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The inhibition of electrons-holes recombination and enhancement of visible light photocatalytic activity were accomplished by the synthesized TiO2/CS nanocomposites system. In this present work, the different weight ratio of TiO2 and chitosan (75:25, 50:50 and 25:75) nanocomposites were synthesized via two-step method. After that, the existing functional groups, size and structure of the nanocomposites system were characterized via FT-IR, TEM and XRD measurements. The band gap of the prepared materials and its excitation and emission spectra were elevated through UV-vis and PL analyses. Moreover, the MO and MB degradation capability of the synthesized TiO2/CS nanocomposites was optimized, and the outcomes are described in detail.
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UNCORRECTED PROOF
Journal of Photochemistry & Photobiology, A: Chemistry xxx (2017) xxx-xxx
Contents lists available at ScienceDirect
Journal of Photochemistry & Photobiology, A: Chemistry
journal homepage: www.elsevier.com
Line defect Ce3+ induced Ag/CeO2/ZnO nanostructure for visible-light photocatalytic
activity
R. Saravanana, Shilpi Agarwalb, Vinod Kumar Guptab, c, , Mohammad Mansoob Khand, F. Graciaa, E. Mosquerae,
V. Narayananf, A. Stepheng,
aDepartment of Chemical Engineering and Biotechnology, University of Chile, Beauchef 850, Santiago, Chile
bDepartment of Applied Chemistry, University of Johannesburg, Johannesburg, South Africa
cDepartment of Biological Sciences, King Abdulaziz University, Jeddah 21589, Saudi Arabia
dChemical Sciences, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong, BE 1410, Brunei Darussalam
eDepartamento de Física, Universidad del Valle, A.A. 25360, Cali, Colombia
fDepartment of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai, 600 025, India
gDepartment of Nuclear Physics, University of Madras, Guindy Campus, Chennai, 600 025, India
ARTICLE INFO
Article history:
Received 27 October 2017
Received in revised form 7 December 2017
Accepted 8 December 2017
Available online xxx
Keywords:
Silver nanoparticles
Narrow band gap
Oxygen vacancy
Defects
Photocatalyts
Visible light
ABSTRACT
This article reports, synthesis and characterization of the ternary Ag/CeO2/ZnO nanostructure which was
tested for visible light photocatalytic degradation of industrial textile effluent. The HR-TEM and XPS results
confirms the presence of line dislocation linear defect induced oxygen vacancy in the ternary Ag/CeO2/ZnO
nanostructure. The oxygen vacancy creates narrow band gap (2.66 eV) was confirmed by DRS. The ternary
Ag/CeO2/ZnO nanostructure showed superior photocatalytic activity compared with pure ZnO, ZnO/Ag and
ZnO/CeO2results because of the narrow band gap, surface plasmon resonance (SPR) of Ag nanoparticles,
synergistic effects, and defects (Ce3+ and oxygen vacancy) in CeO2and ZnO.
© 2017.
1. Introduction
Advancement in nanostructure developments bring out wide range
of industrial, health and environmental applications. The nanomateri-
als acquired have novel properties in which the reactions are carried
out by altering the reaction conditions [1–3]. Currently environmental
hazard is one of the significant topics of scientific topics of research.
There are large number of polluting agents present in the atmosphere
due to exceeding world’s population which encourages huge number
of industries, vehicles and so on. Our day to day life of utilizing pol-
luted air and water does not provide good health benefits, because of
the presence of harmful chemicals [4]. Practice of dumping waste wa-
ters into the fresh water sources like rivers, streams, lakes and oceans
brings about variety of health risks to human beings, plants and an-
imals [4]. Hoffman et al. has reported that more than 70% of waste
disposal includes toxic chemicals, the primary cause for the conta-
mination of underground water resources [5]. One of the major rea-
sons for water pollution is untreated industrial textile dyes, since it
Corresponding authors.
Email addresses: vinodfcy@iitr.ac.in, vinodfcy@gmail.com (V.K. Gupta);
stephen_arum@hotmail.com (A. Stephen)
is being released into most of the water resources without any kind of
treatment processes. It creates harmful environment and hence several
diseases to human beings, plants and animals [4–8].
In recent decades, researchers are putting their efforts to utilize
various semiconductor nano metal oxides for photocatalytic degrada-
tion process in the waste water treatment [5–9]. Photocatalytic degra-
dation process is gaining much attention in degrading the pollutants
by the most inexpensive route, because it requires small amount of
catalysts, no need of special equipment and requires very less energy
for generation of electrons and holes [5,7]. Apart from various metal
oxides, zinc oxide (ZnO) is a cost effective large band gap semicon-
ductor used for versatile applications due to its fascinating proper-
ties like non-toxicity, chemical and physical stability [10–12]. One of
the disadvantage of ZnO is its large band gap that inhibits to make
electrons and holes during the photocatalytic processes under visi-
ble light illumination [13,14]. Recently, modification of ZnO by var-
ious methods to utilize the ZnO based photocatalyst under visible
light irradiation [13,14]. Earlier, we had described that in ZnO/CeO2
nanocomposite the synergetic effect between ZnO and CeO2semicon-
ductor stimulated the formation of more electrons and holes during
visible light irradiation, which promotes superior degradation of meth-
ylene blue in 150 min [15]. In case of ZnO/Ag nanocomposite the
surface defect has induced to inhibit electron-hole pairs recombina
https://doi.org/10.1016/j.jphotochem.2017.12.011
1010-6030/© 2017.
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2 Journal of Photochemistry & Photobiology, A: Chemistry xxx (2017) xxx-xxx
tion during the photocatalytic process, which led to improve the effi-
ciency of the degradation of MB in 2 h under visible light irradiation
[13].
Therefore, the main objective of this work is to synthesize a novel
nanostructure which can be used to degrade dyes and industrial tex-
tile effluent (real samples) under visible light irradiation, enhance
the photocatalytic degradation efficiency and minimize the irradiation
time compared with previously reported photocatalysts [13,15]. The
ternary Ag/CeO2/ZnO nanocomposite was synthesized by an inex-
pensive thermal decomposition method. The morphological, structural
and chemical composition of the photocatalyst was characterized by
various standard techniques. Furthermore, the ternary Ag/CeO2/ZnO
nanostructure was efficiently used to degrade the model dyes such as
MO, MB and Phenol as well as industrial textile effluent (real sample
analysis) under visible light irradiation.
2. Experimental procedure
2.1. Materials
Silver acetate, cerium (III) acetate hydrate, zinc acetate dehydrate,
methylene blue (MB) and methyl orange (MO) were purchased from
Sigma-Aldrich. All the aqueous solutions were prepared using double
distilled water.
2.2. Synthesis of ternary Ag/CeO2/ZnO nanostructure as
photocatalyst
The synthesis of ternary Ag/CeO2/ZnO nanostructure was based
on the vapor to solid mechanism [16]. Based on this mechanism, the
synthesis procedure of ternary Ag/CeO2/ZnO nanostructure as fol-
lows: weight ratio (10:10:80) of silver acetate, cerium (III) acetate hy-
drate and zinc acetate dihydrate (raw materials) were mixed together
and grounded for 3 h using a mortar (agate). The grounded reac-
tants (raw materials) were reserved into an alumina crucible and cal-
cined with the use of muffle furnace at 350 °C for 3 h. At first, the
mixed reactants get dehydrated (100 °C to 150 °C) and gives an-
hydrous mixed acetates. Further, the temperature was slowly rising
(150 °C − 350 °C). In this duration, the mixed acetates was decom-
posed well along with vaporization gets started. Moreover, the muf-
fle furnace temperature was reduced slowly (4 °C per min), the vapor-
ized materials get condensed and settled in a crucible at room tem-
perature. Finally, we got ternary Ag/CeO2/ZnO nanostructure powder
which was used for characterization and photocatalytic degradation of
model dyes and industrial textile effluent (real sample analysis).
2.3. Photocatalytic experiment
In this work, we have preferred industrial textile (real sample) ef-
fluent and two azo dyes (MO and MB) and phenol solution for degra-
dation under visible light irradiation. The degradation of colorants
is extremely important since industrial textile waste water comprises
with a lot of colored and harmful substances [17]. The preparation of
dyes solution and industrial textile effluent procedures were adopted
from previous report13.In short, initially, 500 mg of photocatalyst was
mixed with 500 mL of aqueous solutions of pollutants (MO, MB, Phe-
nol and industrial textile dye) in a 600 mL cylindrical vessel. The so-
lutions were again stirred in the dark for 30 min to complete the ad-
sorption and desorption equilibrium on the photocatalysts. The source
of the visible light was a solar simulator (SCIENCETECH, model No:
SF300B, along with AM 1.5G filter which is due to given standard
solar spectrum. The illumination intensity of a light irradiation at the
sample surface was 100 mW/cm2. Initial (without irradiation) and ir-
radiated samples were analyzed using UV–vis spectrophotometer for
dye degradation and TOC measurements for real textile effluent.
2.4. Characterization details
The structure and crystallite size of the prepared ternary Ag/
CeO2/ZnO nanostructure was determined by X-ray diffractometer
(Rich Seifert 3000, Germany) using Cu Kα1 radiation with
λ = 1.5406 Å. The presence of elements in the photocatalyst and their
oxidation states were examined using X-ray photoelectron spec-
troscopy (XPS, DRA 400–XM1000 OMICRON, ESCA+, Omicron
Nanotechnology, Germany). Specific surface area was calculated us-
ing Brunauer–Emmett–Teller (BET, Micromeritics ASAP 2020,
USA) equation. Surface morphology, elemental analysis and energy
dispersive X-ray spectroscopy (EDS) analyses were carried out us-
ing field emission scanning electron microscope (FE-SEM, HI-
TACHI-SU6600, Hitachi, Japan). The microstructure, interfaces and
elemental mapping was performed by high resolution transmission
electron microscope and scanning transmission electron microscope
(HR-TEM and STEM, Tecnai F20-FEI, USA). The optical band gap
of the photocatalyst was calculated from diffuse reflectance spectra
(DRS) by using a UV–VIS-NIR spectrophotometer (VARIAN CARY
5E, USA). The photocatalytic degradation activities were measured
using UV–vis spectrophotometer (RX1, Perkin − Elmer, USA).
3. Results and discussion
The X-ray diffraction pattern of ternary Ag/CeO2/ZnO nanostruc-
ture is depicted in Fig. 1. All the characteristic peaks are indexed per-
fectly with the JCPDS files. From Fig. 1, it was identified that the
diffraction pattern consists of ZnO, Ag along with CeO2peaks. The
XRD pattern of ZnO shows (100), (002), (101), (102), (110), (103),
(112), (201) and (200) planes which describe the hexagonal structure
(JCDPS No. 79-0208) along with (111), (200), and (202) planes which
corresponds to the cubic structure of Ag (JCPDS No. 89–5899) which
are represented by ‘#’ in Fig. 1. In addition, the ‘*’ mark represented
the (111) and (200) planes for cubic structure of CeO2, which is in ac-
cordance with the JCPDS. No. 65–2975. No other impurities were de-
tected in the XRD pattern. Therefore, XRD result has confirmed the
synthesis of ternary Ag/CeO2/ZnO nanostructure.
Fig. 1. XRD patterns of ternary Ag/CeO2/ZnO nanostructure.
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Journal of Photochemistry & Photobiology, A: Chemistry xxx (2017) xxx-xxx 3
The surface chemical composition and chemical states of the
ternary Ag/CeO2/ZnO nanostructure was examined by XPS and its
survey spectrum is shown in Fig. 2(a) which confirms that it con-
sists of Ag, Ce, Zn, O and C elements. The binding energy (BE)
values at 1021.1 eV and 1044.3 eV represents Zn 2p3/2 and Zn 2p1/
2peaks (Fig. 2(b)) for Zn in ternary Ag/CeO2/ZnO nanostructure
which indicates that Zn exists in +2 oxidation state [13]. The high
resolution XPS spectrum of Ag is shown in Fig. 2(c) which shows
peaks of Ag 3d5/2 and Ag 3d3/2 at BE 366.1 eV and 372.1 eV, re-
spectively, which are core level Ag 3d spectra of the silver nanopar-
ticles (AgNPs) with 6.0 eV splitting between the two peaks, which
is attributed to the complete reduction of Ag+to Ag00 [13,18]. How-
ever, the BE of Ag 3d5/2 shifted to a lower BE compared to the
corresponding value of the synthesized pure metallic Ag (the BE
of Ag00 is 368.2 eV) [17]. This is attributed to the formation of
AgNPs in the nanostructure18. The high resolution
scanning XPS spectrum of cerium along with the satellite peaks are
presented in Fig. 2(d). The binding energies are 881.7 eV and
905.8 eV for Ce 3d5/2 and Ce 3d3/2 peaks which confirm that cerium
exists in +4 oxidation state in the ternary Ag/CeO2/ZnO nanostructure
[19].
In the XPS analysis also confirms the presence of both Ce4+ and
Ce3+ in ternary Ag/CeO2/ZnO nanostructure, which is due to the for-
mation of more defects and/or an amorphous phase of Ce2O3. As indi-
cated by XPS the ternary Ag/CeO2/ZnO nanostructure contained Ce3+
and defects which might lead to the formation of a surface state en-
ergy band of oxygen. The oxygen adsorption, desorption and diffu-
sion processes may occur easily on the surface of the ternary Ag/
CeO2/ZnO nanostructure, that can greatly enhance their optical prop-
erties and imparts visible light photocatalytic activity8. Therefore, a
new Fermi energy level in ternary Ag/CeO2/ZnO nanostructure is
formed, indicating a strong interaction between Ag, CeO2and ZnO
Fig. 2. XPS spectra of ternary Ag/CeO2/ZnO nanostructure (a) Survey spectrum, (b) HR-XPS spectrum of Zn 2p, (c) HR-XPS spectrum of Ag 3d, (d) HR-XPS spectrum of Ce 3d,
and, (e) HR-XPS spectrum of O 1s.
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4 Journal of Photochemistry & Photobiology, A: Chemistry xxx (2017) xxx-xxx
nanoparticles18. Once the AgNPs are formed along with the CeO2,
and ZnO, electron transfer occurs from Ag to CeO2to ZnO because
the work function of silver (4.26 eV) is smaller than that of CeO2
(4.69 eV) and ZnO (5.20 eV) [13,18,20–21]. Fig. 2(e) shows three dif-
ferent kinds of oxygen (529.2, 530.8 and 531.9 eV) on the surface of
ternary Ag/CeO2/ZnO nanostructure which are associated with Zn2+,
Ce4+, and Ce3+ [6,8,22]. Hence, the XPS result has confirmed the syn-
thesis of ternary Ag/CeO2/ZnO nanostructure and there was no any
other impurities found in the samples. Further, the determination of
particle size and morphology of the ternary Ag/CeO2/ZnO nanostruc-
ture are the necessary parameters, because these parameters plays vital
role to get the effective efficiency during the photocatalytic activity.
The morphological analysis of ternary Ag/CeO2/ZnO nanostruc-
ture was carried out by FE-SEM. For the comparison purpose, the pure
ZnO nanorods were synthesized by the same method at same reac-
tion condition and its FE-SEM and EDS are shown by Fig. 3a and
a’. The FE-SEM image of ternary Ag/CeO2/ZnO nanostructure speci-
fies the presence of aggregated nanorods along with spherical shaped
nanoparticles which are shown in Fig. 3(b). From the FE-SEM im-
ages, it was clearly represented that when compared with pure ZnO
nanorods (Fig. 3(a)), the size of ZnO nanorods present in the ternary
Ag/CeO2/ZnO nanostructure was smaller, which may be due to Ag
and CeO2nanoparticles which inhibits the growth of nanorods due to
its nucleation effect [23].
The EDS pattern (Fig. 3b’) confirms the presence and synthesis
of pure ZnO and ternary Ag/CeO2/ZnO nanostructure with their con-
stituent elements. Due to large amount of aggregation, we could not
find out the exact size of the ternary Ag/CeO2/ZnO nanostructure from
the FE-SEM. Therefore, we performed TEM analysis to get the exact
size, morphology, interface and d-spacing of ternary Ag/CeO2/ZnO
nanostructure.
The TEM image of ternary Ag/CeO2/ZnO nanostructure is shown
in Fig. 4(a) which clearly represented the presence of ZnO nanorods
along with Ag and CeO2nanoparticles which are in accordance with
FE-SEM results. The length of the nanorods is around 100 to 150 nm
and the diameter is in the range of 20 − 35 nm. From the HR-TEM
(Fig. 4(b)), we determined d-spacing value of each elements.
The crystallites exhibited (111) plane of Ag showing cubic struc-
ture, (200) plane corresponds to cubic structure of CeO2and (101)
planes for hexagonal structure of ZnO. From the close observation
of HR-TEM (Fig. 4(b)) represents line dislocation linear defect (Fig.
4c) because of formation of very small amount of amorphous Ce2O3,
which promotes oxygen vacancies due to the nucleation effect
[8,13,24]. Amorphous regions are also observed (Fig. 4c) around the
crystalline particles, suggesting the presence of amorphous Ce2O3in
the samples. Hence, the results of FE-SEM and TEM analyses clearly
shows formation of the ternary Ag/CeO2/ZnO nanostructure which
are smaller than the pure ZnO. The particles position in the ternary
nanocomposite is essential parameter to find the interfaces of the syn-
thesized ternary Ag/CeO2/ZnO nanostructure which were identified
by STEM; the parallel bright and dark field images which are shown
in Fig. S1. The elemental mapping (Fig. S2) were carried out based
on STEM image and their spread uniformly rather than being sep-
arated individually or edged. These observations confirm the effec-
tive interfaces which modified the electronic-structure and facilitate
charge-carrier transfer between Ag, CeO2and ZnO [25].
The BET measurement values also in agreement with the TEM
observation. The ternary Ag/CeO2/ZnO nanostructure (39.2 m2g−1)
shows 4.5 times greater surface area than the pure ZnO nanorods
(8.7 m2g−1), due to the nucleation effect between Ag, CeO2and ZnO
that promotes the smaller size of ternary system. Wang et al. observed
similar phenomenon for silver doped into ZnO/SnO2system [26].
The optical band gap of the prepared materials were analyzed by
using Kubelka-Munk function. It was clearly displayed in Fig. 5(a),
the nanocomposite materials indicate narrow bandgap (2.66 eV) when
compared with pure ZnO (3.31 eV). The absorbance band edge (Fig.
Fig. 3. The FE-SEM images and respective EDS spectra of (aand a’) ZnO, and, (band b)ternary Ag/CeO2/ZnO nanostructure.
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Journal of Photochemistry & Photobiology, A: Chemistry xxx (2017) xxx-xxx 5
Fig. 4. (a) TEM image, (b) HR-TEM image, and, (c) line dislocation pattern of ternary Ag/CeO2/ZnO nanostructure.
Fig. 5. (a) K-M function F(R)hν1/2 vs hνplot, and, (b) UV–vis absorbance of the ternary Ag/CeO2/ZnO nanostructure and pure ZnO.
5(b)) of the nanocomposite is wider because it contains Ag, CeO2and
amorphous Ce2O3, whereas the pure ZnO has a very sharp band edge
[27]. This wider band edge is due to oxygen vacancies which generate
intermediate states and so the bandgap is narrow [6,13]. The reflec-
tion of TEM image has evidently showed the oxygen vacancies pre-
sent in this nanocomposite system due to line defect This observation
is of good agreement with the previous reports [6,13,28]. On the other
hand, the improved photocatalytic activity mostly depends on the
prevention of electrons and holes combination [16,18]. The photolu-
minescence results (Fig. S3) were evidently indicated that the inten-
sity of Ag/CeO2/ZnO is suggestively low while compared with pure
ZnO, Ag/ZnO and CeO2/ZnO materials. The lowering intensity spec-
ified that the reduced recombination, which is highly favored for en-
hanced photocatalytic activity [16]. Therefore the ternary material is
expected degrading the solution under visible light condition.
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6 Journal of Photochemistry & Photobiology, A: Chemistry xxx (2017) xxx-xxx
3.1. Visible light photocatalytic degradation
Some of the earlier reports clearly showed that the ZnO have a
wide band gap, hence during the visible light irradiation, it was unable
to create sufficient electrons and holes for photocatalytic degradation
reaction. Therefore, these results show smaller amount of degradation
efficiency [13,15,29,30]. The objective of this work is to synthesize a
novel nanostructure which can be used to degrade dyes and indus-
trial textile effluent under visible light irradiation and minimize the
irradiation time compared with ZnO/Ag (degradation of MB within
120 min) and ZnO/CeO2(degradation of MB within 150 min) which
were previously reported [13,15]. The photocatalytic degradation of
initially mixed solution (dye + catalyst), and the uniform irradiation
time of MB, MO and industrial textile effluent and their correspond-
ing UV–vis absorption spectrum are shown in Fig. 6.
Fig. 6. UV–vis absorption spectra of photocatalytic degradation of (a) MB, (b) MO, (c) industrial textile effluent, and, (d) recycling process of industrial textile effluent using ternary
Ag/CeO2/ZnO nanostructure.
Fig. 7. Schematic diagram representing the electron flow and photocatalytic degradation mechanism of pollutants using ternary Ag/CeO2/ZnO nanostructure.
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Journal of Photochemistry & Photobiology, A: Chemistry xxx (2017) xxx-xxx 7
The UV–vis absorption results evidently showed that when the ir-
radiation time increases, the concentration of dyes decrease and fi-
nally gets straight line which means that the MO and MB has been
degraded completely within 90 min. The nanostructure degraded MB
solution much faster when compared with binary ZnO/Ag and ZnO/
CeO2nanocomposites [13,15]. On the other hand, while compared
with CeO2/C3N4, ZnO/CeO2@HNTs, g-C3N4/CeO2/ZnO and
Ag3PO4/CeO2materials showing lowering rates [31–34]. The photo-
catalytic degradation rate depends on several parameters like method
of synthesis of catalyst, morphology, size, crystallinity, bandgap, par-
ticle size, surface area and the availability of surface hydroxyl groups
[13,15,31–34]. Furthermore, the colorless compound like phenol solu-
tion were carried for degradation process under visible light condition.
The results (Fig. S4) were clearly exhibited the prepared material de-
grade the 98% of phenol solution within 120 min.
For industrial textile effluent degradation, the rate of degradation
of MB and MO is better due to its simple structure and also the indus-
trial textile effluent contains lot of colored dyes, this statement was in
good agreement with the recent literatures [35]. The recycling process
of industrial textile effluent (Fig. 6d) results indicates that the ternary
Ag/CeO2/ZnO nanostructure have good stability. Thus, the nanostruc-
ture is usable for long term environmental remediation process.
Fig. 7 represents the photocatalytic pathway mechanism for the
ternary Ag/CeO2/ZnO nanostructure under visible light irradiation.
This ternary system have two semiconductors ZnO, and CeO2as well
as metallic Ag having different work functions i.e. 5.20 eV [13,20],
4.69 eV [18,21] and 4.26 eV [13,18,20]. respectively. In general,
when the semiconductor interacts with metal, Schottky barrier is
formed and induced the new fermi level [13,20,36]. Therefore, the
ternary Ag/CeO2/ZnO nanostructure forms new fermi energy level
and has lot of free electrons due to the presence of metallic Ag [13,20].
During the photocatalytic degradation, when the visible light falls on
the surface of the ternary Ag/CeO2/ZnO nanostructure, free electrons
are excited due to surface plasmon resonance (SPR) mechanism, the
excited electrons are transferred into the conduction band of CeO2and
ZnO simultaneously [13,20]. The conduction band electrons and other
free electrons react with adsorbed oxygen molecules during the reac-
tion process and get converted into superoxide anion [8]. This super-
oxide anion reacts with water molecules and finally forms hydroxide
radicals. These radicals effectively degrade the colored dyes and in-
dustrial textile effluents under visible light irradiation.
Moreover, Ag/CeO2/ZnO photocatalyst having oxygen vacancies
and Ce3+ due to line defect generates intermediate states which in-
duces narrowing of band gap which was confirmed by DRS and
HR-TEM results37−39. Thus, oxygen vacancies and Ce3+ lead to im-
prove the visible light induced photocatalytic degradation through har-
vesting maximum amount of visible light in short time. The simi-
lar statement has been reported by several other authors [6,8,37,38].
Therefore, we too assume that the ternary Ag/CeO2/ZnO nanostruc-
ture shows excellent efficiency for the degradation of dyes as well as
industrial textile effluent owing to the Ag, Ce3+ and oxygen vacancies
present in this system, which would be helpful to improve the photo-
catalytic degradation activity of the ternary Ag/CeO2/ZnO nanostruc-
ture under visible light irradiation [6,8,13,36,39,40–47].
4. Conclusion
The ternary Ag/CeO2/ZnO nanostructure was successfully synthe-
sized by thermal decomposition method, characterized by standard
techniques (DRS, XRD, XPS, STEM and HR-TEM) and tested for
visible light-induced photocatalytic degradation of colored dyes and
industrial textile effluent (real sample analysis) as well as recycling
process. The synthesized ternary Ag/CeO2/ZnO nanostructure showed
hexagonal and cubic phases which were confirmed by XRD whereas
XPS analysis confirms the presence of Ag, Ce4+, Ce3+, Zn2+ and O.
The XPS and HR-TEM results also confirms the line dislocation linear
defect induced oxygen vacancy in the ternary Ag/CeO2/ZnO nanos-
tructure. The oxygen vacancy creates narrow band gap (2.66 eV),
which was further confirmed by DRS. The oxygen vacancy promotes
intermediate states which induces narrow band gap. The narrow band
gap helps to excite the ternary Ag/CeO2/ZnO nanostructure in visi-
ble light and produces sufficient electrons and holes for the photo-
catalytic degradation reactions. The intermediate state of the ternary
Ag/CeO2/ZnO nanostructure inhibited the electron-hole recombina-
tion, which results in superior photocatalytic activity. The ternary Ag/
CeO2/ZnO nanostructure showed outstanding photocatalytic activity
in short period of visible light irradiation because of the narrow band
gap, surface plasmon resonance (SPR) of Ag nanoparticles, synergis-
tic effects, and defects (Ce3+ and oxygen vacancy) in CeO2and ZnO.
Acknowledgement
We acknowledge the Department of Nuclear Physics and National
Centre for Nanoscience and Nanotechnology, University of Madras,
India for XRD and XPS characterizations.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the
online version, at https://doi.org/10.1016/j.jphotochem.2017.12.011.
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... However, Saravanan et. al., [5] reported that mixed TiO2 will be used in the photodegradation of organics pollutants under visible light by lowering their energy band gap. Also, the use of chitosan (CS) is the safest route to carry out visible light degradation due to that contains hydroxyl and amino groups [5]. ...
... al., [5] reported that mixed TiO2 will be used in the photodegradation of organics pollutants under visible light by lowering their energy band gap. Also, the use of chitosan (CS) is the safest route to carry out visible light degradation due to that contains hydroxyl and amino groups [5]. In addition, the synthesis methods have an important effect on the photocatalytic activity of metal oxide semiconductors [6]. ...
... Thus, this work aims is to study the photocatalytic behavior of TiO2 and CS composites under UV light considering the study reported by Saravanan et. at., [5] of TiO2/CS under visible light. Here, TiO2 nanoparticles and two percentages of TiO2/CS nanocomposites have been synthesized and their properties studied. ...
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... The bandgap energies of TiO 2 was accurately to be 3.20 eV. The sample shows similar values to the theoretical bandgaps energies reported from previous literature with analysis [7,13,20,21]. The TiO 2 photocatalyst exhibited similar bandgap energies and produced electron-hole pairs for photocatalytic activities. ...
... Table 2 presents the other two blank samples in the photocatalysis systems, including the studies conducted on the adsorption of wastewater contaminated with MO pollutants using the single TiO 2 and Cs, separately. The photocatalytic and adsorption properties of 2E2 photocatalyst system compared with that TiO 2 and Cs analysis from previous studies [2,21,28,29]. It indicates that the addition of Cs increased the adsorption of parent TiO 2 up to 56%. ...
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This chapter briefly discusses immense research on chitosan-based nanomaterials as well as also highlights the current developments and their utility in different applications majorly focusing on the biomedical field. Chitosan is a well-known nontoxic, biocompatible, and biodegradable polymer possessing enormous possibilities for structural modification either by chemical or mechanical pathways, thereby generating novel polymeric designs with enhanced properties and functions, particularly in biology. Chitosan has been used as a fascinating biomaterial in developing different types of drug delivery techniques, as regenerative medicine in the area of health science or pharmacy. Tremendous use of agrochemicals for increasing crop production and their protection causes significant health and environmental concerns; therefore, chitosan-based nanomaterials such as nanoparticles, hydrogels, and nanocomposites have been applied in agriculture due to their unique antimicrobial and plant growth-promoting properties. These special properties endorse chitosan with promising potentialities for development in biomedicine fields like drug delivery, gene delivery, cell and molecular imaging, development of different sensors, and the treatment and diagnosis of some diseases like cancer, neurodegenerative diseases, etc. In contrast to the native chitosan, the chitosan-based nanomaterials are known to exhibit improved chemical, mechanical, and physical properties like higher surface area, tensile strength, porosity, conductivity, photo-luminescence, etc. This chapter focuses on the current research aspects of chitosan-based nanomaterials by highlighting their properties and potentialities in different domains.
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... In addition, the observed SPR band of AgNPs was in line with other results that targeted the synthesis of AgNPs nanocomposites such as Deosarkar et al. (2021) who reported an SPR band at 390 nm for silver nanoparticle-graphene oxide (Ag-GO) nanocomposite, Mohandoss et al. (2022) who stated a band at 430 nm for gelatin-cyclodextrin-stabilized silver nanocomposite, and also Ogbonna and Kavaz (2022) as they detected an SPR peak at 435 nm when synthesizing beads of silver-apple pectin nanocomposite. Furthermore, the bandgap energy (Eg) of Ag-Cu/biochar was calculated by Tauc plot (Saravanan et al., 2018;Fazal et al., 2020) to be 3.9 eV as shown in Fig. S1c. The bandgap was estimated by the extrapolation of linear portion of the graph of Kubelka-Munk function (aℎv) 2 versus band gap energy (E g = ℎv = ℎc λ), to the y-axis, where a is absorption coefficient, ℎ is the Plank's constant, and v is the frequency of radiation. ...
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In the current study, a novel, green, low-cost, and sustainable path for the phyto-fabrication of Ag-Cu biochar nanocomposite (Ag-Cu/biochar) by Atriplex halimus biomass and aqueous extract is described. Surface plasmon resonance peaks were detected at 450 nm and 580 nm signifying the formation of both silver and copper nanoparticles, respectively on the biochar surface. XRD analysis confirmed the crystal structure of the phyto-synthesized Ag-Cu/biochar whereas FT-IR, SEM, EDX, and XPS analyses confirmed the successful phytofabri-cation of the composite. Ag and Cu nanoparticles loaded on the biochar surface were almost spherically-shaped with a particle size ranging from 25 nm to 45 nm. Zeta potential of − 25.5 mV showed the stability of Ag-Cu/ biochar. The potential of this novel nanocomposite in the removal of doxycycline (DOX) was evident under different conditions as it reached nearly 100% under the optimum reaction conditions (DOX concentration; 50 ppm, pH; 9, a dose of Ag-Cu/biochar; 0.01 g, temperature; 25 • C, and H 2 O 2 concentration; 100 mM). The promising regeneration of Ag-Cu/biochar was evident as the removal efficiency was 81% after 6 consecutive cycles. Ag-Cu/biochar was also shown an excellent antimicrobial activity against gram-negative bacteria as well a promising antioxidant activity.
... However, a significant catalyst loss was associated with the recovery. Saravanan et al. (2018) emphasized the preparation of TiO 2 /chitosan via the sol-gel method at different weight ratios. With increase in the chitosan loading in the nano-composites, a reduction in the bandgap of the photocatalyst was observed. ...
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Vanillin and folic acid are two important food additives with high nutritional value. Also, the high levels of vanillin and folic acid have side effects, such as allergic reaction (for vanillin) and colonic or rectal cancer (for folic acid). This study describes the fabrication of a highly sensitive sensor for determination of vanillin in the presence of folic acid in food samples. The electro-oxidation of vanillin was studied at a carbon paste electrode modified with cadmium oxide nanoparticle decorated with single wall carbon nanotubes (CdO/SWCNTs) and 1,3-dipropylimidazolium bromide (DPIB) as a binder (CPE/CdO/SWCNTs/DPIB). The electrochemical behavior of vanillin at bare CPE and CPE/CdO/SWCNTs/DPIB were compared, suggesting that the CPE/CdO/SWCNTs/DPIB significantly enhances the electro-oxidation signal of vanillin. In the mixture containing vanillin and folic acid, the oxidation peaks potential for the two compounds were well separated from each other. The square wave voltammetric response for vanillin and folic acid are linear in the dynamic range 0.03–800.0 μM and 0.1–1200 μM, and limit of detection of 9.0 ± 0.1 nM and 0.06 ± 0.01 μM, respectively. The CPE/CdO/SWCNTs/DPIB has been successfully applied to the analysis of vanillin and folic acid in food samples.
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Carboxymethyl chitosan was prepared, grafted with polyacrylamide in the presence of synthesized Fe3O4 nanoparticles and coated with TiO2 (TMPAM-g-CMC). Synthesized materials were characterized using FT-IR spectra, XRD, EDX, SEM, TEM, BET surface area, UV–vis/DRS and PL spectra. MPAM-g-CMC and TMPAM-g-CMC were comparatively investigated for decolorization of Congo red dye solution under visible light irradiation. The effect of various experimental parameters on the decolorization rate was investigated. MPAM-g-CMC and TMPAM-g-CMC showed decolorization rate, 55.4% and 99.2% after 90 and 180 min, respectively. Photocatalytic decolorization follows pseudo-first-order according to Langmiur–Hinshelwood (L–H) model. The decolorization rate by TMPAM-g-CMC attained 92.4% after eight repetitive cycles that confirmed its stability.
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Promoting the spatial separation of photoexcited charge carriers is of paramount significance for photocatalysis. In this work, binary g-C3N4/CeO2 nanosheets are first prepared by pyrolysis and subsequent exfoliation method, then decorated with ZnO nanoparticles to construct g-C3N4/CeO2/ZnO ternary nanocomposites with multi-heterointerfaces. Notably, the type-II staggered band alignments existing between any two of the constituents, as well as the efficient three-level transfer of electron-holes in unique g-C3N4/CeO2/ZnO ternary composites, leads to the robust separation of photoexcited charge carriers, as verified by its photocurrent increased by 8 times under visible light irradiation. The resulting g-C3N4/CeO2/ZnO ternary nanocomposites unveil appreciably increased photocatalytic activity, faster than that of pure g-C3N4, ZnO and g-C3N4/CeO2 by a factor of 11, 4.6 and 3.7, respectively, and good stability toward methylene blue (MB) degradation. The remarkably enhanced photocatalytic activity of g-C3N4/CeO2/ZnO ternary heterostructures can be interpreted in terms of lots of active sites of nanosheet shapes and the efficient charge separation owing to the resulting type-II band alignment with more than one heterointerface and the efficient three-level electron-hole transfer. A plausible mechanism is also elucidated via active species trapping experiments with various scavengers, which indicating that the photogenerated holes and •OH radicals play a crucial role in photodegradation reaction under visible light irradiation. This work suggest that the rational design and construction of type II multi-heterostructures is powerful for developing highly efficient and reusable visible-light photocatalysts for environmental purification and energy conversion.
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In this study, synthesis of novel binary chitosan-SnO2 nanocomposites is reported. Different physical and chemical techniques were used to characterize and analyze the characteristics of the chitosan-SnO2 nanocomposites as photocatalysts. The prepared novel photocatalysts were used to degrade the model dyes such as methyl orange (MO) and rhodamine B (RhB) under different wavelengths (254, 310 and 365 nm) of UV light. The photocatalytic degradation results suggest that the prepared binary chitosan-SnO2 (50:50) nanocomposite shows superior degradation efficiency compared with pure SnO2 and binary chitosan-SnO2 (75:25) nanocomposite owing to its high crystallinity, high surface area, and small particle size. It was also observed that chitosan-SnO2 (50:50) nanocomposite under different wavelengths (254 nm, 310 nm, and 365 nm) of UV light showed highest photocatalytic degradation of methyl orange and rhodamine B at 365 nm irradiation.
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Herein we report synthesis of nano-hetero assembly of superparamagnetic Fe3O4 and bismuth vanadate stacked on Pinus roxburghii derived biochar. Optical studies and band structure analysis indicate the hybridization between the two semiconductors facilitating photodegradation of pollutants in presence of natural sunlight. The nano-heterojunctions have been utilized for removal of emerging micro-pollutants as methylparaben (MeP). 97.4% of MeP degradation was achieved in presence of biochar/Fe3O4/BiVO4 in 2 h. A degradation pathway has also been proposed on basis of Mass spectrometry, chemical oxygen demand analysis and effects of various scavengers. Pinus derived biochar has also been utilized to see its long term effect on soil characteristics and fertility. The biochar has also been used to remove excessive pesticide from soil for lesser bioavailability.
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Photocatalysis has been invariably considered as an unselective process (especially in water) for a fairly long period of time, and the investigation on selective photocatalysis has been largely neglected. In recent years, the field of selective photocatalysis is developing rapidly and now extended to several newer applications. This review focuses on the overall strategies which can improve the selectivity of photocatalysis encompassing a wide variety of photocatalysts, and modifications thereof, as well as the related vital processes of industrial significance such as reduction and oxidation of organics, inorganics, and CO2 transformation. Comprehensive and successful strategies for enhancing the selectivity in photocatalysis are abridged to reinvigorate and stimulate future investigations. In addition, nonsemiconductor type photocatalysts, such as Ti-Si molecular sieves and carbon quantum dots (CQDs), are also briefly appraised in view of their special role in special selective photocatalysis, namely epoxidation reactions, among others. In the end, a summary and outlook on the challenges and future directions in the research field are included in the comprehensive review.