Anal. Method Environ. Chem. J. 4 (1) (2021) 46-57  
Research Article, Issue 1  
Analytical Methods in Environmental Chemistry Journal  
Simultaneous adsorption of cationic and anionic dyes using a  
novel multifunctional mesoporous silica  
Amir Vahid a,*, Majid Abdouss b, Shahnaz Nayeri b, Aliakbar Miran Beigi a  
a Research institute of petroleum industry, Tehran, Iran  
b Faculty of chemistry, Amirkabir University of Technology, Tehran, Iran  
A R T I C L E I N F O :  
Received 17 Nov 2020  
Revised form 22 Jan 2021  
Accepted 15 Feb 2021  
A B S T R A C T  
In the present work a multifunctional nanoadsorbent was synthesized  
via a well-designed stepwise route, led to the grafting of an amine  
group on the interior and acidic sites on the exterior of bimodal  
mesoporous silica nanoparticles (UVM-7). First, amine and thiol  
groups were grafted on the interior and exterior pores of silica  
through co-condensation and post synthesis treatment, respectively.  
Then, the oxidation of thiol on UVM-7 caused to create sulfonic  
acid and the subsequent template extraction was carried out to obtain  
the NH2/UVM-7/SO3H. The results of XRD, the nitrogen sorption,  
SEM, TEM, FT-IR and elemental analysis revealed the presence  
of both types of functional groups on UVM-7. Then, simultaneous  
adsorption of anionic and cationic dyes (Methylene Blue [MB] and  
Direct Red 23 [Dr]) using NH2/UVM-7/SO3H was investigated. UV-  
Vis spectrophotometry was utilized for the determination of dyes in  
single and binary solutions. Langmuir and Freundlich models were  
used for the fitting of obtained experimental adsorption data and the  
constants of both isotherms were calculated for MB and Dr. Morover,  
the calculation of thermodynamic parameters revealed that the  
adsorption of MB and Dr on NH2/UVM-7/SO3H was endothermic  
and spontaneous. Furthermore, the simultaneous adsorption of both  
dyes regardless of their different electrostatic charge is the main  
characteristics of NH2/UVM-7/SO3H which was specially used for  
treatment of industrial wastewater.  
Available online 29 Mar 2021  
Mesoporous silica,  
Methylene Blue (MB) and Direct red (Dr) as the  
1. Introduction  
cationic and anionic dyes have harmful effects on  
human life and environment. Acute exposure to  
MB causes many health effect such as increased  
heart rate and cyanosis jaundice quadriplegia in  
mammals [2,3]. Up to now, the dye adsorption  
studies have focused on solutions containing single  
dye and mixture of dyes [4-6]. The most industrial  
effluents include a mixture of several dyes, so it  
is necessary to study the simultaneous adsorption  
of two or more dyes from aqueous solutions [7,8].  
However, the dyes are resistance to biodegradation  
due to their aromatic structure [9]. Many industrial  
Dyes as a important raw material were used in  
different industries including cloth, plastics,  
tanning, cosmetics and food [1]. Additionally, the  
dyes are one of the most problematic groups as a  
results of their environmental impact. Furthermore,  
the industrial effluents containing dyes may be  
have a carcinogenic effect in humans when,  
discharge to waters without any proper treatment.  
*Corresponding Author: Amir Vahid  
Email: &  
Adsorption of dyes by multifunctional mesoporous silica  
Amir Vahid et al  
technologies, including chemical oxidation [10],  
adsorption [11], the coagulation/flocculation [12],  
the membrane separation and ion exchange [13]  
was used for the adsorption of dyes from industrial  
effluents. Among them, adsorption has been  
known as one of the practical physical processes  
for the treatment and cleaning of wastewaters,  
because it is cost effective and very effective. The  
main problem of this technology is the synthesis of  
low cost adsorbent possesses with high adsorption  
capacity [14]. In multi-dye adsorption, the  
interference of one dye on the other dyes is very  
important [15]. The liquid chromatography [16],  
the capillary electrophoresis [17], the spectrometry  
[18] and the electrochemistry methods [19] are  
used for the analysis of dyes. Due to advantages  
of UV–Vis spectrophotometry such as accuracy  
of results, sensitivity, low cost, easy operation  
and reproducibility, it was used for analysis of  
colored samples [20]. The main drawback of this  
technique is the overlap and interference of broad  
absorption peaks. So, the simultaneous analysis of  
mixture dyes could be carried out using derivative  
spectrophotometry [21]. It was determined based  
on the derivative values of interest compound  
while other components have zero value [22].  
Also, many applications were used by UVM-  
7 in different sciences [23-26]. In this work, the  
synthesis of a multifunctional mesoporous silica  
contains both acidic and basic functional groups  
were reported. At the second step, the adsorption  
of MB / Dr from aqueous solution was carried out  
simultaneously and the adsorption phenomenon  
was studied.  
2. Experimental  
2.1. Reagents and materials  
All reagents with ultra-trace analytical grade such  
as; lead nitrate salt, acids and base solutions were  
purchased from Merck (Darmstadt, Germany). The  
structure of MB and Dr are shown in Figure 1.  
Ultrapure water has been obtained from Millipore  
continental water system (Bedford, USA).  
Tetraethyl orthosilicate (TEOS, (CHO)Si,  
CAS N: 78-10-4, Sigma), triethanolamine  
(TEAH3, CH₁₅NO, CAS N: 102-71-6, Sigma),  
C₁₉H₄₂BrN, CAS N: 57-09-0, Merck) and other  
reagents with analytical grade were prepared from  
Merck or Sigma Aldrich, Darmstadt, Germany.  
The pH adjustments were made using appropriate  
buffer solutions (Merck, Germany).  
Fig.1. The structure of MB(a) and Dr(b)  
Anal. Method Environ. Chem. J. 4 (1) (2021) 46-57  
2.2. Synthesis of UVM-7  
spectrophotometer at 502 and 664 nm for Dr and  
MB, respectively. In binary solution, the best  
wavelength for each dye was find out utilizing first-  
order derivative spectrometry.  
in which triethanol amine (TEAH3), has effect on  
the rate of hydrolysis and condensation of teraethyl  
orthosilicate (TEOS). In a typical synthesis, mixture  
of TEOS and TEAH3 heated up to 120 °C and then  
CTAB (cetyltrimethylammonium bromide) was  
added when the temperature of the solution reached  
to 70°C. After addition of water a suspension was  
formed and aged for 4 hours at ambient temperature.  
The final molar composition of the synthesis mixture  
was 1.0 TEOS : 3.5 TEAH3 : 0.25 CTAB : 90 H2O.  
The product was filtered, washed with water and  
acetone and dried in an oven at 80°C overnight and  
calcined at 550°C for 6 hours.  
The adsorption percentage (R%) and adsorption  
capacity of each dye qe, (mg dye/g adsorbent) was  
calculated according to the following equations  
(Eq.1 and Eq.2):  
C0 Ce)  
(Eq. 1)  
C0 Ce)  
R% =  
2.3. Synthesis of NH2- /UVM-7/SO3H  
(Eq. 2)  
First, 1.0 g of aminopropyle triethoxysilane  
(APTES) was added to the aqueous solution of  
CTAB and after 5 minutes, mixture of TEOS and  
TEAOH, was added to the micellar solution. The  
reactants molar ratio was 1.0 TEOS: 3.5 TEAH3  
: 0.25 CTAB : 90 H2O: 0.20 APTES. After aging,  
the white suspension was filtered and washed  
thoroughly with water and acetone. The white  
precipitate dried in oven over night at 80 °C. At the  
second step, 1.0 g of the as-synthesized NH2/UVM-  
7 and 1.0 g of triethoxysilane propanethiol (TPTES)  
was refluxed in 50 mL of toluene for 12 hours and  
then, the mixture filtered and dried in oven again.  
Then, thiol groups grafted on the external surface  
of the sample was oxidized in 15% H2O2 and 1  
molar solution of H2SO4. Then, CTAB of the as-  
synthesized NH2/UVM-7/SO3H was removed by  
reflux in 1 molar ethanolic solution of HCL for 24  
hours to get access to the internal pores and amine  
groups. The final product was dried in oven at 80  
°C in vacuum oven overnight.  
Where C0 and Ce (mg L-1) are the initial and  
equilibrium concentration of dye, respectively. V  
(L) is the volume of the solution and M (g) is the  
mass of adsorbent used.  
2.5. Characterization  
X-ray diffraction (XRD) patterns were recorded  
using a Philips 1840 diffractometer using nickel-  
filtered Cu Kα (1.5418˚ A) X-ray source, operating  
at 35.4 kV and 28 mA. Textural properties of the  
synthesized samples were measured by nitrogen  
adsorption at 77 K using a BELSORP-max  
apparatus after being out-gassed in vacuum at 120  
°C. ElementalanalysiswascarriedoutusingCHNS-  
Elementar. FT-IR spectra was recorded using a FT-  
IR 70 VERTX Bruker spectrophotometer using  
KBr powder. UV–Vis spectrophotometer was used  
to measure the concentration of the Methylene  
Blue and Direct red23 in aqueous solution. FE-  
SEM images were captured using Mira TESCAN  
3-XMU. Samples were sputtered with gold prior  
to imaging. TEM images were recorded at 150 kV  
operating voltage using a Zeiss microscope.  
2.4. Batch adsorption procedure  
In each test, 0.1 g of adsorbent was added to the 10  
mL of a solution containing a known concentration  
of each dyes while agitating at 250 rpm at 25 °C.  
After 120 minutes the concentration of residual  
dyes in supernatant was determined by UV–Vis  
3. Results and discussion  
3.1. Characterization of NH2/UVM-7/SO3H  
XRD pattern of NH2/UVM-7/SO3H is shown in Figure 2.  
Adsorption of dyes by multifunctional mesoporous silica  
Amir Vahid et al  
A strong and broad diffraction peak can be observed  
which is characterized in bimodal meso/macroporous  
material. This peak can be attributed to diffraction of  
incident X ray from the d100 plane. According to the  
hexagonal symmetry, two weak and broad peaks at  
higher diffraction angles can be assigned to d110 and  
overlap of d200 and d210 planes, respectively.  
pressure, the inflection is not sharp. By approaching  
to the saturated relative pressure, increasing of gas  
uptake led to the sharp increasing of isotherm. This  
can be attributed to the inter particles of UVM type  
material which is also present in NH2/UVM-7/  
SO3H after internal and external grafting of organic  
moieties. The high BET surface area and pore  
volume means that the pore structure/size almost  
preserved after grafting. However, after grafting  
of organic moieties on UVM-7, the sharpness of  
these region slightly decreases. The two inflections  
in NH2/UVM-7/SO3H can be attributed to the  
presence of two types of pore system.  
3.2. Nitrogen physisorption  
The isotherms of UVM-7 and NH2/UVM-7/SO3H  
is shown in Figure 3. The isotherms showed the  
four type of isotherm according to the IUPAC  
classification. In both isotherms, at low relative  
Fig. 2. The XRD pattern of NH2/UVM-7/SO3H  
Fig. 3. The isotherms of UVM-7 and NH2/UVM-7/SO3H  
Anal. Method Environ. Chem. J. 4 (1) (2021) 46-57  
Fig.4. The SEM of NH2/UVM-7/SO3H  
Fig.5. The TEM of NH2/UVM-7/SO3H  
3.3. TEM and SEM  
FT-IR spectra of SO3H/UVM-7/NH2 is shown in  
Figure 6. FT-IR spectroscopy was utilized to indicate  
the existence of NH2 and SO3H functional groups  
on the UVM-7. Two distinct peaks around 457 cm-1  
and 1082 cm-1 is attributed to the symmetric and  
asymmetric stretching bands of Si-O-Si group in the  
framework of UVM-7. A broad peak at around 3451  
cm-1 is assign to the silanol groups on the surface  
of UVM-7. A small absorption band at 1558 cm-1 is  
attributed to the bending vibration of amine group  
which overlapped with symmetric bending vibrations  
of O-H. A stretching mode of NH2 is also overlapped  
with silanol group’s around 3451 cm-1. This indicates  
that the UVM-7 possess of NH2 groups. A shoulder,  
overlapped with asymmetric stretching of Si-O-Si,  
Electron microscopy is a powerful technique  
provides a direct view of porous structure, particle  
morphology and many other information of  
porous materials at nanoscale. The SEM of NH2/  
UVM-7/SO3H reveals the particle size, shape and  
morphology of nanomaterials. Figure 4 illustrates  
the SEM image of NH2/UVM-7/SO3H. The sample  
composed of nanosize particles without presence of  
large agglomerates. The shape of the nanoparticles is  
almost irregular. The TEM image of the NH2/UVM-  
7/SO3H is taken perpendicular to d100 direction of  
pores and is displayed in Figure 5. Pore openings are  
clearly visible. Particle size in sub-ten nanometers  
and is in agreement with those seen in SEM image.  
Fig. 6. The FT-IR spectra of SO3H/UVM-7/NH2