Facial Growth of Polyaniline based Sensors for Gas Sensing Application: Langmuir Theoretical Approach

Facial Growth of Polyaniline based Sensors for Gas Sensing Application: Langmuir Theoretical Approach | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Facial Growth of Polyaniline based Sensors for Gas Sensing Application: Langmuir Theoretical Approach Rishi Pal, Sneh Lata Goyal, Ishpal Rawal This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7315668/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Mar, 2026 Read the published version in Polymer Bulletin → Version 1 posted 11 You are reading this latest preprint version Abstract PANI based sensors has been synthesized for methanol detection i.e. pristine PANI and its composites have been synthesized using chemical oxidative polymerization approach with various doping concentration (00, 10, 20 and 40 wt.%) of manganese dioxide. The PANI/MnO 2 composite with 10wt% of MnO 2 has porous structure as well as small particles size as compared to PANI shown by FESEM analysis. The greatest interaction across PANI and MnO 2 nanoparticles lead to the conversion of PANI from the highly oxidized states to oxidized states and is established using Raman investigation. The FESEM and Raman spectroscopy confirms the preparation of PANI and its composites. The sensing response (%), response and recovery time of fabricated sensors towards the methanol environment has been calculated by measuring the change in surface current of samples in different methanol environments with respect to without methanol environment at room temperature. The PANI/MnO 2 composites show the better response as compared to pristine PANI and response increases with increase in dopant concentration as well as ppm levels of methanol. The maximum response was calculated for PANI/MnO 2 composite with 40wt% of MnO 2 which is ~ 48% and better response time 90 seconds at 60ppm of methanol vapors. The better recovery time was observed for PANI at 40ppm level of methanol vapors. The adsorption and desorption of gas molecules under Langmuir kinetic theory for the adsorption and desorption of methanol has also been thoroughly examined, along with any potential theoretical parallels to the mechanism of gas sensing. Using Langmuir adsorption-desorption kinematic fits, theoretical parameters related to the sensing qualities have been assessed from the experimental curves. Raman Spectroscopy FESEM Gas Sensing Langmuir adsorption-desorption Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction The intrinsic conjugated polymers (ICPs) such that polyaniline (PANI), polyacetylene (PA), Polypyrrole (PPY), poly(3,4-ethylene-dioxythiphene) (PEDOT), Polythiophene (PTh) and poly(phenyl vinyl) (PPV) have lot of potential applications like as photovoltaic devices [ 1 ], secondary batteries [ 2 ], electromagnetic shielding [ 3 ], biological sensors/sensors [ 4 – 6 ], fuel cells [ 7 ] batteries [ 8 ], capacitors [ 9 ], solar cells [ 10 ], memory device [ 11 ] and micro-electronic devices [ 12 ] etc. Out of these applications, the gas sensor is an important application in recent days due to presence of hazard gases in the atmosphere. The concentration of hazardous gases increases day by day because of access of industries, access use of vehicles, population and deforestation etc. These hazard gases directly affected the health of human being as well as rest. The above listed applications are possible due to ability of conjugated polymers to alter the electrochemical, optical, chemical, and mechanical properties by changing the monomer ‘or’ dopants with the polymer. The most common intrinsic conjugated polymer polyaniline used in all applications. Due to the good environmental stability, easy to synthesized and doped with other particles, ability to retain its processing properties, the PANI and its composites [ 13 – 15 ] has much attention by the researchers. Earlier the sensor for the various gas sensing has been used prepared by the PANI and its derivatives [ 16 , 17 ]. Like the hazard gases, the access of organic chemicals such as methanol is dangerous for health and its vapors are toxic in nature. This is simple aliphatic alcohol which is used in drug industries, chemical industries, medicine, clinical fields, even biotechnological process, aspects of hospitals, industrial production, antiterrorism, science and technology, agricultural and ecological monitoring, safeguard, as solvent in paints and as anti-freeze in cars [ 18 – 21 ]. The regular use of methanol and regular work in affected area of methanol gives lots of problems to human health like headache, loss of vision, central nervous system, drowsiness and finally death depending upon level of dose. Thus, the fabrication of appropriate sensor becomes more important which can detect all ppm levels of all hazard gases. The target to efficient sensors along appropriate choice of sensing substance remains important way to appreciable work [ 22 , 23 ]. The performance of sensor materials is known to be significantly impacted by their composition. In order to improve sensor qualities like high response, low operating temperature, and fast response-recovery time, an organic hybrid may arise, which could have a synergistic impact and improve performance. Hybridisation enhances the characteristics of pristine organic materials, as demonstrated by research on a few organic hybrids for gas sensor applications. The gas sensing properties of conjugated polymers are directly connected with the heterogeneity of materials. In the gas sensing characteristics, the sensing mechanisms are most important and required high alertness. Thus, for the better understanding of gas sensing, the charge transportation is important under gas environment. Therefore, in this study, we have been synthesized PANI and PANI/MnO 2 composites for vapors sensing of methanol study based on electrical properties of these materials and a good result may be achieved with interaction between PANI and its composites with methanol vapors. The prepared PANI and its composites were methodically explored for morphological and structural conformations, and the pertinency of the growth materials are recognized for gas sensing applications. The gas sensing properties of synthesized samples have been analyzed with their experimental data and Langmuir theoretical fitting in adsorption and desorption process. Experimental details Preparation of PANI The chemicals required in the growth of desired samples were obtained from the sigma Aldrich (purity more than 99.9%). For the preparation of PANI, aniline hydrochloride solution with 20mM concentration and ammonium persulphate (APS) solution with 25mM concentration were prepared in different beakers under the constant stirring for an hour. After that both solutions were left to cool for an hour in refrigerator. Aniline hydrochloride solution was kept in an ice bath with maintained temperature below 4˚C and added APS solution drop wise, stirred for one hour for oxidization and proper mixing and left for overnight in refrigerator to complete their polymerization. Next day, the precipitate of prepared sample was collected on Wattmann’s filter paper and washed with a sufficient amount of 1M HCl. After that resultant yield was washed with methanol and distilled water alternatively till the filtrate became colorless. The resultant yield obtained of PANI was dried in air and then in vacuum at 45˚C. The prepared sample was converted in powder form with the help of agate pestle mortar and named as S1. PANI prepared under these conditions were taken as standard sample. Preparation of PANI/Manganese dioxide composites For the preparation of PANI/MnO 2 composites, 0.1M solution of 10 weight percentage of MnO 2 is added to 20mM aniline hydrochloride solution when it kept in ice bath with maintained at the temperature between 0–4˚C. Then the precooled 25mM aqueous solution of APS was added drop wise in this solution, maintained at the same temperature then stirred for an hour for proper mixing and oxidization. The resultant solution was left for 24 hours at rest to polymerize in refrigerator. Next day, the precipitate of prepared PANI/MnO 2 composite was collected on Wattmann’s filter paper and washed with a sufficient amount of 1M HCl. After that resultant yield was washed with methanol and distilled water alternatively till the filtrate became colorless. The resultant yield obtained of PANI/MnO 2 composite was dried in air and then in vacuum at 45˚C. The prepared sample was converted in powder form with the help of agate pestle mortar and named as S2. The above-mentioned synthesis route was followed for the preparation of two more PANI/MnO 2 composites with 20 and 40 weight percentage of MnO 2 and named as S3 and S4 respectively. Characterization for PANI and its composites The morphology of the growth samples was analyzed through Field Emission Scanning Electron Microscope (FE-SEM) (FEI NOVA NANO SEM 450) model. The Raman spectroscopy was analyzed through the Jobin Yvon Horibra LABRAM-HR visible (400-1100nm) spectrometer. The Argon laser with 473nm wavelength and 25mW power was used as excitation laser source in Raman spectroscopy. Sensor fabrication For the gas sensing application, we required the materials which can sense the incident gas. So, we used PANI and its composites for the same. For this we required to make sensor which is defined as a resistor whose electrical properties like electrical conductivity changes under the gaseous atmosphere. The sensor contains one or more electrodes on the surface of sensing materials for study of the gas sensing properties. To build up the sensor, we need to convert powder sample in pellet ‘or’ film form. Here in this study, we make sensor in pellet shape. The pellets of prepared samples had been made by using the hydraulic pellet press machine. The die set of diameter 13mm was used to prepare pellet and sufficient amount of sample was put in die set and 100Kg/cm 2 of pressure was applied for all samples. The thicknesses of all pellets were observed to be approximately 0.5mm. To convert the pellet in sensor form, we make two parallel electrodes on one sided surface of pellet using silver (Ag) paint. The PANI sensor (Ag/PANI/Ag) and its composites sensors (Ag/PANI-MnO 2 /Ag) used for study of gas sensing properties are shown in Fig. 1 (a). The gap between parallel electrodes were calculated and found approximately to be 1mm. The sample holder used in the gas sensing properties has 500ml capacity as shown in Fig. 1 (b) which is made by stainless steel. This sample holder was used to observe variations in electrical current under the methanol environment at room temperature [ 24 , 25 ]. The rotary pump (BC2410; British Thomson Houston Ltd.) was attached to the sample holder which was used to create vacuum in the sample holder of order of 10 -3 mbar at room temperature. The Keithley 6517A electrometer and DNM-121 Nano-ammeter were used to calculate electrical parameters for DC conduction during the gas sensing at room temperature. Results and Discussion Field Effect Scanning Electron Microscope The morphological study of prepared PANI (S1) and PANI/MnO 2 composite (S2) was analyzed with help of field effect scanning electron microscope (FE-SEM). Figure 2 (a,b) represents the morphological images of PANI (S1) and PANI/MnO 2 composite (S2) which shows that S1 has bigger molecular size as compared to S2, S2 have more porous structure as compared to S1. This also indicates that the S1 is amorphous in nature while S2 is semi-crystalline in nature as well as uniform distribution of MnO 2 particles in PANI matrix which allow to better adsorption phenomenon by composites. From the FE-SEM images, it is also clear that the morphology of PANI is directly affected with doping of MnO 2 . It has also been observed that the sample prepared with 10wt% doping of MnO 2 having agglomerates of range 0.3 to 3 µm, suggesting that the micro-structural formation of PANI/MnO 2 composites. Raman Spectroscopy The optical study of these prepared samples has been analyzed by using the Raman spectroscopy in the Raman shift range from 490–2180 cm -1 . In the Raman spectrum of all prepared samples, the all necessary peaks confirmed the preparation of desired samples. The Raman spectrum of PANI/MnO 2 is quite similar as PANI. The doublet around 1600cm -1 is observed which is overlapped band of benzonoid and quinoid rings of stretching vibration. The band at 1620 cm − 1 is associated with C-C stretching vibration of the benzonoid ring and the band at 1588cm -1 is associated with C = C stretching vibration of the quinoid ring. The band at 1550cm -1 represents the N-H bending whereas the band at 1492cm − 1 occurred which corresponds to C = N stretching vibration of the quinoid ring. Moreover, bands occurred in the Raman spectrum in which the band at 1417cm -1 is associated with C-C stretching of phenazine structure and another band at 1166 cm − 1 corresponds to C-H bending in quinoid. The band at 808 cm − 1 is associated with amine deformation (C-N-C bending) and band at 516cm -1 is associated with out of plane deformation of benzonoid ‘or’ amine in plane deformation. Hence the Raman spectra of prepared samples show the typical bands associated to the polyaniline emeraldine salt form [ 26 , 27 ]. With the variation in doping concentration, the intensity of most peaks is enhanced which is cleared from the Fig. 3 (a). To analyze enhancement in peaks, we have to deconvolute band around ~ 1335cm − 1 using the Gaussian (80%) + Lorentzian (20%) fitting in two components, which represents the semi-quinone radical stretching mode ‘or’ C ~ N + stretching in polaronic from polarons and the intensity and area under curve increases with doping concentration as shown in Fig. 3 (b). For the better understanding of charge carrier and gas sensing mechanism, we also deconvolute the Raman sift region from 1450cm − 1 to 1650cm − 1 using the Gaussian (80%) + Lorentzian (20%) fitting in four components as shown in Fig. 3 (c) for the samples S1, S2 and S3. From the Fig. 3 (c) it is clear that as the doping takes place in pristine PANI, the area under the curve of bands presents at 1335, 1492, 1550, 1588 and 1617cm − 1 increases shown in Fig. 3 (d) and Table 1 . The benzonoid (at 1617cm − 1 ) and quinoid (at 1588cm − 1 ) rings are directly associated with bipolarons and polarons states respectively. As the doping concentration increases, the area under curve of these two bands increases that means the concentration of bipolarons and polarons increases. With the increase in these charge carriers concentration, the ratio of area under curve of benzonoid to quinoid rings (A B /A P ) found to be increased from 0.88 to 1.33 as shown in Table 1 . The increase in A B /A P suggest to increase in bipolarons more than polarons i.e. the transition of polaronic from bipolaronic state and increase in oxidation level with doping of MnO 2 . Table 1 Area under the C = N stretching vibration of the quinoid ring, band of N-H bending, benzonoid and quinoid rings and A B /A Q ratios for the samples S1-S3 Sample Area Under Curve (x10 − 4 a.u) at A B /A Q 1335cm − 1 1492cm − 1 1550cm − 1 1588cm − 1 (A Q ) 1617cm − 1 (A B ) S1 11.64 10.46 10.13 10.50 09.25 0.88 S2 15.76 11.21 12.13 12.15 12.48 1.03 S3 24.43 12.81 29.23 12.78 17.11 1.34 Gas Sensing studies In the gas sensing applications, the resistance of the sensing materials becomes more important. Like this, the three type of resistance comes across in the gas sensing applications when we sense the gas incident on sensor made by organic semiconducting materials. The first is interface resistance which occurred due to interface between pellet of the sample and prepared electrode on pellet. The second is the surface resistance which is due to the surface of particles of sample and third is bulk resistance which is inside the resistance of particles of sample. More ever, the silver paste of electrodes may have some resistance which comes in role during the conduction. To understand the complete resistance of sensor, the Fig. 4 show the schematic representation of combination of all resistances [ 28 ]. The total conductivity of the sensor can be expressed as [ 29 ] $$\:\frac{1}{\sigma\:}=\:\frac{1}{{\sigma\:}_{c}}+\:\frac{1}{{\sigma\:}_{h}}+\:\frac{1}{{\sigma\:}_{i}}$$ 1 Where σ, σ c , σ h and σ i are total conductivity, intermolecular conductivity, intermolecular hopping conductivity and ionic conductivity respectively. The total conductivity can be enhanced by the change in any resistance out of interface, surface and bulk resistance as well as change in electrode materials but out of these the bulk resistance plays important role due to the hopping mechanism for the conduction through bulk area of sample. With the change in dopant and dopant concentration, the intermolecular conductivity may be changed due to enhancement in physical and chemical properties. The intermolecular hopping conductivity is associated with the polymer chain. The variation in intermolecular hopping conductivity takes place with the variation in polymer chain, hydrogen bonding, dipole-dipole interactions and crystallinity. The ionic conductivity may be enhanced when ions of samples come in contact with the bombarded organic vapors under organic vapors atmosphere. In the present study, we analyzed the conduction properties of sensor made by PANI (Ag/PANI/Ag) and its composites (Ag/PANI-MnO 2 /Ag) under the different environment of methanol vapors at room temperature. The sensor was put in the two probe sample holder to study the conduction properties under the vacuum circumstances of pressure 10 − 3 mbar and at room temperature for 1 hour before gas sensing observation to remove all unwanted gas particles presented in gas chamber [ 30 ]. After the removal of all unwanted atmospheric particles from chamber, no humidity will affect during the gas sensing observation. In the gas chamber two copper strips present which were contacted with the silver electrodes of the sensor for the gas sensing phenomenon. The baseline current (current of samples before exposure of organic vapors) noticed before exposing the gaseous vapors for all samples S1-S4 at voltage 3V and under 10 − 3 mbar pressure. For study the gas sensing properties, all valves of the gaseous chamber should be closed properly. By using the micro-syringes, the gaseous vapors with desirable concentration inserted through inlet valve present on the gas testing chamber. When the sensor come in contact with the gaseous particles, the initial current changed which may be drastically ‘or’ linearly as well as increases ‘or’ decreases. The sample was stabilized under the vacuum circumstances before we start the observation. After the vacuum stabilization, organic vapors of methanol with 40ppm concentration were injected through the needle which is present at right-top side of gas chamber as shown in Fig. 1 When the methanol vapors were injected in the gas chamber, a sudden change in current was observed. The increase in current of PANI sensor is noticed under exposure of methanol vapors till it saturate at constant voltage 3V, the variation of current is observed due to the adsorption of methanol molecules in the PANI matrix. After sometime, no more change is observed in current because maximum adsorption of methanol vapors take place and no more adsorption is allowed. Then the inserted methanol vapors were removed from the gas chamber with the use of vacuum pump and this time the decrease in current was observed due to the desorption of methanol vapors from PANI matrix. The measurement was continued until this doesn’t reach the pre-exposure value of air current of PANI (current value before introducing the vapors in gas chamber). The above reported procedure was followed for the next cycle with 60ppm concentration of methanol vapors and behavior of current was noticed. Under the methanol environment, the variation of current takes place because methanol vapors reacted with the PANI molecules. Generally, after the complete desorption process, the current should reach at its initial value of current of sensor but some methanol vapors adsorbed by the inner layers of PANI matrix which doesn’t come in role during desorption process and high value of current is observed as compared to pre-exposed current. The previously followed procedure for the PANI sensor, the same repeated for the PANI/MnO 2 composites for both concentrations 40ppm and 60ppm levels. The enhancement of current in the exposure of methanol vapors have been noticed which leads to make an effective investigation of gas sensing application at different ppm levels as well as increase in dopant concentration. This is comparative study for PANI and its composites for gas sensing application under the same environmental circumstances. The electric behavior of prepared samples take suitable variation in the form of change in current ‘or’ resistance. From this observation, it is cleared that the adsorption of methanol vapors directly affected the electrical properties of sensor and these electrical properties is different for different ppm levels as well as different dopant concentration. So, the ppm levels of methanol vapors directly connected with change in current ‘or’ conductivity. The result taken from the gas sensing procedure for pristine PANI and its composites were graphically represented and compared with our objective of experiment. The enhancement in the electric current is less for pristine PANI (S1) as compared to its composites (S2-S4) with MnO 2 at the same ppm level which may be clearly understood from the Fig. 5 . The maximum saturated values of current increases with increase in ppm levels from 40ppm to 60ppm as well as increase in dopant concentration from 10wt% to 40wt% of MnO 2 . The minimum variation was observed for pristine PANI (S1) while maximum variation was observed for its composite (S4) in current. The variation in current increases with increase in dopant concentration, this may be due to the increase in available sites for the adsorption of methanol vapors which are cleared from the FE-SEM images of PANI (S1) and its composite (S2). Hence, the hybridization between PANI and manganese dioxide particles provides an appropriate advantage for sensing of methanol vapors towards the MnO 2 . The increase in current under the methanol environment shows the reducing agent behavior of methanol. This signifies that the methanol injected the charge careers as electrons in to samples which results in the enhancement of current ‘or’ conductivity under the methanol environment. In the gas sensing phenomenon, Response (%) is the most important factor to understand effect of vapors on sensor which is defined as the ratio of change in current (ΔI = I g -I o ) to initial current (I o ) (current before the exposure of vapors). Where I g is current under the vapors atmosphere [ 31 ] $$\:Response\:\left(\%\right)=\:\frac{\varDelta\:I}{{I}_{o}}x100=\:\frac{{I}_{g}-{I}_{o}}{{I}_{0}}x100$$ 2 The above Eq. ( 2 ) is used to calculate response in terms of response (%) as shown in Fig. 6 which represents the variation in response (%) with function of time for PANI (S1) and its composites (S2-S4) for 40ppm and 60ppm levels at room temperature. As the ppm levels and dopant concentration has been changed, the variation in response was also observed which can be easily understood by Fig. 6 . So, the response becomes more interesting for PANI/MnO 2 as compared to pristine PANI according to our observation. The minimum response (%) was calculated for S1 which is 17.69% and 19.51% while maximum response (%) was calculated for S4 which is 43.30% and 48.39% at 40ppm and 60ppm respectively. Like as the response (%), the response and recovery time is also two more important factors in the gas sensing application. The response time is defined as time in which the response (%) increases up to 90% values of maximum response during the adsorption process while the recovery time is defined as time in which the response (%) remains 10% of the maximum response (decay to 90% of response) during the desorption process as shown in Fig. 6 . The response and recovery curve was also analyzed which stated that the variation in current is sharply during adsorption and desorption for all prepared samples. The response and recovery time was calculated for the S1-S4 from the graphs (Fig. 6 ). The response and recovery time is different for the different samples at different and same ppm levels. The response time decreases with increase in ppm levels as well as dopant concentration while the recovery time increases with increase in ppm levels as well as dopant concentration for the samples S1-S4 as noted down in Table 2 and plotted as Fig. 7 . Table 2 response (%), response and recovery time of samples (S1-S4) for different ppm levels Sample Response (%) Response time (s) Recovery time (s) 40ppm 60ppm 40ppm 60ppm 40ppm 60ppm S1 17.69 19.51 230 180 190 210 S2 23.38 26.11 210 140 210 240 S3 29.92 33.15 170 120 250 280 S4 43.30 48.39 140 90 290 330 Theoretical approach for the gas sensing application The adsorption and desorption are two important factors for the better understanding of gas sensing phenomenon. During the ejection of vapors, the sensor reacts with the vapors and starts the adsorption of vapors by sensor while during the removal of vapors, the reaction has been stopped between sensor and vapors and desorption comes in role. In 1918, the rate of adsorption and rate of desorption has been explained by Langmuir. The theory of Langmuir adsorption and desorption gives some important factors for the gas sensing application such that (a) homogeneity should be present at the gas sensing surface (b) in the monolayer adsorption; available sites of surface should contribute (c) the presence of others molecules doesn’t affect the energy of adsorbed molecules. The surface coverage of the sites by the vapors given by θ = N(t)/N* and this is defined as the ratio of no. of sites (N(t)) which are used in the adsorption phenomenon by vapor particles to the total no. of sites (N*) available for the adsorption phenomenon. N(t) is the no. of sites at any time t during the adsorption. The Langmuir gave their fitting Eq. (3) this followed for the adsorption process for the sensing of organic vapors with double exponential factor which is written below [ 32 ] y = \(\:\frac{N\left(t\right)}{{N}^{*}}\) = \(\:{A}_{1}\left(1-\text{exp}\left(\frac{-t}{{\tau\:}_{A1}}\right)\right)+{A}_{2}\left(1-\text{exp}\left(\frac{-t}{{\tau\:}_{A2}}\right)\right)\) (3) Where A 1 , A 2 , τ A1 and τ A2 are constants. The constants A 1 and A 2 has unit of pressure while constants τ A1 and τ A2 has unit of time. On the insertion of vapors in gas chamber, the adsorption of vapor particles start by the sites and increase in N(t) take place. After some time, the N(t) become equal to N* and system comes in equilibrium means further no more variation will be observed in current ‘or’ resistance and that time the rate of adsorption become equal to rate of desorption. The calculated values of adsorption factors are tabulated in Table 3 . On the removal of vapors, desorption comes in role which is simple chemical process [ 32 ]. The adsorbed vapors remove from the sites of the surface during the desorption process. For the desorption process, Langmuir gave another fitting Eq. ( 4 ) which is followed for the desorption process with the single exponential factor and given below [ 33 ] $$\:y=\:{D}_{1}\text{exp}\left(\frac{-t}{{\tau\:}_{D}}\right)+{D}_{2}$$ 4 Where D 1 , D 2 and τ D are constants. The D 1 and τ D has unit of pressure and time respectively and D 2 is correction factor. In the Fig. 6 (S1-S4), the theoretical fitting curve has been plotted which is calculated from the adsorption and desorption rate Eqs. (3) and ( 4 ) respectively as well as experimental calculated data also plotted which are well fitted and satisfied for the all. The calculated values of desorption factors are tabulated in Table 4 . This shows the evidence for strong correlation between theoretical data, experimental data and Eq. (3, 4 ) as tabulated in Table 5 . Table 3 Values of constants A 1 , τ A1 , A 2 and τ A2 for S1-S4 calculated from Langmuir curve fitting of adsorption Constant S1 S2 S3 S4 40ppm 60ppm 40ppm 60ppm 40ppm 60ppm 40ppm 60ppm A 1 1.04E-3 -0.176 3.513E-6 -1.610 1.031E-8 -53.912 7.77E-7 -61.413 τ A1 -26.970 -127.076 -15.985 -163.56 -10.406 -304.385 -10.041 -273.63 A 2 -35.025 -47.960 -54.712 -147.84 -99.305 -609.450 -275.38 -663.73 τ A2 -141.847 10.809 -141.869 10.809 -148.550 10.809 -194.29 2.248 Table 4 Values of constants D 1 , τ D and D 2 for S1-S4 calculated from Langmuir curve fitting of desorption Constants S1 S2 S3 S4 40ppm 60ppm 40ppm 60ppm 40ppm 60ppm 40ppm 60ppm D 1 2028.76 80615.30 2266.57 66442.26 1453.93 42072.17 1517.61 53541.80 τ D 65.266 74.510 165.166 186.915 236.339 211.670 166.78 174.413 D 2 30.788 26.672 -16.338 24.293 -50.087 22.688 34.726 38.156 Table 5 Values of %age fit agreed with data for S1-S4 calculated from Langmuir curve fitting of adsorption and desorption Sample Concentration of vapors (ppm) Adsorption (fit agreed with data) (%) Desorption (fit agreed with data) (%) S1 40 99.74 99.48 60 98.78 99.78 S2 40 99.95 99.70 60 98.82 99.86 S3 40 99.48 99.80 60 99.00 99.95 S4 40 99.67 99.96 60 97.78 99.87 Gas sensing mechanism for PANI and its composites When the methanol is injected in gas container, its particles diffuse in PANI matrix easily due to its small size and show high interaction with PANI matrix. Due to diffusion of methanol particles the conductivity of PANI increases. Under the methanol environment, the concentration of polarons increases and these polarons were localized in character. Thus, resultant increase in conductivity occurred due to increase in polarons of PANI by additional polarons from methanol vapors. The present polarons in PANI are converted into bipolarons at the same time polarons produced. This increase in conductivity happened due to ionic conduction, with the methanol acting as a solvent for the chloride ions present in PANI [ 34 ]. Under the methanol environment, increase in conductivity shows the reducing behavior of methanol toward the PANI and increase the polarons and bipolarons in PANI. Under the methanol environment of PANI, the hydrogen bonding takes place via lone pairs on oxygen of methanol and hydrogen of PANI. Thus, the bond between nitrogen and hydrogen of benzonoid part of PANI become weak and show weak interaction which produce the polarons. Like this methanol also reacted with nitrogen of PANI by the hydrogen bonding which leads to polarons conversion in bipolarons (Fig. 8 ). In the PANI, nitrogen atoms are protonated, so these are unavailable for taking part in hydrogen bonding with hydrogen of methanol’s hydroxyl group. Due to hydrogen bonding, the PANI chain pushed apart and uncoiling which gives to increase in conductivity under methanol environment. The sensing mechanism becomes more complicated in composites of PANI due to presence of both p-type PANI and n-type metal oxide in the same system. In composites, gas sensing enhanced by hybridization of metal oxide particles (MnO 2 ) with PANI which gives better gas sensing ability. The uniform dispersion of MnO 2 particles in PANI matrix is one important reason for the enhancement of gas sensing, this provides better porous surface of sensing pellet (Ag/PANI-MnO 2 /Ag) as compare to PANI pellet (Ag/PANI/Ag) [ 35 , 36 ]. This could also be observed by already shown FE-SEM images. Besides this, another important factor is structure of samples for the sensing of composites. In the composites, polymer-metal oxide junction is formed as PANI- MnO 2 where PANI is p-type while MnO 2 is n-type. In PANI and MnO 2 , holes and electrons are majority charge carriers respectively. In composites, some holes from the PANI and some electrons from the MnO 2 diffuse across junction and depletion region formed between PANI and MnO 2 . Hence at junction, electrons transferred to PANI from MnO 2 thus further positively charge layer created on the MnO 2 . Between PANI and MnO 2 the p-n hetero-junction formed so activation energy decreases and gives easily adsorption of methanol vapors. On adsorption of methanol vapors, the increase in current shows the electron donating nature of methanol which increases the efficiency of gas sensing [ 37 , 38 ] Tai et al. [ 39 ] and Li et al. [ 40 ] has reported earlier energy level diagram of PANI/metal oxide nanocomposites for understanding of gas sensing mechanism. The band gap between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) levels in PANI is small as compare to energy band gap between valance band (VB) and conduction band (CB) as shown in Fig. 9 . They explained that due to matching in band gap between the lowest unoccupied molecular orbital (LUMO) of PANI and conduction band (CB) of MnO 2 , the enhancement of charge separation for charge transfer occurring between the lowest unoccupied molecular orbital (LUMO) of PANI and conduction band (CB). For the gas sensing, both PANI and MnO 2 particles take adsorptions of vapors in PANI/MnO 2 composites. On the surface of MnO 2 particles, the oxygen molecules adsorbed and following reaction takes place for the gas sensing [ 41 ] Under environment of reducing gas, the reducing gas injected the electrons in the sensing sample and potential barrier decreases, finally conductivity increases [ 42 ]. Thus, the generally action of the reducing gas (R) on the sensing pellet acts as given below The reducing gas adsorbed the oxygen and an electron ejected which leads to increase in carrier density as well as conductivity i.e. decreases in barrier width (depletion layer). On the other hand, the methanol vapors were adsorbed by the available sites in PANI. The methanol vapors provides more electrons to the HOMO levels of PANI and due to applied field these electrons jump at LUMO of PANI, finally these electrons shifted to CB of MnO 2 as shown in Fig. 9 which further enhances the conduction and leads to increase in current of sensing pellet. At last, it is concluded that in PANI/ MnO 2 composites more electrons are available to take part in conduction as compared to pure PANI for gas sensing [ 43 ]. Conclusion The chemical oxidative polymerization method was used to synthesize PANI and its composites with different weight% of MnO 2 . FESEM image of composite shows the uniform distribution of MnO 2 particles in the PANI matrix and leads to give porous structure. The availability of all required peaks in Raman spectrum of PANI and its composites leads to evident of preparation of desired samples. The increase in ratio of area under the curve of bipolaronic to polaronic band prove that the increase in conductivity and conjugation length at room temperature with dopant concentration. The porous structure of composites leads to more adsorption of methanol vapors as compared to PANI. Using the PANI/MnO 2 composite (40wt% of MnO 2 ) as sensor, the maximum response ~ 48% and better response time 90sec was achieved at 60ppm level. The adsorption and desorption process using the Langmuir equation gives the approximately 99% fitting with the experimental calculated data for all prepared samples. This fitting is a good agreement between the theoretical and experimental data. The prepared samples have single energetic adsorption sites for the adsorption of methanol vapors which is suggested by the theoretical fitted equation for the adsorption process. Declarations Author Contribution Dr. Rishi Pal: Write original manuscript, characterization.Dr. Sneh Lata Goyal: Supervision.Dr. Ishpal Rawal: Review and edit. Acknowledgments The authors are thankful for financial assistance from DST-FIST for providing XRD facility. We also acknowledge the UGC-CSR Indore for provide FESEM and Raman facilities. References Chander S, Tripathi SK, Kaur I (2025) Development in PANI based solar cells: Progress on high-throughput methods, physical-chemical properties and device performance. Next Mater 8:10089 Su X, Liu Y, Liao Z, Bi Y, Ma M, Chen Y, Ma Y, Wan F, Chung KL (2022) Recent progress of polyaniline-based composites in the field of microwave absorption. Synth Met 291:117190 Pal R, Goyal SL, Gupta V, Rawal I (2019) MnO 2 -Magnetic Core-Shell Structured Polyaniline Dependent Enhanced EMI Shielding Effectiveness: A Study of VRH Conduction. 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1","display":"","copyAsset":false,"role":"figure","size":278107,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e The schematic representation of sensor of PANI and its composites \u003cstrong\u003eb\u003c/strong\u003eStainless steel metallic sample holder for gas sensing measurements\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7315668/v1/96c3779baab3a811b9ceb9a5.png"},{"id":96603610,"identity":"f118cc23-1f68-49a0-a041-1a3e1be7bf1d","added_by":"auto","created_at":"2025-11-24 09:10:37","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":786987,"visible":true,"origin":"","legend":"\u003cp\u003eFE-SEM image of \u003cstrong\u003ea\u003c/strong\u003e PANI (S1) and \u003cstrong\u003eb\u003c/strong\u003e PANI/MnO\u003csub\u003e2\u003c/sub\u003e composite (S2) respectively\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7315668/v1/9a965c24f31bb2f911ee3111.jpeg"},{"id":96603200,"identity":"a994a7a1-3d8d-4022-8cdb-f20d42b490de","added_by":"auto","created_at":"2025-11-24 09:07:29","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":986125,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Raman shift of S1-S3, deconvoluted Raman shift of \u003cstrong\u003eb \u003c/strong\u003eC~N\u003csup\u003e+\u003c/sup\u003e stretching (1335cm\u003csup\u003e-1\u003c/sup\u003e) in polaronic from polarons \u003cstrong\u003ec\u003c/strong\u003e bands at 1492, 1550, 1588 and 1617cm\u003csup\u003e-1\u003c/sup\u003e for S1-S3 \u003cstrong\u003ed\u003c/strong\u003e variation in area under curve as function of dopant-on-dopant concentration\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7315668/v1/bd73cacc601236a7331a02bd.jpeg"},{"id":96469196,"identity":"150d63f8-d226-48ee-bc6c-c41364c3bef0","added_by":"auto","created_at":"2025-11-21 11:54:31","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":128935,"visible":true,"origin":"","legend":"\u003cp\u003eelectrical equivalent circuit diagram of sample for the conduction\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7315668/v1/500b03fdf3d71ef6823a0e7d.png"},{"id":96603982,"identity":"deac44a1-ec5e-4b6e-bc7f-c453f06a1441","added_by":"auto","created_at":"2025-11-24 09:12:20","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":864615,"visible":true,"origin":"","legend":"\u003cp\u003eVariation in current as a function of time under different methanol vapors environment for S1-S4 with Langmuir theoretical fitting for adsorption and desorption phenomenon\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7315668/v1/b6e90de219205a077a7fb92a.jpeg"},{"id":96603375,"identity":"53cdb9e9-2aa0-44b7-9b50-b48ccaad0335","added_by":"auto","created_at":"2025-11-24 09:08:41","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1075865,"visible":true,"origin":"","legend":"\u003cp\u003eVariation in Response as function of time for S1-S4 in different ppm levels\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7315668/v1/e9f9f65439dc5d7f29bc444e.jpeg"},{"id":96469206,"identity":"a8ae0439-9616-489e-8581-9a096d0981c1","added_by":"auto","created_at":"2025-11-21 11:54:31","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":501606,"visible":true,"origin":"","legend":"\u003cp\u003eVariation in \u003cstrong\u003ea \u003c/strong\u003eresponse \u003cstrong\u003eb\u003c/strong\u003e response time \u003cstrong\u003ec\u003c/strong\u003e recovery time as function of dopant concentration under methanol environment with 40ppm and 60ppm.\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7315668/v1/bc7a8260cc850059fb3a9d93.jpeg"},{"id":96603491,"identity":"82c72248-5387-435e-b813-aae53b83f311","added_by":"auto","created_at":"2025-11-24 09:09:34","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":5808,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentation of hydrogen bonding reaction between PANI and Methanol.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-7315668/v1/328d61c9090514d0566bf1fa.png"},{"id":96469210,"identity":"e01f87b2-ff54-4f6e-8a2b-051007f132be","added_by":"auto","created_at":"2025-11-21 11:54:31","extension":"jpeg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":581647,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation of energy level diagram for S2-S4 in presence of air and Methanol environment (change to mno2)\u003c/p\u003e","description":"","filename":"floatimage9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7315668/v1/de74dcc74b2688582c1eb71f.jpeg"},{"id":104252033,"identity":"e241081f-205a-4de4-91ac-121640a3636e","added_by":"auto","created_at":"2026-03-09 16:16:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6144528,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7315668/v1/d5e60c39-5bd7-41a9-b5a7-9a58308f43d3.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Facial Growth of Polyaniline based Sensors for Gas Sensing Application: Langmuir Theoretical Approach","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe intrinsic conjugated polymers (ICPs) such that polyaniline (PANI), polyacetylene (PA), Polypyrrole (PPY), poly(3,4-ethylene-dioxythiphene) (PEDOT), Polythiophene (PTh) and poly(phenyl vinyl) (PPV) have lot of potential applications like as photovoltaic devices [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], secondary batteries [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], electromagnetic shielding [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], biological sensors/sensors [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], fuel cells [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] batteries [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], capacitors [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], solar cells [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], memory device [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] and micro-electronic devices [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] etc. Out of these applications, the gas sensor is an important application in recent days due to presence of hazard gases in the atmosphere. The concentration of hazardous gases increases day by day because of access of industries, access use of vehicles, population and deforestation etc. These hazard gases directly affected the health of human being as well as rest. The above listed applications are possible due to ability of conjugated polymers to alter the electrochemical, optical, chemical, and mechanical properties by changing the monomer \u0026lsquo;or\u0026rsquo; dopants with the polymer. The most common intrinsic conjugated polymer polyaniline used in all applications. Due to the good environmental stability, easy to synthesized and doped with other particles, ability to retain its processing properties, the PANI and its composites [\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] has much attention by the researchers. Earlier the sensor for the various gas sensing has been used prepared by the PANI and its derivatives [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eLike the hazard gases, the access of organic chemicals such as methanol is dangerous for health and its vapors are toxic in nature. This is simple aliphatic alcohol which is used in drug industries, chemical industries, medicine, clinical fields, even biotechnological process, aspects of hospitals, industrial production, antiterrorism, science and technology, agricultural and ecological monitoring, safeguard, as solvent in paints and as anti-freeze in cars [\u003cspan additionalcitationids=\"CR19 CR20\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The regular use of methanol and regular work in affected area of methanol gives lots of problems to human health like headache, loss of vision, central nervous system, drowsiness and finally death depending upon level of dose. Thus, the fabrication of appropriate sensor becomes more important which can detect all ppm levels of all hazard gases. The target to efficient sensors along appropriate choice of sensing substance remains important way to appreciable work [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The performance of sensor materials is known to be significantly impacted by their composition. In order to improve sensor qualities like high response, low operating temperature, and fast response-recovery time, an organic hybrid may arise, which could have a synergistic impact and improve performance. Hybridisation enhances the characteristics of pristine organic materials, as demonstrated by research on a few organic hybrids for gas sensor applications.\u003c/p\u003e\u003cp\u003eThe gas sensing properties of conjugated polymers are directly connected with the heterogeneity of materials. In the gas sensing characteristics, the sensing mechanisms are most important and required high alertness. Thus, for the better understanding of gas sensing, the charge transportation is important under gas environment. Therefore, in this study, we have been synthesized PANI and PANI/MnO\u003csub\u003e2\u003c/sub\u003e composites for vapors sensing of methanol study based on electrical properties of these materials and a good result may be achieved with interaction between PANI and its composites with methanol vapors. The prepared PANI and its composites were methodically explored for morphological and structural conformations, and the pertinency of the growth materials are recognized for gas sensing applications. The gas sensing properties of synthesized samples have been analyzed with their experimental data and Langmuir theoretical fitting in adsorption and desorption process.\u003c/p\u003e"},{"header":"Experimental details","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003ePreparation of PANI\u003c/h2\u003e\u003cp\u003eThe chemicals required in the growth of desired samples were obtained from the sigma Aldrich (purity more than 99.9%). For the preparation of PANI, aniline hydrochloride solution with 20mM concentration and ammonium persulphate (APS) solution with 25mM concentration were prepared in different beakers under the constant stirring for an hour. After that both solutions were left to cool for an hour in refrigerator. Aniline hydrochloride solution was kept in an ice bath with maintained temperature below 4˚C and added APS solution drop wise, stirred for one hour for oxidization and proper mixing and left for overnight in refrigerator to complete their polymerization. Next day, the precipitate of prepared sample was collected on Wattmann\u0026rsquo;s filter paper and washed with a sufficient amount of 1M HCl. After that resultant yield was washed with methanol and distilled water alternatively till the filtrate became colorless. The resultant yield obtained of PANI was dried in air and then in vacuum at 45˚C. The prepared sample was converted in powder form with the help of agate pestle mortar and named as S1. PANI prepared under these conditions were taken as standard sample.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003ePreparation of PANI/Manganese dioxide composites\u003c/h3\u003e\n\u003cp\u003eFor the preparation of PANI/MnO\u003csub\u003e2\u003c/sub\u003e composites, 0.1M solution of 10 weight percentage of MnO\u003csub\u003e2\u003c/sub\u003e is added to 20mM aniline hydrochloride solution when it kept in ice bath with maintained at the temperature between 0\u0026ndash;4˚C. Then the precooled 25mM aqueous solution of APS was added drop wise in this solution, maintained at the same temperature then stirred for an hour for proper mixing and oxidization. The resultant solution was left for 24 hours at rest to polymerize in refrigerator. Next day, the precipitate of prepared PANI/MnO\u003csub\u003e2\u003c/sub\u003e composite was collected on Wattmann\u0026rsquo;s filter paper and washed with a sufficient amount of 1M HCl. After that resultant yield was washed with methanol and distilled water alternatively till the filtrate became colorless. The resultant yield obtained of PANI/MnO\u003csub\u003e2\u003c/sub\u003e composite was dried in air and then in vacuum at 45˚C. The prepared sample was converted in powder form with the help of agate pestle mortar and named as S2. The above-mentioned synthesis route was followed for the preparation of two more PANI/MnO\u003csub\u003e2\u003c/sub\u003e composites with 20 and 40 weight percentage of MnO\u003csub\u003e2\u003c/sub\u003e and named as S3 and S4 respectively.\u003c/p\u003e\n\u003ch3\u003eCharacterization for PANI and its composites\u003c/h3\u003e\n\u003cp\u003eThe morphology of the growth samples was analyzed through Field Emission Scanning Electron Microscope (FE-SEM) (FEI NOVA NANO SEM 450) model. The Raman spectroscopy was analyzed through the Jobin Yvon Horibra LABRAM-HR visible (400-1100nm) spectrometer. The Argon laser with 473nm wavelength and 25mW power was used as excitation laser source in Raman spectroscopy.\u003c/p\u003e\n\u003ch3\u003eSensor fabrication\u003c/h3\u003e\n\u003cp\u003eFor the gas sensing application, we required the materials which can sense the incident gas. So, we used PANI and its composites for the same. For this we required to make sensor which is defined as a resistor whose electrical properties like electrical conductivity changes under the gaseous atmosphere. The sensor contains one or more electrodes on the surface of sensing materials for study of the gas sensing properties. To build up the sensor, we need to convert powder sample in pellet \u0026lsquo;or\u0026rsquo; film form. Here in this study, we make sensor in pellet shape. The pellets of prepared samples had been made by using the hydraulic pellet press machine. The die set of diameter 13mm was used to prepare pellet and sufficient amount of sample was put in die set and 100Kg/cm\u003csup\u003e2\u003c/sup\u003e of pressure was applied for all samples. The thicknesses of all pellets were observed to be approximately 0.5mm. To convert the pellet in sensor form, we make two parallel electrodes on one sided surface of pellet using silver (Ag) paint. The PANI sensor (Ag/PANI/Ag) and its composites sensors (Ag/PANI-MnO\u003csub\u003e2\u003c/sub\u003e/Ag) used for study of gas sensing properties are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a). The gap between parallel electrodes were calculated and found approximately to be 1mm.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe sample holder used in the gas sensing properties has 500ml capacity as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b) which is made by stainless steel. This sample holder was used to observe variations in electrical current under the methanol environment at room temperature [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The rotary pump (BC2410; British Thomson Houston Ltd.) was attached to the sample holder which was used to create vacuum in the sample holder of order of 10\u003csup\u003e-3\u003c/sup\u003embar at room temperature. The Keithley 6517A electrometer and DNM-121 Nano-ammeter were used to calculate electrical parameters for DC conduction during the gas sensing at room temperature.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eField Effect Scanning Electron Microscope\u003c/h2\u003e\u003cp\u003eThe morphological study of prepared PANI (S1) and PANI/MnO\u003csub\u003e2\u003c/sub\u003e composite (S2) was analyzed with help of field effect scanning electron microscope (FE-SEM). Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a,b) represents the morphological images of PANI (S1) and PANI/MnO\u003csub\u003e2\u003c/sub\u003e composite (S2) which shows that S1 has bigger molecular size as compared to S2, S2 have more porous structure as compared to S1. This also indicates that the S1 is amorphous in nature while S2 is semi-crystalline in nature as well as uniform distribution of MnO\u003csub\u003e2\u003c/sub\u003e particles in PANI matrix which allow to better adsorption phenomenon by composites. From the FE-SEM images, it is also clear that the morphology of PANI is directly affected with doping of MnO\u003csub\u003e2\u003c/sub\u003e. It has also been observed that the sample prepared with 10wt% doping of MnO\u003csub\u003e2\u003c/sub\u003e having agglomerates of range 0.3 to 3 \u0026micro;m, suggesting that the micro-structural formation of PANI/MnO\u003csub\u003e2\u003c/sub\u003e composites.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eRaman Spectroscopy\u003c/h3\u003e\n\u003cp\u003eThe optical study of these prepared samples has been analyzed by using the Raman spectroscopy in the Raman shift range from 490\u0026ndash;2180 cm\u003csup\u003e-1\u003c/sup\u003e. In the Raman spectrum of all prepared samples, the all necessary peaks confirmed the preparation of desired samples. The Raman spectrum of PANI/MnO\u003csub\u003e2\u003c/sub\u003e is quite similar as PANI. The doublet around 1600cm\u003csup\u003e-1\u003c/sup\u003e is observed which is overlapped band of benzonoid and quinoid rings of stretching vibration. The band at 1620 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is associated with C-C stretching vibration of the benzonoid ring and the band at 1588cm\u003csup\u003e-1\u003c/sup\u003e is associated with C\u0026thinsp;=\u0026thinsp;C stretching vibration of the quinoid ring. The band at 1550cm\u003csup\u003e-1\u003c/sup\u003e represents the N-H bending whereas the band at 1492cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e occurred which corresponds to C\u0026thinsp;=\u0026thinsp;N stretching vibration of the quinoid ring. Moreover, bands occurred in the Raman spectrum in which the band at 1417cm\u003csup\u003e-1\u003c/sup\u003e is associated with C-C stretching of phenazine structure and another band at 1166 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to C-H bending in quinoid. The band at 808 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is associated with amine deformation (C-N-C bending) and band at 516cm\u003csup\u003e-1\u003c/sup\u003e is associated with out of plane deformation of benzonoid \u0026lsquo;or\u0026rsquo; amine in plane deformation. Hence the Raman spectra of prepared samples show the typical bands associated to the polyaniline emeraldine salt form [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. With the variation in doping concentration, the intensity of most peaks is enhanced which is cleared from the Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a).\u003c/p\u003e\u003cp\u003eTo analyze enhancement in peaks, we have to deconvolute band around ~\u0026thinsp;1335cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e using the Gaussian (80%)\u0026thinsp;+\u0026thinsp;Lorentzian (20%) fitting in two components, which represents the semi-quinone radical stretching mode \u0026lsquo;or\u0026rsquo; C\u0026thinsp;~\u0026thinsp;N\u003csup\u003e+\u003c/sup\u003e stretching in polaronic from polarons and the intensity and area under curve increases with doping concentration as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b). For the better understanding of charge carrier and gas sensing mechanism, we also deconvolute the Raman sift region from 1450cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1650cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e using the Gaussian (80%)\u0026thinsp;+\u0026thinsp;Lorentzian (20%) fitting in four components as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c) for the samples S1, S2 and S3. From the Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c) it is clear that as the doping takes place in pristine PANI, the area under the curve of bands presents at 1335, 1492, 1550, 1588 and 1617cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increases shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(d) and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe benzonoid (at 1617cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and quinoid (at 1588cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) rings are directly associated with bipolarons and polarons states respectively. As the doping concentration increases, the area under curve of these two bands increases that means the concentration of bipolarons and polarons increases. With the increase in these charge carriers concentration, the ratio of area under curve of benzonoid to quinoid rings (A\u003csub\u003eB\u003c/sub\u003e/A\u003csub\u003eP\u003c/sub\u003e) found to be increased from 0.88 to 1.33 as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The increase in A\u003csub\u003eB\u003c/sub\u003e/A\u003csub\u003eP\u003c/sub\u003e suggest to increase in bipolarons more than polarons i.e. the transition of polaronic from bipolaronic state and increase in oxidation level with doping of MnO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eArea under the C\u0026thinsp;=\u0026thinsp;N stretching vibration of the quinoid ring, band of N-H bending, benzonoid and quinoid rings and A\u003csub\u003eB\u003c/sub\u003e/A\u003csub\u003eQ\u003c/sub\u003e ratios for the samples S1-S3\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"1\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eArea Under Curve (x10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e a.u) at\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eA\u003csub\u003eB\u003c/sub\u003e/A\u003csub\u003eQ\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1335cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e 1492cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e 1550cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1588cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e(A\u003csub\u003eQ\u003c/sub\u003e) 1617cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e(A\u003csub\u003eB\u003c/sub\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e11.64 10.46 10.13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10.50 09.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.88\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15.76 11.21 12.13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e12.15 12.48\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.03\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e24.43 12.81 29.23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e12.78 17.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.34\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\n\u003ch3\u003eGas Sensing studies\u003c/h3\u003e\n\u003cp\u003eIn the gas sensing applications, the resistance of the sensing materials becomes more important. Like this, the three type of resistance comes across in the gas sensing applications when we sense the gas incident on sensor made by organic semiconducting materials. The first is interface resistance which occurred due to interface between pellet of the sample and prepared electrode on pellet. The second is the surface resistance which is due to the surface of particles of sample and third is bulk resistance which is inside the resistance of particles of sample. More ever, the silver paste of electrodes may have some resistance which comes in role during the conduction. To understand the complete resistance of sensor, the Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e show the schematic representation of combination of all resistances [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe total conductivity of the sensor can be expressed as [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\frac{1}{\\sigma\\:}=\\:\\frac{1}{{\\sigma\\:}_{c}}+\\:\\frac{1}{{\\sigma\\:}_{h}}+\\:\\frac{1}{{\\sigma\\:}_{i}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eWhere σ, σ\u003csub\u003ec\u003c/sub\u003e, σ\u003csub\u003eh\u003c/sub\u003e and σ\u003csub\u003ei\u003c/sub\u003e are total conductivity, intermolecular conductivity, intermolecular hopping conductivity and ionic conductivity respectively. The total conductivity can be enhanced by the change in any resistance out of interface, surface and bulk resistance as well as change in electrode materials but out of these the bulk resistance plays important role due to the hopping mechanism for the conduction through bulk area of sample. With the change in dopant and dopant concentration, the intermolecular conductivity may be changed due to enhancement in physical and chemical properties. The intermolecular hopping conductivity is associated with the polymer chain. The variation in intermolecular hopping conductivity takes place with the variation in polymer chain, hydrogen bonding, dipole-dipole interactions and crystallinity. The ionic conductivity may be enhanced when ions of samples come in contact with the bombarded organic vapors under organic vapors atmosphere.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn the present study, we analyzed the conduction properties of sensor made by PANI (Ag/PANI/Ag) and its composites (Ag/PANI-MnO\u003csub\u003e2\u003c/sub\u003e/Ag) under the different environment of methanol vapors at room temperature. The sensor was put in the two probe sample holder to study the conduction properties under the vacuum circumstances of pressure 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003embar and at room temperature for 1 hour before gas sensing observation to remove all unwanted gas particles presented in gas chamber [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. After the removal of all unwanted atmospheric particles from chamber, no humidity will affect during the gas sensing observation. In the gas chamber two copper strips present which were contacted with the silver electrodes of the sensor for the gas sensing phenomenon. The baseline current (current of samples before exposure of organic vapors) noticed before exposing the gaseous vapors for all samples S1-S4 at voltage 3V and under 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e mbar pressure. For study the gas sensing properties, all valves of the gaseous chamber should be closed properly. By using the micro-syringes, the gaseous vapors with desirable concentration inserted through inlet valve present on the gas testing chamber. When the sensor come in contact with the gaseous particles, the initial current changed which may be drastically \u0026lsquo;or\u0026rsquo; linearly as well as increases \u0026lsquo;or\u0026rsquo; decreases.\u003c/p\u003e\u003cp\u003eThe sample was stabilized under the vacuum circumstances before we start the observation. After the vacuum stabilization, organic vapors of methanol with 40ppm concentration were injected through the needle which is present at right-top side of gas chamber as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e When the methanol vapors were injected in the gas chamber, a sudden change in current was observed. The increase in current of PANI sensor is noticed under exposure of methanol vapors till it saturate at constant voltage 3V, the variation of current is observed due to the adsorption of methanol molecules in the PANI matrix. After sometime, no more change is observed in current because maximum adsorption of methanol vapors take place and no more adsorption is allowed. Then the inserted methanol vapors were removed from the gas chamber with the use of vacuum pump and this time the decrease in current was observed due to the desorption of methanol vapors from PANI matrix. The measurement was continued until this doesn\u0026rsquo;t reach the pre-exposure value of air current of PANI (current value before introducing the vapors in gas chamber). The above reported procedure was followed for the next cycle with 60ppm concentration of methanol vapors and behavior of current was noticed. Under the methanol environment, the variation of current takes place because methanol vapors reacted with the PANI molecules.\u003c/p\u003e\u003cp\u003eGenerally, after the complete desorption process, the current should reach at its initial value of current of sensor but some methanol vapors adsorbed by the inner layers of PANI matrix which doesn\u0026rsquo;t come in role during desorption process and high value of current is observed as compared to pre-exposed current. The previously followed procedure for the PANI sensor, the same repeated for the PANI/MnO\u003csub\u003e2\u003c/sub\u003e composites for both concentrations 40ppm and 60ppm levels. The enhancement of current in the exposure of methanol vapors have been noticed which leads to make an effective investigation of gas sensing application at different ppm levels as well as increase in dopant concentration.\u003c/p\u003e\u003cp\u003eThis is comparative study for PANI and its composites for gas sensing application under the same environmental circumstances. The electric behavior of prepared samples take suitable variation in the form of change in current \u0026lsquo;or\u0026rsquo; resistance. From this observation, it is cleared that the adsorption of methanol vapors directly affected the electrical properties of sensor and these electrical properties is different for different ppm levels as well as different dopant concentration. So, the ppm levels of methanol vapors directly connected with change in current \u0026lsquo;or\u0026rsquo; conductivity. The result taken from the gas sensing procedure for pristine PANI and its composites were graphically represented and compared with our objective of experiment.\u003c/p\u003e\u003cp\u003eThe enhancement in the electric current is less for pristine PANI (S1) as compared to its composites (S2-S4) with MnO\u003csub\u003e2\u003c/sub\u003e at the same ppm level which may be clearly understood from the Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The maximum saturated values of current increases with increase in ppm levels from 40ppm to 60ppm as well as increase in dopant concentration from 10wt% to 40wt% of MnO\u003csub\u003e2\u003c/sub\u003e. The minimum variation was observed for pristine PANI (S1) while maximum variation was observed for its composite (S4) in current. The variation in current increases with increase in dopant concentration, this may be due to the increase in available sites for the adsorption of methanol vapors which are cleared from the FE-SEM images of PANI (S1) and its composite (S2). Hence, the hybridization between PANI and manganese dioxide particles provides an appropriate advantage for sensing of methanol vapors towards the MnO\u003csub\u003e2\u003c/sub\u003e. The increase in current under the methanol environment shows the reducing agent behavior of methanol. This signifies that the methanol injected the charge careers as electrons in to samples which results in the enhancement of current \u0026lsquo;or\u0026rsquo; conductivity under the methanol environment.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn the gas sensing phenomenon, Response (%) is the most important factor to understand effect of vapors on sensor which is defined as the ratio of change in current (ΔI\u0026thinsp;=\u0026thinsp;I\u003csub\u003eg\u003c/sub\u003e-I\u003csub\u003eo\u003c/sub\u003e) to initial current (I\u003csub\u003eo\u003c/sub\u003e) (current before the exposure of vapors). Where I\u003csub\u003eg\u003c/sub\u003e is current under the vapors atmosphere [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:Response\\:\\left(\\%\\right)=\\:\\frac{\\varDelta\\:I}{{I}_{o}}x100=\\:\\frac{{I}_{g}-{I}_{o}}{{I}_{0}}x100$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe above Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) is used to calculate response in terms of response (%) as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e which represents the variation in response (%) with function of time for PANI (S1) and its composites (S2-S4) for 40ppm and 60ppm levels at room temperature. As the ppm levels and dopant concentration has been changed, the variation in response was also observed which can be easily understood by Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. So, the response becomes more interesting for PANI/MnO\u003csub\u003e2\u003c/sub\u003e as compared to pristine PANI according to our observation. The minimum response (%) was calculated for S1 which is 17.69% and 19.51% while maximum response (%) was calculated for S4 which is 43.30% and 48.39% at 40ppm and 60ppm respectively.\u003c/p\u003e\u003cp\u003eLike as the response (%), the response and recovery time is also two more important factors in the gas sensing application. The response time is defined as time in which the response (%) increases up to 90% values of maximum response during the adsorption process while the recovery time is defined as time in which the response (%) remains 10% of the maximum response (decay to 90% of response) during the desorption process as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The response and recovery curve was also analyzed which stated that the variation in current is sharply during adsorption and desorption for all prepared samples. The response and recovery time was calculated for the S1-S4 from the graphs (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). The response and recovery time is different for the different samples at different and same ppm levels. The response time decreases with increase in ppm levels as well as dopant concentration while the recovery time increases with increase in ppm levels as well as dopant concentration for the samples S1-S4 as noted down in Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and plotted as Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eresponse (%), response and recovery time of samples (S1-S4) for different ppm levels\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eResponse (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003eResponse time (s)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eRecovery time (s)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e40ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e60ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e40ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e60ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e40ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003e60ppm\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eS1\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e17.69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e19.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e230\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e190\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e210\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eS2\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e23.38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e26.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e140\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e240\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eS3\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e29.92\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e33.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e170\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e120\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e280\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eS4\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e43.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e48.39\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e140\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e290\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e330\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eTheoretical approach for the gas sensing application\u003c/h2\u003e\u003cp\u003eThe adsorption and desorption are two important factors for the better understanding of gas sensing phenomenon. During the ejection of vapors, the sensor reacts with the vapors and starts the adsorption of vapors by sensor while during the removal of vapors, the reaction has been stopped between sensor and vapors and desorption comes in role. In 1918, the rate of adsorption and rate of desorption has been explained by Langmuir. The theory of Langmuir adsorption and desorption gives some important factors for the gas sensing application such that (a) homogeneity should be present at the gas sensing surface (b) in the monolayer adsorption; available sites of surface should contribute (c) the presence of others molecules doesn\u0026rsquo;t affect the energy of adsorbed molecules.\u003c/p\u003e\u003cp\u003eThe surface coverage of the sites by the vapors given by θ\u0026thinsp;=\u0026thinsp;N(t)/N* and this is defined as the ratio of no. of sites (N(t)) which are used in the adsorption phenomenon by vapor particles to the total no. of sites (N*) available for the adsorption phenomenon. N(t) is the no. of sites at any time t during the adsorption. The Langmuir gave their fitting Eq.\u0026nbsp;(3) this followed for the adsorption process for the sensing of organic vapors with double exponential factor which is written below [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/p\u003e\u003cp\u003ey = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{N\\left(t\\right)}{{N}^{*}}\\)\u003c/span\u003e\u003c/span\u003e = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{A}_{1}\\left(1-\\text{exp}\\left(\\frac{-t}{{\\tau\\:}_{A1}}\\right)\\right)+{A}_{2}\\left(1-\\text{exp}\\left(\\frac{-t}{{\\tau\\:}_{A2}}\\right)\\right)\\)\u003c/span\u003e\u003c/span\u003e (3)\u003c/p\u003e\u003cp\u003eWhere A\u003csub\u003e1\u003c/sub\u003e, A\u003csub\u003e2\u003c/sub\u003e, τ\u003csub\u003eA1\u003c/sub\u003e and τ\u003csub\u003eA2\u003c/sub\u003e are constants. The constants A\u003csub\u003e1\u003c/sub\u003e and A\u003csub\u003e2\u003c/sub\u003e has unit of pressure while constants τ\u003csub\u003eA1\u003c/sub\u003e and τ\u003csub\u003eA2\u003c/sub\u003e has unit of time. On the insertion of vapors in gas chamber, the adsorption of vapor particles start by the sites and increase in N(t) take place. After some time, the N(t) become equal to N* and system comes in equilibrium means further no more variation will be observed in current \u0026lsquo;or\u0026rsquo; resistance and that time the rate of adsorption become equal to rate of desorption. The calculated values of adsorption factors are tabulated in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. On the removal of vapors, desorption comes in role which is simple chemical process [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The adsorbed vapors remove from the sites of the surface during the desorption process. For the desorption process, Langmuir gave another fitting Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e4\u003c/span\u003e) which is followed for the desorption process with the single exponential factor and given below [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:y=\\:{D}_{1}\\text{exp}\\left(\\frac{-t}{{\\tau\\:}_{D}}\\right)+{D}_{2}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eWhere D\u003csub\u003e1\u003c/sub\u003e, D\u003csub\u003e2\u003c/sub\u003e and τ\u003csub\u003eD\u003c/sub\u003e are constants. The D\u003csub\u003e1\u003c/sub\u003e and τ\u003csub\u003eD\u003c/sub\u003e has unit of pressure and time respectively and D\u003csub\u003e2\u003c/sub\u003e is correction factor. In the Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (S1-S4), the theoretical fitting curve has been plotted which is calculated from the adsorption and desorption rate Eqs.\u0026nbsp;(3) and (\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e4\u003c/span\u003e) respectively as well as experimental calculated data also plotted which are well fitted and satisfied for the all. The calculated values of desorption factors are tabulated in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. This shows the evidence for strong correlation between theoretical data, experimental data and Eq.\u0026nbsp;(3,\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e4\u003c/span\u003e) as tabulated in Table \u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eValues of constants A\u003csub\u003e1\u003c/sub\u003e, τ\u003csub\u003eA1\u003c/sub\u003e, A\u003csub\u003e2\u003c/sub\u003e and τ\u003csub\u003eA2\u003c/sub\u003e for S1-S4 calculated from Langmuir curve fitting of adsorption\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"9\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eConstant\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eS1\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003eS2\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eS3\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003eS4\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e40ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e60ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e40ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e60ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e40ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003e60ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003e40ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003e60ppm\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eA\u003c/b\u003e\u003csub\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.04E-3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-0.176\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3.513E-6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e-1.610\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.031E-8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e-53.912\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e7.77E-7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e-61.413\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eτ\u003c/b\u003e\u003csub\u003e\u003cb\u003eA1\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-26.970\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-127.076\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-15.985\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e-163.56\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-10.406\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e-304.385\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-10.041\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e-273.63\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eA\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-35.025\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-47.960\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-54.712\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e-147.84\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-99.305\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e-609.450\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-275.38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e-663.73\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eτ\u003c/b\u003e\u003csub\u003e\u003cb\u003eA2\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-141.847\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e10.809\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-141.869\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e10.809\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-148.550\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e10.809\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-194.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e2.248\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eValues of constants D\u003csub\u003e1\u003c/sub\u003e, τ\u003csub\u003eD\u003c/sub\u003e and D\u003csub\u003e2\u003c/sub\u003e for S1-S4 calculated from Langmuir curve fitting of desorption\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"9\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eConstants\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eS1\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003eS2\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eS3\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003eS4\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e40ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e60ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e40ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e60ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e40ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003e60ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003e40ppm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003e60ppm\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eD\u003c/b\u003e\u003csub\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2028.76\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e80615.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2266.57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e66442.26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1453.93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e42072.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e1517.61\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e53541.80\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eτ\u003c/b\u003e\u003csub\u003e\u003cb\u003eD\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e65.266\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e74.510\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e165.166\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e186.915\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e236.339\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e211.670\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e166.78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e174.413\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eD\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e30.788\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e26.672\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-16.338\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e24.293\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e-50.087\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e22.688\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e34.726\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e38.156\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eValues of %age fit agreed with data for S1-S4 calculated from Langmuir curve fitting of adsorption and desorption\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eConcentration of vapors (ppm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eAdsorption\u003c/p\u003e\u003cp\u003e(fit agreed with data) (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDesorption\u003c/p\u003e\u003cp\u003e(fit agreed with data) (%)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e\u003cb\u003eS1\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e99.74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e99.48\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e98.78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e99.78\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e\u003cb\u003eS2\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e99.95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e99.70\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e98.82\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e99.86\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e\u003cb\u003eS3\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e99.48\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e99.80\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e99.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e99.95\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e\u003cb\u003eS4\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e99.67\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e99.96\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e97.78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e99.87\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eGas sensing mechanism for PANI and its composites\u003c/h2\u003e\u003cp\u003eWhen the methanol is injected in gas container, its particles diffuse in PANI matrix easily due to its small size and show high interaction with PANI matrix. Due to diffusion of methanol particles the conductivity of PANI increases. Under the methanol environment, the concentration of polarons increases and these polarons were localized in character. Thus, resultant increase in conductivity occurred due to increase in polarons of PANI by additional polarons from methanol vapors. The present polarons in PANI are converted into bipolarons at the same time polarons produced. This increase in conductivity happened due to ionic conduction, with the methanol acting as a solvent for the chloride ions present in PANI [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Under the methanol environment, increase in conductivity shows the reducing behavior of methanol toward the PANI and increase the polarons and bipolarons in PANI. Under the methanol environment of PANI, the hydrogen bonding takes place via lone pairs on oxygen of methanol and hydrogen of PANI. Thus, the bond between nitrogen and hydrogen of benzonoid part of PANI become weak and show weak interaction which produce the polarons. Like this methanol also reacted with nitrogen of PANI by the hydrogen bonding which leads to polarons conversion in bipolarons (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn the PANI, nitrogen atoms are protonated, so these are unavailable for taking part in hydrogen bonding with hydrogen of methanol\u0026rsquo;s hydroxyl group. Due to hydrogen bonding, the PANI chain pushed apart and uncoiling which gives to increase in conductivity under methanol environment. The sensing mechanism becomes more complicated in composites of PANI due to presence of both p-type PANI and n-type metal oxide in the same system. In composites, gas sensing enhanced by hybridization of metal oxide particles (MnO\u003csub\u003e2\u003c/sub\u003e) with PANI which gives better gas sensing ability. The uniform dispersion of MnO\u003csub\u003e2\u003c/sub\u003e particles in PANI matrix is one important reason for the enhancement of gas sensing, this provides better porous surface of sensing pellet (Ag/PANI-MnO\u003csub\u003e2\u003c/sub\u003e/Ag) as compare to PANI pellet (Ag/PANI/Ag) [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. This could also be observed by already shown FE-SEM images. Besides this, another important factor is structure of samples for the sensing of composites. In the composites, polymer-metal oxide junction is formed as PANI- MnO\u003csub\u003e2\u003c/sub\u003e where PANI is p-type while MnO\u003csub\u003e2\u003c/sub\u003e is n-type. In PANI and MnO\u003csub\u003e2\u003c/sub\u003e, holes and electrons are majority charge carriers respectively. In composites, some holes from the PANI and some electrons from the MnO\u003csub\u003e2\u003c/sub\u003e diffuse across junction and depletion region formed between PANI and MnO\u003csub\u003e2\u003c/sub\u003e. Hence at junction, electrons transferred to PANI from MnO\u003csub\u003e2\u003c/sub\u003e thus further positively charge layer created on the MnO\u003csub\u003e2\u003c/sub\u003e. Between PANI and MnO\u003csub\u003e2\u003c/sub\u003e the p-n hetero-junction formed so activation energy decreases and gives easily adsorption of methanol vapors. On adsorption of methanol vapors, the increase in current shows the electron donating nature of methanol which increases the efficiency of gas sensing [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTai et al. [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] and Li et al. [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e] has reported earlier energy level diagram of PANI/metal oxide nanocomposites for understanding of gas sensing mechanism. The band gap between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) levels in PANI is small as compare to energy band gap between valance band (VB) and conduction band (CB) as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. They explained that due to matching in band gap between the lowest unoccupied molecular orbital (LUMO) of PANI and conduction band (CB) of MnO\u003csub\u003e2\u003c/sub\u003e, the enhancement of charge separation for charge transfer occurring between the lowest unoccupied molecular orbital (LUMO) of PANI and conduction band (CB).\u003c/p\u003e\u003cp\u003eFor the gas sensing, both PANI and MnO\u003csub\u003e2\u003c/sub\u003e particles take adsorptions of vapors in PANI/MnO\u003csub\u003e2\u003c/sub\u003e composites. On the surface of MnO\u003csub\u003e2\u003c/sub\u003e particles, the oxygen molecules adsorbed and following reaction takes place for the gas sensing [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eUnder environment of reducing gas, the reducing gas injected the electrons in the sensing sample and potential barrier decreases, finally conductivity increases [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Thus, the generally action of the reducing gas (R) on the sensing pellet acts as given below\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe reducing gas adsorbed the oxygen and an electron ejected which leads to increase in carrier density as well as conductivity i.e. decreases in barrier width (depletion layer). On the other hand, the methanol vapors were adsorbed by the available sites in PANI. The methanol vapors provides more electrons to the HOMO levels of PANI and due to applied field these electrons jump at LUMO of PANI, finally these electrons shifted to CB of MnO\u003csub\u003e2\u003c/sub\u003e as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e which further enhances the conduction and leads to increase in current of sensing pellet. At last, it is concluded that in PANI/ MnO\u003csub\u003e2\u003c/sub\u003e composites more electrons are available to take part in conduction as compared to pure PANI for gas sensing [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe chemical oxidative polymerization method was used to synthesize PANI and its composites with different weight% of MnO\u003csub\u003e2\u003c/sub\u003e. FESEM image of composite shows the uniform distribution of MnO\u003csub\u003e2\u003c/sub\u003e particles in the PANI matrix and leads to give porous structure. The availability of all required peaks in Raman spectrum of PANI and its composites leads to evident of preparation of desired samples. The increase in ratio of area under the curve of bipolaronic to polaronic band prove that the increase in conductivity and conjugation length at room temperature with dopant concentration. The porous structure of composites leads to more adsorption of methanol vapors as compared to PANI. Using the PANI/MnO\u003csub\u003e2\u003c/sub\u003e composite (40wt% of MnO\u003csub\u003e2\u003c/sub\u003e) as sensor, the maximum response\u0026thinsp;~\u0026thinsp;48% and better response time 90sec was achieved at 60ppm level. The adsorption and desorption process using the Langmuir equation gives the approximately 99% fitting with the experimental calculated data for all prepared samples. This fitting is a good agreement between the theoretical and experimental data. The prepared samples have single energetic adsorption sites for the adsorption of methanol vapors which is suggested by the theoretical fitted equation for the adsorption process.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eDr. Rishi Pal: Write original manuscript, characterization.Dr. Sneh Lata Goyal: Supervision.Dr. Ishpal Rawal: Review and edit.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eThe authors are thankful for financial assistance from DST-FIST for providing XRD facility. We also acknowledge the UGC-CSR Indore for provide FESEM and Raman facilities.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eChander S, Tripathi SK, Kaur I (2025) Development in PANI based solar cells: Progress on high-throughput methods, physical-chemical properties and device performance. Next Mater 8:10089\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSu X, Liu Y, Liao Z, Bi Y, Ma M, Chen Y, Ma Y, Wan F, Chung KL (2022) Recent progress of polyaniline-based composites in the field of microwave absorption. Synth Met 291:117190\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePal R, Goyal SL, Gupta V, Rawal I (2019) MnO\u003csub\u003e2\u003c/sub\u003e-Magnetic Core-Shell Structured Polyaniline Dependent Enhanced EMI Shielding Effectiveness: A Study of VRH Conduction. 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Chem Eng J 378:122226\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"polymer-bulletin","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pobu","sideBox":"Learn more about [Polymer Bulletin](http://link.springer.com/journal/289)","snPcode":"289","submissionUrl":"https://submission.nature.com/new-submission/289/3","title":"Polymer Bulletin","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Raman Spectroscopy, FESEM, Gas Sensing, Langmuir adsorption-desorption","lastPublishedDoi":"10.21203/rs.3.rs-7315668/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7315668/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePANI based sensors has been synthesized for methanol detection i.e. pristine PANI and its composites have been synthesized using chemical oxidative polymerization approach with various doping concentration (00, 10, 20 and 40 wt.%) of manganese dioxide. The PANI/MnO\u003csub\u003e2\u003c/sub\u003e composite with 10wt% of MnO\u003csub\u003e2\u003c/sub\u003e has porous structure as well as small particles size as compared to PANI shown by FESEM analysis. The greatest interaction across PANI and MnO\u003csub\u003e2\u003c/sub\u003e nanoparticles lead to the conversion of PANI from the highly oxidized states to oxidized states and is established using Raman investigation. The FESEM and Raman spectroscopy confirms the preparation of PANI and its composites. The sensing response (%), response and recovery time of fabricated sensors towards the methanol environment has been calculated by measuring the change in surface current of samples in different methanol environments with respect to without methanol environment at room temperature. The PANI/MnO\u003csub\u003e2\u003c/sub\u003e composites show the better response as compared to pristine PANI and response increases with increase in dopant concentration as well as ppm levels of methanol. The maximum response was calculated for PANI/MnO\u003csub\u003e2\u003c/sub\u003e composite with 40wt% of MnO\u003csub\u003e2\u003c/sub\u003e which is ~\u0026thinsp;48% and better response time 90 seconds at 60ppm of methanol vapors. The better recovery time was observed for PANI at 40ppm level of methanol vapors. The adsorption and desorption of gas molecules under Langmuir kinetic theory for the adsorption and desorption of methanol has also been thoroughly examined, along with any potential theoretical parallels to the mechanism of gas sensing. Using Langmuir adsorption-desorption kinematic fits, theoretical parameters related to the sensing qualities have been assessed from the experimental curves.\u003c/p\u003e","manuscriptTitle":"Facial Growth of Polyaniline based Sensors for Gas Sensing Application: Langmuir Theoretical Approach","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-21 11:54:26","doi":"10.21203/rs.3.rs-7315668/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-12-03T14:06:20+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-02T19:41:26+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-02T12:54:53+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-02T11:07:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"138956214126586119183735226721684769928","date":"2025-11-12T10:42:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"40848418940406045808238012714326476929","date":"2025-11-12T04:20:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"275944548722465163673083093745734681210","date":"2025-11-11T22:42:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-11-11T11:54:08+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-11T07:12:20+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-08T04:37:33+00:00","index":"","fulltext":""},{"type":"submitted","content":"Polymer Bulletin","date":"2025-08-07T07:06:54+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"polymer-bulletin","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pobu","sideBox":"Learn more about [Polymer Bulletin](http://link.springer.com/journal/289)","snPcode":"289","submissionUrl":"https://submission.nature.com/new-submission/289/3","title":"Polymer Bulletin","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"591cf7af-886f-4946-ac3c-3f20a4e8764d","owner":[],"postedDate":"November 21st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-09T16:13:44+00:00","versionOfRecord":{"articleIdentity":"rs-7315668","link":"https://doi.org/10.1007/s00289-026-06352-2","journal":{"identity":"polymer-bulletin","isVorOnly":false,"title":"Polymer Bulletin"},"publishedOn":"2026-03-06 15:57:07","publishedOnDateReadable":"March 6th, 2026"},"versionCreatedAt":"2025-11-21 11:54:26","video":"","vorDoi":"10.1007/s00289-026-06352-2","vorDoiUrl":"https://doi.org/10.1007/s00289-026-06352-2","workflowStages":[]},"version":"v1","identity":"rs-7315668","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7315668","identity":"rs-7315668","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}