_______________________________ Catalytic Studies _______________________________
CHAPTER 5
CATALYTIC ACTIVITIES OF SYNTHESIZED
BIMETALLIC CATION EXCHANGERS BASED ON CERIUM
Heterogeneous catalysis is the most practical method as separation processes are
avoided by keeping catalysts and products in different phases. Heterogeneous solid acid
catalysts provide an attractive alternative to homogeneous liquid acid catalyst as they
possess high catalytic activity and selectivity, lower corrosive effects to the reaction
vessels and reactors and finally, repeated use of solid acid catalyst from a reaction
mixture is easy. The progress of a heterogeneous catalytic reaction can be described by
the sequence of elementary reaction steps, including adsorption, surface diffusion,
chemical transformations of adsorbed species and desorption.
Inorganic cation exchangers of the class of tetravalent metal acid salts possess
good potential for application as a solid acid catalyst. These materials possess structural
hydroxyl groups, the H of the –OH being the exchangeable sites. The presence of acid
sites on such materials indicates good potential for application in Bronsted catalysis.
These inorganic ion exchanger catalysts offer remarkably simple workup procedure and
are reusable without any appreciable loss in its activity. In catalytic reactions, specific
surface areas of the catalysts play an important role which is the characteristic feature of
the material. Ion exchangers possess very high surface area since they have both
internal and external surfaces are available.
5.1. Catalytic activity of TiCeMo and PANI-TiCeMo towards dye degradation
The effluents from textile, leather, food processing, dyeing, paper, cosmetics
and dye manufacturing industries are major sources of pollution179. Pollution from
effluents has become increasingly alarming with the use of a wide variety of dyes in
industries. Many dyes and their breakdown products cause a lot of damage to the
environment180. Nowadays, treating the textile effluents has become an environmental
concern due to scarcity of water and chronic effects on human beings. High molecular
weight and complex molecular structures of synthetic organic dyes cause difficulties in
treatment of these dyes from wastewater. Several biological, physical and chemical
methods have been used for the treatment of industrial textile wastewater. But many of
147
,_______________________________ Catalytic Studies _______________________________
these technologies are cost prohibitive, especially when applied for treating large waste
streams. In the present endeavour, we have employed cerium based cation exchangers
for the degradation of hazardous organic dyes after selective sorption on catalyst
surface. In general, the structure of dye molecules contain functional groups such as –
OH, -SO3H, -NO2, -N=N etc., when contact with the exchanger, these groups interact
with the matrix of the exchanger and get sorbed on the surface of catalysts. The sorption
of dye molecules is also facilitated by the exchange of H+ ions in the exchanger. The
exchanger can be recovered by using suitable eluents and can be reused for the next
cycle.
Cerium based ion exchangers are reported as having enhanced applications like
decolourisation of water by adsorption or degradation of organic dyes54,181. Cerium
based materials have generated great interest due to their redox properties, because of
conversion between trivalent and tetravalent states under oxidation and reduction
conditions. Cerium containing catalysts are broadly used as effective oxidation systems
due to their unique properties such as redox, oxygen release and storage abilities182,183.
During catalytic degradation of dyes present in effluents of various industries,
knowledge of the interaction of certain ions with the cations in the exchanger is very
essential since the catalytic reactions are usually carried out in aqueous medium which
may contain various cations. Cerium based cation exchangers are most applicable for
effluent treatment because almost complete removal of dye molecules is possible by
degradation. Ion exchange character, oxidising power of the exchanger and electron
exchange property of cerium ions as a whole help in the dye degradation process.
The newly synthesized bimetallic cation exchangers TiCeMo and its poly-o-
toluidine composite are found to have the ability to degrade hazardous organic dyes
such as methyl red (MR) and crystal violet (CV) from aqueous solutions. In this work,
the catalytic potential of TiCeMo and PANI-TiCeMo towards the degradation of these
dyes from aqueous solution was carried out. Efforts have also been made to see the
effects of operational parameters such as reaction time, pH, temperature, amount of
catalyst and interference of various metal ions on the degradation of methyl red.
148
, _______________________________ Catalytic Studies _______________________________
5.1.1. EXPERIMENTAL
Methyl red and crystal violet were obtained from Loba Chemie (India).
Deionized water was used throughout the study. All other reagents and chemicals used
were of analytical grade.
Specific surface area of TiCeMo and PANI-TiCeMo exchangers was
determined by gas adsorption (BET) method. UV-Vis Diffuse Reflectance
Spectrophotometer was used for measuring the absorbance.
The catalytic activity of TiCeMo and PANI-TiCeMo for the degradation of MR
and CV was evaluated in laboratory conditions. For this stock solutions (40 ppm) of
dyes were prepared in deionized water and were diluted as and when required. The
catalytic degradation was observed by the addition of 200 mg of the exchangers to 20
mL dye solutions at room temperature without any irradiation and external catalyst.
Decolourisation of the media was measured by taking optical density at their maximum
absorbance wavelength (𝜆max of MR = 521 nm , 𝜆max of CV = 590 nm) in regular time
intervals with the help of UV-Vis DRS. The degradation efficiency was calculated
using Beer’s law184 as;
Initial absorbance − final absorbance
% Degradation = × 100
Initial absorbance
The dye degradation ability of the exchangers was optimized under different
conditions and parameters. The effects of catalyst dosage, pH, temperature, reaction
time and interference of inorganic cations were studied. The effect of catalyst dosage on
catalytic activity was studied at different catalyst doses (100 - 400 mg per 20 mL of 40
ppm dye solutions), keeping temperature 300C. The effect of pH in the range 2-10 was
studied by taking 40 ppm dye solutions, amount of catalyst 200 mg and temperature
300C. The pH of the solution was adjusted after adding the exchanger by using dilute
NH3 and HCl solutions. Initial dye concentration ranging from 10 ppm to 50 ppm was
prepared and degradation experiments were conducted using 200 mg of the exchanger.
To study the effect of temperature on the removal of dyes, the experiments were carried
out at temperatures varying from 300C to 500C with 40 ppm initial dye concentration.
149
CHAPTER 5
CATALYTIC ACTIVITIES OF SYNTHESIZED
BIMETALLIC CATION EXCHANGERS BASED ON CERIUM
Heterogeneous catalysis is the most practical method as separation processes are
avoided by keeping catalysts and products in different phases. Heterogeneous solid acid
catalysts provide an attractive alternative to homogeneous liquid acid catalyst as they
possess high catalytic activity and selectivity, lower corrosive effects to the reaction
vessels and reactors and finally, repeated use of solid acid catalyst from a reaction
mixture is easy. The progress of a heterogeneous catalytic reaction can be described by
the sequence of elementary reaction steps, including adsorption, surface diffusion,
chemical transformations of adsorbed species and desorption.
Inorganic cation exchangers of the class of tetravalent metal acid salts possess
good potential for application as a solid acid catalyst. These materials possess structural
hydroxyl groups, the H of the –OH being the exchangeable sites. The presence of acid
sites on such materials indicates good potential for application in Bronsted catalysis.
These inorganic ion exchanger catalysts offer remarkably simple workup procedure and
are reusable without any appreciable loss in its activity. In catalytic reactions, specific
surface areas of the catalysts play an important role which is the characteristic feature of
the material. Ion exchangers possess very high surface area since they have both
internal and external surfaces are available.
5.1. Catalytic activity of TiCeMo and PANI-TiCeMo towards dye degradation
The effluents from textile, leather, food processing, dyeing, paper, cosmetics
and dye manufacturing industries are major sources of pollution179. Pollution from
effluents has become increasingly alarming with the use of a wide variety of dyes in
industries. Many dyes and their breakdown products cause a lot of damage to the
environment180. Nowadays, treating the textile effluents has become an environmental
concern due to scarcity of water and chronic effects on human beings. High molecular
weight and complex molecular structures of synthetic organic dyes cause difficulties in
treatment of these dyes from wastewater. Several biological, physical and chemical
methods have been used for the treatment of industrial textile wastewater. But many of
147
,_______________________________ Catalytic Studies _______________________________
these technologies are cost prohibitive, especially when applied for treating large waste
streams. In the present endeavour, we have employed cerium based cation exchangers
for the degradation of hazardous organic dyes after selective sorption on catalyst
surface. In general, the structure of dye molecules contain functional groups such as –
OH, -SO3H, -NO2, -N=N etc., when contact with the exchanger, these groups interact
with the matrix of the exchanger and get sorbed on the surface of catalysts. The sorption
of dye molecules is also facilitated by the exchange of H+ ions in the exchanger. The
exchanger can be recovered by using suitable eluents and can be reused for the next
cycle.
Cerium based ion exchangers are reported as having enhanced applications like
decolourisation of water by adsorption or degradation of organic dyes54,181. Cerium
based materials have generated great interest due to their redox properties, because of
conversion between trivalent and tetravalent states under oxidation and reduction
conditions. Cerium containing catalysts are broadly used as effective oxidation systems
due to their unique properties such as redox, oxygen release and storage abilities182,183.
During catalytic degradation of dyes present in effluents of various industries,
knowledge of the interaction of certain ions with the cations in the exchanger is very
essential since the catalytic reactions are usually carried out in aqueous medium which
may contain various cations. Cerium based cation exchangers are most applicable for
effluent treatment because almost complete removal of dye molecules is possible by
degradation. Ion exchange character, oxidising power of the exchanger and electron
exchange property of cerium ions as a whole help in the dye degradation process.
The newly synthesized bimetallic cation exchangers TiCeMo and its poly-o-
toluidine composite are found to have the ability to degrade hazardous organic dyes
such as methyl red (MR) and crystal violet (CV) from aqueous solutions. In this work,
the catalytic potential of TiCeMo and PANI-TiCeMo towards the degradation of these
dyes from aqueous solution was carried out. Efforts have also been made to see the
effects of operational parameters such as reaction time, pH, temperature, amount of
catalyst and interference of various metal ions on the degradation of methyl red.
148
, _______________________________ Catalytic Studies _______________________________
5.1.1. EXPERIMENTAL
Methyl red and crystal violet were obtained from Loba Chemie (India).
Deionized water was used throughout the study. All other reagents and chemicals used
were of analytical grade.
Specific surface area of TiCeMo and PANI-TiCeMo exchangers was
determined by gas adsorption (BET) method. UV-Vis Diffuse Reflectance
Spectrophotometer was used for measuring the absorbance.
The catalytic activity of TiCeMo and PANI-TiCeMo for the degradation of MR
and CV was evaluated in laboratory conditions. For this stock solutions (40 ppm) of
dyes were prepared in deionized water and were diluted as and when required. The
catalytic degradation was observed by the addition of 200 mg of the exchangers to 20
mL dye solutions at room temperature without any irradiation and external catalyst.
Decolourisation of the media was measured by taking optical density at their maximum
absorbance wavelength (𝜆max of MR = 521 nm , 𝜆max of CV = 590 nm) in regular time
intervals with the help of UV-Vis DRS. The degradation efficiency was calculated
using Beer’s law184 as;
Initial absorbance − final absorbance
% Degradation = × 100
Initial absorbance
The dye degradation ability of the exchangers was optimized under different
conditions and parameters. The effects of catalyst dosage, pH, temperature, reaction
time and interference of inorganic cations were studied. The effect of catalyst dosage on
catalytic activity was studied at different catalyst doses (100 - 400 mg per 20 mL of 40
ppm dye solutions), keeping temperature 300C. The effect of pH in the range 2-10 was
studied by taking 40 ppm dye solutions, amount of catalyst 200 mg and temperature
300C. The pH of the solution was adjusted after adding the exchanger by using dilute
NH3 and HCl solutions. Initial dye concentration ranging from 10 ppm to 50 ppm was
prepared and degradation experiments were conducted using 200 mg of the exchanger.
To study the effect of temperature on the removal of dyes, the experiments were carried
out at temperatures varying from 300C to 500C with 40 ppm initial dye concentration.
149
