1) Mesoporous silica (MCM-48) was synthesized using silica fume solid waste and used to support nickel oxide nanoparticles. 2) The MCM-48/nickel oxide composite showed enhanced adsorption capacity and photocatalytic degradation of Congo red dye under visible light compared to nickel oxide alone. 3) Adsorption and photocatalytic degradation experiments using the MCM-48/nickel oxide composite demonstrated it is an efficient and reusable catalyst for removing dye pollutants from water.

1. RESEARCH ARTICLE
Preparation and characterization of MCM-48/nickel oxide
composite as an efficient and reusable catalyst for the assessment
of photocatalytic activity
Mohamed Shaban1
& Ahmed Hamd1,2
& Ragab R. Amin2
& Mostafa R. Abukhadra1,3
& Ahmed Abdel Khalek4
&
Aftab Aslam Parwaz Khan5,6
& Abdullah M. Asiri5,6
Received: 13 January 2020 /Accepted: 25 May 2020
# Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
Mesoporous silica (MCM-48) was synthesized and used as a catalyst for supporting the nickel oxide photocatalyst. The loading
of nickel oxide on MCM-48 results in a considerable reduction in the bandgap energy to 2.4 eV. MCM-48 was used as a catalyst
and back-supporter for the nickel oxide to enhance its photocatalytic properties along with adsorption capacity. Therefore, the
adsorption capacity of MCM-48/Ni2O3 was enhanced by 17.5% and 32.2% compared to Ni2O3 and MCM-48, respectively.
Furthermore, the percentage of photocatalytic degradation was improved by approximately 68.2% relative to the free-standing
Ni2O3. The MCM-48/Ni2O3 proved the chemisorption adsorption mechanism that happens in multilayer form through the
heterogeneous surface. This through fixing such Ni2O3 particles over the nanoporous topography to provide more exposed
hot adsorption and photocatalytic sites for the incident light photons. Therefore, supporting Ni2O3 catalytic particles onto MCM-
48 produces a new category of photocatalytic systems with promising active centers for the efficient degradation of Congo red
dye molecules.
Keywords Mesoporous silica fume . Ni2O3
. MCM-48 . Photocatalyst
Introduction
In the last decade, the extensive use of dyes and pigments in
several industries, such as textile, plastics, and rubbers, result-
ed in large amounts of wastewater polluted by synthetic dyes
(Shengfang and Min 2015). In addition to the damage of water
quality, dyes are the primary source of many environmental
perturbations and cause many diseases like those in the repro-
ductive system, liver and kidney dysfunction, skin irritation,
cancer, dermatitis, and allergy (Gupta et al. 2006). Congo red
dye is commonly utilized in cosmetics, plastics, and rubbers
(Sharma and Janveja 2008). Congo red dye is counted as a
carcinogenic, mutagenic, and toxic synthetic dye; however, it
is characterized by high stability that decreases the decoloriz-
ing efficiency of many traditional approaches (Sharma and
Janveja 2008). Many different methods were suggested to
remove dye pollutants, including physical and chemical pro-
cedures. The commonly used procedures are photocatalytic
degradation, adsorption, ozonation, biodegradation, ion ex-
change, Fenton’s oxidation, and flocculation (Rahman et al.
2013; Duraisamya et al. 2015).
Responsible editor: Sami Rtimi
* Mohamed Shaban
mssfadel@yahoo.com
* Aftab Aslam Parwaz Khan
draapk@gmail.com
1
Nanophotonics and Applications Lab, Physics Department, Faculty
of Science, Beni-Suef University, Beni Suef 62514, Egypt
2
Basic Science Department, Nahda University Beni-Suef (NUB),
Beni Suef, Egypt
3
Geology Department, Faculty of Science, Beni-Suef University, Beni
Suef, Egypt
4
Chemistry Department, Faculty of Science, Beni-Suef University,
Beni-Suef, Egypt
5
Center of Excellence for Advanced Materials Research (CEAMR),
King Abdulaziz University, Jeddah 21589, Saudi Arabia
6
Chemistry Department, King Abdulaziz University, Jeddah 21589,
Saudi Arabia
Environmental Science and Pollution Research
https://doi.org/10.1007/s11356-020-09431-7

2. Metal oxide semiconductors are commonly utilized as het-
erogeneous photocatalysts for their suitable band gaps and
abilities to profiteer the solar power to produce hydroxyl rad-
icals. Nickel oxide, one of the most promising transition metal
oxides, has many potential applications, such as electrochem-
ical capacitors, lithium-ion batteries, gas sensors, water pol-
lutant adsorbers, and photoelectrodes (Li et al. 2017). It may
be synthesized by a few approaches like thermal decomposi-
tion technique, surfactant-assisted technique, spray pyrolysis,
chemical vapor deposition, sol-gel, and chemical precipitation
(Dharmaraja et al. 2006; Sun et al. 2013). Applying semicon-
ducting metal oxides for photocatalytic degradation of dyes
has problems like difficult recovery, small surface area, less
adsorption capacity, and less quantum yield that will lower
their effectiveness in the manufacturing scale (Zhang et al.
2013). Consequently, various kinds of backed catalyst-
supporters are examined as improving techniques for the re-
covery efficiency and the photocatalytic properties of semi-
conductor metal oxides (Sun et al. 2013; Shaban et al. 2017).
Mesoporous materials, activated carbon, palygorskite, zeolite,
and clay minerals are the widely used backed supporters for
the photocatalysts (Shaban et al. 2017; Sun et al. 2013; Zhen
et al. 2012; Shaban and Abukhadra 2017).
Silica mesoporous substances, such as MCM-48 and
MCM-41, are generally specified by higher thermal stability,
higher surface area, regular nanoporous structure (2–50 nm),
and silanol groups on the internal surfaces of the pores (Razieh
et al. 2005). Thus, they are popular as adsorbent substances
and catalyst support (Yongde and Robert 2003). Hexagonal-
phase MCM-41 was mainly utilized as a catalyst support in
many prior scientific studies, whereas a limited number of
researches investigated the cubic-phase MCM-48 for this par-
ticular objective (Zhen et al. 2012). This can be attributed to
the difficulty in the synthesis of MCM-48 as it is an interme-
diate stage formed during the transformation of hexagonal
phases into the lamellar phase. MCM-48–based materials are
branched, interwoven, and 3-dimensional porous structures
that encourage the mass transfer kinetics in catalytic/
adsorption applications.
Solid wastes were considered as the most challenging prob-
lem faced by people. Solid wastes are commonly produced as
byproducts throughout mining processes or industrial activi-
ties, as well as sludge generated from the treatment of waste-
water (Ramachandra and Varghese 2003). Recently, many
articles have been reported for setting new technologies to
reduce the waste amount by recycling process in many appli-
cations. Silica fume is a conventional, very fine byproduct
silica of noncrystalline nature that produced as solid wastes
during the manufacturing of ferrosilicon alloys and silicon
metal (Siddique and Iqbal Khan 2011). It is also known as
micro silica, volatilized silica, or silica dust. It can be used as a
source of reactive silica because more than 95% of the resulted
silica fume is a spherical particle finer than 1 μm in size, i.e.,
the specific surface area of the silica fume ranges from 13,000
to ~30,000 m2
/kg (Silica Fume Association 2005).
Chemically, it is composed of more than 90% SiO2 and small
amounts of manganese oxide, iron oxide, and alkali oxides.
Here, we investigated a novel utilization of massive
amounts of silica fume solid waste for the effective synthesis
of MCM-48 as a catalyst and back-supporter of nickel oxide
nanophotocatalysts. The synthesized MCM-48/nickel oxide
nanocomposite has been evaluated for the massive and simul-
taneous adsorption/photocatalytic remediation of Congo red
dye from the contaminated water under visible light at differ-
ent contact times, dye concentrations, catalyst masses, and pH
values. For comparison, results of the nanocomposite are
compared with the results of the free-standing nickel oxide.
Moreover, isotherms and reactions kinetics had been resolved
to recognize the adsorption/photocatalytic system
mechanisms.
Material and methods
Materials
Sample of silica fume solid waste had been obtained from the
Central Metallurgical Research & Development Institute
(CMRDI, Helwan, Egypt). Ethanol (Aldrich, 95%), ammoni-
um hydroxide (Aldrich, 30–33%), along with
cetyltrimethylammonium bromide (Aldrich, 99%) had been
utilized in MCM-48 synthesis. Nickel (II) chloride hexahy-
drate along with NaOH pellets (Aldrich, 97%) had been uti-
lized in the deposition of nickel oxide catalyst using MCM-48
as support material.
Synthesis of MCM-48/nickel oxide composite
Synthesis of silica MCM-48
MCM-48 mesoporous silica had been synthesized utilizing
the traditional hydrothermal procedure. At first, 2 g of
cetyltrimethylammonium bromide surfactant had been put in-
to 40 mL of deionized water under stirring for 15 min. After
the complete dissolving of the surfactant, 13 mL of NH4OH
had been mixed slowly with the solution. Then, 40 mL of
absolute ethanol had been added under constant stirring for a
further 15 min. Silica fume (1.75 g) had been put into the
solution and stirred for an additional 10 min. After that, the
resulted solution was transferred into Teflon-lined stainless
autoclave and warmed up in an electrical muffle furnace for
48 h at 110 °C. After that, when it cooled down, the developed
mesoporous powder had been cleaned many times using eth-
anol and deionized water and dried at 65 °C overnight. Lastly,
the solution had been annealed for 8 h at 550 °C to eliminate
the organic remnant as shown in Fig. 1.
Environ Sci Pollut Res

3. Synthesis of silica MCM-48/nickel oxide composite
The composite had been prepared with a weight ratio of 1:1
for MCM-48:nickel oxide. After that, 1 g of the prepared
MCM-48 had been dispersed in 50 mL of nickel (II) chloride
hexahydrate solution (0.3 M) in a Teflon bar under
ultrasonication. In the next step, 50 mL of sodium hydroxide
solution had been dropped wisely added to the solution under
ultrasonic irradiation within a hot bass for 6 h at 100 °C. Next,
the final solid substance had been separated from the residual
liquid and washed, often using the distilled water for 12 h at
85 °C. Finally, a calcination process in the air had been carried
out at 450 °C to convert MCM-48/nickel hydroxide to MCM-
48/nickel oxide (Fig. 1).
Sample characterization
X-Ray diffraction patterns of the silica fume and MCM-48/
nickel oxide composite have been measured by an X-ray dif-
fractometer (Philips APD-3720 with CuKα line of wave-
length 0.154 nm) operated at 40 kV along with 20 mA in 5–
70° 2θ-range with a scanning rate of 5°/min. The XRD pattern
of the prepared MCM-48 mesoporous silica has been mea-
sured within 2θ-range from 1° to 10° with a 2° min−1
scanning
velocity. A scanning electron microscope has observed the
surface morphologies of silica fume-based MCM-48 and
MCM-48/nickel oxide composite. (JSM-6510, JEOL,
Tokyo, Japan). A Perkin-Elmer Lambda 900 UV–Vis-NIR
spectrophotometer has measured the optical spectra.
Removal of Congo red dye
Adsorption properties of MCM-48/nickel oxide
The adsorption properties of silica fume-based MCM-48/
nickel oxide were evaluated using Giles’s classification,
Langmuir isotherm model, Freundlich, and Temkin equilibri-
um models (Chaouch et al. 2014; Chrysicopoulou et al. 1998;
Fathal and Ahmed 2015; Giles et al. 1960). These have been
resolved by shaking 0.02 g of the man-made substance with
100 mL Congo red dye of various concentrations (5–40 mg/L
with increment of 5 mg/L) for 24 h. Next, the used solids and
solutions have been separated by the centrifuge and collected
for evaluation with Perkin-Elmer Lambda 900 UV–Vis-NIR
spectrophotometer.
Photocatalytic properties of MCM-48/nickel oxide
The photocatalytic properties of MCM-48/nickel oxide had
been resolved via the effectiveness in the degradation of
Congo red dye. These tests have been done under synthetic
visible light irradiation (400 W blended metal halide lamp with
2 tubes (JLZ400 E40)). The distance from the light source is
fixed at 15 cm to extract SUN irradiation (AM1.5G), and the
reservoir volume was 100 mL. Hotplate magnetic stirrer was
used as the mixing apparatus (model: MS7-H550-pro, China).
The procedures of degradation have been examined after equi-
librium adsorption/desorption of MCM-48 as a function of
lighting time, initial dye concentration, catalyst mass, and the
stability of catalyst for several runs of degradation.
Effect of irradiation time and initial dye concentration
The effect of contact time and the initial Congo red dye con-
centration on the degradation efficacy had been performed by
mixing MCM-48/nickel oxide (0.2 g) with 100 mL of Congo
red dye solutions of different concentrations (5–25 mg/L with
increment of 5 mg/L) for various time intervals from 30 to
420 min. Each experiment had been carried out under the
synthetic visible lighting. Next, the dye solutions were
centrifugated and separated to identify the dye concentration
using the spectrophotometer.
Effect of MCM-48/nickel oxide mass
The catalysts mass effects on the degradation of the dye have
been evaluated by mixing properly various doses of it (0.025,
0.02, 0.015, 0.01, 0.005 g) with 100 mL of the dye solutions
(5 mg/L) as separated assessments for periods that varied from
30 to 240 min underneath the synthetic visible lighting. Next,
the dye solutions have been centrifugated and separated to
figure out the remaining dye concentration.
Fig. 1 Schematic diagram of synthesis steps of MCM-48 loaded by nick-
el oxide using silica fume solid waste as the silica source
Environ Sci Pollut Res

4. Equation (1) has been utilized to calculate the degradation
percentage of Congo red dye;
Degradation %ð Þ ¼
100 C0–Ceð Þ
C0
ð1Þ
Where Ce is the dye concentration after treating and C0 is
the initial dye concentrations.
Effect of the pH value
To study the pH impact on the procedure of dye degradation,
MCM-48/nickel oxide (0.02 g) has been stirred with 100 mL
of Congo red dye solution at various pH values (pH 10, pH 9,
pH 8, pH 6, pH 5, pH 4, pH 3, pH 2) for about 2 h under an
artificial light source. Next, the used solids and solutions were
separated and collected for evaluation.
Stability of the catalyst
The catalyst reusability for many dye degradations runs had
been analyzed by mixing the catalyst (0.02 g) with 100 mL of
5 mg/L Congo red solution. The catalyst was immediately
Fig. 2 XRD patterns of silica fume (a), synthesized MCM-48 (b), and
MCM-48/nickel oxide (c)
Environ Sci Pollut Res

5. washed with distilled water and dried for 1 h at 60 °C to be
ready for use in the next run. This has been repeated for 5 runs
under visible lighting within time intervals from 30 to 240 min.
The role of catalyst support
The dual effect of the synthetic MCM-48 as a catalyst-support
and enhancer for the photocatalytic properties of the nickel
oxide was evaluated by its role in the adsorption and photo-
catalytic degradation of Congo red dye, in which, 0.02 g of
nickel oxide, MCM-48, and MCM-48/nickel oxide was
stirred with 100 mL of 5 mg/L Congo red dye solution in
the dark and in the light for 120 min.
Results and discussion
Structural properties
XRD patterns of MCM-48/nickel oxide, MCM-48 silica,
along with silica fume have been shown in Fig. 2. The XRD
pattern of the used silica fume reflected the amorphous nature
of it, and no characteristic peaks were observed (Fig. 2a).
The synthesized MCM-48 (Fig. 2b) shows the common
XRD pattern of the highly ordered mesoporous MCM-48
(Zhen et al. 2012). It exhibits a characteristic intense peak
corresponding to (211) crystallographic plane. Also, an addi-
tional intensive peak has been noticed corresponding to (220)
crystallographic plane. The existence of these characteristic
peaks of MCM-48 verifies the development of the mesopo-
rous networking along with the absence of various other
interferences.
The XRD pattern of MCM-48/nickel oxide reflected the
development of Ni2O3 as the dominating phase of nickel ox-
ide along with small presences for Ni(OH)2 (Fig. 3c). The
Ni2O3 characteristic peaks had been recognized at 2 =
31.67°, 45.40°, 56.43°, 66.18°, and 75.23° that correspond
to (202), (111), (002), (004), and (311) planes of hexagonal
Ni2O3 (Jiang et al. 2014; Sayan et al. 2015). The typical crys-
tallite size (D) of Ni2O3 has been estimated based upon
Scherrer’s relation (D = 0.9λ/Wcosθ), in which W refers to
half-maximum full-width in radians, θ is the Bragg’s angle,
and λ is the X-ray wavelength (Williamson and Smallman
1956). The approximate value of D was 43 nm.
Furthermore, the average microstrain was approximately
0.053%. To get data about the number of defects in Ni2O3,
the dislocation density (δ) is calculated utilizing the relation of
Smallman’s and Williamson, δ ¼ N
D2 (Khmissi et al. 2016),
where N is equal to unity for the minimum dislocation density
(Williamson and Smallman 1956); 8.54 × 10−6
dislocation/
nm2
is the value of minimum δ that suggests a high-quality
lattice structure of the precipitated Ni2O3.
Morphological properties
The morphological features of silica fume mesoporous MCM-
48 and MCM-48/Ni2O3 composite are shown in Fig. 3. MCM-
48 appears as nano/micro-aggregates of irregular wormy or
cylindrically shaped grains that interlocked with one another
to develop the agglomerated network, as shown in Fig. 3a.
The current interconnected network of silica fume-based
MCM-48 produces a nanoporous matrix that will improve the
surface area/volume ratio (Fig. 3b). The noticed morphology
qualifies the prepared material for many uses in catalyst sup-
port, catalysis, adsorption, and filtration applications.
The SEM image of MCM-48/nickel oxide shows a homog-
enous distribution of nickel oxide particles, which coated the
surface of MCM-48 (Fig. 3c). The nickel oxide particles are
tiny particles of size that ranged from nanograins to micron
particles, either in separated form or aggregates. The interlock
between the nickel oxide deposits resulted in another
nanoporous matrix that will improve the adsorption as well as
the photocatalytic performance of the final product (Fig. 3d).
Optical properties
MCM-48/nickel oxide optical properties have been investigat-
ed as a key parameter in the analysis of the final product’s
photocatalytic performance. Figure 4a represented the
ultraviolet–visible absorbance spectrum of MCM-48/nickel
oxide. The synthesized MCM-48/nickel oxide showed an ex-
tensive absorption band extended from ultraviolet to visible
light region and centered at 420 nm.
Tauc’s equation (Eq. (12)) has been utilized to investigate
the direct optical bandgap, , of the prepared MCM-48/nick-
el oxide;
α ¼ hv−Eg
À Á1=2
=hv ð2Þ
Here, is the absorption coefficient, h represents Planck’s
constant, and v refers to photon frequency. Using the absor-
bance of sample (A), is obtained by Eq. (3) (Ko et al. 2014);
a ¼ 2:303x103
Aβ=lC ð3Þ
Here, β represents the MCM-48/Ni2O3 density, L repre-
sents the quartz cell path (1.0 cm), and C represents the pow-
der’s concentration. Figure 4b shows the bandgap value iden-
tification by the intercept of the linear portion with the hv-axis.
As shown in Fig. 4b, 2.4 eV is the bandgap value of MCM-48/
ƒFig. 3 SEM images of the extracted silica fume-based MCM-48 (a),
enlarged view on the synthetic MCM-48 (b), precipitated Ni2O3 through-
out MCM-48 surface (c), and focus on the morphology of the precipitated
Ni2O3 (d)
Environ Sci Pollut Res

6. nickel oxide, which is smaller than the values obtained for
Ni2O3 as a single component (3.66 and 3.46 eV) (Zohra
et al. 2016). This bandgap shift may be attributed to morpho-
logical and structural parameter changes. As the crystallite
size increased, more atomic orbitals overlapped, and the gap
between the conduction band and valence band, energy gap,
will be decreased. The broadening of the optical bandgap may
be attributed to a wide size-distribution of Ni2O3 particles
from nano to micro range in addition to the existence of
Ni2O3 aggregates and nanoporous features.
Adsorption properties of MCM-48/nickel oxide
composite
Fig. 5 shows the adsorption capability of the synthesized
MCM-48/nickel oxide versus different initial concentrations
of Congo red dye. The quantity of uptake dye enhanced
steadily from 5 to 41 mg/g with increasing dye concentration
from 5 to 40 mg/L. The rate of adsorption reveals a slight
increase with raising the concentration of dye from 30 to
40 mg/L. Then, the uptake equilibrium has been reached at
an initial dye concentration of 30 mg/L. The mechanism of
adsorption has been examined through Giles’s classification
of isotherm curves along with utilizing Temkin isotherm,
Freundlich, and Langmuir models.
A sequence of equilibrium studies was carried out to prove
the role of MCM-48 in the enhancement of Ni2O3 catalytic
performance via adsorption of Congo red dye in the absence
of light illumination. Figure 5a shows that at various concen-
tration levels, the Congo red dye exhibits a sigmoidal isotherm
Fig. 5 Adsorption isotherm curve of Congo red dye using MCM-48/
Ni2O3 (a), Langmuir plotting of adsorption results (b), Freundlich
plotting of the adsorption data (c), and Temkin plotting of the
adsorption data (d)
Fig. 4 (a) The UV–Vis spectrum of MCM-48/Ni2O3 and (b) the calcu-
lated bandgap energy of MCM-48/Ni2O3
Environ Sci Pollut Res

7. curve of inflection point that also characterizes the S-type
isotherm curve. These kinds of isotherm curves are associated
with the existence of cooperative adsorption processes with at
least two opposite mechanisms (Groisman et al. 2004; Hinz
2001). The first mechanism is for solute–solute attraction on
MCM-48/nickel oxide surface. Second, the adsorption of the
solute might be depressed by the competitors of the dissolved
ions in the solution, like a complexation reaction with ligand
(Mohamed et al. 2018). Additionally, the S-type isotherm
curve reflected the vertical orientation of the adsorbed ions
in the surface area of the synthesized composite. Also, it indi-
cates the lower interaction strength between the solute and the
adsorbent as compared to the force interaction between the
adsorbed molecules.
Figure 5b shows the Langmuir isotherm model. This model
proposed monolayer adsorption of the dissolved ions by spe-
cific homogenous energetic adsorption sites (Mohamed et al.
2018). Furthermore, the adsorption happens without interac-
tion between the adsorbed molecules (Shaban and Abukhadra
2017). Equation (4) is the linear form of the Langmuir equa-
tion:
Ce
qe
1 ¼
1
bqmax
þ
Ce
qmax
ð4Þ
where Ce describes the equilibrium concentration of the dis-
solved ions after the treatment (mg/L), qe is the uptake capac-
ity per unit mass of adsorbent at equilibrium (mg/g), qmax is
the quantity of adsorbate per unit mass of adsorbent at com-
plete monolayer coverage (mmol/g), and b is the Langmuir
constant (L/mg). The adsorption of Congo red dye utilizing
the artificial composite is not equipped with the Langmuir
isotherm model (R2
= 0.07) (Fig. 5b). Then, the adsorption
of Congo red dye utilizing MCM-48/nickel oxide cannot be
described by monolayer adsorption.
The heterogeneous adsorption has been described by the
Freundlich isotherm model. Adsorption capacity is exponen-
tially decreased with the binding surface energy because of the
multilayer adsorption (Bagherifam et al. 2014). Equation (5)
shows the Freundlich isotherm model’s linear equation;
Log qe ¼ 1=nð Þ log Ce þ log K F ð5Þ
where n represents the intensity along with KF that represents
the adsorption capacity. The linear regression plotting of log
(Ce) with log (qe) (Fig. 5c) describes the well-fitting of the
experimental data with a high correlation coefficient (R2
=
0.961). From the linear plotting slope, the 1/n value is less
than unity (0.972), which reflected the chemical adsorption
of dye and referred to a heterogeneous surface with minimum
interactions between the adsorbed ions (Bagherifam et al.
2014; Rakshitha and Yashas 2017).
The Temkin model has been examined for describing the
adsorption mechanism of the Congo red dye utilizing MCM-
48/nickel oxide composite. This particular model considers
the adsorption energy of molecules that is directly proportion-
al to adsorbent–adsorbate interaction (Boparai et al. 2011).
This particular model also takes into consideration the inter-
actions between adsorbents and the adsorbed ions. Equation
(6) represents this mode (Temkin and Pyzhev 1940):
qe ¼ BT ln KT þ BT In Ce ð6Þ
where BT = RT/b is a factor associated with the heat of sorption
(J/mol), R is the ideal gas constant (8.314 J/mol), T is the
absolute temperature (K), b is Temkin isotherm constant,
and KT is the Temkin isotherm equilibrium binding constant
(L/g). The plotting of ln (Ce) versus (qe) gives linear regres-
sion plotting with a high correlation coefficient (R2
= 0.94)
(Fig. 5d). This mirrors the excessive physical fitness of the
adsorption data with the Temkin model.
Consequently, it is clear that the adsorption of Congo red
dye using MCM-48/nickel oxide is represented well by the
Freundlich isotherm model followed by the Temkin isotherm
model, i.e., the adsorption occurs in a multilayer form.
Photocatalytic removal of dye
Effect of illumination time
Photocatalytic qualities of the synthesized MCM-48/nickel
oxide had been investigated for the degradation of Congo
red dye under the artificial visible light. The values of the
photocatalytic removal have been examined using 100 mL
of dye solution with various concentrations for different pe-
riods from 30 to 360 min (Fig. 6a). There is a consistent
increase in the removal percent of Congo red dye with increas-
ing the illumination time at all dye concentrations. A control
experiment of dye photolysis by the light was carried out to
effectively evidence the photocatalytic role of MCM-48/nick-
el oxide. Figure 6b shows the photolysis Congo red dye re-
moval versus illumination time. As shown, there is a very
limited effect. The removal% reached 5.3% after 360 min.
The removal efficiency of the dye at different initial dye
concentrations as a function of the illumination time is illus-
trated in Fig. 6c. For the removal% of 5 mg/L dye, the degra-
dation percentage increased from 20% to 97.4% with increase
of the illumination time from 30 to 360 min. Increasing the
initial dye concentration to 25 mg /L raised the degradation
rate from 4.92% to 45.80% with increase of the illumination
time from 30 to 360 min. At the optimum illumination time of
360 min, the removal percentage relative to the initial dye
concentration changed from 97.4% to 45.8% with increase
of the initial dye concentration from 5 to 25 mg/L, as shown
in Fig. 6c. That is, 11.45 and 4.87 mg/L Congo red are re-
moved from the initial dye concentration of 25 and 5 mg/L at
360 min, respectively. Hence, as the initial dye increased, the
quantity of the removed dye is increased. Whereas the
Environ Sci Pollut Res

8. degradation% relative to the initial dye concentration is re-
duced at high dye concentration. This may be related to the
over increase in the amount of adsorbed dyes on the catalyst
surface and the role of high concentration in blocking the
incident photons. This will reduce the number of hydroxyl
radicals generated and the positive holes, which in turn re-
duces the degradation percentage relative to the initial dye
concentration (Behnajady et al. 2006; Khezrianjoo and
Revanasiddappa 2013).
Kinetic modeling
Three kinetic models have been utilized to identify the photo-
catalytic actions of MCM-48/nickel oxide composite in the
degradation of Congo red dye. The investigated models are
stated by Eqs. (7), (8), and (9) for the zero-, first-, and second-
order kinetic models, respectively (Shaban et al. 2017):
dc
dt
¼ −k0 ð7Þ
dc
dt
¼ −k1c ð8Þ
dc
dt
¼ −k2 c2
ð9Þ
where C represents the dye concentration at reaction time t and
k2, k1, and k0 are the kinetic rates of the second-, first- and
zero-order models, respectively. By integrating the previous
equations, Eqs. (10), (11), and (12) show the linear forms of
the three models (Shaban et al. 2017):
Ct ¼ C0−k0t ð10Þ
Ct ¼ C0e−k1t
ð11Þ
1
Ct
¼
1
C0
þ k2t ð12Þ
where Ct represents the Congo red concentration after illumi-
nation time t.
Fitting of the resulted data with a zero-order kinetic model
has been examined from the linear regression plotting of the
illumination time versus the residual dye concentration after
the degradation process (Fig. 7a). The correlation coefficient
(R2
) values reflected the good fitting of the data with the mod-
el. The degree of fitting becomes better with increase of the
dye concentration. Besides, it was observed that the value of
k0 increased as the dye concentration increased from 5 to
25 mg/L (Table 1). For the zero-order model, the degradation
rate is independent of the concentration of the reaction’s com-
ponents, and the reactants saturated the catalyst surface.
By the same fitting method, the linear regression plotting of
ln(C0/C) with illumination time gives the fitting of the experimental
data with the first-order model (Fig. 7b). The modeling parameters
are shown in Table 1. The dye’s photodegradation looks well pre-
sented by the first-order model rather than by the zero-order model
at initial dye concentrations ≤15 mg/L. While at dye concentrations
≥20 mg/L, the results show more fitting with the zero-order model
rather than with the first-order model. This might be related to the
high adsorption of Congo red at the high dye concentrations. This
indicates to change in the operating degradation mechanism or pres-
ence of more than one degradation mechanism at the high concen-
trations of Congo red dye. The degradation rate constant showed a
gradualdecreasewithincreaseoftheinitialdyeconcentration,which
is concordant with the experimental data.
Fig. 6 (a) Effect of irradiation time on the degradation of different
concentrations of Congo red dye using MCM-48 loaded by nickel oxide,
(b) photolysis of Congo red dye removal versus irradiation time, and (c)
variation of dye removal with initial dye concentration after 360 min
Environ Sci Pollut Res

9. Also, the obtained modeling parameters with the second-
order model attained a good correlation coefficient, as shown
in Table 1 and Fig. 7c. Nevertheless, the degradation
outcomes are well represented by the first-order model rather
than the zero-order or second-order model. Therefore, the cat-
alytic photo-degradation process seems to be managed by
either the initial dye concentration or the catalyst mass. An
explanation of the chemical process that may be suggested for
such a reaction was introduced by Dimitrakopoulou et al.
(2012). In contrast, the formation rate of the photocatalytic
oxidizing species (photogenerated valence band holes and
produced hydroxyl radicals) must be a function of catalyst
loading and photon flux. Thus, the formation rate is constant
at the same operating conditions. The increase of the initial
concentration leads to an increase in the probability of the
production of hydroxyl radicals that attacked the dye mole-
cules and increased the degradation rate (Dimitrakopoulou
et al. 2012). Fitting of the degradation data with the kinetic
models revealed the simultaneous working of parallel removal
mechanisms at the used Congo red dye concentrations (Wang
et al. 2008).
Effect of the catalyst dose
Figure 8 represents graphically the effect of the catalyst mass
on the Congo red photocatalytic removal% at various illumi-
nation times. The removal% enhanced steadily with increase
of the used dose of MCM-48/nickel oxide. The degradation
percentage of Congo red dye after 120 min was enhanced
from 16.5% to 85.2% with rise of the catalyst mass from
0.005 to 0.04 g. This may be due to the increase in the
photogenerated hydroxyl radical groups as well as the positive
holes with increase of the catalyst mass. Besides, the adsorp-
tion capacity is increased by increase of the entire surface area
(Huang et al. 2008).
Additionally, it is crucial to suggest that the result of in-
crease of the catalyst dose on the degradation of Congo red
dye reveals a tremendous enhancement with increase of the
illumination time to achieve the maximum removal% at 0.04 g
dose after 240 min. For instance, after 30 min treatment, the
removal enhanced from 5.9% to 43.2% with increase of the
used dose from 0.005 to 0.04 g. While after 240 min, the
removal was improved from 30.4% to 99.6% with increase
of the used dose. This correlated with the accessibility of more
Fig. 7 Fitting of the degradation data with the zero-order kinetic model
(a), first-order kinetic model (b), and second-order kinetic model (c)
Table 1 Parameters of the zero-,
first-, and second-order kinetic
models for dye degradation by
MCM-48/nickel oxide composite
Kinetic model Parameters 5 mg/L 10 mg/L 15 mg/L 20 mg/L 25 mg/L
Zero-order kinetic model k (mg/min)
R2
0.0119
0.85
0.021
0.937
0.0242
0.982
0.029
0.988
0.0323
0.9929
First-order kinetic model K1 (min−1
)
R2
0.011
0.997
0.0052
0.9920
0.0029
0.995
0.0022
0.989
0.0018
0.996
Second-order kinetic model k2 (L/mol min)
R2
0.0241
0.829
0.0015
0.973
0.0004
0.968
0.0296
0.988
0.03235
0.9921
Environ Sci Pollut Res

10. time for thrilling more electrons on the catalyst surface and
growing the amount of adsorbed dye molecules.
“
Effect of the pH value
Figure 9 represents the relationship between the pH value of
the solution and the removal of Congo red dye utilizing
MCM-48/nickel oxide photocatalyst. The dye’s removal is
reduced steadily with increase of the pH value and reaches
the optimum removal in the acidic conditions. The removal
percentage reduces from 97.2% to 46.4% with increase of the
pH value from 3 to 10. The acidic conditions lead to surface
protonation, so the catalyst surface gets positively charged,
which improves the uptake of acidic dyes, such as Congo
red dye (Abudaia et al. 2013; Shaban et al. 2017).
Furthermore, the basic conditions induce a decrease in hy-
droxyl radicals’ oxidation potential (Sun et al. 2007). Thus,
the increase of the pH value resulted in an ongoing reduction
in the removal of Congo red dye using MCM-48/nickel oxide
photocatalyst. The zero-point charge (ZPC) is known as the
pH at which solid material submerged in an electrolyte leading
to zero net electrical charges on its surface. The pH drift
method was used to determine the ZPC value of the compos-
ite, which is found to be pH 4.5. Therefore, the composite
surface is positively charged at pH values less than 4.5 and
negatively charged at pH values more than 4.5. At pH < 4.5, a
significantly electrostatic physical attraction happens between
the positively charged MCM-48/nickel oxide surface and the
anionic Congo red dye. So, pH 4 was selected for the other
tests to avoid the high acidic conditions and to be encouraging
for the Congo red adsorption onto the MCM-48/nickel oxide
surface.
Reusability
The MCM-48/nickel oxide photocatalyst stability for 5 runs of
dye degradation has been studied by stirring 0.02 g of the cat-
alyst with 100 mL of 5 mg/L Congo red dye for illumination
time that ranged from 30 to 360 min for each run. The loss in
the catalyst mass with the washing process after each run was
calculated, and the error was set into the account during the
calculation of the removal. The removal portion of dye utilizing
MCM-48/nickel oxide exhibits increased effectiveness for the
examined 5 runs and getting the highest degradation value after
360 min. The acquired removal values at the optimum time are
97.8%, 93.6%, 90.12%, 85.33%, and 69.3% for the five suc-
cessive runs. The degradation effectiveness of run 2 reduced by
4.2% relative to run 1. Whereas the successive runs from 3 to 5
were decreased by 7.68%, 12.47%, and 28.5%, respectively
(Fig. 10). The loss of the catalyst efficiency after the 3rd run
may be attributed to the blockage of active sites on the surface
of the catalyst by the residue of the adsorbed dye molecules.
The common trend for the degradation curves of the studied
runs exhibits no equilibrium phase, which refers to the applica-
bility of the catalyst to remove more Congo red dye with in-
crease of the illumination time.
Time (min)
Removalofdye%
Fig. 10 The reusability of MCM-48/Ni2O3 for degradation of Congo red
dye for five runs
Removalofdye%
Catalyst dose (g)
Fig. 8 Effect of the catalyst dose in the photocatalytic removal of Congo
red dye
pH
Removalofdye%
Fig. 9 Effect of pH value on the removal of the Congo red dye
Environ Sci Pollut Res

11. Role of the catalyst support
Narges and Alireza reported that the photocatalytic properties
of semiconductor metal oxide increase considerably when
loaded on a highly porous surface (Narges and Alireza
2015). To evaluate the role of MCM-48 in enhancing the
photocatalytic properties of the dye, the removal of 5 mg/L
Congo red dye using nickel oxide, MCM-48, and MCM-48/
nickel oxide in the dark (D) and in the presence of the source
of light (L) is carried out for 120 min (Fig. 11). There is a
considerable difference in the removal percentage of Congo
red dye for the used nickel oxide, MCM-48, and MCM-48/
nickel oxide in the dark. Nickel oxide, MCM-48, and MCM-
48/nickel oxide catalysts achieve removal percentage of
15.4%, 30.1%, and 47.6%, respectively. This reflects the en-
hancement of the adsorption capacity after loading the nickel
oxide onto MCM-48 as the removal percentage increased by
32.2% and 17.5% as compared to pure nickel oxide and silica
fume-based MCM-48, respectively. Under the light irradia-
tion, the pure phase of MCM-48 exhibits no photocatalytic
properties. It shows no increase in the removal percentage,
while the removal percentage using nickel oxide and MCM-
48/nickel oxide increased to 24.6% and 92.8%, respectively.
Therefore, there is an enhancement in photocatalytic degrada-
tion by 68.2%. The heterogeneous photocatalytic degradation
involves the following three steps: (a) adsorption of the dye,
(b) absorption of the light by the used catalyst, and (c) charge
transfer reactions to generate the required radicals for dye
degradation (Perera et al. 2012). The degradation can occur
through direct degradation of the dye by the photogeneration
of positive holes from the catalyst or through their role in the
production of hydroxyl radicals (Zouzelka et al. 2016). The
role of MCM-48 appears to be related to the adsorption ca-
pacity and the high surface area of MCM-48. Without using
MCM-48 as a catalyst support, the nickel oxide particles tend
to agglomerate to each other, and in turn, the present active
sites will be reduced (Narges and Alireza 2015), i.e., using of
MCM-48 as catalyst support might result in the fixing of the
nickel oxide particles throughout the porous structure and
prevent them from the agglomeration. This provides more
exposed active sites from the catalyst to the incident photons,
besides the increase of the amount of adsorbed dye molecules
close to the generated positive holes (Alireza and Shahriari
2014). Based on the obtained results, supporting nickel oxide
particles onto MCM-48 is a promising active center for the
simultaneous adsorption/photo-degradation of Congo red dye.
Possible routes of dye degradation
Illumination of MCM-48/Ni2O3 under the visible light allows
the excitation of the valence band electrons to the conduction
band. According to one of the two mechanisms, positive holes
are generated in the valence band and contributed to the de-
composition of the present dye molecules (Fig. 12). In the 1st
mechanism, the produced holes can oxidize the dye contami-
nants by immediate electron transfer (Reza et al. 2015). In the
2nd mechanism, the created holes react with the electron-
donors to produce oxidizing free radicals (hydroxyl radicals)
that will oxidize the dye molecules on the surface of the cat-
alyst (Akbal et al. 2015). The enhancement in the photocata-
lytic performance of the synthetic MCM-48/Ni2O3 is related
to the interaction effect of MCM-48 and the photocatalytic
Fig. 12 Schematic proposal of the process action routes
Removalofdye%
Fig. 11 The role of catalyst support in enhancing the adsorption capacity
and photocatalytic properties
Environ Sci Pollut Res

12. effect of Ni2O3. The usage of MCM-48 as catalyst support
improves the adsorption capability of MCM-48/Ni2O3 toward
the Congo red dye. Besides, the photocatalytic degradation of
Congo red dye using MCM-48/Ni2O3 can be summarized,
based on the literature for photocatalysts, in the following
Eqs. (13)–(18) (Tarigh et al. 2015):
MCM−48=Ni2O3 þ hv→MCM−48=Ni2O3 e−
CB; hþ
VB
À Á
ð13Þ
MCM−48=Ni2O3 e−
ð Þ þ O−
2→MCM−48=Ni2O3 þ O•−
ð14Þ
MCM−48=Ni2O3 hþ
ð Þ þ H2O→MCM−48=Ni2O3
þ Hþ
þ OH•
ð15Þ
MCM−48=Ni2O3
e þ MB→ MCM−48=Ni2O3ð Þe−
þ CRþ•
ð16Þ
CRþ•
þ O−
2→Degraded products ð17Þ
CRþ•
þ OH•
→Degraded 1products ð18Þ
Conclusion
Silica fume-based MCM-48 has been synthesized and charac-
terized as a catalyst and back-support to the Ni2O3
photocatalyst. Loading of Ni2O3 onto MCM-48 reduces the
bandgap energy to 2.4 eV. Silica fume-based MCM-48 as
catalyst support for Ni2O3 enhanced the adsorption capacity
of Congo red dye by 17.5% and 32.2% higher than the ad-
sorption by MCM-48 and Ni2O3, respectively. Besides, the
photocatalytic degradation percentage increased by about
68.2% relative to the degradation percentage using Ni2O3 as
a single component. The adsorption mechanism of MCM-48/
Ni2O3 is a multilayer chemisorption process and fitted well
with the Freundlich equilibrium model. The usage of MCM-
48 as Ni2O3 catalyst support increases the surface area/volume
ratio, prevents the agglomeration of Ni2O3 particles, and pro-
vides a high density of active or hot adsorption and
photocatalyst sites for the incident optical photons.
Acknowledgments The Egyptian Academy partially supported this work
for scientific research and technology (ASRT/1515/2017).
References
Abudaia JA, Sulyman MO, Elazaby KY, Ben-Ali SM (2013) Adsorption
of Pb (II) and cu (II) from aqueous solution onto activated carbon
prepared from dates stones. Int J Environ Sci Develop 2:191–195
Akbal F, van Driel BA et al (2015) Photocatalytic degradation of organic
dyes in the presence of titanium dioxide under UV and solar light:
effect of operational parameters. Environ Prog 24:317–322
Alireza NE, Shahriari E (2014) Photocatalytic decolorization of methyl
green using Fe(II)-o-phenanthroline as supported onto zeolite Y. Ind
Eng Chem 20:2719–2726
Bagherifam S, Komarneni S, Lakzian A, Fotovat A, Khorasani R, Huang
W, Ma J, Hong S, Cannon FS, Wang Y (2014) Highly selective
removal of nitrate and perchlorate by organoclay. Appl Clay Sci
95:126–132
Behnajady MA, Modirshahla N, Hamzavi R (2006) Kinetic study on
photocatalytic degradation of CI acid yellow 23 by ZnO
photocatalyst. J Hazard Mater B 133:226–232
Boparai HK, Joseph M, O’Carroll DM (2011) Kinetics and thermody-
namics of cadmium ion removal by adsorption onto nano zerovalent
iron particles. J Hazard Mater 186:458–465
Chaouch N, Ouahrani MR, Laouini SE (2014) Adsorption of lead (II)
from aqueous solutions onto activated carbon prepared from
Algerian dates stones of Phoenix dactylifera L (Ghars variety) by
H3 PO4 activation. Orient J Chem 30:1317–1322
Chrysicopoulou P, Davazoglou D, Trapalis C, Kordas G (1998) Optical
properties of very thin ( 100 nm) sol-gel TiO2 films. Thin Solid
Films 323:188–193
Dharmaraja N, Prabuc P, Nagarajand S, Kimb CH, Parkb JH, Kimb HY
(2006) Synthesis of nickel oxide nanoparticles using nickel acetate
and poly(vinyl acetate) precursor. Mater Sci Engin: B 128:111–
114
Dimitrakopoulou D, Rethemiotaki I, Frontistis Z, Xekoukoulotakis NP,
Venieri D, Mantzavinos D (2012) Degradation, mineralization and
antibiotic inactivation of amoxicillin by UV-A/TiO2 photocatalysis.
J Environ Manag 98:168e174
Duraisamya R, Kiruthigaa PM, Hirpayeb BY, Berekuteb AK (2015)
Adsorption of azure B dye on rice husk activated carbon: equilibri-
um, kinetic and thermodynamic studies. Int J Water Res 5(2):18–28
Fathal ES, Ahmed LM (2015) Optimization of photocatalytic
decolourization of methyl green dye using commercial zinc oxide
as catalyst. Journal of Kerbala University, 13 No. 1 Scientific
Giles CH, McEwan TH, Nakhawa SN, Smith D (1960) Studies in ad-
sorption: part XI. A system of classification of solution adsorption
isotherms and its use in diagnosis of adsorption mechanisms and in
measurement of specific surface areas of solids. J Chem Soc:3973–
3993
Groisman L, Rav-Acha C, Gerstl Z, Mingelgrin U (2004) Sorption of
organic compounds of varying hydrophobicities from water and
industrial wastewater by long- and short-chain organoclays. Appl
Clay Sci 24:159–166
Gupta VK, Mohan D, Saini VK (2006) Studies on the interaction of some
azo dyes (naphthol red-J and direct orange) with nontronite mineral.
J Colloid Interface Sci 298:79–86
Hinz C (2001) Description of sorption data with isotherm equations.
Geoderma 99:225–243
Huang YH, Huang YF, Chang PS, Chen CY (2008) Comparative study
of oxidation of dye-reactive black B by different advanced oxidation
processes: Fenton, electro-Fenton and photo-Fenton. J Hazard
Mater 154:655–662
Jiang G, Nana T, Jie L, Kun Y, Zhiwei J, Xuecheng C, Xin W, Ewa M,
Tao T (2014) Synergistic effect of activated carbon and Ni2O3 in
promoting the thermal stability and flame retardancy of polypropyl-
ene. Polym Degrad Stab 99:18–26
Khezrianjoo S, Revanasiddappa HD (2013) Photocatalytic degradation of
acid yellow 36 using zinc oxide photocatalyst in aqueous media. J
Catal 582058:6
Khmissi H, El Sayed AM, Shaban M (2016) Structural, morphological,
optical properties and wettability of spin-coated copper oxide; influ-
ences of film thickness, Ni, and (La, Ni) co-doping. J Mater Sci 51:
5924–5938. https://doi.org/10.1007/s10853-016-9894-7
Ko H, Yang G, Wang M, Zhao X (2014) Isothermal crystallization kinet-
ics and effect of crystallinity on the optical properties of nanosized
CeO2 powder. Ceram Int 40:6663–6671
Environ Sci Pollut Res

13. Li H, Mab H, Yang M, Wang B, Shao H, Le W, Yu R, Wang D (2017)
Highly controlled synthesis of multi-shelled NiO hollow micro-
spheres for enhanced lithium storage properties. Mater Research
Bull 87:224–229
Mohamed F, Abukhadra MR, Shaban M (2018) Removal of safranin dye
from water using polypyrrole nanofiber/Zn-Fe layered double hy-
droxide nanocomposite (Ppy NF/Zn-Fe LDH) of enhanced adsorp-
tion and photocatalytic properties. Sci Total Environ 640–641:352–
363
Narges A, Alireza NE (2015) Modification of clinoptilolite nano-particles
with iron oxide: increased composite catalytic activity for
photodegradation of cotrimoxazole in aqueous suspension. Mater
Sci Semicond Process 31:684–692
Perera SD, Mariano RG, Vu K, Nour N, Seitz O, Chabal Y, Balkus KJ
(2012) Hydrothermal synthesis of graphene-TiO2 nanotube com-
posites with enhanced photocatalytic activity. ACS Catal 2:949–995
Rahman A, Urabe T, Kishimoto N (2013) Color removal of reactive
procion dyes by clay adsorbents. Proc Environ Sci 17:270–278
Rakshitha R, Yashas SR (2017) Removal of nitrate from water by chito-
san, clay and activated carbon as adsorbents: a mini review. Int J
Eng Res Appl 7(10):46–51
Ramachandra TV, Varghese SK (2003) Exploring possibilities of achiev-
ing sustainability in solid waste management. Environ Health 45(4):
255–264
Razieh N, Ali RM, Zahra H, Tahereh A (2005) Pd-functionalized MCM-
41 nanoporous silica as an efficient and reusable catalyst for pro-
moting organic reactions. RSC Adv 5:16029–16035
Reza KM, Kurny ASW, Gulshan F (2015) Parameters affecting the pho-
tocatalytic degradation of dyes using TiO2: a review. Appl Water
Sci. https://doi.org/10.1007/s13201-015-0367-y
Sayan D, Swarupananda BB, Mahua GC, Raj SB, Suman H, Chandan
KG (2015) Synthesis of pure nickel(III) oxide nanoparticles at room
temperature for Cr(VI) ion removal. RSC Adv 5:54717–54726
Shaban M, Abukhadra MR (2017) Geochemical evaluation and environ-
mental application of Yemeni natural zeolite as sorbent for Cd2+
from solution: kinetic modeling, equilibrium studies, and statistical
optimization. Environ Earth Sci 76:2–16
Shaban M, Abukhadra MR, Hamd A, Amin RR, Khalek AA (2017)
Photocatalytic removal of Congo red dye using MCM-48/Ni2O3
composite synthesized based on silica gel extracted from rice husk
ash; fabrication and application. J Environ Manag 204:198–199
Sharma J, Janveja B (2008) A study on the removal of Congo red dye
from the effluents of textile industry using rice husk carbon activated
by steam. Rasayan J Chem 1:936–942
Shengfang L, Min T (2015) Removal of cationic dyes from aqueous
solutions by a low-cost biosorbent longan shell. Desalination
Water Treatment:1–7. https://doi.org/10.1080/19443994.2014.
1001444
Siddique R, Iqbal Khan M (2011) Supplementary cementing materials,
engineering materials, Springer-Verlag Berlin Heidelberg, DOI:
https://doi.org/10.1007/978-3-642-17866-5_2
Silica Fume Association (2005( Silica fume manual. 38860 Sierra Lane,
Lovettsville, VA 20180, USA
Sun JH, Sun SP, Sun JY, Sun RX, Qiao LP, Guo HQ, Fan MH (2007)
Degradation of azo dye acid black 1 using low concentration iron of
Fenton process facilitated by ultrasonic irradiation. J Ult Sonochem
14:761–766
Sun D, Zhang Z, Wang M, Wu Y (2013) Adsorption of reactive dyes on
activated carbon developed from Enteromorpha prolifera. American
J Anal Chem 4:17–26
Tarigh GD, Shemirani F, Maz'hari NS (2015) Fabrication of a reusable
magnetic multi-walled carbon nanotube–TiO2 nanocomposite by
electrostatic adsorption: enhanced photodegradation of malachite
green. RSC Adv 5:35070–35079
Temkin MJ, Pyzhev V (1940) Kinetics of ammonia synthesis on promot-
ed iron catalysts. Acta Physiochim URSS 12:217–222
Wang N, Li J, Zhu L, Dong Y, Tang H (2008) Highly photocatalytic
activity of metallic hydroxide/titanium dioxide nanoparticles pre-
pared via a modified wet precipitation process. J Photochem
Photobiol A 198:282–287
Williamson GK, Smallman RE (1956) Dislocation densities in some
annealed and cold-worked metals from measurements on the X-
ray Debye-Scherrer spectrum. Philos Mag 1:34–46
Yongde X, Robert M (2003) Facile and high yield synthesis of
mesostructured MCM-48 silica crystals. J Mater Chem 13:657–659
Zhang B, Shi R, Zhang Y, Pan C (2013) CNTs/TiO2composites and its
electrochemical properties after UV light irradiation. Prog Nat Sci
Mater Int 23(2):164–169
Zhen W, Xinbo C, Hongjun D, Lu Y, Huixiang S (2012) One-step syn-
thesis of highly active Ti-containing Cr-modified MCM-48 meso-
porous material and the photocatalytic performance for decomposi-
tion of H2S under visible light. Appl Surface Sci 258:8258–8263
Zohra N, Riaz KS, Naseem S, Zia R (2016) Synthesis and characteriza-
tion of Ni2O3 thin films. The World Congress on Advances in Civil,
Environmental, and Materials Research, Korea
Zouzelka R, Kusumawati Y, Remzova M, Rathousky J, Pauporté T
(2016) Photocatalytic activity of porous multiwalled carbon nano-
tube-TiO2 composite layers for pollutant degradation. J Hazard
Mater 317:52–59
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Environ Sci Pollut Res