The characteristics and photocatalytic activities of BiOCl as highly efficient photocatalyst

Article abstract of DOI:10.1016/j.molstruc.2011.10.046

BiOCl was synthesized by hydrolysis method. In order to evaluate their photocatalytic activity, this compound was tested on the degradation reaction of methylene green in aqueous solution. The characterization of the compound included: X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopic image (TEM). MG could be efficiently degraded in aqueous suspension of BiOCl under visible light irradiation. Complete removal of aqueous methylene green (MG) was realized after visible light irradiation for 120 min with existing BiOCl as a catalyst. The decrease of the chemical oxygen demand (COD), the formation of inorganic products (SO42- and NO3-) confirmed complete mineralization of aqueous MG during the photocatalytic process.

Full text of DOI:10.1016/j.molstruc.2011.10.046

Journal of Molecular Structure 1007 (2012) 196–202
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
The characteristics and photocatalytic activities of BiOCl as highly
efficient photocatalyst
Brijesh Pare , Bhawna Sarwan , S.B. Jonnalagadda b
a
a,
⇑
a
Laboratory of Photocatalysis, Department of Chemistry, Govt. Madhav Science Post Graduate College, Vikram University, Ujjain, MP 456 010, India
Department of Chemistry, University of KwaZulu – Natal, Westville, Durban, South Africa
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 August 2011
Received in revised form 20 October 2011
Accepted 20 October 2011
Available online 9 November 2011
BiOCl was synthesized by hydrolysis method. In order to evaluate their photocatalytic activity, this com-
pound was tested on the degradation reaction of methylene green in aqueous solution. The characteriza-
tion of the compound included: X-ray diffraction (XRD), scanning electron microscopy (SEM) and
transmission electron microscopic image (TEM). MG could be efficiently degraded in aqueous suspension
of BiOCl under visible light irradiation. Complete removal of aqueous methylene green (MG) was realized
after visible light irradiation for 120 min with existing BiOCl as a catalyst. The decrease of the chemical
Keywords:
BiOCl
Methylene green
Visible light irradiation
Photocatalysis
Mineralization
2ꢀ
ꢀ
oxygen demand (COD), the formation of inorganic products (SO4 and NO ) confirmed complete miner-
3
alization of aqueous MG during the photocatalytic process.
Ó 2011 Elsevier B.V. All rights reserved.
1
. Introduction
2 4 4 2 6 2 6 2 3
and Sm), AgAlO , InTaO , BiVO , Bi WO , Bi MoO and Bi S [8–
1
5]. These semiconductors are excellent candidates for degrading
Photocatalysis, a ‘‘green’’ technique has been the subject of
organic pollutants upon excitation with light. Among them, bis-
muth and its related compounds have attracted much attention
numerous investigations as it is an attractive technique for the
complete destruction of undesirable contaminants and toxic
chemicals by using solar or artificial light illumination [1].
Methylene green dye (showed in Fig. 1) commonly known as basic
dye has been widely used for coloring paper, tannin mordant
cotton and silk, and in wool dyeing printing industries, so it was
chosen as a model contaminant for the present study. Heteroge-
neous photocatalysis assisted by various semiconductors has been
considered as a cost-effective alternative as a pre- or post treat-
ment of biological treatment processes for the purification of
dye-containing wastewater [2–4]. Among various metal oxide
4 2 6
under visible light. These compounds, such as BiVO , Bi WO , Bi2-
MoO and Bi show high photocatalytic activity, because of the
6
2 3
S
3
+
2
Bi with s -configuration and the layered crystal structure of re-
lated compounds. As one of the related compounds, Bi-based oxy-
chlorides, which have received wide attention in visible light, have
a potential application as photocatalysts owing to their scientific
and technological importance in the environmental purification,
especially in waste water treatment [4]. Recently, Zhu and co-
workers reported that 3D HAd BiOCl showed much higher photo-
catalytic activity for degradation of Rhodamine-B (RhB) dye under
ultraviolet light irradiation [16]. Liu et al. investigated nano BiOCl
microsphere prepared by the solvothermal method. They found
that BiOCl nano microsphere exhibits a good dye-sensitized visible
light photocatalytic activity [17]. An [18] and Zhang [19] first time
found that BiOCl exhibited excellent photocatalytic activity on deg-
radation of Rh B and MO dye under both UV and visible light irra-
diation. Herein, we report BiOCl for photocatalytic degradation of
MG in aqueous suspension irradiated by visible light. Some
researchers have been reported that the photocatalytic activity
closely relates with the diameter size and the structure of the
photocatalysts [12,13]. BiOCl is known as a tetragonal structure
with lattice constants of a = b = 0.38953 Å, c = 0.73734 Å. In the
structure, each Bi atom is eight-coordinated by four O and four
Cl atoms to form a decahedron shape, the four O and four Cl atoms
2
semiconductors, TiO is the most widely studied photocatalyst
for environment remediation owning to its unique photocatalytic
efficiency, low cost, nontoxicity, and high stability [5–7]. One
obstacle to its effective utilization is the inefficient absorption of
visible light. A simple and interesting approach to extend the
catalyst absorption toward visible region has become one of the
most important topics in photocatalysis. Off late, layered structure
compounds were found to use as efficient photocatalysts for
degradation of pollutants under light irradiation. The typical
1
layered photocatalysts are AgInW
2
O
8
2
, RbLnTa O
7
(Ln
4
La, Pr, Nd
⇑
Corresponding author. Tel.: +91 9424561196.
E-mail addresses: brijeshpare2009@hotmail.com (B. Pare), sarbhawna@gmail.
com (B. Sarwan).
0
022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.10.046

B. Pare et al. / Journal of Molecular Structure 1007 (2012) 196–202
197
2.3. Characterization
X-ray powder diffraction pattern of the prepared sample has
been recorded on a Rigaku D/MAX B diffractometer equipped with
CuK (k = 0.15418 nm) radiation under 40 kV and 1000 mA and
a
scanning range 10–80°. The average crystallite size (D) of the par-
ticles was calculated according to the following Scherer’s equation
[
23,24]:
Fig. 1. Chemical structure of methylene green.
0
:9k
D
hkl
¼
ð2Þ
constructed two faces, respectively. The decahedrons are linked to
each other by sharing a common O–Cl edge along a and b axes in
infinite layers. The presence of strong internal static electric fields
perpendicular to the Cl layer and the bismuth oxide-based fluorite-
like layer enables the effective separation of the photoinduced
electron–hole pairs, assisting a high photocatalytic performance
b cos h
Where, Dhkl is the average crystallite size (nm), k is the wave-
length of CuK radiation (k = 0.154056 nm), b is the full-width at
a
half maximum intensity (FWHM) of the peak (radians), h is the
Bragg’s angle of diffraction, and k is constant usually applied as
0.9. The surface morphology of the particles of as-prepared sample
has been investigated by scanning electron micrographs (SEM)
(JEOL JSM-5600 F accelerating voltage 5 kV). The morphology and
microstructure of as-prepared sample was analyzed by transmis-
sion electron microscopy (TEM) by Tecnai 20 G2 (Plate/CCD Cam-
era). Diffuse reflectance spectra (DRS) of the catalyst in
wavelength range of 200–800 nm has been obtained by using
UV–vis spectrophotometer (Perkin Elmer Lambda 950).
[
20]. The goal of this work is to explore these series of materials
to achieve maximum photocatalytic activity behaviors under visi-
ble irradiation. Two main aspects have been studied: The first
ꢀ
one was to determine the formation of NO3 as well as the evalua-
tion of the total mineralization during the process monitored by
COD. The second aspect was to study the effect of N
on degradation.
2
bubbling
2
. Experimental
3
. Results and discussion
2.1. Preparation of BiOCl
3
.1. Structural studies
BiOCl powder was synthesized by a hydrolysis method. In this
synthesis reagent Bi (AR, Aldrich) was dissolved in excessive
concentrated hydrochloric acid (AR, Merck), to receive a transpar-
ent BiCl -HCl aqueous solution. When the pH value of the solution
O
2 3
The XRD pattern of as-prepared BiOCl, shown in Fig. 2a and b.
The intense and narrow diffraction peaks imply a well-crystallized
BiOCl powder material. The XRD pattern shows that all the peaks
are well indexed to the tetragonal phase according to the PDF #
850861 data files. The crystal lattice parameters of BiOCl were cal-
culated to be a = b = 0.38953 Å, c = 0.73734 Å, which were consis-
tent with literature [4,20]. The average crystallite size calculated
by using the Scherer formula is 39.6 nm.
3
was adjusted between 2 and 3 with ammonia (AR, Shanghai), the
white colloid appeared. After the colloid was heated at 40 °C for half
an hour, a powdery BiOCl material consisting of small plate-like
crystals was obtained. The precipitates were washed several times
ꢀ
with distilled water until no Cl was left in the solution and then
dried at 40 °C in oven for 6 h before further characterization [20].
To test the stability of the sample during the photocatalytic pro-
cess, we have analyzed it again at the end of the process by XRD.
The XRD pattern of BiOCl after the photocatalytic reaction is shown
in Fig. 2b. Figure shows that the XRD pattern of BiOCl did not
change even after the reaction was completed, indicating that the
photocatalyst was stable during the reaction and can be used
repeatedly [25,20].
The SEM image (Fig. 3a) shows the overall morphology of the
product. It can be clearly the morphology of BiOCl is dominated
with plates [4,20]. The TEM image of the individual plate in
Fig. 3b indicates that plates have a flat surface and tended to form
2.2. Experimental procedure
The photocatalytic degradation of MG has been carried out in
slurry type batch reactor having double walled Pyrex vessel. The
reaction temperature was kept at 25 °C by using a water circula-
tion. For a typical photocatalytic experiment, 1.5 g of the prepared
BiOCl was added to 100 mL of the methylene green (MG) aqueous
solution. Suspension was kept in a dark for 15 min to establish
adsorption–desorption equilibrium. The suspension containing
MG and the photocatalyst was then irradiated under the visible
light, and the photocatalytic reaction timing started. The irradia-
tion was carried out by using 500 W halogen lamp (Philips, India)
which emitted irradiation comparable to sunlight. The doubled
wall Pyrex vessel was placed on a magnetic stirrer. At specific time
intervals, an aliquot (3 mL) of the mixture was withdrawn and
centrifuged for 2 min at the rate of 3500 rpm to remove the BiOCl
particles in order to asses the extent of decolorization photometri-
ꢀ
cally. NO3 ions were detected by using nitrate ion selective
electrode, ISE – 8735 (OMEGA) and Double Junction Reference
_
Electrode, PHE 3211 equipped with nitrate ion meter. The COD
was determined by the potassium dichromate reflux method
[
21,22]. The efficiency of photocatalytic process was calculated as:
C
0
ꢀ C
%
efficiency ¼
ꢁ 100
ð1Þ
C
0
where C
at different time intervals of photocatalytic process.
0
is the initial COD/absorbance and C is the COD/absorbance
Fig. 2. XRD pattern of BiOCl particles (a) before and (b) after the photocatalytic
reaction.

1
98
B. Pare et al. / Journal of Molecular Structure 1007 (2012) 196–202
(
b)
(a)
(
d)
(
c)
(110)
(200)
Fig. 3. (a) SEM image of BiOCl particles. (b) TEM image of an individual plate. (c) The selective area electron diffraction of an individual plate. (d) TEM image of BiOCl.
an octahedral shape with about 100 nm in diameter. The selective
area electron diffraction (SAED) pattern of an individual plate
(Fig. 3c), shows well defined electron diffraction spots (ED) of the
tetragonal phase could be index to (110) and (200) panels of the
BiOCl. Fig. 3d reveals the lattice spacing of 0.27 nm, which is con-
sistent with the (110) plane of BiOCl [26].
The BiOCl layered structure is presented in Fig. 4. The crystal
2
structure [20] can derive from the fluorite like (CaF ) structure. Fig-
ure shows the Bi atom is coordinated with four O atoms in one base
and four Cl atoms in another. The Bi and four O atoms form a
tetragonal pyramid; meanwhile the Bi atom and four Cl atoms
form another tetragonal pyramid in the opposite but asymmetric
direction and two pyramids are interlaced, clearly presented in
Fig. 4b. It can be seen that asymmetric decahedral geometry with
a bismuth center is constructed. The O atom coordinates with four
Bi atoms and the Cl atom is bonded with four Bi atoms. The tetrag-
2 2 2 2 2
onal [Bi O ] slabs ‘‘sandwich’’ by two Cl slabs and a [Bi O Cl ] layer
forms which are stacked together by the nonbonding (van der
Waals) interaction. From another viewpoint, Fig. 4a also shows
that the stacking sequence of the crystal is ꢂ ꢂ ꢂ Cl–Bi–O–Bi–Cl Cl–
Bi–O–Bi–Cl ꢂ ꢂ ꢂ. There is a weak nonbonding interlayer (van der
Waals) interaction along the c-axis. Therefore, structure is not clo-
sely packed in this direction. When one photon excites one elec-
tron from Cl 3p states to Bi 6p states in BiOCl, one pair of a hole
and an excited electron appear. The BiOCl with layered structure
could provide the space large enough to separate and conduct
the photogenerated hole–electron pair efficiently, which could
increase their photocatalytic activities. BiOCl has an indirect-
Fig. 4. (a) Front view of BiOCl layered structure. (b) Asymmetric decahedral
geometry with a Bi center.
transition band-gap so that the excited electron has to travel cer-
tain k-space distance to be emitted to valence band. This reduces
the recombination probability of the excited electron and the hole.
Both the open (loose packed) structure and indirect transitions
may benefit the hole–electron separation and the charge transport.
Thus these characteristics are favorable to the photocatalytic
reactions [27,20].

B. Pare et al. / Journal of Molecular Structure 1007 (2012) 196–202
199
The optical property of the BiOCl sample was measured using
UV–vis spectroscopy. The result showed that the sample reveal sig-
nificant increase in the photoabsorption at wavelength P 400 nm.
The band gap energy for BiOCl can be calculated from a plot of
was closely related to light wavelength. As a result, the change in
wavelength influences directly the amount of photons participate
in photoreaction. We have also performed the photocatalytic deg-
radation of MG in dark condition, as mentioned earlier (Fig. 6).
Thus it can be assumed that the photocatalytic degradation of
MG over BiOCl has been induced by light. In Fig. 7, it can be seen
that 71.4% MG degradation achieved around k > 390 nm and
54.3% in k > 400 nm. These results indicated that BiOCl showed
higher photocatalytic activity for MG degradation not only in UV
light region but also in visible light region.
1/2
(ahm
)
versus photon energy (hm) (Fig. 5). The intercept of the tan-
gent to the plot can give a good approximation of the band gap en-
ergy for BiOCl. The band gap energy estimated from the intercept
of the tangent to the plot is 3.2 eV, this observation was also made
by Wang et al. and Zhang et al. [28,19].
We further investigated the pH dependent photocatalytic activ-
ity of BiOCl, as shown in Fig. 8. A variation in pH from 2.36 to 8.57
greatly influences the photodegradation of MG in aqueous BiOCl
suspension. The photodegradation efficiency increases with de-
crease in pH. Since MG dye is cationic, it is obvious that their
adsorption on the photocatalyst surface is not possible in acidic
medium due to repulsive forces between negatively charged BiOCl
surface and dye. Therefore degradation efficiency of dye was ob-
served in basic medium. The prevailing pH of the solutions affects
the mode and extent of adsorption of MG on the BiOCl surface and
thus, indirectly, photodegradation rate of MG.
To assess the stability of the BiOCl in the photocatalytic reac-
tion, BiOCl was re-examined for two extra cycles. As shown in
Fig. 9 (II), (III), the high photocatalytic performance of the as-pre-
pared BiOCl for MG degradation was effectively maintained for
120 min of testing. After three cycles of repetition tests for photo-
degradation of MG, catalyst did not exhibit any significant loss of
activity. This experimental result indicated that BiOCl is more sta-
ble and has good photocatalytic performance on degradation of MG
3
.2. Photocatalytic experiments
Methylene green dye was chosen as a model contaminant to
evaluate the photocatalytic activity. Fig. 6 shows the photocatalytic
efficiency of BiOCl photocatalysts was evaluated by performing
degradation of MG. The results showed that degradation of MG
solution very low under visible light irradiation in the absence of
BiOCl and also BiOCl suspension was unable to initiate the dye deg-
radation in dark. Both light and BiOCl semiconductor particles
were very important for the degradation of MG aqueous solution.
By comparing the processes with blank tests, it was revealed that
the degradation process of MG was the predominant process
though photosensitization might also contribute some.
To confirm the photoreaction is induced by light, further we
studied the effect of the light wavelength on MG degradation using
different cut-off filters. The results showed that the photocatalytic
activity of BiOCl reduced with increasing light wavelength which
indicates that the change in photocatalytic properties over BiOCl
[
29,20].
Fig. 5. Plot of (
ah
m
)1/2 versus h
m
for BiOCl.
Fig. 7. Dependence of methylene green degradation on the light wavelength (k)
over BiOCl.
Fig. 6. The photodegradation of MG (a) with BiOCl (b) without catalyst (c) in dark
ꢀ
1
ꢀ1
Experimental conditions: [MG] = 50 mg L , [BiOCl] = 1.5 g mL , pH = 8.3.
Fig. 8. Dependence of photocatalytic properties over BiOCl on pH.

2
00
B. Pare et al. / Journal of Molecular Structure 1007 (2012) 196–202
Fig. 9. MG degradation by BiOCl at pH 8.3 (I) the first cycle; (II) the second cycle;
III) the third cycle; C , initial concentration of MG; C, residual concentration of MG.
2ꢀ
ꢀ
Fig. 11. Formation of SO4 and NO3 ions during the photodegradation of MG
(
(
0
ꢀ1
50 mg L ) in BiOCl aqueous dispersions under visible irradiation, pH = 8.3.
3.3. Formation of mineralization products
of sulfate ions on photocatalyst surface, as it has been already re-
ported for the degradation of other sulfur containing dyes [30–
To have a further insight, whether MG is mineralized or not, the
þ
3
2]. The nitrogen atoms with ꢀ3 oxidation state produced NH
4
inorganic ions formation and COD removal during the photocata-
lytic reaction was carried out. It was observed that the COD exhib-
ited a substantial decrease with irradiation time. For instance, after
a period of 2 h, the COD was reduced to about 38% of its initial va-
lue while at the end of the experiment (8 h) more than 97% of the
COD has been removed (Fig. 10). Consequently, the complete min-
eralization of MG was achieved after 8 h of visible light irradiation
in the presence of BiOCl because of the formation of more stable
intermediates towards oxidation. The result implies that both
mechanisms of degradation and mineralization play important
roles for the photocatalytic effects under visible light irradiation.
The COD analysis also showed dye sensitizations of catalyst. As
shown in Fig. 10, the COD removal of MG has been nearly main-
tained unchanged when MG was almost decolorized after 4 h,
which indicated that the dye sensitization involving an interaction
between BiOCl and MG [18].
þ
ꢀ
cations, subsequently NH cations were converted into NO ions.
4
3
It was obvious that aqueous MG was mainly mineralized rather
than being bleached [33].
As we know that the process of photocatalysis is the direct
absorption of photons by the band gap of the semiconductor and
generates electron–hole pairs. Here, the excitation of an electron
from the valence band to the conduction band is initiated by light
absorption with energy equal to or greater than the band gap of the
semiconductor. However, the band gap of white BiOCl is 3.2 eV,
which seems not be able to absorb visible light. In this connection
the interesting results have been reported by An et al. [18]. They
investigated that white BiOCl surprisingly turns to gray under vis-
ible light irradiation (k = 400–520 nm). It was also reported that
the EPR spectra of BiOCl proved the emergence of oxygen vacancy
which has changed the band gap of BiOCl. They observed that the
broad absorption band at above 400 nm is assigned to the oxygen
vacancy states, which are between 0.75 and 1.18 eV and below the
minimum level of the conduction band [34]. Therefore, the gray
BiOCl has the ability to absorb visible light irradiation. Similar sit-
uation is occurred in our present work, as these oxygen vacancies
could trap the electron and reduce the charge pair recombination,
which results in good photocatalytic performance in the degrada-
tion of MG.
Analysis of inorganic ions revealed as expected the formation of
ꢀ
2ꢀ
NO and SO4 in solution. As depicted in Fig. 11, the amount of
3
2
ꢀ
ꢀ
SO4 and NO3 ions increased with increasing irradiation time. Note
2
ꢀ
that the amount of SO ions released into the solution is lower
4
than that expected from stoichiometry. It was observed that the
concentration of sulfate ions increases rapidly at the first 3 h and
ꢀ1
tends to reach a plateau of ca. 27 mg L after 2 h. This can be
ꢀ
attributed to the fast elimination of the SO3 moiety in solution.
The photocatalysis of semiconductors is a complicated process,
which can be affected by electron structure, crystal structure, lat-
tice defects, surface morphology, etc.
This behavior can be ascribed to a partially irreversible adsorption
One of the photocatalytic degradation mechanisms of MG under
visible light irradiation was as follows: the direct absorption of
photons by BiOCl resulted in the generation of excited electrons
within the conduction band and photogenerated holes within the
valence band of BiOCl. The excited electrons could be captured
2
by surface adsorbed O , which degreased the recombination of
photogenerated electrons and holes. Consequently, the photogen-
erated holes could act as the oxidizing species for inducing MG
photodegradation. Another two possible degradation mechanisms
of MG with BiOCl has been proposed as follows: for photocatalytic
degradation of MG under visible light irradiation, the initial pro-
cess of MG degradation could be explained by Schemes 1 and 2.
As shown in Scheme 1, the generated hydroxyl radicals could fur-
ther oxidize the MG. As shown in Scheme 2, a photosensitization
process with MG as a sensitizer has realized, and the degradation
mechanism of MG in this process could be described by Scheme
2, in which MG adsorbed on BiOCl was excited by visible light irra-
Fig. 10. COD removal of the solution and efficiency %.
diation and then an electron was injected from the excited MG to

B. Pare et al. / Journal of Molecular Structure 1007 (2012) 196–202
201
Vis. light
¯
3.5. Structure–property relationship
h+ + e¯
BiOCl
(3)
(4)
The photocatalytic oxidation of the organic contaminants is clo-
sely related to two factors – efficient photo-induced electron hole
separation and transfer, and the structure of the band gap in the
photocatalyst [38,29]. In the process of photocatalytic degradation,
photogenerated electrons–hole separation is necessary to prevent
recombination of the photogenerated electrons and holes. The
internal electric fields are one of the important parameters to eval-
uate the ability of electron–hole separation and transport to the
surface to degrade the absorbed organic molecules. Generally,
¯
e
¯
+ O2
O2•
+
•OH
h + OH
(
5)
Scheme 1. Suggested photocatalytic degradation mechanism of BiOCl.
*
Vis. light
MG(ads)
MG(
ads)
(6)
BiOCl (e ) + MG (ads) (7)
2 2 2
the presence of internal electric fields between [Bi O ] and [Cl ]
are favorable for the efficient photoinduced electron–hole separa-
tion and transfer to the surface to degrade the adsorbed dye mol-
ecule [39,18].
+
MG (* ads) + BiOCl
¯
•
¯
(
8)
Band structure of BiOCl was calculated by TB-LMTO program
¯
BiOCl + O
BiOCl (e ) + O2
2
[
20]. From the calculated results of BiOCl, the density of states of
the BiOCl can be derived. The conduction band minimum (CBM)
of the oxychloride should be mainly composed of Bi 6p state, and
the valence band maximum (VBM) primarily consists of O 2p,
and Bi 6s hybrid orbitals. It has been found that the Bi 6s orbital
is largely dispersed around the top of valance band and the bottom
of conduction band, which is more beneficial to increasing the
mobility of photogenerated carriers. This might also be one of
the reasons for its better catalytic capability [35,20]. Moreover,
as mentioned earlier; An et al. have reported that oxygen vacancies
were created in the BiOCl under visible light irradiation which was
monitored by EPR spectrum [18]. The oxygen vacancies might also
form in our present study. Thus these oxygen vacancies could trap
the electron and reduced the charge pair recombination which re-
sults in good photocatalytic performance in the degradation of MG.
Scheme 2. Suggested photosensitization degradation mechanism of MG in the
presence of BiOCl.
the conduction band of BiOCl where the electron was scavenged by
molecular oxygen [19,34].
3.4. Role of added oxygen
The existence of oxygen in the suspension plays an important
role in the photocatalytic degradation of organic pollutants. The
oxygen molecule acts as an electron acceptor and decreases the
electron–hole pair recombination [35]. In order to determine the
effect of dissolved oxygen on the degradation of MG, the suspen-
2
sion purged with N to drive out a part of dissolved oxygen. The
experimental results showed that the degradation of MG was
much higher in the presence of molecular oxygen as presented in
Fig. 12. The photocatalytic mechanism shows that the surface re-
dox reactions initiated by photogenerated electrons and holes start
the photocatalytic degradation of organics. If the surface chemical
4. Conclusion
In summary, the BiOCl as photocatalyst with layered structure
has been synthesized by a hydrolysis method. The material pos-
sesses higher photocatalytic activities for both UV and visible light.
The high activity closely related with the internal electric field be-
tween [Bi O ] and [Cl ] slabs. The photocatalytic degradation of
2
reactions of CB electrons are blocked by N purging, the VB holes
would have a tendency to be consumed by the accumulated elec-
trons via the electron–hole recombination inside the catalyst,
hence, the photocatalytic degradation process would be signifi-
cantly restrained [36]. As discussed in Eqs. (3) to (5) in Scheme 1,
in the aerated condition, the oxygen accepts the conduction band
electron and gives rise to a superoxide radical anion which further
reacts with the hydrogen ion to form a hydroxyl radical in the sys-
tem which in turn increases the degradation rate [37]. The degra-
dation rate inhibited after oxygen was used up, indicates that the
oxygen is the main source of the active species [35].
2
2
2
methylene green with BiOCl has been investigated under visible
light irradiation. Simultaneously, the mineralization of aqueous
MG led to the formation of end products such as nitrate and sulfate
ions remarkable decrease of COD during the reaction was observed
which suggests that BiOCl/visible light system might be regarded
as an effective way for treating of textile industry wastewater. This
work not only provides an example of shape-dependent photocat-
alytic properties but also opens new possibilities to provide some
insight into layered structure semiconductors photocatalysts for
degrading organic pollutants and other applications.
Acknowledgment
Authors acknowledge support and laboratory facilities provided
by Principal, Dr. Usha Shrivastava and Dr. U.C. Maiwal, Head,
department of Chemistry, Madhav Science College, Ujjain, India.
Also the authors would like to thank the UGC-DAE CSR, Indore
for their help in XRD, TEM experiments and UV–Vis measurements.
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