Photocatalytic degradation of bisphenol-A with g-C3N4/MoS2-PANI nanocomposite: Kinetics, main active species, intermediates and pathways

Article abstract of DOI:10.1016/j.molliq.2020.113339

The novel highly porous photocatalyst g-C₃N₄/MoS₂-PANI (polyaniline) is fabricated successfully via an in-situ polymerization and is characterized via UV–vis DRS, FTIR, TGA, SEM, XRD, TEM, XPS and BET. The synergistic effect of MoS₂ and g-C₃N₄ into PANI matrix prompted its outstanding catalytic activities for bisphenol-A (BPA) degradation in liquid solution. The photocatalytic efficiency of the photocatalyst reaches to about 92.66% degradation of BPA that was recorded within 60 min. The scavenger or radical trapping effect supports the role of the photogenerated species and its interaction for the degradation of BPA. The chemical kinetics and possible photocatalytic degradation mechanism were also described and supported theoretical calculation DFT. Moreover, the fabricated nanocomposite exhibits outstanding reusability and shows excellent catalytic activity after six cycles, offering a facile and active process for the treatment of toxic organic pollutants under visible light and that can be used for the environmental remediation.

Full text of DOI:10.1016/j.molliq.2020.113339

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Photocatalytic degradation of bisphenol-A with g-C3N4/
MoS2-PANI nanocomposite: Kinetics, main active species,
intermediates and pathways
Tansir Ahamad, Mu Naushad, Yahya Alzaharani, Saad M.
Alshehri
PII:
S0167-7322(20)30729-7
DOI:
https://doi.org/10.1016/j.molliq.2020.113339
MOLLIQ 113339
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
3 February 2020
4 May 2020
8 May 2020
Please cite this article as: T. Ahamad, M. Naushad, Y. Alzaharani, et al., Photocatalytic
degradation of bisphenol-A with g-C3N4/MoS2-PANI nanocomposite: Kinetics, main
active species, intermediates and pathways, Journal of Molecular Liquids (2020),
https://doi.org/10.1016/j.molliq.2020.113339
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Photocatalytic degradation of bisphenol-A with g-C3N4/MoS2-PANI nanocomposite:
Kinetics, main active species, intermediates and pathways
Tansir Ahamad*, Mu Naushad, Yahya Alzaharani, Saad M. Alshehri
Department of Chemistry, College of Science, King Saud University, Riyadh, Saudi Arabia
Abstract
The novel highly porous photocatalyst g-C3N4/MoS2-PANI (polyaniline) is fabricated
successfully via an in-situ polymerization and are characterized via UV–vis DRS, FTIR, TGA,
SEM, XRD, TEM, XPS and BET. The synergistic effect of MoS2and g-C3N4intoPANI matrix
prompted its outstanding catalytic activities for bisphenol-A (BPA) degradation in liquid
solution. The photocatalytic efficiency of the photocatalyst reaches to about 92.66 % degradation
of BPA that was recorded within 60ꢀmin. The scavenger or radical trapping effect support the
role of the photogenerated specie and its interaction for the degradation of BPA. The chemical
kinetics and possible photocatalytic degradation mechanism were also described and supported
theoretical calculation DFT. Moreover, the fabricated nanocomposite exhibits outstanding
reusability and show excellent catalytic activity after six cycles, offering a facile and active
process for the treatment of toxic organic pollutants under visible light and that can be used for
the environmental remediation.
Keywords: Photocatalyst; FTIR; MoS2; PANI; bisphenol-A
*Corresponding author: T. Ahamad, tahamed@ksu.edu.sa
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1. Introduction
Industrial waste is the main source of water contamination, because several industries used clean
water to remove their waste and their effluent and influent contaminates the water source
including ground water, rivers, lakes and oceans. Nowadays, industrial waste such as dyes, toxic
metals, pharmaceuticals and endocrine-disrupting compounds (EDCs)in water and wastewater have
been becoming a globally concerning issue[1-3]. Bisphenol-A is an EDCs wieldy used as raw
materials in several industries for the manufacturing of epoxy resins, polycarbonates, containers
for foods and water bottles[4, 5]. BPA and its derivatives were release into the environment not
only by discharging from industry, but also from migration, usage and disposal methods. World
Health organization declare a low dose of BPA to human may suppress a gene vital to nerve cell
and cause hypertension and cell disorders[6-8]. Therefore, the removal of BPA from waste water
is of highly consequence. Several procedures has been employed for the treatment of BPA from
contaminated water, including ozonation, membrane filtration, reverse osmosis, chemical
coagulation, chlorination, adsorption chemical oxidation, electrochemical oxidation, biological
methods, and photocatalytic degradation[9-12]. Among these methods, photocatalytic
degradation has benefits of simple, environmental friendly and fast technique to remove the toxic
pollutants from contaminated water[13-16]. During the photocatalytic degradation the electrons
were move from the valence band to the conduction band under after irradiation of lights and
resulting generated species such the holes (h+), electrons, free radicals and other spices degardate
the organic pollutants into non-toxicCO2 and H2O [17-20]. Previously several semiconductor-
based photocatalyst have been used including metal oxide, metal sulfide, organic and inorganic
semiconductors and hybrid materials. Among these, metal sulfide, molybdenum sulfide (MoS2),
is afamous2D and n-type semiconductor (1.6-1.80ꢀeV), that have outstanding photocatalytic
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activates under visible light. However, the main disadvantages of MoS2 based photocatalyst is its
extraordinary rate of electron-hole recombination, the recombination of the electrons and hole
reduce its catalytic efficiency [21-23]. Therefore, MoS2 catalyst need the modified to stop or
decreased the recombination of the elections and hole. In this way, organic semiconductor with
high surface area with superior chemical stability, graphitic carbon nitride (g-C3N4) that have a
band gap 2.79 eV, can be used as excellent photocatalyst or catalyst support with MoS2 [24-26].
For example, Lan et al. modified g- C3N4 with MoS2 and the results revealed that the separation
efficiency of photogenerated charge carriers were obviously improved [23]. Thus, the MoS2/g-
C3N4 nanocomposites exhibited superior performance through the degradation of organic
pollutants than pure g-C3N4. Even though the conjugation between MoS2 and g-C3N4 show
superior photocatalytic activities then individuals but also suffer from some limits such as
difficulty of separation and recovery and high aggregation tendency [27-29]. To overcome these
problem, many researchers reported the used of sporting agents such as activated carbon,
conjugated polymer, graphene and CNTs. Specially conjugated polymers, PANI is a p-type
material with extraordinary h+ transporting capability, along with fast charge separation
tendency, slow charge recombination rate in electron transfer processes and excellent stability
[30-32]. Moreover, the presence of quinone and benzene groups with delocalized π-conjugated
structures and electrochemically active sites in the PANI structure makes it a good candidate for
coupling with other semiconductors [33, 34]. It has been reported that it is widely used in
combination with nanocomposite to improve properties, such as PANI/MOS2 [35],
PANI/graphene/MoS2 [36] and MoS2-PANI-CdS [37]. In addition, PANI as a hole transfer
material can rapidly transfer holes of MOS2 the surface of the catalyst, resulting in an improved
photocatalytic performance and stability. In the present study, we have fabricated the novel
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photocatalyst MoS2/g-C3N4/PANI via in-situ polymerization and used for the photocatalytic
degradation of BPA under visible light. The effect of pH, initial concentration and effect of
scavengers and the kinetics was also studied to know the mechanism of photocatalytic
degradation for BPA. The formation of the photogenerated spices and intermediates during the
photocatalytic degradation were determined using ESR and GC-Mass respectively and supported
via theoretical calculation, DFT.
2. Experimental
2.1. Materials
Chemicals used for experiments are sodium molybdate (Na2MoO4 99.99%), melamine (99%),
aniline (99%), thiourea, C10H14N2Na2O8 (EDTA-2Na), C3H8O (IPA), C6H4O2 (BQ), 5,5-
Dimethyl-1-pyrroline N-oxide (DMPO, C6H11NO), bishphenol-A. All the chemicals are of
analytical grade purchased from Merck and Aldrich.
2.2.Synthesis
2.2.1. Preparation of MoS2/g-C3N4
To prepared pure g-C3N4,10ꢀg of melamine powder was heated at 550ꢀ°C for 3ꢀh under the follow
of air, the resulting light yellow product was grinder and sonicated for 30 min to get the g-C3N4
sheets, then flittered, washed off and dried. In the next step, g-C3N4 powder (5.0 g), Na2MoO4.
2H2O (2.4 gm), and thiourea (3.0 g) were added to a beaker and dispersed using prob sonicator
for 1h, and then were transferred into a Teflon-lined stainless steel autoclave. The sealed
autoclave was heated at 200ꢀ°C for 24ꢀh to get the nanocomposite. After natural cooling, the
product was centrifuged and washed off three times with ethanol and deionized water to get g-
C3N4/MoS2.
2.2.2 Preparation of the photocatalyst
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To fabricate the photocatalyst, 2.0g g-C3N4/MoS2was dispersed in 50 mL CH3COOH (1 M) and
then aniline (2.4 mL) was added to this mixture dropwise drop with continuous starring, the
reaction system was cooled using ice bath. To this solution of ammonium persulphate (5.84 g,
0.46 M) was added drop wise drop. All the reaction was carried out in 200 ml sealed flask under
the flow of N2 and irradiated with ultrasonic wave using for 2 h, at room temperature. Finally,
the mixture was poured and the product was washed and dried to get the photocatalyst g-
-
C3N4/MoS2 PANI. The fabricated photocatalyst was characterized and used as photocatalyst for
the degradation of BPA the details of characterization and photocatalytic assay is provided in
supporting information.
3. Results and discussion
The nanocomposite was fabricated using MoS2 and g-C3N4 and PANI as shown in figure-1. The
FTIR spectra of g-C3N4,g-C3N4/MoS2 and g-C3N4/MoS2-PANI are shown in figure 2(a), the
spectra of pure g-C3N4exhibitsthe show peaks at 3150-3240, 1642, 1550, 1462, 1404, 1320, and
1230 cm-1 corresponding to the NH2, C=N, C=C, C-N, C-C, C-O respectively. Another peaks at
813 cm-1 assigned to the triazine unit in its bending mode[38, 39]. The FTIR spectrum of
MoS2/g-C3N4 show similar FTIR peaks as found in the case of pure g-C3N4, and support their
analogous frameworks. However, the main peak at about 495ꢀcm−1from Mo-S vibrations of g-
C3N4/MoS2 was observed. The FTIR spectra of the MoS2/g-C3N4/PANI show the FTIR peaks at
1580, 1502, 1300, 1175, and 862ꢀcm-1were appeared due to C=C stretching of quinonoid and
benzeniod rings, C–N stretching vibration, C–H in of PANI molecules[40, 41]. The
thermogravimetric analysis of the g-C3N4, MoS2/g-C3N4 and MoS2/g-C3N4/PANI was carried out
under the flow of air and the results support that the presence of conjugated polymer matrix
PANI in the nanocomposite. Initial the weight loss was due to the presence of humidity and
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o
adsorbed solvent. While in the case of the main degradation was occurs after 600 C and no
o
residue was found at 800 C. The nanocomposite g-C3N4/MoS2 the show the higher thermal
stability then the that of the g-C3N4 and the residue weight was found to be 76.21 %. While in the
case of the photocatalyst the residue was found to be 44.53 % that support the presence of MoS2.
The XRD spectrum of the g-C3N4, MoS2/g-C3N4and MoS2/g-C3N4/PANI are represented in
figure 3(a). The XRD pattern for g-C3N4, show only two peaks at 2θ of 27.4° and 14.8° due to
the (002) and (100) planes of g-C3N4 (JCPDS No. 87-1526). While, in the case of g-C3N4/MoS2,
some additional peaks at 28.2, 32.72, 39.5, 49.43 and 58.7 belongs to (002), (100), (103), (105)
and (110) MoS2 planes were found. However, the peak belong to the pure g-C3N4 at27.4 was
shifted to 27.8 in the case of g-C3N4/MoS2 support the interfacial contact between theg-C3N4 and
MoS2[42-44]. Furthermore, in the case of the photocatalyst, the peak intensity become lower
than that of g-C3N4/MoS2, which is support the presence of PANI and the crystalline and original
structure of MoS2 and g-C3N4 into the PANI matrix[45, 46]. The Raman spectra of the
photocatalyst is illustrated in figure 3(b), the results revealed that the presence of g-C3N4 was
supported by the appearance of two peaks at 1326 and 1588 cm-1 and ID/ IG was found to be 0.94.
while the presence of MoS2 in the nanocomposites was supported by the presence of Raman
peaks at 408 and 452 cm-1 belongs to A1g and A2u respectively.
Figure 4(a) and 4(b), showed the SEM image of g-C3N4/MoS2 and g-C3N4/MoS2-PANI. As
shown in 4(a), the g-C3N4/MoS2shownagglomerated and the flaky structure. It was observed that
both the MoS2and g-C3N4 tightly linked to each other. The SEM image of the g-C3N4/MoS2 -
PANI revealed that g-C3N4/MoS2are uniformly dispersed into the PANI matrix and surface when
compared with the SEM and TEM image of pure g-C3N4 and g-C3N4/MoS2 as in supporting
figure SF-1. Because of the dispersibility of g-C3N4/MoS2, it is not easy to agglomerate together,
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which confirms the essential sites for electron and whole transport and increases its charge
transfer. The TEM image of the g-C3N4/MoS2-PANI display that the g-C3N4 and MoS2and PANI
are obviously exposes close interaction between g-C3N4/MoS2 as shown in figure 4(c). The close
interaction between the components support the conductivity and the electron transfer during the
photocatalytic degradation of the BPA. In figure 4(d), the HRTEM image of the nanocomposite
show that g-C3N4/MoS2 nanostructure are placed and tightly embedded into the conducting PANI
matrix. The lattice spacing of 0.62 nm and 0.07 supports the (002) and (100) planes of MoS2
respectively[47, 48].The composition and the oxidation states of ions ing-C3N4/MoS2-PANI was
observed by the XPS spectra. Figure 5(a), shows wide scan of g-C3N4/MoS2-PANI and support
the presence of C, N, Mo, O and S elements. The deconvoluted C1s pack consists four main
peaks at 284.23ꢀeV, 285.46ꢀeV, 286.08ꢀeV and 287.47ꢀeV corresponding to C-C/C=C, C-N/C-O,
-C=O, and -C=N groups respectively as illustrated in figure 5(b)[49, 50]. figure 5(c) show the N
1s XPS spectrum which was splits into four peaks at 398.84ꢀeV, 399.01ꢀeV, 400.76ꢀeV and
+
401.56ꢀeV, which are associated with -N=, -NH-, -+NH= and -NH2 configurations, respectively
[51]. Figure 4(d) show the high-resolution XPS spectra of Mo3dand deconvoluted in to four
peaks at 228.40 and 232.24ꢀeV corresponding to Mo4+ 3d5/2, Mo4+3d3/2, Mo4+ 3d5/2, and Mo4+
3d3/2 respectively. The core level spectrum of S 2p was mainly split two peaks at 161.40 and
162.9ꢀeV assigned to the S2p3/2 and S2p1/2 respectively, another less intense peak 166.21 eV is
corresponding to at the S2− ions in photocatalyst [52, 53]. These results also confirm the
existence of MoS2and g-C3N4 into the PANI matrix. The N2adsorption/desorption isotherms of
the nanocomposites were illustrated figure 6(a), both the nanocomposites exhibited type IV
adsorption isotherms related to the mesoporous structures. The values of BET surface area of g-
C3N4/MoS2 andg-C3N4/MoS2-PANI composites are 247.60ꢀm2/g and 184.21ꢀm2/g respectively.
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The BJH plot is shown in supporting figure SF-2. High surface area of g-C3N4/MoS2-PANI
affords more active positions for BPA molecules, and increased the photocatalytic efficiency of
the fabricated g-C3N4/MoS2-PANI. The UV-vis DSR spectra of as fabricated g-C3N4, MoS2/g-
C3N4 and g-C3N4/MoS2-PANI are illustrated in figure 6(b). The fabricated nanostructures g-
C3N4 show the adsorption in the region of 466 nm and matched with the band gap 2.21 eV.
While after interaction with MoS2, in the case of the g-C3N4/MoS2, another adsorption peaks
between 565 to 650 nm occurs which support the photocatalytic activates in visible light. The of
g-C3N4/MoS2-PANIexhibit the UV-visible peak with les intensity between 285-330 nm and 640
nm assigned to the PANI with MoS2. The band gap of the photocatalyst was calculated using
Tauc plots as shown in supporting figure SF-3, and found to be about 2.67 eV in the case of
photocatalyst.
3.1.Photocatalytic degradation of BPA
The photocatalytic degradation of the BPA was first carried out in dark to get the equilibrium
between the catalyst and BPA adsorption. As displayed in figure 7(a), it was observed that no
degradation of BPA was found under the irradiation of visible light without catalyst due to the
stability of BPA in visible light. On the other hand, in the presence of catalyst g-C3N4/MoS2 and
g-C3N4/MoS2-PANI about to 69.8 and 92.66%, degradation was achieved respectively, after
60ꢀmin visible-light irradiation at room temperature in neutral solution (pH 7). These results
indicate that the PANI in MoS2/g-C3N4/PANI, can improve the catalytic activity compared with
MoS2/g-C3N4 due to increasing the conductivity and charge carrier properties and exhibit
excellent catalytic activities for BPA photocatalytic degradation under visible light. In order to
investigate the effect of initial concentration of BPA, the experiments were carried out and
MoS2/g-C3N4/PANI show 92.66 %, 88.59 %, 85.76 %, 82.79 % and 78.68 % degradation of
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BPA with 20, 30, 40, 50 and 60ꢀmg/L initial concentration respectively as shown in figure 7(c).
These outcomes exposed that the catalytic efficiency of the catalyst was decreased with
increasing the initial concentration of BPA, because of the shading effect for light resulting the
degradation was decreased radically[17, 54]. Figure 7(b and d) shows the BPA degradation
kinetics using as-fabricated photocatalysts and with exposure of BPA concentration. The
degradation rate constants were calculated using flowing equation:
(1)
Where, t and k are the reaction time(min) and rate constant (min−1) respectively. The calculated
kinetic rates (k) for degradation of BPA with g-C3N4/MoS2 and g-C3N4/MoS2-PANI were found
to be 0.0266 and 0.0395ꢀmin−1, respectively. As the initial concentration of BPA was increased
the rate constant was decreased and found to be 0.0395, 0.0337, 0.0300, 0.0272 and 0.0241min−1
with 20,30,40,50 and 60ꢀmg/L concentration respectively and support the degradation was
follows pseudo-first-order kinetics with respect to the BPA concentration using g-C3N4/MoS2-
PANI catalyst at room temperature.
-
It was noticed that the contaminated water contains various inorganic ions such as NO3 , Cl-,
2-
-
SO4 , and HCO3 , these co existing ions, affect the catalytic efficiency of the photocatalysts. As
-
2-
shown in supporting figure SF-4, it was observed that in the presence of NO3 and SO4 ions no
obvious change in the photocatalytic degradation curves were occurs. While in the case of Cl-
ion the catalytic efficiency was decreased, this may be due to reducing of light adsorption and
-
contamination of the catalyst. In the case of the HCO3 , a significant change in the catalytic
activities were observed and only 92.66%, BPA degradation was achieved after 60 min. The
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-
HCO3 can behave as scavenger and reduced the formation of photogenerated species resulting
reduce the catalytic activities.
Based on the physiochemical structure of the photocatalyst g-C3N4/MoS2-PANIand
photocatalytic experimental results, to explain the degradation a Z-scheme mechanism was
proposed and is schematically illustrated in Figure 9. In the case of g-C3N4/MoS2-PANI, the
conducting polymer PANI avoid the recombination of the electrons and hole Moreover, the
photogenerated spices including the holes, electrons and radicals moved to the catalysts surface
easily due to the conducting nature of PANI.
The migration, transfer and recombination processes of photogenerated electron–hole pairs and
the electrical conductivity of photocatalysts were determine using photoluminescence (PL)
spectrum, electrochemical impedance spectroscopy (EIS) and with the photocurrent density
curve. As shown in figure SF-5(a), the PL spectrum of the nanocomposites are illustrated and the
results revealed that the intensity of the g-C3N4 was decreased after combination with MoS2 in g-
C3N4/MoS2. Which was further decreased in the case of g-C3N4/MoS2-PANI. This may be due to
decreasing of the transporting length of photoexcited carriers, suggesting that the recombination
of carriers in g-C3N4/MoS2-PANI are effectively suppressed. The electrical conductivity of the
photocatalyst were determine using ESI spectra as shown in Figure SF-5(b). It was notices that
g-C3N4/MoS2-PANI shows the smaller semicircle radius of the Nyquist plots indicate the lower
charge transfer resistance and a higher charge transfer efficiency compared to g-C3N4and g-
C3N4/MoS2. To investigate the separation of photogenerated electron–hole pairs more deeply
photocurrent responses were recorded. Supporting Figure SF- 5c, indicate that the photocurrent
density curve of the as-samples via several on and off cycles under intermittent light irradiation.
As fabricated nanocomposite, g-C3N4/MoS2-PANI shows extraordinarily growing produced
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photocurrent density compared to the pure g-C3N4 and g-C3N4/MoS2 due to the optimum
photogenerated charge separation efficiency.
3.2 Detection of photogenerated species
To determine the photogenerated species involved during the photocatalytic degradation of BPA
using as-fabricated catalyst MoS2/g-C3N4/PANI the scavengers, radical trapping experiment was
carried out. As shown in figure 8(b), the radical trapping experiment results revealed that, the
●
main active species for BPA photodegradation process over g-C3N4/MoS2-PANIare OH and
−
•O2 . Because the catalytic activities of decreased from 92.66 % to 36.35%, 43.21 %, 67.16 %
and 73.41 % in the presence of IPA (1 mM), BQ (1 mM), EDTA-2Na (1 mM), and K2Cr2O7 (1
mM) [55-57], and their kinetic plots are illustrated in supporting figure SF-6. Moreover, to
confirm the presence of these photogenerated species during the degradation of BPA, the EPR
test with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) technique was carried out under the dark
and visible light irradiation after 5ꢀand 10 minutes and illustrated in figure 8(c and d). it was
−
found that no EPR peaks noticed under the dark condition for both DMPO-●O2 and DMPO-
●OH. While, under the visible light irradiation, four characteristic ESR signal for DMPO-●OH,
-
and DMPO-●O2 were observed. As the irritation time was increased from 5 to 10 min the
−
intensity of the ESR peaks increased gradually. The results indicate that the ●O2 and ●OH are
formed into BPA aqueous solution using g-C3N4/MoS2-PANI.
3.3 Regeneration
The stability and the reusability test of the C3N4/MoS2-PANI catalyst was carried out for six
cycles to degrade of BPA under similar condition. The reusability results revealed that as-
fabricated catalyst show excellent reusability and no noticeable degradation efficiency was
decreased during the first four cycles (the efficiency of the catalyst was 98.7 % at cycle 4),
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however the degradation efficiency of the catalyst was observed about to 98.2% and 97.8 %,
respectively as shown in figure 8(a). these results support that the fabricated nanocomposites can
be used as an excellent reusable catalyst for the catalytic degradation of BPA in aqueous
solution.
3.4 Degradation mechanism and DFT calculation
To understand the photocatalytic degradation mechanism of BPA using g-C3N4/MoS2-PANI, the
intermediates were determine using LC-MS analysis and the frontier electron density was used to
determine the point charge of over the BPA molecules the proposed mechanism for the catalytic
degradation of BPA is illustrated in figure 9[58, 59]. According to frontier orbital theory, the
atoms with high fe = 2FED2HOMO values or large negative charges were attacked by electrophilic
such h+, while the atoms with high fn= 2FED2LUMOor large positively charges were attack by
●
−
nucleophilic such as O2 reaction, while with higher fr= FED2HOMOꢀ+ꢀFED2LUMO values are
favorably attacked by ●OH. As shown in supporting table-1, it was observed that HOMO behave
as electron rich while the LUMO as an electron deficient molecular orbitals as shown in
supporting figure SF-3. It was observed that the aromatic ring C bond (C1, C14) was closely
enclosed by the iso-surface of Fukui index, which was proposed to be most weak for radical
attack due to higher value of fr(0.186).In first step, ●OH were attack to the aromatic ring of BPA to
give intermediate (i) and then (ii). The formation of hydroxylated derivatives by the reaction
of hydroxyl radicals with aromatic rings is well-known and supported via MS spectra due to the
appearance the MS peaks at m/z at 244 and 257.On the other hand, the atoms with relative higher
frin the case of intermediate (i), including C1, C2, N13 and C14, are more vulnerable to radical
attack, resulting the dicarboxylic acid intermediate (iii) is observed with m/z 260 and further
degraded into di-carbonyl compound (vii) with m/z value 217. When the ●OH free radical attack
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on the non-aromatic carbon with intermediate (i), two possible intermediate with m/z value 110
for pyrocatechol(iv) and 134 for 4-(prop-1-en-2-yl) phenol(v) which was further converted into
4-(2-hydroxypropan-2-yl)phenol (vi) and detected via m/z 151. The intermediated (iii) was
●
attacked with OH free radical and produced hydroquinone which was is oxidized in to
benzoquinone and supported via m/z peaks at110 and 108 respectively. As the reaction went on,
small carboxyl groups such as pyruvic acid, oxalic acid and fumaric acid etc, and aliphatic
compounds are gradually formed, which slowly and progressively mineralized into CO2and H2O
after sufficient reaction time[60-62].
4. Conclusion
In summary, a high-performance photocatalyst C3N4/MoS2-PANI was fabricated successfully
and used for the degradation of BPA. g-C3N4/MoS2-PANI sample was demonstrated 1.5 times
higher photocatalytic degradation rates than the g-C3N4/MoS2sample towards the
photodegradation of BPA. The improved photodegradation activity of MoS2/g-C3N4/PANI might
be due to the conducting behavior of PANI as well as good structural morphology and surface
state. Moreover, the photogenerated spices holes and electrons were transfer to nanocomposites
surface because of the conductivity of PANI matrix. The trapping study suggested that ●OH and
-
●O2 played the key role in degradation of BPA over g-C3N4/MoS2-PANIcatalyst. The reusability
results indicated excellent stability of the catalyst after 6 cycles. This work proposed promising
method to develop a photocatalyst with high efficiency and excellent re-usability for the
degradation of BPA and other organic pollutants in industrial waste water.
5. Acknowledgement
The authors extend their sincere appreciation to the Deanship of Scientific Research at King
Saud University for funding this Research Group (RG-1438-026).
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6. References
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Conflict of interests
☐ The authors declare that they have no conflict of interest or personal relationships that could have
appeared to influence the work reported in this paper.
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550 oC
Air
g-CN4
3
g-CN4
3
Melamine
200 oC, 24 h
H
N
H
N
N
N
N
n
m
NH2
H
N
H
N
N
(NH4)2SO
2
8
n
m
g-CN4/MoS
3
2
H
H
MoS
2
N
N
N
N
n
m
g-CN4/MoS-PANI
3
2
Figure 1: Schematic pathway for the fabrication of the photocatalyst
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(a)
(b)
100
80
60
40
20
0
C N / MoS -PANI
3 4
2
2
C N / MoS
3 4
C N
3 4
C N
3 4
C N / MoS
3 4
2
C N / MoS -PANI
3 4
2
0
200
400
600
800
4000 3500 3000 2500 2000 1500 1000 500
Temperature (oC)
Wavenumber (cm-1)
Figure 2: (a) FTIR spectra (b) TGA curves of the C3N4, C3N4/MoS2 and C3N4/MoS2-PANI
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C N /MoS -PANI
(a)
(b)
3
4
2
2
C N /MoS
3
4
4
C N
3
ID/IG=0.94
10
20
30
40
2θ (deg.)
50
60
70
80
300
600
900 1200 1500 1800
Raman Shift (cm-1)
Figure 3: (a) XRD of C3N4, C3N4/MoS2 and C3N4/MoS2-PANI
(b) Raman spectra for C3N4/MoS2-PANI
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(b)
(a)
(d)
(c)
g-C N4
3
Figure 4: (a) SEM image of C3N4/MoS2 and C3N4/MoS2-PANI (b) SEM image of C3N4/MoS2-
PANI (c) TEM image of C3N4/MoS2-PANI (c) HRTEM image of C3N4/MoS2-PANI
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(b)
(c)
(a)
C 1s
N 1s
N 1s
C 1s
g-C3N4
O1s
g-C3N4/MoS2
g-C3N4/MoS2-PANI
Mo 3d
S 2p
292
290
288
286
284
282
404
402
400
398
396
1200 1000 800 600 400 200
0
Binding Energy (eV)
Binding Energy (eV)
Binding Energy (eV)
Mo3d
Mo4+3d5/ 2
S2p
O1s
(f)
(d)
(e)
S2p3/ 2
Mo4+3d3/ 2
Mo6+3d5/ 2
Mo6+3d3/ 2
S2p1/ 2
S 2-
2
538
536
534
532
530
528
526
240 238 236 234 232 230 228 226
175
170
165
160
Binding Energy (eV)
Binding Energy (eV)
Binding Energy (eV)
Figure 5: (a) XPS spectra of C3N4, C3N4/MoS2 and C3N4/MoS2-PANI (b) C1s (c) N1s (d) Mo3d
(e) S 2p and (f) O1s of C3N4/MoS2-PANI
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300
250
200
150
100
50
(a)
(b)
N2 adsorption for g-C3N4/MoS2
N2 desorption for g-C3N4/MoS2
N2 adsorption for g-C3N4
g-C3N4/MoS2-PANI
g-C3N4/MoS2
g-C3N4
N2 desorption for g-C3N4
N2 adsorption for g-C3N4/MoS2-PANI
N2 desorption for g-C3N4/MoS2-PANI
200 300 400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/Po)
Wavelength (nm)
Figure 6: N2 adsorption-desorption isotherm and (b) DSR-UV –visible spectra of C3N4,
C3N4/MoS2 and C3N4/MoS2-PANI
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3.0
100
80
60
40
20
0
(a)
(b)
Linear fitting for dark
Linear fitting for g-C N
2.5
2.0
1.5
1.0
0.5
0.0
3
4
Linear fitting for g-C N /MoS
3
4
Linear fitting for g-C N /MoS -PANI
3
4
2
without catalyst
C3N4
C3N4/MoS2
C3N4/MoS2-PANI
-20
0
20
40
60
0
10
20
30
40
50
60
Time (min)
Time (min)
100
80
60
40
20
0
(c)
(d)
2.5
2.0
1.5
1.0
0.5
0.0
Linear fitting for 20 mg/L
Linear fitting for 30 mg/L
Linear fitting for 40 mg/L
Linear fitting for 50 mg/L
Linear fitting for 60 mg/L
20 mg/L
30 mg/L
40 mg/L
50 mg/L
60 mg/L
-20
0
20
40
60
0
10
20
30
40
50
60
Time (min)
Time (min)
Figure 7. (a) Photocatalytic degradation BPA curves using several catalysts; (b) kinetic curves of
BPA degradation; (c) Effect of BPA concentration during the photocatalytic degradation (d)
kinetic curves of BPA degradation at different concentration
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-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
e- e- e- e-
1.40 (eV)
-0.07 (eV)
e- e- e-
h+ h+ h+ h+
1.40 (eV)
2.09 (eV)
h+ h+ h+
g-CN
3 4
H2O+CO2
MoS
2
H2O
PANI
●HO
Figure 8: Proposed catalytic for the degradation of BPA using C3N4/MoS2-PANI
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●
(a)
(b)
DMPO- OH
100
80
60
40
20
0
10min. in light
5 min.in light
Indark
IPA
BQ
EDTA-2Na
K2Cr2O7
No scavenger
3460
3480
3500
3520
3540
3560
-20
0
20
40
60
Time (min)
Magnetic Field (Gauss)
105
●
−
(c)
DMPO- O2
(d)
10min. in light
100
95
90
85
80
75
70
5 min.in light
Indark
3460
3480
3500
3520
3540
3560
1
2
3
4
5
6
Magnetic Field (Gauss)
Cycles
Figure 7. (a) Effect of scavenges (b) ESR spectra of DMPO-∙OH in dark and light (c) ESR
-
spectra of DMPO-∙O2 in dark and light (d): Reusability of the catalyst C3N4/MoS2-PANI after 6
cycles
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10
15
9
6
1
8
14
13
7
5
4
OH
11
2
17HO
OH 16
3
12
OH
pyrocatechol
m/z =110
OH
OH
H
HO
HO
OH
HO
Open Ring Stracture
H
H
H
4-(prop-1-en-2-yl)phenol
OH
HO
O
OH
OH
OH
m/z =134
OH
OH
HO
m/z = 243
OH
O
HO
OH
OH
OH
HO
O
H O
4-(2-hydroxypropan-2-yl)phenol
m/z =151
OH
OH
O
H O
OH
OH
OH
OH
OH
HO
HO
HO
OH
OH
OH2
HO
OH
OH
HO
m/z = 257
4-(2-hydroxypropan-2-yl)benzene-1,2-diol
OH
OH
O
O
m/z =168
O
O
OH
OH
OH
H
OH
OH
m/z = 260
OH
O
m/z = 217
OH
OH
CO2 + H2O
HO
OH
O
O
hydroquinone
m/z =110
m/z =108
OH
Figure 10: Degradation mechanism and intermediates during the degradation of BPA using
C3N4/MoS2-PANI
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Highlights
 MoS2/g-C3N4-PANI was fabricated successfully
 MoS2/g-C3N4-PANI shows enhanced photocatalytic activity for BPA degradation
 The photocatalytic rate of BPA was found to be 92.66% after 60 min
 Photocatalytic degradation mechanism and intermediates of BPA was identified
 The hybrid catalyst is found to be stable for repeated cycles of experiment
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