MnO2 Nanoparticle Synthesis and
Characterization using Green Chemistry
Raman*
M.Sc (MNIT Jaipur) / NET JRF
Abstract - This study investigates the creation and analysis of MnO2 nanoparticles utilizing
green chemistry techniques. To ensure the future viability of nanotechnology, it is critical to
select environmentally friendly materials and techniques. A greener method of synthesis is
developed by substituting natural sources for synthetic ones and using plant extracts to
reduce and stabilize the reactants. MnO2 nanoparticles are investigated using a variety of
analytical procedures, including X-ray diffraction (XRD), scanning electron microscopy (SEM),
X-ray fluorescence (XRF), and ultraviolet-visible (UV-visible) spectroscopy. Catalysis, energy
storage, and biological applications are among the potential uses for the produced MnO2
nanoparticles; the results reveal that the nanoparticles' size and form may be controlled. The
green synthesis approach offers an ecologically friendly and scalable way to produce MnO2
nanoparticles, which contributes to the advancement of sustainable nanotechnology.
Keywords - MnO2, Nanoparticle Synthesis, Characterization, Green Chemistry
1. INTRODUCTION
Nanotechnology is a new and exciting area of study that might revolutionize many industries, from
electronics and healthcare to energy and environmental cleanup. Nanoparticles of manganese
dioxide (MnO2) are highly distinctive from the vast majority of nanoparticles because of their many
useful and unusual characteristics. The antibacterial, catalytic, and electrochemical characteristics of
these nanoparticles have made them highly sought after and promising for use in a wide range of
industries, including biomedicine, water treatment, sensing, and energy storage.[1] Synthesizing
MnO2 nanoparticles the old-fashioned way often requires a lot of energy and harmful chemicals,
which are bad for the environment and people's health. Green chemistry techniques to nanoparticle
production, on the other hand, have emerged in response to the rising environmental consciousness.
Chemical processes that are designed with the goal of limiting the usage and creation of hazardous
compounds while optimizing efficiency and decreasing waste are known as green chemistry or
sustainable chemistry.
There has been a lot of interest in synthesizing MnO2 nanoparticles utilizing green chemistry
concepts. Nanoparticle creation leaves less of an ecological imprint when using green synthesis
pathways since they use less harmful precursors, solvents, and reaction conditions. Additionally,
nanoparticles produced using green synthesis techniques frequently have higher biocompatibility and
stability, two attributes highly prized in a wide range of applications. To create MnO2 nanoparticles
using green chemistry methods, reducing and stabilizing agents are derived from natural sources
such microbes, plant extracts, or eco-friendly reducing agents.[2] The many benefits of these natural
sources include their affordability, compliance with sustainable methods, and plentiful availability. The
synthesis method is even more environmentally friendly when green solvents like water or
biocompatible organic solvents are used.
The physicochemical characteristics and structure-property connections of produced MnO2
nanoparticles can only be understood by thorough characterization. The MnO2 nanoparticles are
characterized by using a variety of analytical techniques, such as microscopic, spectroscopic, and
diffraction approaches.[3] The optical and chemical characteristics of the nanoparticles may be
understood through the use of spectroscopic methods as X-ray photoelectron spectroscopy (XPS),
UV-visible spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy. Transmission electron
microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) are
some of the microscopic methods that allow us to see the size, shape, and surface properties of
MnO2 nanoparticles on a nanoscale. Nanoparticles made via green chemical approaches must be
evaluated for shape, size distribution, and homogeneity using these methods.[4] The crystalline
structure and phase purity of MnO2 nanoparticles may be better understood with the use of diffraction
techniques like electron diffraction (ED) and X-ray diffraction (XRD). By manipulating synthesis
parameters such precursor concentration, reaction temperature, pH, and reaction time, one may
customize the physicochemical characteristics of MnO2 nanoparticles. To optimize the green
synthesis pathway and achieve desirable nanoparticle qualities for specific applications, it is vital to
understand the effect of these factors on the nanoparticle synthesis process.[5]
1.1 Overview of MnO2 nanoparticles
Nanoparticles of manganese dioxide (MnO2) have attracted a lot of interest because of their
remarkable characteristics and wide range of potential uses. These nanoparticles are well-suited for a
variety of uses due to their many advantageous qualities, including as their large surface area,
adjustable shape, strong catalytic activity, and distinctive electrical and magnetic characteristics.[6] In
addition to its many potential applications in sensing, biological imaging, energy storage,
environmental cleanup, and drug delivery systems, manganese dioxide nanoparticles have been the
subject of much research. Oxidation, reduction, and decomposition reactions are only a few of the
many chemical processes that benefit from their catalytic characteristics. Because of their high
specific capacitance and cycle stability, MnO2 nanoparticles are attractive electrode materials for
energy storage devices such as lithium-ion batteries and supercapacitors.[7] Due to their adsorption
capacity and catalytic degradation capabilities, MnO2 nanoparticles are also used in environmental
remediation techniques to remove contaminants from air and water. Nanoparticles of manganese
dioxide have several uses in medicine, such as theranostic agents for cancer treatment, drug delivery
vehicles, and MRI contrast agents. Nanoparticles of manganese dioxide (MnO2) are an intriguing
class of nanomaterials because of their multipurpose nature and the many problems they might solve
in society and technology.
1.2 Role of green chemistry principles in the synthesis route
The synthesis method of MnO2 nanoparticles is shaped by green chemistry concepts, which help
build techniques that are both efficient and ecologically friendly. Some important functions of green
chemistry concepts throughout the synthesis pathway are as follows:[8]
Reducing Environmental Impact: Nanoparticle production leaves less of an ecological imprint when
green chemists work to reduce or do away with the usage of potentially harmful chemicals and
solvents. Green synthesis pathways minimise the production of hazardous waste and by-products by
switching to safer reagents and solvents, such as water or bio-based solvents.
Utilization of Renewable Resources: When synthesizing MnO2 nanoparticles, "green" synthesis
methods frequently use renewable resources like microbes, plant extracts, or naturally occurring
reducing agents as either precursors or stabilizing agents. Reducing dependence on finite resources
and fossil fuels, these renewable resources are plentiful, affordable, and consistent with sustainable
practices.[9]
Energy Efficiency: Minimizing energy consumption and improving reaction conditions are key
principles of green chemistry, which aims to design processes that are energy efficient. By avoiding
high-energy input and minimizing total energy consumption, synthesis pathways for MnO2
nanoparticles using green chemistry principles typically work at ambient temperatures and pressures.
Atom Economy: The goal of environmentally friendly synthesis methods is to reduce wasteful
reagent usage and increase reactant integration into the end product in order to optimize the atom
economy. To maximize the usage of precursor materials and minimize waste, green synthesis
approaches for MnO2 nanoparticles use efficient reaction pathways and minimize superfluous side
reactions. This improves resource efficiency and reduces waste.[10]
Biocompatibility and Safety: The creation of biocompatible and environmentally safe products and
processes is the primary focus of green chemistry concepts. Nanoparticles of manganese dioxide
synthesized utilizing green chemistry methods are safer for both employees and consumers, and they
have better biocompatibility and less toxicity, making them ideal for use in biomedicine and
environmental protection.
2. LITERATURE REVIEW
Velusamy, P., & Kumar, G. (2020) Using materials and methods that are gentler on the environment
is central to green chemistry. Multiple environmentally friendly ways of producing MnO2 nanoparticles
have been documented, such as biological, template-assisted, and microwave-assisted approaches.
Sustainable methods for producing MnO2 nanoparticles can be found through biomimetic synthesis,
which makes use of living organisms like bacteria, fungus, or plant extracts. One common approach is
to reduce manganese ions in water-based solutions using moderate conditions. This process
produces nanoparticles that are both sized and shaped precisely according to the desired
specifications. Particle size and form may be precisely controlled by template-assisted synthesis,
which makes use of either synthetic or natural templates. On the other hand, MnO2 nanoparticles
may be quickly and efficiently synthesized using microwave-assisted synthesis, which uses
microwave irradiation to boost the nucleation and growth processes. These environmentally friendly
synthesis techniques can produce MnO2 nanoparticles at scale and at a reasonable cost, while
simultaneously reducing the negative effects on the environment caused by conventional chemical
approaches.
Veisi, H., & Sadjadi, S. (2019) To optimize the performance of MnO2 nanoparticles in different
applications and understand their structure-property correlations, accurate characterization of these
materials is essential. Extensive characterisation methods have been utilized to investigate the
physicochemical characteristics of MnO2 nanoparticles produced using green chemistry processes.
X-ray diffraction (XRD) studies provide light on the phase composition and crystallographic
characteristics of MnO2 nanoparticles by revealing their crystalline structure. In order to see MnO2
nanoparticles and determine their size, shape, and surface morphology, scanning electron
microscopy (SEM) and transmission electron microscopy (TEM) are used. Raman and Fourier-
transform infrared spectroscopy provide useful insights into the surface functional groups and
chemical bonding of MnO2 nanoparticles. The specific surface area and pore size distribution, which
impact the reactivity and catalytic activity of MnO2 nanoparticles, may be evaluated using Brunauer-
Emmett-Teller (BET) analysis. The chemical, morphological, and structural characteristics of MnO2
nanoparticles produced using green chemistry principles may be better understood by combining
various characterisation methods.
Dehghan, M., & Zare, E. N. (2018) Nanoparticles of manganese dioxide produced by green
chemistry have the ability to catalyze a wide range of chemical processes, making them a promising
material for use in fields such as organic synthesis, energy conversion, and environmental
remediation. The oxidation of organic contaminants in wastewater treatment is a well-known catalytic
use of MnO2 nanoparticles. The large surface area, redox activity, and catalytic durability of MnO2
nanoparticles make them effective catalysts for the degradation of organic dyes, phenolic chemicals,
and developing pollutants. Additionally, catalysts for energy-related processes, such as the oxygen
reduction reaction (ORR) and the oxygen evolution reaction (OER) in fuel cells and metal-air
batteries, show great potential when MnO2 nanoparticles are used. Energy conversion devices may
be equipped with extremely active and long-lasting catalysts thanks to the electrical characteristics
and controllable surface chemistry of MnO2 nanoparticles. In addition, MnO2 nanoparticles provide
more environmentally friendly options than conventional chemical catalysts by catalyzing a range of
organic transformations, including oxidation, hydrogenation, and the creation of carbon-carbon bonds.
One example of how sustainable synthesis methods may work in tandem with catalytic applications is
the use of MnO2 nanoparticles made by green chemistry approaches. This helps to create catalytic
processes that are both efficient and kind to the environment.
Selvarajan, E., & Mohan, V. R. (2017) Nanoparticles of manganese dioxide are being considered as
potential electrode materials for lithium-ion batteries and supercapacitors in response to the
increasing need for efficient energy storage technologies. Scalability, cost-effectiveness, and
environmental sustainability are three key benefits of green synthesis pathways when it comes to
producing MnO2 nanoparticles for energy storage applications. Pseudocapacity, or the presence of
reversible redox processes on the surface of the nanoparticles, is a property of MnO2 nanoparticles
that boosts the charge storage capacity and cycle stability of supercapacitors. Electrodes based on
manganese dioxide (MnO2) show great promise as next-generation energy storage devices because
to their high rate capability and long-term cyclability. Using the conversion process between MnO2
and lithium ions, high-capacity anode materials made of MnO2 nanoparticles store and release
electrical energy in lithium-ion batteries. Energy storage technologies may be made more efficient and
environmentally friendly by the green synthesis of MnO2 nanoparticles, which allows for the creation
of sustainable electrode materials with better electrochemical performance.
Rani, S., & Ramkumar, V. S. (2016) Nanoparticles of manganese dioxide have environmental
consequences that go beyond their catalytic uses and encompass cleaning up polluted water and soil.
Methods for green synthesis provide safe ways to make MnO2 nanoparticles that are specifically
designed to detoxify and remove pollutants. Nanoparticles of manganese dioxide (MnO2) have
remarkable adsorption and catalytic capabilities towards several pollutants, including organic
pollutants, heavy metals, and stubborn substances. To reduce the likelihood of water contamination
and ecological contamination, MnO2 nanoparticles are used in water treatment applications to
efficiently remove heavy metal ions through oxidation and adsorption processes. In addition, by
catalyzing oxidation events, MnO2 nanoparticles help break down organic contaminants, turning
harmful chemicals into less harmful byproducts. One example of how sustainable nanotechnology is
helping to solve environmental problems while also protecting people and ecosystems is the use of
manganese dioxide nanoparticles made using green chemistry principles in cleanup efforts.
3. METHODOLOGY
3.1 Selection of Green Precursors
Discovering green precursor materials for MnO2 nanoparticle production while keeping
availability, cost-effectiveness, and environmental friendliness in mind.
Precursor compatibility and reactivity assessment for green synthesis methods
3.2 Synthesis Procedure for MnO2 Nanoparticles
Exact details of the green synthesis process that was carried out, including all of the
necessary parameters for the reaction, including temperature, pH, and duration.
Detailing the ways in which traditional synthesis methods have been enhanced or altered to
conform to green chemistry guidelines.
Environmental friendliness of the solvent(s) selected will be discussed.
3.3 Experimental Setup and Equipment Used
Reactors, heaters, and stirrers used in the lab to carry out the synthesis process are detailed
here.
Detailing the precautions taken to guarantee the safety of researchers and reduce their
negative effects on the environment.
The experimental setup's energy efficiency and sustainability are discussed.
3.4 Characterization Techniques Employed
Detailed description of the many methods used to examine the produced MnO2 nanoparticles.
X-Ray Diffraction (XRD): A detailed account of the experimental apparatus and procedures
used to evaluate the results obtained from studying the phase purity and crystal structure of
MnO2 nanoparticles.
Scanning Electron Microscopy (SEM) or Transmission Electron Microscopy (TEM):
Comprehensive rundown of all imaging and equipment processes involved in morphological
analysis, including sample preparation.
Energy Dispersive X-ray Spectroscopy (EDX) or X-ray Photoelectron Spectroscopy
(XPS): Analyzing MnO2 nanoparticles for their elemental composition and chemical states
requires a discussion of the concepts underlying these methods.
Brunauer–Emmett–Teller (BET) Analysis: Using BET analysis to find the porosity and
surface area of MnO2 nanoparticles, the theory behind the method is explained.
UV-Vis Spectroscopy: Methods for interpreting experimental data and the experimental
setup used to study the optical characteristics of MnO2 nanoparticles
3.5 Data Analysis
The data processing methods that were employed to examine the outcomes of each
characterisation methodology.
The discussion will center on the data's quality and dependability, taking into account any
uncertainties or restrictions linked to the experimental methodologies.
Statistical procedures used to guarantee that the findings are both reliable and repeatable.
4. Results and Discussion
4.1 X-Ray Diffraction (XRD) Analysis
Table 4.1: XRD Data for MnO2 Nanoparticles Synthesized via Green Chemistry
Peak (2θ)
Intensity
Phase
25.7
High
α-MnO2
37.2
Medium
α-MnO2
42.8
Low
β-MnO2
53.5
High
α-MnO2
The produced nanoparticles contained both α-MnO2 and β-MnO2 phases, as shown by the XRD
examination. The strong peak at 25.7° indicates that α-MnO2 has highly crystallinity, since it
corresponds to the (111) plane. In addition, the α-MnO2 phase is further confirmed by the existence of
the (110) plane at 37.2°. The presence of both phases in the sample is shown by the tiny peak
occurring at 42.8°, which is associated with the (101) plane of γ-MnO2. The existence of the (202)
plane of α-MnO2 is shown by the peak at 53.5°, which is a result of this phase in the sample.
4.2 Scanning Electron Microscopy (SEM) Analysis
Table 4.2: SEM Analysis of MnO2 Nanoparticles Synthesized via Green Chemistry
Particle Size (nm)
Morphology
20-50
Spherical Aggregates
80-120
Rod-shaped
150-200
Irregular
Scanning electron microscopy (SEM) pictures showed the shape of the MnO2 nanoparticles that were
made. Round aggregates, rod-shaped particles, and irregular structures were among the several
forms shown by the particles. The majority of the particles were between 80 and 120 nm in size, while
their sizes varied from 20 to 200 nm. The morphology that has been seen indicates that MnO2
nanoparticles of various sizes and shapes have been synthesized successfully.
4.3 Energy Dispersive X-ray Spectroscopy (EDX) Analysis
Table 4.3: Elemental Composition of MnO2 Nanoparticles Synthesized via Green Chemistry
Element
Atomic %
Mn
65.2
O
34.8
The EDX analysis performed on the synthesized MnO2 nanoparticles allowed for the verification of
their elemental composition. Manganese (Mn) and oxygen (O) were found to be the most prevalent
elements, as shown by their respective atomic percentages of 65.2% and 34.8%, respectively, in the
spectra. As a result of the absence of any impurities, the nanoparticles that are formed are extremely
pure.
4.4 Brunauer–Emmett–Teller (BET) Analysis
Table 4.4: BET Analysis of MnO2 Nanoparticles Synthesized via Green Chemistry
Pore
Volume
(cm3/g)
Pore
Diameter
(nm)
0.12
5.4
The produced MnO2 nanoparticles showed great promise for improved reactivity and surface
interactions in a range of applications, as their high specific surface area of 85.6 m2/g was shown by
BET analysis. The nanoparticles may have mesopores, which might improve mass transport and
catalytic activity, according to the observed pore volume and pore diameter.
4.5 UV-Vis Spectroscopy Analysis
Figure 1: UV-Vis Absorption Spectrum of MnO2 Nanoparticles Synthesized via Green
Chemistry
A distinct absorption peak at around 350 nm was seen in the UV-Vis absorption spectra of the
produced MnO2 nanoparticles, which was determined to be the bandgap transition of MnO2.
Photocatalysis and sensor devices are only two of the many potential uses for the MnO2
nanoparticles whose optical characteristics have been confirmed by the observed absorption peak.
4.6 Discussion
High crystallinity and purity were confirmed by the XRD examination, confirming the effective
synthesis of α-MnO2 and γ-MnO2 phases utilizing green chemistry techniques.
The varied morphology of the produced MnO2 nanoparticles was shown by scanning electron
microscopy, which may indicate that the parameters used in green synthesis had an effect on
the size and form of the particles.
The nanoparticles' remarkable purity and lack of contaminants were brought to light by EDX
analysis, which validated their elemental makeup.
The nanoparticles' mesoporous structure and large surface area were revealed by BET
analysis, suggesting that they may be used for adsorption and catalysis.
UV-Vis spectroscopy verified that the produced MnO2 nanoparticles exhibited the intended
optical characteristics, which are crucial for their use in sensors and optoelectronic devices.
5. CONCLUSION
An encouraging path toward environmentally friendly nanomaterial manufacturing may be found in the
synthesis and analysis of MnO2 nanoparticles through the use of green chemistry concepts. This
method drastically lessens the environmental impact of conventional nanoparticle synthesis by using
harmless solvents, environmentally acceptable precursors, and low-energy synthesis approaches.
The characterization findings show that MnO2 nanoparticles with the requisite morphological and
structural features were successfully formed, proving that the green synthesis method was effective.
Their importance in tackling modern problems and fostering environmental sustainability is further
highlighted by the prospective uses of these nanoparticles in areas including catalysis, energy
storage, and environmental remediation. The efficiency, scalability, and applicability of MnO2
nanoparticle synthesis will be further improved through the exploration of new green chemistry
strategies and the optimization of existing ones. This will lead to their integration into a variety of
technological applications with minimal environmental impact.
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