Treatment of hydrophobic polycyclic aromatic hydrocarbons and
toxicity using GO-TiO2-Sr(OH)2/SrCO3 nanocomposite via
photocatalytic degradation
RUKİYE ÖZTEKİN a , *, DELİA TERESA SPONZA a
a Department of Environmental Engineering
Dokuz Eylül University
Tınaztepe Campus, 35160 Buca/Izmir,
TURKEY
Abstract: - In this study, the effects of increasing sun light irradiation time (30 min, 120 min, 240 min and 360
min), increasing photocatalytic power (10 W, 50 W and 100 W), increasing graphene oxide (GO) nanoparticle
concentrations (2 mg/l, 4 mg/l and 8 mg/l), increasing titanium dioxide (TiO2) nanoparticle concentrations (1
mg/l, 3 mg/l, 6 mg/l and 9 mg/l), increasing GO-TiO2-Sr(OH)2/SrCO3 nanocomposite concentrations (1 mg/l, 2
mg/l and 4 mg/l) on the destructions of four hydrophobic polycyclic aromatic hydrocarbons (PAHs) in a real
petrochemical industry wastewater in Izmir (Turkey) were investigated. The yields in more hydrophobic PAHs
with high benzene rings [benzo[a]pyrene (BaP) and benzo[k]fluoranthene (BkF)] were as high as the less
hydrophobic PAHs with lower benzene rings [acenaphthylene (ACL) and carbazole (CRB)]; at pH=7.0, at 22oC
after 360 min sun light irradiation time, respectively. Maximum 97%ACL, 98%CRB, 98%BaP and 99%BkF
PAHs removals was detected at 4 mg/l GO-TiO2-Sr(OH)2/SrCO3 nanocomposite concentration, under 100
mW/cm2 sun light intensity, at 100 W photocatalytic power, at 360 min sun light irradiation time, at pH=7.0
and at 22oC, respectively. The effective PAHs concentrations caused 50% mortality in Daphnia magna cells
increased from initial EC50=342.56 mg/l to EC50=631.05 mg/l, at pH=7.0 and at 22oC after 360 min
photocatalytic degradation time resulting in a maximum acute toxicity removal of 99.99%, at 4 mg/l GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite concentration. The Daphnia magna acute toxicity was significantly reduced.
Key-Words: - Daphnia magna acute toxicity; graphene oxide; GO-TiO2-Sr(OH)2/SrCO3 nanocomposite;
petrochemical industry wastewater; photocatalytic degradation; polycyclic aromatic hydrocarbons; titanium
dioxide.
Received: April 8, 2022. Revised: October 29, 2022. Accepted: December 2, 2022. Published: December 31, 2022.
1 Introduction
Polycyclic aromatic hydrocarbons (PAHs) are an
important class of persistent organic pollutants
(POPs), and have been ubiquitously found in the
environment, [1]. Besides the natural sources, PAHs
are often from anthropogenic sources such as
incomplete combustion of fossil fuels, and
accidental spillages of crude and refined oils, [2, 3].
Due to their persistence and potential harmful
impact on the ecosystem and human health, PAHs
have been classified as priority pollutants by the
United States Environmental Protection Agency
(USEPA), [4].
Wastewater treatment plants, especially those
serving industrial areas, consistently receive
complex mixtures containing a wide variety of
organic pollutants. Groups of compounds present in
the petrochemical industries include polycyclic
aromatic hydrocarbons (PAHs), which are listed as
US-EPA and EU priority pollutants, and
concentrations of these pollutants therefore need to
be controlled in treated wastewater effluents, [5].
PAHs are ubiquitous environmental pollutants with
mutagenic properties, which have not been included
in the Turkish guidelines for treated waste
monitoring programs, [6]. Several hydroxy-PAHs
such as hydroxylated derivatives of Benzo[a]pyrene
(BaP) and Chrysene (CHR) have been shown to
possess estrogenic activity and cause damage to
DNA leading to cancer and possibly other effects,
[6, 7]. As a consequence of their strongly
hydrophobic properties and their resistance to
biodegradation, PAHs are not always quantitatively
removed from wastewaters by activated sludge
treatments, which very efficiently relocate them into
treated effluents.
Titanium dioxide (TiO2) is the most used
photocatalyst due to its environment friendliness,
abundant supply and cost-effectiveness, [8].
However, due to the wide bandgap (3.2 eV for
anatase and 3.0 eV for rutile), [9], TiO2 can only be
excited in the ultraviolet (UV) range, which
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accounts for only 4% of the solar radiation, [10].
Therefore, various efforts have been attempted to
extend the utilization of TiO2 to the visible light
range ( > 40% of the solar energy), such as
metal/non-metal doping, noble metal deposition,
semiconductors coupling, and photosensitization,
[11, 12].
Graphene is a flat monolayer of carbon atoms
tightly packed into a two-dimensional honeycomb
lattice. In recent years, graphene has attracted a
great deal of attentions for its potential applications
in many fields, such as nano-electronics, fuel-cell
technology, supercapacitors, and catalysts, [13, 14].
Graphene oxide (GO) is one of the most important
precursors of graphene, and thus, they share similar
sheet structures and properties such as high stability
and semiconducting characteristics, [10, 15]. GO
can enhance the light absorption via expanding the
photo-responsive range to visible light and suppress
the charge recombination by serving as a photo-
generated electron transmitter, when coupled with
TiO2 , [10]. To further enhance the conductivity and
reduce the bandgap, noble metals (e.g., gold,
palladium and platinum) are often incorporated to
the GO-TiO2 nanocomposite by surface deposition,
[10, 16].
Compared with noble metals, strontium (Sr), as
an alkaline earth metal, has much wider and richer
sources, and it is the 15th most abundant element in
the Earth’s crust with an estimated abundance of
nearly 360 mg/l, [17]. Sr has been widely employed
as a dopant for various semiconductors (e.g., TiO2,
zinc oxide and germanium dioxide) to enhance the
photocatalytic activities, [18]. Moreover, the OH
and carbonate forms of Sr (Sr(OH)2/SrCO3) have
been reported to have high photocatalytic activity
under visible-light irradiation, [19-21].
The reactive oxygen species (ROS) formed
during TiO2 photocatalysis include the hydroxyl
radical (OH●), superoxide anion radical (O2- ●),
hydroperoxyl radical (HO2 ●), singlet oxygen (1O2),
and their subsequent reactions with the target
contaminants occur at or very near the TiO2 surface,
[8, 22]. OH● radicals, generated on the surface of
the catalyst following oxidation of water from the
positive holes of TiO2, are non-selective oxidizing
species with strong oxidation potential (2.80 V) that
rapidly react with most organic compounds with
rate constants in the order of 106 - 1010 1/M.s, [23].
Various studies have investigated the degradation of
MC-LR in pure solutions or crude extracts with
TiO2 photocatalysis to study the effect of specific
water quality parameters, [24-27], or the properties
of the photocatalyst used, [24, 28-32]. Solar light
activated materials have also been tested to reduce
application cost, [27-29, 30, 33, 34]. Herein, sulfate
radical generating oxidants were added as a way to
reduce the energy requirements of the photocatalytic
system for the removal of MC-LR as most of the
light activated materials are not currently mass
produced. Sulfate radicals (SO4- ●) are among the
strongest oxidants known for the abstraction of
electrons (2.5 V - 3.1 V), [35, 36]. They are much
stronger than OH● radicals (1.89 V - 2.72 V), [23],
and other commonly used in the drinking water
industry oxidants, such as permanganate (E=1.70
V), [37], and hypochlorous acid (E=1.49 V), [38].
SO4- ● radicals can be produced through homolytic
dissociation of the oxidants through heat and
radiation and e- transfer mechanisms from Fenton-
like reagents, [39-41]. Neta et al., [36], reported that
owing to their selectivity, SO4 - ● radicals are more
efficient oxidants for the removal of organic
compounds with unsaturated bonds and aromatic
constituents than the OH ● radicals. Yet there are
limited studies on SO4- ● based AOPs (compared
with OH●) for the degradation of recalcitrant organic
contaminants and especially cyanotoxins, [41-44].
Even fewer studies have investigated the effect of
coupling SO4- ● radical generating oxidants with
TiO2 on the removal of emerging contaminants with
various light sources. Furthermore, simulated solar
irradiation (SSI) has been used in the SSI/TiO2/PS
treatment, [45], and showed higher potential for the
removal of the pesticide DEET compared with the
SSI/TiO2/H2O2 system. PS was also coupled with
TiO2 photocatalysts for the degradation of dyes
under solar, [46], and UV radiation, [47].
The aim of this study was to examine the effects
of increasing GO-TiO2-Sr(OH)2/SrCO3
concentrations (1 mg/l, 2 mg/l and 4 mg/l),
increasing GO concentrations (2 mg/l, 4 mg/l and 8
mg/l), increasing TiO2 concentrations (1 mg/l, 3
mg/l, 6 mg/l and 9 mg/l), increasing photocatalytic
powers (10 W, 50 W and 100 W) and increasing sun
light irradiation times (30 min, 120 min, 240 min
and 360 min) on the photocatalytic degradation of
four hydrophobic PAHs namely ACL, CRB, BaP
and BkF in a real petrochemical industry
wastewater, at pH=7.0 and at 22oC, respectively.
Furthermore, the effects of the operational
conditions in a real petrochemical industry
wastewater on the removal of acute toxicity were
also determined using Daphnia magna.
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2. Materials and Methods
2.1. Material Synthesis
GO was synthesized according to the modified
Hummers method, [48], and titanium dioxide
nanoparticles (Nano-TiO2) were prepared following
the approach reported in Xu et al., [49]. Supporting
Information (SI) Text S1 provides detailed
procedures for the preparation of GO and Nano-
TiO2. The GO-TiO2 nanocomposite was then
synthesized through the sono-chemical reaction of
Nano-TiO2 in the presence of the GO, [15]. In brief,
3 g of the mixture of GO and Nano-TiO2 (mass
ratio=2/1) was added to 100 ml of distilled water,
and stirred for 0.5 h at room temperature (22±1°C).
The suspension was then sonicated for 1 h. The
resultant composite was recovered by filtration,
rinsed with ethanol and then freeze-dried to yield
the GO-TiO2 composites. Subsequently, dispersing
known mass of GO-TiO2 (30 wt% of the final mass)
in a 500 ml of sodium hydroxide (NaOH) solution
(1 M), and a pre-determined amount of strontium
chloride (SrCl, 0.5 M) was added dropwise to the
dispersion at a rate of 2.0 ml/min using a Titronic
Universal titrator (SCHOTT, Mainz, Germany). The
resulting material, GO-TiO2-Sr(OH)2/SrCO3, was
then filtered, washed with distilled water until no
chloride was detected in the washing water, and
then freeze-dried for 48 h. For comparison, a GO-
Sr(OH)2/SrCO3 nanocomposite was also prepared
by the similar procedure with 20 wt% GO but
without TiO2.
2.2. Material Characterization
The X-ray diffraction (XRD) measurements were
performed on a PW1820 X-ray diffractometer
(Philips, Amsterdam, Netherlands) using Cu Kα
radiation. Scanning electron microscopy (SEM)
images were obtained with a JSM-840A electron
microscope (JEOL, Tokyo, Japan) equipped with
energy dispersive X-ray (EDX) micro-analytical
system (EDAX, Mahwah, NJ, USA). The EDX
analysis was performed at -263.15oC magnification
to map the distribution of Sr and Ti on the
nanocomposite surface. Fourier transform-infrared
(FTIR) measurements were carried out with a
Nicolet 560 FTIR spectrometer on KBr wafers
(Thermo Fisher Scientific Inc., MA, USA). The
spectra were recorded from 4000 1/cm to 400 1/cm
at a resolution of 4 1/cm. Nitrogen (N2) adsorption-
desorption isotherms were measured using AS1Win
(Quantachrome Instruments, FL, USA) at the liquid
N2 temperature of -196.15oC, from which Brunauer-
Emmett-Teller (BET) specific surface area (SBET),
micropore volume (Vmic), total pore volume (Vt),
and pore size distribution (PSD) were derived.
Potentiometric titration measurements were carried
out with a T50 automatic titrator (Mettler Toledo,
Columbia, MD, USA) and the total surface charge
(Qsurf, mmol/g) of the nanocomposite was then
calculated. Differential thermal gravimetric (DTG)
analysis was conducted on an STA449F3 instrument
(Netzsch, Selb, Germany). Reactive oxydizing
agents such as potassium peroxymonosulfate (PMS,
HSO5-), potassium persulfate (PS, K2S2O8), and the
quenching agent sodium thiosulfate (Na2S2O3) were
purchased from Sigma-Aldrich (Poole, UK).
2.3. Photocatalytic Degradation
Simulated sun light was generated using a 94041A
solar simulator (Newport Corporation, Irvine, CA).
A cylindrical quartz tank reactor with a Pyrex pillar
(80×70 mm) was fabricated as the photoreactor. The
light intensity reached the reactor was 100 mW/cm2.
The detailed information on the solar simulator and
photoreactor has been reported elsewhere, [50].
PAHs were purchased from Alfa Aesar (Ward Hill,
MA, USA), and a stock solution of 2 g/l was
prepared in methanol. Deionized (DI) water
(Millipore Co., 18.2 MΩ·cm) was used in preparing
all aqueous solutions. Typically, the photocatalytic
degradation kinetic tests were conducted under the
following conditions: solution volume=250 ml,
initial PAHs concentration=1 mg/l, 5 mg/l and 10
mg/l, catalyst dosage=50 mg/l, pH=7.0±0.2, and
T=22±1oC, respectively. The solution-photocatalyst
mixture was first stirred in the dark for 2 h to allow
PAHs adsorption to reach equilibrium.
Subsequently, photodegradation was initiated by
exposing the reactor to the simulated sun light.
2.4. Analytical Methods
UV–Visible spectra of solutions were obtained
using an HP 8453 UV–Vis spectrophotometer
(Agilent Technologies, Santa Clara, CA, USA).
PAHs concentration was determined using an HP
1100 HPLC system (Agilent Technologies, Santa
Clara, CA, USA) with a detection limit of 2.5 μg/l at
the UV detection wavelength of 250 nm.
Photodegradation intermediates were analyzed using
an HP7890A/HP5975C gas chromatography-mass
spectrometry (GC–MS) system (Agilent
Technologies, Santa Clara, CA, USA).
The contributions of various reactive oxygen
species (ROS) during the photocatalytic degradation
process were investigated by adding scavengers to
selectively quench radicals; i.e., potassium
peroxymonosulfate (PMS, HSO5-), potassium
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persulfate (PS, K2S2O8), and the quenching agent
sodium thiosulfate (Na2S2O3) were used.
2.4.1. PAHs Measurements
For PAHs and some metabolites (hydroxy-benzoic
acid, benzoic acid) analyses the samples were first
filtered through a glass fiber filter (47 mm-diameter)
and to collect the particle-phase in series with a
resin column (~10 g XAD-2) and to collect
dissolved-phase polybrominated diphenyl ethers.
Resin and water filters were ultrasonically extracted
for 60 min with a mixture of 1/1 acetone: hexane.
All extracts were analyzed for four PAHs (Table 1)
gas chromatographically (Agilent 6890N GC)
equipped with a mass selective detector (Agilent
5973 inert MSD). A capillary column (HP5-MS, 30
m, 0.25 mm, 0.25 µm) was used. The initial oven
temperature was kept at 50oC for 1 min, then raised
to 200oC at 25oC/min and from 200oC to 300oC at
8oC/min, and then maintained for 5.5 min. High
purity He(g) was used as the carrier gas at constant
flow mode (1.5 ml/min, 45 cm/s linear velocity).
PAHs and their metabolites were identified on the
basis of their retention times, target and qualifier
ions and were quantified using the internal standard
calibration procedure. To determine the degradation
intermediates, samples (10 ml each) were collected
at 0 min, 30 min, 120 min, 240 min and 360 min.
The hydrophobic PAHs (ACL, CRB, BaP and BkF)
were performed using a HPLC (Agilent-1100) with
a method developed by Lindsey and Tarr, [51]. The
chromatographic conditions for the hydrophobic
PAHs (ACL, CRB, BaP and BkF) determination
were as follows: C-18 reverse phase HPLC column
(Ace 5C18; 25-cm x 4.6-mm, 5 μm, mobile phase:
50/50 (v/v) methanol/organic-free reagent water).
pH, temperature, oxidation-reduction potential
(ORP) were monitored following Standard Methods
2550, 2580 and 5220 D, [52]. H2O2 was quantified
with a colorimetric method following Standard
Method 3550, [52].
Table 1: Energy efficiency of photocatalysis with
different sun light intensities at ambient conditions
after 360 min sun light irradiation time in
petrochemical industry wastewater (n=3, mean
values, n: deionized water and petrochemical
industry wastewater containing PAHs)
Energy efficiency of photocatalysis with different
sun light intensities
Sun light
intensity
(W/cm2)
Power
density
(W/ml)
Specific energy
(kWh/kg COD-
in influent)
COD
removal
efficiency
(%)
17
0.12
8.29
47
38
0.91
8.90
59
24.03
1.34
9.26
68
39.09
1.71
9.91
77
46
1.97
10.83
80
52.3
2.38
12.42
86
2.5. Data Analysis
The pseudo-first-order kinetic model was employed
to fit the kinetic data, [12, 50], (Equation 1):
(1)
Where, Ct and C0 are the PAHs concentrations (μg/l)
at the reaction time of t and 0 min, respectively, and
k is the rate constant (1/min). The integration of
UV–Vis absorbance of PAHs was achieved using
the software OriginPro 8 (OriginLab Corporation,
Northampton, MA, USA). The correlation fittings
between the reaction rate constant and various water
quality parameters were conducted by using
OriginPro 8 or GraphPad Prism 6 (GraphPad
Software, Inc., La Jolla, CA, USA). The fitting
models included fourth-order polynomial and
sigmoidal (Boltzmann and DoseResp functions)
equations.
2.6. Daphnia magna Acute Toxicity Test
To test toxicity 24 h old Daphnia magna were used
as described in Standard Methods, [52]. After
preparing the test solution, experiments were carried
out using 5 or 10 Daphnia magna introduced into
the test vessels. These vessels had 100 ml of
effective volume at pH=7.0-8.0, providing a
minimum DO concentration of 6 mg/l at an ambient
temperature of 20oC-25oC. Young Daphnia magna
were used in the test (≤ 24 h old). A 24 h exposure
is generally accepted as standard for a Daphnia
acute toxicity test. The results were expressed as
mortality percentage of the Daphnia magna.
Immobile animals were reported as dead Daphnia
magna.
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2.7. Statistical Analysis
ANOVA analysis of variance between experimental
data was performed to detect F and P values, i.e. the
ANOVA test was used to test the differences
between dependent and independent groups, [53].
Comparison between the actual variation of the
experimental data averages and standard deviation is
expressed in terms of F ratio. F is equal (found
variation of the date averages/expected variation of
the date averages). P reports the significance level,
d.f indicates the number of degrees of freedom.
Regression analysis was applied to the experimental
data in order to determine the regression coefficient
R2 (Statgraphics, Centurion XV, sofware, 2005),
[54]. The aforementioned test was performed using
Microsoft Excel Program.
All experiments were carried out three times and
the results are given as the means of triplicate
samplings. The data relevant to the individual
pollutant parameters are given as the mean with
standard deviation (SD) values.
3. Results and Discussion
3.1. Raw Wastewater
Characterization of raw petrochemical wastewater
taken from the influent of the aeration unit of a
petrochemical industry wastewater treatment plant,
İzmir, Turkey was performed. The results are given
as the mean value of triplicate sampling. The mean
values for pH, ORP were recorded as 7.21 mV and
28.20 mV, respectively. The mean TSS and TVSS
concentrations were measured as 310.3 mg/l and
250.6 mg/l, respectively. The mean DO, BOD5,
CODtotal, CODdissolved concentrations were 1.78 mg/l,
584 mg/l, 1475 mg/l and 1127 mg/l while the Total-
N, NH4-N, NO3-N, NO2-N, Total-P, PO4-P and oil
concentrations were measured as 15.40 mg/l, 2.20
mg/l, 1.80 mg/l, 0.05 mg/l, 10.60 mg/l, 6.80 mg/l
and 206 mg/l, respectively. The less hydrophobic
ACL and CRB concentrations were 124.2 mg/l and
3.60 mg/l while the more hydrophobic BaP and BkF
concentrations were measured as 5.41 mg/l and 0.64
mg/l, respectively, in the petrochemical industry
wastewater. Physical and chemical properties of the
PAHs in petrochemical industry wastewater studied
in this work was shown at Table 2.
* Table 2 can be found in Appendix section.
3.2. Characterization of photocatalysts
The XRD spectra of the prepared nanocomposites
(GO-Sr(OH)2/SrCO3 and GO-TiO2-Sr(OH)2/SrCO3)
(Figure 1). For both composite materials, the
diffraction peak at about 2θ=10° is attributed to GO,
[55]. For GO-Sr(OH)2/SrCO3, the broad peaks at
2θ=25°, 2θ=28°, 2θ=36° and 2θ=43° are assigned to
the crystalline phase of SrCO3 (JCPDS Card No.
005-0418), whereas weak peaks for Sr(OH)2,
Sr(OH)2.H2O and Sr (OH)2.8H2O were also
observed as confirmed by JCPDS Cards Nos. 27-
0847, 28-1222, and 27-1438, respectively, [56]. The
XRD pattern of GOTiO2-Sr(OH)2/SrCO3 showed
much sharper peaks than those of GO-Sr
(OH)2/SrCO3, indicating well-developed crystalline
phases. The peaks at 2θ=25°, 2θ=28°, 2θ=36° and
2θ=43° are attributed to TiO2 belonging to the rutile
phase (JCPDS Card No. 88-1175), while minor
peaks from the anatase phase (JCPDS Card No. 84-
1268) were also observed, [49, 57]. Besides, the
peaks at 2θ=24°, 2θ=32.7°, 2θ=40.1°, 2θ=46.6°,
2θ=57.8° and 2θ=67.9° can be attributed to the
perovskite-type phase of cubic symmetry of SrTiO3
(STO) (JCPDS Card No. 86-0179), [58, 59].
* Figure 1 can be found in Appendix section.
The SEM images with the EDX maps of the
elemental distribution (Figure 2a, Figure 2b, Figure
2c, Figure 2d, Figure 2e), Sr and/or Ti's GO-
Sr(OH)2/SrCO3 and GO-TiO2-Sr(OH)2/SrCO3
reveals that it is distributed quite uniformly in
nanocomposite matrices. The nano-rods in Figure
(2a) are SrCO3, while the nanospheres on the GO
surface in Figure (2c) are likely to be the aggregates
of SrTiO3 nanoparticles with an average diameter of
about 1 μm, [60].
* Figure 2 can be found in Appendix section.
Figure (3a) shows the FTIR spectrum for GO.
The characteristic bands are assigned as follows:
carboxyl groups at 1070 1/cm and 1760 1/cm, C]C
stretching vibration of the sp2 carbon skeletal
network at 1600 1/cm, OH groups at 1380 1/cm
and 1000 1/cm , and epoxy groups at 900 1/cm,
[55]. The peak at 1240 1/cm can be attributed to the
S]O asymmetric stretching vibrations arising from
sulfones or sulfates that were formed upon graphite
oxidation with H2SO4 (SI Text S1). Figure (3b)
presents the FTIR spectra of the nanocomposite
materials, i.e., GO-Sr (OH)2/SrCO3 and GO-TiO2-
Sr(OH)2/SrCO3. The characteristic bands of GO are
clearly seen in the spectra of both nanocomposites.
For GO-Sr (OH)2/SrCO3, the bands at 1071 1/cm
and 1760 1/cm are attributed to the asymmetric and
symmetric stretching vibrations of the carboxylate
groups. The band at 1446 1/cm is attributed to the
asymmetric stretching vibration of carbonate anion
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(CO3−2) in SrCO3 that has a D3h symmetry, while
the bands at 860 1/cm and 600 1/cm are assigned
to the vibrations of the CO3−2 due to bending out of
plane and in plane, respectively, [56]. The bands at
3200 1/cm, 1380 1/cm and 1000 1/cm are due to
stretching mode of –OH groups and can be
attributed to Sr(OH)2, Sr(OH)2.H2O and
Sr(OH)2.8H2O. For GO-TiO2-Sr(OH)2/SrCO3, a new
broad peak was observed in the range of 550–780
1/cm , which can be ascribed to the TiO2 stretching,
[60]. The bands at 1760 1/cm and 1384 1/cm for
the carboxylate groups disappeared, indicating that
these groups have been bounded to TiO2. The bands
at 3200 1/cm, 1384 1/cm and 1020 1/cm were
diminished, indicating that less crystalline phases of
Sr(OH)2, Sr(OH)2.H2O and/or Sr(OH)2.8H2O were
formed, [56].
* Figure 3 can be found in Appendix section.
The textural features of the nanocomposites were
investigated with the N2 adsorption-desorption
isotherms and the results are shown in Figure 4a.
According to the International Union of Pure and
Applied Chemistry (IUPAC), the shape of the
isotherm for the GO-Sr(OH)2/SrCO3 nanocomposite
can be classified as a combination of Type II and
Type III, indicating the coexistence of mesopores
and macropores, [61]. The deviation of the
desorption isotherm from the adsorption isotherm
(hysteresis) can be attributed to the presence of slit
or bottle neck pores. The isotherm displayed a
significant increase of N2 uptake at P/Po > 0.95,
indicating the presence of external surface area
and/or textural porosity. In contrast, the isotherm for
GO-TiO2-Sr(OH)2/SrCO3 conforms to the Type II
isotherm, which is characteristic of low-porosity
materials or materials with large macropores, [61].
The decrease of the mesopores and macropores
volume in GO-TiO2-Sr(OH)2/SrCO3 can be
attributed to occupying part of the pores by TiO2
and SrTiO3 reaction products. The inset in Figure 4b
presents the pore size distributions for GO, GO-
Sr(OH)2/SrCO3 and GO-TiO2-Sr(OH)2/SrCO3
estimated by the density functional theory (DFT)
calculations of the N2 adsorption data. The presence
of mesopores and macropores is clearly evident in
GO, which are then sharply diminished with the
addition of Sr(OH)2/SrCO3 and TiO2. Moreover, the
specific surface area of GO-TiO2-Sr(OH)2/SrCO3
(5.64 m2/g) was found 75% less than that of GO-
Sr(OH)2/SrCO3 (21.47 m2/g), and the pore volume
of GO-TiO2-Sr(OH)2/SrCO3 (0.0319 cm3/g) was
84% less than that of GO-Sr(OH)2/SrCO3 (0.1842
cm3/g).
* Figure 4 can be found in Appendix section.
3.3. Effect of Increasing GO Nanoparticle
Concentrations during Hydrophobic PAHs
Treatment with Photocatalytic Degradation
under Sun Light Irradiation
Preliminary studies showed that the optimum sun
light intensity, irradiation time, pH, and temperature
were 100 mW/cm2, 360 min, pH=7.0 and at 22oC,
respectively in the presence of 7 mg/l GO
nanocomposite concentration (data not shown). The
effects of increasing GO nanoparticle concentrations
(2 mg/l, 4 mg/l and 8 mg/l) on the removals of
PAHs [less hydrophobic (ACL, CRB) and more
hydrophobic (BaP, BkF)] in petrochemical industry
wastewater under 100 mW/cm2 sun light intensity,
at 360 min sun light irradiation time, at pH=7.0 and
at 22oC, respectively (Table 3; SET 1). The
maximum removals of 87%ACL, 87%CRB,
85%BaP and 84%BkF hydrophobic PAHs in
petrochemical industry wastewater were measured
at 8 mg/l GO nanoparticle concentration under 100
mW/cm2 sun light intensity, at 100 W photocatalytic
power, at 360 min sun light irradiation time, at
pH=7.0 and at 22oC, respectively (Table 3; SET 1).
The increasing GO nanoparticle concentrations were
positively affect the photocatalytic degradation of
hydrophobic PAHs (ACL, CRB, BaP and BkF)
(Table 3; SET 1).
* Table 3 can be found in Appendix section.
3.4. Effect of Increasing TiO2 Nanoparticle
Concentrations during Hydrophobic PAHs
Treatment with Photocatalytic Degradation
under Sun Light Irradiation
The preliminary studies showed that the optimum
removals for PAHs [less hydrophobic (ACL, CRB)
and more hydrophobic (BaP, BkF)] were obtained at
8 mg/l TiO2 concentration, under 98 mW/cm2 sun
light intensity, at 95 W photocatalytic power, at 350
min sun light irradiation time, at pH=7.1 and at
22oC (data not shown). The effects of increasing
TiO2 nanoparticle concentrations (1 mg/l, 3 mg/l, 6
mg/l and 9 mg/l) were measured to detect the PAHs
yields [less hydrophobic (ACL, CRB) and more
hydrophobic (BaP, BkF)] in petrochemical industry
wastewater under 100 mW/cm2 sun light intensity,
at 100 W photocatalytic power, at 360 min sun light
irradiation time, at pH=7.0 and at 22oC, respectively
(Table 3; SET 2). The removals of BaP, BkF, ACL
and CRB PAHs increased from 75% up to 86% as
the TiO2 nanoparticle concentrations was increased
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from 1 mg/l up to 6 mg/l, whereas 1 mg/l - 3 mg/l
TiO2 nanoparticle concentrations did not
significantly contribute to the hydrophobic PAHs
(ACL, CRB, BaP and BkF) removals in
petrochemical industry wastewater (Table 3; SET
2). The maximum 89%ACL, 90%CRB, 91%BaP
and 92%BkF hydrophobic PAHs removals in
petrochemical industry wastewater were detected at
9 mg/l TiO2 nanoparticle concentration, under 100
mW/cm2 sun light intensity, at 100 W photocatalytic
power, at 360 min sun light irradiation time, at
pH=7.0 and at 22oC, respectively (Table 3; SET 2).
The increasing of TiO2 nanoparticle concentrations
positively affected the photocatalytic degradation of
hydrophobic PAHs (ACL, CRB, BaP and BkF) in
petrochemical industry wastewater during sun light
irradiation process (Table 3; SET 2).
3.5. Effect of Increasing GO-TiO2-
Sr(OH)2/SrCO3 Nanocomposite
Concentrations during Hydrophobic PAHs
Treatment with Photocatalytic Degradation
under Sun Light Irradiation
Based on the preliminary studies the optimum
removals of some less hydrophobic (ACL, CRB)
and more hydrophobic (BaP, BkF)] PAHs in
petrochemical industry wastewater were researched
at 100 mW/cm2 sun light intensity, at 100 W
photocatalytic power, at 360 min sun light
irradiation time, at pH=7.0 and at 22oC, respectively
at 3 mg/l GO-TiO2-Sr(OH)2/SrCO3 concentrations
(Table 3; SET 3). The removals in BaP, BkF, ACL
and CRB in petrochemical industry wastewater
increased from 92%, up to 99% as the GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite concentration was
increased from 1 up to 4 mg/l, at 100 mW/cm2 sun
light intensity, at 100 W photocatalytic power, at
360 min sun light irradiation time and at 22oC,
respectively (Table 3; SET 3). The maximum
97%ACL, 98%CRB, 98%BaP and 99%BkF
hydrophobic PAHs removals in petrochemical
industry wastewater were found at 4 mg/l GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite concentration under
100 mW/cm2 sun light intensity, at 100 W
photocatalytic power, at 360 min sun light
irradiation time, at pH=7.0 and at 22oC,
respectively. The increasing GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite concentrations were
found to be positively affect for the photocatalytic
degradation of hydrophobic PAHs (ACL, CRB, BaP
and BkF) in petrochemical industry wastewater
(Table 3; SET 3).
An optimum GO-TiO2-Sr(OH)2/SrCO3
nanocomposite concentration of 4 mg/l increase the
ionic strength of the aqueous phase, driving the
PAHs to the bulk–bubble interface in a
photocatalytic reactor. This, increases the
partitioning of the PAH species upon radical
scavengers in a photocatalytic reactor. Beyond the
partitioning enhancement, the presence of salt
reduces the vapor pressure and increases the surface
tension of the PAHs, [62]. Therefore, the solubility
of the solution decreases and the diffusion of solutes
decreases from the bulk solution to the bubble–
liquid interface with administration of decreasing
GO-TiO2-Sr(OH)2/SrCO3 nanocomposite
concentrations in the photocatalytic reactor, [63].
The high PAH removals in raised GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite concentrations can
be explained by the fact that a higher amount of
GO-TiO2-Sr(OH)2/SrCO3 nanocomposite will create
more salting out effect than the lower amount and
thus increase the interfacial concentration of the
PAHs. In our study, no contribution of GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite > 4 mg/l to the PAH
yields could be attributed to the synergistic and
antagonistic effects of the by-products and to the
more hydrophobic (BaP, BkF) and less hydrophobic
(ACL, CRB) nature of PAHs present in
petrochemical industry wastewaters (Table 3; SET
3).
3.6. Effect of Increasing Sun Light
Irradiation Times during Hydrophobic
PAHs Treatment with Photocatalytic
Degradation under Sun light Irradiation
The effects of increasing sun light irradiation times
(30 min, 120 min, 240 min and 360 min) were
measured in PAHs [less hydrophobic (ACL, CRB)
and more hydrophobic (BaP, BkF)] in
petrochemical industry wastewater under 100
mW/cm2 sun light intensity, at 100 W photocatalytic
power, at pH=7.0 and at 22oC, respectively (Table 3;
SET 4).
The removals of BaP, BkF, ACL and CRB
increased from 56%-65% up to 72%-79% as the sun
light irradiation times was increase from 30 min up
to 240 min, whereas 30 min - 120 min sun light
irradiation times dis not significantly contribute to
the hydrophobic PAHs (ACL, CRB, BaP and BkF)
removals in petrochemical industry wastewater was
not observed (Table 3; SET 4). The maximum
81%ACL, 80%CRB, 80%BaP and 84%BkF
hydrophobic PAHs removals in petrochemical
industry wastewater were indicated at 360 min sun
light irradiation time, under 100 mW/cm2 sun light
intensity, at 100 W photocatalytic power, at pH=7.0
and at 22oC, respectively (Table 3; SET 4). The
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increasing sun light irradiation times were affected
positively effect for the photocatalytic degradation
hydrophobic PAHs (ACL, CRB, BaP and BkF) in
petrochemical industry wastewater during sun light
irradiation process (Table 3; SET 4).
3.7. Effect of Increasing Photocatalytic
Powers during Hydrophobic PAHs
Treatment with Photocatalytic Degradation
under Sun Light Irradiation
The effects of increasing photocatalytic powers (10
W, 50 W and 100 W) were measured in PAHs [less
hydrophobic (ACL, CRB) and more hydrophobic
(BaP, BkF)] in petrochemical industry wastewater
under 100 mW/cm2 sun light intensity, at 360 min
sun light irradiation time, at pH=7.0 and at 22oC,
respectively (Table 3; SET 5).
The removals of BaP, BkF, ACL and CRB
increased from 56%-69% up to 69%-78% as the
photocatalytic powers was increase from 10 W up to
50 W, whereas 10W-50 W photocatalytic powers
did not significantly contribute to the hydrophobic
PAHs (ACL, CRB, BaP and BkF) removals in
petrochemical industry wastewater was not obtained
(Table 3; SET 5). The maximum 84%ACL,
86%CRB, 88%BaP and 89%BkF hydrophobic
PAHs removals in petrochemical industry
wastewater were indicated at 100 W photocatalytic
power, under 100 mW/cm2 sun light intensity, at
360 min sun light irradiation time, at pH=7.0 and at
22oC, respectively (Table 3; SET 5). The increasing
photocatalytic powers were affected positively
effect for the photocatalytic degradation
hydrophobic PAHs (ACL, CRB, BaP and BkF) in
petrochemical industry wastewater during sun light
irradiation process (Table 3; SET 5).
3.8. Photocatalytic Activity
PAHs is resistant to photolysis under sun light, [63].
The control tests showed that nearly 85% of PAHs
in petrochemical industry wastewater still retained
in the solution after 360 min sun irradiation time
(Table 4 and Figure 5) and the pseudo-first-order
rate constant was k=0.0006±0.0001 1/min. The
addition of TiO2 nanoparticle in petrochemical
industry wastewater enhanced the photodegradation
rate by 3 folds (k=0.0016 1/min) (Table 4 and
Figure 5). The addition of GO in petrochemical
industry wastewater increased the photodegradation
yield (k=0.0019±0.0001 l/min) (Table 4 and Figure
5). The UV light in the sun light irradiation is the
main driving energy for the photocatalytic activity
of TiO2 , [12]. The synthesized GO-Sr(OH)2/SrCO3
showed a slightly better photocatalytic activity
(k=0.0021±0.0001 1/min) than TiO2 and GO
nanoparticle in petrochemical industry wastewater
(Table 4 and Figure 5). As expected, the GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite in petrochemical
industry wastewater exhibited the highest
photocatalytic activity and greatly accelerated the
photocatalytic degradation rate. It was shown a
synergistic interaction among the three
nanocomponents, i.e., GO, TiO2 and
Sr(OH)2/SrCO3, which can facilitate utilization of
both UV and visible light energy in the sun light
irradiation in petrochemical industry wastewater.
Table 4: The rate constants of GO, TiO2 and GO-
TiO2-Sr(OH)2/SrCO3 after photocatalytic
degradation with sun light irradiation process in
petrochemical industry wastewater.
Sun
light
irradi
ation
time
(min)
k (1/min)
Control
GO
TiO2
GO-
TiO2-
Sr(OH)2
/SrCO3
30
0.0001±
0.00001
0.0005±
0.0001
0.0004±
0.0001
0.0009±0
.0001
120
0.0003±
0.0001
0.0011±
0.0001
0.0009±
0.0001
0.0013±0
.0001
240
0.0005±
0.0001
0.0014±
0.0001
0.0012±
0.0001
0.0017±0
.0001
360
0.0006±
0.0001
0.0019±
0.0001
0.0016±
0.0001
0.0021±0
.0001
* Figure 5 can be found in Appendix section.
In the photocatalytic activity of GO-TiO2-
Sr(OH)2/SrCO3 firstly, the hybridization of the two
coupling semiconductors (TiO2 and Sr(OH)2/SrCO3)
shifted the optical absorption to the higher
wavelength region and impel the transfer of photo-
excited electron and holes to opposite directions
(data not shown), [16, 21, 64]. Secondly, the GO
sheets can further promote the transport of the
photo-excited electrons, and thus inhibit the
recombination of electrons and holes. And thirdly,
the reaction product SrTiO3 has high photocatalytic
activity, [64], and can also contribute to the
enhanced photodegradation of PAHs.
3.9. Contribution of Reactive Oxygen Species
(ROS) on the Photocatalytic Yields of PAHs
In generally, photocatalytic oxidation processes,
ROS (potassium peroxymonosulfate (PMS, HSO5-),
potassium persulfate (PS, K2S2O8) and the
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quenching agent sodium thiosulfate (Na2S2O3)
generated during the photocatalytic reactions are
mainly responsible for the degradation of organic
pollutants, [65]. Preliminary studies showed that
among the concentrations studied with 1.1 mg/l
PMS, 0.9 mg/l PS and 0.79 mg/l Na2S2O3 highest
photooxidation yields was detected.
PS and PMS can undergo homolytic dissociation
of the peroxide bond from radiation or thermal
activation and give SO4- ● radicals, and SO4- and
OH● radicals, respectively (Equation 2 and Equation
3), [41].
(2)
(3)
The oxidants can also act as electron acceptors of
the photo-excited electron from the conduction band
of GO-TiO2-Sr(OH)2/SrCO3 and through electron
transfer mechanisms to give additional SO4- ● radical
and OH● radical based on the reactions listed below
(Equation 4, Equation 5 and Equation 6), [66- 68].
(4)
(5)
(6)
Heat activation of oxidants did not contribute on
radical formation because of the temperature in the
reactor and the relatively short treatment times
compared to what was reported needed in the
literature, [41]. On the other hand, homolytic
dissociation of the peroxide bond of the oxidants
through radiation seems to be a more probable
mechanism. Even though, both oxidants have low
absorption in the UVA range, the adsorption of PS
at λ=365 nm is four times the one of PMS, when
measured in solutions of the same concentration of
active species, [39]. This indicates that PS has a
better ability to adsorb photons compared to PMS
and therefore, more radicals can be formed. The
remaining PMS and form peroxymonosulfate
radicals (SO5- ●) (Equation 7 and Equation 8) that
have significantly reduced oxidation ability and
higher selectivity (redox potential 1.1 V, at pH=7.0)
to SO4- ● radicals (Table 5).
(7)
(8)
On the other hand, reaction of PS with a SO4- ●
radical will cause the formation of another SO4- ●
radical (Equation 9) which leaves the oxidative
capacity of the system unaltered. The effects of
(PMS, HSO5-), (PS, K2S2O8) and Na2S2O3 on the
photocatalytic degradation rates of the studied BkF
PAH were tabulated (Table 5).
(9)
Table 5: Contributions of ROS to photocatalytic
degradation of BkF PAH in petrochemical industry
wastewater by GO-TiO2-Sr (OH)2/SrCO3 under
simulated solar irradiation.
Scavengers
Scavenging
radicals
k (1/min)
None (Only GO-
TiO2-Sr
(OH)2/SrCO3)
-
0.0061
PMS
HSO5 -
0.0062
PS
K2S2O8
0.0067
Na2S2O3
SO4-2
0.0063
3.10. Photodegradation Pathway
At Table 6 and Figure 6 presents the reaction
intermediates during the photocatalytic degradation
of hydrophobic PAHs (ACL, CRB, BaP and BkF) in
petrochemical industry wastewater by GO-TiO2-
Sr(OH)2/SrCO3 under sun light irradiation process.
It is noteworthy that the reaction rate and selectivity
can be altered by the reaction matrix. For example,
using dimethyl carbonate instead of water as the
medium, the selectivity of TiO2 for the partial
photooxidation of hydrophobic PAHs (ACL, CRB,
BaP and BkF) in petrochemical industry wastewater
was enhanced.
Table 6: By-products of BkF, BaP and ACL PAHs
in petrochemical industry wastewater at 100
mW/cm2 sun light intensity, at 250 ml solution
volume, at 1 mg/l initial PAHs concentration, at
pH=7.0±0.2, at 22°C, at 360 min sun light
irradiation time, respectively (n=3, mean±SD).
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PAHs
name
Initial PAH
concentration
(mg/l)
Photocatalytic
degradation
metabolites
(mg/l)
BkF
0.804 ± 0.001
benzoic acid: 0.21
± 0.002
FL: 0.59 ± 0.005
BaP
0.077 ± 0.003
benzoic acid: 0.028
± 0.001
PY: 0.0040 ±
0.00014
ACL
53.42 ± 0.05
NAP: 44.13 ± 0.07
* Figure 6 can be found in Appendix section.
3.11. Determination of the Acute Toxicity of
Studied PAHs on Daphnia magna before and
after Treatment of Hydrophobic PAHs
under Photocatalytic Degradation at
Different Experimental Conditions
The raw petrochemical industry wastewater samples
induced 95% motility inhibition to Daphnia magna
cells (Table 7). This inhibition could be attributed to
the mixed recalcitrant carcinogenic hydrophobic
PAHs with high benzene rings and to the synergistic
effects of the aforementioned more hydrophobic
PAHs with less hydrophobic PAHs in petrochemical
industry wastewaters. When Daphnia magna were
exposed to the effluent samples treated with only
photolysis without catalyst at 22oC for 360 min sun
light irradiation time a significant reduction in
inhibition (10.01%) was not observed (the inhibition
decreased from initial 98% to 88%). In other words,
photolysis alone was not sufficient to remove the
toxicity of recalcitrant by-products from the
petrochemical industry wastewater (Table 7). The
maximum removals in inhibition were observed in
photocatalytic degraded petrochemical industry
wastewater containing 8 mg/l GO nanoparticle, 9
mg/l TiO2 nanoparticle and 4 mg/l GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite concentrations at a
neutral pH=7.0 after 360 min sun light irradiation
time, at 22oC, respectively. A decreasing toxicity
trend due to long sun light irradiation time with
catalyst can be explained by the formation of less
toxic by-products over time. The petrochemical
industry wastewater containing TiO2 nanoparticles >
10 mg/l displayed toxicity to Daphnia magna after
360 min sun light irradiation time. Similarly, GO
nanoparticle and GO-TiO2-Sr(OH)2/SrCO3
nanocomposite concentrations > 10 mg/l and > 6
mg/l caused inhibition to Daphnia magna motility
after 360 min sun light irradiation time and at 22oC.
A significant correlation between Daphnia manga
acute toxicity and TiO2, GO and GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite concentrations in
petrochemical industry wastewater was observed
after 360 min sun light irradiation time according to
multiple regression analysis (R2=0.87, F=17.99.
p=0.001).
* Table 7 can be found in Appendix section.
Toxicity results showed that both high
concentrations of GO, TiO2 and GO-TiO2-
Sr(OH)2/SrCO3 influence the toxicity of PAH
mixtures which may interact with the PAHs and
their degraded metabolites to form different by-
products during photocatalytic degradation in
petrochemical industry wastewater. These by-
products exhibit synergistic and antagonistic
toxicity effects on Daphnia magna as well. The
effective PAH concentrations in petrochemical
industry wastewater caused 50% mortality in
Daphnia magna cells (EC50 value as mg/l) increased
from initial 342.56 mg/l to EC50=631.05 mg/l, at
pH=7.0 and at 22oC after 360 min sun light
irradiation time resulting in a maximum acute
toxicity removal of 99.99% at 1 mg/l GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite concentration (Table
7; SET 1). The EC50 value increased from initial
342.56 mg/l to EC50=587.45 mg/l at 6 mg/l TiO2
concentration in petrochemical industry wastewater
after 360 min sun light irradiation time, at pH=7.0
and at 22oC resulting in a maximum acute toxicity
removal of 94% (Table 7; SET 3). The EC50 value
increased from initial 342.56 mg/l to EC50=630.45
mg/l at 8 mg/l GO nanoparticle concentration in
petrochemical industry wastewater was measured to
99.94% maximum acute toxicity removal, at
pH=7.0, at 22oC after 360 min sun light irradiation
time, respectively (Table 7; SET 3). In this acute
toxicity reduction, the EC50 value of petrochemical
industry wastewater increased to EC50=631.05 mg/l.
Low acute toxicity removals found at high GO
nanoparticle concentrations in petrochemical
industry wastewater could be attributed to their
detrimental effect on the Daphnia magna cells
(Table 7; SET 1).
A strong significant correlation between EC50
values and PAH removals showed that the Daphnia
magna acute toxicity test alone can be considered aa
a reliable indicator of petrochemical industry
wastewater toxicity (R2=0.87, F=17.99. p=0.001).
International Journal on Applied Physics and Engineering
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Similarly, a strong linear correlation between
threshold concentrations of GO, TiO2, GO-TiO2-
Sr(OH)2/SrCO3 and decrease in inhibitions in
petrochemical industry wastewater was observed
(R2=0.91, F=3.89, p=0.001) while the correlation
between the inhibition decrease and GO, TiO2 and
GO-TiO2-Sr(OH)2/SrCO3 nanocomposite
concentrations above the threshold values was weak
and not significant (R2=0.38, F=3.81, p=0.001). In
this study, the Daphnia magna acute toxicity test
alone can be considered a reliable indicator of
petrochemical industry wastewater toxicity.
4. Conclusions
The results of this study showed that the
hydrophobic PAHs in a real petrochemical industry
wastewater with high benzene rings could be
removed as successfully as the less hydrophobic
PAHs (ACL and CRB) and more hydrophobic
PAHs (BaP and BkF) with photocatalytic
degradation under sun light irradiation process.
The maximum removals of 87%ACL, 87%CRB,
85%BaP and 84%BkF hydrophobic PAHs in
petrochemical industry wastewater were observed at
8 mg/l GO nanoparticle concentration under 100
mW/cm2 sun light intensity, at 100 W photocatalytic
power, at 360 min sun light irradiation time, at
pH=7.0 and at 22oC, respectively. The maximum
89%ACL, 90%CRB, 91%BaP and 92%BkF
hydrophobic PAHs removals in petrochemical
industry wastewater were detected at 9 mg/l TiO2
nanoparticle concentration, under 100 mW/cm2 sun
light intensity, at 100 W photocatalytic power, at
360 min sun light irradiation time, at a pH of 7.0
and at 22oC, respectively. The maximum 97%ACL,
98%CRB, 98%BaP and 99%BkF hydrophobic
PAHs removals in petrochemical industry
wastewater were found at 4 mg/l GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite concentration under
100 mW/cm2 sun light intensity, at 100 W
photocatalytic power, at 360 min sun light
irradiation time, at pH=7.0 and at 22oC,
respectively.
The addition of TiO2 nanoparticle in
petrochemical industry wastewater enhanced the
photodegradation rate by 3 folds (k=0.0016 1/min).
The addition of GO nanoparticle in petrochemical
industry wastewater increased the photodegradation
yield (k=0.0019±0.0001 l/min). The synthesized
GO-Sr(OH)2/SrCO3 in petrochemical industry
wastewater showed a slightly better photocatalytic
activity (k=0.0021±0.0001 1/min) than TiO2 and
GO nanoparticle. As expected, the GO-TiO2-
Sr(OH)2/SrCO3 nanocomposite in petrochemical
industry wastewater exhibited the highest
photocatalytic activity and greatly accelerated the
photocatalytic degradation rate. It was shown a
synergistic interaction among the three
nanocomponents, i.e., GO, TiO2 and
Sr(OH)2/SrCO3, which can facilitate utilization of
both UV and visible light energy in the sun light
irradiation. 1.1 mg/l PMS, 0.9 mg/l PS and 0.79
mg/l Na2S2O3 highest photooxidation yields in
petrochemical industry wastewater was detected.
The effective PAH concentrations in
petrochemical industry wastewater caused 50%
mortality in Daphnia magna cells (EC50 value as
mg/l) increased from initial 342.56 mg/l to
EC50=631.05 mg/l, at pH=7.0 and at 22oC after 360
min sun light irradiation time resulting in a
maximum acute toxicity removal of 99.99% at 1
mg/l GO-TiO2-Sr(OH)2/SrCO3 nanocomposite
concentration.
In sum, GO-TiO2-Sr(OH)2/SrCO3
nanocomposites in petrochemical industry
wastewater holds the potential to serve as a highly
effective and robust photocatalyst for energy-
effective photodegradation of PAHs (and potentially
other persistent organic pollutants) in complex water
matrices, and the multiplicative model is a useful
tool for predicting the photocatalytic performances
under several experimental conditions.
Acknowledgement:
This research study was undertaken in the
Environmental Microbiology Laboratories at Dokuz
Eylül University Engineering Faculty
Environmental Engineering Department, İzmir,
Turkey. The authors would like to thank this body
for providing financial support.
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Contribution of Individual Authors to the
Creation of a Scientific Article (Ghostwriting
Policy)
Post-Dr. Rukiye Öztekin and Prof. Dr. Delia Teresa
Sponza took an active role in every stage of the
preparation of this article.
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
This research study was undertaken in the
Environmental Microbiology Laboratories at Dokuz
Eylül University Engineering Faculty
Environmental Engineering Department, İzmir,
Turkey. The authors would like to thank this body
for providing financial support.
Creative Commons Attribution License 4.0
(Attribution 4.0 International, CC BY 4.0)
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APPENDIX
Table 2: Physical and chemical properties of the PAHs in petrochemical industry wastewater studied in this
work
PAHs
CAS-
No
MF
MW
(g/
mol)
TM
(oC)
TB
(oC)
SW
(25oC)
(mg/l)
VP
(25oC)
(mm
Hg)
H (25oC)
(atm
m3/mol)
log
KOA
(25oC)
log
KOW
SORC
ACL
208-96-
8
C12H8
152
93
280
16.1
6.68E-
03
1.14E-04
6.34
3.94
23.56E
+10
CRB
86-74-8
C12H9N
167
246
355
1.8
7.50E-
07
1.16E-06
8.03
3.72
24.67E
+10
BkF
207-08-
9
C20H12
252
217
480
0.0008
9.70E-
10
5.84E-08
11.37
6.11
0.45E+
8
BaP
50-32-8
C20H12
252
177
495
0.00162
5.49E-
09
4.57E-07
11.56
6.13
0.32
E+8
Acenaphthylene (ACL), Carbazole (CRB), Benzo[k]fluoranthene (BkF), Benzo[a]pyrene (BaP)
MF: Molecular Formula, MW: Molecular weight, TM: Melting point (oC), TB: Boiling point(oC), SW: Solubility
in water (mg/l), VP: Vapor pressure (mm Hg), H: Henry's law constant (atm m3/mol), log KOA: Octanol-air
coefficient, log KOW: Octanol-water coefficient, SORC: second-order reaction rate constants (mg/l.s).
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Figure 1: XRD patterns of GO-Sr(OH)2/SrCO3 and GO-TiO2-Sr(OH)2/SrCO3 nanocomposites in petrochemical
industry wastewater
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(a)
(b)
(c)
(d)
(e)
Figure 2: SEM images of (a) GO-Sr(OH)2/SrCO3, (b) Sr distribution EDX map with GO-Sr(OH)2/SrCO3, (c)
GO-TiO2-Sr(OH)2/SrCO3, (d) Sr distribution EDX map with GO-TiO2-Sr(OH)2/SrCO3 and (e) Ti distribution
EDX map in petrochemical industry wastewater.
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(a)
(b)
Figure 3: FTIR spectra of (a) GO and (b) GO-Sr(OH)2/SrCO3 versus GO-TiO2-Sr(OH)2/SrCO3
nanocomposites in petrochemical industry wastewater.
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(a)
(b)
Figure 4: (a) Nitrogen adsorption-desorption isotherms and (b) pore size distribution of GO, GO-Sr
(OH)2/SrCO3 and GO-TiO2-Sr(OH)2/SrCO3 in petrochemical industry wastewater.
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Table 3: Effect of increasing experimental parameters on photocatalytic degradation of hydrophobic PAHs in a
petrochemical industry wastewater under sun light irradiation process, at 100 mW/cm2 sun light intensity, at
pH=7.0 and at 22oC, respectively (n=3, mean values).
Set
Parameters
Hydrophobic PAHs removals (%)
Less
hydrophobic
More
hydrophobic
ACL
CRB
BaP
BkF
1
GO nanoparticle concentrations (mg/l)
2
54
56
59
58
4
71
73
70
69
8
87
87
85
84
2
TiO2 nanoparticle concentrations (mg/l)
1
59
57
64
75
3
63
66
77
81
6
76
78
83
86
9
89
90
91
92
3
GO-TiO2-Sr(OH)2/SrCO3 nanocomposite
concentrations (mg/l)
1
76
75
80
92
2
89
84
86
97
4
97
98
98
99
4
Sun light irradiation times (min)
30
56
61
60
65
120
65
68
65
66
240
74
76
72
79
360
81
80
84
84
5
Photocatalytic powers (W)
10
56
62
67
69
50
69
70
78
74
100
84
86
88
89
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Figure 5: Photocatalytic degradation of PAHs in petrochemical industry wastewater by various synthesized
catalysts, at 100 mW/cm2 sun light intensity, at 250 ml solution volume, at 1 mg/l initial PAHs concentration, at
50 mg/l catalyst dosage, at 360 min sun light irradiation time, at pH=7.0 and at 22°C, respectively.
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Figure 6: Photocatalytic degradation of PAHs in petrochemical industry wastewater by GOTiO2-
Sr(OH)2/SrCO3 in the various radical scavengers, at 100 mW/cm2 sun light intensity, at 250 ml solution
volume, at 1 mg/l initial PAHs concentration, at 50 mg/l catalyst dosage, at 200 mg/l TBA dosage, at 200 mg/l
NaN3 dosage, at 200 mg/l BQ dosage and at 4000 U/ml CAT dosage, at pH=7.0±0.2, T=22±1°C, respectively.
International Journal on Applied Physics and Engineering
DOI: 10.37394/232030.2022.1.8
Ruki
ye Özteki
n, Deli
a Teresa Sponza
E-ISSN: 2945-0489
82
Volume 1, 2022
Table 7: Effect of sun light irradiation times during photocatalytic degradation process in petrochemical
industry wastewater on the acute toxicity (EC50) removal efficiencies at different operational conditions at
pH=7.0 and at 22oC (n=3, mean values).
Set
s
IAT
Operational conditions
PDA at
22oC
(Control)
GO
TiO2
GO-TiO2-Sr(OH)2/SrCO3
EC50
t=0
AT
Ri
SLI
T a
EC50
AT
R
G
O
b
EC50
t=360
AT
Re
Ti
O2
c
EC50
t=360
AT
Re
GO-TiO2-
Sr(OH)2/Sr
CO3d
EC50
t=360
AT
Re
1
342.
56
98
30
359.
04
2.0
1
2
631.
05
99.9
9
1
484.
67
67
1
590.
56
97.0
0
2
342.
56
98
120
364.
78
6.2
3
4
604.
67
90.0
0
3
545.
56
78
2
626.
56
99.0
0
3
342.
56
98
240
377.
67
8.3
4
8
540.
78
76.9
9
6
587.
45
94
4
630.
45
99.9
4
4
342.
56
98
360
380.
12
10.
01
9
504.
67
70
IAT: Initial acute toxicity; a: sun light irradiation times (min); b: GO concentration (mg/l); c: TiO2 nanoparticle
concentrations (mg/l); d: GO-TiO2-Sr(OH)2/SrCO3 nanocomposite concentration (mg/l); PDA: Photocatalytic
degradation alone without additives (Control); EC50 t=0 : Initial acute toxicity before photocatalytic degradation
(mg/l); ATRi: Initial inhibition percentage before photocatalytic degradation; EC50 : Acute toxicity after
photocatalytic degradation in control versus sun light irradiation time (mg/l); ATR: Acute toxicity removal (%)
in control versus sun light irradiation time; ATRe: Acute toxicity removal (%) after 360 min sun light
irradiation time; EC50 t=360 : acute toxicity after 360 min sun light irradiation time (mg/l).
International Journal on Applied Physics and Engineering
DOI: 10.37394/232030.2022.1.8
Ruki
ye Özteki
n, Deli
a Teresa Sponza
E-ISSN: 2945-0489
83
Volume 1, 2022
