Environmental remediation of Cr(VI) solutions by photocatalytic reduction using Ag-Er(OH)3 nanocomposite

Article abstract of DOI:10.1016/j.jallcom.2015.01.293

A hydrothermal method was use to prepare Er(OH)₃ nanoparticles, and a photoassisted deposition method was used to deposit silver onto the surface of those nanoparticles. Er(OH)₃ and Ag/Er(OH)₃ nanocomposites were character

Full text of DOI:10.1016/j.jallcom.2015.01.293

Journal of Alloys and Compounds 632 (2015) 735–740
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
Environmental remediation of Cr(VI) solutions by photocatalytic
reduction using Ag–Er(OH) nanocomposite
3
Aramice Y.S. Malkhasian a, , Reda M. Mohamed a,b,c
⇑
a
Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
Advanced Materials Department, Central Metallurgical R&D Institute, CMRDI, P.O. Box 87 Helwan, Cairo, Egypt
Center of Excellence in Environmental Studies, King Abdulaziz University, P.O. Box 80216, Jeddah 21589, Saudi Arabia
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A hydrothermal method was use to prepare Er(OH)3 nanoparticles, and a photoassisted deposition
Received 5 November 2014
Received in revised form 20 January 2015
Accepted 21 January 2015
Available online 7 February 2015
3 3
method was used to deposit silver onto the surface of those nanoparticles. Er(OH) and Ag/Er(OH) nano-
composites were characterized by BET, XRD, XPS, PL, UV–Vis and TEM measurements. The photocatalytic
performance of the nanoparticles with respect to the photocatalytic reduction of chromium(VI) under UV
light irradiation was determined. The results reveal that the silver particles were well dispersed onto the
surface of the Er(OH)
was observed to be smaller than that of the Er(OH)
of the Er(OH) nanoparticles by the deposition of silver particles. The Ag/Er(OH)
0.15 wt%) exhibit the lowest band gap and highest photocatalytic activity for the reduction of Cr(VI).
3
nanoparticles. Additionally, the surface area of the Ag/Er(OH)
nanoparticles due to the blocking of some pores
nanocomposites
3
nanocomposites
Keywords:
3
Er(OH)
3
3
3
Ag doping
Photocatalyst
Cr(VI) reduction
(
The photocatalytic performance of the 0.15 wt% Ag/Er(OH)
3
nanocomposites was stable after the reuse
of the nanoparticles for the reduction of Cr(VI) after five uses.
Ó 2015 Elsevier B.V. All rights reserved.
1
. Introduction
photocatalysts for environmental cleanup. As previously men-
tioned, the energy gap of TiO is 3.2 eV, which is equivalent to a
photon in the UV region with a wavelength of 380 nm. Therefore,
TiO requires near-UV light to act as a photocatalyst. The holes that
are formed in TiO are highly oxidizing, which leads to the forma-
tion of OH radicals. Therefore, inorganic species that possess more
positive reduction potentials relative to the conduction band of a
semiconductor provide more electrons for reaction. In recent years,
increasing attention has been focused on the photocatalytic reduc-
2
Photocatalysis describes the change in the rate of a photoreac-
tion in the presence of a catalyst. In a photocatalytic reaction, light
is absorbed by a semiconductor. Any photoreaction that occurs in
the presence of a catalyst depends on the ability of the semicon-
ductor to create electron–hole pairs to proceed, which conse-
quently generates free radicals, such as hydroxyl radicals, that in
turn are able to undergo further reactions. Since the discovery of
2
2
TiO
process has been referred to as the advanced oxidation process
AOP). There are various methods for developing an advanced oxi-
dation process via the synthesis of new photocatalysts that can
function more efficiently than TiO . The synthesis of new semicon-
ductors that function as photocatalysts, e.g., for the degradation of
organic contaminants and water splitting using solar energy, is
2
inevitable. TiO , the most widely used photocatalyst, is photoactive
2
for use in the electrolysis of water [1], the commercially used
2
tion of inorganic contaminants. TiO photocatalytic reduction is
well reported to be effective in removing various toxic metal ions,
such as mercury [9,10], arsenic [11,12] and chromium [13–17]. The
physical and chemical properties of chromium depend on the
molecular structure of the chromium compounds considered.
These compounds primarily exist in two oxidation states: Cr(III)
and Cr(VI). Cr(VI) compounds are more toxic, more soluble and
more mobile (because of being weakly adsorbed on the inorganic
surfaces) than Cr(III) compounds. According to the United States
EPA, Cr(VI) is considered a high priority hazard due to the dangers
of the presence of chromium in drinking water. Chromium electro-
plating, leather tanning and paint industries are the main sources
of Cr(VI). Efforts have been undertaken to remove Cr(VI) by reduc-
ing it to Cr(III), which is 100 times less toxic and less mobile. The
reduction process involves the neutralization or alkalization of
(
2
for UV photons and inactive under visible light because of its large
band gap (3.20 eV) [2–6]. The UV region covers only approximately
4
% of the entire solar spectrum, whereas visible light covers 45% of
the spectrum. Therefore, research efforts focus on visible-
light-sensitive photocatalysts as the most inexpensive source of
⇑
Corresponding author. Tel.: +966 593399741; fax: +966 2 6952292.
E-mail address: amalkhasian10@gmail.com (A.Y.S. Malkhasian).
3
the containing solution by precipitating Cr(OH) . Further reduction
http://dx.doi.org/10.1016/j.jallcom.2015.01.293
925-8388/Ó 2015 Elsevier B.V. All rights reserved.
0

7
36
A.Y.S. Malkhasian, R.M. Mohamed / Journal of Alloys and Compounds 632 (2015) 735–740
tion of chromium(VI) in the samples was estimated with a UV–Vis spectrophotom-
eter (V-570, JASCO, Japan) at 540 nm using the standard diphenylcarbazide method
is performed to obtain Cr(0) [7,8]. The following semiconductors
photocatalysts) have been used for the photoreduction of Cr(IV)
to the less toxic Cr(III):ZnO, Hombikat UV 100, Degussa P25 and
WO [18]. These semiconductors have been studied as a function
(
[
28].
The photoreduction efficiency of chromium(VI) (%), was measured by applying
the following equation:
3
of the pH of the slurry, the initial Cr(VI) concentration and the
amount of the semiconductor used in the slurry. All of these quan-
tities produce increasing amounts of the Cr(VI) reduced photo-
product with a decrease in pH. It has been suggested that the
reaction mechanism is acid-catalyzed. The reaction mechanism
varies to first order with the initial concentration of Cr(VI). Note
that other non-photocatalytic methods (mainly analytic tech-
niques) are used to remove Cr(VI) ions from industrial wastewater
via different techniques, such as reduction [19,20], reduction fol-
lowed by chemical precipitation [21], adsorption on activated
charcoal [22], solvent extraction [23], freeze separation and reverse
osmosis [24], ion exchange [25] and electrolytic methods [26]. The
removal of chromium [27] from inorganic waste can be accom-
plished by conventional techniques, such as chemical precipita-
tion, ion exchange, electrochemical and adsorption. Each of these
techniques has its own disadvantages, for example, an inability
to meet health and hazards regulations, high energy consumption
and highly toxic hazardous waste. The best of these techniques
should meet the maximum pollutant level (Cr = 0.05 mg/L) at a
low cost. To the best of our knowledge, there are no reports on
%
photoreduction efficiency ¼ ðC
o
ꢀ C
t
Þ=C
o
ꢁ 100
where C is the initial concentration of chromium(VI) in the solution at zero time and
o
C
t
is the concentration of chromium(VI) in the solution at time t.
3
. Results and discussion
3.1. Structural, morphological and compositional characterizations
Fig. 1 shows the XRD patterns of the Er(OH)
nanocomposites. The results reveal that the nanocomposites are
mainly composed of Er(OH) , which indicates that the lack of dif-
fraction peaks due to Ag in the patterns of the Ag/Er(OH) samples
is because the wt% of Ag is below the XRD detection limit or per-
haps because Ag is well dispersed on surface of the Er(OH)
nanoparticles.
Fig. 2 shows the XPS spectra of Ag 3d for a sample of Ag/
Er(OH) . The results reveal the presence of Ag metal in the sample
via the two peaks for Ag 3d5/2 and Ag3d3/2 at 284.7 eV and
3 3
and Ag/Er(OH)
3
3
3
3
2
87.7 eV, respectively.
the reduction of chromium(VI) in aqueous solution by Er(OH)
The present study presents the synthesis and characterization of
Ag/Er(OH) and the evaluation of its photocatalytic activity for
the reduction of chromium(VI) in the aqueous phase.
3
.
3 3
Fig. 3 shows TEM images of Er(OH) and Ag/Er(OH) nanocom-
posites. The results show that an increase in the wt% of Ag
increases the dispersion of Ag on the surface of the Er(OH) nano-
particles. Additionally, an increase in the wt% of Ag to 0.15%
increases the homogeneity of the Ag particle size on the surface
3
3
2
. Experimental
3
of the Er(OH) nanoparticles. This homogeneity decreases at higher
2
.1. Preparation of photocatalyst
concentrations of silver, i.e., 0.20 wt%, which suggests that there is
an optimum content for the deposition of Ag ions that controls the
size and homogeneity of the doped silver.
3
A hydrothermal method was used to prepare Er(OH) nanoparticles. All of the
chemicals used as starting materials were provided by Sigma–Aldrich. In a typical
synthesis, 2 mmol of erbium(III) nitrate pentahydrate, 15 mmol of urea and 1 g of
cetyltrimethylammonium were dissolved at room temperature in 70 ml of water
and then stirred for 30 min. The resulting mixture was kept in a Teflon-lined stain-
less steel autoclave at 100 °C for 24 h. The obtained mixture was washed with dis-
tilled water and ethanol absolute several times and finally dried for 24 h at 60 °C.
3.2. Surface area analysis
3 3
The texture parameters of the Er(OH) and Ag/Er(OH) nano-
PAD-Ag/Er(OH)
sized using the following photo-assisted deposition (PAD) route: Ag metal was
deposited onto Er(OH) with an aqueous solution of silver nitrate under UV-light
irradiation. The samples were dried at 60 °C and treated via reduction
3
(containing 0.05, 0.10, 0.15 or 0.20 wt% of Ag metal) was synthe-
composites are presented in Table 1. The SBET values for Er(OH)
3
and 0.05 wt% Ag/Er(OH) , 0.10 wt% Ag/Er(OH) , 0.15 wt% Ag/
3
3
3
Er(OH)
3
and 0.20 wt% Ag/Er(OH)
3
were determined to be 53, 47,
H
2
2
ꢀ
1
45, 43 and 38 m /g, respectively. The total pore volume of Ag/
(
20 ml min ) at 80 °C for 2 h.
3 3
Er(OH) is smaller than that of the Er(OH) sample due to the
blocking of some pores by the deposition of Ag metal. The presence
2.2. Characterization techniques
X-ray diffraction (XRD) analysis was performed at room temperature with a
Bruker axis D8 using Cu K radiation (k = 1.540 Å). The specific surface area was cal-
culated from N -adsorption measurements, which were obtained using a Nova
000 series Chromatech apparatus at 77 K. Prior to the measurements, the samples
a
0
.15 wt % Ag/Er(OH)3 after
2
2
were treated under vacuum at 100 °C for 2 h. The band gap of the samples was iden-
tified by UV–visible diffuse reflectance spectroscopy (UV–Vis-DRS), which was per-
formed in air at room temperature over the wavelength range of 200–800 nm using
0.20 wt % Ag/Er(OH)3
0
.15 wt % Ag/Er(OH) before
3
a
UV/Vis/NIR spectrophotometer (V-570, JASCO, Japan). Transmission electron
microscope (TEM) analysis was conducted with a JEOL-JEM-1230 microscope, and
samples were prepared by suspension in ethanol, followed by ultrasonication for
0.10 wt % Ag/Er(OH)3
3
0 min. Subsequently, a small amount of this solution was placed onto a carbon-
coated copper grid and dried before loading the sample into the TEM. X-ray photo-
electron spectroscopy (XPS) studies were performed using a Thermo Scientific K-
ALPHA, XPS, England. Photoluminescence (PL) emission spectra were recorded
using a Shimadzu RF-5301 fluorescence spectrophotometer.
0
.05 wt % Ag/Er(OH)3
Er(OH)3
2.3. Photocatalysis experiment
The application of the synthesized nanoparticles for the photoreduction of chro-
mium(VI) was studied under UV irradiation. The experiments were performed
using a horizontal cylinder annular batch reactor. The photocatalyst was irradiated
using a xenon lamp (300 W). In a typical experiment, the desired weight of the cat-
alyst was suspended in 500 ml of a 150 mg/l K Cr O solution. The reaction was
2 2 7
performed isothermally at 25 °C, and the samples in the reaction mixture were
1
0
20
30
40
2-theta, degree
50
60
70
analyzed at different time intervals for a total reaction time of 1 h. The concentra-
Fig. 1. XRD patterns of Er(OH)
3
and Ag/Er(OH)
3
nanocomposites.

A.Y.S. Malkhasian, R.M. Mohamed / Journal of Alloys and Compounds 632 (2015) 735–740
737
1000
of mesopores in all samples was confirmed by the similar values of
BET and S in most samples, as presented in Table 1.
S
t
Ag 3d
3.3. Optical characterization
8
6
4
2
00
00
00
Fig. 4 shows the UV–Vis diffuse reflectance spectra of the
Er(OH) and Ag/Er(OH) nanocomposites. The results demonstrate
that the deposition of silver metal onto the surface of Er(OH) leads
to a shift in the absorption edge of Er(OH) from 325 nm to
94 nm. The UV–Vis spectra were used to calculate the direct band
gap of the Er(OH) and Ag/Er(OH) nanocomposites based on a
3
3
3
3
3
3
3
method used by Mohamed [29]. The band gap energies were calcu-
lated using the following equation:
E
g
¼ 1239:8=k
00
3
80
375
370
365
360
where E is the band gap (eV) and k is the wavelength (nm) of the
g
absorption edges in the spectrum; the results are tabulated in
Table 2.
Binding energy, eV
Fig. 2. XPS spectra of Ag 3d for the 0.15 wt% Ag/Er(OH)
3
sample.
The results reveal that an increase in the wt% of silver from
0
.05 wt% to 0.15 wt% decreases the band gap from 3.81 eV to
A
B
Ag
C
D
F
3 3
Fig. 3. TEM images of Er(OH) and Ag/Er(OH) nanocomposites, where the wt% of Ag is 0.0 (A), 0.05 (B), 0.10 (C), 0.15 (D) and 0.20 (F).

7
38
A.Y.S. Malkhasian, R.M. Mohamed / Journal of Alloys and Compounds 632 (2015) 735–740
Table 1
Texture parameters of Er(OH)
3
and Ag/Er(OH)
3
nanocomposites.
2
2
2
2
3
3
3
Sample
S
BET (m /g)
S
t
(m /g)
S
micro (cm /g)
S
ext (cm /g)
V
p
(cm /g)
V
micro (cm /g)
V
meso (cm /g)
r (Å)
Er(OH)
3
53.00
47.00
45.00
43.00
38.00
56.00
50.00
48.00
44.00
39.00
32.00
30.00
29.00
28.00
21.00
21.00
17.00
16.00
16.00
14.00
0.200
0.145
0.122
0.115
0.098
0.164
0.120
0.100
0.095
0.055
0.050
0.025
0.022
0.020
0.018
30.00
40.00
50.00
55.00
50.00
0
0
0
0
.05 wt% Ag/Er(OH)
3
3
3
3
.10 wt% Ag/Er(OH)
.15 wt% Ag/Er(OH)
.20 wt% Ag/Er(OH)
Note:
(
(
(
(
S
S
V
V
BET) I BET-surface area (S ) I surface area derived from Vlꢀt plots.
t
mic) I surface area of micropores (Sext) I external surface area.
p
) I total pore volume (Vmic) I volume of micropores.
ꢀ
mes) I volume of mesopores (r ) I mean pore radius.
0
0
0
0
0
.15 wt % Ag/Er(OH) after
3
Er(OH)3
.15 wt % Ag/Er(OH) before
3
0
0
.05 wt % Ag/Er(OH)3
.20 wt % Ag/Er(OH)3
.10 wt % Ag/Er(OH)3
.05 wt % Ag/Er(OH)3
.10 wt % Ag/Er(OH)3
0.20 wt % Ag/Er(OH)3
0.15 wt % Ag/Er(OH)3
Er(OH)3
4
00
450
500
550
2
00 250 300 350 400 450 500 550 600 650 700 750 800
Wavelength (nm)
Wavelength, nm
Fig. 5. PL spectra of Er(OH)
3
and Ag/Er(OH)
3
nanocomposites.
3 3
Fig. 4. UV–Vis absorption spectra of Er(OH) and Ag/Er(OH) nanocomposites.
1
00
Table 2
0.15 wt % Ag/Er(OH)3
Band gap energy of Er(OH)
nanocomposites.
3
and Ag/Er(OH)
3
9
8
0
0
0.20 wt % Ag/Er(OH)3
0
.10 wt % Ag/Er(OH)3
Sample
Er(OH)
Band gap energy, eV
0.05 wt % Ag/Er(OH)3
3
3.81
3.52
3.37
3.11
3.14
70
60
Er(OH)3
0
0
0
0
.05 wt% Ag/Er(OH)
.10 wt% Ag/Er(OH)
.15 wt% Ag/Er(OH)
.20 wt% Ag/Er(OH)
3
3
3
3
5
4
3
0
0
0
3
.11 eV. However, there is no significant effect on the band gap at a
high wt% of silver greater than 0.15. Therefore, there is an optimum
content of deposited silver that controls the band gap.
We investigate the separation and recombination of photogen-
erated charge carriers and the transfer of the photogenerated elec-
trons and holes by gathering photoluminescence (Pl) emission
spectra. The results indicate that an increase in the wt% of silver
20
10
0
0
10
20
30
40
50
60
Reaction time, min
deposited on the Er(OH)
.15 wt% leads to a decrease in the Pl intensity. However, there is
no significant effect on the Pl intensity at a high wt% of silver above
.15. Therefore, there is an optimum content of deposited silver
3
nanoparticles from 0.05 wt% to
Fig. 6. Effect of the wt% of Ag on the photocatalytic activity of Er(OH)
posites for the reduction of Cr(VI).
3
nanocom-
0
0
that yields the carrier lifetime required for e–h recombination, in
agreement with the UV–Vis results (see Fig. 5).
2 2 7 2 2 7
conditions: K Cr O concentration of 125 ppm, K Cr O volume of
500 ml and photocatalyst weight of 0.30 g. The results reveal that
the photocatalytic activity increased from 48.5% to 100% with an
increase in the wt% of silver from 0 wt% to 0.15 wt%. However,
further increasing the wt% of silver above 0.15 wt% led to a
decrease in the photocatalytic activity from 100% to 97%. This
decrease was observed because a high wt% of silver hinders the
3.4. Photocatalytic activities
Fig. 6 shows the effect of the wt% of Ag on the photocatalytic
3
activity of Er(OH) nanoparticles for the reduction of Cr(VI) under
UV irradiation; the experiment was performed under the following
3
penetration of light to the surface of Er(OH) , thereby decreasing

A.Y.S. Malkhasian, R.M. Mohamed / Journal of Alloys and Compounds 632 (2015) 735–740
739
4
3
3
2
2
1
1
0000
5000
0000
5000
0000
5000
0000
100
Cr 2p
8
6
0
0
5
7
1
1
1
2
0 ppm
5 ppm
00 ppm
25 ppm
50 ppm
00 ppm
40
20
5000
0
0
6
05
600
595
590
585
580
575
570
0
10
20
30
40
50
60
Binding energy, eV
Reaction time, min
Fig. 7. XPS spectra of Cr 2p for the 0.15 wt% Ag/Er(OH)
the reduction of Cr(VI) solution.
3
sample after being used for
Fig. 9. Effect of the initial Cr(VI) solution concentration on the photocatalytic
reduction of the Cr(VI) solution.
100
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
1
00
80
6
4
2
0
0
0
0
0.3 g/l
0
0
1
1
.6 g/l
.9 g/l
.2 g/l
.6 g/l
0
10
20
30
40
50
60
1
2
3
4
5
Reaction time, min
Number of cycle
3
Fig. 8. Effect of loading of the 0.15 wt% Ag/Er(OH) sample on the photocatalytic
reduction of the Cr(VI) solution.
Fig. 10. Recycling and reuse of photocatalysts for the photocatalytic reduction of
the Cr(VI) solution.
the photocatalytic performance of Er(OH)
reduction of Cr(VI). Fig. 7 shows the XPS spectra of Cr 2p for the
.15 wt% Ag/Er(OH) sample after it was used to reduce a Cr(VI)
solution. The results reveal the presence of Cr(III) in the sample
by the two peaks for Cr 2p3/2 and Cr 2p1/2 (Fig. 7), which confirm
that Cr(VI) was reduced to Cr(II).
3
with respect to the
0
3
Fig. 9 shows the effect of the initial Cr(VI) solution concentra-
tion on the photocatalytic reduction of the Cr(VI) solution under
UV irradiation, which was studied by varying the initial Cr(VI)
solution concentration from 25 ppm to 150 ppm in the presence
Fig. 8 shows the effect of loading the 0.15 wt% Ag/Er(OH)
ple on the photocatalytic reduction of the Cr(VI) solution under UV
irradiation; the experiment was performed under the following
3
sam-
3
of 0.15 wt% Ag/Er(OH) photocatalyst. The results demonstrate
that the photocatalytic activity remained nearly unchanged with
an increase in the initial Cr(VI) solution concentration from
50 ppm to 125 ppm after the 30 min of reaction time required to
complete the reduction of Cr(VI). However, for initial Cr(VI) solu-
tion concentrations above 125 ppm, the reaction time required to
complete the reduction of Cr(VI) was increased to 40 min and
55 min by increasing the initial Cr(VI) solution concentration to
150 ppm and 200 ppm, respectively. The photocatalytic activity
depends on the hydroxyl free radicals reaching the surface of the
catalyst and then reacting with the Cr(VI) solution; therefore,
increasing the initial Cr(VI) solution concentration increases the
probability of a reaction between the free radicals and the Cr(VI)
solution, thereby increasing the photocatalytic activity. A further
increase in the initial Cr(VI) solution concentration decreases the
conditions: K
2
Cr
2
O
7
concentration of 125 ppm, K
2 2 7
Cr O volume
of 500 ml and a 0.15 wt% Ag/Er(OH)
3
nanocomposites photocata-
lyst. The results reveal that photocatalytic performance, in terms
of a%, after 60 min was increased from 84% to 100% with an
increase in the weight of the photocatalyst from 0.3 g/l to 0.6 g/l.
The reaction time required to complete the reduction of Cr(VI)
was decreased to 60 min, 50 min and 30 min as the weight of the
photocatalyst was increased to 0.6 g/l, 0.9 g/l and 1.2 g/l,
respectively. However, the reaction time required to complete
the reduction of Cr(VI) was increased again to 40 min with an
increase in the weight of the photocatalyst above 1.2 g/l; that is,
the optimum weight of the photocatalyst is 1.2 g/l.

7
40
A.Y.S. Malkhasian, R.M. Mohamed / Journal of Alloys and Compounds 632 (2015) 735–740
photocatalytic activity because the active sites of the photocatalyst
are blocked by the Cr(VI) solution, which prevents UV light from
penetrating the surface of active sites.
Fig. 10 shows the results obtained regarding the recycling and
reuse of photocatalysts for the photocatalytic reduction of the
Cr(VI) solution. The experiment was carried out under the
following conditions: a reaction time of 30 min, a Cr(VI) solution
Acknowledgments
This work was funded by the Deanship of Scientific Research
(DSR), King Abdulaziz University, Jeddah, under grant number
(130-135-D1435). The authors therefore acknowledge the DSR
for technical and financial support.
concentration of 125 ppm and 1.2 g/l of 0.15 wt% Ag/Er(OH)
3
nano-
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composite. The results show that the photocatalytic activity
remains nearly unchanged after five uses, which means that the
photocatalyst is stable in the photocatalytic reduction of the Cr(VI)
[
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before the reaction. This finding indicates that the structure of the
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3
0
.15 wt% Ag/Er(OH)
3
does not change during the photocatalytic
[
process. In addition, the UV–Vis spectra of the 0.15 wt% Ag/Er(OH)
3
(
sample before and after being reused five times are shown in Fig. 4.
It was also observed that the absorption spectrum of the 0.15 wt%
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[
[
Ag/Er(OH)
observed before the reaction. This result indicates that the struc-
ture of 0.15 wt% Ag/Er(OH) does not change during the photocat-
3
sample after the first five cycles was similar to that
143.
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[
[
[
3
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alytic process. Therefore, this photocatalyst can be separated and
recycled while maintaining its stability, making it a promising
material for environmental remediation.
[
[
189–194.
4
. Conclusions
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[
[
[
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3
In summary, a Ag/Er(OH) nanocomposite photocatalyst was
successfully synthesized and proven to be a promising catalyst
due to its high efficiency in reducing the pollutant Cr(VI) under
UV light. The band gap of the Er(OH) photocatalyst can be con-
3
[
[
22] M. Lotfi, N. Adhoum, Sep. Purif. Technol. 26 (2–3) (2002) 137–146.
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509–512.
trolled by controlling the weight percent of silver that is deposited
onto the surface of the photocatalyst. The results of photocatalytic
studies reveal that the highest photocatalytic activity and stability
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[
[
[
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were obtained for the 0.15 wt% Ag/Er(OH)
catalyst, which can be used to reduce 100% of Cr(VI) to Cr(III) after
0 min.
3
nanocomposite photo-
[
[
28] T.X. Wang, S.H. Xu, F.X. Yang, Mater. Lett. 83 (2012) 46–48.
29] R.M. Mohamed, Desalin. Water Treat. 50 (2012) 147–156.
3