Facile synthesis of light harvesting semiconductor bismuth oxychloride nano photo-catalysts for efficient removal of hazardous organic pollutants

Article abstract of DOI:10.1371/journal.pone.0172218

In the present work, bismuth oxychloride nanoparticles-a light harvesting semiconductor photocatalyst-were synthesized by a facile hydrolysis route, with sodium bismuthate and hydroxylammonium chloride as the precursor materials. The as-synthesized semiconductor photocatalysts were characterized using X-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, Field emission scanning electron microscopy, Xray photoelectron spectroscopy and Photoluminescence spectroscopy techniques. The crystal structure, morphology, composition, and optical properties of these facile synthesized bismuth oxychloride nanoparticles (BiOCl NPs) were compared to those of traditional bismuth oxychloride. In addition, the photocatalytic performance of facile-synthesized BiOCl NPs and traditional BiOCl, as applied to the removal of hazardous organic dyes under visible light illumination, is thoroughly investigated. Our results reveal that facile-synthesized BiOCl NPs display strong UV-Vis light adsorption, improved charge carrier mobility and an inhibited rate of charge carrier recombination, when compared to traditional BiOCl. These enhancements result in an improved photocatalytic degradation rate of hazardous organic dyes under UV-Vis irradiance. For instance, the facile-synthesized BiOCl NPs attained 100% degradation of methylene blue and methyl orange dyes in approximately 30 mins under UV-Vis irradiation, against 55% degradation for traditional BiOCl under similar experimental conditions.

Full text of DOI:10.1371/journal.pone.0172218

RESEARCH ARTICLE
Facile synthesis of light harvesting
semiconductor bismuth oxychloride nano
photo-catalysts for efficient removal of
hazardous organic pollutants
1
2
2
3
Zaki S. Seddigi , Mohammed A. Gondal *, Umair Baig , Saleh A. Ahmed , M.
1
4
5
2
A. Abdulaziz , Ekram Y. Danish , Mazen M. Khaled , Abul Lais
1
Department of Environmental Health; Faculty of Public Health and Health informatics, Umm Al Qura
a1111111111
a1111111111
a1111111111
a1111111111
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University, Makkah, Saudi Arabia, 2 Laser Research Group, Department of Physics, King Fahd University of
Petroleum & Minerals, Dhahran, Saudi Arabia, 3 Chemistry Department, College of Applied Sciences, Umm
Al-Qura University, Makkah, Saudi Arabia, 4 Chemistry Department, Faculty of Science, King Abdulaziz
University Jeddah, Saudi Arabia, 5 Department of Chemistry, King Fahd University of Petroleum & Minerals,
Dhahran, Saudi Arabia
*
magondal@kfupm.edu.sa
OPEN ACCESS
Abstract
Citation: Seddigi ZS, Gondal MA, Baig U, Ahmed
SA, Abdulaziz MA, Danish EY, et al. (2017) Facile
synthesis of light harvesting semiconductor
bismuth oxychloride nano photo-catalysts for
efficient removal of hazardous organic pollutants.
PLoS ONE 12(2): e0172218. doi:10.1371/journal.
pone.0172218
In the present work, bismuth oxychloride nanoparticles–a light harvesting semiconductor
photocatalyst–were synthesized by a facile hydrolysis route, with sodium bismuthate and
hydroxylammonium chloride as the precursor materials. The as-synthesized semiconductor
photocatalysts were characterized using X-ray diffraction analysis, Fourier transform infra-
red spectroscopy, Raman spectroscopy, Field emission scanning electron microscopy, X-
ray photoelectron spectroscopy and Photoluminescence spectroscopy techniques. The
crystal structure, morphology, composition, and optical properties of these facile synthe-
sized bismuth oxychloride nanoparticles (BiOCl NPs) were compared to those of traditional
bismuth oxychloride. In addition, the photocatalytic performance of facile-synthesized BiOCl
NPs and traditional BiOCl, as applied to the removal of hazardous organic dyes under visible
light illumination, is thoroughly investigated. Our results reveal that facile-synthesized BiOCl
NPs display strong UV-Vis light adsorption, improved charge carrier mobility and an inhib-
ited rate of charge carrier recombination, when compared to traditional BiOCl. These
enhancements result in an improved photocatalytic degradation rate of hazardous organic
dyes under UV-Vis irradiance. For instance, the facile-synthesized BiOCl NPs attained
100% degradation of methylene blue and methyl orange dyes in approximately 30 mins
under UV-Vis irradiation, against 55% degradation for traditional BiOCl under similar experi-
mental conditions.
Editor: Yogendra Kumar Mishra, Institute of
Materials Science, GERMANY
Received: August 17, 2016
Accepted: February 1, 2017
Published: February 28, 2017
Copyright: © 2017 Seddigi et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper.
Funding: This work was supported by the King
Abdul Aziz City for Science and Technology
(KACST) through the Science & Technology Unit at
Umm Al-Qura University for funding through
Project No. 12-NANO2317-10 as part of the
National Science, Technology and Innovation Plan.
The support by King Fahd University of Petroleum
and Minerals is also gratefully acknowledged.
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
Otherwise, the funders had no role in study design,
data collection and analysis, decision to publish, or
preparation of the manuscript. The funding
agencies supported in terms of financial support
for equipment, chemicals, and salaries of Principal
Investigator (ZSS) and Co-Investigators (SAA,
MAA, EYD, MMK) and students.
Introduction
Water pollution is a colossal problem as it encourages the transmission of waterborne diseases,
especially in developing nations. Recently, industries that deal with textile, leather, bleaches
and dyes for plastic production, cosmetics, packaging, along with photographic commercial
enterprises which utilize coloring materials, have been discovered to release their wastewater
into streams without appropriate pre-discharge treatment. These effluents, which contain
organic pollutants and dyes that are non-biodegradable and synthetically stable poisons are
the main reasons for waterborne infections among human beings [1]. Supplying potable water
to the populace has been a pressing need of various governmental and non-governmental
organizations. Different techniques have been devised and various others are in process in
order to make water suitable for human consumption. Different methods have been applied in
treating and removing these contaminants from wastewater like flocculation, adsorption,
membrane separation and advanced oxidation process (heterogenous catalysis) [2–10]. Out of
the various methodologies and removal methods, development of advanced photo-catalysts
remains a “method of choice” for complete degradation of hazardous environmental pollut-
ants (found in drinking water supplies and waste water streams) into harmless carbon dioxide
and water [10–20]. Photo-catalysis uses light-sensitive catalysts to accelerate chemical reac-
tions. In brief, a photo-catalyst absorbs photons, which create photo-generated electron–hole
charge carriers, and these migrate to the catalyst surface to effect useful chemical transforma-
tions, such as dye degradation and solar fuel generation. To achieve its desired outcome, a
photo-catalyst must possess certain requisite features: a desirable band gap, appropriate band
edge positions (i.e. HOMO & LUMO), large surface area, thermodynamic stability and recy-
clability [21–22]. There are many classes of compounds that fulfill these criteria, the most
prominent of them being metal oxides such as oxides of titanium, zinc, tin etc. As stated ear-
lier, light absorption induces charge separation by photo-exciting electrons from the valence
band to the conduction band, forming an electron/hole pair (e-/h+). The positive holes that
migrate to the photocatalyst surface have the potential to oxidize harmful organic substrates
into harmless substances like CO and H O [23–24]. For instance, the holes can produce OH
Competing interests: All authors declares no
competing financial interest.
2
2
-
radicals by oxidizing OH anions, which can react with pollutants and convert them to more
benign substance [25].
Metal oxides (TiO , ZnO, SnO and CeO ) are particularly well-suited to the aforemen-
2
2
2
tioned degradation process due to their abundance in nature, biocompatibility and remarkable
stability in an array of conditions [26–27]. Metal oxides have a prominent role to play in
photocatalytic degradation processes such as the purification of waste water, by killing bacteria
and removing other pollutants, which leaves polluted water reusable. Semiconductor photoca-
talysis has been considered as green, cheap, quick and effective strategy to totally remove the
organic pollutants because of its effectiveness, simplicity and low cost [28–29].
In particular, bismuth-based semiconductors have gained tremendous consideration as a
result of its strong UV-visible light absorption, lower harmful effects on the environment, and
remarkable photocatalytic action against hazardous pollutants [30–31]. Bismuth oxyhalides
[BiOX (X = Cl, Br, I)], are an important class of bismuth ternary compounds in view of its
optical properties. For quite a long time, they were applied as ferroelectrics, stockpiling materi-
als, and shades. However, contemporary research endeavors have been more inclined towards
designing, preparing, and applying bismuth-based semiconductors for photocatalytic uses.
The impressive photocatalytic action of bismuth-based semiconductors is to a great extent
28-31
accounted for by its open crystalline structure and its indirect optical transitions.
Owing
to the promising results obtained in terms of the photocatalytic properties of the aforemen-
tioned bismuth-based semiconductors, it was thought to realize the potential of such materials
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
as effective photocatalyst for complete mineralization of hazardous environmental pollutants
into harmless carbon dioxide. Therefore, crystalline, semiconducting bismuth oxychloride
nanoparticles were synthesized through a facile, simple hydrolysis route, using sodium bis-
muthate and hydroxylammonium chloride as the starting materials, and were then character-
ized by several advanced analytical techniques. The adsorption as well as photocatalytic
performance have been appraised by degradation of model organic pollutants (methylene blue
dye and methyl orange dye). The results of these findings are presented herein this paper.
Materials and methods
Chemical and reagents
All the chemicals and reagents were of analytical grade and used without further purification.
Hydroxylammonium chloride (HONH .HCl) and Sodium bismuthate (NaBiO ) 80% were
2
3
procured from Sigma Aldrich, USA. Organic dyes (Methyl orange and Methylene Blue) were
procured from Fisher Scientific, New Jersey (USA). Deionized (DI) water was utilized
throughout the entire examination, where ever necessary.
Synthesis of bismuth oxychloride nanocatalyst
In a typical experiment, crystalline bismuth oxychloride nanoparticles (denoted by BiOCl-X,
X = 4 and 24) were synthesized through a facile hydrolysis route, with sodium bismuthate and
hydroxylammonium chloride as the starting materials. X (X = 4 and 24) denotes the percent-
age weight of hydroxylammonium chloride. Firstly, 1 g of sodium bismuthate was suspended
in 100 ml of deionized water, and stirred by aid of a magnetic stirrer. In the following step, X g
(X = 4 and X = 24) of hydroxylammonium chloride was dissolved in 100 ml of DI water and
allowed to form a clear solution, then this clear solution was added to the above suspension
under magnetic stirring in a dropwise fashion. The stirring was performed for 24 hours under
room temperature until a white precipitate was formed. The solid sample was washed with
deionized water thoroughly through centrifugation until a neutral pH was obtained. Lastly, the
BiOCl formed was harvested and subsequently dried at 70˚C for 24 hours in air.
On the other hand, the traditional BiOCl (BiOCl-T) were synthesized via an oxidation-
hydrolysis reaction between sodium bismuthate and hydrochloric solution (HCl, 37 wt. %). In
a typical synthesis, 4 g of sodium bismuthate was suspended in 50 ml of deionized water under
magnetic stirring. In the next step, 20 ml of HCl solution was added into the suspension in a
dropwise manner until the sodium bismuthate powder completely dissolved. After adding 250
ml of deionized water to the solution from the previous step, white precipitate of BiOCl-T
appeared. This white precipitate of BiOCl-T was collected by centrifugation, and thoroughly
washed using deionized water until a neutral pH was obtained. The final product which is tra-
ditional BiOCl was then dried at 70˚C for 24 hours in air.
Characterizations
The crystal structure was examined using X-ray diffraction analysis (XRD, Bruker Advance
D8) with Cu Kα radiation. The data was collected for the following range: 10˚ < 2θ < 80˚. The
morphologies and elemental composition were investigated using field-emission scanning
electron microscopy (TESCAN FERA3 FE-SEM) accompanied with an energy-dispersive X-
ray spectroscopy (EDS). In other to further affirm the elemental composition, X-ray photoelec-
tron spectroscopic (XPS) analysis were carried out using ESCALAB-250Xi System (Thermos-
Scientific), utilizing Al Kα as the incidence radiation source. Attenuated total reflectance Fou-
rier Transform Infrared (ATR-FTIR) spectra were carried out at room temperature using
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
Nicolet iS50 FT-IR Spectrometer. Raman spectroscopy analysis was also examined using
Thermo-Scientific Raman analyzer, this was done under ambient condition at room
temperature.
Photo-degradation operation process
Sorption performance. Sorption performance study was accomplished to ascertain the
sorption kinetics. In a typical sorption study, 50 mg of the as-prepared BiOCl catalysts, were
mixed in 100 ml of aqueous solution of MO with a concentration of 20 mg/L; this suspension
was kept under dark condition and under magnetic stirring at a speed of 300 rpm and at room
temperature for 30 mins. The suspension was then thoroughly centrifuged after each batched
experiment, and the absorbance was carried out to calculate the concentration of (Methyl
orange dye) MO using UV-Vis spectrophotometer (JASCO V-670). In comparison, this pro-
cess was repeated for MB (Methylene blue dye) with the same experimental conditions.
Photocatalytic activity test. A 500W Xenon lamp (Oriel, USA) was used as light source
for the degradation of different compounds on the as-prepared BiOCl. Standard solutions of
contaminants (MO and MB dyes) was photodegraded by the addition of a particular amount
of the as-prepared catalyst in a typical photo-degradation experiment. Aqueous suspensions of
contaminant and catalyst mixture was collected and centrifuged (4000 rpm, 3mins) after irra-
diation, at fixed intervals to remove particles. The filtrate‘s absorbance was then measured by
UV-Vis spectroscopy (JASCO V-670) which was in turn used to obtain the concentration of
the contaminant. The concentration difference between the initial contaminant solution and
the mixture suspension reveals the extent of adsorption of the contaminant by the as-prepared
catalyst.
Results and discussion
Structural properties
The crystalline phase of the as-prepared BiOCl-T, BiOCl-4 and BiOCl-24 photo-catalysts is
investigated using X-ray diffraction analysis, and the spectra are shown in Fig 1. The intense
and sharp diffraction peaks (as evidenced by a large height/FWHM ratio) suggest that the as-
synthesized BiOCl samples are well-crystallized. All of the diffraction peaks can be indexed to
the tetragonal structure of BiOCl (space group: P4/nmm). The (0 0 1) peak at 11.75˚ is attrib-
uted to the periodic stacking structure among [Cl–Bi–O–Bi–O–Cl] layers along the c-axis. The
diffraction intensity ratios of I(110)/I(001) were calculated for BiOCl-T, BiOCl-4 and BiOCl-
24 and found to be 3.13, 0.26 and 0.62 respectively. This implies that growth of the {001} facets
were enhanced in BiOCl-4 and BiOCl-24 as compared to BiOCl-T. In addition, the sizes along
the [1 1 0] crystallographic direction exhibited the following order: BiOCl-T > BiOCl-24 >
BiOCl-4. From this, it is evident that the crystal growth behavior along the basal ab plane is
inhibited in the case of nanosynthesized BiOCl as compared to traditional BiOCl.
Optical properties
The FT-IR spectra of as-prepared BiOCl-T, BiOCl-4 and BiOCl-24 photocatalyst are presented
-1
in Fig 2. In the FT-IR spectra, the characteristic bands at around 1623 cm are attributed to
the O-H bending vibrations. The absence of any further prominent bands appearing in the
-1
region of 2500 and 1600 cm reinforces the aforementioned proposition that water molecules
are largely absent from all 3 samples, which is indicative of highly pure BiOCl material. The
-1
only very strong band occurs at about 528 cm in all 3 spectra, and it corresponds to valent
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
Fig 1. XRD patterns of as-prepared BiOCl-T, BiOCl-4 and BiOCl-24 Photocatalyst.
doi:10.1371/journal.pone.0172218.g001
symmetrical A -type vibrations of the Bi-O stretching mode, alluding to highly pure BiOCl
2u
being formed.
Fig 3 shows the Raman spectra of synthesized BiOCl-T, BiOCl-4 and BiOCl-24 photocata-
lyst. The spectra show one strong and 2 very weak bands. In general, symmetry vibrations give
-1
rise to Raman bands of grater intensity than asymmetry vibration. The strong band at 145 cm
observed in the nanosynthesized samples BiOCl-T, BiOCl-24 and BiOCl-4) was assigned to
(
-1
A1g internal Bi-Cl stretching mode. The weaker band at 201 cm can be assigned to the E
g
-1
internal Bi-Cl stretching mode. Lastly, a very weak peak (barely visible) at about 399 cm is
attributed to E and B band produced by the motion of oxygen atoms. These wavenumbers
g
1g
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
Fig 2. FTIR spectra of as-prepared BiOCl-T, BiOCl-4 and BiOCl-24 Photocatalyst.
doi:10.1371/journal.pone.0172218.g002
are consistent with values reported in the literature, implying that high-purity BiOCl has been
synthesized.
To explore the loss of photogenerated electron-hole pairs by recombination, room tempera-
ture photoluminescence spectra of the 3 BiOCl samples (BiOCl-T, BiOCl-4 and BiOCl-24) are
recorded and shown in Fig 4. The emission spectrum was acquired with an excitation wave-
length of 253 nm. There is a strong correlation between the PL emission intensity and charge
carrier recombination. A higher PL emission intensity implies a higher recombination of the
charge carriers, which adversely affects photocatalytic performance, since the separated charge
carriers are primarily responsible for the photocatalytic degradation performance. Hence, a
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Fig 3. Raman spectra of as-prepared BiOCl-T, BiOCl-4 and BiOCl-24 Photocatalyst.
doi:10.1371/journal.pone.0172218.g003
loss of these charge carriers by recombination implies reduced degradation capability of the
photocatalyst. The traditional BiOCl (BiOCl-T) displayed a strong emission band centered at
396 nm with high emission intensity. However, the emission intensity of facile synthesized
BiOCl-24 and BiOCl-4 were decreased by 80% and 95% respectively, demonstrating the
reduction of electron hole pair recombination, which brings about enhanced photocatalytic
performance, for the aforementioned reasons. Nano-synthesized BiOCl exhibits lower
charge recombination because the migration distance of the charge carriers from the point
of generation (within the nanoparticle volume) to the surface is shorter, due to smaller nano-
particle size. This leads to a proportionally shorter migration time, and thus lower volume
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Fig 4. PL spectra of as-prepared BiOCl-T, BiOCl-4 and BiOCl-24 Photocatalyst.
doi:10.1371/journal.pone.0172218.g004
recombination probability, which leads to more charge carriers migrating to the surface suc-
cessfully for effecting photocatalytic dye degradation. This results in an enhanced photocataly-
tic rate.
Morphological properties
The field emission scanning electron (FE-SEM) micrographs of BiOCl-T, BiOCl-4 and BiOCl-
24 photocatalyst are shown in Fig 5. In (Fig 5A–5C), the morphological topographies of as-
prepared BiOCl-T (traditional BiOCl) shows that the BiOCl-T has flake-like structure. How-
ever, the morphology of BiOCl-4 and BiOCl-24 nano-synthesized photocatalyst [Fig 5D–5F
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
Fig 5. FE-SEM images of BiOCl-T (a-c), BiOCl-4 (d-f) and BiOCl-24 photo-catalyst (g-i) at different magnifications.
doi:10.1371/journal.pone.0172218.g005
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
and 5G–5I] are substantially different from that of BiOCl-T. The FE-SEM micrographs in (Fig
5D–5F and 5G–5I) clearly prove that the BiOCl-4 and BiOCl-24 are composed of several simi-
larly sized nano-spherical structures assembled hierarchically yielding granules. The granules
for different nano-samples (BiOCl-4 and BiOCl-24) have slightly different morphology. Mini-
mization of total system energy drives these nano-spherical structures to coalesce into 3D hier-
archical nano structures by self-assembly (obviating the need for any templates) as spherical
shapes minimize surface energy. A light-harvesting advantage of the self-assembled nano-
structure is that light can be multiply-reflected within the interconnected nano-spheres, which
can enhance the light absorption capacity of the photocatalyst. Another advantage of these
nanoscale photocatalyst grains is that their specific surface area is larger which leads to an
increase in the photocatalysts’ dye adsorption capacity (due to a larger active surface area,
since dye molecules are only surface-adsorbed). This eventually leads to an enhanced dye
removal rate.
The elemental composition of BiOCl-T, BiOCl-4 and BiOCl-24 photocatalyst were also
confirmed using the EDX Spectra shown in (Fig 6A, 6B and 6C) which shows Bi, O, and Cl
are present. Quantitative EDX analysis shows that the atomic ratio of Bi/O/Cl in BiOCl-T,
BiOCl-4 and BiOCl-24 photocatalyst are 0.97: 0.92: 0.90, 1:0.91:0.92 and 1:0.95:96 respectively,
close to 1:1:1, indicating that the composition of the as-synthesized products is indeed BiOCl.
XPS studies were carried out to further investigate the surface chemical compositions and
valence band states of the BiOCl-T, BiOCl-4 and BiOCl-24 photocatalyst, and the spectra are
shown in Fig 7. The upper left plot in Fig 7A shows a typical survey scan for BiOCl-T over a
large energy range at low resolution. This figure demonstrates that BiOCl-T contains Bismuth,
Oxygen and Chloride, alluding to the presence of BiOCl photocatalyst. The high resolution
scan of Bi 4f, O 1s and Cl 2p states are given in Fig 7A. From high-resolution XPS spectra, a
typical 4f7/2 (158.8 eV) and 4f5/2 (164.2 eV) doublet in Bi 4f signal can be found, which is
accounted for by the spin-orbit coupling effect, suggesting the tri-valence chemical state in
BiOCl sample. The O1s peak at 529.6 eV is attributed to the oxygen anions in the Bi-O bond
from the [–O–Bi–O–Bi–O–] slabs in BiOCl. A characteristic doublet for chloride anions was
also observed at 2p3/2 (197.4 eV) and 2p1/2 (199.0 eV) in Cl 2p, which is accounted for by the
characteristic electronic structure of chloride anions.
Photocatalytic degradation mechanism
The scheme in Fig 8 represents the proposed photocatalytic reaction mechanism over BiOCl
semiconducting nanoparticles for the degradation of methyl orange and methylene blue dye.
-
+
There is photo-generation of electrons (e ) and holes (h ) by light irradiation upon the photo-
-
+
catalyst in the solution. These e —h pairs are charge carriers which are used in subsequent
redox reaction such as oxygen reduction and water oxidation to yield reactive oxygen species
-
2
-
like O , OH . These highly reactive radicals are responsible for oxidative degradation of the
pollutant (methylene blue and methyl orange) into mineralized products such as CO and
2
H O. However, these charge carriers have an intrinsic tendency to recombine (into radiant
2
heat) by volume and surface recombination processes before they have managed to catalyze
the desired redox reactions; this reduces the efficiency of the photocatalyst. Hence, there is a
strong need to ensure effective separation and migration of the electron and hole pairs.
Photocatalytic performance
Fig 9 depicts temporal changes in the UV-Vis spectra of MB aqueous solution in photo-degra-
dation reaction with the BiOCl-T, BiOCl-4 and BiOCl-24 photocatalyst. The concentration of
MB decreased drastically (100%) using BiOCl-24 and BiOCl-4 photocatalyst under UV-visible
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
Fig 6. The EDX spectrum of (a) BiOCl-T, (b) BiOCl-4 and (c) BiOCl-24 photo-catalyst.
doi:10.1371/journal.pone.0172218.g006
light irradiation within 36 min and 48 min respectively. However, with BiOCl-T under 60 min
of irradiations, the remaining concentrations of MB is still approximately 20%. Displayed in
Fig 10 is the BiOCl-T, BiOCl-4 and BiOCl-24 photocatalytic degradation curves of MB under
UV-visible light irradiation source along with a catalyst-free experimental run (for control
,
purpose). Adsorption-desorption equilibrium was attained between the catalyst particles and
the dye solution by continuous stirring in the dark for half an hour before illumination. The
photo-catalytic activity was shown by the ratio of the final to initial concentration (C/C ) of
o
the dye solution at different time interval upon degradation by the different catalysts under
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
Fig 7. XPS analysis of as-prepared (a) BiOCl-T, (b) BiOCl-4 and (c) BiOCl-24 Photocatalyst.
doi:10.1371/journal.pone.0172218.g007
irradiation. Here, C is the initial concentration of methyl orange after equilibration while C is
o
the concentration at a certain time after irradiation. The activity of the BiOCl-T, BiOCl-4,
BiOCl-24 photocatalysts was investigated in the photo-catalytic decomposition of methylene
blue dye used as probe molecule under UV-visible light irradiation (Fig 10). As shown in Fig
10(A), in the absence of any photocatalyst the MB dye is very stable. It was clear that the facile
synthesized BiOCl-4, BiOCl-24 photocatalysts exhibited an enhanced degradation rate and the
degradation efficiency was higher than that of traditional BiOCl-T. This is mainly because of
enhanced charge carrier transport, improved crystallinity and reduced charge transport
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
Fig 8. Schematic illustration of the possible photocatalytic reaction mechanism over BiOCl semiconducting nanoparticles.
doi:10.1371/journal.pone.0172218.g008
resistance. The photo-activity was further investigated by plotting -ln(C/C ) against time (Fig
o
1
0B), which shows the decomposition kinetics in the form of a linear profile. Hence, using the
C
À Á
classical equation: ln
¼ k:t, where k is the so called degradation rate constant. The k values
Co
presented represent a good measurement of the overall photo-degradation rate and are shown
in Fig 10(B) by fitting curves of the data for a period of 0–60 min. Similarly, the activity of the
BiOCl-T, BiOCl-4 and BiOCl-24 photocatalysts was investigated in the photo-catalytic decompo-
sition of methyl orange dye (Fig 11). As shown in Fig 11(A), in the absence of any photocatalyst
the MO dye is very stable. It is clear that the facile synthesized BiOCl-4, BiOCl-24 photocatalysts
exhibited an enhanced degradation rate and the degradation efficiency was higher than that of
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
Fig 9. Time resolved UV-Vis spectra of MB solution in the presence of BiOCl-T (a), BiOCl-4(b) and BiOCl-24(c).
doi:10.1371/journal.pone.0172218.g009
traditional BiOCl-T. The photo-activity was further investigated by plotting -ln(C/C ) against
o
time (Fig 11B) showing the decomposition kinetics with linear profile.
The spectroscopic data of MB solution in the presence of BiOCl-24 under visible light irra-
diation in the UV range indicates the absence of lower hydrocarbons (see S1 File). However
for the detection of CO and other final products of the photo degradation, a control experi-
2
ment was conducted in the presence of quantitative amounts of oxygen in a closed steel vessel
equipped with quartz window. After UV irradiation lasting 30 min in the presence of BiOCl-
24 catalyst, the gaseous products were collected and introduced into GC/MS system (Agilent
7
890B). The CO peak was detected at a retention time of 5.79 mins min (see S1 File), which
2
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
Fig 10. (a) Changes of MB concentration over BiOCl-T, BiOcl-4, BiOCl-24 photocatalystphotocatalystphotocatalysts as a function of irradiation time and
photolysis of MB dye (without catalyst) as a function of irradiation time. (b) Pseudo First-order plots for the photocatalytic degradation over BiOCl-T, BiOcl-4,
BiOCl-24 catalysts and without catalyst. Experimental conditions: Catalyst = 50 mg, Volume of methylene blue solution = 100 mL, initial methylene blue
-1
solution concentration = 10 mg L .
doi:10.1371/journal.pone.0172218.g010
Fig 11. (a) Changes of MO concentration over BiOCl-T, BiOcl-4, BiOCl-24 photocatalystphotocatalystphotocatalysts as a function of irradiation time and
photolysis of MB dye (without catalyst) as a function of irradiation time. (b) Pseudo First-order plots for the photocatalytic degradation over BiOCl-T, BiOcl-4,
BiOCl-24 catalysts and without catalyst. Experimental conditions: Catalyst = 50 mg, Volume of methyl orange solution = 100 mL, initial methyl orange
-1
solution concentration = 10 mg L .
doi:10.1371/journal.pone.0172218.g011
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
Fig 12. The cycling runs for the photo-degradation of MB dye in the presence of BiOCl-24 under UV-
light irradiation.
doi:10.1371/journal.pone.0172218.g012
was further analyzed by a mass spectrum to investigate the split pattern. We observed the mass
+
+
+
peaks of CO , CO and O at 44, 28 and 16 respectively which is assigned to CO fragments
2
2
in the mass spectrum (see S1 File). The GC and Mass data shows the complete degradation of
the dyes and their conversion into CO as the major product.
2
The photo-corrosion resistance of the photocatalyst is best evaluated by multiple degrada-
tion cycles to assess its performance after repeated usage. For this paper, the same photocata-
lyst sample was used in 5 consecutive runs of degradation experiment, to measure changes in
photocatalytic performance under repeated usage. As exemplified in Fig 12, the catalyst dis-
plays excellent photocatalytic degradation ability even in the 5th usage cycle, attaining almost
the same degradation rate after 30 mins for all 5 cycles. This attests to its remarkable photo-
corrosion resistance and durability, which is of significant economic value as the catalyst can
be recycled for several cycles.
Conclusions
In the present work, bismuth oxychloride light harvesting semiconductor nanocatalyst was
successfully synthesized through a facile hydrolysis route, with sodium bismuthate and hydro-
xylammonium chloride as the starting materials. The facile synthesized bismuth oxychloride
nanoparticles exhibited an enhanced photodegradation performance relative to traditionally
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
synthesized bismuth oxychloride. BiOCl-24 nanocatalyst exhibited the best photo-catalytic
activity by degrading methylene blue and methyl orange to 100% under UV-visible radiation
in 24 and 36 mins respectively. The improved performance compared to traditional BiOCl was
due to enhanced charge carrier transport, improved crystallinity and reduced charge transport
resistance. The present work not only provides a new route to obtain the band gap engineered
bismuth oxychloride light harvesting semiconductor nanocatalyst, but also allows one to syn-
thesize new photocatalysts having effective applications both under sunlight and artificial light
for the degradation and mineralization of hazardous pollutants from drinking water supplies
and industrial waste water.
Supporting information
S1 Fig. (a) UV-Vis spectra of MB solution in the presence of BiOCl-24 under visible light irra-
diation showing that no absorption was noticed for lower hydrocarbon products was noticed,
(
b) GC chromatogram of CO showing presence of CO peak in the degraded product and (c)
2 2
Mass spectrum of CO2.
(
TIFF)
S1 File. Supporting Information.
DOCX)
(
Acknowledgments
The authors wish to acknowledge the support of King Abdul Aziz City for Science and Tech-
nology (KACST) through the Science & Technology Unit at Umm Al-Qura University for
funding through Project No. 12-NANO2317-10 as part of the National Science, Technology
and Innovation Plan. The support by King Fahd University of Petroleum and Minerals is also
gratefully acknowledged.
Author Contributions
Conceptualization: MAG.
Data curation: UB ZSS AL.
Formal analysis: UB ZSS AL.
Investigation: UB MAG ZSS AL.
Methodology: UB MAG ZSS AL.
Project administration: SAA MAA EYD MMK.
Resources: ZSS UB MAG SAA MAA EYD MMK AL.
Software: UB AL.
Supervision: MAG.
Validation: ZSS UB MAG SAA MAA EYD MMK AL.
Visualization: UB ZSS MAG SAA MAA EYD MMK AL.
Writing – original draft: UB ZSS MAG SAA MAA EYD MMK AL.
Writing – review & editing: UB ZSS MAG AL.
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Light harvesting semiconductor bismuth oxychloride nano photocatalysts
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