CHAPTER I
INTRODUCTION OF MnO₂
1
,Introduction
In today’s world, there is a demand for highly efficient, versatile, flexible, and energy storage
devices that Can confirm energy storage faster than traditional energy storage systems like
batteries. Energy storage Devices such as fuel cells, sodium and lithium-ion batteries, super
capacitors, and others are currently Available. Super capacitors may be a viable alternative to
batteries for energy storage devices because of Their (Super capacitor) long lifetime, quick
energy delivery, high power application, high current density, High power density etc. The
electrodes of super capacitors must have some properties like high specific area, Cost effective,
free from corrosion, light-weight, high electrical conductivity, good chemical stability etc.
Manganese dioxide ( MnO₂) is a suitable material for the production of electrodes in super
capacitor since It’s raw materials abundant in nature, inexpensive and also possess all required
properties. Transition metal Oxide (like RuO 2 , MnO₂,Co3O4 ,NiO,V2O5 and Fe3O4 ) has got a
lot of interest recently as a Super capacitor electrode material because of their large specific
capacitance around ( 150-900 F/g ), low Cost, high energy density, wide operating temperature
range, chemical stability, and ease of manufacture. Super capacitors, which have a rapid charge-
discharge property, a high energy density, a large number of Charging-discharging cycles or a
long life, and a high power density, are gaining popularity as energy storage devices. Charge is
stored on the electrode materials’ surfaces in electrical double-layer capacitors (EDLCs) by
electrolytic ion adsorption or desorption, and in pseudo capacitors, which rely on fast redox
Reactions on the electrode materials’ surface, are the two forms of super capacitors. The most
commonly Utilized pseudocapacitive substance is manganese dioxide. Protons and alkali ions
could improve Electrochemical performance by acting as charge carriers in the charging-
discharging process. The sample’s Porous shape has a significant impact on capacitive
performance, which improves ion accessibility and Cation diffusivity. Nano walls, nano disks,
multi pods, and nano sheets have all been explored with various Morphologies. In general, there
are two types of MnO₂synthesis processes. The first method is solution Method and second
method is microwave hydrothermal approach. For greater morphological control, the Solution
approach is preferred for nanostructure production MnO₂a promising green material has attracted
considerable
2
,Interests in virtue of its low cost, high environmental compatibility And wide structural diversity
combined with unique physical and Chemical properties . Transition-metal oxides have been
shown To be excellent electrode active materials due to their chemical Stability, variable valence
etc. Important applications of nano-sized MnO₂include preparation of cathode materials of
alkaline batteries , electrochemical capacitors , smart windows , the active Layer for gas sensors
and photocatalyst. In accomplishing the Synthesis and manipulation of the nanostructured nickel
oxide, a Variety of strategies have been employed, such as evaporation, Sputtering,
electrodeposition, thermal decompositionAnd sol-gel techniques. Thermal decomposition
method has some Advantages such as simple process, low cost and easiness to obtain High purity
products hence it is quite promising and facile route for Industrial applications. Many reports
have concerned the synthesis Of NiO nanocrystals, including NiO nanorings [15], nanosheets,
Nanoribbons and nanoclusters .
1.1 Nature of MnO2
MnO₂ nanoparticles were Synthesized by different methods including co-precipitation
Microemulsion, sol-gel , sonochemical , hydrothermal and electrochemical methods . MnO₂was
the most unusual One in terms of its structural properties at ambient pressure, which Are largely
determined by the strong tendency for linear coordination Of O-Mn-O chain geometry . The
structure of MnO₂is built up of Planar O- Mn-O zigzag chains lying in the ac-plane. The band
gap of The MnO₂Structures at room temperature was measured to be 2.19 eV From the
photoconductivity, and n-type electrical conductivity has been Reported [26-28]. In this
manuscript, the production method of MnO₂Nanostructures is reported. One-dimensional (1-D)
nanostructures Of MnO₂nanocomposites were prepared by solid-state thermal Decomposition of
the asproduced Mn(CH3COO)2 Nanostructures.
The utilized method has many advantages since it is a controllable, Free solvent,
template less, and economical method. The produced Nanostructures were characterized by
SEM, TEM, XRD, AFM, PL, and TGA Nanomaterials and nanotechnologies attract tremendous
attention towards recent researches. New Physical properties and new technologies both for
sample preparation and device fabrication educe an Enormous role in development of
nanoscience. There are various methods of preparing nanomaterials
3
, Including Gas condensation, Vacuum deposition and vaporization, Chemical Vapor Deposition
(CVD), Chemical Vapor Condensation (CVC), Sol-Gel and Chemical precipitation (co-
precipitation) method. In the Present report we are also focusing the Coprecipitation method for
the synthesis of MnO₂nanoparticles. In This method, the required metal cations from a common
medium are co-precipitated usually as hydroxides, Carbonates, oxalates and citrates.MnO₂can
exist in different structural forms α, β, γ, δ, ε and λ types and so on. Based on the different
(MnO₂) links, formed structure can be divided into three categories: chin like, the sheet or
layered and the 3D-structure [1]. MnO₂is the best catalysts due to its low toxicity and it is the
environmental benign. It is The low band gap material (1.33 eV), having high optical constant
which also shows good ferroelectric Catalytic and properties [2]. The green synthesis of MnO₂
nanoparticles has been reported from Syzygium Aromaticum i.e. clove extract (CE) as reducing
agent as well as stabilizing agent by Vineet et al, 2017. Another study, shows production of
MnO₂, from Kalopanax pictus i.e. castor aralia leaf extract for Degradation of dyes by Sun et al,
2015. Similarly, Muhamed et al, 2017, reported the biosynthesis of MnO₂By lemon and turmeric
curcumin extract as reducing and capping agent respectively and also investigated Their
antibacterial and antifungal activities. Wright et al, 2016 reported Shewanella laihica as a
strongest Oxidizer Manganese oxides form a diverse transition metal oxide family that comprises
of manganese (II) oxide (MnO), trimanganese tetraoxide (Mn3O4), manganese (III) oxide
(Mn2O3) and manganese (IV) oxide or manganese dioxide (MnO₂), manganese (VI) oxide
(MnO3), manganese (VII) oxide (Mn2O7) [3]. Manganese oxides are mostly chosen to act as
catalysts because of their beneficial redox nature and potent for oxygen storage or release [4].
MnO₂is thought to be the most popular star of the family and appears in the form of pyrolusite
mineral in nature [5]. MnO₂can hold itself stable upto 500 ˚C, beyond this point it degenerates
into Mn2O3 [6]. Falling under the division of n-type semiconductors, MnO₂exists in the
numerous multidimensional forms of α-, β-, γ-, δ- and λ-MnO₂which are all built on typically
linked MnO6 octahedral units [7].Manganese dioxide (MnO₂) is an interesting transition metal
oxide that promises high energy density, structural flexibility, thermal stability, low cost, easy
preparation and environmental safety. The fascinating electrochemical traits of
MnO₂nanostructures are being exploited in catalysis, biosensors, supercapacitors, dry cell
batteries and ion sieves . Wet chemical routes such as hydrothermal, chemical precipitation,
4
INTRODUCTION OF MnO₂
1
,Introduction
In today’s world, there is a demand for highly efficient, versatile, flexible, and energy storage
devices that Can confirm energy storage faster than traditional energy storage systems like
batteries. Energy storage Devices such as fuel cells, sodium and lithium-ion batteries, super
capacitors, and others are currently Available. Super capacitors may be a viable alternative to
batteries for energy storage devices because of Their (Super capacitor) long lifetime, quick
energy delivery, high power application, high current density, High power density etc. The
electrodes of super capacitors must have some properties like high specific area, Cost effective,
free from corrosion, light-weight, high electrical conductivity, good chemical stability etc.
Manganese dioxide ( MnO₂) is a suitable material for the production of electrodes in super
capacitor since It’s raw materials abundant in nature, inexpensive and also possess all required
properties. Transition metal Oxide (like RuO 2 , MnO₂,Co3O4 ,NiO,V2O5 and Fe3O4 ) has got a
lot of interest recently as a Super capacitor electrode material because of their large specific
capacitance around ( 150-900 F/g ), low Cost, high energy density, wide operating temperature
range, chemical stability, and ease of manufacture. Super capacitors, which have a rapid charge-
discharge property, a high energy density, a large number of Charging-discharging cycles or a
long life, and a high power density, are gaining popularity as energy storage devices. Charge is
stored on the electrode materials’ surfaces in electrical double-layer capacitors (EDLCs) by
electrolytic ion adsorption or desorption, and in pseudo capacitors, which rely on fast redox
Reactions on the electrode materials’ surface, are the two forms of super capacitors. The most
commonly Utilized pseudocapacitive substance is manganese dioxide. Protons and alkali ions
could improve Electrochemical performance by acting as charge carriers in the charging-
discharging process. The sample’s Porous shape has a significant impact on capacitive
performance, which improves ion accessibility and Cation diffusivity. Nano walls, nano disks,
multi pods, and nano sheets have all been explored with various Morphologies. In general, there
are two types of MnO₂synthesis processes. The first method is solution Method and second
method is microwave hydrothermal approach. For greater morphological control, the Solution
approach is preferred for nanostructure production MnO₂a promising green material has attracted
considerable
2
,Interests in virtue of its low cost, high environmental compatibility And wide structural diversity
combined with unique physical and Chemical properties . Transition-metal oxides have been
shown To be excellent electrode active materials due to their chemical Stability, variable valence
etc. Important applications of nano-sized MnO₂include preparation of cathode materials of
alkaline batteries , electrochemical capacitors , smart windows , the active Layer for gas sensors
and photocatalyst. In accomplishing the Synthesis and manipulation of the nanostructured nickel
oxide, a Variety of strategies have been employed, such as evaporation, Sputtering,
electrodeposition, thermal decompositionAnd sol-gel techniques. Thermal decomposition
method has some Advantages such as simple process, low cost and easiness to obtain High purity
products hence it is quite promising and facile route for Industrial applications. Many reports
have concerned the synthesis Of NiO nanocrystals, including NiO nanorings [15], nanosheets,
Nanoribbons and nanoclusters .
1.1 Nature of MnO2
MnO₂ nanoparticles were Synthesized by different methods including co-precipitation
Microemulsion, sol-gel , sonochemical , hydrothermal and electrochemical methods . MnO₂was
the most unusual One in terms of its structural properties at ambient pressure, which Are largely
determined by the strong tendency for linear coordination Of O-Mn-O chain geometry . The
structure of MnO₂is built up of Planar O- Mn-O zigzag chains lying in the ac-plane. The band
gap of The MnO₂Structures at room temperature was measured to be 2.19 eV From the
photoconductivity, and n-type electrical conductivity has been Reported [26-28]. In this
manuscript, the production method of MnO₂Nanostructures is reported. One-dimensional (1-D)
nanostructures Of MnO₂nanocomposites were prepared by solid-state thermal Decomposition of
the asproduced Mn(CH3COO)2 Nanostructures.
The utilized method has many advantages since it is a controllable, Free solvent,
template less, and economical method. The produced Nanostructures were characterized by
SEM, TEM, XRD, AFM, PL, and TGA Nanomaterials and nanotechnologies attract tremendous
attention towards recent researches. New Physical properties and new technologies both for
sample preparation and device fabrication educe an Enormous role in development of
nanoscience. There are various methods of preparing nanomaterials
3
, Including Gas condensation, Vacuum deposition and vaporization, Chemical Vapor Deposition
(CVD), Chemical Vapor Condensation (CVC), Sol-Gel and Chemical precipitation (co-
precipitation) method. In the Present report we are also focusing the Coprecipitation method for
the synthesis of MnO₂nanoparticles. In This method, the required metal cations from a common
medium are co-precipitated usually as hydroxides, Carbonates, oxalates and citrates.MnO₂can
exist in different structural forms α, β, γ, δ, ε and λ types and so on. Based on the different
(MnO₂) links, formed structure can be divided into three categories: chin like, the sheet or
layered and the 3D-structure [1]. MnO₂is the best catalysts due to its low toxicity and it is the
environmental benign. It is The low band gap material (1.33 eV), having high optical constant
which also shows good ferroelectric Catalytic and properties [2]. The green synthesis of MnO₂
nanoparticles has been reported from Syzygium Aromaticum i.e. clove extract (CE) as reducing
agent as well as stabilizing agent by Vineet et al, 2017. Another study, shows production of
MnO₂, from Kalopanax pictus i.e. castor aralia leaf extract for Degradation of dyes by Sun et al,
2015. Similarly, Muhamed et al, 2017, reported the biosynthesis of MnO₂By lemon and turmeric
curcumin extract as reducing and capping agent respectively and also investigated Their
antibacterial and antifungal activities. Wright et al, 2016 reported Shewanella laihica as a
strongest Oxidizer Manganese oxides form a diverse transition metal oxide family that comprises
of manganese (II) oxide (MnO), trimanganese tetraoxide (Mn3O4), manganese (III) oxide
(Mn2O3) and manganese (IV) oxide or manganese dioxide (MnO₂), manganese (VI) oxide
(MnO3), manganese (VII) oxide (Mn2O7) [3]. Manganese oxides are mostly chosen to act as
catalysts because of their beneficial redox nature and potent for oxygen storage or release [4].
MnO₂is thought to be the most popular star of the family and appears in the form of pyrolusite
mineral in nature [5]. MnO₂can hold itself stable upto 500 ˚C, beyond this point it degenerates
into Mn2O3 [6]. Falling under the division of n-type semiconductors, MnO₂exists in the
numerous multidimensional forms of α-, β-, γ-, δ- and λ-MnO₂which are all built on typically
linked MnO6 octahedral units [7].Manganese dioxide (MnO₂) is an interesting transition metal
oxide that promises high energy density, structural flexibility, thermal stability, low cost, easy
preparation and environmental safety. The fascinating electrochemical traits of
MnO₂nanostructures are being exploited in catalysis, biosensors, supercapacitors, dry cell
batteries and ion sieves . Wet chemical routes such as hydrothermal, chemical precipitation,
4
