Hierarchical electromagnetic absorption in micro-waveguide stuffed with magnetic media for resin-based composites of graphene nanosheets and manganese oxides

Waveguide configurations of hierarchical system are proposed as new microstructures for composites in absorbing enhancement. Supercritical fluid (SCF) one-pot exfoliation of layered graphite and manganese oxide mixing materials is developed to obtain a hierarchical system, containing graphene nanosheets (GNS) and exfoliated manganese oxides (EMO) in different sizes. Composites with GNS–EMO embedded in epoxy resin matrix are produced for a design of dielectric and magnetic loss integrated absorber. Volume fraction of GNS–EMO in composites is given for an optimal quantity of resin epoxy in fixation and formation. The effect of mixing ratios between electric and magnetic components is provided for the design of dielectric and magnetic loss integrated absorbers. Frequency shifting phenomena are revealed in the component adjusting course. Excluding the offsetting sizes, reflection loss of composites is enhanced as thickness increases. Synergistic effect of electric and magnetic coordinated materials demonstrates the superiority of micro-waveguide structures in GNS–EMO composite absorber.     

Resistive switching characteristics of ZnO–graphene quantum dots and their use as an active component of an organic memory cell with one diode-one resistor architecture

We investigated the resistive switching characteristics of a polystyrene:ZnO–graphene quantum dots system and its potential application in a one diode-one resistor architecture of an organic memory cell. The log–log I–V plot and the temperature-variable I–V measurements revealed that the switching mechanism in a low-current state is closely related to thermally activated transport. The turn-on process was induced by a space-charge-limited current mechanism resulted from the ZnO–graphene quantum dots acting as charge trap sites, and charge transfer through filamentary path. The memory device with a diode presented a ∼10³ I_ON/I_OFF ratio, stable endurance cycles (10² cycles) and retention times (10⁴ s), and uniform cell-to-cell switching. The one diode-one resistor architecture can effectively reduce cross-talk issue and realize a cross bar array as large as ∼3 kbit in the readout margin estimation. Furthermore, a specific word was encoded using the standard ASCII character code.     

An analytical model for optimizing the performance of graphene based silicon Schottky barrier solar cells

In this paper, a model taking into account the effects of carrier loss mechanisms has been developed. The model simulates the photovoltaic properties of the graphene/n-type silicon Schottky barrier solar cells (G/n-Si_SBSC), and it can reproduce the experimentally determined parameters of the G/n-Si_SBSC. To overcome the low efficiencies of G/n-Si_SBSC, their performances have been optimized by modifying the work function of graphene and Si properties, accounted for variation of its thickness and doping level. The obtained results show that the work function of graphene has the major impact on the device performance. Also, the temperature dependence of the G/n-Si_SBSC performance is investigated.     

Microwave assisted ultrafast synthesis of graphene oxide based magnetic nano composite for environmental remediation

We have successfully synthesized multi-layer graphene oxide and graphene oxide based magnetic nanocomposite (M/GO) by microwave-assisted modified Hummers’ method for removal of toxic lead (Pb²⁺) and cadmium (Cd²⁺) ions from aqueous solution. The X-ray diffraction spectra of synthesized graphene oxide and M/GO confirm increased interlayer spacing along c-axis. Raman spectra revealed the good quality of synthesized GO and M/GO. The wrinkles were seen in the SEM images of synthesized graphene oxide. The presence of conjugated double bond (CC) and carbonyl (CO) were confirmed by using the UV–Vis spectroscopic spectra. Brunauer–Emmett–Teller (BET) analysis showed high (126 m²/g) surface area M/GO composite which accounts for large number of active binding sites for the adsorption of heavy metal ions. The adsorption studies revealed that Pb²⁺ ions were efficiently adsorbed on GO sheets. Interestingly, M/GO showed better adsorption for cadmium ions.     

Managing the degree of exfoliation and number of graphene layers using probe sonication approach

We have demonstrated a fast, versatile, and scalable approach to synthesize high-quality few layer graphene sheets with low defect ratio and high crystallinity produced from exfoliation of graphite flakes in DMF by using probe sonication. The effect of sonication time on degree of exfoliation and number of graphene layers has been fully investigated. The degree of exfoliation of graphene sheets as a function of sonication time has been successfully analyzed by XRD, UV-Vis spectroscopy, TEM, and BET studies. The morphological changes at different sonication times have also been observed by SEM. A structural and defect characterization of graphene sheets has been discussed in detail by Raman spectroscopic technique. The shift in position of 2D Raman band and its de-convolution provided information about formation of multi to few layer graphene sheets with sonication. Moreover, Raman results are highly consistent with TEM studies as per number of graphene layers is concerned.     

Appropriate conditions for preparing few-layered graphene oxide and reduced graphene oxide

Oxidation time and exfoliated conditions of graphite oxides (GOs) were investigated to prepare few–layer graphene oxide and reduced graphene oxide via a modified Hummers approach. Different oxidative degree of GOs was prepared by changing oxidation time, and the effects of oxidative degree of GOs in different oxidation time were studied by XRD, FT-IR. Afterwards, highly oxidized GOs were used as precursor to prepare graphene oxide and reduced graphene oxide by ultrasonic dispersion method and thermal expansion method. The exfoliated conditions (ultrasonic power and ultrasonic time, thermal exfoliated temperature) were investigated to prepare few-layered graphene oxide and reduced graphene oxide.     

Electrochemical determination of hydrazine based on polydopamine-reduced graphene oxide nanocomposite

In this work, a simple and mild procedure was employed to synthesize polydopamine-reduced graphene oxide (PDA-RGO) nanocomposites, where the sheets of graphene oxide were functionalized firstly with PDA through self-polymerization. FTIR was used to confirm that the GO sheets had been functionalized successfully with PDA and reduced. Besides, UV-Vis and X-ray diffraction spectroscopy were employed to further demonstrate the formation of RGO. The electrochemical property of the PDA-RGO has been studied by the determination of hydrazine. The results indicated that the electrochemical oxidation of hydrazine was significantly improved by the obtained PDA-RGO nanocomposite due to the increased available surface area of electrode. A quick amperometric response was observed with the electrochemical sensor based on PDA-RGO nanocomposite for the hydrazine measurement in a wide linear range of 0.03–100 μM, where the limit of the detection was 0.01 μM.     

Electrochemical deposition of polypyrrole/graphene oxide composite on microelectrodes towards tuning the electrochemical properties of neural probes

By exploiting the electrostatic interaction between positively charged pyrrole cation radicals and negatively charged graphene oxide (GO) sheets, we prepared polypyrrole/graphene oxide (PPy/GO) composite films by a one-step electrochemical process. We studied the effects of the polymerization current density and the GO content in electrolyte on the formation of PPy/GO coatings onto platinum neural microelectrode sites. As compared with pure PPy film, PPy/GO coatings show a rougher surface feature with micrometer-scale bulges. The impedance of the PPy/GO coated Pt electrode is only about 10% of the bare Pt electrode at the biological relevant 1 kHz, while the charge capacity density is more than two orders of the magnitude of the bare Pt electrode. Moreover, the PPy/GO coated Pt electrodes show higher performance than the PPy coated electrodes for the application of neural probe.     

Label-free electrochemical immunosensor for sensitive detection of kanamycin

A novel label-free electrochemical immunosensor for sensitive detection of kanamycin based on water-soluble graphene sheet (WGS)/prussian blue-chitosan (PB-CTS)/nanoporous gold (NPG) composited film has been reported. PB was selected as an electron transfer mediator, and was modified onto the electrode together with WGS through electrostatic adsorption. Then NPG was immobilized onto the as-prepared film for biomolecules anchoring. The electroactivity of PB was greatly enhanced in the presence of WGS and NPG. It could mainly be ascribed to the fact that the good conductivity of WGS and NPG promoted electron transfer and enhanced the sensitivity. kanamycin antibody, as a model, was immobilized onto the composite film for the detection of kanamycin. Under optimum conditions, the amperometric signal of PB decreased linearly with kanamycin concentration (0.02-14 ng mL⁻¹), a linear calibration plot (y = 1.3817 + 4.7544x, r = 0.9993), resulting in a low limit of detection (6.31 pg mL⁻¹). The novel immunosensor for the detection of kanamycin in real sample with satisfactory results has been proved. In addition, this method would be easily adapted for the detection of other residual antibiotics in animal derived foods.     

Highly Stretchable and Sensitive Flexible Strain Sensor Based on Fe NWs/Graphene/PEDOT:PSS with a Porous Structure

With the rapid development of wearable smart electronic products, high-performance wearable flexible strain sensors are urgently needed. In this paper, a flexible strain sensor device with Fe NWs/Graphene/PEDOT:PSS material added under a porous structure was designed and prepared. The effects of adding different sensing materials and a different number of dips with PEDOT:PSS on the device performance were investigated. The experiments show that the flexible strain sensor obtained by using Fe NWs, graphene, and PEDOT:PSS composite is dipped in polyurethane foam once and vacuum dried in turn with a local linearity of 98.8%, and the device was stable up to 3500 times at 80% strain. The high linearity and good stability are based on the three-dimensional network structure of polyurethane foam, combined with the excellent electrical conductivity of Fe NWs, the bridging and passivation effects of graphene, and the stabilization effect of PEDOT:PSS, which force the graphene-coated Fe NWs to adhere to the porous skeleton under the action of PEDOT:PSS to form a stable three-dimensional conductive network. Flexible strain sensor devices can be applied to smart robots and other fields and show broad application prospects in intelligent wearable devices.