Recent advancements in polymer based nanocomposites through electrospinning for gas sensing applications

Syed Muhammad Imran; Muhammad Zafar; Taskeen Zafar; Asifa Amanat; Fazila Khalil; Zulfiqar Ali; Woo Young Kim

doi:10.25259/AJC_1382_2025

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Review Article

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doi:

10.25259/AJC_1382_2025

Recent advancements in polymer based nanocomposites through electrospinning for gas sensing applications

Syed Muhammad Imran^a,†, Muhammad Zafar^b,†, Taskeen Zafar^c,†, Asifa Amanat^a,†, Fazila Khalil^a,†, Zulfiqar Ali^c, Woo Young Kim^d,*

aDepartment of Chemical Engineering, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan

bInstitute of Energy and Environmental Engineering, University of the Punjab, Lahore, Pakistan

cDepartment of Chemistry, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan

dDepartment of Electronic Engineering, Faculty of Applied Energy System, Jeju National University, Jeju-si, Jeju Special Self-Governing Province, Korea

^†Authors contributed equally to this work and share co-first authorship

*Corresponding author: E-mail address: semigumi@jejunu.ac.kr (W.Y. Kim)

Received: 2025-11-14, Accepted: 2026-04-08, Epub ahead of print: 2026-08-17,

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Abstract

Polymer based nanocomposites have emerged as a versatile and efficient class of materials for gas sensing technologies due to their unique combination of flexibility, tunable properties, and cost effectiveness. This review presents a comprehensive overview of the synthesis, structural characteristics, and operational mechanisms of polymer nanocomposites-based gas sensors. Flexible and low-power sensing platforms are crucial for air pollution monitoring. Polymer-based nanocomposites present a promising alternative to traditional gas sensors, especially metal oxide (MO) systems, as they operate at room temperature and offer mechanical flexibility and adjustable surface chemistry. Electrospinning has emerged as a highly effective technique for producing nanofibrous structures that enhance gas sensing due to their large surface area and improved gas diffusion. The addition of functional nanofillers to electrospun polymer matrices further improves detection sensitivity, selectivity, and charge transfer. The impact of key electrospinning parameters, includes polymer concentration, surface tension, solution conductivity, and environmental influences like relative humidity. It elaborates on various gas sensing mechanisms, detailing their principles and material compatibility. Recent advancements in conjugated polymers are also highlighted, particularly in hybrid nanostructures with metal oxides and carbon-based nanomaterials to improve sensitivity, selectivity, and stability. This review also explores the real-world applications in environmental monitoring, medical diagnostics, and volatile organic compound (VOC) detection, along with analysis and challenges including humidity interference, stability issues, and field deployment. Overall, this review work underlines the immense potential of polymer nanocomposites as next generation gas sensing materials and identifies future research directions for optimizing their performance in practical applications.

Keywords

Carbon-based nanomaterial

Conductive polymer

Functional polymer

Gas sensing

Nanocomposite

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1. Introduction

Today, humanity is challenged with providing more energy to meet the needs of more people and a growing economy, all with minimal impact on the environment [1]. Air pollution has become a major problem for the world, endangering the climate as well as the health of many individuals. People inhale polluted air in the form of smog in cities and unclean smoke inside homes, causing many dangers. As culture and technology advance, various harmful gases such as NO₂, SO₂, CO₂ and NH₃ are showing up more in our environment. They are creating more risk for both nature and human beings. There has been a significant effect of industrialization on the environment. Back in the years before the Industrial Revolution, which started around 1750, greenhouse gases were present in the air in much lower concentrations, equivalent to 250 to 300 ppm. Yet, in 2021, that level rose by 41% and there are now no signs that it will slow down. These air pollutants are mainly placed in three classes, all of which need constant and careful monitoring to reduce their negative outcomes [2].

Air pollution needs to be controlled by innovative systems that can detect all harmful substances promptly and within the given safety and environmental standards [3]. Optical spectroscopy and gas chromatography followed by mass spectrometry are accurate but do have several limitations. Usually, these techniques require a lot of time and funds and cannot be used for continuous monitoring of buildings or environments in outdoor or industrial sectors. Therefore, people are now resorting to gas sensors because they are simpler and more effective for monitoring the environment. Currently, these sensors are used to keep an eye on clean air and detect various emissions from industries. Yet another benefit is that sensors share information on the concentration and types of pollutants which help quickly plan and respond to issues. Unlike laboratory tests, gas sensors are affordable, simple to use, accept less space, and give fast results. This is why gas sensors are most often used for repeated, remote and all-around surveillance [4]. Statistics from Manisalidis et al [5] show that toxic gases in the environment have a relationship to about a quarter of all global deaths and are a serious threat to children’s health. Figure 1. shows the major categories of hazardous gases, including toxic, flammable, and asphyxiant gases The pollution contributed to approximately seven million deaths in 2016; it was the fourth cause of death in the world, caused by both home and environmental pollution. With such critical data, developing sophisticated methods for gas sensing has become a priority point for environmental monitoring. Materials conventionally used in gas-sensing devices include metal oxide semiconductors (MOS), conducting polymers, and carbon-based materials. The outstanding aspect of MOS materials is the simplicity of synthesis, high detection potential, low price, and structural robustness. One serious MOS-based sensors limitation is their requirement for increased temperatures and high-power consumption, which precludes them from energy-efficient or wearable sensing applications. Air pollution is still a major worldwide issue that requires the use of portable, sensitive, and dependable gas monitoring devices. Conventional gas sensors, such as those based on MO, have high sensitivity, but they frequently have rigid device designs, high working temperatures, and high power consumption. On the other hand, because of their room-temperature functioning, mechanical flexibility, adjustable surface chemistry, and suitability for low-power electronics, polymer-based nanocomposites have become a potential material platform. These materials get over the inherent drawbacks of polymer-only sensors by incorporating functional nanofillers into polymer matrices, which improves environmental stability, charge transfer, and selectivity. Consequently, a key and revolutionary option for next-generation air quality monitoring systems is polymer-based nanocomposites. Although polymers used for conducting are excellent at working under room temperature, their vulnerability to degradation when exposed to humid environments is a big impediment to their general usage. Graphene and carbon nanotubes (CNTs) of which carbon form parts of the materials are ideal because of their great sensitivity and large surface-area-to-volume ratios. However, slow response and recovery and limits from poor van der Waals bonding to gases compromise their performance. Scientists have proposed several ways to overcome the weaknesses of these materials, such as microstructure improvements applied to sensing elements, use of light-assisted activation, and use of advanced materials such as two-dimensional transition metal dichalcogenides. A particularly good method is a hybridization of materials based on carbon and MOS. The confluence of MOS and carbon-based material utilizes the strong chemical reactivity and stability of MOS with added sensitivity and surface capability of carbon-based materials. Moreover, metal oxides can be coated on chemically modified different sensing materials such as polymers, CNTs and metal nanoparticles thus enhancing key sensing qualities such as selectivity, sensitivity, and reversibility. With the help of these material engineering methods, it is possible to make advanced gas sensors which can be used for environmental detection in real-time, portability, and fieldwork with improved performance potential [6].

Schematic representation of hazardous gas categories, including toxic gases, flammable gases, and asphyxiant gases Reprinted with permission from [5] copyright 2026.

Experts have now pointed out that adding carbon-based substances to MOS gas sensors enhances their performance. Integrating graphene or carbon nanotubes with MOS, in addition to controlling the structure, has increased sensor sensitivity, selectivity and overall function. Those that can measure gas accurately at normal room temperature are most fascinating. Because of these sensors, we can use eco-friendly and health-oriented wearables, firefighter fabric and even smartphones to estimate air quality around us. More importantly, these sensors are essential for defense and military functions by quickly helping to identify and track air conditions and harmful gases that may come from the use of explosives [7]. It is commonly used to find CO₂ in industrial and workplace areas. Higher CO₂ levels in the air can harm workers’ breathing and cause the greenhouse effect, so checking for them is necessary. Traditional CO₂ sensors, often made from rigid ceramic-based materials, tend to operate at high temperatures and require substantial energy input, limiting their practical use in portable or wearable formats. In response, researchers have turned to flexible and hybrid sensor technologies, which offer lower energy consumption and can function effectively at lower temperatures. These advanced sensors are typically composed of polymers such as polyethyleneimine (PEI), poly (3, 4-ethylenedioxythiophene) (PEDOT), polyethylene glycol (PEG), and polyaniline (PANI) combined with carbon-based materials like graphene and carbon nanotubes. The performance of these flexible sensors, however, can be influenced by several external factors, including temperature variations, humidity levels, gas concentration, and the physical bending or curvature of the sensor substrate. While recent developments have shown promise, several technical challenges such as stability, durability, and large-scale manufacturability still hinder the widespread commercialization of flexible CO₂ sensors. Nonetheless, continued research into hybrid sensor designs and material innovations presents substantial opportunities for overcoming these barriers and realizing next-generation gas sensing technologies [8].

Advanced sensors will require sensing materials that are structured carefully, as this helps achieve the needed high performance such as enhanced sensitivity, selectivity, quick response, fast recovery and reliable long-term use. Among various fabrication techniques, electrospinning has become one of the most effective methods to produce polymer-based nanocomposite gas sensors. For effective gas adsorption and diffusion, this technique makes it possible to produce continuous nanofibrous networks with a high surface area-to-volume ratio, linked porosity, and variable fiber shape. Additionally, functional nanofillers may be uniformly incorporated into the polymer matrix using electrospinning, which improves charge transport channels and increases the sensitivity and selectivity of sensing. Owing to these advantages, electrospun polymer nanocomposites have drawn a lot of interest as cutting-edge platforms for flexible, low-power gas sensing applications of the future. Electrospinning is seen as a highly valued method for fabricating materials due to its capability to produce thin lines or nanostructures that have adjustable shape and chemical properties. When a high voltage affects a polymer, the polymer solution or melt is converted to a jet that becomes thinner and longer because of the electrostatic repulsion it encounters. When the solvent dries as the jet travels, the resulting solid material is spread as continuous ultrafine fibers on a grounded surface. Because of these features, these fibrous mats are often chosen for gas sensing applications due to their high surface area-to-volume ratio, very small fiber widths and how they are permanently connected through pores. Because of their structures, these materials absorb more gas in different areas, removing it efficiently and rapidly from the sensing layer as shown in Figure 2. It is also important to note that thanks to electrospinning, it is quite simple to work with many functional nanomaterials such as metal oxides, carbon nanotubes, graphene variants and others, inside the polymeric matrix while spinning [9]. Because of this combination, polymer-based nanocomposite fibers have improved mechanical flexibility, can be easily formed and retain integrity, in addition to higher electrical conductivity, a stronger ability to react with chemicals and improved properties with specific gases. Gas sensing qualities such as performance, sensitivity and reliability are better than those seen from either pristine polymers on their own or the inorganic materials themselves. Electrospinning can be used for various substrates, costs less and allows for large-scale manufacturing, therefore making it an excellent approach for gas sensors dedicated to wearable, flexible and monitoring technologies. Conventional MO-based sensors and polymer-only sensors, which had problems including high working temperatures, power consumption, and poor selectivity in humid conditions, have been overcome by recent developments in gas sensing technology. The fabrication of polymer-based nanocomposites that combine 2D materials, metal nanoparticles, and carbon nanostructures improves selective gas adsorption, active surface area, and charge transfer. Charge transfer is greatly improved by the formation of conductive percolation networks, and the selectivity and sensitivity of gas adsorption are increased by designed interfacial interactions and tailored surface chemistry. Comparative studies demonstrate lower detection limits, faster response times, improved repeatability, and enhanced environmental stability in nanocomposite systems compared to polymer-only sensors. These nanocomposites are perfect for next-generation air quality monitoring applications since they operate at room temperature, have more mechanical flexibility, and are compatible with portable electrical devices [10].

Graphical overview showing the development of electrospun nanofiber-based gas sensors as an alternative to traditional ceramic sensors, highlighting gas interaction mechanisms and their diverse applications Reprinted with permission from [6] copyright 2026.

The purpose of this review is to provide a comprehensive overview of recent advancements in polymer-based nanocomposites for gas sensing applications, highlighting the synergistic roles of polymer matrices and nanofillers in enhancing sensor performance. It aims to summarize current material systems, fabrication techniques, and sensing mechanisms, while comparing key performance metrics such as sensitivity, selectivity, and response time. While previous studies address polymers or nanomaterials separately, a focused and comprehensive review of electrospun polymer-based nanocomposite gas sensors remains limited, which justifies the timeliness of this review. Moreover, the review points out the challenges presently encountered, related to stability and selectivity, and suggests recent studies to help design advanced sensors usable in environmental, industrial, and medical fields.

2. Fundamentals of polymer-based nanocomposites

2.1. Nanocomposites

Nanocomposites have developed to offer advantageous substitutes for the limitations of many engineering materials. The dispersed matrix and dispersion phase components of nanocomposites can be used to categorize them. Composites that have at least one phase with dimensions in the nanometer range (1 nm = 10^–9 m) are called nanocomposites. By regulating the components of the composite parts in a stoichiometric manner inside the nanocluster phase, nanocomposite materials have emerged as viable options to overcome the limits of monolithics and micro composites. Nanocomposites have recently attracted a lot of attention and are utilized in a variety of industries, such as automotive, electronics, packaging, paints, biomedicine, and coatings. According to the presence of polymer. It can be categorized into polymer-based and non-polymer-based nanocomposites [11].

The non-polymer-based nanocomposite materials can be classed as follows:

I.

Metal/Metal nanocomposite
II.

Ceramic/Ceramic nanocomposites
III.

Metal/Ceramic nanocomposites

Polymer based nanocomposites are categorized as follows:

I.

Polymer/Polymer nanocomposites
II.

Polymer/Ceramic nanocomposite
III.

Polymer/Layered Silicate nanocomposites
IV.

Bio-composites
V.

Inorganic/Organic Hybrid nanocomposite
VI.

Inorganic/Organic Polymer nanocomposites

A critical feature of polymer-based nanocomposites is the enhancement of nanofiller dispersion in a polymer matrix with varying chemical characteristics. This is a nontrivial task and is a crucial requirement to assure uniform qualities for this type of composite as shown in Figure 3. Nanocomposite sensors are utilized to build sensitive and responsive sensors that precisely detect numerous chemical, physical, and biological characteristics [12].

Different constituents of polymer matrix nanocomposites Reprinted with permission from [13] copyright 2026.

A new area of technology called polymer nanocomposites provides high-performance materials with distinctive and creative qualities that are perfect for a wide range of cutting-edge applications [13]. The ultimate properties of nanocomposites, as well as their acceptable applications, are directly dependent on the polymer matrix utilized, the size and shape of the nanofillers, their functional groups, quantities, dispersion into the polymer matrix, and interfacial interactions [14].

Nanocomposites have the following key benefits over other composite materials:

A high surface/volume ratio makes it possible to use fillers with small sizes and close spacing.
Superior mechanical qualities, scratch resistance, and excellent ductility without strength loss.
Enhanced optical qualities (particle size affects light transmission).

2.2. Techniques used in synthesis of polymer-based nanocomposites

The mechanical, thermal, electrical, optical, and magnetic properties of the polymers are typically the primary determinants in the selection process. The selection of the polymers must consider additional characteristics, though, such as hydrophobic/hydrophilic balance, chemical stability, biocompatibility, opto-electronic properties, and chemical functions (such as solvation, wettability, templating effect, etc.). A high concentration of nano-fillers, such as graphene or carbon nanotube, may give the polymer new characteristics like high electrical conductivity, refractive index, dielectric, and mechanical qualities as well as a special reaction to specific stimuli like pH, light, heat, and magnetic fields [15]. The three primary types of polymer nanocomposite synthesis techniques are solution mixing, melt intercalation, template synthesis, and in situ polymerization.

2.2.1. In situ polymerization

This broad technique is used to create polymer nanocomposites. In this process, monomer and nanoparticles are mixed in an appropriate solvent. To put it simply, the polymer nanocomposite is created by intercalating monomers with nanoparticles and then polymerizing them with an appropriate reagent or free radical initiator. With entirely distinct properties from the original antecedents, this approach aids in the synthesis of multidimensional, well-defined structures. The in-situ technique aids in regulating the shape and size of the particles [16].

2.2.2. Melt intercalation

For the synthesis of polymer nanocomposites, melt intercalation or melt blending is the most popular technique. In melt blending, polymers are melted to produce a viscous liquid using a high shear mixer, the nanofillers are combined and heated to a high temperature to disperse them throughout the polymer matrix. This procedure, which is seen in Figure 4, involves heating the polymer matrix to its glass transition temperature, adding the filler, and kneading the mixture until it is evenly distributed. Processing parameters include temperature, filler interlayer tensions, compatibility of the polymer matrix and the fillers, mixing periods and speeds, and filler surface preparation all affect the degree of intercalation [17]. It has been shown to be both economical and ecologically beneficial. The fact that this procedure does not require any kind of solvent is one of its key benefits.

Several typical conducting polymers commonly used in electronic and sensing applications. [24] Reprinted with permission from [24] copyright 2026.

2.2.3. Solution mixing

Solution mixing is generally thought to be an easy method for creating nanocomposite materials. In solution-based procedures, the monomer is typically suspended in a solvent, typically with the aid of ultrasonication, and the colloidal suspension is subsequently combined with a polymer solution. It is important that the solvent used to dissolve the polymer, and the one utilized to create the colloidal suspension are miscible. Following that, the solvent system can either be allowed to evaporate, or the solution can be centrifuged to extract the product [18].

2.2.4. Template synthesis

By using an aqueous or gel solution containing the polymer and the silicate building blocks, this approach synthesizes the clay minerals inside the polymer matrix. Nucleation takes place during processing, and the polymer permits the growth of inorganic host crystals that are confined within the layers.

2.3. Types of filler used in polymer based nanocomposites

Nanofillers are solid additions that differ from the polymer matrix in terms of content and structure. They are rarely biological materials and are primarily inorganic. Fillers come in two varieties, such as active and inactive. While inactive fillers increase quantities by lowering prices, active fillers improve mechanical and physical qualities. Compared to clean polymers, nanofillers enhance the characteristics of nanocomposites and increase their appeal as mentioned in Table 1 [19], Overview of Nanocomposites Techniques. Numerous variables, such as the filler’s aspect ratio (length/diameter), degree of dispersion and orientation inside the matrix, and adhesion at the filler-matrix interface, affect how much of the properties are enhanced.

Table 1. Overview of nanocomposite synthesis techniques.

Method	Applications	Advantage	Disadvantage
In-situ intercalative polymerization	Manufacturing of thermoplastics and a nylon–montmorillonite nanocomposite	Linking is enabled through the tethering effect.	Slow reaction rate; reliance on clay exfoliation.
Melt intercalation	Manufacturing of thermoplastic nanoparticles	An alternative technique for in-situ polymerization	Restricted use with polyolefin.
Template synthesis	Creation of hydroxide-based double-layer nanocomposites	Encourage the silicate layers to disperse in a single step without the onium ion present.	Clay mineral synthesis necessitates feverish temperatures, which breaks down the polymers.

The performance of nanocomposites is also significantly influenced by the unique characteristics of the nanofillers, including enhanced electrical properties, mechanical strength, toughness, thermal stability, and thermal conductivity. Fullerenes, graphene, carbon nanotubes, and its derivatives, including nanodiamonds, graphene oxide, and carbon-based quantum dots, are examples of carbon-based nanomaterials [20].

2.3.1. Carbon nanotubes

Because of their exceptional mechanical qualities, high environmental stability, and unique, highly adjustable conductivity, for chemical detection, carbon nanotubes composed entirely of carbon atoms are perfect. Combining polymer gas-sensing materials, which generally have low chemical stability and conductivity but high sensitivity and selectivity, with carbon nanotubes, appears to be a win-win situation. Based on the quantity of carbon layers they contain, CNTs are often classified into two categories. With sizes ranging from 0.4 to 2 nm, single wall carbon nanotubes (SWCNTs), or single-walled carbon nanotubes, are composed of a single graphene layer, and are typically found as hexagonally packed bundles. The intricate structure of with two or more cylinders, multi-walled carbon nanotubes (MWCNTs) are formed, each of which is composed of graphene sheets. The sizes fall between one and three nanometers [21].

2.3.2. Graphene

Perfectly two-dimensional, graphene has superior crystalline structure and improved electrical characteristics. Graphene is a carbon sheet that is one atom thick and has a hexagonal lattice structure, often known as a honeycomb crystal lattice structure. The physical, chemical, and biomedical domains are showing a great deal of interest in graphene as novel nanomaterials with remarkable physical properties, including a high surface-to-volume ratio, remarkable mechanical strength, excellent electrical conductivity, exceptionally high thermal conductivity, and biocompatibility. As a kind of nanofiller, graphene can readily assist in enhancing the heat conductivity of polymeric materials [22].

2.3.3. Conducting polymers

CPs are polymers that have metallic-oriented magnetic, electrical, and optical properties together with a chain network that exhibits highπ-conjugation as structures shown in Figure 4. Many CPs, including as polythiophene (PT), PEDOT, polyparaphenylene (PPP), PANI, polypyrrole (PPy), polyacetylene (PA), and others, have developed with a wide range of applications because to their intrinsically high conductivities [23].

2.4. Advantages of nanocomposites in gas sensing

Currently, there is a high demand for gas sensing devices owing to important health, safety, environmental, and financial considerations. This has led to a significant demand for inexpensive, dependable, small, low-power gas sensors because of their many uses [24]. One of the most important technologies for the quick, accurate, sensitive, and efficient detection of gases, chemical vapors, and explosives is the gas sensor. The environmental significance of gas sensor materials is widely acknowledged, and in recent years, several studies on various gas sensor materials have been reported Table 2 [25-30]. Numerous publications have described a variety of nanoparticle kinds, including metal oxide (MO), mixed metal oxide, polymers, carbon nanotubes (CNT), and graphene oxide (GO). Many MOS, including PdO, SnO₂, Ni₂O₃, and ZnO, are often employed gas-sensing substances. These MO sensors still have certain drawbacks, such as low sensitivity, poor selectivity, and high operating temperature; to address these issues and improve sensing capabilities, the modification of MO by other components has generated a lot of interest in creating new material. These CNMs/conducting polymer nanocomposites are currently leading the way in improving the overall electrical sensing activity, thermal stability, mechanical strength, and chemical properties by modifying or functionalizing the structural features of CPNs [31]. The most promising technologies for improving the performance of sensors and biosensors are those based on polymers. Hydrogels, conducting polymers and their composites, molecular imprinted polymers (MIP), and other polymeric materials are utilized in sensor devices. Modifiable chemical qualities, such as reactivity, biocompatibility, flexibility, and resistance to degradation, are another benefit of polymer-based sensors. In addition to operating at room temperature, the CPs have built-in benefits such low cost, quick fabrication, lightweight, and a high degree of material design freedom [32]. Because of their superior electrochemical and electrical characteristics, as well as their affordability, long-term stability, and ease of synthesis, conducting polymers are frequently employed as an efficient species for gas detection. Numerous attempts have been made to improve sensing performance, such as functionalization, redox doping, and increasing the active surface area. The physiochemical, chemical, and interfacial properties of materials are enhanced by the nanoscale size. Nanocomposites’ morphology can alter the interface, which is necessary to improve several characteristics. Mechanically reinforced electrospun nanofiber networks, moisture-tolerant or crosslinked polymer matrices, and protective encapsulating layers can all improve sensor resilience. Furthermore, dependability in variable field settings is enhanced via environmental calibration and cycle stability testing.

Table 2. Summary of various gas sensors showing target gases with their morphologies, gas concentrations, and detection ranges.

Target gas	Material & morphology	Detection range	Response	Gas concentration (ppm)	Refs.
NH₃	PPy thin film	4000–10,000 ppm	2.56	10,000 ppm	[25]
Methanol	PEDOT: PSS films	35–1000 ppm	1.09	700 ppm	[26]
H₂	PPy nanowire arrays	1300–12,000 ppm	1.01	12,000 ppm	[27]
Ethanol	PANI thin film	0–32 ppm	1.64	32 ppm	[28]
NO₂	PPy thin film	10 – 100 ppm	1.36	100 ppm	[29]
HCl	Polypyrrole nanosheets	20–100 ppm	24	100 ppm	[30]

Two important elements that improve the performance of materials are mixing and surface treatment. First, adding nanofillers to polymer matrices like nanoparticles, nanowires, or nanotubes enhances sensing efficacy by increasing the surface area accessible for gas interaction. This larger surface area makes it possible for better gas adsorption and quicker reaction times, which raises the sensor’s sensitivity. Furthermore, by functionalizing the nanofillers or altering the polymer matrix, nanocomposites may be engineered to display selectivity towards gases, making it possible to identify target gases within intricate gas mixes. Charge carrier transport between polymer molecules of the usual p-conjugated structure of the CPs is disrupted by the physical and chemical interactions of gas molecules. To modify the sensing characteristics by recognizing the relationship between electrical transport and target gas molecules, polymer chemical structures, morphologies, redox characteristics, and charge transfer capabilities are essential [33].

3. Electrospinning

Nanofibers with different morphologies may be made using the conventional technique of electrospinning, which is frequently employed for large-scale production. An effective method for creating a nanofiber matrix is electrospinning. Numerous applications for electrospinning matrices include affinity membranes, filtration systems for air and water purification, wound treatment, tissue engineering, solar cells, biosensors, cell regeneration, cosmetics, and medication delivery systems. In 1929, the production of aerosols through the application of electric potentials to fluids was demonstrated. The first mechanism to spray liquid under the influence of electric charges was patented by Morton and Cooley in the same year. The investigations have been made to show how much charge the fluid requires to regulate the surface tension of the drop. The device was updated and patented in 1942 for its current function. Research conducted between 1940s and 1960s was primarily concerned with achieving fibers with reduced size, homogeneity, optimal parameters, and equipment design. In the 1990s, many investigations on the adaptability of producing and utilizing electrospun particles have been conducted since educational institutions adopted electrospinning technology. Electrospinning is the process of spinning fibers using electrostatic forces [34].

Subbiah et al. [35] claims that electrospinning is an electrostatic spinning technique that has been used extensively in science and technology for more than 30 years as features mentioned in Table 3. Electrospinning is a simple method that requires little equipment. But the fibers’ homogeneity, shape, and porosity are affected by the processing and solution conditions. When one polymer’s parameter is changed, another polymer produces a completely different outcome, and the manufactured fibers are the product of several diverse factors working together. The kind of electrospinning technique has a major impact on the manufacture of fibers, according to Bhattaria et al. [36] in addition to the parameters of the process and solution. Thus, solution vs. melt electrospinning and nozzle arrangement are the two primary factors to consider in electrospinning type; collector modification was included as a third. Before electrospinning, five techniques for adding drugs were also demonstrated: surface modification, emulsion, mixing, multidrug delivery, and multilayer coating.

Table 3. Advantages, disadvantages and applications of electrospinning [34-35].

Electrospinning
Advantages	Disadvantages	Applications
High fabrication flexibility allows precise control over nanofiber microstructure, arrangement, and diameter,	Limited functional groups fibers may lack functional groups necessary for certain applications, requiring post-treatment modifications to enhance functionality.	Sensors Gas/Pressure/Strain/Chemical/Piezoelectric sensors
Wide material selection: Compatible with various polymers and additives, enhancing functionality	Inconsistent fiber morphology: Difficulty in achieving uniform fiber diameters and structures can lead to variability in performance.	Textile Protective clothes Chemical retardant fabrics Fire retardant fabrics
Efficient production: Capable of producing fibers quickly, suitable for large-scale applications.	Process sensitivity: The electrospinning process is sensitive to environmental conditions (e.g., humidity, temperature), which can affect fiber formation and quality	Energy sector Supercapacitor Li-ion batteries Solar cells
High surface area: Nanofibers have a high surface area-to-volume ratio, improving interaction with surrounding environments in applications like filtration and tissue engineering.	Post-Treatment necessity: Often requires chemical modifications to improve surface properties or incorporate bioactive components, adding complexity to the fabrication process.	Filtration process: Air filtration Vehicle cabin filtration Liquid Filtration
3D structure capability: Can create complex 3D nanofiber structures beneficial for tissue engineering and filtration applications through techniques like sequential electrospinning and gas-foaming.		Biomedical applications: Drug delivery system Tissue Engineering Wound dressing

3.1. Principle and equipment for electrospinning

A high-voltage power supply, a metallic needle (spinneret), and a collecting plate (a grounded collector) that is always positioned between the spinneret and the collector are the three main components of an electrospinning apparatus The process begins with the polymer solution being placed in a syringe. For accuracy, the polymer solution in the syringe is guaranteed to be free of air bubbles. The syringe is attached to a metallic needle. A syringe pump supplies the metallic needle, which controls the solution’s flow rate. To produce a “Taylor cone,” a high-voltage power source, typically between 1 and 30 kV, is applied at the nozzle of the metallic needle to a liquid droplet of the polymer solution.

By stretching and electrifying the droplet, the generated charges are evenly dispersed throughout the surface. Droplet experiences are characterized by two main forms of electrostatic forces: coulomb and electrostatic repulsion. The surface tension is offset by electrostatic repulsion, while the external electric field applies coulomb forces. Before being deposited on the counter-electrode, a process of stretching and thrashing will be experienced by the electrified jet to create homogeneous, continuous nanofibers as steps mentioned in Figure 5 [37].

3.2. Parameters affecting electrospinning process

3.2.1. Voltage

It is well known that when the applied voltage increases, so does the electric field strength. However, even at short working distances and high electric field intensities, a critical voltage is needed to form the cone for fiber production. When a high voltage is supplied, the imbalanced effect causes the prepared fiber to display a broad size dispersion. The shape of the fiber is clearly influenced by the applied electrical voltage. To create stable jets that form continuous threads, the electrostatic force and the solution’s surface tension must be matched. The liquid jets will be expelled from the cone tip as soon as the applied voltage above the critical value. If the solution viscosity is extremely low, the bead-generating jets, also known as electrospray, will not be stable. To promote the development of homogeneous and smooth fibers, high voltages can stretch the jets completely by producing a greater electrical field (bigger electrostatic forces) and more charges to the droplet surface or solution at the needle’s tip (higher columbic forces) [38].

Ding et al. [39] found that when the applied electrical voltage raised the fiber diameters reduced. Additionally, with a higher applied electrical voltage (20 kV), it was observed that fibers with more consistent diameters. The electrostatic force acting on the solution jet should rise with a stronger electric field, enabling the formation of thinner fibers. Another study discovered that when the voltage was raised from 15 to 30 k, the nanofibers’ average diameter dropped by 25% [40].

3.2.2. Feed rate

At low feed rates, the needle has a vacuum inside of it. Nevertheless, the polymer builds up on the edge of the tip at greater flow rates, disrupting the Taylor cone’s formation. For every applied voltage, a stable Taylor cone must be produced and maintained, which requires an ideal feed rate value. It has been observed that the polymer solution’s feed rate has a significant impact on the shape of the polymer fiber. When the feed rate is adequate for fiber formation, there is an optimal feed rate. More solutions will be produced at a higher feed rate, or excess, this will produce beaded fibers [41]. Ding et al. [39] found that when the feed rate rose, the average diameter remained nearly constant. This implies that the morphology, diameter, size, and uniformity of the electrospun fibers are not significantly impacted by the feed rate.

3.2.3. Tip-to-collector working distance (TCD)

The TCD increases the intensity of the electric field, but its main effects are on the solvent’s evaporation in the solution and a polyvinyl alcohol (PVA) macromolecular chain’s stretching. When the TCD falls, the electric field becomes stronger. While moving through the electrical field, electrostatic force is used to stretch polymer jets. The polymer jets remain elastic while the solvent evaporates during this procedure. According to reports, the likelihood of fiber contraction, or shrinking, rises as the working distance increases. The fiber diameter is gradually raised as the working distance increases to reach an ideal point, after which the fibers’ uniformity decreases as the distance increases and some fractures are even visible. This is done to achieve uniformity if the fiber diameter is observed to drop. However, changing the TCD across a short range of 10 to 15 cm did not prevent the production of defects or pearled fibers [42].

3.2.4. Polymer concentration

The concentration of polymers is an important operational parameter in the electrospinning process that significantly affects the morphology of the fiber. Because of their high viscosity, the fibers’ ability to form is impeded by high concentration solutions. Because of their high viscosity, the solutions are extremely difficult to pass through the syringe needle and form nanofibers when exposed to an electrostatic force. To maximize the final electrospinning fibers, one of the crucial criteria needed is a suitable solution concentration. Bead formation in nanofibers can be caused by an exceptionally low solution viscosity. The stable jets in a moderately high viscosity solution travel to the electrode and eventually form homogeneous fibers on the collecting grounded electrode without breaking because of the high viscosity’s cohesive nature [43].

3.2.5. Surface tension

Solution surface tension is crucial to electrospinning because it is the primary force that counteracts the repulsive force of the charges on the jet surface. As a result, it affects how the Taylor cone forms, how the solution jet starts, and how much the fiber diameter grows. Additionally, the production of beaded filaments is the result of turbulence in the solution jet caused by high surface tension, which has the same effect as low viscosity. A larger voltage is needed to generate fibers if the surface tension is high. The surface tension is no longer appropriate if it is too low. Depending on the formulation, the surface tension of an aqueous solution plateaus at 40 and 50 mN/m after dropping dramatically at low concentrations for a range of 0.1 to 0.2 weight percent polymer content. As concentration rises, macromolecules adsorb at the air–water interface, which results in a drop in surface tension. The surface tension of polymer solutions remains constant across the concentration ranges utilized in electrospinning, irrespective of the molecular weight and concentration of polymers employed, signifying solution saturation [44]. In addition to lowering PVA-based solutions’ surface tension with solvents other than water, smooth nanofibers can be created by employing a low-surface-tension co-solvent. Using a surfactant is another method that produces homogenous nanofibers [45].

3.2.6. Conductivity

Jet instability modes’ amplitude is related to a fluid’s conductivity. Because a solution with high conductivity can carry charges more easily than one with low conductivity, the solution jet will extend more. This feature is less important than the other physio-chemical properties of solutions. High electric fields create jet instabilities in highly conductive solutions, which raise the mean diameter and dispersion of the resultant nanofibers by causing instabilities near the Taylor cone [46]. Nanofibers shape is also influenced by the conductivity of the solutions. Itoh et al. [47] found that adding salt increased conductivity, which in turn produced ribbon-like fibers. All other physio-chemical characteristics are influenced by the chemical makeup of these species and their interactions with macromolecules, which also affect how salts affect the shape and average diameter of the nanofibers.

3.2.7. Relative humidity

The structure and development of PVA nanofibers, which vary in thickness and shape, are influenced by relative humidity. Quicker solvent evaporation at low relative humidity produces thinner nanofibers, whereas increasing humidity inhibits solvent evaporation and produces thinner ones. Since PVA is hydrophilic, its development and physical properties are impacted by the humidity in the surrounding environment. As relative humidity rises, nanofibers’ diameter falls, resulting in stiffer structures and an irregular fiber shape. The mechanical properties of nanofibers with diameters greater than 250 nm are consistent because of size-dependent surface effects.

4. Gas sensing mechanism in polymer-based nanocomposites

Gas sensing mechanisms are central to a wide range of applications, including homeland security, healthcare diagnostics, industrial safety, and environmental monitoring. These mechanisms enable the identification and quantification of various gases from combustible compounds to toxic pollutants across different environments. Polymer-based nanocomposites have emerged as a promising class of gas sensing materials due to their high sensitivity, mechanical flexibility, processability, and tunable chemical and physical properties [48]. These materials are made up of a polymer matrix with embedded nanomaterials such as nanoparticles, nanotubes, nanowires, or nanosheets. Typical polymers include PANI, PPy, and PEDOT, while the nanomaterials often comprise CNTs, graphene, metal oxides (e.g., ZnO, TiO₂), and noble metal nanoparticles such as Au and Ag [49].

These materials appear in two main forms here. The fact that CPs (and their composites with PVC or PMMA) can change their electrical behavior rapidly when exposed to gas with acid/base or oxidizing/reducing characteristics at room temperature has led to their fast development and use in key areas. Still, they do not work well as gas sensors since they are not very sensitive, lack the ability to choose between various gases and are quite fragile due to their low conductivity and attraction to moist air and volatile organic compounds (VOCs) [50].

On the positive note, researchers solved these issues by inventing hybrid products that mix the easy-to-use feature of CPs with quick and wide metal oxides. Some frequently explored mixtures have shown excellent results, including PANI-ZnO, PPy-SnO₂, PTh-TiO₂, and PEDOT-CuO, and they are sensitive, selective and stable to NO₂, CO, NH₃ and H₂S as mentioned in Figure 6. However, the results from processing can be very different depending on the methods for synthesis, the types of polymers, the shape of nanofillers and how much is added which makes deeper study and adjustment essential. Or the process to be more sensitive, the active parts and surface of the catalyst should be increased. The success of these processes is largely decided by how well nanomaterials connect to the gas molecules found in the polymer [51].

Graphical illustration of conducting polymer–metal oxide hybrid nanocomposites and their gas selectivity [52] Reprinted with permission from [52] copyright 2026.

Sensors were made more effective by combining nanomaterials with specific chemical groups and forming hybrid nanocomposites [52]. PANI and these conducting polymers have a Chemiresistive ability that can change when they are exposed to acetone. It has been reported that an acetone gas sensor based on WO₃/PANI composite can detect 10 ppm of acetone at room temperature [53]. In a ternary nanohybrid, MOF-derived ZnO nanopolyhedra, S, N-doped graphene quantum dots (GQDs), and PANI combine to maximize the benefits of each individual component. PANI adds to overall conductivity and stability, GQDs improve electrical conductivity and reactivity, and ZnO offers a large surface area and semiconductor qualities. For trace acetone detection at room temperature, this showed ppb-level sensitivity, high responsiveness, quick response/recovery time, consistent repeatability, exceptional selectivity, and exceptional long-term stability. The gas sensing process in polymer-based nanocomposites relies on interactions between gas molecules and the nanocomposite [54]. The gas sensing performance of polymer-based nanocomposites is governed by multiple synergistic mechanisms. When target gas molecules give or take electrons from conductive nanofillers like metal nanoparticles, CNTs, or graphene derivatives, charge transfer interactions take place. Resulting in measurable changes in electrical resistance. Furthermore, polymer swelling effects are important, especially in chemiresistive sensors where gas absorption induces the polymer matrix to expand volumetrically, changing conductive routes and modifying resistance. Moreover, sensitivity and selectivity are improved by the depletion or accumulation zones created by heterojunction formation at the interface of p-type polymers and n-type MO nanofillers. Compared to systems with only one component, the combined contribution of these processes allows for better detection limits, faster response-recovery behavior, and more selectivity.

At the beginning, gas molecules attach themselves to the outside layers of the nanoparticles within the polymer material. This adsorption can occur through physisorption (weak van der Waals forces) or chemisorption (strong chemical bonds). This adsorption transfers charge between gas molecules and nanoparticles. For example, reducing gases like NH₃ contributes electrons to the sensing material, whereas oxidizing gases like NO₂ remove electrons. This charge transfer affects the nanocomposites electrical characteristics, namely its conductivity [55]. Changes in conductivity due to gas adsorption are then converted into an electrical signal that can be monitored and associated with gas concentration. These gas sensors’ effectiveness depends on factors such as the surface area of the nanomaterials, the interaction between different parts, whether the sensor can detect specific gases and various environmental factors like temperature and humidity Hydrophobic surface modification, controlled pore design, and the incorporation of functional nanomaterials can all help to decrease humidity interference, which enhances signal transmission and reduces competitive adsorption. A larger surface area gives more adsorption sites, which leads to increased sensitivity. Strong connections between the polymer and nanoparticles allow efficient charge transfer and stability, while functionalizing the materials can improve selectivity for certain gases [56]. Polymer-based nanocomposites provide diverse benefits for gas sensing, including increased sensitivity due to the greater surface area and active sites afforded by nanoparticles. Their versatility enables them to be processed into a variety of forms, including films, fibers, and coatings. Furthermore, their chemical and physical properties may be easily tailored to specific applications, making them very versatile. In addition, these materials are less costly to produce than other sensing materials. Polymer-based nanocomposite gas sensors are widely used in environmental monitoring to detect pollutants such as NO₂, CO, and VOCs, industrial safety monitoring of hazardous gases, healthcare applications such as breath analysis for medical diagnostics, and food quality control by detecting spoilage gases such as NH₃ and H₂S [57]. To summarize, polymer-based nanocomposites allow for versatile and efficient gas sensing. These materials’ unique properties enable great sensitivity and selectivity in a variety of applications. Gas sensing systems in polymer-based nanocomposites are commonly classified into three categories: chemiresistive, capacitive, and optical sensing. Each mechanism uses a distinct transduction pathway to convert chemical interactions with gas molecules into observable electrical or optical signals.

4.1. Chemiresistive sensing mechanism

Chemiresistive sensing is one of the most researched gas sensing techniques, because of its ease of use, affordability, and rapid response time. Chemiresistive sensors detect changes in the electrical resistance of a sensing material when exposed to a target gas. This resistance change is proportional to the gas concentration and is normally measured using two electrodes. The effectiveness of a chemiresistive sensor is usually evaluated using key performance metrics such as sensitivity, selectivity, response and recovery time, working temperature, and limit of detection [58]. Polymer nanocomposites are ideal for chemiresistive sensing. However, their performance is heavily dependent on the interfacial compatibility of the polymer matrix and nanofillers. A good dispersion and strong contact between the two are required for efficient charge transfer. This can be improved by employing polar polymers or chemically altering the nanofillers. Nano structuring the sensing layer improves gas sensing properties by increasing surface area and modifying charge transport channels [59]. In most cases, the sensing material is deposited onto interdigitated electrodes using techniques such as spin coating, dip coating, drop casting, or more advanced methods like physical/chemical vapor deposition and the sol–gel method. When exposed to gases, the variation in resistance is caused by charge transfer between the gas molecules and the sensing layer. Reducing gases (e.g., NH₃) donate electrons, while oxidizing gases (e.g., NO₂) withdraw electrons, affecting the concentration of charge carriers and hence the resistance [60].

4.2. Capacitive sensing mechanism

Capacitive sensors were shown to sense a variety of gases, including H₂, O₂, NH₃, NO₂, and NH₃, VOCs such as ethanol, methanol, formic acid, and relative humidity (RH). Capacitive gas sensors are electrochemical sensors that use the changing dielectric characteristics of the sensing layer to detect the presence of a target gas. These changes are tracked by measuring capacitance values in polymer-based nanocomposites, which respond directly to interactions between gas molecules and the nanocomposite. Capacitive sensors provide a basic construction with great reliability, cheap fabrication costs, and higher selectivity [61].

Both material choice and structural design are important for capacitive sensors to guarantee the sensor’s high sensing capability. The sensitive layer is developed by incorporating nanofillers such as metal oxides, carbon nanotubes, or graphene into the polymer matrix to improve the polymer’s sensitivity and dielectric characteristics. The dielectric constant varies as gas molecules contact with the sensitive layer owing to physical adsorption, chemical reactions, or changes in the nanocomposites structure as shown in Equation 1.

(1)

\begin{matrix} C = ε_{0} ε_{r} \frac{A}{d} \end{matrix}

where A is the area of the plate, d is the distance between two parallel plates that may be used to determine the thickness of the dielectric layer, ε_r is the relative permittivity of the dielectric layer, and ε_o= 8.8541878176 × 10^-2 F/m is the vacuum permittivity. Capacitive sensing requires a change in the sensor’s ε_r, A, or d value due to the targeted gas or vapor. The capacitance of a sensor device is principally affected by the dielectric properties of the target vapor and the detecting layer. Because humidity pervades the whole atmosphere, it can significantly affect a capacitive sensor’s sensitivity, reaction time, and recovery capacity [62].

4.3. Optical sensing mechanism

This technique provides a sensitive, selective method of measuring gases, without contact, using the changes in light attributes caused by the interaction with the molecules of the target gas as shown in Figure 7. As a basis, this principle enables many sensors to change the properties of light into an electric signal that is related to the amount of gas in the system [63].

Schematic representation of an optical fiber–based gas sensor employing evanescent field interaction for selective gas detection Reprinted with permission from [53] copyright 2026..

Optical sensing is possible by taking advantage of the light-handling performance of nanoparticles in polymer-based nanocomposites. Adding plasmonic particles from gold or silver to polymer mixtures allows for the use of surface plasmon resonance (SPR) technology in sensing. Exposure to gas molecules on the nanocomposites surface alters the surface around it. Consequently, you can observe a shift in the location of the SPR resonance. Moreover, both methods including monitoring the optical wave guide modes and using interferometry, are helpful for detecting how gas alters the refractive index of polymer nanocomposites.

As another approach, you could use luminescent nanomaterials such as quantum dots, organic dyes, or various metal oxides, in the polymer construction. Here, target gas molecules can influence the brightness of the light or the wavelength at which it is emitted. The signal from the sensor is the luminescence shift that was perceived. Overall, the polymer matrix supports the sensing element by providing toughness, helping to mix the nanomaterials more evenly, increasing the stability of the sensing layer and either selectively blocking or controlling movement of gases to the sensing area. One of the best things about optical gas sensors relying on polymer nanocomposites is that they are more sensitive, react very quickly, do not get affected by electromagnetic fields and can operate remotely. The best application of these is when it matters to them that electrical current might be sparked, as they avoid coming into direct touch with the electrical contacts in the sensing layer. Hence, although these sensors provide unique features, the fabrication stage for optical gas sensors requires sophisticated optical instruments, making it more complicated to produce them. The way optical sensor works is closely linked to several points, for example, how the gas is bonded to the nanocomposite, the characteristics of the nanomaterial and the permeability of the polymer to gas as well as the influence of temperature and relative humidity [64].

5. Recent advances in polymer-based nanocomposites for gas sensing applications

A variety of polymers from the conducting polymer, thermoplastic, elastomer, and other categories have been employed in the case of polymer nanocomposites. The nanocomposite sensors demonstrated high sensitivity to chemical, biological, ionic, and gaseous species in addition to electronic signals. Structural and surface engineering approaches can improve the long-term stability of polymer-based nanocomposite gas sensors under temperature and humidity fluctuations. Tailoring electrospun fiber shape enhances mechanical robustness and resistance to deformation. Furthermore, incorporating hydrophobic and thermally stable nanofillers reduces degradation induced moisture, while protective coatings and surface functionalization minimize interference from the environment. In real-world conditions, these combined strategies significantly improve sensor reliability and long-term operating stability. New developments include printed flexible electrodes, downsized signal-conditioning circuits, room-temperature operable nanocomposites, and low-power wireless modules have made integration with wearable and portable electronics much easier. Lightweight and energy-efficient sensor systems that are appropriate for real-time mobile applications are made possible by these advancements. Many academics have been interested in developing a polymer-based gas sensor in recent years to detect volatile compounds quickly and accurately to track the decay process. As a result, CPs’ unique and remarkable qualities have generated a lot of attention in gas sensor technology compared to traditional inorganic materials. Polyaniline nanocomposites can detect CO and NOx species for gas sensing. The gas sensors made from polypyrrole nanocomposite can also effectively detect NOx molecules. Similarly, sensors made of polythiophene nanocomposite may detect hydrazine gas [65]. Wu et al. [66] created the nanocomposite sensor built from graphene, polypropylene, and polyaniline nanofiller. To create nanoparticles, simple in situ polymerization and dip coating methods were used. Ammonia emissions and volatile sulfur compounds were detected using the developed nanocomposite sensor.

G. Fan et al. [67] developed a hierarchical nanohybrid ammonia detection sensor by employing ultrasonic spray-assisted in-situ polymerization to produce PANI on tungsten trioxide (WO₃) nano-plates through an intercalation-exfoliation process with varying PANI/WO₃ molar ratios. The nanohybrid sensor (PANI-WO₃) demonstrated superior ammonia detection capabilities compared to PANI nanocrystals or WO₃ nanoplates under the same operating conditions. Zhang et al. [68] developed polypyrrole-nickel oxide (PPy-NiO) nanocomposites for NO₂ gas sensors at room temperature utilizing an in-situ growing technique that involves a hydrothermal. At the optimal molar ratio between PPy and NiO, the composite sensor’s (PPy-NiO) response was thirty times higher than that of the bare NiO sensor, with a lower detection limit of 49 ppb. Sonker et al. [69] have created a polyaniline-TiO₂ nanocomposite thin-film CO₂ sensor that responds to 1000 ppm CO₂ at ambient temperature with response and response/recovery times of 53% and 6.2/5.7 min, respectively. Zegebreal al. [70] explained how to use the in situ electrochemical polymerization approach to create PPy-TiO₂ hybrid nanocomposite thin film for moisture sensing on an Al substrate. Hu et al. [71] examined the ammonia sensing capabilities of a fascinating substance made by polymerizing aniline on hollow nickel oxide (NiO). Zhang et al. [72] examined the PPy/NiO nanohybrid sensor’s gas detection capabilities by altering the molar ratios of its constituent parts. The composite sensor (PPy-NiO) has a lower detection limit of 49 ppb and a response thirty times higher than the bare NiO sensor at the optimal molar ratio between PPy and NiO. The gap between the original design and its practical implementation has been closed by developments in nanocomposite sensor technology. Nanoparticle dispersion in the matrix, polymer type, nanofiller concentrations, and matrix–nanofiller interactions all significantly enhance the nanomaterials’ sensing capabilities in nanocomposite sensors.

6. Applications of polymer nanocomposites in gas sensing

6.1. Monitoring of toxic gases

Nanocomposites made from polymers and nanocarbons show chemically sensitive characteristics, strength, durability, and flexible electron conductivity for gas sensors. By interacting with polymers, graphene or its derivatives, carbon nanotubes, fullerenes, etc., extended π-systems were created to aid in effective electron conduction. Furthermore, reports have been made about the range of metal oxides with polymer nanocomposites, including titania, zinc oxide, silver oxide, tin oxide, and many more. High performance nanocomposites are therefore sensitive and selective to harmful gases, such as organic vapors, nitrogen, sulfur, and carbon oxides. Essential conjugated polymers like polyaniline, polypyrrole, and polythiophene exhibit NOx detecting properties. Furthermore, methane, sulfur oxide, nitrogen, and halogens may all be detected using conductive nanocomposites supplemented with nanoparticles. Polyaniline nanocomposites can detect CO and NOx species for gas sensing. The gas sensors made from polypyrrole nanocomposite can also effectively detect NOx molecules. Similarly, sensors made of polythiophene nanocomposite could identify hydrazine gas [65]. High sensitivity and repeatability are characteristics of all these sensors. For instance, the ability to detect hydrocarbons and NOx gases has been investigated using nanomaterials based on polyaniline/tin oxide, polypyrrole/tin oxide, poly (ethylene dioxythiophene)/tin oxide, etc. High sensitivity and selectivity were demonstrated by each of these sensing materials. Qin et al. [73] developed a composite sensor that uses silicon nanowires (SiNWs) and silver nanoparticles (Ag NPs) modified polypyrrole. In comparison to pure PPy-SiNWs and SiNWs, the sensor’s reaction to ammonia concentrations at 80% relative humidity was 78% and 208% greater, respectively. Electronic, chemical, and anti-humidity sensitization were credited with the sensor’s improved ammonia detecting, which made it a quick, reversible, selective, and ultrasensitive clinical diagnostic tool.

6.2. Medical diagnosis

Gas sensors’ versatility and innovation make them a breakthrough in respiratory monitoring. With their real-time, non-invasive monitoring capabilities, breathing rate, depth, and patterns may be precisely assessed. They are also easily incorporated into daily life due to their easy long-term monitoring capabilities. This ongoing observation improves quality of life and treatment efficacy by assisting in the early identification of any respiratory problems [74]. The ability of gas sensors to monitor without pain and provide vital information for averting emergencies makes them especially beneficial for children, the elderly, and special groups. A disposable mask with a Ti3C2Tx/PANI-PP composite sensor built into it was created by Wu et al. [75] used a wireless bluetooth module to measure human respiration rates in real time. An essential metric for evaluating respiratory health, the sensor’s sensitivity to variations in exhaled breath’s carbon dioxide content is remarkable. Wu et al. [76] presented an innovative method to wearable health monitoring technology that focuses on real-time respiratory rate monitoring using a sensor implanted in a disposable mask. Ammonia gas, a biomarker in breath that suggests physiological or metabolic abnormalities, is highly responsive to the sensor, which uses a polyaniline/carbon nanotube (PANI/CNT) nanocomposite. Its unique design makes it easy to incorporate into daily wear, encouraging non-invasive medical surveillance.

6.2.1. Disease diagnosis

The ability of gas sensors to bend and stretch makes them a revolutionary sensor technology that can track changes in the gas composition of the environment in real time. These sensors have enormous promise for diagnosing illnesses, particularly for the early identification of respiratory conditions like chronic obstructive pulmonary disease (COPD) and asthma. Through ongoing monitoring of exhaled gases, physicians may modify treatment regimens in response to variations in gas composition, improving the accuracy and efficacy of therapies. Intestinal gas composition is also impacted by intestinal conditions such as gastric ulcers and inflammatory bowel disease. By putting flexible gas sensors inside a patient’s body, it is feasible to track changes in intestinal gases in real time, which aids medical professionals in understanding how the disease progresses and directs the creation of treatment strategies [77]. Some diseases cause metabolic alterations that alter the makeup of exhaled gases, gas sensors may also be useful in the early detection of infected patients. Personalized healthcare and non-invasive illness diagnostics have shown potential using gas sensors. Chen et al. [78] created a flexible electronic nose with metal ions that showed cross-reactive reactions to several gases at ambient temperature. Wang et al. [79] reported an extremely sensitive chemical sensor modeled after butterfly wings. When compared to data taken in a static environment, the sensor’s sensitivity significantly dropped due to a dilution effect. Flexible gas sensors are expected to find wider uses in the medical industry because of ongoing technical breakthroughs, resulting in revolutionary improvements in the detection and treatment of disease.

6.2.2. Implantable medicine

Gas sensors, which provide continuous and real-time monitoring of the interior environment of the human body, are an essential element of implanted health monitoring. Healthcare practitioners can get more accurate health information, identify physiological abnormalities, and initiate early intervention and therapy by monitoring changes in the concentrations of biochemical gases such as oxygen, carbon dioxide, and nitrogen oxides. This is necessary for thorough patient care and monitoring as well as for giving physicians more accurate diagnostic standards. Because every person has unique physiological traits and medical requirements, flexible gas sensors also serve as a foundation for customized treatment. Flexible gas sensors that are implanted may be customized to meet the needs of individual patients, enabling personalized treatment programs and health monitoring. This improves patient satisfaction and treatment results. By relaxing blood arteries and improving blood flow, nitric oxide, a naturally occurring substance generated by the human body, is essential for maintaining health [80]. However, diseases such as chronic obstructive lung disease are associated with exposure to nitrogen dioxide.

6.3. Volatile organic compounds (VOC)

The superior electric properties and large specific surface area of carbon-based sensors, like graphene, carbon nanotubes and Mxene have allowed for the successful detection of VOC analytes and allowed for precise and dependable examination of VOC vapors, even at minimal levels and room temperature. Most VOCs gases, including alcohols, aldehydes, and aromatic compounds pose a serious risk to human health and the environment since they are very dangerous and carcinogenic [81]. For instance, one of the most prevalent VOCs and the main indoor contaminant is HCHO, which is released by building materials. Even modest levels of HCHO gas exposure can induce respiratory issues in humans, including tightness in the chest, throat discomfort, and shortness of breath. Chronic exposure to high levels of HCHO gas would increase the risk of acute poisoning, chronic toxicity, and nasal malignancies [82]. Selectivity is also improved by polymer-based nanocomposites, which inhibit cross-sensitivity and allow preferential adsorption of VOCs and hazardous gases through tailored chemical interactions between functionalized nanofillers and target gases. Hadano et al. [83] made rGO powder using a Hummers approach that was modified. Spherical agglomerations of rGO were placed between the PANI chains; they were created because of the plasticizing influence of N-methyl-2-pyrrolidone (NMP) solvent that was introduced during the creation of this composite. This rGO-PANI composite was employed as an NH₃ sensor under a closed system but a fixed concentration of NH₃ was controlled. Furthermore, it was discovered that the PEEK’s sulfonation degree was favorable to the gas’s selectivity for the first time, it showed promise in the investigation of highly selective systems and methanol sensing devices.

7. Challenges and future perspectives

The sensor can detect many types of gases because it is exceptionally efficient. Even so, the research and application of plastic are constrained by working environments, moisture, and heat. conducting polymers (CPs) exhibit a similar increase in conductivity with rising temperature to other semiconductors. It consists of gas adsorption by the material and a mutual reaction occurring during gas sensing. A rise in temperature encourages more adsorption to occur at a lower point compared to desorption. When performing redox reaction-based sensing, sometimes a higher temperature improves results, but it does so because reactions occur more quickly. Since organic compounds tend to struggle in elevated temperatures, CPs cannot withstand up to 500°C as easily as metal oxides do. That is why room temperature sensors often use CPs gas sensors. Apart from other problems, conductive polymer gas sensors experience decreased performance due to the impact of humidity on their devices. Since humidity is easily sensitive to many CP sensors, it is considered a major analyte. As a result, measuring gas in a humid environment involves considering both the response to gas and the response to water vapor [84]. Water and the target gas occur side by side and usually fight for the same adsorption site on the material, so as moisture increases, sensitivity declines since the sites are already full of water. It is important for gas sensors made from polymer-based nanocomposites to guarantee that the polymer and additional nanoparticles do not clash. If sensors made from PANI incorporate metal oxides such as zinc oxide (ZnO) or titanium dioxide (TiO₂), it is vital for their nanoparticles to be dispersed uniformly. The room-temperature tests on the PANI-PB-ZnO nanocomposite and ZnO sensors involved gas sensing of various amounts of acetone, ammonia, and ethanol. From the testing, the PANI-PB-ZnO sensor could respond to ammonia gas in a straight manner at room temperature. Unlike other sensors, the ZnO took longer to react to ammonia gas. Due to the presence of additional active sites for removing electrons, the sensitivity of the PANI-PB-ZnO sensor has increased. Because it responds uniquely to ammonia, the PANI-PB-ZnO sensor could be used for detecting ammonia [85]. Because their chemical properties are not the same, nanoparticles clump together which results in a smaller surface area and reduces the sensitivity of the probe. One way to fix this is by modifying the surface of nanoparticles or by using compatibilizers to better spread them inside the matrix.

7.1. Stability and reliability issues

One of the major challenges in the deployment of polymer-based nanocomposite gas sensors is their long-term stability and reliability. These sensors are often exposed to varying environmental conditions, including humidity, temperature changes, and exposure to different gases, which can degrade their performance over time. For example, the electrical characteristics of the sensor may change due to oxidation of the nanomaterials or plasticization of the polymer matrix, producing values that are not accurate. Ensuring that these sensors maintain their sensitivity and accuracy over extended periods in real-world conditions is crucial. Even though electrospun nanocomposites’ large surface area increases sensitivity, it also poses serious problems for long-term stability and dependability in real-world settings because the exposed polymer chains are prone to oxidation and plasticization over time, which can cause baseline drift and reduced accuracy [86]. To solve this, scientists are looking into several ways to increase stability, like adding stronger nanomaterials or creating protective coatings that can shield the sensors from the elements without affecting how well they work. Future studies should also focus on developing mechanically robust and moisture-stable polymer matrices, improving nanofiller dispersion by enhanced surface functionalization, and developing scalable production methods including roll-to-roll electrospinning and printing. Standardized evaluations of long-term durability in authentic environmental settings are also crucial.

Humidity interference is considered a significant obstacle, as water molecules compete with the target gas for adsorption sites, thereby substantially reducing sensitivity, especially for polar analytes. Efforts to mitigate this issue concentrate on surface engineering, particularly through th33e integration of hydrophobic functional groups or the application of fluorinated polymers to enhance the fiber surface’s ability to repel water vapor [87]. An alternative strategy entails the creation of integrated sensor arrays featuring a dedicated humidity sensor, which enables the sensing system to mathematically adjust for signal variations caused by humidity, thereby enhancing the reproducibility of the final measurement.

7.2. Selectivity and specificity enhancement

Enhancing the selectivity and specificity of polymer-based nanocomposite gas sensors is another critical area of focus. Although these sensors can detect a broad variety of gases, it is still difficult to differentiate between them precisely. This is especially crucial for applications that call for the detection of certain gases, including VOCs or hazardous industrial chemicals. The selectivity of these sensors is being enhanced by advances in nanomaterial design, such as the use of functionalized nanocomposites or molecularly imprinted polymers [88].

7.3. Integration with electronic devices

For gas sensors made from polymer-based nanocomposites to be used widely, they should be able to connect easily with electrical devices. It refers to connecting sensors to various devices like wearable electronics, industry monitoring systems, and cellphones, as well as developing efficient and low-energy interfaces that manage gathering and recording sensor information. There are many studies underway in flexible electronics and some even focus on the mechanical properties of electro spun nanofibers. The summary of critical conditions and prospects helps encourage the making of advanced polymer nanocomposite meshes and supports the use and integration of these meshes in electronic devices with exceptional practicality and reliability in many applications. Polymers in general are usually used to hold other materials, function as adhesives, shield products, carry electrical charge and form the main part of a product. Due to how flexible they are, polydimethylsiloxane (PDMS), poly (ethylene terephthalate) (PET), polyimide (PI) and Eco flex are used most often as materials for flexible electronics. Because conductive polymers can be adjusted, are flexible and have different π-conjugated features like PANI, PPy and polythiophene (PT), among others, people are very interested in them. Lately, several reviews have gathered information on the use of fibers and textiles based on metals, carbon compounds and conductive polymers in both wearable electronics and devices for energy storage and harvesting. On the other hand, researchers have not studied the ways in which polymer mesh composites can be applied to various flexible electronics, including bioelectronics, transparent conductors, strain/pressure sensors, electronic skin, flexible displays, energy harvesting and storage systems [89]. Compact, portable sensing systems need the development of flexible printed circuits that can be combined with nanofiber sensors.

7.4. Environmental application and field deployment

Finally, it is not easy to use these sensors in the field for both industrial pollution detection and air quality monitoring. In addition, sensors for electroencephalography (EEG) must function properly in difficult or changeable conditions. It should be capable of handling different temperature and humidity levels, stay clear of fouling and withstand influences from other environmental factors. Today, reviewing the quality of air inside buildings is considered an important environmental concern. Exposure to VOCs in the air inside your home can cause environmental illness. In 2007–2009, the danger of VOCs to health was highlighted thanks to diseases linked to low-quality dry walls used in many homes. Still, because the levels are very low and there is a wide range of VOCs, identifying them is complex. For this reason, search is on for a real-time technique that continuously checks indoor VOCs. Using electronics or assembly of metal/metal oxide nanoparticles along with a special conducting polymer surface, researchers can now choose which VOCs their sensors detect [90]. These nanocomposites are selective because their metal nanoparticles are assembled on the same conducting polymer film. Additionally, there is a need to develop means to build many of these sensors for large area networks and to integrate them with the current monitoring systems used in the environment.

8. Conclusions

Electrospun polymer based nanocomposites have emerged as promising materials for gas sensing due to their lightweight nature, mechanical flexibility, processability and tunable properties. By incorporating nanofillers such as CNTs, graphene, and metal oxides, the sensing performance particularly sensitivity, selectivity and stability can be significantly enhanced. This review highlighted the roles of different polymers (conjugated, thermoplastic, thermosetting and natural) and the impact of key electrospinning parameters like polymer concentration, surface tension, conductivity, and humidity on fiber morphology. The primary sensing mechanisms (chemiresistive, capacitive and optical) were explored demonstrating the versatility of polymer nanocomposites across various detection modes. Recent advancements have enabled room temperature sensing, fast response/recovery times, and improved selectivity through hybrid material systems. Applications span environmental monitoring, medical diagnostics, and VOC detection. However, challenges remain in achieving long term stability, environmental tolerance (e.g., moisture interference) and reproducibility. Future research should focus on optimizing filler dispersion, enhancing sensor robustness under variable conditions, and developing scalable fabrication methods. Integration polymer nanocomposite sensors flexibility in real time portable sensing platforms. Polymer nanocomposites hold substantial promise for next generation gas sensors combining material versatility with functional performance across a broad range of applications.

CRediT authorship contribution statement

Syed Muhammad Imran: Conceptualization, original draft, Writing, review & editing; Muhammad Zafar: Writing, review & editing; Taskeen Zafar: Writing – review & editing, Software; Asifa Amanat: Writing, review & editing, Software; Fazila Khalil: Writing, review & editing; Zulfiqar Ali: review & editing; Wo Young Kim: Resources, Supervision.

Declaration of competing interest

There are no conflicts of interest.

Data availability

Data will be available on demand.

Declaration of generative AI and AI-assisted technologies in the writing process

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1. Introduction

2. Fundamentals of polymer-based nanocomposites

2.1. Nanocomposites
2.2. Techniques used in synthesis of polymer-based nanocomposites
2.3. Types of filler used in polymer based nanocomposites
2.4. Advantages of nanocomposites in gas sensing

3. Electrospinning

3.1. Principle and equipment for electrospinning
3.2. Parameters affecting electrospinning process

4. Gas sensing mechanism in polymer-based nanocomposites

4.1. Chemiresistive sensing mechanism
4.2. Capacitive sensing mechanism
4.3. Optical sensing mechanism

5. Recent advances in polymer-based nanocomposites for gas sensing applications

6. Applications of polymer nanocomposites in gas sensing

6.1. Monitoring of toxic gases
6.2. Medical diagnosis
6.3. Volatile organic compounds (VOC)

7. Challenges and future perspectives

7.1. Stability and reliability issues
7.2. Selectivity and specificity enhancement
7.3. Integration with electronic devices
7.4. Environmental application and field deployment

8. Conclusions

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Recent advancements in polymer based nanocomposites through electrospinning for gas sensing applications

Abstract

Keywords

Carbon-based nanomaterial

Conductive polymer

Functional polymer

Gas sensing

Nanocomposite

1. Introduction

2. Fundamentals of polymer-based nanocomposites

2.1. Nanocomposites

2.2. Techniques used in synthesis of polymer-based nanocomposites

2.2.1. In situ polymerization

2.2.2. Melt intercalation

2.2.3. Solution mixing

2.2.4. Template synthesis

2.3. Types of filler used in polymer based nanocomposites

2.3.1. Carbon nanotubes

2.3.2. Graphene

2.3.3. Conducting polymers

2.4. Advantages of nanocomposites in gas sensing

3. Electrospinning

3.1. Principle and equipment for electrospinning

3.2. Parameters affecting electrospinning process

3.2.1. Voltage

3.2.2. Feed rate

3.2.3. Tip-to-collector working distance (TCD)

3.2.4. Polymer concentration

3.2.5. Surface tension

3.2.6. Conductivity

3.2.7. Relative humidity

4. Gas sensing mechanism in polymer-based nanocomposites

4.1. Chemiresistive sensing mechanism

4.2. Capacitive sensing mechanism

4.3. Optical sensing mechanism

5. Recent advances in polymer-based nanocomposites for gas sensing applications

6. Applications of polymer nanocomposites in gas sensing

6.1. Monitoring of toxic gases

6.2. Medical diagnosis

6.2.1. Disease diagnosis

6.2.2. Implantable medicine

6.3. Volatile organic compounds (VOC)

7. Challenges and future perspectives

7.1. Stability and reliability issues

7.2. Selectivity and specificity enhancement

7.3. Integration with electronic devices

7.4. Environmental application and field deployment

8. Conclusions

CRediT authorship contribution statement

Declaration of competing interest

Data availability

Declaration of generative AI and AI-assisted technologies in the writing process

References

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