Silicon-grafted Ag/AgX/rGO nanomaterials (X = Cl or Br) as dip-photocatalysts for highly efficient p-nitrophenol reduction and paracetamol production

Article abstract of DOI:10.1002/aoc.4757

In this work, plasmonic Ag/AgX/rGO (X?=?Cl or Br) nano-photocatalysts were grafted with silicon by adding trimethylsilyl chloride as silicon precursor. The synthesized Ag/AgX/rGO-Si hybrids showed a large improvement of photocatalytic activity towards the synthesis of p-aminophenol (PAP) as well as paracetamol (acetaminophen; APAP) through the photoreduction of p-nitrophenol (PNP). The prepared catalysts Ag/AgX/rGO were characterized using SEM, XRD, FTIR and the reduction reaction of p-nitrophenol was monitored by UV–Vis measurements, GC/MS and ¹HNMR data. From the results, it was demonstrated that the rate order of reduction process of the PNP to PAP and to APAP under visible light irradiation of the samples was as follows; Ag/AgBr/rGO-Si?>?Ag/AgCl/rGO-Si?>?Ag/AgBr/rGO?>?Ag/AgCl/rGO. The reaction mechanism had been postulated that was supported with the spectroscopic data. In addition, the catalysts were recovered from the reaction medium and re-used in three cycles that indicated the reusability and stability of the catalysts. This study was featured by the following; i) fast reaction, ii) the reduction of p-nitrophenol to paracetamol was performed in a facile one-pot reaction compared to previous approaches that tends to reduce the production cost, and iii) investigations on the catalytic properties of Ag/AgX/rGO in organic transformations open the door to find a benefice of these catalysts in other organic reactions and in the development in the synthesis of pharmaceutical products.

Full text of DOI:10.1002/aoc.4757

Received: 27 June 2018
DOI: 10.1002/aoc.4757
Revised: 7 September 2018
Accepted: 17 November 2018
F U L L P A P E R
Silicon‐grafted Ag/AgX/rGO nanomaterials (X = Cl or Br) as
dip‐photocatalysts for highly efficient p‐nitrophenol
reduction and paracetamol production
Yasser A. Attia1
| Yasser M.A. Mohamed2
1 National Institute of Laser Enhanced
Sciences, Cairo University, 12613, Egypt
2 Photochemistry Department, National
Research Center, Dokki, Giza 12622,
Egypt
In this work, plasmonic Ag/AgX/rGO (X = Cl or Br) nano‐photocatalysts were
grafted with silicon by adding trimethylsilyl chloride as silicon precursor. The
synthesized Ag/AgX/rGO‐Si hybrids showed a large improvement of photocat-
alytic activity towards the synthesis of p‐aminophenol (PAP) as well as paracet-
amol (acetaminophen; APAP) through the photoreduction of p‐nitrophenol
(PNP). The prepared catalysts Ag/AgX/rGO were characterized using SEM,
XRD, FTIR and the reduction reaction of p‐nitrophenol was monitored by
Correspondence
Yasser A. Attia, National Institute of Laser
Enhanced Sciences, Cairo University,
12613, Egypt.
1
Email: yasserniles@niles.edu.eg
UV–Vis measurements, GC/MS and HNMR data. From the results, it was
Y. M. A. Mohamed, Photochemistry
Department, National Research Center,
Dokki, Giza, 12622, Egypt.
demonstrated that the rate order of reduction process of the PNP to PAP and
to APAP under visible light irradiation of the samples was as follows;
Ag/AgBr/rGO‐Si > Ag/AgCl/rGO‐Si > Ag/AgBr/rGO > Ag/AgCl/rGO. The
reaction mechanism had been postulated that was supported with the spectro-
scopic data. In addition, the catalysts were recovered from the reaction
medium and re‐used in three cycles that indicated the reusability and stability
of the catalysts. This study was featured by the following; i) fast reaction, ii) the
reduction of p‐nitrophenol to paracetamol was performed in a facile one‐pot
reaction compared to previous approaches that tends to reduce the production
cost, and iii) investigations on the catalytic properties of Ag/AgX/rGO in
organic transformations open the door to find a benefice of these catalysts in
other organic reactions and in the development in the synthesis of pharmaceu-
tical products.
Email: y.m.a.mohamed@outlook.com
KEYWORDS
Ag/AgX nanocomposites, P‐aminophenol, paracetamol, photocatalysis, reduced graphene oxide
1 | INTRODUCTION
such as solar light, and the possibility to avoid hazardous
reagents, unsafe solvents and high temperatures and
Paracetamol is one of the oldest over‐the‐counter (OTC)
active pharmaceutical ingredient that produced in huge
quantities per year. Therefore, a sustainable synthetic
route for the production of paracetamol in high purity is
demanded. Among of recent synthetic approaches is the
photocatalysis.[1] The sustainability of photocatalysis
mainly comes from the exploitation of renewable sources,
pressures.[2,3] The commercially available photocatalysts
can utilize only UV light energy, and at relatively low
quantum yield. Hence, it is highly desirable to find novel
photocatalysts that are simple to produce, inexpensive,
and also able to utilize the visible spectrum of solar
radiation. The photo‐nanocatalysis plays dual role as
heterogeneous as well homogeneous catalysis and have
Appl Organometal Chem. 2018;e4757.
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© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4757

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ATTIA AND MOHAMED
beneficial physical and chemical properties. Metal nano-
particles are known to be promising material for the
increase in the field rising heterogeneous catalysis in a
variety of organic transformations.[4,5] From these
observations, we aimed to present in our study an easily
prepared Ag/AgX/r‐GO (X = Cl or Br) nanocatalysts with
cost effective and absorb at visible light effectively.[6–14]
In recent years, Ag/AgX (X = Cl, Br, I) nanoparticles have
been extensively examined as active catalysts for degrada-
tion of dyes.[15–24] Zhu et al. reported that Ag/AgBr/GO
hybridized nanocomposite could be facilely synthesized
by means of a surfactant‐assisted assembly protocol,[16]
where an oil/water microemulsion is used as the
synthesis medium. To date, these catalysts have not been
tested in the synthetic organic chemistry for the synthesis
of fine chemicals. As a part of our ongoing program
on the use of heterogeneous photocatalysts in organic
synthetic paths,[1] herein we demonstrated in this work
that silicon‐grafted with Ag/AgX/rGO nanocomposites
displayed distinctly enhanced photocatalytic activity
for the highly efficient synthesis of p‐aminophenol and
paracetamol.
(k = 1.54186 A°). The XRD patterns were recorded from
20° to 70° 2θ with a step size of 0.020° 2θ and collecting
10s per step. FT‐IR spectra were recorded with a Nicolet
6700 infrared spectrophotometer to determine the specific
functional groups present on the surface. 1H NMR spectra
were determined on Bruker Avance DPX spectrometer at
300 MHz. and they were recorded with trimethylsilane as
internal standard in DMSO‐d6. Chemical shifts (δ) are
given in ppm. GC/MS spectra were determined on a
Shimadzu QP5050A quadrapole mass spectrometer that
operated in the electron impact ionization mode (EI) at
70 eV with an interface temperature of 300 °C.
2.3 | Catalyst preparation
Graphene oxide (GO) was prepared using a modified
Hummer's method.[25] In a typical procedure, H2SO4
(150 ml) was added into a flask containing graphite (6 g)
in an ice bath under stirring. After that, potassium per-
manganate (KMnO4) (18 g) was slowly added to the above
mixture, and the ice bath was removed after several
minutes. The color of the solution turned to dark green
under continued stirring for 2 hr at 35 °C. Then, water
(300 ml) was slowly added to the reaction mixture and
the conical flask was bathed in boiling water; the reaction
mixture was kept at this temperature for another 30 min.
After that, the flask was cooled in an ice bath, and distilled
water (1 L) was added to stop the reaction. H2O2 (30%)
(20 mL) was added to reduce the residual permanganate
to soluble manganese ions. Eventually, the precipitation
was centrifuged and washed with 1 M HCl and distilled
water several times, and then vacuum dried at 60 °C for
24 hr. After heating the filtrate at 60 °C for 4 hr, dry GO
powder was obtained. The Dried GO powder (100 mg)
was loaded in a beaker that was covered with aluminum
foil which had many punched pores and placed on a hot
plate set at 350 °C for 10 min in a hood. The resulting black
powder of rGO was then collected from the beaker.[26]
2 | EXPERIMENTAL
2.1 | Materials
Graphite powder, (Alfa Aesar, 325 mesh, 99.9995%),
AgNO3 (Sigma‐Aldrich, >99%), potassium permanganate
(KMnO4, Alfa Aesar), cetyltrimethylammonium chloride
(CTAC, Alfa Aesar, 95%) and cetyltrimethylammonium
bromide (CTAB, Alfa Aesar, 95%) were used as received
without further purification. Sulfuric acid (H2SO4),
hydrochloric acid (HCl), sodium hydroxide (NaOH),
hydrogen peroxide (H2O2), ethylene glycol (EG), p‐
nitrophenol (PNP), trimethylsilyl chloride (TMSCl),
acetic anhydride (AC2O) and Sodium boronhydride
(NaBH4) were purchased from Sigma‐Aldrich.
2.2 | Characterization
2.4 | Synthesis of Ag/AgX/rGO
nanostructures via water/oil
microemulsion
UV–Vis spectra were measured with a Perkin Elmer
Lambda 40 UV–visible spectrophotometer using 1‐cm path
length Hellma quartz cuvettes. Scanning electron micros-
copy (SEM) images were obtained with a ZEISS FE‐SEM
ULTRA Plus (equipped with EDX analyzer) microscope
with a Philips CM20 microscope, operating at an accelerat-
ing voltage of 200 kV. Several drops from the sample
dispersion were deposited onto an aluminum pin stub
and left to evaporate at room temperature. X‐ray diffrac-
tion (XRD) measurements were performed using a Philips
PW1710 X‐ray diffractometer using Cu Ka radiation
In a typical process, a 400 μL aqueous solution of rGO
nanosheets (1 mg mL−1) and a 500 μL aqueous solution
of AgNO3 (0.1 mol L−1) were added dropwise into a
10 mL chloroform solution of (8.23x10−3 mol L−1) CTAB
for Ag/AgBr/rGO or CTAC for Ag/AgCl/rGO composites,
successively within 10 min under magnetic stirring. The
vigorous stirring was maintained for another 20 min,
after which a milky dispersion containing Ag/AgX/rGO
hybrid nanocomposites was obtained. The resulting

ATTIA AND MOHAMED
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white‐yellowish solids were collected by centrifugation
(10000 rpm, 10 min) and washed thoroughly first with eth-
anol and then with ultrapure Milli‐Q water by repeating
centrifugations. When only AgNO3 species, but no rGO
nanosheets were employed, the corresponding Ag/AgX
species could also be thus synthesized via a parallel
process. The aforementioned synthetic method was per-
formed without being protected from the ambient light.
the reaction mixture, Ag/AgX/rGO nanocatalyst (1 wt%)
was added that was followed subsequently by the addition
of NaBH4 (1 mol%) and then TMSCl (1 mol%). The reac-
tion was stirred at room temperature under visible light
radiation using halogen lamp (HALOPAR 20 75 W 230 V
30‐GU10, Italy) for appropriate time. The reaction was
monitored by UV–Vis spectroscopy. After the reaction
completion, the solvent was evaporated using rotavapor
to obtain the crude products that were collected and
purified by using short column chromatography (SiO2,
EtOAc/Hexane, 2:8, 3:7, 4:6 and 1:1).
2.5 | General procedure for the synthesis
of p‐aminophenol
To a solution of p‐nitrophenol (1 mmol) in methanol:
H2O (1:1, 20 ml), Ag/AgX/rGO nanocatalyst (1 wt%)
was added and it was followed subsequently by the
addition of NaBH4 (1 mol%) and then trimethylsilyl
chloride (TMSCl) (1 mol%). The reaction was stirred at
room temperature under visible light radiation using
halogen lamp (HALOPAR 20 75 W 230 V 30‐GU10, Italy)
for appropriate time. The reaction was monitored by
UV–Vis spectroscopy. After the reaction completion, the
solvent was evaporated using rotavapor to obtain the
crude products that were collected and purified by
crystallization (ethanol:dioxane, 2:1).
3 | RESULTS AND DISCUSSION
Experimentally, our Ag/AgX/rGO hybrid nanocompos-
ites were easily synthesized by adding an aqueous
solution of rGO and silver nitrate (AgNO3) dropwise into
a chloroform solution of surfactants (CATB or CTAC)
successively. The corresponding Ag/AgX (X = Cl or Br)
species were obtained through an allied process when
only AgNO3 but no rGO nanosheet was involved. An
opaque system with a yellowish and white yellowish
color was obtained in sequence, respectively, after the
dropwise addition of an aqueous solution of rGO nano-
sheet and AgNO3 into a chloroform solution of surfac-
tants. This is owing to the incompatibility between
water and chloroform and the formation of the target
nanostructures.[27] The morphologies of the produced
nanostructures were characterized by scanning electron
microscopy (SEM), as outlined in Figure 1.
2.6 | General procedure for the synthesis
of paracetamol
A mixture of p‐nitrophenol (1 mmol) and acetic anhydride
(1 mmol) was dissolved in methanol: H2O (1:1, 6 ml). To
FIGURE 1 Typical SEM images of the synthesized Ag/AgBr (a), Ag/AgBr/rGO (b), Ag/AgCl (c), and Ag/AgCl/rGO (d) nanocomposites

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ATTIA AND MOHAMED
It can be seen that nanoparticles with an average
characteristic peaks of Ag/AgX appear with low intensity
in case of Ag/AgX/rGO composites confirming the
loading of Ag/AgX nanospecies on graphene sheets.
The existence of metallic Ag in our nanostructure
could be confirmed by the XRD investigation. As shown
in Figure 5, the XRD pattern of Ag/AgBr and Ag/AgBr/
rGO obtained via an oil/water microemulsion system dis-
play distinct diffraction peaks (2θ) at 26.7° (111), 30.9°
(200), 44.3° (220), 52.5° (311), 55.0° (222), 64.5° (400),
71.1° (331), 73.2° (420), and 38.2° (111), 44.3° (200),
64.5° (220), 74.9° (311), which are ascribed to the diffrac-
tions of cubic phase of AgBr (JCPDS file: 6–438) and that
of metallic Ag (JCPDS file: 65–2871), respectively.[8] Also,
the XRD pattern of the prepared sample displays distinct
diffraction peaks (2θ) at 38.2° (111), 44.6° (200), 64.8°
(220), 77.9° (311), and 27.7° (111), 32.1° (200), 46.2°
(220), 54.7° (311), 57.4° (222), 67.4° (400), 74.4°(331),
respectively, which correspond to the typical cubic phase
of metallic Ag (JCPDS file: 65–2871) and that of AgCl
(JCPDS file:31–1238).[19,20]
These results indicate the presence of metallic Ag in
our nanostructures, and it suggests the formation of
Ag/AgX‐based nanocomposites. We note that negligible
diffraction peaks that attributed to rGO nanosheets could
be detected in the cases of Ag/AgX/rGO. As verified by
other researchers that when rGO is hybridized with
inorganic components, the diffraction peak ascribing to
rGO could hardly be observed by XRD. This is owing to
the low diffraction intensity of rGO.
diameter of ca. 315 nm and 432 nm could be obtained
in the cases of Ag/AgBr and Ag/AgCl nanospecies,
respectively. Well‐defined nanospheres, whose average
diameter is ca ~ 124 nm and 200 nm whose surface is
distinctly enwrapped with gauze‐like rGO nanosheets,
could be obtained in the cases of Ag/AgBr/rGO and
Ag/AgCl/rGO hybrid nanocomposites, respectively. The
smaller size of Ag/AgX nanospheres observed from the
Ag/AgX/rGO systems compared with that of the corre-
sponding Ag/AgX systems might be due to the existence
of rGO nanosheets in these systems because it has
recently been demonstrated that rGO, an unconventional
amphiphile, could act as a surfactant in an oil–water
system, which might be able to further improve the
dispersibility of water phase in the chloroform solution
of surfactants.[28]
The chemical composition of Ag/AgX (Cl or Br)/rGO
was analyzed by an energy dispersive spectrometer (EDS)
spectrum on an SEM that showed the presence of (C, O,
Cl and Ag) with (32.05 wt%, 4.16 wt%, 12.78w% and
51.01 wt%) (Figure 2a) and (C, O, Br and Ag) with
(24.35 wt%, 5.59 wt%, 28.91w% and 41.15 wt%)
(Figure 2b), respectively. These results are confirming
that the as prepared samples are of high purity and the
Ag/AgX NPs were homogeneously formed on the
graphene sheets and they are free from aggregation. As
well as, the oxygen containing groups like carboxyl and
hydroxyl groups in GO serve as anchoring sites to direct
coating process.
Generally, it was reported that a bare of Ag/AgX
species had visible light responsivity.[19,20,29] Hence, the
produced nanostructures Ag/AgCl, Ag/AgBr, Ag/AgCl/
rGO and Ag/AgBr/rGO were subjected to the UV–Vis
spectral measurements. As shown in Figure 3, it can be
seen that all of the investigated Ag/AgX‐based species
display strong absorption both in the ultraviolet and
visible regions. This suggests the existence of metallic
Ag species in all of our samples, which could arouse
plasmon resonance absorptions in the visible region.
The absorption spectra of Ag/AgX/rGO nanocomposites
display a distinct absorption of rGO at ca ~ 255 nm,
confirming the existence of rGO sheets in these
systems.[30]
In order to verify the hybridization of Ag/AgX with
rGO in Ag/AgX/rGO composites, their Fourier transform
infrared spectra (FT‐IR) together with that of powdery r‐
GO was measured as depicted in Figure 4. It could be
seen that the powdery r‐GO displays several characteristic
bands at 3410 cm−1 for O‐H stretching and 1650 cm−1 for
C=C band. These bands appear clearly with high inten-
sity in case of Ag/AgX/rGO nanocomposites. As well as,
the aliphatic bands of the capped surfactants and the
3.1 | Evaluation the photocatalytic
performance towards paracetamol
production
The Ag/AgCl/rGO and Ag/AgBr/rGO nanocatalysts were
utilized as dip‐catalysts in chemical transformation of p‐
nitrophenol (PNP) to p‐aminophenol (PAP). In a first
series of experiments, the UV–Vis absorbance of the
PNP was measured to give absorption peak at 318 nm.
Then PNP was mixed with NaBH4 was to form a yellow
solution that showed maximum absorbance at 400 nm.
This peak is characterized to PNP anion indicating
that the PNP was remained without any conversion
(Figure 6) (see Table 1).
Upon the addition of either Ag/AgCl/rGO or
Ag/AgBr/rGO nanocatalysts (1 wt%) in the presence of
excess of NaBH4 (10 mM) to an aqueous solution contain-
ing PNP (0.1 mM) in the dark using glove box resulted
again in the formation of a yellow solution indicating that
both catalysts are not effective in the dark (see Table 1).
In another experiment, when the two reactions were
performed under visible light using Halogen lamp, it

ATTIA AND MOHAMED
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FIGURE 2 EDS analysis of (a) Ag/AgCl/rGO and (b) Ag/AgBr/rGO photo‐nanocatalysts
was observed from UV–Vis data after 5 min that a new
peak at 300 nm simultaneously appeared which is charac-
terized by p‐aminophenol (PAP) for both two reactions
and then by following the reaction using UV–Vis spec-
trometry, it was observed that the PNP was converted to
PAP after 90 min in case of using Ag/AgCl/rGO catalyst,

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ATTIA AND MOHAMED
FIGURE 3 Typical UV–Vis spectra of Ag/AgBr/rGO, Ag/AgCl/
rGO, Ag/AgBr, and Ag/AgCl nanocomposites
FIGURE 6 Absorption spectra of PNP only (a) and PNP in the
presence of NaBH4 under visible light irradiation for 60 minutes (b)
TABLE 1 Comparison between the prepared nanocomposites for
PAP production from PNP reduction as functions of yield and time
of reaction
FIGURE 4 Typical FT‐IR spectra of the powdery Ag/AgBr, Ag/
AgBr/rGO, Ag/AgCl and Ag/AgCl/rGO nanostructures
Product
yield %
Time
(min)
Reaction Conditions
NaBH4 (10 mmol) + PNP (0.1 mmol)
‐
60
90
Ag/AgCl/rGO (1 wt%) + NaBH4
(10 mmol) + PNP (0.1 mmol)
85
Ag/AgBr/rGO (1 wt%) + NaBH4
(10 mmol) + PNP (0.1 mmol)
88
92
70
50
Ag/AgCl/r‐GO (1 wt%) + NaBH4
(1 mol%) + TMSCl (1 mol%) +
PNP (1 mmol)
Ag/AgBr/r‐GO (1 wt%) + NaBH4
(1 mol%) + TMSCl (1 mol%) +
PNP (1 mmol)
95
20
while the reduction reaction was completed after 70 min
by using Ag/AgBr/rGO catalyst (Figure 7a,b). From the
results, it was investigated that Ag/AgBr/rGO is more
efficient than Ag/AgCl/rGO based on the consumed time
for completing the conversion of PNP to PAP.[31] One aim
FIGURE 5 XRD pattern of Ag/AgBr, Ag/AgBr/rGO, Ag/AgCl
and Ag/AgCl/rGO nanocatalysts synthesized via an oil/water
micro‐emulsion

ATTIA AND MOHAMED
7 of 11
FIGURE 7 Absorption spectra of PNP in the presences of NaBH4 and Ag/AgCl/rGO (a), Ag/AgBr/rGO (b), Ag/AgCl/rGO‐Si (c) and
Ag/AgBr/rGO‐Si nanoctalysts (d), respectively under visible light irradiation
of this study was to enhance the catalytic activity of the
two catalysts by using TMSCl as a source of silicon, which
will promote us to use NaBH4 in catalytic amount instead
of large excess amount. NaBH4 (1 mol%) was mixed with
PNP to form PNP ion. Then the catalyst Ag/AgCl/rGO
(1 wt%) or Ag/AgBr/rGO (1 wt%) was loaded and
followed subsequently by the addition of TMSCl
(1 mol%). In both reactions, a clear solution was formed
after 3 min. It was observed that the reaction was com-
pleted after 50 min in case of Ag/AgCl/rGO‐Si while it
was completed after 20 min in case of Ag/AgBr/rGO‐Si
based on UV–Vis data (Figure 7c,d). The photoreduction
of PNP to PAP rate order under visible light irradiation
of the samples is: Ag/AgBr/rGO‐Si > Ag/AgCl/rGO‐
Si > Ag/AgBr/rGO > Ag/AgCl/rGO (Table 1). These
results indicate that the photocatalytic activity can
become highly effective after mixing Ag/AgX/rGO
composites with TMSCl as a source of silicon.
These results were encouraging us to prepare paracet-
amol through one pot synthesis starting from PNP as raw
material. Again, two parallel experiments were carried
out by mixing PNP with acetic anhydride, NaBH4 and
TMSCl. Interestingly, after 15 min in case of Ag/AgCl/
rGO and after 8 min in case of Ag/AgBr/rGO, paraceta-
mol was obtained that exhibited absorbance at 242 nm
besides the formation of PAP that was shown absorbance
FIGURE 8 Absorption spectra of PNP reduction in the presence
of Ac2O and NaBH4 by using Ag/AgCl/rGO‐Si (a) and Ag/AgBr/
rGO‐Si (b) nanocomposites, respectively
at 300 nm. After purification, the afforded residue, para-
cetamol and PAP were formed in 86% and 13% isolated
yields in case of Ag/AgCl/rGO‐Si nanocomposites,
while the products were formed in 93% and 6% isolated
the most efficient nanocatalyst indicating that paraceta-
mol (m/z = 151) was formed through cascade reduction
processes. The reaction was started by the reduction of
yield in case of Ag/AgBr/rGO‐Si nanocomposites (see
Figure 8 and Table 2).
Interpretation of GC/MS analysis after 5 minutes of
the reaction progress in case of Ag/AgBr/r‐GO‐Si hybrid;
p‐nitrophenol (m/z
=
109) to p‐nitrosophenol

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ATTIA AND MOHAMED
TABLE 2 Comparison between the prepared nanocomposites for
paracetamol production from PNP reduction as functions of yield
and time of reaction
(m/z
=
123) that was readily reduced to 4‐
hydroxyphenylhydroxylamine (m/z = 125) and then it
was converted sequentially to p‐aminophenol
(m/z = 123) that was attacked by acetic anhydride
to produce paracetamol (m/z = 151) (Figure 9 and
Scheme 1).
Product yield Time
Reaction Conditions
% APAP:PAP
(min)
Ag/AgCl/rGO (1 wt%) + NaBH4
(1 mol%) + PNP (1 mmol) + Ac2O
(1 mmol) + TMSCl (1 mol%)
86:13
15
The synthesis of p‐aminophenol from p‐nitrophenol
1
1
was proved by H NMR spectra. In Figure 9b, the H
NMR spectrum showed a chemical shift (δ) at 6.95 ppm
characteristic for aromatic protons in comparison with
the 1H NMR of the starting material; p‐nitrophenol
(Figure 10a) which showed two doublet peaks at
δ = 6.54 ppm and δ = 7.95 ppm (Figure 10b). In addition,
when p‐nitrophenol was treated with acetic anhydride
Ag/AgBr/rGO (1 wt%) + NaBH4
(1 mol%) + 1 mmol PNP+ 1 mmol
Ac2O + TMSCl (1 mol%)
93:6
8
1
in the presence of Ag/AgBr/rGO‐Si hybrid catalyst, H
NMR spectrum in Figure 9c showed singlet peak at
δ = 2.03 ppm characteristic for CH3, two doublet peaks
at δ = 6.96 ppm and 7.27 ppm for aromatic protons
and two broad single peaks at δ = 9.51 ppm and
δ = 10.01 ppm for OH and NH, respectively indicating
the formation of paracetamol.
On the basis of the above‐mentioned experimental
facts and analysis, we could propose an explanation for
the enhanced photocatalytic performance observed from
our Ag/AgX/r‐GO‐Si hybrid nanocomposites. The
distinct plasmon absorption in the visible region, which
is aroused by the existing metallic Ag0 species, makes
our photocatalysts visible‐light drivable. It is clear that
the metallic Ag plays an important role on the photoin-
duced stability of Ag/AgX composite, which has a great
effect on its photocatalytic performance. Ag/AgX (Cl
or Br) is widely used to modify the semiconductor
photocatalysts. The highly dispersed AgX species can
improve the separation efficiency of photo‐generated
charge carriers, and enhance the photocatalytic activity
of the substrates. Furthermore, under visible light
FIGURE 9 GC/MS of the reduction reaction of 4‐NP and
production of paracetamol after 5 min using Ag/AgBr/rGO‐Si
nanocatalyst
SCHEME 1 The detection of reaction sequence for the synthesis
of paracetamol using GC/MS analysis
1
1
FIGURE 10 1H NMR of paracetamol (a), H NMR of p‐aminophenol (b), H NMR of p‐nitrophenol (c)

ATTIA AND MOHAMED
9 of 11
irradiation, photogenerated electron–hole pairs are
separated on the surface of Ag NPs due to the surface
plasmon resonance (SPR) effect. Recently, the type of
plasmonic photocatalyst, Ag/AgX (X = Cl or Br) had
been developed for the high absorption of visible light
and excellent photodecoloration of organic pollutants
due to the strong surface plasmon resonance (SPR) effect
of metallic Ag nanoparticles (Ag NPs).[6–10] The size of
Ag/AgX nanospecies in the case of Ag/AgX/rGO hybrid
nanocomposites is smaller than that of bare Ag/AgX
nanospecies, which might also contribute partially to a
nice photocatalytic performance. Moreover, Ag/AgX
and r‐GO components might serve as electron donor
and electron acceptor, respectively, in the Ag/AgX/rGO
hybrid nanocomposites. As a result, the photogenerated
electrons could migrate into rGO nanosheets through a
percolation process during the photocatalytic perfor-
mance.[31] This could essentially promote the charge
separation/transfer and thus suppress the charge
recombination of electron–hole pairs, enhancing the
photocatalytic performance towards the reduction
(hydrogenation) of p‐nitrophenol and production of para-
cetamol. However, in case of Ag/AgX/rGO‐Si catalysts,
TMSCl as a precursor of silicon was added to the reac-
tion and the rGO sheets seemed to be more hydrophobic
rGO sheets due to the present alkyl chains which
explained the increased efficiency. On another words,
Our synthetic approach was initiated by production of
reduced GO from GO which was verified by the presence
of some of ‐OH and ‐COOH groups in the graphene
structure; in particular, more in the edges. This can be
an explanation why rGO is water soluble. So, Cl− can
be easily removed from TMSCl by these ‐OH and ‐COOH
groups forming C–O–Si bonds as confirmed by Attia
et al.[1,2] This so called protecting process was
contributed in developing hydrophobic rGO sheets and
subsequently leads to increase the catalytic proficiency.
Therefore, the presence of silicon increases the
photogeneration of electrons and holes enhancing the
catalytic performance of Ag/AgX/rGO‐Si hybrid
nanocatalyst and enhancing the reduction of
p‐nitrophenol and one‐pot production of paracetamol
from PNP (see Scheme 2).
Finally, in a comparison between the efficiency of
Ag/AgX/rGO photocatalysts with the previously
reported approaches that had been developed for the
synthesis of paracetamol (APAP) (Scheme 3). The first
route was the hydrogenation of p‐nitrophenol (PNP)
to the corresponding APAP in presence of acetic acid
under hydrogen atmosphere as reducing agent under
at 100 °C for 24 hr (Scheme 3, route 1).[32] Another
approach in which APAP was prepared by the reaction
of 4‐hydroxyacetophenone with a hydroxylamine salt to
obtain 4‐hydroxyacetophenone oxime, followed by a
Beckmann rearrangement in the presence of a catalyst
e.g. CF3COOH, thionyl chloride or amberlyst 15 at
118 °C for
4 hr under pressure (80 mmHg to
10 atm.) (Scheme 3, route 2).[33] An alternative route
for the direct synthesis of APAP was demonstrated by
the reaction of hydroquinone with ammonium acetate
(10 eq.) and acetic acid (5 eq.) at 220 °C for 15 hr
(Scheme 3, route 3).[34] From the aforementioned results,
the described methods suffer some drawbacks such as
performing the reaction at elevated temperature, long
reaction time and low selectivity of the produced product.
Therefore, our investigated synthetic strategy for direct
synthesis APAP from PNP could be considered as a
greener approach due to the following characteristic
features, (a) performing the reaction under visible light
irradiation at ambient conditions, (b) APAP was produced
SCHEME 2 The mechanism of the reduction of p‐nitrophenol
using Ag/AgX/rGO‐Si nanocatalysts under visible light irradiation
SCHEME 3 A comparison between the reported approaches and
our investigated method for the synthesis of paracetamol

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ATTIA AND MOHAMED
TABLE 3 Recycling of the reduction reaction using Ag/AgCl/
rGO‐Si nanocomposites after 15 min And Ag/AgBr/rGO‐Si nano-
composites after 8 min, respectively
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In summary, catalytic activity of silicon‐grafted Ag/AgX/
rGO nanocomposites was tested in the reduction of
p‐nitrophenol (PNP) to produce p‐aminophenol (PAP)
and then the study was extended for the synthesis of
paracetamol (APAP) that revealed that Ag/AgBr/rGO‐Si
nanohybrid was a highly efficient catalyst. A possible
reaction mechanism was proposed. The presented
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This research did not receive any specific grant from
funding agencies in the public, commercial, or not‐for‐
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Research Center (Egypt), and National Institute of Laser
Enhanced Sciences, Cairo University (Egypt) for provid-
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Yasser A. Attia https://orcid.org/0000-0002-5830-2250

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How to cite this article: Attia YA, Mohamed
YMA. Silicon‐grafted Ag/AgX/rGO nanomaterials
(X = Cl or Br) as dip‐photocatalysts for highly
efficient p‐nitrophenol reduction and paracetamol
production. Appl Organometal Chem. 2018;e4757.
https://doi.org/10.1002/aoc.4757
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US4524217 patent, 1985.
[34] R. Joncour, N. Duguet, E. Métay, A. Ferreirab, M. Lemaire,
Green Chem. 2014, 16, 2997.