Chitosan‐based composite membranes containing chitosan‐coated carbon nanotubes for polymer electrolyte membranes

Considering the poor dispersion and inert ionic conduction ability of carbon nanotubes (CNTs), functionalization of CNTs is a critical issue for their application in polymer electrolyte membranes. Herein, CNTs were functionalized by the polyelectrolyte, chitosan (CS), via a facile noncovalent surface‐deposition method. The obtained CS‐coated CNTs (CS@CNTs) were then incorporated into the CS matrix and fabricated composite membranes. The CS coating can enhance the compatibility between CNTs and the matrix, thus ensuring the homogenous dispersion of CS@CNTs and effectively improved the mechanical properties of the composites. Moreover, the CS coating can make CS@CNTs act as an additional proton‐conducting pathway through the membranes. The CS/CS@CNTs‐1 composite shows the highest proton conductivity of 3.46 × 10⁻² S cm⁻¹ at 80°C, which is about 1.5‐fold of the conductivity of pure CS membrane. Consequently, the single cell equipped with CS/CS@CNTs‐1 membrane exhibits a peak power density of 47.5 mW cm⁻², which is higher than that of pure CS (36.1 mW cm⁻²).     

Mg/Na-doped rutile TiO2 nanofiber mats for high-speed and anti-fogged humidity sensors

Mg²⁺ and Na⁺ doped rutile TiO₂ nanofibers have been prepared through in situ electrospinning technique and calcination with poly(vinyl pyrrolidone) (PVP) nanofibers as sacrificed template. The as-prepared composite nanofibers are spin-coated onto a ceramic substrate with three pairs of carbon interdigital electrodes to measure its humidity sensing behaviors. The product exhibits high-speed response (2 s) and recovery (1 s) for detecting moisture. Additionally, under UV irradiation, a water contact angle (θ) of nearly 0° has been observed based on the product, providing our humidity sensor with the anti-fogged properties.     

Sulfur Encapsulated in a TiO2‐Anchored Hollow Carbon Nanofiber Hybrid Nanostructure for Lithium–Sulfur Batteries

A hollow carbon nanofiber hybrid nanostructure anchored with titanium dioxide (HCNF@TiO₂) was prepared as a matrix for effective trapping of sulfur and polysulfides as a cathode material for Li–S batteries. The synthesized composites were characterized and examined by X‐ray diffraction, nitrogen adsorption–desorption measurements, field‐emission scanning electron microscopy, scanning transmission electron microscopy, and electrochemical methods such as galvanostatic charge/discharge, rate performance, and electrochemical impedance spectroscopy tests. The obtained HCNF@TiO₂–S composite showed a clear core–shell structure with TiO₂ nanoparticles coating the surface of the HCNF and sulfur homogeneously distributed in the coating layer. The HCNF@TiO₂–S composite exhibited much better electrochemical performance than the HCNF–S composite, which delivered an initial discharge capacity of 1040 mA h g^?1 and maintained 650 mAh g^?1 after 200 cycles at a 0.5 C rate. The improvements of electrochemical performances might be attributed to the unique hybrid nanostructure of HCNF@TiO₂ and good dispersion of sulfur in the HCNF@TiO₂–S composite.     

Nitric oxide measurement in biological and pharmaceutical samples by an electrochemical sensor

A nitric oxide (NO) electrochemical sensor was developed via one-step construction of gold nanoparticles (GNPs)–chitosan (CS) nanocomposite sensing film on a glassy carbon electrode (GCE) surface. This method is very simple and convenient. The GNPs–CS film which is controllable and stable exhibits catalytic activity to NO oxidation. The anodic peak potential significantly shifted negatively compared with that at bare GCE. The high sensitivity and good stability of developed method have been coupled to a wide linear range from 3.60 × 10⁻⁸ to 4.32 × 10⁻⁵ M for the quantitative analysis of NO. The detection limit of 7.20 nM is much lower than the vast majority of reported methods. This NO sensor has been successfully applied to NO measurement in biological and pharmaceutical samples. Real-time amperometric data show that the addition of L-arginine (L-Arg) can cause a slow release of NO from a whole rat kidney with a maximum concentration of ca. 150 nM. The concentration of NO monitoring from the drug sample was calculated to be ca. 1.60 μM.     

Fabrication of robust superhydrophobic coatings using PTFE‐MWCNT nanocomposite: Supercritical fluid processing

Fabrication of polymer‐carbon composite nanostructure with good dispersion of each other is critical for the desired application due to the nanostructure flaws, agglomeration, and poor absorption between the 2 materials. Fabrication of superhydrophobic surface coating composites of polytetrafluoroethylene (PTFE) with multiwalled carbon nanotubes (MWCNTs) through supercritical fluid processing was explored in this study. Homogeneity of the composite was characterized by X‐ray diffraction and Raman spectroscopy studies, which reveal that the PTFE and MWCNT are uniform in the composite. Microstructural surface evaluation of field‐emission scanning electron microscope and high‐resolution transmission electron microscope studies display that the coating composite possesses roughness structures and fibrillation of the superhydrophobic surface coating. Superhydrophobic character was evaluated on fiber‐reinforced plastic (FRP) sheets, which showed that the prepared coating composite surface showed self‐cleaning properties with a high water contact angle of 162.7°. The surface wettability was studied by increasing different temperatures (30°C to 300°C) in PTFE‐MWCNT composite, which reveals that the FRP sheets were thermally stable up to 200°C and afterward; they transformed from superhydrophobic to hydrophilic state at 250°C. The superhydrophobic surfaces are thermally stable in extreme environmental conditions, and this technique may be used and extendable for large‐scale applications.     

Application of nanostructure ZnLI2 complex in construction of optical pH sensor

This is for the first time that application of complex nanostructure is reported as pH indicator in PVC matrix. This new optical pH sensor was constructed based on incorporation of ZnLI₂ complex nanostructure in PVC matrix. The synthesized nanostructure ZnLI₂ complex was characterized by SEM and XRD technique. The membrane solution was speared on the glass plate to provide thin film and the membrane surface morphology was investigated via field emission scanning microscope (FE‐SEM) technique. Central composite design (CCD) combined with desirability function (DF) was applied to find the best experimental composition of membrane providing the highest absorbance. These conditions were found in correspondence with 3 mg of pH indicator, 3 mg of ionic additive and 1.5 mg/mg of DBP/PVC weight ratio. Under optimum conditions, the proposed pH sensor has two linear working ranges of 4 ‐ 8 at 393 nm (R² = 0.9897) and 5 ‐ 8 (R² = 0.9982) at 570 nm with response time of 4 min. The pK_a of proposed pH optical sensor was calculated through three methods that found to be 5.63. The present optical sensor shows stability after 2 months without any significant divergence in response properties (less than 5% RSD). Furthermore, current pH optode was exhibited good repeatability (RSD = 1.14%) as well as reproducibility (RSD = 4.06%). No significant variation was observed on sensor response with increasing the ionic strength in the range of 0.0–0.5 M of sodium chloride. All above features indicated that the proposed sensor can be successfully used for detection of pH in solutions with different ionic strength.     

Carbon-based conductive rubber composite for 3D printed flexible strain sensors

Polymeric-based flexible electronic devices are in high demand due to its wide range of applications. Natural rubber (NR) shows a great potential as matrix phase for flexible conductive polymer composites with its high elasticity and fatigue resistance. In this study, a new 3D printable conductive NR (CNR) composite was developed for strain sensor applications. Different contents of conductive carbon black (CCB) were mixed with NR latex to investigate the effect of the filler content on electrical and mechanical properties of the composites. The best-known CNR composite with the CCB content of 12 phr was selected in order to produce the feedstock for the stereolithography process (SLA). The morphological, electrical, and mechanical properties of cast and 3D-printed samples were investigated and compared. Although the 3D-printed CNR sample had slightly lower conductivity than the cast one, it possessed comparable tensile strength and elongation at break, with values of 12.4 MPa and 703%, respectively. In addition, electrical responses of the CNR samples were investigated to demonstrate the electromechanical property of the material as a strain sensor. The 3D-printed CNR sample exhibited the highest electromechanical sensitivity with a gauge factor (GF) of 361.4 (ε = 210%–300%) and showed good repeatability for 500 cycles. In conclusion, the development of this 3D printable functional material with great sensing capability will pave the way for innovative designs of personalized sensing textiles and other smart wearable devices.     

Highly sensitive and ultrafast response surface acoustic wave humidity sensor based on electrospun polyaniline/poly(vinyl butyral) nanofibers

Polyaniline (PANi) composite nanofibers were deposited on surface acoustic wave (SAW) resonator with a central frequency of 433 MHz to construct humidity sensors. Electrospun nanofibers of poly(methyl methacrylate), poly(vinyl pyrrolidone), poly(ethylene oxide), poly(vinylidene fluoride), poly(vinyl butyral) (PVB) were characterized by scanning electron microscopy, and humidity response of corresponding SAW humidity sensors were investigated. The results indicated that PVB was suitable as a matrix to form nanofibers with PANi by electrospinning (ES). Electrospun PANi/PVB nanofibers exhibited a core–sheath structure as revealed by transmittance electron microscopy. Effects of ES collection time on humidity response of SAW sensor based on PANi/PVB nanofibers were examined at room temperature. The composite nanofiber sensor exhibited very high sensitivity of ∼75 kHz/%RH from 20 to 90%RH, ultrafast response (1 s and 2 s for humidification and desiccation, respectively) and good sensing linearity. Furthermore, the sensor could detect humidity as low as 0.5%RH, suggesting its potentials for low humidity detection. Attempts were done to explain the attractive humidity sensing performance of the sensor by considering conductivity, hydrophilicity, viscoelasticity and morphology of the polymer composite nanofibers.     

A miniature chemiresistor sensor for carbon dioxide

A carpet-like nanostructure of polyaniline (PANI) nanothin film functionalized with poly(ethyleneimine), PEI, was used as a miniature chemiresistor sensor for detection of CO₂ at room temperature. Good sensing performance was observed upon exposing the PEI–PANI device to 50–5000 ppm CO₂ in presence of humidity with negligible interference from ammonia, carbon monoxide, methane and nitrogen dioxide. The sensing mechanism relied on acid–base reaction, CO₂ dissolution and amine-catalyzed hydration that yielded carbamates and carbonic acid for a subsequent pH detection. The sensing device showed reliable results in detecting an unknown concentration of CO₂ in air.     

Co-precipitation synthesis,humidity sensing and photoluminescence properties of nanocrystalline Co2+ substituted zinc(II)molybdate (Zn1–xCoxMoO4; x = 0, 0.3, 0.5, 0.7, 1)

Zinc-cobalt molybdate composites (Zn_1–xCo_xMoO₄; x = 0, 0.3, 0.5, 0.7, 1) were synthesised by a simple co-precipitation method and characterised by thermogravimetric/differential thermal analysis (TG/DTA), Fourier transform-infrared (FT-IR), Fourier transform Raman (FT-Raman) spectroscopy, X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM/EDAX) and transmission electron microscopy (TEM). The surface area was calculated by BET analysis in the adsorption/desorption isotherm. The humidity sensing properties of zinc-cobalt molybdates were tested by dc electrical measurements at different relative humidity environments (RH = 5–98%). The electrical resistance of the composites linearly decreases and the maximum sensitivity of 3672 ± 110 was observed for the Zn_0.3Co_0.7MoO₄ (ZnCM-4) composite towards humidity, which is calculated by the relation S_f = R_5%/R_98%, where the response time is 200 s and the recovery time is 100 s. Photoluminescence (PL) measurement at the room temperature of ZnM-1 composite exhibited a blue emission peak at 475 nm (λ_em) when excited at a wavelength (λ_ex) of 430 nm. During Co²⁺ substitution in Zn²⁺ matrix, a green and red emission peak was observed when excited at a wavelength (λ_ex) of 520 nm.     

Nanoflake-like cobalt hydroxide/ordered mesoporous carbon composite for electrochemical capacitors

Nanocomposites consisting of mesoporous carbon CMK-3 and cobalt hydroxide nanoflakes are synthesized by a chemical precipitation method. The successful growth of nanometer-sized Co(OH)₂ flakes on the surface of CMK-3 is confirmed by scanning electron microscopy. The Co(OH)₂/CMK-3 composite electrodes are investigated for its use in the electrochemical capacitors with cyclic voltammograms, chronopotentiometric measurements, and electrochemical impedance spectroscopy. Experimental studies reveal that the Co(OH)₂/CMK-3 composite electrode with the 20 wt.% CMK-3 presents excellent electrochemical performance with specific capacitance of 750 F/g (or 910 F/g after being corrected for the weight percentage of the Co(OH)₂ phase). The overall improved electrochemical behavior accounts for the unique structure design in the Co(OH)₂/CMK-3 composite in terms of porous nanostructure, large specific surface area, and good electrical conductance. The Co(OH)₂/CMK-3 composite electrode also shows better rate capability and cyclic stability, suggesting its potential applications as the electrode materials for electrochemical capacitors.     

Capacitive characteristics of nanocomposites of conducting polypyrrole and functionalized carbon nanotubes: effects of in situ dopant and film thickness

The nanocomposites of functionalized single-walled carbon nanotubes (FSWNTs) and conducting polypyrrole (PPy) doped by FSWNTs, Cl⁻, toluenesulfonate (TOS⁻), and dodecylbenzenesulfonate (DBS⁻), respectively, were electrochemically co-deposited to evaluate their applicability in supercapacitors. The effects of the dopants, with focus on their mass, size and surfactivity, and film thickness on the capacitive characteristics were investigated in 3 M KCl aqueous solution. Although the nanostructure of composites can admittedly improve the capacitive properties, dopant anion was demonstrated to be a more essential factor. The specific capacitance of PPy-TOS/FSWNT nanocomposites was greater than that of pristine PPy/FSWNT nanocomposites and PPy-DBS/FSWNT nanocomposites by ten and 100 times, respectively. Furthermore, PPy-TOS/FSWNT nanocomposites exhibited the lowest dependence of capacitance on the charging–discharging rate and composite thickness due to its high electronic and ionic conductivity resulting from the appropriate doping level and size of TOS^- as well as the synergic effect of PPy-TOS and FSWNTs. In addition, PPy-TOS/FSWNT nanocomposites presented a remarkably stable cycling performance.     

Facile simultaneous polymerization enabled in-situ confinement of size-tailored GeO2 nanocrystals in continuous S-Doped carbons for lithium storage

GeO₂ is a promising anode material for lithium ion batteries due to its high theoretical capacity (1126 mAh g^?1 for reversibly storing 4.4 Li⁺), and moderately low operating voltage (<1.5 V). Nevertheless, the fabrication of truly durable GeO₂ anode with satisfactory rate capability and cycling stability remains a big challenge because of its inherent low conductivity, and the large volume expansion upon charge-discharge that causes severe capacity fading. In this study, an innovative nanostructure with size-adjustable GeO₂ nanoparticles (16–26 nm) embedded in continuous S-doped carbon (GeO₂/S-doped carbon, GSC) has been successfully fabricated via a facile in-situ simultaneous polymerization method followed by heat treatment. The electrochemical results indicate that the as-prepared GSC composites show high reversible capacity (672.9 mAh g^?1 at 50 mA g^?1), superior rate capability (332.9 mAh g^?1 at 1000 mA g^?1), and long-term cycle life (179 mAh g^?1 after 500 cycles at 1000 mA g^?1) as anode materials for lithium ion batteries. The excellent electrochemical performance of GSC nanocomposites could be ascribed to the homogeneous and continuous S-doped carbon matrix, which provides shortened ion diffusion pathway, increased electrical conductivity, enhanced structural stability, and introduced surface/interface property.     

Novel low humidity sensor made of TiO(2) nanowires/poly(2-acrylamido-2-methylpropane sulfonate) composite material film combined with quartz crystal microbalance

A novel ceramic nanowires of TiO₂ and poly(2-acrylamido-2-methylpropane sulfonate) (TiO₂ NWs/PAMPS) composite material films coated on quartz crystal microbalance (QCM) was prepared as a low humidity sensor. The 50 wt.% of TiO₂ NWs/PAMPS composite material films showed excellent sensitivity (2.63 −ΔHz/Δppm_v) at 31.5 ppm_v), linearity (R² = 0.9959) and acceptable response time (64 s at 34.6 ppm_v). The low humidity sensing mechanism was discussed in terms of surface texture and nanostructured morphology of the composite materials. Moreover, the adsorption dynamic analysis, molecular mechanics calculation (association constant), was used to elucidate the effect of adding 50 wt.% TiO₂ NWs into PAMPS in the increased sensitivity of low humidity sensing.     

Multiparametric optimization of a new high-sensitive and disposable mercury (II) electrochemical sensor

An electrochemical sensor for mercury (II) determination was developed by modifying the surface of a commercial screen-printed carbon electrode (SPCE) with a polystyrene sulfonate-NiO-carbon nanopowder composite material. Mercury measurements were performed by differential pulse anodic stripping voltammetry (DPASV). Sensor composition and measurement conditions were optimized using a multivariate experiment design. A screening experiment by using a Plackett-Burman design was first performed in order to determine the main contributing factors to the electrochemical response. The most important factors were employed to establish the interactions between different experimental variables and get the best conditions for mercury determination. For this purpose, a five level central composite design and a response surface methodology were used. The optimized method using the developed NiO-PSS-SPCE sensor presents a very low limit of detection of 0.021 μg L⁻¹ and a linear response over two concentration ranges with two different slopes, from 0.05 to 2.0 μg L⁻¹ and between 2.0 and 75 μg L⁻¹. The sensor was successfully applied to mercury determination in water samples.     

Ru oxide/carbon fabric composites for supercapacitors

Ru oxide/carbon fabric composites (Ru oxide/CF) were prepared by impregnating carbon fabric (CF) with a hydrous RuO₂ suspension. Their properties were characterized by scanning electron microscopy, impedance spectroscopy, cyclic voltammetry, and constant current discharging. Specific capacitance increased with increasing loading of Ru oxide. The apparent average specific capacitance of the Ru oxide component reached 1,085 F g⁻¹ for a 9.15% loading, with a peak of 1,984 F g⁻¹ at approximately 0.3 V vs Ag/AgCl. The presence of Ru oxide decreases the ionic resistance of the CF and appears to increase its specific capacitance by generating additional electroactive surface functionality.     

Electrochemical capacitance of the composite of poly (3,4-ethylenedioxythiophene) and functionalized single-walled carbon nanotubes

The homogenous coating of poly (3,4-ethylenedioxythiophene) (PEDOT) on carbon nanotubes was realized by using functionalization of single-walled carbon nanotubes (SWNTs) in this study. Consequently, the PEDOT/functionalized SWNTs (PEDOT/F-SWNTs) composites, with size of around 100nm, which is much smaller than that of PEDOT, were prepared by the electrochemical method. Its small granule increased the active/nonactive mass ratio and reduced the ions diffusion length. Therefore, its specific capacitance of the composite was up to 200F g^?1, which was remarkably greater than that of PEDOT. Furthermore, the PEDOT/F-SWNTs composites had very rapid charge/discharge ability with specific capacitance of 180F g^?1 at scanning rate of 200mV s^?1 and 170F g^?1 at frequency of 1Hz, which is an important practical advantage. In addition, such composite had a good cycling performance and a wide potential window.     

Comparative studies on zirconia and graphene composites obtained by one-step and stepwise electrodeposition for deoxyribonucleic acid sensing

In this paper, the comparison of two kinds of electrochemically reduced graphene oxide (ERGNO) and zirconia composites, obtained by one-step (ZrO₂–ERGNO) and stepwise (ZrO₂/ERGNO) electrodeposition for DNA sensing, is systematically studied. The resulting composites were characterized by scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry. The results indicated that the ZrO₂–ERGNO presented fine globular nanostructure. However, ZrO₂/ERGNO presented agglomerate massive microstructure due to the absence of the oxygen-containing groups of graphene oxide, confirming the oxygen-containing groups provided a better affinity for the deposition of ZrO₂. Due to the strong binding of the phosphate groups of DNA with the zirconia film, DNA probes were attached on the ZrO₂-based composites. ZrO₂–ERGNO/Au owning fine nanostructure presented larger surface area than microstructured ZrO₂/ERGNO/Au. Moreover, compared with microstructured ZrO₂/ERGNO, the nanostructured ZrO₂–ERGNO provided more accessible space for immobilized DNA probe hybridization with target sequence, which consequently resulted in higher hybridization efficiency. Therefore, the ZrO₂–ERGNO was chosen for fabricating DNA sensor with a limit of detection 1.21 × 10⁻¹⁴ mol L⁻¹.     

Two-dimensional copper oxide/zinc oxide nanoflakes with three-dimensional flower-like heterostructure enhanced with electrocatalytic activity toward nimesulide detection

The strategy of building two-dimensional (2D) metal oxide nanoflakes has inspired several innovations in different fields of application on account of its tremendous significance. It includes ultrathin planar surface, large charge carrier mobility, and tunable band structures, providing unprecedented features for sensing. Moreover, the intercalation of 2D dimensions to 3D superstructures will result in improved and dual advantages of both 2D/3D. The construction of 2D/3D copper oxide zinc oxide nanocomposite as electrode material for specific detection of nimesulide (NMS) is herein reported. The conversion of 2D CZ nanoflakes to 3D CZ microflowers was possibly achieved via the self-assembly process. This simple and cost-effective development of the CZ composite was characterized for evaluating the physical, chemical, and morphological properties. The highly crystalline nature of CZ was observed from powder X-ray diffraction and X-ray photoelectron spectroscopy analysis. The formation of 2D nanoflakes of CZ was strongly confirmed from field emission scanning electron microscopy and high-resolution transmission electron microscopy images. To verify the strong attachments, Fourier transforms infrared spectroscopy spectra were analyzed. Electrochemical sensing of NMS at CZ fabricated glassy carbon electrode reflects higher electrocatalytic activity with a linear range of NMS addition from 0.299 μM to 319.15 μM. The lower detection limit was about 0.005 μM with a sensitivity of 7.152 μAμM^?1 cm². The CZ nanocomposite will be more applicable for sensing several drugs with enriched active sites, higher conductivity, and large surface area raised from low-cost metal oxides when compared with highly conducting materials.     

Electrochemical performance of sulfur composite cathode materials for rechargeable lithium batteries

The structure and characteristic of carbon materials have a direct influence on the electrochemical performance of sulfur-carbon composite electrode materials for lithium-sulfur battery.In this paper,sulfur composite has been synthesized by heating a mixture of elemental sulfur and activated carbon,which is characterized as high specific surface area and microporous structure.The composite,contained 70%sulfur,as cathode in a lithium cell based on organic liquid electrolyte was tested at room temperature....