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European Journal of Applied Sciences – Vol. 12, No. 2
Publication Date: April 25, 2024
DOI:10.14738/aivp.122.16797
Assem, H. D., Donkor, M. E. K., Tamakloe, R. Y., & Nkum, R. K. (2024). A Review of UV-Vis on Polymers; Polyaniline (PANI) and Its
Nanocomposites. European Journal of Applied Sciences, Vol - 12(2). 322-346.
Services for Science and Education – United Kingdom
A Review of UV-Vis on Polymers; Polyaniline (PANI) and Its
Nanocomposites
Humphrey Darkeh Assem
Department of Physics Kwame Nkrumah University
Science and Technology Kumasi-Ghana (West Africa)
Michael Edem Kweku Donkor
Department of Physics Kwame Nkrumah University
Science and Technology Kumasi-Ghana (West Africa)
Reuben Yao Tamakloe
Department of Physics Kwame Nkrumah University
Science and Technology Kumasi-Ghana (West Africa)
Robert K. Nkum
Department of Physics Kwame Nkrumah University
Science and Technology Kumasi-Ghana (West Africa)
ABSTRACT
In recent years, the utilization of Polyaniline (PANI) and its nano-composites has
garnered considerable attention across diverse domains encompassing electronics,
sensing technologies, and energy storage applications due to their multifaceted
utility. Central to the investigation of their properties is UV-Vis spectroscopy, which
has emerged as an indispensable analytical tool. This review aims to shed light on
recent advancements in UV-Vis spectroscopic techniques as applied to PANI films
and their corresponding nano-composites. The discourse begins by explaining the
fundamental principles of UV-Vis spectroscopy and its relevance in examining the
electronic transitions within PANI and its nano-composites. Subsequently, the
synthetic methodologies employed for fabricating PANI films and nano-composites
are expounded upon, with particular emphasis on discerning the influence of
various parameters on their optical attributes. Furthermore, the implications of
dopants, oxidants, and nano structural configurations on the UV-Vis spectra of PANI
are meticulously examined. Additionally, this review delves into the applications of
UV-Vis spectroscopy in shedding more light on the structural and optical attributes
of PANI-based materials tailored for specific functions such as chemical sensing,
optoelectronics, and energy storage systems. Recent advancements in the
development of innovative PANI nano-composites endowed with augmented
optical properties are scrutinized, highlighting their potential utility across a
spectrum of technological domains. Moreover, the challenges and prospective
avenues in harnessing UV-Vis spectroscopy for the characterization of PANI films
and nano-composites are deliberated upon, with strategies proposed to overcome
limitations including spectral superposition, sample preparation intricacies, and
the interpretation of complex spectra. Furthermore, prospective directions for
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Assem, H. D., Donkor, M. E. K., Tamakloe, R. Y., & Nkum, R. K. (2024). A Review of UV-Vis on Polymers; Polyaniline (PANI) and Its Nanocomposites.
European Journal of Applied Sciences, Vol - 12(2). 322-346.
URL: http://dx.doi.org/10.14738/aivp.122.16797
further research endeavours aimed at leveraging the full potential of UV-Vis
spectroscopy in enhancing the comprehension and application scope of PANI-based
materials are mapped out.
Keywords: Polyaniline (PANI), Nano-composites, UV-Vis spectroscopy, Spectroscopic
techniques, Electronic transitions, Synthetic methodologies, Optical attributes, Dopants,
Oxidants, Nano structural configurations, Structural attributes, Chemical sensing,
Optoelectronics
HIGHLIGHTS
1. Polyaniline (PANI) and its nanocomposites exhibit versatility in applications spanning
electronics, sensing technologies, and energy storage, underscoring their broad utility
across diverse domains.
2. UV-VIS spectroscopy emerges as a pivotal analytical tool for scrutinizing the optical
properties of PANI films, offering indispensable insights into their optical
characteristics.
3. The fabrication techniques employed significantly impact the optical properties of PANI
films and nanocomposites, highlighting the importance of method selection in tailoring
their optical performance.
4. UV-VIS spectroscopy plays a crucial role in the comprehensive characterization of PANI
materials, enabling a nuanced understanding essential for their effective utilization
across varied applications.
5. Addressing challenges inherent in UV-Vis spectroscopy stands to enrich the
understanding and application scope of PANI materials, necessitating the development
of strategies to mitigate issues such as spectral superposition and complexities in
sample preparation and interpretation.
INTRODUCTION
Polyaniline (PANI) has garnered significant attention across various disciplines due to its
diverse electrical, optical, and chemical properties (Beygisangchin et al., 2024; Banerjee, 2019).
The application of PANI thin films and nano-composites in fields such as sensors, optoelectronic
devices, and energy storage systems underscores the necessity of comprehending their optical
behavior for improved functionality. UV-Vis spectroscopy emerges as a crucial analytical
method for investigating these materials, providing deep insights into their electronic structure
and interactions. PANI, as a member of conducting polymers, presents intriguing features
stemming from the delocalization of π-electrons along its backbone, which can be manipulated
through chemical doping or structural modifications (Ibanez et al. 2018). The fabrication of
PANI thin films through techniques like spin-coating, dip-coating, or electrochemical
deposition offers controlled environments for property exploration. UV-Vis spectroscopy,
rooted in ultraviolet and visible light absorption, serves as a valuable tool for unraveling
electronic transitions within PANI thin films, including π-π* transitions and charge transfer
interactions. Analyzing absorption spectra aids in identifying characteristic peaks, facilitating
deductions about structural and electronic alterations. Moreover, this academic review seeks
to extensively explore UV-Vis spectroscopy, including its basic principles, complexities in
instrumentation, wide-ranging applications, and inherent limitations, supported by relevant
scholarly sources. The underlying principle of UV-Vis spectroscopy lies in the interaction
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between matter and ultraviolet and visible light, resulting in electronic transitions and
distinctive spectra, based on the energy disparity between ground and excited states (Förster,
2004; Penner, 2017). Moreover, nano-composites incorporating PANI exhibit enhanced
properties compared to pristine polymer films, with UV-Vis characterization enabling the
exploration of interactions between the polymer matrix and nanofillers, alongside the
assessment of nanofiller morphology and concentration effects on optical properties.
Applications
UV-Vis spectroscopy finds applications in quantitative analysis, qualitative analysis, structural
analysis, kinetic studies, DNA and protein analysis, and environmental monitoring (Harris,
2010; Pan et al., 2017). One common application is the determination of substance
concentration using the Beer-Lambert law,
A = εlc − − − − − − − − − − − (17)
where absorbance (A) is proportional to the molar absorptivity coefficient (ε), path length (b),
and concentration (c). The technique is versatile, allowing the analysis of liquids, solids, and
gases. UV−Vis−NIR spectrometer is able to monitor absorbance, A or transmittance, T in UV –
Vis wavelength range. The relation between incident light of intensity, I and transmitted light
of intensity I0 and Transmittance, T is given by:
T =
I
I0
− − − − − − − − − (18)
and transmission rate is given by:
(T%) = (
I
I0
)100%
Absorbance, A is the inverse of transmittance, T and given by log 1
T
= log I0
I
Thus,
A = −logT = εlc − − − − − − − − − − − (19)
While absorbance displays a proportionality with sample concentration according to Beer's law
and the optical path, transmittance is independent of sample concentration. Additionally, when
the optical path is 1 cm and the concentration of the target substance is 1 mol/l, the
phenomenon is referred to as molar absorption (Tolbin et al., 2017). Molar absorption
coefficient is a property of the substance that is typical under certain circumstances. The
spectrometer can then be used to capture the UV-Vis spectrum.
UV-VIS SPECTROSCOPY IN MOLECULAR ANALYSIS
UV-Visible (UV-Vis) spectroscopy holds paramount significance in molecular analysis by
concentrating on the intricate interplay between electromagnetic fields and matter. This
analytical technique employs ultraviolet and visible light, inducing diverse electronic
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Assem, H. D., Donkor, M. E. K., Tamakloe, R. Y., & Nkum, R. K. (2024). A Review of UV-Vis on Polymers; Polyaniline (PANI) and Its Nanocomposites.
European Journal of Applied Sciences, Vol - 12(2). 322-346.
URL: http://dx.doi.org/10.14738/aivp.122.16797
transitions such as σ – σ*, n – σ*, n – π*, and π – π*, thereby affording valuable insights into
distinct molecular orbitals (Zhao et al., 2020). The foundational principle of UV-Vis
spectroscopy is grounded in the premise that chemical entities possess the capability to absorb
ultraviolet or visible light, culminating in the generation of distinctive spectra. At the core of
spectroscopy lies the essential interaction between light and matter. The creation of a spectrum
ensues when matter undergoes light absorption through processes of excitation and de- excitation. Excitation occurs when electrons within the matter move from a ground state to an
excited state upon absorption of ultraviolet radiation. The quantity of UV-Vis radiation
assimilated by an electron corresponds to the energy difference, E, between its ground state
and the excited state (Khan, 2019). This relationship is encapsulated by the expression:
∆E = E1 − E0 = hν =
hc
λ
− − − − − − − − − (20)
The elevation of electrons to excited states or anti-bonding orbitals is a consequence of the
absorption of incident UV-Vis radiation. For this transition to transpire, the photon energy must
precisely align with the energy requisite for the promotion of an electron to the subsequent
higher energy state. At the crux of this process lies the foundational concept of absorption
spectroscopy. Three distinct categories of ground state orbitals play a pivotal role in the
transition of electrons: n-atomic, π-molecular orbitals, and σ-molecular orbitals, alongside anti- bonding orbitals such as the π*- and σ*-orbitals (Sykes, 1986). A noteworthy instance of
electronic transition involves the excitation of an electron from a σ-bonding orbital to a σ-anti- bonding orbital, denoted as a σ – σ* transition. Analogously, the π – π* transition signifies the
excitation of an electron from a lone pair to an antibonding π orbital. Electronic transitions
induced by the absorption of UV and visible light encompass σ – σ*, n – σ*, n – π*, and π – π*.
The σ – σ* and n – σ* transitions entail higher energies, typically manifesting in the far UV
region. Consequently, saturated groups exhibit limited absorption within the UV spectrum.
Conversely, molecules featuring unsaturated centers undergo n – π* and π – π* transitions,
characterized by lower energies and consequently manifesting at longer wavelengths than
transitions to σ* anti-bonding orbitals.
UV-VIS SPECTROSCOPY FOR OBTAINING ANALYTICAL INFORMATION
UV-visible spectroscopic data holds significant utility in both qualitative and quantitative
analyses of various compounds or molecules. Regardless of the specific analytical objective, it
is imperative to employ a reference cell to nullify any potential influence from the solvent in
which the compound is dissolved. For quantitative assessments, precise calibration of the
instrument using known concentrations of the compound in a solution with identical solvent
composition to that of the unknown sample becomes imperative. Conversely, if the aim is solely
to ascertain the presence of a compound within the sample, the construction of a calibration
curve may be deemed unnecessary (Blasco-Gomez, 2000). However, in scenarios such as
degradation studies or reactions where the determination of compound concentration is
pivotal, the establishment of a calibration curve becomes indispensable. Constructing a
calibration curve necessitates the utilization of at least three concentrations of the compound,
although employing five concentrations is preferred to enhance curve accuracy. These
concentrations should span from slightly above the estimated concentration of the unknown
sample to approximately an order of magnitude lower than the highest concentration (Smith,
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2015). It is paramount that these calibration solutions be meticulously prepared using digital
pipettes and volumetric flasks instead of less precise implements like graduated cylinders and
beakers. Additionally, the calibration solutions should be evenly spaced apart to ensure a
robust calibration curve.
Limitations
While UV-Vis spectroscopy finds extensive utility, it is not without inherent limitations. The
technique offers constrained insights into particular functional groups, and the presence of
absorbing species from external sources can introduce inaccuracies in the obtained results.
Inadequate sensitivity may pose challenges in detecting low concentrations, and the
opaqueness of certain samples may necessitate the application of specialized analytical
methods (Hanson, 1995).
UV-Vis-NIR Spectrophotometer
The UV-Vis-NIR spectrophotometer is designed for the measurement of light absorbance or
transmittance across the ultraviolet-visible (UV-Vis) wavelength range in a given medium. It
encompasses essential components including UV and visible light sources, such as deuterium
or hydrogen lamps and tungsten/halogen lamps respectively, alongside a monochromator,
sample holder in the form of cuvettes, a detector, and a display interface. This instrumentation
facilitates the examination of samples in various states, thereby furnishing invaluable data for
a comprehensive UV-Vis spectrum as depicted in Figure 1. Upon exposure to incident light, an
object experiences fundamental optical phenomena such as absorption, reflection, or
transmission. The spectrophotometer serves as a pivotal tool for quantifying the extent of light
absorption within the UV and Vis spectra. It gauges the intensity of light transmitted through
the sample, contrasting it against a baseline measurement derived from the incident light
source. Through the application of the Beer-Lambert Law, which delineates a direct correlation
between the concentration of a substance in a sample, the path length traversed by light, and
the resultant light absorption, the spectrophotometer is proficient in determining the
concentration of specific analytes present within the sample (Purcell, 2013).
Figure 1: UV-Vis spectrum
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Assem, H. D., Donkor, M. E. K., Tamakloe, R. Y., & Nkum, R. K. (2024). A Review of UV-Vis on Polymers; Polyaniline (PANI) and Its Nanocomposites.
European Journal of Applied Sciences, Vol - 12(2). 322-346.
URL: http://dx.doi.org/10.14738/aivp.122.16797
INSTRUMENTATION FRAMEWORK: PARTS AND FUNCTION OF THE UV-VIS
SPECTROPHOTOMETER
A conventional UV-Vis spectrophotometer constitutes essential elements, including a light
source, monochromator, sample holder, detector, and data processor. The light source emits a
continuous spectrum encompassing ultraviolet (UV) and visible (Vis) light wavelengths, while
the monochromator selectively isolates precise wavelengths for analysis. Upon interaction with
the sample, directed light undergoes transmission or reflection, and the resulting signal is
captured by the detector (Skoog et al., 2018). Subsequently, the acquired data undergoes
processing to generate absorption or transmission spectra, facilitating comprehensive analysis.
This instrumentation finds ubiquitous utility across diverse scientific domains such as
chemistry, biochemistry, physics, and environmental science.
Light Source
In UV-Vis spectrometry, having a light source capable of emitting radiation across a wide range
of wavelengths is fundamental. Typically, a xenon lamp is utilized as a high-intensity light
source suitable for both UV and visible ranges. However, it's important to note that compared
to tungsten and halogen lamps, xenon lamps are less stable and more costly (Tyson, 1984).
Hence, UV-Vis spectrophotometers commonly incorporate two distinct lamps: a deuterium
lamp for UV radiation and a halogen or tungsten lamp for visible light emission, ensuring
comprehensive illumination coverage. These two lamps are employed to achieve optimal light
intensity within the instrument. During the measurement of light intensity, the spectrometer
must transition smoothly between the two light sources. A smoother transition occurs when
this switchover takes place within the wavelength range of 300 to 350 nm, as both the visible
and UV light sources emit comparable amounts of light at this wavelength.
Wavelength Selector
In order to optimize the spectral analysis of samples by harnessing the emitted wavelengths
from the light source, meticulous wavelength selection is paramount for tailoring the analytical
process to the characteristics of the analyte and sample under investigation (Jofre and Savio,
2023). Within the realm of UV-visible spectrometry, the cornerstone of wavelength selection
lies in the utilization of the monochromator, esteemed for its proficiency in isolating light into
precise wavelength bands. Radiation comprising a spectrum of wavelengths is directed into the
monochromator via the entrance slit. Upon encountering the dispersing element at a
predetermined angle, the incident beam undergoes dispersion, a pivotal phase in wavelength
segregation. Typically, the monochromator incorporates a prism mechanism that facilitates the
separation of the diverse wavelengths within the incident beam, thereby inducing non-linear
dispersion. Consequently, only radiation of a singular color, aligned with a specific wavelength,
is permitted to exit the monochromator, proceeding through subsequent stages or the exit slit
for further analysis. The illumination source in UV-visible spectrophotometry typically involves
a UV lamp, often a deuterium lamp for the UV range (190-400 nm), and a tungsten lamp for the
visible range (400-800 nm). For more extensive spectral coverage across both UV and visible
regions, sophisticated UV-Vis spectrophotometers may employ a xenon lamp (Liauw et al.,
2010). The monochromator component serves as a pivotal element in this setup, effectively
segregating polychromatic light into discrete wavelengths, thus facilitating precise wavelength
selection for analytical purposes.
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Prism or Grating
Monochromators can utilize prisms or diffraction gratings to disperse light into its constituent
wavelengths.
Sample Compartment
This section holds the sample undergoing analysis and is designed to allow light passage
through the sample. In the framework of a single-beam spectrophotometer, the entirety of
radiation emitted from the light source traverses the sample as a unified beam. These
instruments discern colour by assessing disparities in light source intensities prior to and
subsequent to sample introduction (Aceto et al., 2014). Typically, the wavelength range spans
from 190 to 750 nm, though extensions up to 1100 nm are feasible. Conversely, in the
configuration of a double-beam spectrophotometer, the radiation originating from the light
source diverges into two separate beams: one transits through the sample while the other
solely penetrates the reference material. Analogously, double-beam spectrophotometers offer
a wavelength range spanning 190 to 1100 nm. Additionally, these instruments gauge
absorbance in relation to wavelength or the ratio between sample and reference beam
intensities.
Cuvette
Typically made of quartz or glass, the cuvette is a transparent container holding the liquid or
solution under analysis.
Figure 2: Schematic diagram of a cuvette-based UV-Vis spectroscopy system. Credit: Technology
Networks
Detector
The detector gauges the light intensity passing through the sample at a designated wavelength.
Detectors in UV-visible spectroscopy are predicated upon photoelectric coatings or
semiconductor materials, which facilitate the conversion of incident light emanating from the
sample into an electrical signal or current. The magnitude of the current corresponds directly
to the intensity of the incident light (Podborska et al., 2020). These detectors are characterized
by low noise levels and heightened sensitivity, thereby ensuring a linear response.
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Assem, H. D., Donkor, M. E. K., Tamakloe, R. Y., & Nkum, R. K. (2024). A Review of UV-Vis on Polymers; Polyaniline (PANI) and Its Nanocomposites.
European Journal of Applied Sciences, Vol - 12(2). 322-346.
URL: http://dx.doi.org/10.14738/aivp.122.16797
Furthermore, individual detectors exhibit distinct wavelength ranges and sensitivities tailored
to specific analytical requirements. Ultimately, data acquisition typically involves the
presentation of absorbance plotted against wavelength (measured in nanometers) within the
UV and visible regions of the electromagnetic spectrum.
Photodiode Array Detector
Many modern UV-Vis spectrophotometers use a photodiode array detector, enabling
simultaneous measurement at multiple wavelengths.
Wavelength Selector
This component chooses the desired light wavelength for analysis.
Rotating Grating or Prism
Users can select a specific wavelength by rotating the grating or prism. Amplifier and Signal
Processor. The signal from the detector, usually weak, requires amplification and processing
for accurate measurement.
Amplifier
Enhances the weak signal. Signal Processor: Converts the analog signal into a digital signal for
further analysis. Display and Data Output:
Results, including absorbance values at different wavelengths, are presented on the
instrument's screen.
Data Output
Findings can be exported to a computer or other data storage devices for subsequent analysis
and documentation. Comprehending the various components and functions of a UV-Vis
spectrophotometer is crucial for effective utilization in scientific applications, such as
quantifying sample concentrations based on their absorption characteristics.
Figure 3: A simplified schematic of the main components in a UV-Vis spectrophotometer. Credit:
Dr. Justin Tom.
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Figure 4: Set-up for UV-Vis Spectroscopy
Figure 5: UV-Vis Spectrophotometer
INSIGHTS FROM UV-VIS CHARACTERIZATION
In addition to chemical analysis, numerous physical methodologies are employed to ascertain
purity and discern the composition of substances. Among these techniques, including the
determination of melting point, refractive index, and density, Ultraviolet and Visible (UV/VIS)
light spectroscopy holds considerable prominence across diverse sectors such as market
segmentation, research domains, production, and quality control for substance classification
and investigation. The UV/VIS spectrophotometer gauges light absorption by the sample when
exposed to UV light, with each substance exhibiting distinctive light absorption properties. The
degree of light absorption correlates with the substance concentration in the sample,
facilitating quantitative analysis via UV/VIS spectrometry. Modern UV/Vis spectrophotometers
offer rapid, facile, reliable, and precise results. This discourse delineates various applications
of UV/Vis spectrophotometry. The UV-Visible spectrophotometer is designed to quantify and
assess samples utilizing Ultraviolet-visible light spanning a wavelength range of 200nm to
900nm. In 1814, Fraunhofer Gesellschaft developed a spectroscope for sunlight measurement,
subsequently discovering 574 dark fixed lines, commonly known as Fraunhofer lines. He
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Assem, H. D., Donkor, M. E. K., Tamakloe, R. Y., & Nkum, R. K. (2024). A Review of UV-Vis on Polymers; Polyaniline (PANI) and Its Nanocomposites.
European Journal of Applied Sciences, Vol - 12(2). 322-346.
URL: http://dx.doi.org/10.14738/aivp.122.16797
further refined his work in 1821 by developing a diffraction grating for light separation from
the sun. Forty years later, David Rittenhouse devised the first artificial diffraction grating. In
1941, Arnold O Beckman introduced the inaugural commercial UV-Visible spectrophotometer
for sample quantity and quality determination. The initial instrument utilized a quartz prism to
disperse the light source (from the tungsten lamp) into absorption spectra, with a phototube
serving as the detector in lieu of the modern photodiode. UV-Vis spectrophotometry measures
both light intensity transmitted and sample absorption, reflecting sample properties. Although
the optical principle of contemporary UV-Vis spectrophotometers has undergone minimal
alteration, recent advancements in optical components have rendered modern UV-Vis
spectrophotometers more resilient, expedient, adaptable, and compact. UV-Vis
characterization of polyaniline thin films furnishes invaluable insights into various critical
facets. Firstly, doping induces significant alterations in the electronic structure and
conductivity of polyaniline, with UV-Vis spectroscopy serving as an essential tool for
monitoring the doping process. Alterations in absorption spectra, such as the emergence of new
peaks or shifts in peak positions, denote the incorporation of dopant molecules and subsequent
modifications in the polymer's electronic milieu (Harisha et al., 2008). Secondly, the optical
characteristics of polyaniline are intricately linked to the extent of π-conjugation along the
polymer chain. UV-Vis spectroscopy aids in evaluating conjugation length by scrutinizing the
energy of π-π* transitions, with extended conjugation lengths typically resulting in lower
energy transitions and redshifts in absorption peaks (Li et al., 2014). Lastly, UV-Vis
spectroscopy facilitates the identification of structural variations in polyaniline thin films, such
as changes in chemical structure or morphology (Sun et al., 2015). Modifications in absorption
peak intensity or broadening may signify defect formation, aggregation, or alterations in
polymer conformation. It is imperative to underscore that UV-Vis spectroscopy remains a
potent and indispensable analytical tool across diverse scientific disciplines. Its simplicity,
versatility, and cost-effectiveness render it a preferred choice for research, analysis, and quality
assurance endeavors. By furnishing pertinent insights into the electronic structure and
composition of materials, UV-Vis spectroscopy continues to significantly propel advancements
in both scientific inquiry and industrial applications.
LIMITATIONS OF UV-VIS SPECTROSCOPY
The constraints of UV-Vis spectroscopy encompass limited sensitivity for trace analysis,
particularly for compounds with low absorption coefficients or at low concentrations (Li and
Hur, 2017), potential challenges in distinguishing overlapping absorption bands in complex
samples (Ríos-Reina and Azcarate 2022), and the method's inherent incapacity to provide
detailed structural information, especially for intricate molecules or mixtures (Chen et al.,
2018). Additionally, UV-Vis spectroscopy may necessitate extensive sample preparation for
certain samples and might not effectively probe specific chemical environments or interactions
within a sample (Saleh, 2020). Its restricted wavelength range, ranging from the ultraviolet to
the visible regions of the electromagnetic spectrum, limits its applicability for certain types of
analysis (Munjanja and Sanganyado, 2015), and quantitative analysis can be hindered by
factors such as sample matrix effects and instrumental drift (Jürgens et al., 2007). Furthermore,
solvent effects, temperature sensitivity, and instrumental limitations, including stray light and
detector constraints, pose additional hurdles in achieving accurate and precise measurements
(McMahon, 2008; Upstone, 2000).
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In their study published in 2011, Sridevi et al. described the synthesis process of polyaniline
(PANI) nanocomposites using various dopants and characterized their optical properties using
UV-Visible spectroscopy. The authors employed a method involving the addition of Aniline,
Sulphuric acid, and dopant acid into a round bottom flask containing Millipore water, followed
by stirring to form a homogeneous aqueous dispersion. Different dopants, including CSA and
PTSA, were used, and the acid was added drop-wise with suitable concentration, followed by
stirring in a magnetic stirrer. The polymerization process commenced with the slow addition
of Auric acid, leading to a color change indicating the formation of PANI. The synthesized PANI
was then washed with acetone and dried to obtain PANI powder. UV-Visible spectra of the PANI
Emeraldine salt powder in N-methyl 2-pyrrolidone (NMP) were recorded using a Hitachi UV- Visible spectrometer. The spectra exhibited three characteristic absorbance peaks
corresponding to π-π * transition, polaron-π * transition, and polaron-transition, indicating
effective doping with primary and secondary dopants (Figure 6). Interestingly, PANI-Au
nanocomposites did not show the surface plasmon resonance (SPR) absorption band of Au at
520 nm, suggesting deep incorporation of Au particles into the polymer chain.
Figure 6: UV-Vis spectra of PANI/Au composites with different dopant acids.
This investigation yields valuable insights into the synthesis and optical characteristics of
polyaniline (PANI) nanocomposites, thereby enriching the advancement of sophisticated
materials across diverse applications. The implications drawn from the results are manifold.
Initially, the detection of three distinctive absorbance peaks corresponding to specific
transitions - specifically, π-π* transition, polaron-π* transition, and polaron-transition -
denotes proficient doping with primary and secondary dopants. Such observations underscore
a successful alteration of the material's electronic configuration, which holds significant
relevance across a spectrum of applications, notably in the realms of electronic and
optoelectronic devices. Moreover, the absence of the characteristic surface plasmon resonance
(SPR) absorption band of gold (Au) at 520 nm within the PANI-Au nanocomposites suggests a
profound integration of Au particles within the polymer matrix. This phenomenon indicates a
robust interaction between the polymer framework and the Au nanoparticles, potentially
culminating in heightened mechanical, electrical, or optical attributes. In aggregate, these
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Assem, H. D., Donkor, M. E. K., Tamakloe, R. Y., & Nkum, R. K. (2024). A Review of UV-Vis on Polymers; Polyaniline (PANI) and Its Nanocomposites.
European Journal of Applied Sciences, Vol - 12(2). 322-346.
URL: http://dx.doi.org/10.14738/aivp.122.16797
findings underscore the potential for customized material characteristics through adept doping
strategies and nanoparticle integration, thereby paving the path for advancements in domains
including sensors, catalysis, and nanoelectronics.
The study by Sironi et al. (2015) details the synthesis and characterization of polyaniline
emeraldine base and P4ADPA, followed by the preparation of doped forms using salicylic and
5-sulfosalicylic acids. Polyaniline emeraldine base was synthesized through the reaction of
aniline with HCl and K2S2O8, resulting in a green solid with a 65% yield. P4ADPA was
synthesized using 4-(aminodiphenyl) aniline, HCl, H2O2, and FeCl36H2O, yielding a dark blue- green solid with a 52% yield. The preparation of doped forms involved deprotonation, re- protonation with acids, and subsequent filtration and drying. UV-Vis spectroscopy
characterized the samples, revealing characteristic peaks for benzenoid rings and azaquinoid
moieties (Figure 7). The study highlighted differences in doping levels between salicylic and 5-
sulfosalicylic acids, affecting film morphology and protonation degree. The research
underscores the importance of these findings for understanding interactions between dopants
and polymer chains as changes in absorption spectra can indirectly reflect variations in film
morphology. For instance, variations in film thickness, roughness, or density can affect light
absorption and result in shifts or broadening of absorption peaks (Ciambriello et al., 2022).
Figure 7: UV-Vis plot for PANI and its Nanocomposites
In another study, Solonaru and Grigoras (2017) synthesized reduced graphene
oxide/polyaniline sulfonate (r-GO/PAnS) composites with different mass ratios using in-situ
oxidative polymerization. Graphene oxide (GO) was obtained from graphite powder via the
Hummers method and subsequently reduced to r-GO using hydrazine hydrate. The composites
were prepared by dispersing r-GO in aqueous acidic solution, adding aniline sulfonate (AnS),
and initiating polymerization with ammonium peroxydisulfate. The resulting nanocomposites,
labelled as r-GO/PAnS-1, r-GO/PAnS-2, and r-GO/PAnS-3, were characterized by UV-Vis
spectroscopy. The spectra exhibited characteristic peaks for electronic conjugation within r-GO
and π-π* transitions in PAnS. Increasing PAnS content enhanced the visibility of UV absorption
characteristic for PAnS as shown in Figure 8.
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Figure 8: UV-Vis plot for PANI and its graphene nanocomposites
The investigation contributes valuable insights into the synthesis and characterization of r- GO/PAnS composites, which hold promise for diverse applications across multiple domains.
Analysis via UV-Vis spectroscopy has yielded significant findings, with identified peaks
indicative of electronic conjugation within r-GO and π-π* transitions within PAnS across the r- GO/PAnS-1, r-GO/PAnS-2, and r-GO/PAnS-3 composite variants. These outcomes validate the
successful synthesis process and offer detailed elucidation of critical structural and optical
attributes. The discernible presence of characteristic peaks serves to substantiate the
composite formation, affirming the persistence of electronic characteristics within r-GO and the
presence of extended conjugated systems within PAnS. Furthermore, the progressive
enhancement in the discernibility of UV absorption features attributed to PAnS with escalating
PAnS content underscores the direct influence exerted by PAnS concentration on optical
characteristics. Such revelations bear considerable significance in the realm of material
characterization, furnishing indispensable insights essential for the fine-tuning of composite
compositions and the comprehensive comprehension of their behavior across an array of
applications, notably within the realms of optoelectronics and sensor technologies.
Li et al. (2015) detailed the synthesis of FePOs and polyaniline (PANI) composites under
varying conditions, exploring the impact of pH, temperature, molar ratios of H2O2: aniline, and
reaction time. FePOs were prepared through a method involving FeCl2 ·4H2O, NaH2PO2 55.H2O,
and polyvinylpyrrolidone (PVP), resulting in a product collected after centrifugation, washing,
and drying. For PANI synthesis, PSS was dispersed in a buffer solution, and aniline monomer
was added. The polymerization was catalyzed by FePOs and initiated by ammonium
peroxydisulfate. UV-Vis spectra of PANI synthesized under different conditions revealed
characteristic absorption bands at 430 nm and 800 nm, indicative of an intermediate redox
state and the emeraldine state of PANI, respectively (Figure 9).
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European Journal of Applied Sciences, Vol - 12(2). 322-346.
URL: http://dx.doi.org/10.14738/aivp.122.16797
resulting films revealed distinct spectra, with films derived from different solvent solutions
displaying characteristic peaks at 325, 430, and 750–800 nm, indicative of doped polyaniline
(PANI). Notably, the film derived from an NMP solution exhibited a discernible shoulder at
approximately 620 nm, alongside absorption bands at 325, 430, and extending beyond 900 nm.
This observation suggests incomplete doping of PANI in the film derived from the NMP solution
(Mohammad, 2001). Incomplete doping can have implications for the material's conductivity,
optical properties, and stability, affecting its suitability for various applications. Additionally,
understanding the factors influencing doping efficiency, such as solvent choice, is crucial for
optimizing the synthesis process and tailoring PAni films for specific applications, such as in
sensors, electronic devices, or energy storage systems.
The study conducted by Hussin et al. (2017) focused on the synthesis and characterization of
water-soluble polyaniline (PANI) and its derivatives with cellulose compounds. The authors
utilized various chemicals, including Aniline (Ani), methylcellulose (MC), hydroxypropyl
cellulose (HPC), hydroxypropyl methylcellulose (HPMC), and ammonium persulfate (APS)
obtained from Sigma-Aldrich, as well as Hydrochloric acid (HCl, 37%) from Lab Scan Sdn. Bhd.
All chemicals were used without further purification. The synthesis process involved the use of
a dialysis tube with a 14kDa molecular weight cut-off (MWCO) to create water-soluble PANI
through chemical oxidation polymerization. Aniline served as the monomer, cellulose
derivatives acted as steric stabilizers, 1M HCl functioned as a dopant, and APS served as an
initiator. The procedure included dissolving 0.5 g of MC in 1M HCl at 80 °C, followed by the
careful addition of Ani at 0 °C. After stirring for 3 hours, APS was slowly introduced to initiate
polymerization, which continued for 24 hours.
The resulting polymer was purified through dialysis with 1M HCl as the dialysate for 6 hours to
remove unreacted monomers and oligomers. The same procedure was repeated for PANI-HPC
and PAni-HPMC with equivalent amounts of HPC and HPMC. The electrical conducting
behaviour of PAni-cellulose derivatives was analyzed through UV-Vis spectroscopy in the
wavelength range of 300 nm to 900 nm. The UV-Vis spectra revealed three essential absorption
bands for PAni, including a free-carrier tail above 800 nm (indicating π–polaron transition
band), an absorption band around 450 nm (polaron- π* transition band caused by protonation
of PAni backbone), and an absorption band around 350 nm (π- π* electron transition within
the benzenoid ring). The study interpreted the results by comparing the UV-Vis spectra of
water-soluble PAni-cellulose derivatives. The disappearance of the absorption band around
350 nm in the complexes suggested interaction between PAni chains and water-soluble
polymers (Figure 11).
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Figure 11: UV-Vis graph on PANI and its cellulose derivatives
Additionally, the cellulose derivatives' rigid and expanded chain structures, facilitated by
hydrogen bonding with amine groups on PANI chains, were discussed as factors contributing
to the extended conformation of the complexes. The absorption bands around 800 nm, showing
a free-carrier tail, indicated the possibility of extended conformation in the near-infrared (NIR)
region, leading to higher conductivity. The study concluded that water-soluble PANI-cellulose
derivatives indeed exhibit an extended conformation, as evidenced by their UV-Vis spectra. The
ramifications of the outcomes are profound and varied. The UV-Vis spectroscopic examination
unveiled three pivotal absorption bands delineating the characteristics of polyaniline (PANI):
an extension beyond 800 nm indicative of a π–polaron transition band, an absorption band
centered around 450 nm attributed to the polaron-π* transition band arising from PANI
backbone protonation, and an absorption band approximately at 350 nm representing the π- π* electron transition within the benzenoid ring. The explication of the findings entailed a
comparative analysis of UV-Vis spectra encompassing water-soluble PANI-cellulose
derivatives. The absence of the absorption band near 350 nm within the complexes implied an
interplay between PANI chains and water-soluble polymers. Furthermore, the discourse delved
into the rigid and expanded chain structures of cellulose derivatives, facilitated by hydrogen
bonding with amine groups on PANI chains, as elements fostering the elongated conformation
of the complexes. The detection of absorption bands nearing 800 nm, denoting a free-carrier
tail, hinted at the prospect of an elongated conformation within the near-infrared (NIR)
spectrum, potentially auguring heightened conductivity. These revelations elucidate the
intricate molecular interplays within PANI-cellulose complexes, furnishing insights into their
structural attributes and conductivity traits, pivotal for their applicability across diverse
domains such as sensor technology, electronics, and energy storage.
Alam et al. (2013) conducted a synthesis of polyaniline (PANI) in its emeraldine salt form
utilizing the redox process involving aniline, ammonium peroxy disulfate (APS) as an oxidant,
and hydrochloric acid (HCl). Subsequently, the PANI salt underwent conversion to emeraldine
base upon treatment with ammonium hydroxide solution. The PANI-SnO2 nanocomposite was
synthesized via the co-precipitation method, where tin chloride dihydrate (SnCl2·4H2O) was
dissolved in distilled water followed by the addition of ammonium solution under vigorous
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Assem, H. D., Donkor, M. E. K., Tamakloe, R. Y., & Nkum, R. K. (2024). A Review of UV-Vis on Polymers; Polyaniline (PANI) and Its Nanocomposites.
European Journal of Applied Sciences, Vol - 12(2). 322-346.
URL: http://dx.doi.org/10.14738/aivp.122.16797
stirring. PANI (5-10 wt%) was then introduced to the solution, resulting in the precipitation of
the composite, which was subsequently washed and dried. Characterization of the PANI-SnO2
nanocomposite was performed using UV-Vis spectroscopy, revealing a red shift in absorption
transition indicative of successful interaction between the metal nanoparticles and the polymer
chain. Furthermore, the synthesis process of the PANI-SnO2 nanocomposite via in situ chemical
polymerization of aniline with ammonium persulphate as the oxidizing agent yielded a well- crystalline structure with a uniform distribution of SnO2 nanoparticles within the PANI matrix.
Notably, strong chemical interaction between PANI and SnO2 nanoparticles was observed,
contributing to the observed red shift in UV-Vis spectra. This successful synthesis approach via
the co-precipitation method holds promise for the development of advanced materials
endowed with enhanced properties. The well-crystalline structure and homogeneous
dispersion of SnO2 nanoparticles within the PANI matrix are indicative of successful
incorporation and dispersion of the nanoparticles, potentially leading to improved material
performance (Faisal et al., 2020). The observed strong chemical interaction between PANI and
SnO2 nanoparticles, as evidenced by UV-Vis spectroscopy, suggests the formation of a stable
composite material with promising applications across various fields such as optoelectronics,
sensors, and energy devices. The successful synthesis and characterization of the PANI-SnO2
nanocomposite offer valuable insights into the design and development of novel hybrid
materials tailored for advanced technological applications. UV-Vis spectroscopy emerges as a
crucial analytical tool for assessing the optical properties of materials, including their
absorption and transmission characteristics in the ultraviolet and visible regions. This
technique facilitates the elucidation of electronic transitions and band gaps, providing valuable
information regarding the electronic structure and energy levels of materials.
Figure 12: UV–Vis spectra of (a) SnO2, (b) PANI and (c) PANI/SnO2 nanocomposite.
Moreover, UV-Vis spectroscopy enables the investigation of interactions between different
components in nanocomposite materials, such as PANI and SnO2 nanoparticles, through the
observation of absorption spectra and associated band shifts. The red shift observed in the UV-
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Vis spectra of the PANI-SnO2 nanocomposite signifies successful interaction between the metal
nanoparticles and the polymer chain, underscoring the formation of a composite material with
modified optical properties. Figure 12 presents the UV–Vis spectra of SnO2, PANI, and the
PANI/SnO2 nanocomposite, visually illustrating the spectral characteristics of each component
and the resultant composite material. Overall, UV-Vis spectroscopy emerges as a valuable tool
for characterizing the optical behavior and potential applications of nanocomposite materials,
particularly in optoelectronic, sensing, and energy-related devices.
Choudhury's (2009) comprehensive research delved into the experimental synthesis and
characterization of polyaniline/silver (PANI/Ag) nanocomposites. The synthesis process
involved the procurement of analytical grade aniline monomer, silver nitrate (AgNO3), and
sodium borohydride (NaBH4) from Sigma–Aldrich (USA), while reagent grade ammonium
peroxodisulphate ((NH4)2S2O8), hydrochloric acid (HCl), and ethanol were acquired from Merck
India Ltd. The synthesis of nanosized silver particles commenced with the chemical reduction
of AgNO3 using NaBH4 in deionized (DI) water. Different mole percentages of AgNO3 were
dissolved in deionized water to prepare silver nitrate solutions, which were subsequently
subjected to reduction by the gradual addition of the aqueous solution of NaBH4. This process
yielded yellowish-red colloidal silver nanoparticles, with dynamic light scattering (DLS) and
transmission electron microscopy (TEM) revealing average particle diameters of
approximately 3 nm and 5 nm, respectively. PANI/Ag nanocomposites were synthesized
through an in-situ chemical oxidation polymerization process. Aniline-hydrochloride was
introduced into the previously prepared Ag nanoparticles colloid, followed by the addition of
the aqueous solution of (NH4)2S2O8.
Figure. 13: UV–vis absorption spectra of pure PANI (a) and PANI/Ag nanocomposites prepared
with Ag concentrations of 0.5 mol% (b), 1.5 mol% (c) and 2.5 mol% (d).
The resulting mixture underwent a reaction under constant stirring at low temperature for 12
hours, after which the product was filtered, washed, and dried. Pure PANI was synthesized
using the same chemical polymerization method in the absence of silver colloid. For UV–vis
spectroscopic analysis, both pure PANI and PANI/Ag nanocomposite samples in powder form
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et al. (2017), and Geethalakshmi et al. (2015). Furthermore, Zheng et al. (2021) effectively
correlated experimental results with established literature, reinforcing the validity of their
findings. Through meticulous experimentation and analysis, the authors have contributed
significantly to the understanding of PANI synthesis and characterization, paving the way for
advancements in the field. Through meticulous analysis of UV–Vis spectra, the study identified
distinct absorption bands corresponding to different structural motifs within PANI chains
(Figure 14).
Figure 14: UV–Vis spectra of polymerization of polyaniline synthesized by varying
(a)APS/aniline molar ratio (b) HCl concentration.
This provided crucial insights into the structural evolution of PANI nanostructures, essential
for tailoring their properties for various applications. Moreover, the study revealed a
correlation between absorption band intensity and conductivity, elucidating the doping level
of PANI and emphasizing the importance of understanding its structural features in relation to
its electrical properties. The validation of these findings through comparison with established
literature enhanced their credibility, reinforcing the existing body of knowledge on PANI
synthesis and characterization. Overall, Zheng et al.'s research contributes significantly to
advancing the understanding and application of PANI in the field of conductive polymer
materials.
SUMMARY
Polyaniline (PANI) has garnered significant interest in diverse scientific fields due to its
versatile electrical, optical, and chemical properties. The utilization of PANI thin films and nano- composites in applications such as sensors, optoelectronic devices, and energy storage systems
underscores the necessity of comprehending their optical behavior for enhanced functionality.
UV-Vis spectroscopy emerges as a crucial analytical tool for investigating PANI materials,
offering profound insights into their electronic structure and interactions. PANI, as a
conducting polymer, exhibits intriguing characteristics resulting from the delocalization of π- electrons along its backbone, modifiable through chemical doping or structural alterations.
Fabrication methods like spin-coating, dip-coating, or electrochemical deposition provide
controlled environments for exploring PANI properties. UV-Vis spectroscopy facilitates the
examination of electronic transitions within PANI thin films, aiding in the identification of
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Assem, H. D., Donkor, M. E. K., Tamakloe, R. Y., & Nkum, R. K. (2024). A Review of UV-Vis on Polymers; Polyaniline (PANI) and Its Nanocomposites.
European Journal of Applied Sciences, Vol - 12(2). 322-346.
URL: http://dx.doi.org/10.14738/aivp.122.16797
characteristic peaks and deductions about structural and electronic modifications. Despite its
utility, UV-Vis spectroscopy has limitations such as limited sensitivity for trace analysis and
challenges in distinguishing overlapping absorption bands. Several studies have explored the
synthesis and characterization of PANI and its composites using UV-Vis spectroscopy,
providing valuable insights into their optical properties and potential applications in various
domains.
CONCLUSION
The multifaceted properties of polyaniline (PANI) have garnered significant attention in
various scientific fields, with its applications ranging from sensors to energy storage systems.
Understanding the optical behavior of PANI thin films and nano-composites is crucial for
enhancing their functionality, with UV-Vis spectroscopy serving as a pivotal analytical
technique in this regard. By delving into electronic transitions within PANI materials, UV-Vis
spectroscopy offers profound insights into their structural and electronic modifications.
Looking ahead, the future prospects of PANI research intertwined with UV-Vis spectroscopy
are promising. Continued advancements in characterization techniques and instrumentation
will enable researchers to delve deeper into the intricate properties of PANI materials.
Furthermore, the exploration of PANI nano-composites and their interactions with various
nanofillers opens up avenues for tailoring their optical properties for specific applications, such
as optoelectronic devices and sensors. Moreover, as demonstrated by recent studies, the
synthesis and characterization of PANI-based materials using UV-Vis spectroscopy provide
valuable insights into their structural evolution and performance. Further research efforts
focusing on optimizing synthesis parameters, understanding dopant-polymer interactions, and
exploring novel applications will undoubtedly drive the field forward. In essence, the
combination of PANI and UV-Vis spectroscopy holds immense potential for addressing current
challenges and innovating future technologies across diverse domains. As researchers continue
to unravel the intricacies of these materials and their optical properties, the possibilities for
advancement and application are boundless.
Conflict of Interest: We, the authors, declare no conflicts of interest that could influence this
study. We have no financial or personal relationships affecting outcomes.
Funding: NA
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