CHAPTER - 3
RESEARCH METHODOLOGY
3.1. Materials
All the chemicals and reagents used in this study were of analytical grade with
high percentage purity. The reagents used include tin (VI) chloride (E-Merck Ltd.,
India), dihydrogen phosphate and cellulose acetate (CDH Pvt. Ltd., India), styrene
(Sigma-Aldrich, India), sodium hydroxide (Qualigens, India), sodium dihydrogen
phosphate, sodium nitrate and ethylenediamine tetra acetic acid (Loba Chemi. Pvt.
Ltd., India), sodium hydroxide and sodium chloride (Rankem-Avantor, India).),
chromium nitrate (CDH India), cobalt nitrate (CDH India), zinc nitrate (CDH Pvt.
Ltd., India), magnesium nitrate (CDH Pvt. Ltd., India), barium nitrate (Loba Chemi
Pvt. Ltd., India), sodium nitrate (CDH Pvt. Ltd., India), ferrous nitrate (Loba Chemi.
Pvt. Ltd., India), copper nitrate (Loba Chemi. Pvt. Ltd., India), lead nitrate (Loba
Chemi. Pvt. Ltd., India), methylene blue (S.D. Fine, Pvt. Ltd., India). The phenolic
compounds o-cresol, m-cresol, pyrocatechol, resorcinol, tannic acid, salicylic acid,
α-naphthol, β-naphthol, picric acid and hydroquinone are supplied by Loba Chemi.
Pvt. Ltd., India and Qualigens, India. All the reagents were used as received without
further purification. Double distilled water was used for each preparation and all
dilutions.
3.2. Instruments
X-ray diffractometer (X’pert Pro Analytical, Netherlands), Fourier transform
infrared (FTIR) spectrophotometer (Perkin Spectrum-400), scanning electron
microscope with energy-dispersive X-ray (JEOL, JSM-6610LL, Japan), transmission
electron microscope (Hitachi H7500 model, Germany), thermogravimetry analysis
(TGA) (Shimadzu thermal analyser TGA50 model-Japan), an electronic balance
(Sartorius, Japan), digital pH meter (Elico LI10 model, India), muffle furnace (MSW275, India), magnetic stirrer and digital oven were used. The ultraviolet–visible (UVVis) spectra were recorded using Systronics 2202 double beam spectrophotometer.
3.3. Synthesis of composite ion exchangers
The different hybrid ion exchangers have been synthesized using sol-gel
method. The methods of synthesis of different ion exchangers are discussed as
follows:
45
3.3.1. Synthesis of cellulose acetate-tin (IV) phosphate nanocomposite
(CA/TPNC) ion exchanger
Cellulose acetate-tin (IV) phosphate nanocomposite or nanohybrid ion
exchanger has been synthesized using sol-gel method at 0-1 pH and room
temperature. In this method, 0.1 M sodium dihydrogen phosphate and 0.1 M tin (IV)
chloride were mixed in 1:1 ratio with constant stirring at room temperature.The pH of
the resulting mixture was adjusted to 0-1 by adding 0.1 N HNO3. After complete
addition, the mixture was stirred for 1h to obtain the precipitates of tin (IV) phosphate
(TP). The gel of cellulose acetate (CA) in formic acid was prepared and added to the
precipitates of tin (IV) phosphate slowly with constant stirring. The resultant mixture
was stirred for 4 h on the magnetic stirrer at room temperature. This mixture was kept
for 24 h for digestion with occasional shaking. Then the precipitates were filtered and
washed with double distilled water several times to remove the impurities if present.
The precipitates of cellulose acetate-tin (IV) phosphate nanocomposite ion exchanger
(CA/TPNC) obtained were dried at 50oC in a hot air oven. The dried precipitates were
converted into H+ form by putting in 0.1 M HNO3 solution for 24h with occasional
shaking. The precipitates of CA/TPNC were filtered and washed with distilled water
to remove the excess of the acid. In a similar way different samples of nanocomposite
ion exchanger have been synthesized by varying the molar ratio of different
constituents and ion exchange capacities were determined as shown in Table 4.1.1.
The ion exchange capacity of Sample-4 was found to be maximum and thus was
selected for further detailed studies.
3.3.2. Synthesis of cellulose acetate-tin (IV) molybdate nanocomposite (CA/TMNC) ion
exchanger
Cellulose acetate-tin (IV) molydate nanocomposite (CA/TMNC) ion
exchanger was prepared by sol-gel method in two steps. In First step, 0.1 M solution
of tin (IV) chloride was mixed with 0.1M solution of sodium molybdate in 1:1 ratio
by volume with constant stirring at room temperature. The pH of the resulting
solution was adjusted to 0-1 with the help of 1M HNO3.This mixture was stirred for
30 min to obtain the precipitates of tin (IV) molybdate (TM). In second step, the gel
of cellulose acetate (CA) was prepared and added slowly to the precipitates of tin (IV)
molydate with constant stirring. The resultant mixture was stirred for 4 h on the
46
magnetic stirrer at room temperature. The whole solution was kept overnight for
digestion with random shaking. After removing the mother liquid, solution was
filtered and washed with distilled water to eliminate excess of reagents. Precipitates of
CA/TMNC were dried at 50oC temperature. The dried precipitates were converted
into H+ form by putting in 0.1 M HNO3 solution for 24h with occasional shaking. The
precipitates of CA/TMNC were filtered and washed with distilled water to remove the
excess of acid. Similarly, different samples of nanocomposite ion exchanger have
been synthesized and the ion exchange capacities were determined. The ion exchange
capacity of different synthesized hybrid material were shown in Table 4.2.1. The ion
exchange capacity of sample-3 (S-3) was found to be maximum and thus was selected
for further studies.
3.3.3. Synthesis of styrene-tin (IV) phosphate nanocomposite (ST/TPNC) ion
exchanger
A simple and ambient sol-gel method has been used for the synthesis of
styrene-tin (IV) phosphate nanocomposite ion exchanger (ST/TPNC). The synthesis
of nanocomposite ion exchanger has been carried out in two stages. In the first stage,
inorganic precipitates of tin (IV) phosphate (TP) were prepared by mixing sodium
dihydrogen phosphate (0.1 M) and tin (IV) chloride (0.1 M) in 1:1 volume ratio with
constant stirring at room temperature. 1 M HNO3 was added to maintain the pH of the
mixture solution between 0-1. The resultant slurry containing the precipitates of tin
(IV) phosphate was stirred for 1 h. In the next step, styrene (ST) solution was
prepared in ethyl alcohol and added to above precipitates of tin (IV) phosphate with
continuous stirring for 5 h. The resultant white precipitates were kept for digestion for
24 h with occasional stirring. Then the supernatant liquid was decanted, precipitates
filtered and washed with double distilled water and dried at 50oC temperature. The
dried precipitates of ST/TPNC were cracked into small granules of uniform size and
converted into H+ form by treating with 0.1 M HNO3 for 24 h with random shaking.
The precipitates were then filtered and washed several times with double distilled
water in order to remove any excess of acid sticking to the particles. The ST/TPNC
obtained was dried at 50oC in a hot air oven. A number of samples of ST/TPNC ion
exchanger were synthesized by varying the concentration of styrene (Table 4.3.1).
47
3.3.4. Synthesis of styrene-tin (IV) molybdate nanocomposite (ST/TMNC) ion
exchanger
The preparation of styrene-tin (IV) molydate nanocomposite (ST/TMNC) ion
exchanger was carried out in two steps. Firstly, 0.1 M solution of tin (IV) chloride
was mixed with 0.1M solution of sodium molybdate in 1:1 ratio by volume with
constant stirring at room temperature. The pH of the solution was adjusted to 0-1 with
the help of 1M HNO3.The resultant slurry was stirred for 1 h to form the precipitates
of tin (IV) molybdate. Further, the solution of styrene (ST) was prepared in ethanol
and added slowly to the precipitates of tin (IV) molybdate with constant stirring. The
resultant mixture was stirred for 5 h on the magnetic stirrer at room temperature. The
whole solution was kept overnight for digestion with random shaking. After removing
the mother liquid, solution was filtered and washed with distilled water to eliminate
the excess of reagents. The precipitates of ST/TMNC ion exchanger were dried at
50oC temperature. The dried precipitates were converted into H+ form by putting in
0.1 M HNO3 solution for 24h with occasional shaking. The precipitates of ST/TMNC
ion exchanger were filtered and washed with double distilled water to remove the
excess of the acid. In a similar way different samples of nanocomposite ion exchanger
have been synthesized and ion exchange capacities were determined (Table 4.4).
Based on ion exchange capacity sample-3 (S-3) was selected and studied in detail.
3.4. Physicochemical properties
Different physicochemical properties of synthesized hybrid ion exchange
material have been examined. These properties indicated the behavior and nature of
the synthesized materials. Some of these properties are discussed as follow:
3.4.1. Ion exchange capacity (IEC)
The ion exchange capacity of different hybrid or composite ion exchangers
was determined by the standard column process as reported earlier in the literature
(Siddiqi and Pathania, 2003). In this process, 1.0 g dry mass of ion exchange material
in H+ form was kept in a glass column fitted with glass wool support at the bottom.
The complete elution of H+ ions from the composite ion exchanger column was
carried out by passing 1 M solution of NaCl. The flow rate of the effluent was kept at
0.5 mL min-1. The effluent was collected and titrated against standard solution of 0.1
48
M NaOH. The ion exchange capacity of the nanocomposite ion exchangers were
calculated using the formula:
IEC =
NXV
mg/g
W
Where IEC is the ion exchange capacity. N and V (mL) are the normality and volume
of the alkali solution, respectively. W (g) is the amount of ion exchanger.
Based upon Na+ ion exchange capacity and percentage yield the samples were
selected for further detailed studies.
3.4.2. Thermal stability
The effect of temperature on the ion exchange capacity of different
nanocomposite ion exchangers was studied by heating 1.0 g of material in H+ form at
different temperatures for 1 h in digital muffle furnace (Innamuddine et al., 2007).
The weight and the color of the composite materials was noted after heating and Na+
ion exchange capacity was determined after cooling at room temperature by standard
column process as discussed in section 3.4.1.
3.4.3. pH titration
Topp and pepper method was used to perform the pH titration studies of
different composite ion exchangers (Topp & Pepper, 1949). In this method, 0.4 g of
nanocomposite ion exchanger in H+ ions form was taken each in 250 mL conical
flasks. The equimolar solution of alkali metal hydroxides (NaOH) and their chlorides
(NaCl) in different volume ratio were mixed in the flasks. The final volume of the
solution was maintained at 50 mL in each flask. The pH of the solution was recorded
after every 24 h till the equilibrium was attained. The pH of the mixture at equilibrium
was then plotted against the milli equivalents of OH- ions added.
3.4.4. Effect of eluent concentration
The effect of eluent concentration was investigated to determine the optimum
concentration of eluent for the complete elution of H+ ions from the ion exchangers.
In this, a fixed volume (250mL) of sodium nitrate solutions of different
49
concentrations were used to elute the H+ ions from the nanocomposite ion exchange
material. The eluent was passed through the column containing 1.0 g of ion exchanger
with a flow rate of 1mLmin-1. The collected effluent was titrated against 0.1M NaOH
solution.
3.4.5. Elution behavior
1.0 M NaNO3 eluent concentration was optimized for the complete removal of
H+ ions from the nanocomposite ion exchanger. In this, a column containing 1.0g of
ion exchange material in H+ form was eluted with 1.0 M NaNO3 solution. The effluent
was collected in fractions of 10 mL at a flow rate of 1 mL min-1. Each collected
fraction was titrated against standard NaOH solution.
3.4.6. Distribution coefficient studies (Kd)
The distribution coefficients of different metal ions metal ions Mg2+,
Mn2+Ba2+, Pb2+, Cr3+, Cd2+, Zn2+, Cu2+, Fe3+, Ni2+, Al3+, and Co2+onto nanocomposite
ion exchange material were determined using batch method in double distilled water
system. In this process, 0.3 g of dried samples of ion exchanger in H+ form were
equilibrated with 20 mL of different metal ions solutions and kept for 24 h at room
temperature with random shaking. The concentration of metal ions in the solution
before and after equilibrium was determined by standard EDTA method and atomic
absorption spectrophotometer (Reiliy et al., 1959). The distribution coefficient (Kd) of
different metal ions was calculated using the formula as:
I-F
V
Kd = ____ X __ mL g-1
M
F
Where I (g/L) and F (g/L) are the initial and final concentration of the metal
ions in solution, respectively. V is the volume of the solution (mL) and M is the
amount of ion exchange material (g).
3.5. Characterization techniques
In this study, the different techniques were used to characterize the
synthesized hybrid ion exchangers. These characterization techniques indicated the
size, morphology and nature of the synthesized composite materials. Some of the
50
important techniques used to characterize the hybrid nano material have been
discussed as follow:
3.5.1. Fourier transform infrared spectroscopy (FTIR)
Infrared spectroscopy is a powerful analytical technique, which provides
useful information about the structure of the molecules and bonding. The different
bands in FTIR spectra of the material correspond to the characteristic functional
groups and the bonds present. FTIR spectra of composite ion exchangers were
recorded using KBr disc method. In this technique, 10 mg of material was thoroughly
mixed with 100 mg of KBr. Then an appropriate pressure was exerted to form a
transparent disc. The FTIR spectra of the composite ion exchangers were recorded
between the range of 400 to 4000 cm-1.
3.5.2. X-ray (XRD) Studies
It has been used to provide useful information of molecule such as crystallinity
of the material, lattice parameters, grain size, bond lengths and plane spacing. Thus,
the XRD technique was used for the identification of unknown sample. The
characteristic spectrum consists of discrete energy, which occurs due to the X- rays
emitted by transition of electrons from K shell into L shell, gives rise to copper Kα
peaks. The transition of electrons from the M shell gives Kβ peaks and the electrons
from the N shell gives Kα peaks. Kα and Kβ peaks are the most prominent in the
peaks characteristic spectrum. When the required parameters are met, the X-rays that
get scattered from a crystalline solid interfere constructively and produce a diffracted
beam of light.
The d spacing between diffraction planes is calculated using Bragg’s
diffraction formula (Humphreys, 2013)
nλ =2d sinθ
Where λ = wavelength of X-ray, d = inter planar spacing, θ = diffraction angle and
n = 0, 1, 2, 3 etc.
X-ray diffraction studies were used to determine the phase purity and
crystalline size of the material. X-ray diffraction pattern of the composite ion
exchangers was recorded by X-ray diffractometer using CuKα radiations. The
51
instrument was equipped with graphite monochromator and operated at 40 kV and 30
mA. The spectrum of composite ion exchanger was recorded in the range 10o to 80o at
2θ.
3.5.3. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX)
studies
The morphology of synthesized samples was studied using a scanning electron
microscopeat different magnifications. SEM analysis was done using QUANTA 250
FEI D9393 scanning electron microscope. In SEM analysis the composite material
was stocked over a holder and gold-sputtered before examination. The elemental
composition of the composite ion exchangers was determined by energy dispersive Xray coupled with scanning electron microscopy.
3.5.4. Transmission electron microscopy (TEM)
TEM have been used for the production of images at higher resolutions
compared to other conventional light microscopes. TEM has been used for major
analysis in physical and biological sciences. In TEM analysis, 0.01 mg of material
was added to minimum quantity of ethanol to form fine suspension. The suspension
was sonicated in ultrasonic cleaner for 30 minutes. Then the drop of suspensions was
placed onto a carbon copper grid and analysed using high resolution transmission
electron microscopy Hitachi, H7500, Germany.
3.5.5. UV-visible spectroscopy
The UV-visible spectrophotometer has been used to find out the band gap of
synthesized composite ion exchangers. In this method, 5 mg of composite ion
exchangers was dispersed in ethanol. The suspension was ultrasonicated for 1 h. Then
UV–visible spectrum was recorded using double beam spectrophotometer. The same
process was repeated for all the composite ion exchangers. Where A=absorbance and
L = length of light path through the sample in cm.
The UV-visible spectral data was used for the determination of optical band
gap of various semiconductor metal oxide nanoparticles using the Tauc relation
(Dinesha et al., 2010).
52
αhν = A (hν- Eg)n
Where, α is the absorption coefficient, d is the thickness of the sample, Eg is
the energy band gap, n (1/2, 1, 2) band gap parameter dependent on the degree of
transition, n=1/2 for direct band gap semiconductors and hν is incident photon energy.
3.5.6. Thermogravimetric analysis (TGA/DTA)
The thermal analysis was used to determine the physical property of a
substance as a function of temperature whilst the substance is subjected to a
controlled temperature program (Duval, 1963).Thermal analysis has been used to
determine the thermal stability, material characterization, compositional analysis,
simulation of industrial processes, kinetic studies and corrosion studies etc. The
thermal gravimetric analysis is used to study the change in the weight of samples with
variation in temperature in a controlled atmosphere.
In this analysis, powdered sample of the hybrid ion exchanger was heated in a
nitrogen atmosphere in the temperature range of 50°C to 750°C. The thermal stability
and percentage weight loss was analyzed through TGA/DTA instrument.
3.6. Applications of composite ion exchangers
The synthesized composite ion exchange materials have been explored for
different analytical applications. These applications are discussed as follow:
3.6.1. Photocatalytic activity
The photocatalytic experiment was carried out in a batch reactor at 30±0.5°C. In
this method, 2 x 10-5 M solution of methylene blue (MB) dye was prepared in double
distilled water. 0.1 g of composite/hybrid ion exchanger in H+ form was added into
100mL solution of MB with continuous stirring. In adsorption experiments, the slurry
composed of dye solution and composite ion exchanger suspension was stirred
magnetically and placed in dark to establish adsorption desorption equillibrium. In
case of photocatalytic studies, the suspension composed of dye and catalyst was
stirred for 15 minutes and exposed to natural solar light radiations. The 5mL of
solution was withdrawn at different intervals of time and centrifuged. The absorbance
was recorded at a wavelength of 662 nm and kinetics of MB degradation was studied.
The percent degradation of dye was calculated using formula as:
53
% Degradation
Co Ct
X 100
Co
where, Co and Ct are the concentrations of dye at equilibrium and at time t.
The rates of photocatalytic degradation of dye was determined using pseudo –
first - order kinetic model as follow:
dC
dt
r
k
t
On integrating the above equation, we get
In
C
C
K
t
Where, kappt is the apparent rate constant, Co is the concentrations of dye before
illumination and Ct is the concentration of dye at time t.
3.6.2. Antimicrobial activity
The colony forming unit (CFU) method was used to investigate the
antibacterial/antimicrobial activity of composite ion exchanger against E. coli bacteria
culture. In this method, nutrient agar plates from a solution of agar were prepared to
examine the susceptibility of E. coli to composite material. A 100-µL sample of
bacterial suspension cultured in NB (with a concentration of 105 or 107 CFU/mL of E.
coli) was plated on a nutrient agar plate. The plates were then supplemented with
different amounts of material and were incubated further at 37°C. After 24 h of
incubation the number of resultant colonies were counted. The plates without
composite material incubated under the same conditions were used as control. The
counts from different independent experiments corresponding to a particular sample
were averaged.
3.6.3. Binary separation of metal ions
The binary separation of different metal ions have been performed on the
column of ion exchangers. In this method, 1 g of ion exchanger in H+ form was placed
in a glass column with glass wool support at bottom. The mixture of different metal
ions to be separated was then loaded by passing through the column at slow rate (1.0
54
mL min-1). This mixture was recycled at least 3-4 times through the column. Then the
column was washed with distilled water to remove the unabsorbed metal ions. The
metal ions adsorbed on the exchanger were eluted with different concentrations of
HNO3. The flow rate of the effluent was maintained at 1.0 mLmin-1 until the metal
ions were eluted out from the column. The effluents were collected in 10 mL fractions
and concentrations of metal ions were determined by atomic absorption
spectrophotometer and EDTA method.
3.6.4. Separation of phenols
Phenols have been reported as great threat to environment and human health.
Therefore, their detection and separation from water system is of great concern.
Different steps have been used for the separation of phenols from mixtures using the
synthesized hybrid ion exchangers such as:
3.6.4.1. Preparation of thin layer chromatography (TLC) plates
The ion exchange material in powder form was thoroughly mixed with
cellulose in 1:4 ratios. Then 10% CaSO4was added to the above mixture as binder.
The slurry was formulated by mixing 10 g of above mixed power material in 50 mL
of double distilled water. The slurry was spread over the glass plate of 18cm x 20cm
dimension to form uniform thin layer of 0.2 mm thickness. The TLC plates were then
dried in a hot air oven at 50oC.
3.6.4.2. Preparation of visualizers
The following visualizers were prepared for the detection of phenolic
compounds:
(i) 1mL saturated solution of AgNO3 was added into 20 mL of acetone with
continuous stirring. Water was added drop wise into the above solution until the
precipitates of AgNO3 just dissolved. For better visualization the plates were heated at
105oC.
(ii) The phenols which are not detected with above visualizer can be detected with 25% solution of K4[Fe (CN) 6] in HCl.
55
3.6.4.3. Development of chromatogram
For chromatographic study, 1% solution of the test material was applied by
means of a fine capillary at one end of the plates. After drying the spots, the plates
were kept for developing in 20cm x 22cm x 9cm chromatography chamber at room
temperature (25±2oC) containing appropriate mobile phase. The complete
development of chromatogram was considered until the mobile phase had ascended
upto 15cm. The developed plates were again dried at 100oC.The locations of different
phenols were located by treatment of plate surface with solution of appropriate
detector. The Rf values of different phenols were recorded and compared.