Search

Water pollution is nowadays a global problem and the effective detection of pollutants is of fundamental importance. Herein, a facile, efficient, robust, and rapid (response time < 2 min) method for the determination of important quinone-based industrial pollutants such as hydroquinone and benzoquinone is reported. The recognition method is based on the use of screen-printed electrodes as sensing platforms, enhanced with carbon-based nanomaterials. The enhancement is achieved by modifying the working electrode of such platforms through highly sensitive membranes made of Single- or Multi-Walled Carbon Nanotubes (SWNTs and MWNTs) or by graphene nanoplatelets. The modified sensing platforms are first carefully morphologically and electrochemically characterized, whereupon they are tested in the detection of different pollutants (i.e., hydroquinone and benzoquinone) in water solution, by using both cyclic and square-wave voltammetry. In particular, the sensors based on film-deposited nanomaterials show good sensitivity with a limit of detection in the nanomolar range (0.04 and 0.07 μM for SWNT- and MWNT-modified SPEs, respectively) and a linear working range of 10 to 1000 ppb under optimal conditions. The results highlight the improved performance of these novel sensing platforms and the large-scale applicability of this method for other analytes (i.e., toxins, pollutants). [ABSTRACT FROM AUTHOR]

We studied electromagnetic properties of pyrolytic carbon (PyC) films with thicknesses from 9 nm to 110 nm. The PyC films consisted of randomly oriented and intertwined graphene flakes with a typical size of a few nanometers were synthesized by chemical vapor deposition (CVD) at 1100 °C on a quartz substrate. The reflectance and transmittance of these films in Ka-band, 26--37 GHz, were studied both experimentally and theoretically. The discovered remarkably high absorption loss of up to 50% of incident power, along with chemical stability, makes PyC films attractive for electromagnetic (EM) interference shielding in space and airspace communication systems, as well as in portable electronic devices occupying this frequency slot. Since, in practical applications, the PyC film should be employed for coating of dielectric surfaces, two important issues to be addressed are: (i) which side (front or back) of the substrate should be covered to ensure maximum absorption losses; and (ii) the frequency dependence of absorbance/transmittance/reflectance of binary PyC/quartz structures in the Ka-band. [ABSTRACT FROM AUTHOR]

We propose an original technique for the fabrication of terahertz (THz) metasurfaces comprising a 3D printed regular array of polymer hemispheres covered with a thin conductive layer. We demonstrate that the deposition of a thin metal layer onto polymer hemispheres suppresses the THz reflectivity to almost zero, while the frequency range of such a suppression can be considerably broadened by enhancing the structure with graphene. Scaling up of the proposed technique makes it possible to tailor the electromagnetic responses of metasurfaces and allows for the fabrication of various components of THz photonics. [ABSTRACT FROM AUTHOR]

Composite materials with 83 wt.% of the 0.7Pb(Mg 1 / 3 Nb 2 / 3 )O 3 -0.3PbTiO 3 distributed in phosphate-bonded ceramics were prepared at three different pressures. A phosphate matrix comprises a mixture of an aluminum phosphate binder and melted periclase, MgO. All samples demonstrate a homogeneous distribution of the ferroelectric perovskite phase and are thermally stable up to 900 K. At higher temperatures, the pyrochlore cubic phase forms. It has been found that the density of the composites non-monotonously depends on the pressure. The dielectric permittivity and losses substantially increase with the density of the samples. The fabricated composites demonstrate diffused ferroelectric–paraelectric transition and prominent piezoelectric properties. [ABSTRACT FROM AUTHOR]

The patterning of arrays of aligned multi-walled carbon nanotubes (MWCNTs) allows creating metastructures for terahertz (THz) applications. Here, the strips and columns from MWCNTs vertically grown on silicon substrates are prepared using CO2 laser treatment. The tops of the patterned arrays are flat when the laser power is between 15 and 22 W, and craters appear there with increasing power. Laser treatment does not destroy the alignment of MWCNTs while removing their poorly ordered external layers. The products of oxidative destruction of these layers deposit on the surfaces of newly produced arrays. The oxygen groups resulting from the CO2 laser treatment improve the wettability of nanotube arrays with an epoxy resin. We show that the patterned MWCNT arrays absorb the THz radiation more strongly than the as-synthesized arrays. Moreover, the pattern influences the frequency behavior of the absorbance. [ABSTRACT FROM AUTHOR]

This paper investigates the electrical properties in the microwave range of a contact made by graphene nanoplatelets. The final goal is that of estimating the range of values for the equivalent electrical complex permittivity of a contact obtained by integrating low-cost graphene in the form of nanoplatelets (GNPs) into a high-frequency electrical circuit. To this end, a microstrip-like circuit is designed and realized, where the graphene nanoplatelets are self-assembled into a gap between two copper electrodes. An experimental characterization is carried out, both to study the structural properties of the nanomaterials and of the realized devices, and to measure the electromagnetic scattering parameters in the microwave range by means of a microstrip technique. A full-wave electromagnetic model is also derived and used to investigate the relationship between the measured quantities and the physical and geometrical parameters. The combined use of the experimental and simulation results allows for retrieving the values of the equivalent complex permittivity. The equivalent electrical conductivity values are found to be well below the values expected for isolated graphene nanoplatelets. The real part of the electrical relative permittivity attains values comparable to those obtained with GNP nanocomposites. [ABSTRACT FROM AUTHOR]