS-1
Figure 5. Effect of aeration on the photocatalytic degradation of phe-
nol over nanocrystalline TS-1 thin film (Reaction conditions: [phenol] =
50 ppm; pH = 6ꢃ7; flow rate = 8 ml/min).
The photocatalytic degradability of phenol over nanocrys-
talline TS-1 was investigated by conducting controlled
experiments except under two different conditions such
as with and without TS-1 coatings. The results are pre-
sented in Figure 4. In the absence of TS-1 coatings under
UV radiation, there was no change in concentration was
observed. On the other hand, in the presence of TS-1 coat-
ings under UV radiation, decrease in phenol concentra-
tion with irradiation time was observed. Almost all the
phenol molecules were degraded at 130 min. Hence it is
understood that phenol is stable under UV radiation. Most
3.5. Effect of Aeration
The effect of air on the photocatalytic degradation of phe-
nole was studied with a nanocrystalline TS-1 thin film
with a thickness of 130 min and at a constant flow rate of
8 ml/min with and without aeration conditions. Complete
degradation of phenol was achieved for the aerated sys-
tem in 137 min of irradiation. However, in the non-aerated
system, 165 minutes of irradiation was required (Fig. 5). It
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importantly it is understood that nanocrystalline TS-1 thin
IP: 222.175.36.19 On: Wed,w2a8s rOepcot r2te0d15in0v9a:4ri9o:u2s9studies that aeration provides the
film is an active photocatalyst for the degradation of phe-
Copyright: American Scientific Publishers
required oxygen for scavenging photoelectrons and form-
nol in aqueous solution. TOC analysis showed that around
97% the organic carbon were oxidized to carbon dioxide.
The estimated carbon di oxide formed during the degra-
dation of phenol agreed with the theoretical value on the
basis of molecular weight and concentrations employed.
Therefore it is confirmed that phenol is photo-mineralized
into CO2 and H2O during the degradation of phenol under
UV radiation over nanocrystalline TS-1 thin film.
ing superoxide anion radicals, which participate in the
photo oxidation of the phenol.29 In addition, it is accepted
that without aeration, the reaction was not completely
stopped, which indicates that superoxide anion radicals are
not the only oxidizing species involved in photocatalytic
process. In our previous studies on photocatalytic degra-
dation of acid violet 19 dye, we have shown that positive
hole, hydroxyl radical and superoxide anion radical are the
main oxidizing species involved in photocatalytic oxida-
tion process.30ꢀ31
50
3.6. Effect of Flow Rate
Without TS-1 thin film
40
With TS-1 thin film
The effect of flow rate on the photocatalytic degradation
of phenol was studied in the range of 2–10 ml/min. It is
well-known that by decreasing the flow rate the contact
time of the reactant increases in the reactor and so the
removal efficiency increases. To optimize the flow rate,
time taken to degrade 50% of the phenol (t0ꢃ5) was stud-
ied. The percentage removal of phenol was calculated at
various irradiation times. The time taken to degrade 50%
removal of the phenol was found to decrease with increas-
ing the flow rate of 2–10 ml/min, but the extent of decrease
between 9 ml/min and 10 ml/min was small (Fig. 6). Since
the optimum flow rate is the maximum speed with good
degradation efficiency, in the current work 9 ml/min was
used for further studies.
30
20
10
0
0
20
40
60
80
100
120
140
Time (min)
Figure 4. Photocatalytic degradability of phenol over nanocrystalline
TS-1 thin film (Reaction conditions: [phenol] = 50 ppm; pH = 6ꢃ7; Flow
rate = 8 ml/min).
7348
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Khayyat et al.
Photocatalytic Oxidation of Phenolic Pollutants and Hydrophobic Organic Compounds in Industrial Wastewater
85
80
75
70
65
60
55
50
45
30 ppm
100
40 ppm
50 ppm
80
60
40
20
0
60 ppm
70 ppm
80 ppm
90 ppm
100 ppm
0
30
60
90
120
150
180
210
2
4
6
8
10
Time (min)
Flow rate (ml/min)
Figure 8. Effect of initial concentration of phenol on the photocatalytic
degradation of phenol over nanocrystalline TS-1 thin film (Reaction con-
ditions: [phenol] = 30 ppm to 100 ppm; pH = 7; Flow rate = 9 ml/min).
Figure 6. Effect of flow rate on the photocatalytic degradation of phe-
nol over nanocrystalline TS-1 thin film (Reaction conditions: [phenol] =
50 ppm; pH = 6ꢃ7; flow rate = 2 to 10 ml/min).
of degradation increases with increase in the phenol con-
centration upto 60 ppm, and the increase becomes slowed
down between 60 ppm and 90 ppm. There is a decrease
in the degradation rate at high phenol concentration, viz.,
100 pm. The different situations in reaction rate at different
initial concentrations could be explained as follows: The
increase in rate at lower phenol concentrations is due to
more number of adsorbed phenol molecules undergo oxi-
dation on the surface of the photocatalyst.32ꢀ33 The lesser
3.7. Effect of pH
The effect of pH on the photocatalytic degradation of phe-
nol was studied in the pH range of 4–10. The pH of the
solution is adjusted initially using dil. NaOH and dil HCl
and it is not controlled during the course of the reaction.
The effect of pH on the initial degradation rate of phe-
nol is given in Figure 7. It can be seen that initially with
increasing pH from 4 to 5, a steep increase in reaction rate
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was observed; between the pH values 5 and 8, the reaction
IP: 222.175.36.19 On: Wedi,n2cr8eaOsectin20re1a5ct0io9n:4ra9t:e2b9etween 60 to 90 ppm is due to the
rate was almost constant; further increase in pH (pH = 10)
Copyright: American Scientific Publishers
fact that the catalyst sites get saturated by the adsorbed dye
resulted in the decrease of degradation rate.
molecules beyond 60 ppm. The decrease in reaction rate at
100 ppm is due to high saturation of phenol molecules on
the catalyst surface at this concentration.
3.8. Effect of Phenol Concentration
The photocatalytic degradation of phenol at different initial
concentration in the range of 30–100 ppm was investigated.
Figure 8 shows the degradation of phenol as a function
of time. Figure 9 indicates the initial degradation rate of
phenol at different initial phenol concentrations. The rate
3.9. Comparison of Degradation
Efficiency of Chlorophenols
Chlorophenols are more readily taken up by organisms, and
are thus more toxic, at lower pH levels. This is because the
more hydrophobic undissociated property of chlorophenols
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
4
5
6
7
8
9
10
pH
20
30
40
50
60
70
80
90 100 110
[Phenol] ppm
Figure 7. Effect of pH on the photocatalytic degradation of phenol over
nanocrystalline TS-1 thin film (Reaction conditions: [phenol] = 50 ppm;
pH = 4 to 10; Flow rate = 9 ml/min).
Figure 9. Effect of initial concentration of phenol on the initial reaction
rate of phenol degradation of phenol over nanocrystalline TS-1 thin film.
J. Nanosci. Nanotechnol. 14, 7345–7350, 2014
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Photocatalytic Oxidation of Phenolic Pollutants and Hydrophobic Organic Compounds in Industrial Wastewater
Khayyat et al.
can penetrate into the cell membranes and are more fat sol-
uble than the dissociated forms. The degradation efficiency
of monochloro and dicloro phenols are compared under
controlled conditions. The degadation efficiency of ortho-,
meta- and para-cholorophenols exhibited the following
order: orthocholo phenol > para cholophenol > meta
choloro phenol. Comparative studies on the degradation
efficiency of mono-di- and tri-chlorophenols showed the
following order: monochlorophenol > dichlorophenol >
trichlorophenol. This shows that the degradation efficiency
decreases as the number of chlorine atom attached to ben-
zene ring increases. Similar results were also observed
by Jung et al.34 In the photocatalytic process, chlorine
attached to phenol forms chloride ions by photomineraliza-
tion process, which decreases the hydroxyl ion radicals for
oxidation.
3. L. Selva Roselin, G. R. Rajarajeswari, R. Selvin, V. Sadasivam,
B. Sivasankar, and K. Rengaraj, Solar Energy 73, 281 (2002).
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3.10. Photocatalytic Degradation of
Phenolic Wastewater
Phenolic waste water was simulated with a phenol con-
centration of 300 mg/L.35 The time taken for the complete
degradation of phenol in the waste water was found to be
6 hrs.
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18. N. R. E. N. Impens, P. van der Voort, E. F. Vansant, Microporous
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3.11. Reusability of Nanocrystalline TS-1 Thin Film
The reusability of the nanocrystalline TS-1 thin film
showed that there was a small decrease in reaction rate
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4. CONCLUSIONS
The present study demonstrates that nanocrystalline TS-1
thin film showed photocatalytic activity for the degrada-
tion of phenol in aqueous solution. TOC analysis showed
that around 97% the organic carbon were oxidized to car-
bon dioxide. The photocatalytic degradation efficiency was
found to improved under aeration condition. The opti-
mum flow rate, initial concentration 9 ml/min and 60 ppm,
respectively. The degradation rate was affected by the solu-
tion pH, and the suitable pH range was found to 5 to 8. The
reusability study of the TS-1 thin film showed that there
was a significant decrease in degradation rate was observed.
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Acknowledgment: This work was funded by the Dean-
ship of Scientific Research (DSR), King Abdulaziz Uni-
versity, Jeddah, under grant No. (363-003-D1434). The
authors, therefore, acknowledge with thanks DSR techni-
cal and financial support.
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References and Notes
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Received: 12 November 2013. Accepted: 21 November 2013.
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