Reduced Graphene Oxide-zinc Oxide Research Articles

Structural, microstructural and optical characteristics of rGO-ZnO nanocomposites via hydrothermal approach

This paper describes the production and characterizations of reduced graphene oxide-zinc oxide (rGO-ZnO) nanocomposites fabricated via hydrothermal approach. Firstly, rGO powder was produced via modified Hummers' method and ZnO nanoparticles using chemical co-precipitation. The nanocomposites structural, microstructural and optical characteristics were determined using X-ray diffraction (XRD), infrared spectroscopy (FTIR), Raman spectroscopy and Ultraviolet–visible (UV–Vis) spectroscopy. The findings demonstrated the effective synthesis of rGO-ZnO nanocomposites with evenly distributed ZnO nanoparticles on the surface of reduced graphene oxide sheets. rGO-ZnO nanocomposites with different concentrations ratio rGO:ZnO in composition of 10:0. 7.5:2.5, 5:5, 2.5:7.5, and 0:10 (weight percentage) were formed. An average crystallite size (Davg) was observed to be decreasing with an increasing concentration of ZnO in to rGO from ∼13.96 nm to ∼21.36 nm which is supported by Williamson-Hall (W–H) extrapolation. The FTIR spectra showed the functional groups belongs to intrinsic and extrinsic vibrations v1 and v2 at ∼410 cm−1 for rGO and metal‒oxygen (Zn–O) stretching vibrations ∼400 cm−1 to ∼500 cm−1 for rGO-ZnO nanocomposites. On rising ZnO content in the rGO-ZnO nanocomposites, a slight variation in band positions was caused due to the microstructural changes. Raman spectroscopy revealed certain peaks (D, G, for rGO; E2, A1 (TO), LO for ZnO) in various compositions. The research demonstrates how the composition of a material affects its vibrational characteristics, which is crucial for customizing the material for certain applications. The optical energy band gap of rGO-ZnO 75 % was recorded to be ∼4.94 eV, and highest for rGO with 5.44 eV. The optical energy band gap decreased from 5.44 eV to 4.94 eV. This decrease can be attributed to the influence of the smaller crystallite size and fluctuations in microstructural properties caused by the rGO-ZnO nanocomposite. The obtained rGO-ZnO nanocomposites can be utilized for opto-electronic device applications.

Enhanced photocatalytic degradation of methylene blue dye using eco-friendly synthesized rGO@ZnO nanocomposites

Industrial chemical pollutants such as methylene blue (MB) dye are released into the water body and potentially cause harm to the human and aquatic biosphere. Therefore, this study aims to synthesize eco-friendly nanocatalysts, i.e., reduced graphene oxide (rGO), zinc oxide (ZnO), and reduced graphene oxide-zinc oxide (rGO@ZnO) nanocomposites, for efficient photocatalytic degradation of MB dye. A graphite rod was obtained from waste dry cell batteries for the electrochemical exfoliation synthesis of graphene oxide (GO) and rGO. For the eco-friendly synthesis of ZnO and rGO@ZnO nanocatalysts, Croton macrostachyus leaf extract was used as a reducing and capping agent. The synthesized nanocatalysts were characterized using a UV–Vis spectrophotometer, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy with energy-dispersive X-ray. The eco-friendly synthesized rGO, ZnO, and rGO@ZnO nanocatalysts were applied for the photocatalytic degradation of MB dye using direct sunlight irradiation. At optimum parameters, photocatalytic degradation of MB dye efficiency reached up to 66%, 96.5%, and 99.0%, respectively. Furthermore, kinetics of the photodegradation reaction based on rGO, ZnO, and rGO@ZnO nanocatalysts follow pseudo-first-order with a rate constant of 2.16 × 10–3 min−1, 4.97 × 10−3 min−1, and 5.03 × 10−3 min−1, respectively. Lastly, this study promotes a low catalyst load (20 mg) for the efficient photodegradation of MB dye.

Hexavalent chromium removal using reduced graphene oxide-zinc oxide composite fabricated via simple pyrolysis method

The contamination of water by heavy metals from various industrial effluents is a significant factor contributing to the scarcity of clean water worldwide. To address this issue, there is a need to develop low-cost adsorbents to remove heavy metals from contaminated water reduced graphene oxide (rGO) based composites are efficient adsorbers of heavy metals. In this study, a green and rapid single-step heating process was utilized to prepare both rGO and rGO/ZnO composite materials, avoiding the use of any toxic reagents. The rGO/ZnO composite synthesized from sucrose and zinc acetate demonstrates a remarkable ability to adsorb hexavalent chromium (Cr(VI)). The Cr adsorption studies were carried out by varying adsorbent, contact time, initial pH, and concentration. The adsorption efficiency of the composite is five times higher than that of pure rGO. The adsorption mechanism of Cr(VI) onto the adsorbent is electrostatic interaction, complexation, pore filling, and reduction, identified through Zeta potential measurement, BET, EDX, and XPS analysis. These studies suggest that rGO/ZnO composite has great potency as a cost-effective and efficient adsorbent for removing Cr(VI) contaminants from industrial effluents.

Adsorption and Kinetics Studies of Cr (VI) by Graphene Oxide and Reduced Graphene Oxide-Zinc Oxide Nanocomposite.

In this work, graphene oxide (GO) and its reduced graphene oxide-zinc oxide nanocomposite (rGO-ZnO) was used for the removal of Cr (VI) from aqueous medium. By employing a variety of characterization techniques, morphological and structural properties of the adsorbents were determined. The adsorption study was done by varying concentration, temperature, pH, time, and amount of adsorbent. The results obtained confirmed that rGO-ZnO is a more economical and promising adsorbent for removing Cr (VI) as compared to GO. Kinetic study was also performed, which suggested that sorption of Cr (VI) follows the pseudo-first-order model. For equilibrium study, non-linear Langmuir was found a better fitted model than its linearized form. The maximum adsorption capacity calculated for GO and rGO-ZnO nanocomposite were 19.49 mg/g and 25.45 mg/g, respectively. Endothermic and spontaneous nature of adsorption was detected with positive values of ΔS (change in entropy), which reflects the structural changes happening at the liquid/solid interface.

Enhanced adsorptional-photocatalytic degradation of chloramphenicol by reduced graphene oxide-zinc oxide nanocomposite

Improper discharge of waste dry cell batteries and untreated antibiotics laden effluents to the environment pose serious threat to the sustenance of the ecosystem. In this study, synthesis of reduced graphene oxide-ZnO (rGO-ZnO) nanocomposite was achieved via a bioreduction process using waste dry cell battery rod as graphene oxide (GO) precursor. The nanocomposite was applied in the ultraviolet photocatalytic degradation of chloramphenicol (CAP) at 290 nm in the presence of hydrogen peroxide. RGO-ZnO nanocomposite was characterized by SEM, TEM, XRD, BET and FTIR. TEM image of the nanocomposite revealed a polydispersed, quasi-spherical zinc oxide on a coarse reduced graphene oxide surface. XRD patterns showed sharp, prominent crystalline wurtzite hexagonal phases of ZnO and rGO. BET surface area of the nanocomposite was 722 m2/g with pore size of 2 nm and pore volume of 0.4 cc/g. % photo-removal efficiency increased with increasing irradiation time but diminished at higher pH, temperature and CAP concentration. Photocatalytic adsorption process fitted more accurately into the Freundlich model (R2 = 0.99) indicating a multilayer adsorption mechanism. 92.74% reduction in chemical oxygen demand (COD) level of veterinary effluent was obtained after treatment with the nanocomposite thus affirming its effectiveness in real waste water samples.

Facile construction of three-dimensional porous netlike reduced graphene oxide/zinc oxide composite aerogels as the lightweight, flame retardant, compression resilience and high-performance electromagnetic wave absorbers

In this work, reduced graphene oxide/zinc oxide (RGO/ZnO) composite aerogels were constructed through a one-pot hydrothermal route. Results manifested that the composite aerogels had the extremely low density and a unique three-dimensional porous network structure, and lots of ZnO particles were almost homogeneously loaded on the rippled surfaces of lamellar RGO. Moreover, the micromorphology and electromagnetic absorbing properties of composite aerogels were facilely regulated by changing the additive amounts of sodium citrate. Notably, the optimal minimum reflection loss reached −79.1 dB at a matching thickness of 2.49 mm and maximum effective absorption bandwidth achieved 7.7 GHz under a thickness of 1.97 mm and filling ratio of 20.0 wt%. Furthermore, the attained composite aerogels presented excellent flame retardant and compression resilience properties. Additionally, the possible electromagnetic dissipation mechanism was proposed. This work provided a reference for the design and preparation of RGO-based dielectric composites as the multifunctional electromagnetic wave absorbers.

Reduced graphene oxide-zinc oxide nano-composites for gas sensing applications

Reduced graphene oxide-zinc oxide nano-composites for gas sensing applications

One-pot wet chemical synthesis of reduced graphene oxide-zinc oxide nanocomposites for fast and selective ammonia sensing at room temperature

The present study focuses upon the response of nanocomposites of reduced graphene oxide (rGO) and zinc oxide (ZnO) towards ammonia gas at room temperature. We have synthesized reduced graphene oxide-zinc oxide nanocomposites (rGO-ZnO) by wet chemical route via in-situ one-pot method. The as-synthesized samples were characterized using FT-IR spectroscopy, Raman spectroscopy, X-ray Diffraction, Scanning Electron Microscopy (SEM) and high resolution Transmission Electron Microscopy (HR-TEM) techniques. The average crystallite size of the ZnO sample and rGO-ZnO sample, determined by Williamson-Hall analysis of the XRD results, were calculated to be 20.62 nm and 13.21 nm respectively. The TEM analysis suggests that these nanocomposites comprise of ZnO nanoparticles of average size about 10.8 nm, anchored on rGO sheets. At 300 K, the chemiresistive gas sensing response of pure rGO and rGO-ZnO towards subsequently increasing concentrations (from 20 ppm to 200 ppm) of ammonia gas has been studied. rGO-ZnO samples were prepared by varying the concentration of precursor GO dispersion (0.5, 0.75, 1, 1.25, 1.5 mg/mL). The optimal nanocomposite material (1 mg/mL) is found to exhibit excellent selectivity towards ammonia with a response of 8.92 % towards 20 ppm NH3 and a response time of 8 s. The response is found to increase with increase in ppm level of gas. The selectivity of the synthesized nanocomposite towards ammonia has been confirmed by exposing it to 20 ppm of various other gases such as methanol, ethanol, acetone, propanol and chloroform. The response towards these gases was lower as compared to that towards NH3. To assess the potential of the material in practical applications, the effect of ambient humidity on the sample’s surface resistance was studied. The ammonia sensing response in the presence of humidity was found to vary only by 1.5 % from 10 % RH to 70 % RH, beyond which it saturated. The rGO-ZnO nanocomposite sensing material also displayed good reversibility over subsequent exposure cycles and efficient stability of response with aging. The mechanism of NH3 sensing is understood on the basis of heterojunction interactions between rGO and ZnO in the nanocomposites.

Thermal-hydraulic behavior of lotus like structured rGO-ZnO composite dispersed hybrid nanofluid in mini channel heat sink

An experimental investigation in mini channel heat sink has been performed to assess the thermal-hydraulic behavior of composite dispersed hybrid nanofluid. Reduced graphene oxide-Zinc oxide (rGO-ZnO) nanocomposite particles have been synthesized and dispersed in water to prepare hybrid nanofluid with 0.01% volume concentration. Effects of different Reynolds number (50–600), volumetric flow rate (0.1–0.5 lpm), heat flux (33.33–66.67 W/cm2), channel aspect ratio (2.5–5; corresponding hydraulic diameter: 1.14–1.33 mm) on heat transfer, pressure drop and their relative performance characteristics are examined in details. Reduction in channel aspect ratio from 5 to 2.5 (hydraulic diameter from 1.33 to 1.11 mm) enhances the convective heat transfer coefficient by 47.2% at a flow rate of 0.5 lpm. The heat transfer coefficient significantly increases by about 17.41%, with rise in heat flux from 33.33 W/cm2 to 66.67 W/cm2. The effect of heat flux on the friction factor is not significant throughout the Reynolds number range. Performance evaluation criteria has a decreasing-increasing-decreasing trend with flow rate for all channel aspect ratios and heat fluxes. An optimal flow rate has been observed for the figure of merit at all the combinations of heat flux and channel aspect ratio. The figure of merit has a maximum value of 1.39 for a channel aspect ratio of 3.75 (i.e., hydraulic diameter of 1.26 mm) and heat flux of 66.67 W/cm2.

Adsorption and visible-light photocatalytic performance of a graphene derivative for methylene blue degradation

Reduced graphene oxide-zinc oxide (rGO-ZnO) composite was prepared by one-step method. TGA and FTIR results revealed the reduction of oxygen containing groups of the precursor graphene oxide. SEM images for the composite showed ZnO nanoparticles distributed on the surface as well as between graphene sheets. To understand the role of rGO-ZnO on the removal of a dye pollutant the experiments were carried out using methylene blue (MB) as the model dye. The composite was incorporated at various dosages to MB solutions, which were stored at 25 °C under visible light for 2 h. The effective adsorption capacity of rGO sheets, combined with the photocatalyst properties of ZnO, makes the composite highly efficient for applications in water purification.

Reduced graphene oxide-zinc oxide nanocomposite as dispersive solid-phase extraction sorbent for simultaneous enrichment and purification of multiple mycotoxins in Coptidis rhizoma (Huanglian) and analysis by liquid chromatography tandem mass spectrometry

In the current study, a robust dispersive solid-phase extraction (dSPE) strategy using reduced graphene oxide-zinc oxide (rGO-ZnO) nanocomposite as the sorbent was proposed for separation, purification and enrichment of 12 mycotoxins in Coptidis rhizoma (Huanglian). The targeted mycotoxins included aflatoxin B1, aflatoxin B2, aflatoxin G1, aflatoxin G2, aflatoxin M1, alternariol-methylether, mycophenolic acid, ochratoxin A, penitrem A, nivalenol, zearalenone and zearalanone. The rGO-ZnO nanocomposite was successfully synthesized through hydrothermal process by a modified Hummers method, and further characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), FTIR spectroscopy, ultraviolet-visible spectroscopy and X-ray diffraction (XRD). Several key parameters affecting the performance of the dSPE approach were extensively investigated, and after optimization, acetonitrile/water/formic acid (80/19/1, v/v/v) as the extraction solution, 2% acetonitrile as the adsorption solution, 15 mg rGO-ZnO as the sorbent, n-hexane as the washing solution, and methanol/formic acid (99/1, v/v) as the desorption solution presented an excellent purification and enrichment efficiency. Under the optimal dSPE procedure followed by analysis with ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), adequate linearity (R2 ≥ 0.991), high sensitivity (limit of quantification in the range of 0.09-0.41 µg kg−1), acceptable recovery (70.3-105.7%) and satisfactory precision (RSD 1.4-15.0%) were obtained. The analysis of 12 selected mycotoxins was also carried out in real Coptidis rhizoma (Huanglian) samples for applicability evaluation of the established method.

Testing the effect of imidazolium ionic liquid and citrate derivative on the properties of graphene-based PHBV/EVA immiscible blend

Reduced graphene oxide-zinc oxide composite (rGO-ZnO) was incorporated at 0.2 mass% content in immiscible 1:1 poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/poly(ethylene-co-vinyl acetate) (EVA) blends by melt extrusion. Using the same conditions, samples of PHBV, EVA, the neat blend and plasticized hybrids were also obtained. The effect of rGO-ZnO and the plasticizers, acetyl tert-butyl citrate (ATBC) and ionic 1-butyl-3-methylimidazolium hexafluorophosphate (bmim+PF6ˉ), on the properties of the hybrid materials were evaluated. X-ray diffraction results indicated that rGO-ZnO and the plasticizers affected the materials crystallinity. Differential scanning calorimetry showed that rGO-ZnO influenced the melt and cold crystallization, functioning as heterogeneous nucleating agent for PHBV. Dynamic mechanical analyses revealed improved compatibilization by adding ATBC to the hybrid blend. This result was corroborated by the higher ductility observed for ATBC-plasticized hybrids, in relation to the hybrids plasticized by bmim+PF6ˉ. Using bmim+PF6ˉ as the plasticizer led to hybrid materials with significantly better oxygen barrier properties, similar to polyethylene.

Preparation and thermal conductivity investigation of reduced graphene oxide-ZnO nanocomposite-based nanofluid synthesised by ultrasound-assisted method

ABSTRACT Preparation of water-based nanofluid containing reduced graphene oxide-zinc oxide (rGO-ZnO) nanocomposite particles synthesised by ultrasonic-assisted method has been carried out in this work. Energy-dispersive X-ray spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray pPhotoelectron sSpectroscopyand Raman spectroscopy were used to confirm the successful formation of the nanocomposite. The reduction of GO and attachment of the ZnO nanoparticles to it was evident from all the characterisation techniques. For 0.1 vol.% of rGO-ZnO nanocomposite-based nanofluid, the thermal conductivity was found to be 2.95 W/mK at 50°C. It further increased with increase in temperature and concentration of the nanofluid, for which a new correlation has been proposed, which can satisfactorily predict the behaviour. Also, comparison of thermal conductivity of rGO-ZnO nanocomposite-based nanofluid with nanofluids containing rGO, ZnO nanoparticles and other rGO-based nanocomposite particles has been done. This study suggests a possible application of the rGO-ZnO nanocomposite-based nanofluid for various heat transfer applications.

Reduced Graphene Oxide-Zinc Oxide Flower-Like Composite for Glass-Ionomer Materials Reinforcement

Composites based on graphene oxide (GO), reduced graphene oxide (RGO) and zinc oxide (ZnO) with different mass ratios (8, 100 and 600) were synthesized through the hydrothermal method at 100 °C and used as reinforcement materials to commercial glass-ionomers cements (GIC). X-ray diffraction (XRD) characterization confirmed the graphite oxidation and ZnO formation as a wurtzite phase. Infrared spectroscopy analyses showed bands of oxygen-containing groups on the GO surface, which reduced after thermal treatment and RGO formation. D and G bands were observed in all samples synthesized, which presented morphology similar to flowers with a crystallite size of 18 nm. The effect on the mechanical properties of GIC after reinforcement with 0.1 wt% of RGO and 3 wt% of the composites was evaluated using a one-way analysis of variance (ANOVA). It was verified slight improvements in the hardness of GIC.

Characterization Studies of Reduced Graphene Oxide/Zinc Oxide Nanocomposites Synthesized by Hydrothermal Method

Reduced graphene oxide/zinc oxide (RGO/ZnO) nanocomposites were synthesized by facile hydrothermal method; this method consists of exfoliation of graphite with modified Hummer's method and synthesis of (RGO/ZnO) nanocomposites using hydrothermal method. X-ray diffraction, TEM and FT-IR spectroscopy were used for structure morphological characterization. Optical properties of the samples were studied by measuring their optical absorbance. It can be concluded from XRD analysis that there are improvements of crystallinity associated with the increase of the crystallite size, as well as the increase in both of the (Zn-O) bond length and unit cell volume with the increase of ZnO ratio in RGO/ZnO nanocomposites. The morphological studies confirmed that the scale of ZnO particles is large and the size distribution is not uniform in samples of RGO/ZnO and that most particles have average size of about 9 nm while some particles even have larger size. The optical absorption spectra show that the excitonic peak of the as-prepared samples is red shifted from 268 nm to 376 nm for reduced grapheme oxide (RGO) with the increase of ZnO ratio, and the optical band gap changes from 2.39 for pure RGO to 3.34 eV for pure ZnO. The effect of UV irradiation on the optical absorption nanocomposites at different UV doses was carried out using UV lamp.

Enhancing the Mechanical and Electrical Properties of Poly(Vinyl Chloride)-Based Conductive Nanocomposites by Zinc Oxide Nanorods

A simple approach to decorate multi-walled carbon nanotube (MWCNT)–reduced graphene oxide (RGO) hybrid nanoparticles with zinc oxide (ZnO) nanorods is developed to improve the electrical and mechanical properties of poly(vinyl chloride) (PVC)/MWCNT–RGO composites. The ZnO nanorods act as “joint” in three-dimensional (3D) MWCNT–RGO networks and the hybrid particles strongly interact with PVC chains via p-π stacking, hydrogen bonds, and electrostatic interactions, which we confirmed by scanning electron microscopy (SEM) and Raman analysis. By introducing the ZnO nanorods, the RGO–ZnO–MWCNT hybrid particles increased 160% in capacitance compared with MWCNT–RGO hybrids. Moreover, the addition of RGO–ZnO–MWCNT to PVC resulted in the mechanical properties of PVC being enhanced by 30.8% for tensile strength and 60.9% for Young’s modulus at the loadings of 2.0 weight percent (wt.%) and 1.0 wt.%, respectively. Meanwhile, the electrical conductivity of PVC increased by 11 orders of magnitude, from 1 × 10−15 S/m to 1 × 10−4 S/m for MWCNT–ZnO–RGO loading at 5.0 wt.%.

Facile in-situ formation of rGO/ZnO nanocomposite: Photocatalytic remediation of organic pollutants under solar illumination

Herein, we present a facile hydrothermal route for the preparation of hierarchical mesoporous zinc oxide (ZnO) and reduced graphene oxide-zinc oxide (ZnOrGO) composites for degradation of organic pollutants from natural water resources. Morphologies of the as-synthesized materials were carried out by electron microscopy in scanning and transmission modes. Thermal stability of the as-prepared products was characterised by thermogravimetric-differential thermal analysis. Crystal structure and phase purity of the materials was characterised by powder x-ray diffraction, micro-Raman, and X-ray photoelectron spectroscopy analysis. Optical properties of the as-prepared materials were investigated by ultra violet-diffused reflectance and photoluminescence spectroscopy analysis. Photocatalytic activity of the as-prepared materials was estimated by evaluating the degradation kinetics of methylene blue (MB) dye in aqueous solution under standard solar light illumination. The calculated rate constant of the ZnrGO is found to be ∼2.831 h−1 which is ∼6.3 times higher than the estimated rate constant of the as-prepared pristine ZnO (0.455 h−1). The exceptional photocatalytic activity of the as-prepared ZnrGO composites is attributed to the account of their synergetic effect, porous structure, and effective separation of charge carriers. Finally, based on the obtained experimental results viable photocatalytic mechanism has been proposed.

Chemical free synthesis of graphene oxide in the preparation of reduced graphene oxide-zinc oxide nanocomposite with improved photocatalytic properties

In the present investigation, the reduced graphene oxide – zinc oxide (rGO-ZnO) was prepared by rapid microwave-assisted hydrothermal technique. The chemical free graphene oxide (GO), synthesized by Tang Lau technique, was used in the preparation of rGO-ZnO nanocomposite. The GO gets reduced to rGO during microwave irradiation and provides the necessary nucleation site for the ZnO nanorods to grow in [0 0 0 1] direction. These ZnO nanorods were completely wrapped with rGO sheets, confirmed by the synchrotron XRD and TEM techniques. The phases and cell parameters were calculated by Rietveld method. The prepared composite was used for the photodegradation of methyl orange (MO) dye from water under UV light. Investigation revealed that the incorporation of rGO into the ZnO increased the photodegradation ability of the bare ZnO. The performance of the composite is also compared with the rGO-ZnO nanocomposite, where rGO was prepared by Hummer’s method. rGO obtained from Tang Lau method formed stable and efficient composite with ZnO and exhibited higher activity compared to the composite, wherein rGO was prepared from conventional Hummer's method. Under UV light, the ZnO liberates photoelectrons which reacts with surface oxygen to form superoxide radicals (O−2) and (OH−) in the water medium. The rGO nanosheets could reduce the charge recombination during the reaction. The active species adsorbs the MO molecules and degrades into CO2, H2O and other byproducts. More than 3.5 times increase in the rate constant was observed for rGO-ZnO compared to the bare ZnO.

Ultra-Sensitive Non-Enzymatic Ethanol Sensor Based on Reduced Graphene Oxide-Zinc Oxide Composite Modified Electrode

In this paper, we report a reduced Graphene Oxide (rGO)-Zinc Oxide (ZnO) composite-based non-enzymatic ethanol sensor with an ultra-high sensitivity of 508.91 $\mu $ AmM−1cm−2 which is, to the best of our knowledge, ~8 folds higher than previously reported electrochemical ethanol sensors. The rGO-ZnO composite was synthesized by a wet chemical method wherein the reduction of GO and intimate interfacial contact between ZnO NPs and rGO were achieved simultaneously. The sensing of ethanol was explicated by means of current-potential (I–V) technique. The sensor exhibited reproducible response with insignificant variations in current tested across multiple electrodes and responded linearly to ethanol in the range of 0.5–5 mM ( $R^{2}=0.957$ ). The sensor also showed lower limit of detection. The significant improvement in sensitivity is attributed to the improved surface activity and faster charge separation owing to formation of the nano-Schottky barrier at rGO-ZnO interface. This approach is beneficial as it eliminates the use of conducting binder along with the functional material for ethanol sensing. This ultra-sensitive, binder free rGO-ZnO-based sensor offers a simple, low cost approach for ethanol detection in food, pharmaceutical, bio fuel industries, and environmental analyses.

Extruded hybrids based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and reduced graphene oxide composite for active food packaging

Abstract Hybrid materials, formed by the incorporation of a reduced graphene oxide-zinc oxide (rGO-ZnO) composite at 3, 6 and 9 mass% contents, into glycerol-plasticized poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), were prepared by melt extrusion. The rGO-ZnO composite was synthesized by the simultaneous reduction of zinc diacetate and GO, at 20:1 ratio, and characterized. Changes in the infrared spectra, X-ray diffractograms and Raman spectra, obtained for the hybrids in comparison to PHBV, evidenced the formation of physical interactions between matrix and filler. The opposite effects exerted by the addition of plasticizer and rGO-ZnO contributed to slight variations in dynamic glass transition temperature. Bactericidal activity was found against Escherichia coli as a result of direct contact between bacteria cells and the hybrids surface. Migration tests to food simulants, with the exception of acetic acid solution, revealed that the amount of ZnO that migrated were bellow the upper level recommended for Zn2+.