Enhanced catalytic activity of one-dimensional CdS @TiO2 core-shell nanocomposites for selective organic transformations under visible LED irradiation

Article abstract of DOI:10.1016/j.jphotochem.2021.113404

In this study, we are interested in the photocatalytic activity under visible LED irradiation of one- dimensional (1D) CdS @TiO₂ core–shell nanocomposites (CSNs) prepared through a facile and convenient method. For the synthesis of 1D CdS@TiO₂ core/shell structure, titania source (Tetrabutyl titanate) was hydrolyzed by water vapor transmission on the surface of CdS nanowires (NWs) which were prepared via solvothermal method. The characterization of 1D CdS@TiO₂ core–shell nanocomposites (CdS@TiO₂ CSNs) was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis spectroscopy, and UV–Vis diffuse reflectance spectroscopy (DRS). The as-synthesized sample was utilized for the selective reduction of nitro compounds to benzimidazole and anilide, and also the reduction of benzophenones to alcohol under blue LED irradiation. The 1D CdS@TiO₂ CSNs exhibited enhanced photoactivity compared with the pure TiO₂, CdS nanowires and commercial TiO₂-P25. The excellent reusability of the photocatalyst was examined for six runs. The results demonstrated that the prepared sample has the potential to provide a promising visible light-driven photocatalyst for other organic transformations.

Full text of DOI:10.1016/j.jphotochem.2021.113404

Journal of Photochemistry & Photobiology, A: Chemistry 418 (2021) 113404
Contents lists available at ScienceDirect
Journal of Photochemistry & Photobiology, A: Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Enhanced catalytic activity of one-dimensional CdS @TiO2 core-shell
nanocomposites for selective organic transformations under visible
LED irradiation
,
,c,
Parvin Eskandaria *, Zahra Zandb, Foad Kazemib *, Moosa Ramdarb
a Department of Chemistry, Zanjan Branch, Islamic Azad University, 49195-467 Zanjan, Iran
b Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Gava Zang, 49195-1159 Zanjan, Iran
c Center for Climate and Global Warming (CCGW), Institute for Advanced Studies in Basic Sciences (IASBS), Gava Zang, 45137-66731 Zanjan, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this study, we are interested in the photocatalytic activity under visible LED irradiation of one- dimensional
(1D) CdS @TiO2 core–shell nanocomposites (CSNs) prepared through a facile and convenient method. For the
synthesis of 1D CdS@TiO2 core/shell structure, titania source (Tetrabutyl titanate) was hydrolyzed by water
vapor transmission on the surface of CdS nanowires (NWs) which were prepared via solvothermal method. The
characterization of 1D CdS@TiO2 core–shell nanocomposites (CdS@TiO2 CSNs) was performed using X-ray
diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis
spectroscopy, and UV–Vis diffuse reflectance spectroscopy (DRS). The as-synthesized sample was utilized for the
selective reduction of nitro compounds to benzimidazole and anilide, and also the reduction of benzophenones to
alcohol under blue LED irradiation. The 1D CdS@TiO2 CSNs exhibited enhanced photoactivity compared with
the pure TiO2, CdS nanowires and commercial TiO2-P25. The excellent reusability of the photocatalyst was
examined for six runs. The results demonstrated that the prepared sample has the potential to provide a
promising visible light-driven photocatalyst for other organic transformations.
Photocatalysis
CdS@TiO2 core/shell
Selective reduction
Aromatic nitro compounds
Carbonyl compounds
LED irradiation
1. Introduction:
[40,41]. Coupling TiO2 with CdS has been very promising as calcula-
tions have shown that the potential gradient at the interface of TiO2/CdS
In recent years, a great deal of attention has been devoted to pho-
tocatalytic processes for selective organic transformations under visible
light because of its environmental friendliness and using renewable
energy sources [1–4]. Designing and exploiting photocatalyst semi-
conductors that can operate well under visible light are of great interest
and importance [5]. Extensive research in this area has been recently
directed toward the development of new and efficient photocatalysts to
achieve a photocatalytic selective transformation of organic compounds
[6–25]. Among those, photocatalytic reduction of organic compounds
such as hydrogenations of alkenes and alkynes [26], reduction of aro-
matic nitro compounds [17,27–34], aldehydes and ketones [35–39], and
using modified semiconductors have achieved promising results. Among
various photocatalysts reported so far, TiO2 (low cost, non-toxicity,
stability against photocorrosion) and CdS (low band gap) have attrac-
ted special interest [5]. However, the application of TiO2 because of its
wide band gap (for anatase 3.2 eV) remains confined to UV light
enhances the efficiency of charge separation and narrow band gap in
CdS (2.4 eV) also promotes efficient visible light photoactivity [5]. The
TiO2/CdS composites have been extensively studied for their applica-
tions in photocatalysis [42–47]. For example, Wu et al have reported the
synthesis of one-dimensional CdS/TiO2 nanofiber composites for a series
of selective oxidizing of alcohol into corresponding aldehydes under
visible light irradiation [48]. Recently, intensive studies have been
performed on the CdS QDs-sensitized TiO2 photocatalysts. Lu et al. re-
ported significant improvement in the efficiency of the degradation of
organic compounds by incorporating CdS QDs into the TiO2 mesoporous
using bifunctional linker and mercaptopropionic acid (MPA) [49]. Pan
et al. reported the incorporation of chemically reduced graphene oxide
(RGO) in CdS precursor solution with TiO2 suspension using microwave-
assisted method to form CdS–TiO2–RGO composites for visible-light
photocatalytic degradation of methyl orange [50]. Besides, deposition
of noble metal co-catalyst (e.g. Pt or Au) onto the CdS/TiO2 composites
* Corresponding authors.
E-mail addresses: eskandari.p14@gmail.com (P. Eskandari), kazemi_f@iasbs.ac.ir (F. Kazemi).
https://doi.org/10.1016/j.jphotochem.2021.113404
Received 30 April 2020; Received in revised form 25 May 2021; Accepted 1 June 2021
Available online 10 June 2021
1010-6030/© 2021 Elsevier B.V. All rights reserved.

P. Eskandari et al.
Journal of Photochemistry & Photobiology, A: Chemistry 418 (2021) 113404
was applied for efficient visible-light-driven hydrogen generation
[51,52]. Higashimoto reported the selective dehydrogenation of aro-
matic alcohols to the corresponding carbonyl compounds and hydrogen
by Pd-deposited CdS–TiO2 photocatalysts in aqueous solutions using
visible light [53]. This group also reported one-pot synthesis of imine
from benzyl alcohol and nitrobenzene by CdS/TiO2 [54].
were dried in a vacuum at 70 ◦C for 6 h.
The Synthesis of 1D CdS @TiO2 CSNs: First, CdS NWs (0.3 g)
powder was sonicated thoroughly in 20 ml of absolute ethanol for 20
min. Then, TBOT (1.5 ml) dissolved in 30 ml of absolute ethanol was
added to it. The mixture was stirred at room temperature for 4 h. After 4
h, a flow of vapor water was transmitted to the mixture for 4 h. Thus, the
water did not contact TBOT directly and the fierce hydrolysis was
avoided. Followed by aging in a closed beaker at room temperature for
36 h, the yellow precipitates obtained were collected and washed with
deionized water three times, then dried under vacuum at 60 ◦C for 12 h.
The dried sample was calcined at 400 ◦C for 1 h.
Although CdS is an excellent candidate as visible-light-driven pho-
tocatalyst, visible-light-induced photogenerated holes on the surface of
CdS lead to the dissolution of their crystal lattice [55]. Therefore, many
efforts have been made to protect CdS from photocorrosion; Coating
with TiO2 could protect CdS from photocorrosion. Core-Shell nano-
structure could exhibit improved physical and chemical properties; thus,
providing a new way to tailor the properties of the nanomaterials. Xu
et al. reported the syntheses of CdS NSPs@TiO2 core ꢀ shell and one-
dimensional CdS@TiO2 core ꢀ shell with enhanced visible-light pho-
toactivity for selective photocatalytic oxidation of alcohols [56]. Indeed,
this hetero-system would possess the optimal band gap of one constit-
uent CdS and the photocorrosion stability of the TiO2. Photogenerated
electrons and holes in the semiconductors improved the design of het-
erogeneous catalytic systems that can promote efficient one-pot syn-
thesis. Recently, One-pot photocatalytic processes that produce
benzimidazole, N-alkylation, and imines directly from alcohols and nitro
compounds were reported with Pt-TiO2, Ag-TiO2, and TiO2-P25 nano-
particles under UV and sunlight [57–62]. Our group has reported on
activated amorphous TiO2 coated into periodic mesoporous organosilica
(PMOs) [63], mesoporous C-N codoped nano TiO2 [64], β-Cyclodextrin/
TiO2 [65], TiO2-P25 [66,67], and CdS [68,69] as efficient photocatalysts
for the synthesis of selective organic transformation under visible light.
Herein, we have demonstrated that selective photocatalytic activity in
the reduction of nitro and carbonyl compounds under blue LED irradi-
ation could be addressed by a simple preparation of one-dimensional
CdS@TiO2 core/shell nanocomposites (1D CdS@TiO2 CSNs). For the
preparation of 1D CdS@TiO2 CSNs, titania source (Tetrabutyl titanate)
was hydrolyzed by water vapor transmission on the surface of CdS
nanowires which were prepared via the solvothermal method. To our
knowledge, there has been no precedent example of 1D CdS@TiO2 CSNs
used for the selective reduction of organic compounds under visible LED
irradiation. The results showed that 1D CdS@TiO2 CSNs exhibited
higher photocatalytic activity than bare CdS NWs, pure TiO2, and
commercial TiO2-P25.
The preparation of pure TiO2: The 1D CdS@TiO2 CSNs (1 g) was
added to the 20 ml of HCl (1 M) solution and the mixture was stirred
magnetically for 1 h to remove the CdS. The white precipitate was
collected and washed with DI water three times, then dried under vac-
uum at 70 ◦C.
2.3. Photocatalytic activity
The photocatalytic selective reduction of various nitro compounds
and benzophenone derivatives was performed as follows:
Reaction conditions for the synthesis of benzimidazole: A
mixture of o-nitroaniline (0.02 mmol), 1D CdS@TiO2 CSNs (0.02 g), and
4 ml EtOH was transferred into a round bottom Pyrex flask (5 ml). The
reaction mixture was degassed by argon gas, sealed with a septum, and
irradiated by blue LED (2 × 3 W) for 30 h. After the reaction, the mixture
was centrifuged to remove the catalyst particles. The remaining solution
was analyzed using thin-layered chromatography (TLC) and the product
yields were determined by monitoring gas chromatography (GC). Also,
the desired product was extracted by plate chromatography, and eluted
with n-hexane/EtOAc. Assignments of the products were made by 1H
NMR and 13CNMR spectroscopy.
Reaction conditions for the synthesis of anilide: The aromatic
nitro compounds (0.02 mmol) and acetic anhydride (0.025 mmol) were
carried out in the presence of 1D CdS@TiO2 CSNs (0.02 g) in EtOH (4
ml) and irradiated by blue LED (2 × 3 W) for 20–35 h. After the reaction,
the mixture was centrifuged to remove the catalyst particles. The
remaining solution was analyzed using thin-layered chromatography
(TLC) and the product yields were determined by GC. The desired
product was extracted by plate chromatography, and eluted with n-
hexane/EtOAc. Assignments of the products were made by 1H NMR and
13CNMR spectroscopy.
2. Experimental section
Reaction conditions for the reduction of benzophenone de-
rivatives: The benzophenone (0.05 mmol), Ammonium formate (0.02
g), 1D CdS@TiO2 CSWs (0.02 g), and 5 ml i-PrOH were transferred into a
round bottom Pyrex flask (10 ml). Then the reaction mixture was
degassed by argon gas, sealed with a septum, and irradiated by blue LED
(3 W) for 24 h. After this time, the catalyst was simply separated by
centrifugation and the remaining solution was analyzed using thin-
layered chromatography (TLC) and the product yields were deter-
mined by GC and HPLC. The desired product was extracted by plate
chromatography, and eluted with n-hexane/EtOAc. Assignments of the
products were made by 1H NMR and 13CNMR spectroscopy. The con-
version of ketone substrate, the yield of alcohol, and the selectivity for
alcohol were defined as follows:
2.1. Materials
Chemicals and apparatus: Tetrabutyl titanate (TBOT, C16H36O4Ti),
ethylenediamine (C2H8N2), sodium diethyldithiocarbamate trihydrate
(C5H10NNaS2⋅3H2O), cadmium chloride (CdCl2⋅2H2O), and absolute
ethanol (C2H6O) were obtained from Sigma Aldrich. All materials were
used as received without further purification. Deionized (DI) water was
used in all experiments.
2.2. The preparation of photocatalyst
The Synthesis of CdS Nanowires: Cadmium dieth-
yldithiocarbamate Cd (S2CNEt2)2 was prepared by precipitation from a
mixture of NaS2CNEt2.3 H2O (1.5 g, 6.66 mmol) and CdCl2⋅2H2O (0.729
g, 3.33 mmol) in deionized water (50 ml). The white precipitate was
collected and washed with deionized water three times, then dried
under vacuum at 70 ◦C for 6 h. The CdS nanowires were grown through a
modified method [70]. 1.124 g of Cd (S2CNEt2)2 was dissolved in 70 ml
of ethylenediamine, and then added to a Teflon-lined stainless steel
autoclave with a capacity of 100 ml. The autoclave was maintained at
180 ◦C for 24 h and then allowed to cool to room temperature. The
yellowish precipitate was collected and washed with DI water and
ethanol to remove the residue of organic solvents. The final products
Conversion (%) = (C0 ꢀ Cketone)/C0 × 100
Yield (%) = Calcohol/C0 × 100
Selectivity (%) = Calcohol/ (C0 ꢀ Cketone) × 100
Where C0 is the initial concentration of ketone, Cketone and Calcohol are
the concentration of the ketone substrate and the corresponding alcohol
respectively, after the photocatalytic reaction.
3. Results and discussion:
The X-ray diffraction, as shown in Fig. 1, was used to determine the
crystallographic structure of the as-prepared CdS nanowires (NWs) and
2

P. Eskandari et al.
Journal of Photochemistry & Photobiology, A: Chemistry 418 (2021) 113404
O 1s was observed at 531 eV. Furthermore, the amount of TiO2 depos-
ited on a CdS nanowire has been determined by atomic absorption
spectroscopy (AAS). It is found that the percentage of Ti in sample 1D
CdS@TiO2 CSNs (CdS@TiO2-1.5) is 30%.
For investigating the optical properties of the photocatalysts, a
comparison of the UVꢀ vis diffuse reflectance spectra over CdS NWs, 1D
CdS @TiO2 CSNs, and pure TiO2 is depicted in Fig. 4a. It can be seen
from spectra that the CdS NWs can absorb visible light with a wave-
length of about 520 nm. For 1D CdS@TiO2 CSNs, the light absorption
was extended to the visible-light region and the UV absorption band was
also observed at ~ 350 nm that can be attributed to the band edge ab-
sorption of TiO2. For pure TiO2, their absorption displays a characteristic
in UV region with a wavelength below 400 nm, which can be attributed
to the intrinsic band gap of TiO2.
Also, a slight variation in the CdS NWs band gap and 1D CdS@TiO2
CSNs is observed from the inset of Fig. 4b. More specifically, the band
gap over 1D CdS@TiO2 CSNs is approximately 2.39 eV, which is
widened slightly in comparison with that of pure CdS nanowires at 2.31
eV. It could be inferred from the spectra that the visible light could
transmit through the TiO2 shell; thus, leading to no obvious decrease in
the absorption capacity of visible light over 1D CdS@TiO2 CSNs though
TiO2 having no visible-light absorption. The results indicate that both
CdS NWs and 1D CdS@TiO2 CSNs can be photoinduced under the illu-
mination of visible light, by which photocatalytic redox reactions can be
driven.
Fig. 1. XRD patterns of as-prepared CdS NWs, 1D CdS@TiO2 CSNs, and
pure TiO2.
1D CdS@TiO2 nanocomposites (1D CdS@TiO2 CSNs). The diffraction
peaks at 2θ = 24.8◦, 26.5◦, 28.2◦, 36.6◦, 43.7◦, 47.9◦, 50.9◦, 51.8◦,
52.8◦, 66.8◦, 69.2◦, 70.9◦, 72.3◦, and 75.4◦can be attributed to hexag-
onal (wurtzite) CdS phase (JCPDS card no. 41–4019) [52]. The char-
acteristic diffraction peaks of TiO2 could not be seen from the pattern of
1D CdS@TiO2 CSNs due to its relatively low diffraction intensity.
Moreover, the (100) peak of hexagonal CdS might also overlap with the
primary characteristic peak of TiO2 at approximately 2θ = 25.4◦. For
further verification of this hypothesis, we performed an etching treat-
ment on the 1D CdS@TiO2 CSNs sample using HCl (1 M) solution to
remove the CdS [52].
Recently, light-emitting diodes (LEDs) with a low electrical power
requirement in the visible spectra offer a promising replacement for
conventional light sources in many applications. Using LED lamps as a
light source offers several advantages such as high photon efficiency,
low voltage electrical power source, power stability, emission in broader
spectral wavelengths, and no need for cooling during long time opera-
tion [71]. It was shown in Fig. 5 that the absorption edge of 1D
CdS@TiO2 CSNs in green, red, and blue LED emission area [72] was
investigated, and the improved absorption was observed in blue LED
emission area.
The XRD spectra showed the peak attributed to TiO2 anatase in 2θ =
25◦ after HCl etching. This confirms that the CdS nanowires were
decorated by TiO2. Moreover, CdS NWs and 1D CdS@TiO2 CSNs were
verified by the following scanning electron microscopy (SEM) analysis.
The SEM images of CdS NWs and 1D CdS@TiO2 CSNs indicated the
coating of TiO2 onto CdS NWs. Fig. 2 shows the typical SEM images of
CdS NWs and CdS@TiO2 CSNs resulting from the coating of TiO2 onto
CdS NWs. As seen in Fig. 2a–b, the as-prepared CdS NWs exhibit the wire
To examine the photocatalytic activity of 1D CdS@TiO2 CSNs under
LED irradiation, our investigation commenced with nitrobenzene as a
model substrate under various reaction parameters to screen for the
optimum reaction conditions and the results are summarized in Table 1.
To our delight, when nitrobenzene (0.02 mmol) was treated with 1D
CdS@TiO2 CSNs (0.08 g) in EtOH (4 ml) and the resulting mixture was
stirred under blue LED (3 W) for 20 h, the corresponding aniline was
obtained in 100% yield (Table 1, entry 1). Next, various amounts of
photocatalyst were examined. Reducing the amount of photocatalyst
(0.02 g) caused a drastic decrease in product yield (Table 1, entry 3). It is
pleasing to find that yield products can be increased by increasing the
wattage LED (from 3 W to 6 W) (Table 1, entry 4). Attempts to highlight
the role of LED wavelength were also investigated. The result has shown
that the use of Green LED led to poorer yields (Table 1, entry 6, 7).
Eventually, the optimized reaction conditions were photocatalyst (1D
CdS@TiO2 CSNs, 0.02 g), nitrobenzene (0.02 mmol) in EtOH (4 ml), and
blue LED (6 W) at 20 h. As shown in Table 1, it can be observed that 1D
CdS@TiO2 CSNs exhibit the highest photoactivity than the CdS NWs,
pure TiO2, and TiO2-P25 in the reduction of nitrobenzene to aniline
under blue LED irradiation. For example, under blue LED (6 W) irradi-
ation for 20 h, the conversion for nitrobenzene and yield for aniline is
100% over the 1D CdS@TiO2 CSNs, which is much higher than the
values obtained over CdS NWs (13% conversion and 12% yield), pure
TiO2 (10 > yield), and TiO2-P25 (15% conversion). Thus, it can be
concluded that decorating TiO2 onto the CdS NWs can significantly
enhance the photocatalytic activity of both CdS NWs and TiO2 semi-
conductors toward selective reduction of nitrobenzene in a suitable
amount of substrate than under LED illumination. A Photoluminescence
(PL) measurement has been applied to determine the charge separation
efficiency of the 1D CdS@TiO2 CSNs. Fig. 6 shows that the PL intensity
of 1D CdS@TiO2 CSNs is weaker than that of CdS nanowire. The result
morphology with a length of about 1–2 μm and an average diameter of
ca. 40–100 nm. Besides, it can be seen from Fig. 2c–d that TiO2 particles
were densely coated onto the surface of CdS NWs; thus, forming the 1D
CdS@TiO2 CSNs. The SEM results confirmed that after the secondary
solvothermal process, the TiO2 was efficiently decorated on CdS NWs
(Fig. S5a–d, ESI†). The TEM images indicate that the TiO2 shell was
efficiently located on CdS NWs surface and the interface between core
and shell can be easily distinguished (Fig. 2e–g and S4 a-b, ESI†). Ac-
cording to the HRTEM image (Fig. 2h), the lattice spacing of d = 0.34 nm
corresponds to the (002) crystallographic planes of hexagonal CdS, and
the fringes of d = 0.35 nm correspond to the interplanar spacing of the
(101) planes of anatase TiO2, which are consistent with the results of
XRD patterns. Fig. S2 and Table S1 (Supporting Information) show the
N2 adsorption ꢀ desorption isothermals and the surface area of CdS Nw
(a) and samples Cd@TiO2-x. The BET surface area of the CdS Nw is
measured to be ca. 27.5 m2/ g. With increased content of TiO2, exhibit
increased surface area and pore volume up to about 55.4 m2/g and 0.35
cm3/g, as shown in Table S1. Surface chemical compositions of a 1D
CdS@TiO2 CSNs have been studied by X-ray photoelectron spectroscopy
(XPS) (Fig. 3). TiO2 exhibited two peaks with binding energy of 459.0
and 464.5 eV for Ti 2p3/2 and Ti 2p1/2 reveal a Ti4+ oxidation state. The
binding energies of Cd 3d observed at 405.4 and 412.1 eV for Cd 3d5/2
and Cd 3d3/2 confirm a bivalent oxidation state for Cd. It is also found
that the binding energy of S 2p is 161 eV, indicating that a S2ꢀ oxidation
state exists on the sample surface. On the other hand, binding energy of
3

P. Eskandari et al.
Journal of Photochemistry & Photobiology, A: Chemistry 418 (2021) 113404
Fig. 2. SEM images of CdS NWs (a-b) and 1D CdS@TiO2 CSNs (c-d), TEM images of an individual 1D CdS@TiO2 CSNs (e-g) and HRTEM image of 1D CdS@TiO2
CSNs (h).
4

P. Eskandari et al.
Journal of Photochemistry & Photobiology, A: Chemistry 418 (2021) 113404
syntheses of one-pot benzimidazoles and anilides from nitro compounds
were investigated. Benzimidazole, anilide and their derivatives have
been the subject of much research due to the widely were utilized in the
fragrance, confectionery, and pharmaceutical industries [66,73–75].
The photoirradiation of ethanol solutions that contained various ortho-
phenylenenitroaniline and the 1D CdS@TiO2 CSNs photocatalyst suc-
cessfully afforded the corresponding benzimidazoles (Table 2). The re-
sults have indicated that 1D CdS@TiO2 CSNs promoted the rapid and
selective production of 2-methyl-benzimidazole after 30 h irradiation in
high yield. Synthesis of methyl- benzimidazole was carried out with
TiO2-P25 at the same reaction and the result was compared with that of
1D CdS@TiO2 CSNs. This reaction was very slow and the resulting
product was <10% even for 50 h irradiation (Table 2, entry 5). A
mechanism for the production of benzimidazole in the presence of 1D
CdS@TiO2 CSNs is proposed as illustrated in Scheme 1. Under visible-
light irradiation (λ ≥ 420 nm), photoinduced carriers are created and
migrate to the CdS surface. First, the holes in the valence band of CdS
can directly oxidize the solvent ethanol that is adsorbed on the surface of
the photocatalyst to form corresponding aldehyde I. The photogenerated
electrons can more easily transfer to TiO2 surface owing to their intimate
interfacial contact and matchable energy band position [43]. Simulta-
neously, the photogenerated electrons in the conduction band of TiO2
can directly reduce the dinitro compound that is adsorbed on the surface
Fig. 3. XPS survey scan of 1D CdS@TiO2 CSNs and High resolution XPS spectra
of hybrid CdS@TiO2 (c) Cd 3d; (d) Ti 2p (e) S 2p (f).
confirms that the recombination of the photoinduced charge carrier is
greatly inhibited in the 1D CdS@TiO2 CSNs. The separated charge car-
riers are considered to be beneficial for improved photocatalytic
activity.
In the next phase of our study, we investigated the effect of TiO2 shell
amounts on the surface of CdS NWs in the photoreduction of nitroben-
zene. For this purpose, the 1D CdS@TiO2 core/shell nanocomposites
were synthesized by 0.5 and 2.5 ml TBOT (CdS@TiO2-0.5 and
CdS@TiO2-2.5). The sample CdS@TiO2-1.5 (1.5 ml TBOT) has the
highest conversion of nitrobenzene (~100%), and the selectivity of
aniline is ~100% after 20 h of visible LED light irradiation. It is found
that the amount of TiO2 plays an important role in the photocatalytic
activities of the as-prepared samples. Initially, the increase in the
amount of TiO2 precursor (TBOT) from 0.5 ml to 1.5 ml can improve the
photocatalytic activity of the as-prepared sample because of the increase
in the amount of TiO2 on the surface of CdS nanowire. When the amount
of TiO2 precursor is greater than 1.5 ml, excess TiO2 will load on the
surface of the CdS nanowire. Therefore, sample CdS@TiO2-2.5 has low
absorption in the visible light region. As a result, sample CdS@TiO2-1.5
(1D CdS@TiO2 CSNs) shows the highest catalytic activity for the selec-
tive reduction of nitrobenzene to aniline (Table 1 entry12 and 13).
Considering the design of heterogeneous photocatalysis systems that
encourage efficient one-pot synthesis is currently the focus of attention
[57]. In continuation of our work on the reduction of nitro compounds,
Fig. 5. Wavelength distributions of blue, green, and red LED lamp (a-c) and
UV–Vis diffuses reflectance spectra of 1D CdS@TiO2 CSNs.
Fig. 4. (a) UV–Vis diffuse reflectance spectra (DRS) of the samples of CdS NWs, 1D CdS@TiO2 CSNs, and pure TiO2, (b) Plot of the transformed Kubelka-Munk
function versus the energy of light absorbed by the CdS NWs, 1D CdS@TiO2 CSNs and pure TiO2.
5

P. Eskandari et al.
Journal of Photochemistry & Photobiology, A: Chemistry 418 (2021) 113404
Table 1
Table 2
Photoreduction of nitrobenzene with 1D CdS@TiO2 CSNs.
Photosynthesis of benzimidazoles and anilides by 1D CdS@TiO2 CSNs under
blue LED irradiation.
Entry
Nitrocompounds
Product
Time
(h)
Yield
(%) a
90
1b
30
2
3
4
30
30
30
95
90
85
Entry
Photocatalyst (g)
Time
(h)
Yield
(%) a
Conversion
(%)
LED (W)
1b
2c
3
1D CdS@TiO2 CSNs
(0.08)
20
20
20
20
50
40
40
40
40
40
40
30
20
100
100
45
100
100
45
Blue (3
W)
1D CdS@TiO2 CSNs
(0.05)
Blue (3
W)
1D CdS@TiO2 CSNs
(0.02)
Blue (3
W)
5c
50
20
<10
4
1D CdS@TiO2 CSNs
(0.02)
100
<20
10
100
<20
10
Blue (6
W)
6 d
97
5 d
6
1D CdS@TiO2 CSNs
(0.02)
Blue (9
W)
1D CdS@TiO2 CSNs
(0.02)
Green (6
W)
7
8
35
20
80
98
7
1D CdS@TiO2 CSNs
(0.02)
15
15
Green (9
W)
8
CdS NWs (0.02)
30
30
Blue (6
W)
9
Pure TiO2 (0.02)
CdS NWs (0.02)
TiO2-P25 (0.02)
<10
<10
15
<10
<10
15
Blue (6
W)
10
11
12 e
13f
Blue (6
W)
9
35
20
97
95
Blue (6
W)
CdS@TiO2 ꢀ 2.5
(0.02)
5
20
Blue (6
W)
10
CdS@TiO2 ꢀ 0.5
(0.02)
80
80
Blue (6
W)
11 e
50
10
[a] GC Yield, [b] 1D CdS@TiO2 CSNs (0.08 g), [c] 1 D CdS@TiO2 CSNs (0.05 g),
[d] Nitro compounds (0.06 mmol), [e] CdS@TiO2 was synthesized by 2.5 ml
TBOT, [f] CdS@TiO2 was synthesized by 0.5 ml TBOT.
[a] GC analysis [b] Reaction condition for the synthesis of benzimidazole: Nitro
compounds (0.02 mmol), 1D CdS@TiO2 CSNs (0.02 g), and 4 ml EtOH were
degassed by argon gas and irradiated with blue LED (6 W). [c] In the same re-
action condition by TiO2-P25. [d] Reaction condition for the synthesis of anilide:
Reaction conditions: nitro compound (0.02 mmol), acetic anhydride (0.02
mmol), 1D CdS@TiO2 CSNs (0.02 g), and EtOH (4 ml) were degassed by argon
gas and irradiated with blue LED (6 W). [e] In the same reaction condition by
TiO2-P25.
pushes the equilibrium away from III. The nitrogen atom in the hy-
droxylamine group attacks the imino carbon to close the ring. Further
dehydration leads to benzimidazole.
In the following photocatalytic reduction of nitrobenzene containing
functional groups (CN, Me, COCH3, and COPh) in the presence of acetic
anhydride gave the corresponding N-phenylacetamide in excellent
yields (Table 2, entries 6–10). The condensation of the photocatalytic
formed aniline and anhydride produced N-phenylacetamide. Moreover,
as shown in the results, the presence of TiO2-P25 gives N-phenyl-
acetamide with 10% yield, while it is 97% yield in the presence of 1D
CdS@TiO2 CSNs (Table 2, entry 11, 6).
To continue evaluating the photocatalytic activity of the prepared
nanostructure, the reduction of Benzophenone (BP) derivatives were
performed under blue LED (λ ≥ 420 nm) irradiation. The reduction of
ketones to alcohols is a significant transformation in organic synthesis
and chemical industry [76–78]. Initially, the photocatalytic reduction of
BP was chosen as the model reaction. When the reaction was carried out
using BP (0.05 mmol) and 1D CdS@TiO2 CSNs (0.02 g) in i-PrOH (5 ml)
under blue LED (3 W) irradiation for 24 h, alcohol was obtained in 10%
yield. It is interesting that using ammonium formate (HCO2NH4)
significantly enhanced the conversion and alcohol yield (Table 3, entry
2). Generally, HCO2NH4 is used as a hole scavenger for the reduction of
Fig. 6. Photoluminescence (PL) spectra of CdS nanowire and 1D
CdS@TiO2 CSNs.
of the photocatalyst to form corresponding 2-nitroaniline, II (Fig. S10,
ESI†). The condensation between aldehyde I and the amino group of II
forms an imine, III. At room temperature and in the presence of a
considerable amount of water, III is in equilibrium with the aniline and
aldehyde. However, the further reduction of III into hydroxylamine, IV,
6

P. Eskandari et al.
Journal of Photochemistry & Photobiology, A: Chemistry 418 (2021) 113404
been noted that in the 4-methoxy benzophenone, increasing the amount
of photocatalyst above 0.04 g did not enhance the conversion yield, and
increasing the number of HCO2NH4 from 0.02 g to 0.04 g had a negli-
gible effect. Also, increasing the reaction time beyond 40 h did not affect
the yield. The photocatalytic reduction of BP derivatives is a well-
documented process and it has been shown that it is normally accom-
panied by the formation of pinacol via coupling of radicals over widely
used CdS-based photocatalyst [81,82].
The recyclability of the photocatalyst was also examined by the
reduction of BP as a test model and it was found that the recovery can be
successfully achieved in six successive reaction runs (Fig. S12 ESI†). In
each run, the leaching of Cd and Ti into solution was negligible as
determined by atomic absorption spectroscopy (AAS) (less than the
detection limit of 1 ppm). In addition, the stability structure of 1D
CdS@TiO2 CSNs in this mild photoreduction condition was confirmed
by SEM, TEM, and XRD analyses (Figs. S6, S7, and S8 ESI†).
4. Conclusions
In summary, 1D CdS@TiO2 CSNs were synthesized through hydro-
lysis of the titania source (Tetrabutyl titanate) by water vapor trans-
mission on the surface of CdS nanowires which were prepared via
hydrothermal method. The effect of TiO2 shell thickness on the surface
of CdS nanowire was studied on the photocatalytic properties of 1D
CdS@TiO CSNs. The selective reduction of nitroaren to anilide and
benzimidazoles, and also benzophenones to alcohol by the 1D
CdS@TiO2 CSNs under visible LED irradiation confirmed high photo-
catalytic efficiency compared to pure TiO2, CdS NWs and commercial
TiO2-P25. The excellent reusability for six runs shows the good stability
of the synthesized sample. The strong coupling between CdS and TiO2
could promote photocatalytic activity and stability. This system couples
the advantages of good stability and reusability of the photocatalyst and
low electrical power of LED irradiation as a visible light source, which
makes it a promising visible-driven photocatalyst for other organic
transformations.
Scheme 1. Proposed reaction mechanism for the formation of benzimidazole
compounds over the 1D CdS@TiO2 CSNs under visible light irradiation.
organic compounds [69,79]. A control experiment conducted without
1D CdS@TiO2 CSNs showed no reaction (Table 3, entry 5). As expected,
1D CdS@TiO2 CSNs exhibited much higher photocatalytic activity than
bare CdS NWs and pure TiO2 (Table 3, entries 8 and 9). To determine the
optimal reaction conditions, the impact of other hole scavengers such as
sodium formate and sodium oxalate [80] were examined in the photo-
catalytic reduction of BP; it was found that HCO2NH4 was better suited
for this purpose, with i-PrOH as a solvent. Notably, the selectivity of
reaction in EtOH decreased more in comparison to i-PrOH (Table 3,
entry 6). The reduction of BP in i-PrOH with HCO2NH4 (0.02 g) and
photocatalyst (0.02 g) led to complete substrate conversion and afforded
the alcohol excellent selectivity (Table 3, entry 2).
CRediT authorship contribution statement
Parvin Eskandari: Conceptualization, Formal analysis, Investiga-
tion, Methodology, Visualization, Writing - original draft, Writing - re-
view & editing. Zahra Zand: Conceptualization, Formal analysis,
Investigation, Methodology, Visualization, Writing - original draft,
Writing - review & editing. Foad Kazemi: Funding acquisition, Project
administration, Resources, Supervision, Validation, Conceptualization,
Data curation. Moosa Ramdar: Methodology.
As shown in Table 4, various BP derivatives, containing both
electron-donating and electron-withdrawing groups, were selectively
converted to the corresponding alcohols in excellent yields under the
optimal reaction conditions (Table 4, entries 1–5). These results show
that electronic effects seem to have a significant effect on the final
product yields for electron-rich and electron-deficient substrates. It has
Table 3
Optimization of Reaction Conditions in the Photocatalytic Reduction of Benzophenone derivatives.
Entry
Photocatalyst (g)
Ammonium formate (g)
Conversion (%)
Alcohol (%)a
Pinacol (%)
1
0.02
0.02
0.01
0.02
0
0
10
10
100
90
65
0
0
2
0.02
0.02
0.01
0.1
100
100
80
0
3b
4b
5
10
15
0
0
6b, c
7d
8e
9f
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
100
0
90
0
10
0
<10
<10
<10
<10
0
0
[a] GC yield, [b] HPLC analysis yield [c] EtOH as a solvent [d] Reaction in dark [e] CdS nanowire [f] pure TiO2.
7

P. Eskandari et al.
Journal of Photochemistry & Photobiology, A: Chemistry 418 (2021) 113404
Table 4
Photocatalytic reduction of benzophenone derivatives.
Entry
1
Substrate
Conversion (%)
100
Alcohol (%)a
100
Pinacol (%)
0
Selectivity (%)
100
2
100
60
100
60
0
0
0
100
100
100
3b
4
100
100
5c
100
80
20
80
Reaction conditions: BP (0.05 mmol), 1D CdS@TiO2 CSNs (0.02 g), HCO2NH4 (0.02 g) in i-PrOH (5 ml) under blue LED (3 W) irradiation. [a] GC yield, [b] HCO2NH4
(0.04 g), [c] HPLC yield.
[9] X. Lang, W. Ma, C. Chen, H. Ji, J. Zhao, Selective aerobic oxidation mediated by
Declaration of Competing Interest
TiO2 photocatalysis, Acc. Chem. Res. 47 (2) (2014) 355–363, https://doi.org/
10.1021/ar4001108.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[10] S. Munir, D.D. Dionysiou, S.B. Khan, S.M. Shah, B. Adhikari, A. Shah, Development
of photocatalysts for selective and efficient organic transformations, J. Photochem.
Photobiol. B 148 (2015) 209–222, https://doi.org/10.1016/j.
jphotobiol.2015.04.020.
[11] T.P. Yoon, M.A. Ischay, J. Du, Visible-light photocatalysis as a greener approach to
photochemical synthesis, Nat. Chem. 2 (7) (2010) 527–532, https://doi.org/
10.1038/nchem.687.
Acknowledgments
[12] D.M. Schultz, T.P. Yoon, Solar synthesis: prospects in visible-light photocatalysis,
Science 343 (2014) 1239176–1239176. https://doi.org/10.1126/
science.1239176.
The authors gratefully acknowledge the support provided by the
Institute for Advanced Studies in Basic Sciences (IASBS).
[13] Q.i. Xiao, E. Jaatinen, H. Zhu, Direct photocatalysis for organic synthesis by using
plasmonic-metal nanoparticles irradiated with visible light, Chem. Asian J. 9 (11)
(2014) 3046–3064, https://doi.org/10.1002/asia.201402310.
[14] X. Guo, C. Hao, G. Jin, H.-Y. Zhu, X.-Y. Guo, Copper nanoparticles on graphene
support: an efficient photocatalyst for coupling of nitroaromatics in visible light,
Angew. Chem. Int. Ed. 53 (7) (2014) 1973–1977, https://doi.org/10.1002/
anie.201309482.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.jphotochem.2021.113404.
[15] Y.L. Cui, X.N. Guo, Y.Y. Wang, X.Y. Guo, Visible-light-driven photocatalytic N-
arylation of imidazole derivatives and arylboronic acids on Cu/graphene catalyst,
Sci. Rep. 5 (2015) 12005–12014, https://doi.org/10.1038/srep12005.
[16] Q.i. Xiao, Z. Liu, A. Bo, S. Zavahir, S. Sarina, S. Bottle, J.D. Riches, H. Zhu, Catalytic
transformation of aliphatic alcohols to corresponding esters in O2 under neutral
conditions using visible-light irradiation, J. Am. Chem. Soc. 137 (5) (2015)
1956–1966, https://doi.org/10.1021/ja511619c.
References
[1] J.C. Colmenares, R. Luque, Heterogeneous photocatalytic nanomaterials: prospects
and challenges in selective transformations of biomass-derived compounds, Chem.
Soc. Rev. 43 (3) (2014) 765–778, https://doi.org/10.1039/C3CS60262A.
[2] X. Lang, X. Chen, J. Zhao, Heterogeneous visible-light photocatalysis for selective
organic transformations, Chem. Soc. Rev. 43 (1) (2014) 473–486, https://doi.org/
10.1039/C3CS60188A.
[17] Q.i. Xiao, S. Sarina, E.R. Waclawik, J. Jia, J. Chang, J.D. Riches, H. Wu, Z. Zheng,
H. Zhu, Alloying gold with copper makes for a highly selective visible-light
photocatalyst for the reduction of nitroaromatics to anilines, ACS Catal. 6 (3)
(2016) 1744–1753, https://doi.org/10.1021/acscatal.5b0264310.1021/
acscatal.5b02643.s001.
[3] J. Kou, C. Lu, J. Wang, Y. Chen, Z. Xu, R.S. Varma, Selectivity enhancement in
heterogeneous photocatalytic transformations, Chem. Rev. 117 (3) (2017)
1445–1514, https://doi.org/10.1021/acs.chemrev.6b00396.
[18] Y. Chen, Y. Wang, W. Li, Q. Yang, Q. Hou, L. Wei, L. Liu, F. Huang, M. Ju,
Enhancement of photocatalytic performance with the use of noble-metal-decorated
TiO2 nanocrystals as highly active catalysts for aerobic oxidation under visible-
light irradiation, Appl. Catal. B 210 (2017) 352–367, https://doi.org/10.1016/j.
apcatb.2017.03.077.
[4] D. Friedmann, A. Hakki, H. Kim, W. Choi, D. Bahnemann, Heterogeneous
photocatalytic organic synthesis: state-of-the-art and future perspectives, Green
Chem. 18 (20) (2016) 5391–5411, https://doi.org/10.1039/C6GC01582D.
[5] T. Al-Fahdi, F. Al Marzouqi, A.T. Kuvarega, B.B. Mamba, S.M. Al Kindy, Y. Kim,
R. Selvaraj, Visible-light active CdS@ TiO2 core-shell nanostructures for the
photodegradation of chlorophenols, J. Photochem. Photobiol. A 374 (2019) 75–83,
https://doi.org/10.1016/j.jphotochem.2019.01.019.
[19] T. Tana, X.-W. Guo, Q.i. Xiao, Y. Huang, S. Sarina, P. Christopher, J. Jia, H. Wu,
H. Zhu, Non-plasmonic metal nanoparticles as visible-light photocatalysts for the
selective oxidation of aliphatic alcohols with molecular oxygen at near ambient
conditions, Chem. Commun. 52 (77) (2016) 11567–11570, https://doi.org/
10.1039/C6CC05186C.
¨
[6] B. Konig, Photocatalysis in organic synthesis-past, present, and future, Eur. J. Org.
Chem. 2017 (2017) 1979–1981, https://doi.org/10.1002/ejoc.201700420.
[7] C. Ling, X. Ye, J. Zhang, J. Zhang, S. Zhang, S. Meng, X. Fu, S. Chen, Solvothermal
synthesis of CdIn2S4 photocatalyst for selective photosynthesis of organic aromatic
compounds under visible light, Sci. Rep. 7 (2017) 1–16, https://doi.org/10.1038/
s41598-017-00055-5.
[20] X. Wang, D. Baiyila, X. Li, Macroporous TiO2 encapsulated Au@Pd bimetal
nanoparticles for the photocatalytic oxidation of alcohols in water under visible
light, RSC Adv. 6 (109) (2016) 107233–107238, https://doi.org/10.1039/
C6RA22299D.
[8] X. Chen, J. Zhang, X. Fu, M. Antonietti, X. Wang, Fe-g-C3N4-catalyzed oxidation of
benzene to phenol using hydrogen peroxide and visible light, J. Am. Chem. Soc.
131 (33) (2009) 11658–11659, https://doi.org/10.1021/ja903923s.
[21] M.-Q. Yang, N. Zhang, Y.-J. Xu, Synthesis of fullerene–, carbon nanotube–, and
graphene–TiO2 nanocomposite photocatalysts for selective oxidation: a
comparative study, ACS Appl. Mat. Int. 5 (3) (2013) 1156–1164, https://doi.org/
10.1021/am3029798.
8

P. Eskandari et al.
Journal of Photochemistry & Photobiology, A: Chemistry 418 (2021) 113404
[22] M. Qamar, R.B. Elsayed, K.R. Alhooshani, M.I. Ahmed, D.W. Bahnemann, Highly
efficient and selective oxidation of aromatic alcohols photocatalyzed by
nanoporous hierarchical Pt/Bi2WO6 in organic solvent-free environment, ACS
Appl. Mat. Int. 7 (2) (2015) 1257–1269, https://doi.org/10.1021/am507428r.
[23] J. Si, Y.a. Liu, S. Chang, D.i. Wu, B. Tian, J. Zhang, AgBr@TiO2/GO ternary
composites with enhanced photocatalytic activity for oxidation of benzyl alcohol to
benzaldehyde, Res. Chem. Intermed. 43 (4) (2017) 2067–2080, https://doi.org/
10.1007/s11164-016-2747-9.
[46] X. Li, X. Chen, H. Niu, X. Han, T. Zhang, J. Liu, H. Lin, F. Qu, The synthesis of CdS/
TiO2 hetero-nanofibers with enhanced visible photocatalytic activity, J. Colloid
Interface Sci. 452 (2015) 89–97, https://doi.org/10.1016/j.jcis.2015.04.034.
[47] Sudheer Kumar Yadav, P. Jeevanandam, Thermal decomposition approach for the
synthesis of CdS–TiO2 nanocomposites and their catalytic activity towards
degradation of rhodamine B and reduction of Cr (VI), Ceram. Int. 41 (2) (2015)
2160–2179, https://doi.org/10.1016/j.ceramint.2014.10.016.
[48] Na Qin, Yuhao Liu, Weiming Wu, Lijuan Shen, Xun Chen, Zhaohui Li, Ling Wu,
One-dimensional CdS/TiO2 nanofiber composites as efficient visible-light-driven
photocatalysts for selective organic transformation: synthesis, characterization,
and performance, Langmuir 31 (3) (2015) 1203–1209, https://doi.org/10.1021/
la503731y.
[24] P. Zhang, P. Wu, S. Bao, Z. Wang, B. Tian, J. Zhang, Synthesis of sandwich-
structured AgBr@Ag@TiO2 composite photocatalyst and study of its photocatalytic
performance for the oxidation of benzyl alcohols to benzaldehydes, Chem. Eng. J.
306 (2016) 1151–1161, https://doi.org/10.1016/j.cej.2016.08.015.
[25] B. Han, S. Liu, Y.-J. Xu, Z.-R. Tang, 1D CdS nanowire–2D BiVO4 nanosheet
heterostructures toward photocatalytic selective fine-chemical synthesis, RSC Adv.
5 (21) (2015) 16476–16483, https://doi.org/10.1039/C4RA16397D.
[26] M. Anpo, N. Aikawa, S. Kodama, Y. Kubokawa, Photocatalytic hydrogenation of
alkynes and alkenes with water over titanium dioxide. hydrogenation accompanied
by bond fission, J. Phys. Chem. 88 (12) (1984) 2569–2572, https://doi.org/
10.1021/j150656a028.
[49] S. Qian, C. Wang, W. Liu, Y. Zhu, W. Yao, X. Lu, An enhanced CdS/TiO2
photocatalyst with high stability and activity: effect of mesoporous substrate and
bifunctional linking molecule, J. Mater. Chem. 21 (2011) 4945–4952, https://doi.
org/10.1039/C0JM03508D.
[50] T. Lv, L. Pan, X. Liu, T. Lu, G. Zhu, Z. Sun, C.Q. Sun, One-step synthesis of
CdS–TiO2–chemically reduced graphene oxide composites via microwave-assisted
reaction for visible-light photocatalytic degradation of methyl orange, Catal. Sci.
Technol. 2 (2012) 754–758, https://doi.org/10.1039/C2CY00452F.
[51] H. Park, W. Choi, M.R. Hoffmann, Effects of the preparation method of the ternary
CdS/TiO2/Pt hybrid photocatalysts on visible light-induced hydrogen production,
J. Mater. Chem. 18 (2008) 2379–2385, https://doi.org/10.1039/B718759A.
[52] Jun Fang, Lin Xu, Zhenyi Zhang, Yupeng Yuan, Shaowen Cao, Zheng Wang,
Lisha Yin, Yusen Liao, Can Xue, Au@TiO2–CdS ternary nanostructures for efficient
visible-light-driven hydrogen generation, ACS Appl. Mater. Interfaces 5 (16)
(2013) 8088–8092, https://doi.org/10.1021/am4021654.
´
´
[27] A. Hernandez-Gordilloa, V.R. Gonzalez, Silver nanoparticles loaded on Cu-doped
TiO2 for the effective reduction of nitro-aromatic contaminants, Chem. Eng. J. 261
(2015) 53–59, https://doi.org/10.1016/j.cej.2014.05.148.
[28] Z. Chen, S. Liu, M.-Q. Yang, Y.-J. Xu, Synthesis of uniform CdS nanospheres/
graphene hybrid nanocomposites and their application as visible-light
photocatalyst for selective reduction of nitro organics in water, ACS Appl. Mater.
Interfaces 5 (10) (2013) 4309–4319, https://doi.org/10.1021/am4010286.
[29] M. Kaur, C.M. Nagaraja, Template-free synthesis of Zn1–xCdxS nanocrystals with
tunable band structure for efficient water splitting and reduction of nitroaromatics
in water, ACS Sustainable Chem. Eng. 5 (5) (2017) 4293–4303, https://doi.org/
10.1021/acssuschemeng.7b0032510.1021/acssuschemeng.7b00325.s001.
[30] Q. Xiao, Z. Liu, F. Wang, S. Sarina, H. Zhu, Tuning the reduction power of visible-
light photocatalysts of gold nanoparticles for selective reduction of nitroaromatics
to azoxy-compounds—tailoring the catalyst support, Appl. Catal., B 209 (2017)
69–79, https://doi.org/10.1016/j.apcatb.2017.03.002.
[53] Shinya Higashimoto, Yoshimi Tanaka, Ryo Ishikawa, Shoko Hasegawa,
Masashi Azuma, Hiroyoshi Ohue, Yoshihisa Sakata, Selective dehydrogenation of
aromatic alcohols photocatalyzed by Pd-deposited CdS–TiO2 in aqueous solution
using visible light, Catal. Sci. Technol. 3 (2) (2013) 400–403, https://doi.org/
10.1039/C2CY20607B.
[54] Shinya Higashimoto, Yuta Nakai, Masashi Azuma, Masanari Takahashi,
Yoshihisa Sakata, One-pot synthesis of imine from benzyl alcohol and nitrobenzene
on visible-light responsive CdS–TiO2 photocatalysts, RSC Adv. 4 (71) (2014)
37662–37668, https://doi.org/10.1039/C4RA06231K.
[31] Z. Liu, Y. Huang, Q.i. Xiao, H. Zhu, Selective reduction of nitroaromatics to azoxy
compounds on supported Ag–Cu alloy nanoparticles through visible-light
irradiation, Green Chem. 18 (3) (2016) 817–825, https://doi.org/10.1039/
C5GC01726B.
[55] Yanhong Tang, Xu Hu, Chengbin Liu, Perfect inhibition of CdS photocorrosion by
graphene sheltering engineering on TiO2 nanotube array for highly stable
photocatalytic activity, Phys. Chem. Chem. Phys. 16 (46) (2014) 25321–25329,
https://doi.org/10.1039/C4CP04057K.
[32] S. Fuldner, P. Pohla, H. Bartling, S. Dankesreiter, R. Stadler, M. Gruber, A. Pfitzner,
B. Konig, Selective photocatalytic reductions of nitrobenzene derivatives using
PbBiO2X and blue light, Green Chem. 13 (2011) 640–643, https://doi.org/
10.1039/C0GC00857E.
[56] Siqi Liu, Nan Zhang, Zi-Rong Tang, Yi-Jun Xu, Synthesis of One-dimensional CdS@
TiO2 core-shell nanocomposites photocatalyst for selective redox: the dual role of
TiO2 shell, ACS Appl. Mater. Interfaces 4 (11) (2012) 6378–6385, https://doi.org/
10.1021/am302074p.
[33] A. Kumar, P. Kumar, S. Paul, S.L. Jain, Visible light-assisted reduction of
nitrobenzenes using Fe (bpy)+3 2/rGO nanocomposite as photocatalyst, Appl. Sur.
Sci. 386 (2016) 103–114, https://doi.org/10.1016/j.apsusc.2016.05.139.
[34] L. Zhang, X. He, X. Xu, C. Liu, Y. Duan, L. Hou, Q. Zhou, C. Ma, X. Yang, R. Liu,
F. Yang, L. Cui, C. Xu, Y. Li, Highly active TiO2/g-C3N4/G photocatalyst with
extended spectral response towards selective reduction of nitrobenzene, Appl.
Catal. B 203 (2017) 1–8, https://doi.org/10.1016/j.apcatb.2016.10.003.
[35] P. Sharma, Y. Sasson, A photoactive catalyst Ru–g-C3N4 for hydrogen transfer
reaction of aldehydes and ketones, Green Chem. 19 (3) (2017) 844–852, https://
doi.org/10.1039/C6GC02949C.
[57] Y. Shiraishi, M. Ikeda, D. Tsukamoto, S. Tanaka, T. Hirai, One-pot synthesis of
benzimidazoles by simultaneous photocatalytic and catalytic reactions on Pt@TiO2
nanoparticles, Angew. Chem. Int. Ed. 49 (2010) 1656–1660, https://doi.org/
10.1002/anie.200906573.
[58] Y. Shiraishi, M. Ikeda, D. Tsukamoto, S. Tanaka, T. Hirai, One-pot synthesis of
imines from alcohols and amines with TiO2 loading Pt nanoparticles under UV
irradiation, Chem. Commun. 47 (2011) 4811–4813, https://doi.org/10.1039/
C0CC05615D.
¨
[36] T. Ghosh, T. Slanina, B. Konig, Visible-light photocatalytic reduction of aldehydes
[59] Qianqian Wang, Youquan Deng, Feng Shi, NaF regulated aqueous phase synthesis
of aromatic amides and imines catalyzed by Au/HT, Catal. Sci. Technol. 4 (6)
(2014) 1710–1715, https://doi.org/10.1039/C4CY00210E.
by Rh(iii)–H: a detailed mechanistic study, Chem. Sci. 6 (2015) 2027–2034,
https://doi.org/10.1039/C4SC03709J.
´
[37] S. Kohtani, S. Nishioka, E. Yoshioka, H. Miyabe, Kinetic study on photocatalytic
hydrogenation of acetophenone derivatives on titanium dioxide, Catal. Sci.
Technol. 4 (2014) 1084–1091, https://doi.org/10.1039/C3CY00879G.
[38] S. Kohtani, S. Nishioka, E. Yoshioka, H. Miyabe, Dye-sensitized photo-
hydrogenation of aromatic ketones on titanium dioxide under visible-light
irradiation, Catal. Commun. 43 (2014) 61–65, https://doi.org/10.1016/j.
catcom.2013.09.006.
[60] David Stíbal, Jacinto Sa, Jeroen A. van Bokhoven, One-pot photo-reductive N-
alkylation of aniline and nitroarene derivatives with primary alcohols over
Au–TiO2, Catal. Sci. Technol. 3 (1) (2013) 94–98, https://doi.org/10.1039/
C2CY20511D.
[61] K. Selvam, B. Krishnakumar, R. Velmurugan, M. Swaminathan, A simple one-pot
nano titania mediated green synthesis of 2-alkylbenzimidazoles and indazole from
aromatic azides under UV and solar light, Catal. Commun. 11 (4) (2009) 280–284,
https://doi.org/10.1016/j.catcom.2009.10.015.
[39] S. Kohtani, M. Mori, E. Yoshioka, H. Miyabe, Photohydrogenation of acetophenone
using coumarin dye-sensitized titanium dioxide under visible-light irradiation,
Catalysts 5 (2015) 1417–1424, https://doi.org/10.3390/catal5031417.
[40] G. Palmisano, V. Augugliaro, M. Pagliaro, L. Palmisano, Photocatalysis: a
promising route for 21st century organic chemistry, Chem. Commun. (2007)
3425–3437, https://doi.org/10.1039/B700395C.
[62] K. Selvam, M. Swaminathan, An easy one-step photocatalytic synthesis of 1-aryl-2-
alkylbenzimidazoles by platinum loaded TiO2 nanoparticles under UV and solar
light, Tetrahedron Lett. 52 (26) (2011) 3386–3392, https://doi.org/10.1016/j.
tetlet.2011.04.090.
[63] Sedigheh Abedi, Babak Karimi, Foad Kazemi, Mihnea Bostina, Hojatollah Vali,
Amorphous TiO2 coated into periodic mesoporous organosilicate channels as a new
binary photocatalyst for regeneration of carbonyl compounds from oximes under
sunlight irradiation, Org. Biomol. Chem. 11 (3) (2013) 416–419, https://doi.org/
10.1039/C2OB26907D.
[41] Amy L. Linsebigler, Guangquan Lu, John T. Yates, Photocatalysis on TiO2 surfaces:
principles, mechanisms, and selected results, Chem. Rev. 95 (3) (1995) 735–758,
https://doi.org/10.1021/cr00035a013.
[42] J.C. Yu, L. Wu, J. Lin, P.S. Li, Q. Li, Microemulsion-mediated solvothermal
synthesis of nanosized CdS-sensitized TiO2 crystalline photocatalyst, Chem.
Commun. (2003) 1552–1553, https://doi.org/10.1039/B302418K.
[43] Nan Zhang, Yanhui Zhang, Xiaoyang Pan, Min-Quan Yang, Yi-Jun Xu, Constructing
ternary CdS–graphene–TiO2 hybrids on the flatland of graphene oxide with
enhanced visible-light photoactivity for selective transformation, J. Phys. Chem. C
116 (34) (2012) 18023–18031, https://doi.org/10.1021/jp303503c.
[44] Z. Tian, N. Yu, Y. Cheng, Z. Wang, Z. Chen, L. Zhang, Hydrothermal synthesis of
graphene/TiO2/CdS nanocomposites as efficient visible-light-driven
photocatalysts, Mat. Lett. 194 (2017) 172–175, https://doi.org/10.1016/j.
matlet.2017.02.048.
[64] M. Abdollahi Kakroudi, F. Kazemi, B. Kaboudin, Highly efficient photodeoximation
under green and blue LEDs catalyzed by mesoporous C-N codoped nano TiO2,
J. Molec. Catal. A 392 (2014) 112–119, https://doi.org/10.1016/j.
molcata.2014.04.036.
[65] Mazaher Abdollahi Kakroudi, Foad Kazemi, Babak Kaboudin, β-cyclodextrin–TiO2:
green nest for reduction of nitroaromatic compounds, RSC Adv. 4 (95) (2014)
52762–52769, https://doi.org/10.1039/C4RA08059A.
[66] Z. Zand, F. Kazemi, A. Partovi, Photocatalytic synthesis of anilides from
nitrobenzenes under visible-light irradiation: 2 in 1 reaction, J. Photochem.
Photobiol. B 152 (2015) 58–62, https://doi.org/10.1016/j.
[45] W. Dong, F. Pan, L. Xu, M. Zheng, C. Haur Sow, K. Wu, G.Q. Xu, W. Chen, Facile
synthesis of CdS@TiO2 core–shell nanorods with controllable shell thickness and
enhanced photocatalytic activity under visible-light irradiation, Appl. Surf. Sci.
349 (2015) 279–286, https://doi.org/10.1016/j.apsusc.2015.04.207.
jphotobiol.2015.02.010.
[67] Zahra Zand, Foad Kazemi, Saber Hosseini, Development of chemoselective
photoreduction of nitro compounds under solar light and blue LED irradiation,
9

P. Eskandari et al.
Journal of Photochemistry & Photobiology, A: Chemistry 418 (2021) 113404
Tetrahedron Lett. 55 (2) (2014) 338–341, https://doi.org/10.1016/j.
synthesis of benzimidazoles, New J. Chem. 42 (2018) 6449–6456, https://doi.org/
10.1039/C8NJ00351C.
tetlet.2013.11.023.
[68] P. Eskandari, F. Kazemi, Preparation and Characterization of Fe3O4/SiO2/CdS
nanocomposites as efficient magnetic photocatalysts for the reduction of nitro
compounds under visible LED irradiation, J. Photochem. Photobiol. A 364 (2018)
233–239, https://doi.org/10.1016/j.jphotochem.2018.06.011.
[69] P. Eskandari, F. Kazemi, Z. Zand, Photocatalytic reduction of aromatic nitro
compounds using CdS nanostructure under blue LED irradiation, J. Photochem.
Photobiol. A 274 (2014) 7–12, https://doi.org/10.1016/j.
[76] F.Z. Su, L. He, J. Ni, Y. Cao, H.Y. He, K.N. Fan, Efficient and chemoselective
reduction of carbonyl compounds with supported gold catalysts under transfer
hydrogenation conditions, Chem. Commun. (2008) 3531–3533, https://doi.org/
10.1039/B807608A.
[77] Yan Zhu, Huifeng Qian, BethanyA. Drake, Rongchao Jin, Atomically Precise Au25
(SR)18 nanoparticles as catalysts for the selective hydrogenation of α, β-unsaturated
ketones and aldehydes, Angew. Chem. Int. Ed. 49 (7) (2010) 1295–1298, https://
jphotochem.2013.09.011.
doi.org/10.1002/anie.200906249.
´
´
[70] P. Yan, Y. Xie, Y. Qian, X. Liu, A cluster growth route to quantum-confined CdS
nanowires, Chem. Commun. (1999) 1293–1294, https://doi.org/10.1039/
A901821B.
[78] E. Albiter Escobar, M.A. Valenzuela Zapata, S. Alfaro Hernandez, S. O. Flores Valle,
´
´
´
O. Ríos Berny, V.J. Gonzalez Angeles, I. Cordova Reyes, Photocatalytic reduction of
benzophenone on TiO2: effect of preparation method and reaction conditions. J.
Mex. Chem. Soc. 54 (2010) 133–138. https://doi.org/10.29356/jmcs.v54i3.924.
[79] Siqi Liu, Zhang Chen, Nan Zhang, Zi-Rong Tang, Yi-Jun Xu, An efficient self-
assembly of Cds nanowires-reduced graphene oxide nanocomposites for selective
reduction of nitro organics under visible-light irradiation, J. Phys. Chem. C 117
(16) (2013) 8251–8261, https://doi.org/10.1021/jp400550t.
[71] Rajesh J. Tayade, Thillai Sivakumar Natarajan, Hari C. Bajaj, Photocatalytic
degradation of methylene blue dye using ultraviolet light emitting diodes, Ind. Eng.
Chem. Res. 48 (23) (2009) 10262–10267, https://doi.org/10.1021/ie9012437.
[72] P. Eskandari, F. Kazemi, Y. Azizian, convenient Preparation of CdS nanostructures
as a highly efficient photocatalyst under blue LED and solar light irradiation, Sep.
Pur. Technol. 120 (2013) 180–185, https://doi.org/10.1016/j.
seppur.2013.09.039.
[80] Zhi Geng, Zhiting Chen, Zhaoyang Li, Xin Qi, Xia Yang, Wei Fan, Yingna Guo,
Leilei Zhang, Mingxin Huo, Enhanced photocatalytic conversion and selectivity of
nitrate reduction to nitrogen over AgCl/TiO2 nanotubes, Dalton Trans. 47 (32)
(2018) 11104–11112, https://doi.org/10.1039/C8DT01915K.
[73] Hongyu Wang, Richard E. Partch, Yuzhuo Li, Synthesis of 2-alkylbenzimidazoles
via TiO2-mediated photocatalysis, J. Org. Chem. 62 (15) (1997) 5222–5225,
https://doi.org/10.1021/jo970253j.
[81] Tsutomu. Shiragami, Chyongjin. Pac, Shozo. Yanagida, Visible-light-induced two-
electron-transfer photoreductions on cadmium sulfide: effects of morphology,
J. Phys. Chem. 94 (2) (1990) 504–506, https://doi.org/10.1021/j100365a002.
[82] Shozo Yanagida, Tomoyuki Ogata, Akihiro Shindo, Hiroji Hosokawa,
Hirotaro Mori, Takao Sakata, Yuji Wada, Semiconductor photocatalysis: size
control of surface-capped CdS nanocrystallites and the quantum size effect in their
photocatalysis, Bull. Chem. Soc. Jpn. 68 (3) (1995) 752–758, https://doi.org/
10.1246/bcsj.68.752.
[74] Suvendu Samanta, Sudipto Das, Papu Biswas, Photocatalysis by 3,6-disubstituted-s-
tetrazine: visible-light driven metal-free green synthesis of 2-substituted
benzimidazole and benzothiazole, J. Org. Chem. 78 (22) (2013) 11184–11193,
https://doi.org/10.1021/jo401445j.
[75] A. Eskandari, M. Jafarpour, A. Rezaeifard, M. Salimi, A dendritic TiO2–Co(ii)
nanocomposite based on the melamine catalyzed one-pot aerobic photocatalytic
10