Free-standing TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>/PANI composite nanofibers for ammonia sensors

Free-standing TiO₂–SiO₂/polyaniline (TS/PANI) composite nanofibers were prepared by electrospinning, in situ polymerization and calcination method. The effect of tetra-n-butyl titanate (TBT) in the electrospinning solution on the morphology and the ammonia sensing properties of TS/PANI composite nanofibers were investigated. The obtained nanofibers were characterized by scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, thermo-gravimetric analysis and gas sensor test system. It is proved that too much TBT in the solution would make the fibrous morphology and ammonia sensing properties worse. Gas sensing tests showed that the TS/PANI composite nanofibers ammonia sensor can work at room temperature and possess ideal response values, selectivity and repeatability. With the increase in TiO₂ content in the TS nanofibers, the ammonia sensing properties were improved because of the increase in P–N heterojunctions formed between TiO₂ and PANI in the sensors.     

Preparation of modified MWCNTs-doped PANI nanorods by oxygen plasma and their ammonia-sensing properties

Multi-wall carbon nanotubes (MWCNTs)-doped polyaniline (PANI) nanopowders were prepared by chemical oxidation polymerization. Then, the MWCNTs-doped PANI nanopowders were modified by a radio frequency (RF) oxygen plasma source. The morphology and structure of modified MWCNTs-doped PANI nanorods were analyzed by SEM and FI-IR. Gas sensors were fabricated based on plasma modified MWCNTs-doped PANI nanorods to detect ammonia at room temperature. The response amplitude of the gas sensor based on modified MWCNTs-doped PANI nanorods was much higher than those of MWCNTs-doped PANI nanopowders and pure PANI nanopowders sensors, respectively, in ammonia concentration range of 10–150 ppm. Cross responses of modified MWCNTs-doped PANI nanorods sensor to ammonia, ethanol, formaldehyde, and toluene were tested. The sensor showed good selectivity and stability. The sensing mechanism of modified MWCNTs-doped PANI nanorods gas sensor was analyzed.     

Polyaniline as a Gas-Sensor Material

Polyaniline (PANI) was synthesized by oxidative polymerization of aniline using ammonium persulfate in an acid medium. The polyaniline salt was converted to base form by treatment with ammonium hydroxide. The polyaniline base was dissolved in N-methyl pyrrolidone (NMP) for film casting. The cast film was doped with HCl for obtaining higher conductivity. Both doped and undoped PANI films were characterized by UV-visible, FTIR, and XRD analyses. The electrical conductivity of the PANI film was studied by a four-point probe method at room temperature. Finally, ammonia gas-sensing characteristics of the prepared polyaniline film were studied by measuring the change in electrical conductivity on exposure to ammonia gas at different concentrations. The influence of concentration of acid during polymerization of aniline and dopant concentration on the gas sensing characteristics of PANI film are reported in this paper.     

Sputter-deposition of silver nanoparticles into ionic liquid as a sacrificial reservoir in antimicrobial organosilicate nanocomposite coatings

We present a new approach for fabricating robust, regenerable antimicrobial coatings containing an ionic liquid (IL) phase incorporating silver nanoparticles (AgNPs) as a reservoir for Ag(0)/Ag(+) species within sol-gel-derived nanocomposite films integrating organosilicate nanoparticles. The IL serves as an ultralow volatility (vacuum-compatible) liquid target, allowing for the direct deposition and dispersion of a high-density AgNP "ionosol" following conventional sputtering techniques. Two like-anion ILs were investigated in this work: methyltrioctylammonium bis(trifluoromethylsulfonyl)imide, [N(8881)][Tf(2)N], and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [emim][Tf(2)N]. Silver ionosols derived from these two ILs were incorporated into silica-based sol-gel films and the resultant antimicrobial activity evaluated against Pseudomonas aeruginosa bacteria. Imaging of the surface morphologies of the as-prepared films established a link between an open macroporous film architecture and the observation of high activity. Nanocomposites based on [N(8881)][Tf(2)N] displayed excellent antimicrobial activity against P. aeruginosa over multiple cycles, reducing cell viability by 6 log units within 4 h of contact. Surprisingly, similar films prepared from [emim][Tf(2)N] presented negligible antimicrobial activity, an observation we attribute to the differing abilities of these IL cations to infiltrate the cell wall, regulating the influx of silver ions to the bacterium's interior.     

Thin polyaniline and polyaniline/carbon nanocomposite films for gas sensing

We have studied the gas sensing properties of five polyaniline-based materials—thick and thin PANI films, nanocomposite PANI/MWNT and PANI/SWNT films, and PANI nanogranules embedded in a polyvinylpyrrolidone matrix. The films (except for the latter) were deposited within the induction period of the polymerization process on gold interdigitated micro electrodes. Their sensitivity to NH₃, H₂, ethanol, methanol, and acetone was measured. The thin PANI film (~ 100 nm thick) prepared by a lift-off process had the sensitivity to ammonia below 0.5 ppm, which was higher than that of nanocomposite films. Two materials—thick PANI film and nanocomposite PANI/MWNT film—exhibited a shallow minimum in the temperature dependence of resistance (at 313 K and 319 K), which is a feature exploitable in practical applications, since the gas sensors should be insensitive to small temperature fluctuations at these temperatures.     

Influence of dopant in the synthesis, characteristics and ammonia sensing behavior of processable polyaniline

Polyaniline (PANI) was synthesized by oxidative polymerization of aniline as well as aniline hydrochloride by ammonium persulfate in the presence of para-toluene sulfonic acid (PTSA). This helped in direct usage of the conducting PANI solution for film casting and use as a device for ammonia gas sensing. Viscosity change with applied shear rate was measured for both the polymers. Solid PANI powder was isolated from its tetrahydrofuran solution by using methanol as non-solvent. Thermogravimetric analysis investigated the thermal properties of the solid PANI salts. Elemental analysis of both PANI synthesized in presence of PTSA and PANI synthesized in presence of HCl and PTSA was investigated. A thin coherent film of both the conducting PANI were deposited on glass slides precoated with poly vinyl alcohol (PVA) crosslinked with maleic acid (MA) and was directly used in the sensor device. The morphology of the deposited films was analyzed by scanning electron micrograph. The films were further characterized by Attenuated total reflectance Fourier transformed infrared spectroscopy, ultra violet-visible spectroscopy and X-ray diffraction analyses. Finally, both the doped PANI films on MA crosslinked PVA coated glass slides were used to measure the conductivity and ammonia gas-sensing characteristics.     

Impact of interfacial interactions on optical and ammonia sensing in zinc oxide/polyaniline structures

Zinc oxide/polyaniline (ZnO/PANI) hybrid structures have been investigated for their optical and gas sensing properties. ZnO nanoparticles, prepared by the sol–gel method, pressed in the form of pellets were used for gas sensing. The hybrid ZnO/PANI structure was obtained by the addition of PANI on the surface of ZnO. The UV–Vis absorption of the modified pellets show band edge at 363 nm corresponding to ZnO, while a change in the absorption peaks for PANI was observed. The possible interaction between Zn^2?+? of ZnO and NH-group of PANI was confirmed using Raman spectroscopy studies. The results reveal that the hybrid structures exhibit much higher sensitivity to NH $_{{3}}$ gas at room temperature than blank ZnO, which is sensitive to NH₃ gas at higher temperature. This enhancement has been attributed to the creation of active sites on the ZnO surface due to the presence of PANI.     

Investigation of solar-induced photoelectrochemical water splitting and photocatalytic dye removal activities of camphor sulfonic acid doped polyaniline-WO_3-MWCNT ternary nanocomposite

The camphor sulfonic acid doped polyaniline-WO_3-multiwall carbon nanotube(CSA PANI-WO_3-CNT)ternary nanocomposite was synthesized during in-situ oxidative polymerization and characterized by Fourier transform infrared(FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction(XRD), Field emission scanning electron microscopy(FESEM), X-ray photoelectron spectroscopy(XPS), Transmission electron microscopy(TEM), and Energy-dispersive X-ray spectroscopy(EDS). The application of CSA PANIWO_3-CNT ternary nanocomposite was investigated as the photocatalyst in the degradation of methylene blue dye(MB) and as the noble metal-free photoanode in photoelectrochemical water splitting under solar light irradiation. The degradation percentage of MB dye after 60 min illumination by CSA PANI-WO_3-CNT ternary nanocomposite reached 91.40% which was higher than that of pure WO_3(43.45%), pure CSA PANI(48.4%) and CSA PANI-WO_3 binary nanocomposite(85.15%). The photocurrent density of indium tin oxide(ITO)/CSA PANI-WO_3-CNT photoanode obtained 0.81 m A/cm~2 at 1.23 V vs. reversible hydrogen electrode under illumination which was 1.27, 2.13, and 4.26 times higher than that of the ITO/CSA PANI-WO_3(0.64 m A/cm~2), ITO/pure CSA PANI(0.38 m A/cm~2), and ITO/pure WO_3(0.19 m A/cm~2). Also,the applied bias photon-to-current efficiency(ABPE) of ITO/CSA PANI-WO_3-CNT was obtained 0.11%which showed two-fold, four-fold, and five-fold enhancements compared to the ITO/CSA PANI-WO_3,ITO/CSA PANI, and ITO/WO_3, respectively. The electrochemical impedance spectroscopy, as well as the Mott-Schottky results, confirmed the better photoelectrocatalytic activity of ITO/CSA PANI-WO_3-CNT in comparison with ITO/WO_3, ITO/CSA PANI, and ITO/CSA PANI-WO_3. The observed improvement in the photocatalytic and photoelectrocatalytic performances of WO_3 in the presence of CSA PANI is due to the formation of type-II heterojunction between WO_3 and CSA PANI which allows the separation of charge carriers easier and faster. On the other hand, MWCNT addition to the CSA PANI-WO_3 nanocomposite provided the conducting substrate for efficient interfacial charge separation as well as transferring.     

Predicting $$\hbox {CO}_{2}$$ Solubility in Imidazole Ionic Liquids for Use in Absorption Refrigeration Systems by Using the Group Contribution Equation of State Method

Traditional absorption refrigeration such as \(\hbox {H}_{2}\hbox {O}\)–LiBr- and \(\hbox {NH}_{3}\)–\(\hbox {H}_{2}\hbox {O}\)-based refrigeration has limited applications because of several issues, including crystallization, corrosion, and large volume. \(\hbox {CO}_{2}\)–ionic liquids (ILs) as new absorption working pairs were investigated in this study. The objective was to use the group contribution equation of state (GC-EOS) method to predict the solubilities of binary systems containing high-pressure \(\hbox {CO}_{2}\)–imidazole bis(trifluoromethanesulfonimide) ILs and to investigate the applicability and accuracy of the GC-EOS model. The results showed that at pressures up to 11.0 MPa and temperatures of 273 K to 400 K, the \(\hbox {CO}_{2}\) solubility in the ILs increased with increasing system pressure but decreased with increasing temperature, and its variation rate was lower at higher pressures or temperatures. Also, \(\hbox {CO}_{2}\) solubility increased in the order of [emim][\(\hbox {Tf}_{2}\hbox {N}\)] < [bmim][\(\hbox {Tf}_{2}\hbox {N}\)] < [hmim][\(\hbox {Tf}_{2}\hbox {N}\)] < [omim][\(\hbox {Tf}_{2}\hbox {N}\)], indicating that longer alkyl chains of identical IL families resulted in higher \(\hbox {CO}_{2 }\) solubility. The model prediction of \(\hbox {CO}_{2}\) solubility in the four different ILs showed reasonable consistency with the corresponding experimental results from the literature; the largest deviation was 5.7 % for \(\hbox {CO}_{2}\)-[emim][\(\hbox {Tf}_{2}\hbox {N}\)]. Therefore, it can be concluded that the GC-EOS model is a promising theoretical solution that can be used to search for suitable \(\hbox {CO}_{2}\)–IL working pairs for absorption refrigeration systems.     

Synthesis of ultra-fine conducting polyaniline micro/nanotubes using fiber template and their NH3 gas sensitivity

We have recently fabricated ultra-fine conducting polyaniline (PANI) tubes with high gas sensitivity. This route includes two steps. Firstly, aniline polymerizes on the surface of a suitable fiber template prepared by electrospun nitrocellulose (NC). Then, the NC fiber template is dissolved and the ultra-fine PANI tubes are obtained. The structure of the conducting PANI tubes is characterized by IR spectrum and wide-angle X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicate that the PANI shows the shape of ultra-fine tubes with average inner diameter of 250-350 nm. The wall thickness of the ultra-fine PANI tubes increases with increasing the content of oxidant. The conductivity of the doped PANI tubes is about 6.9 x 10(-2) S. The results of gas sensitivity of the ultra-fine PANI tubes indicate that the PANI tubes can act as "electronic nose" to detect toxic NH3 gas below 20 ppm.     

Fabrication of PANI–ZnO nanocomposite thin film for room temperature methanol sensor

In the recent past, polymer–metal oxide nanocomposites have been identified as one of the key and new class of materials for fabricating gas sensors owing to their swift redox characteristics. In this line of thought, chemical oxidative process was employed to synthesize zinc oxide (ZnO) and polyaniline (PANI) nanocomposite thin films with different mass concentrations of ZnO to explore their gas sensing signatures. X-ray diffraction patterns and Fourier transform infrared spectra confirmed the formation of pure ZnO and PANI–ZnO composites. Field emission scanning electron micrographs revealed the leaf like structure of ZnO, porous nature of PANI and the uniformly distributed blend of these two structures for the composite films. Further, the room temperature gas/vapour sensing characteristics revealed the selective nature of nanocomposite films towards methanol vapour in the presence of other vapours with better response, swift response and recovery times of 7 and 20 s respectively.     

Spray synthesis of rapid recovery ZnO/polyaniline film ammonia sensor at room temperature

As an excellent room temperature sensing material, polyaniline (PANI) needs to be further investigated in the field of high sensitivity and sustainable gas sensors due to its long recovery time and difficulty to complete recovery. The ZnO/PANI film with p‒n heterogeneous energy levels have successfully prepared by spraying ZnO nanorod synthesized by hydrothermal method on the PANI film rapidly synthesized at the gas‒liquid interface. The presence of p‒n heterogeneous energy levels enables the ZnO/PANI film to detect 0.1‒100 ppm (1 ppm = 10⁻⁶) NH₃ at room temperature with the response value to 100 ppm NH₃ doubled (12.96) and the recovery time shortened to 1/5 (31.2 s). The ability of high response and fast recovery makes the ZnO/PANI film to be able to detect NH₃ at room temperature continuously. It provides a new idea for PANI to prepare sustainable room temperature sensor and promotes the development of room temperature sensor in public safety.     

A composite of polyelectrolyte-grafted multi-walled carbon nanotubes and in situ polymerized polyaniline for the detection of low concentration triethylamine vapor

Multi-walled carbon nanotubes (MWNTs) grafted with sodium polystyrenesulfonate (NaPSS) were deposited on an interdigitated gold electrode decorated with a layer of positively charged poly(diallyldimethylammonium chloride) by a self-assembly method. Then polyaniline (PANI) was in?situ polymerized on the surface of the MWNTs to prepare a composite. The structure and morphology of the composite were investigated by Raman spectroscopy and scanning electron microscopy. The electrical responses of the composite to triethylamine vapor of low concentrations were measured at room temperature. It was found that the composite exhibited a linear response to the vapor in the range of 0.5-8?ppm with the highest sensitivity of ～80%, which is much higher than that of MWNTs and PANI separately, and an obvious synergetic effect was observed. In addition, the detection limit was as low as the ppb level, and reversible and relatively fast responses (t(90%)～200?s and ～10?min for sensing and recovery, respectively) were observed. The sensing characteristics are highly related to the gas responses of PANI, and a sensing mechanism considering the interaction of MWNTs and PANI was proposed.     

Preparation of gold/polyaniline/multiwall carbon nanotube nanocomposites and application in ammonia gas detection

Composites of multiwall carbon nanotubes (MWNTs), polyaniline (PANI), and gold nanoparticles were prepared by one pot synthesis. Based on the interaction between aniline monomers and MWNTs, aniline molecules were adsorbed and polymerized on the surface of MWNTs. The nanocomposites were characterized by transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoemission spectroscopy (XPS). The sensors based on Au/PANI/MWNT nanocomposites were tested for on-line monitoring of ammonia gas. The results show that the as-prepared sensors have superior sensitivity, and good repeatability upon repeated exposure to ammonia gas.     

Synthesis and characterization of polyaniline-camphorsulphonic acid nanotube film

Polyaniline (PANI) nanotubes were prepared in the bulk solution and as films using the aniline oxidation with ammonium peroxydisulfate in aqueous solutions of camphorsulfonic acid (CSA). The in situ PANI films produced during the oxidation of aniline in CSA and also in hydrochloric acid solutions were followed by monitoring the frequency changes of quartz crystal microbalance (QCM). The kinetics of the film formation were discussed. The scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) showed PANI nanotubes. In addition, nanorods and nanoflowers composed from nanofibers and nanoflakes are also present to some extent. The nanotubes were characterized using UV-Vis spectroscopy.     

A Fiber-Optic Sensor for Monitoring Trace Ammonia in High-Temperature Gas Samples With a ${hbox{CuCl}}_{2}$-Doped Porous Silica Optical Fiber as a Transducer

An optical fiber chemical sensor for detecting/monitoring trace ammonia in high-temperature gas streams has been developed. This sensor uses a ${hbox{CuCl}}_{2}$-doped porous silica optical fiber, prepared via a previously reported sol-gel process, as a transducer. Trace ammonia in a gas sample diffuses into the porous fiber to react with the doped agent to form a ${hbox{Cu}}^{2+}$-ammonia complex. The concentration of the ${hbox{Cu}}^{2+}$ -ammonia complex inside the porous silica optical fiber is proportional to ammonia concentration in the gas sample, to which the sensing porous silica fiber is exposed. Therefore, ammonia concentration in the gas sample can be detected through detecting the optical absorption signal of the formed ${hbox{Cu}}^{2+}$-ammonia complex inside the fiber by using a fiber-optic UV/Vis absorption spectrometric method. This sensor can be used to reversibly monitor trace ammonia in a gas sample at an elevated temperature up to 450 $^{circ}$C in the tested range. A detection limit of 0.24 ppmv ammonia in an air gas sample was achieved when the sensor was tested at a temperature of 450 $^{circ}$ C.      

All-aerosol-jet-printed highly sensitive and selective polyaniline-based ammonia sensors: a route toward low-cost,low-power gas detection

Journal of Materials Science - We report the design and scalable fabrication of a low-cost and low-power polyaniline-based (PANI) ammonia (NH3) gas sensor on polyimide (PI) substrates using...     

聚苯胺纳米矩形管的制备与表征

以樟脑磺酸(CSA)为掺杂剂、过硫酸铵为氧化剂.在水溶液体系中通过苯胺原位聚合制得直径为300～600nm的聚苯胺纳米矩形管,其导电率为0.1～1S/cm.通过扫描电镜(SEM)和透射电镜(TEM)对产物的形貌进行表征.发现n(CSA)/n(ANi)将影响产物的形貌.利用傅立叶红外光谱(FT-IR)和紫外一可见光谱(Uv_vis)对聚苯胺分子结构进行表征,发现产物是质子化掺杂的聚苯胺.通过X射线衍射(XRD)分析发现,聚苯胺纳米矩形管比纤维结构具有更好的分子链排列规整性.     

Flexible Transparent Films Based on Nanocomposite Networks of Polyaniline and Carbon Nanotubes for High‐Performance Gas Sensing

A flexible, transparent, chemical gas sensor is assembled from a transparent conducting film of carbon nanotube (CNT) networks that are coated with hierarchically nanostructured polyaniline (PANI) nanorods. The nanocomposite film is synthesized by in‐situ, chemical oxidative polymerization of aniline in a functional multiwalled CNT (FMWCNT) suspension and is simultaneously deposited onto a flexible polyethylene terephthalate (PET) substrate. An as‐prepared flexible transparent chemical gas sensor exhibits excellent transparency of 85.0% at 550 nm using the PANI/FMWCNT nanocomposite film prepared over a reaction time of 8 h. The sensor also shows good flexibility, without any obvious decrease in performance after 500 bending/extending cycles, demonstrating high‐performance, portable gas sensing at room temperature. This superior performance could be attributed to the improved electron transport and collection due to the CNTs, resulting in reliable and efficient sensing, as well as the high surface‐to‐volume ratio of the hierarchically nanostructured composites. The excellent transparency, improved sensing performance, and superior flexibility of the device, may enable the integration of this simple, low‐cost, gas sensor into handheld flexible transparent electronic circuitry and optoelectronic devices.