A shape tailored gold-conductive polymer nanocomposite as a transparent electrode with extraordinary insensitivity to volatile organic compounds (VOCs)

In this study, the transparent conducting polymer of poly (3,4-ethylenendioxythiophene): poly(styrene sulphonate) (PEDOT:PSS) was nanohybridized via inclusion of gold nanofillers including nanospheres (NSs) and nanorods (NRs). Such nanocomposite thin films offer not only more optimum conductivity than the pristine polymer but also excellent resistivity against volatile organic compounds (VOCs). Interestingly, such amazing properties are achieved in the diluted regimes of the nanofillers and depend on the characteristics of the interfacial region of the polymer and nanofillers, i.e. the aspect ratio of the latter component. Accordingly, a shape dependent response is made that is more desirable in case of using the Au nanorods with a much larger aspect ratio than their nanosphere counterparts. This transparent nanocomposite thin film with an optimized conductivity and very low sensitivity to organic gases is undoubtedly a promising candidate material for the touch screen panel production industry. Considering PEDOT as a known material for integrated electrodes in energy saving applications, we believe that our strategy might be an important progress in the field.Peer reviewe

Eco-friendly all-carbon paper electronics fabricated by a solvent-free drawing method

Here we report the fabrication of high-performance all-carbon temperature and infrared (IR) sensors with a solvent-free multiwalled carbon nanotube (MWCNT) trace as the sensing element and commercial graphite pencil trace as the electrical contact on recyclable and biodegradable cellulose filter paper without using any toxic materials or complex procedures. The temperature sensor shows a large negative temperature coefficient of resistance (TCR) in the range of −3100 ppm K−1 to −4900 ppm K−1, which is comparable to available commercial temperature sensors, and an activation energy of 34.85 meV. The IR sensor shows a high responsivity of 58.5 V W−1, which is greater than reported IR sensors with similar dimensions. A detailed study of the conduction mechanism in MWCNTs with temperature and the photo response with IR illumination was done and it was found that the conduction is due to thermally assisted hopping in band tails and the photo response is bolometric in nature. The successful fabrication of these sensors on cellulose filter paper with a comparable performance to existing components indicates that it is possible to fabricate high-performance electronics using low-cost, eco-friendly materials without the need for expensive clean-room processing techniques or harmful chemicals

High-performance solid-state supercapacitor based on sustainable synthesis of meso-macro porous carbon derived from hemp fibres via CO2 activation

Most porous carbons have been prepared using KOH, ZnCl2 as activating agents via chemical activation process, where toxic chemicals, elevated temperature and multi-stage preparation are involved. Herein, we report synthesis of porous carbon from hemp fibre (HFPC) via single step, low temperature carbonization followed by CO2 physical activation for high-performance solid state supercapacitor application in a PVA-KOH hydrogel as gel electrolyte. Detailed characterization and optimization studies based on varying the duration (hours) of activation yields HFPC-30 material that comprises of interconnected carbon network of meso and macro pores with a high specific surface area of 1060 m2g−1. This enables rapid ion transfer and efficient electrode- electrolyte interaction and HFPC-30 exhibit an excellent half-cell specific capacitance of ~600 Fg−1 at 1 Ag−1. The assembled symmetric supercapacitor device with HFPC-30 delivers a full-cell specific capacitance of ~457 Fg−1 in PVA-KOH hydrogel as gel electrolyte. A maximum specific energy of 25.3 Whkg−1 at ~4320 Wkg−1 specific power is obtained, which is very high compared to other reported carbon materials. Further, the assembled supercapacitor device works until 2V delivering a capacitance retention of ~85% after 10,000 cycles. Thus, biomass derived porous carbon material in a hydrogel electrolyte presents a novel strategy for developing highly promising sustainable electrodes for high energy, solid state supercapacitor applications

Divulging the electrochemical hydrogen storage of ternary BNP-doped carbon derived from biomass scaled to a pouch cell supercapacitor

Activated carbon materials have been studied extensively as electrode materials for supercapacitors (SCs), but their poor capacitance and energy density have hampered their growth. We present a one-step synthesis of a ternary boron-nitrogen-phosphorous-doped carbon (BNPC) from biomass hemp fibre to determine its electrochemical hydrogen storage ability using SC applications. FESEM micrographs reveal mixed morphologies like square, diamond and cylindrical-shaped nanosheets, confirming the hetero-atom doping into the carbon skeleton. The optimized BNPC electrode delivers a half-cell specific capacitance and hydrogen-storage capacity of 520 Fg-1 (1 Ag-1) and 360 mAhg−1 (10 mVs−1), respectively. To demonstrate the practicability of the as-prepared BNPC electrode, a symmetric pouch-cell supercapacitor device was assembled which exhibits a full-cell specific capacitance of 262.56 Fg-1 at 1 Ag-1 and a specific energy of ~118 Wh kg−1 at a specific power of ~5759 Wkg-1 with an operating potential window of 1.8 V and 99.7% capacitance retention over 10,000 cycles. This excellent electrochemical performance can be ascribed to the synergetic properties of fast-electrolyte-ion diffusion due to the doping of heteroatoms into the carbon matrix, high conductivity and high specific surface area and effective microporosity of BNPC (1555.5 m2g-1). Also, the chemical stability of the BNPC materials, was investigated with density functional theory (DFT)-single point calculations, where the least molecular orbital energy gap was obtained by the BNPC, which confirms its structural stability. Thus, the prepared ternary BNP-doped carbon derived from biomass has provided a new direction to enhance the electrochemical energy storage potential

3D, large-area NiCo2O4 microflowers as a highly stable substrate for rapid and trace level detection of flutamide in biofluids via surface-enhanced Raman scattering (SERS)

A one-pot hydrothermal synthesis of three-dimensional (3D), large-area, bimetallic oxide NiCo2O4 (NCO) microflowers has been developed as a novel substrate for surface-enhanced Raman scattering (SERS) detection of flutamide in biological fluids. The 3D flower-like morphology of the NCO is observed via FESEM micrographs, while the orthorhombic phase formation is confirmed through XRD spectra. Due to the presence of multiple coordination cations of the 3D NCO microflowers (such as Ni2+ and Co2+), the high surface area and surface roughness, the NCO-modified indium tin oxide (NCO/ITO) SERS substrate exhibits a linear detection range from 0.5-500 nM with a low limit of detection (LOD) of 0.1 nM. The SERS substrate provides a high enhancement factor of 1.864 × 106 with an accumulation time of 30 s using a laser source of λ = 532 nm, which can be ascribed to the excellent and rapid interaction between the flutamide molecule and the NCO microflower substrate that leads to photoinduced charge transfer (PICT) resonance. The NCO/ITO substrate exhibits excellent homogeneity and high chemical stability. Besides, the substrate displays an excellent selectivity to flutamide molecules in the existence of other metabolites such as urea, ascorbic acid (AA), glucose, NaCl, KCl, CaCl2, and hydroxyflutamide. The NCO/ITO substrate is successful in the trace-level detection of flutamide in simulated blood serum samples. The strategy outlined here presents a novel strategy for the efficacy of transition metal oxides (TMOs) based electrodes useful for a wide variety of bioanalytical applications

Low cost, flexible and biodegradable touch sensor fabricated by solvent-free processing of graphite on cellulose paper

There is a strong demand for flexible user interface technology with a desired size and shape to make real world objects touch-interactive. In this regard, plastic based touch sensors have been widely used on account of their adaptability. However, their fabrication involves eco-unfriendly procedures like lithography or other cleanroom processes which contribute greenhouse gases (GHG) and hence raises the need for exploring alternative green fabrication methods. In this work, we report the fabrication of an inexpensive, flexible, biocompatible, low power and environmentally benign interdigitated capacitive (IDC) touch sensor based on cleanroom-free and solvent-free processing of graphite on paper (GOP). The performance of touchpad with four touch sensor keys was evaluated by integrating it with Arduino UNO development board and it functioned similar to the conventional touchpads which are fabricated by utilizing complex procedures and expensive equipments on plastic substrates. The influence of the number and the overlap length of electrode digits on touch sensor performance was investigated and optimized based on variation in capacitance with the interaction of finger with the touch sensor for better performance and enhanced user experience. The pressure due to strength of the touch and strain induced due to bending and folding of the touch sensor resulted in insignificant variation in capacitance and no change in functionality. This suggests that the flexible and robust GOP based touchpad can be used in diverse applications such as user interface for medical diagnostics, health, environment and security monitoring devices where low cost, eco-friendly, flexible, durable and stable touch control is required. This approach of developing highly advanced, efficient yet biodegradable paper electronics which doesn’t involve the use of any toxic, flammable or corrosive gases nor chemicals paves the way for next generation green and sustainable eco-friendly electronics

Solvent-free fabrication of biodegradable all-carbon paper based Field Effect Transistor for human motion detection through strain sensing

There has been a huge demand for low-cost, eco-friendly, flexible and wearable electronics which find applications in personal health monitoring. Flexible electronics based on plastic substrates have been extensively studied in this regard because of their versatility. However, their fabrication involves energy consuming complex procedures and processing of eco-unfriendly materials which limit their use to certain specific applications. Here we report the fabrication of a flexible all-carbon field effect transistor (FET) using a economically efficient, recyclable and biodegradable cellulose paper as both substrate as well as dielectric and pencil graphite as source, drain, channel and gate without using any expensive, toxic or non-biodegradable materials. The FET transfer characteristics shows ambipolar behavior which can be utilized in analog electronics applications like rectifier, mixer and frequency multipliers and its mobility was found to be very high compared to reduced graphene oxide based FETs. The FET was utilized as a strain sensor which shows excellent sensitivity for very low strains (of both tensile and compressive type) which is comparable to and even better than recently reported carbon nanotube and graphene based strain sensors. The sensitivity of the FET based strain sensor can be modulated by varying the gate voltage under strain. Furthermore, we investigated the performance of the sensor by integrating it with hand gloves to detect human motion. The results indicate that the sensor can be utilized in patients surveillance in healthcare and human-machine interface (HMI) applications. The successful fabrication of this paper based all-carbon transistor using only paper and pencil graphite and its application in human motion detection using strain sensing indicates that this approach can be used for developing highly scalable, low cost, low energy, flexible green electronics for healthcare without using any sophisticated fabrication methods or toxic chemicals

UV/ozone assisted local graphene (p)/ZnO(n) heterojunctions as a nanodiode rectifier

Here we report the fabrication of a novel graphene/ZnO nanodiode by UV/ozone assisted oxidation of graphene and demonstrate its application as a half-wave rectifier to generate DC voltage. The method involves the use of electrospinning for one-step in situ synthesis and alignment of single Gr/ZnO nanocomposite across metal electrodes. On subsequent UV illumination, graphene oxidizes, which induces p type doping and ZnO being an n type semiconductor, thus resulting in the formation of a nanodiode. The as-fabricated device shows strong non-linear current–voltage characteristic similar to that of conventional semiconductor p–n junction diodes. Excellent rectifying behavior with a rectification ratio of ~103 was observed and the nanodiodes were found to exhibit long-term repeatability in their performance. Ideality factor and barrier height, as calculated by the thermionic emission model, were found to be 1.6 and 0.504 eV respectively. Due to the fact that diodes are the basic building blocks in the electronics and semiconductor industry, the successful fabrication of these nanodiodes based on UV assisted p type doping of graphene indicates that this approach can be used for developing highly scalable and efficient components for nanoelectronics, such as rectifiers and logic gates that find applications in numerous fields

Solvent-free fabrication of paper based all-carbon disposable multifunctional sensors and passive electronic circuits

In light of recent interest in the green fabrication of electronics, we report eco-friendly engineered temperature sensors, pH sensors, humidity sensors and passive resistor-capacitor (RC) filters by solventfree processing of graphite on cellulose paper. This was achieved via direct writing of graphite pencil on cellulose paper which involves the deposition of few layers to multi layers of conductive graphene flakes intercalated by clay and wax. The temperature sensor exhibits a negative temperature coefficient of resistance of -4232 ppm K-1, which is comparable to that of conventional temperature sensors (platinum, nickel, and copper) that are fabricated by capital intensive and complex procedures. The dynamic response of the temperature sensor shows its repeatability with excellent response time of 13.5 s. The all-carbon pH sensor could efficiently distinguish acidic, alkaline and neutral solutions with significant sensitivity from 1.77 k Omega pH(-1) to 2.21 k Omega pH(-1). The higher sensitivity of the pH sensor is attributed to the oxygen functional groups present in pencil graphite which undergoes protonation and deprotonation in presence of H+ and OH- ions to alter the conductivity of graphite trace. The interdigitated capacitive humidity sensor shows a linear response to humidity with fast response (1.5-2 s) and recovery times (6-7 s). These fast response and recovery times are due to fast adsorption and evaporation kinetics of water molecules on polar OH groups of cellulose fibers in paper, which depends on porosity of the paper. The versatility of the pencil-on-paper approach was further explored by drawing resistor and interdigitated capacitor in series to fabricate in-plane all-carbon RC filter which demonstrate anticipated functionality with a cut-off frequency of 6 kHz. To the best of our knowledge, no studies have been reported on direct-write graphite on paper based in-plane all carbon passive electronic circuits, pH sensor and humidity sensor. This cleanroom-free approach further expands the scope of graphite on paper as a functional material in developing sensors and circuits for greener consumer electronics thereby causing no environmental contamination either in their production or disposal

Low-density, stretchable, adhesive PVDF-polypyrrole reinforced gelatin based organohydrogel for UV photodetection, tactile and strain sensing applications

In this work, we report an adhesive, mechanically robust Polyvinylidene fluoride (PVDF)-polypyrrole reinforced gelatin organohydrogel as a multifunctional, and conductive platform for photodetector, highly sensitive tactile, and strain sensor applications. Morphological studies reveal the formation of PVDF/polypyrrole/gelatin microspheres enclosed with nanosheets like structure on the surface of the organohydrogel confirming the interaction of the primary amines of the cationic PVDF-polypyrrole nanocomposite with the anionic carboxylic chains of gelatin. Structural characterization confirms the characteristic scattering bands of β- phased PVDF and polypyrrole. The synthesized organohydrogel when used as a UV photodetector exhibits a rapid response time of 25 ms, excellent responsivity of 14 A/W and external quantum efficiency of 26%, caused due to the effective separation of photogenerated charge carriers at the polymer-hydrogel interface. The recoverable organohydrogel-based tactile sensor exhibited a sensitivity of 32.39 kPa−1 in the wide linear range of 0.1 – 55 kPa. Further, the strain sensor displayed a gage factor of 27.8 in the dynamic sensing range of 8.6% to 61% which is much higher than the existing class of similar reports. The sensing mechanism can be attributed to the piezo-electric polarizability of the β- phase PVDF and high conductivity of polypyrrole and gelatin in the flexible organohydrogel. The effective reinforcement of PVDF and polypyrrole in the gelatin matrix enhances the tensile strength, elastic properties, conductivity with least dependency on humidity and temperature. The polymer composite reinforced gelatin organohydrogel has a shelf-life of 30 days. © 202