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  • Open access
  • 63 Reads
EMI Shielding of Carbon Nanoparticles/Polymer Composites at Terahertz Frequency Region.
Published: 30 August 2018 by MDPI AG in 1st International Online Conference on Nanomaterials session Materials

Significant progress has taken place in the past few years in developing terahertz devices to make use of their superior capabilities in radio astronomy, security screening, chemical analysis, medical imaging, biological sensing, etc. With such advance in terahertz devices, electromagnetic interference shielding (EMI) in the terahertz frequency region is becoming significantly important. In this work, we examine the time-domain spectroscopy, THz-TDS, performance of carbon nanoparticles/epoxy nanocomposites. Two types of carbon nanoparticles (carbon nanofibers and multi-walled carbon nanotubes) with different carbon contents (0.5, 1.0, 2.0, 2.5 wt. %) were used to fabricate epoxy nanocomposites using both sonication and mechanical stirring processes and were experimentally investigated in terahertz (0.1-1.0 THz) frequency range. Shielding efficiency, together with the dielectric properties of both types of carbon-epoxy nanocomposites were studied and compared with that of neat epoxy as a reference. We demonstrate the potential use of carbon nanofibers and multi-walled carbon nanotubes for THz-EMI applications and show that the variation of carbon contents in epoxy matrix can greatly affect EMI shielding efficiency.

  • Open access
  • 37 Reads
Design of a new iron catalyst by mechanochemistry using rice husk as a green silica source
Published: 30 August 2018 by MDPI AG in 1st International Online Conference on Nanomaterials session Materials

Biomass has become an alternative to replace petroleum derived materials. Several methodologies for its valorization have been investigated to obtain high value products in a more sustainable way. Rice husk (RH) is an agricultural waste that contains up to 20 wt% of silica. Microwave assisted extraction was employed to remove metal ions from rice husk to obtain a highly pure mesoporous silica. Biogenic silica (RH-Silica) was employed as a support to design a new iron oxide catalyst (Fe/RH-Silica) by an efficient mechanochemical process. Synthesized materials were characterized by different techniques including N2 physisorption, XRD, TEM, SEM and DRIFT. Materials presented excellent properties and a high activity in organic reactions. Fe/RH-Silica catalyst was tested in the selective oxidation of styrene and the alkylation of toluene under microwave irradiation. High conversion and selectivity were achieved for the desire products.

  • Open access
  • 49 Reads
Rice Starch-Templated Synthesis of Nanostructured Silica and Hematite
Published: 30 August 2018 by MDPI AG in 1st International Online Conference on Nanomaterials session Synthesis

Synthesis of nanostructured materials is not straightforward that involve the complicated use of surfactant templates. Currently, only non-renewable resources that are hazardous and toxic are used to produce the surfactant templates in the industries. This study presents an environmentally friendly and efficient route for the synthesis of nanostructured of both silica and hematite using rice starch as a promising biomaterials template. The rice starch-templated synthesis yield both hematite and silica with nano-sized and high surface area. In particular, the nanostructured silica showed a pseudo-spherical morphology with nano-sized from 13 to 22 nm, amorphous structure and surface area of 538.74 m2•g−1. On the other hand, the nanostructured hematite showed an oval-shaped morphology with nano-sized from 24 to 48 nm, rhombohedral structure, and surface area of 20.04 m2•g−1. Interestingly, both synthesized silica and hematite showed capability as good nano-catalysts. More importantly, the used of rice starch-template a greener approach in the synthesis of nanomaterials have been successfully outlined.

  • Open access
  • 26 Reads
Near-Infrared pH Sensor based on SPEEK-Polyaniline Polyelectrolyte Complex
Published: 31 August 2018 by MDPI AG in 1st International Online Conference on Nanomaterials session Materials

Polyelectrolyte complex (PEC) membrane based on sulfonated poly(ether ether ketone) and polyaniline (SPEEK-PANI) was developed for pH sensing application. Aniline was polymerized in the presence of SPEEK membrane by using in situ chemical oxidative polymerization to yield an ionically crosslinked SPEEK-PANI membrane. The fabricated membrane exhibited sensitivity in the physiological pH range of 2-8. The PEC membrane pH sensor showed good absorption properties in the near-infrared region (NIR). The membrane showed fast response during de-doping process (< 30 s), while longer response times are essential for doping process from low pH region to neutral or basic pH region, which is attributed to the presence of ionic interaction in the self-doped polyaniline structure. SPEEK-PANI membrane exhibited slightly higher water uptake as compared to neat SPEEK membrane. The membrane exhibited good stability as it was stored in 1M HCl solution for more than 2 years without physical or visual deterioration. A preconditioning step in 1 M HCl ensures obtaining reproducible results and allows for the pH sensor to be used repeatedly.

  • Open access
  • 41 Reads
Structural and Optical characteristics of PVA:C-Dot composites: Tuning the absorption of Ultra Violet (UV) region
Published: 31 August 2018 by MDPI AG in 1st International Online Conference on Nanomaterials session Materials

In this work the influence of carbon nano-dots (CNDs) on absorption of ultra violet (UV) spectra in hybrid PVA based composites was studied. The FTIR results reveals the complex formation between PVA and CNDs. The shifting was observed in XRD spectrum of PVA:CNDs composites compared to pure PVA. The strong absorption was observed in the absorption spectra of the composite samples. The intense absorption peaks appeared at 280 nm and 330 nm are ascribed to n-π* and π-π* transition. The absorption edge shifted to lower photon energy sides with increasing CNDs. The refractive index increased linearly with increasing CNDS concentration. The optical dielectric constant which is related to the density of states was studied. The optical dielectric loss parameter was used to study the optical band gap of the samples. Taucs model was used to determine the type of electronic transition in the samples.

  • Open access
  • 28 Reads
Design and use of nanostructured heterogeneous catalysts for the unsaturated alcohols selective oxidation
Published: 03 September 2018 by MDPI AG in 1st International Online Conference on Nanomaterials session Posters

Since the discovery of the MCM-41 and FSM-16 in the early 1990`s of the last century, great and fascinating progress has been made in the design, preparation, characterisation and application of mesoporous silica materials. The mesoporous silica MCM-41 was successfully synthesized and used as the support to immobilize transition metals, such as nickel and ruthenium. High-surface-area supports like mesoporous silica afford highly dispersed metal oxide species which are the key parameter in the rather difficult liquid-phase oxidation of cyclohexene. The synthesized material has high specific surface area, narrow pore size distribution, and large pore with high wall thickness which is very suitable for using as support material. The transitional metals were effectively dispersed on MCM-41 by the direct synthesis method and kept the original 2D hexagonal mesostructure. The obtained nanostructured heterogeneous catalysts were characterized by N2 adsorption, ultraviolet-visible, XPS and X-ray absorption spectroscopy. X-ray absorption spectroscopy showed the presence of Ru-O bonds, suggesting a higher number of oxidic species. The adopted procedure was simple, green and efficient for unsaturated alcohols oxidation, such as 1-buten-3-ol. The use of a clean oxidant such as H2O2, was an important feature of a green chemical reaction since it resulted only water as by-product. The nanostructured heterogeneous catalysts enabled a better accessibility of active sites to bulky substrate molecules, reflected in the high conversions and better selectivity.

  • Open access
  • 38 Reads
Efficient and eco-friendly mechanical milling preparation of anatase/rutile TiO2-Glucose composite with energy gap enhancement
Published: 04 September 2018 by MDPI AG in 1st International Online Conference on Nanomaterials session Synthesis

In the current study, Anatase/rutile TiO2 and Anatase/rutile TiO2@Glucose composites were successfully prepared by a simple method using mechanical technique. The as-prepared composite materials powders were characterized by Powder X-ray diffraction analysis (PXRD), Scanning electronic microscopy (SEM) and Solid-state UV-visible spectroscopy. X-ray patterns showed the fractional phase transformation from TiO2 anatase to rutile. SEM observations revealed that the particle shape was affected by ball milling process. EDS analysis exhibits quantitatively the elemental composition of Ti and O. UV-Visible spectroscopy confirmed that the bandgap is slightly affected using Tauc.

  • Open access
  • 19 Reads
From Nano Scale Silver Particles to Metallic Bulk Sizes: Increase of Silver Ion Reduction Rate in Chitosan:AgNO3 Polymer electrolyte Mediated by Titanium Dioxide Filler
Published: 04 September 2018 by MDPI AG in 1st International Online Conference on Nanomaterials session Spectroscopy & Microscopy

Synthesis of silver ion conducting polymer composites and its optical, electrical and morphological properties were conducted. In the study various amounts of titanium dioxide (TiO2) was added to the chitosan:silver nitrate (CS:AgNt) system. The appearance of SPR peak for CS:AgNt system and CS:AgNt doped with 1 wt.% TiO2 and disappearance of SPR peak for the system incorporated with 5 wt.% TiO2 reveals the formation of silver particle from nano scales to bulk metallic sizes. The optical microscope images reveal the formation of silver particles with bulk metallic sizes at wt.% TiO2 filler . The SEM images show silver particles with small sizes for CS:AgNt and CS:AgNt incorporated with 1 wt.% TiO2. To make sure the reduction process of silver ions to metallic silver particles the impedance spectroscopy has been carried out. The decrease of dielectric constant and DC conductivity at high TiO2 concentration was correlated with the results of UV-vis and morphological achievments. Shifting of tanδ loss peak towards the lower frequency side at 5 wt.% TiO2 is an evident for the decrease in conductivity. The results of the present work reveals that silver ion conducting polymer electrolytes mediated by TiO2 filler are not suitable for electrochemical device application. Distinct peaks become visible in Mi spectra whereas no peaks can be seen in dielectric loss spectra.

  • Open access
  • 15 Reads
Ionic liquid gating of semiconductor nanostructure-based devices
Published: 05 September 2018 by MDPI AG in 1st International Online Conference on Nanomaterials session Devices & Energy

The operation of an ionic liquid-gated field effect transistor based on a single InAs nanowire will be presented and discussed. The voltage-biased ionic liquid implements the electric-double-layer inducing the field effect in the semiconductor nanostructure, and this allows to achieve the full control over the nanowire transistor. The ionic liquid gate is up to 40 times more performing with respect to the back-gate. The temperature dependence of the resistance, measured for different doping levels, reveals a clear change in the behavior of the nanostructure from fully semiconducting to quasi-metallic. Perspectives of the use of liquid gating techniques to operate nanodevices based on III-V semiconductor nanostructures will be discussed. These include fundamental and applied studies such as carrier density induced phase-transitions to bioelectronics, light emission and detection at the nanoscale, bio-sensing.

  • Open access
  • 22 Reads
Effects of vinyltriethoxysilane and maleic anhydride grafted polypropylenes on the morphological, thermal, rheological and mechanical properties of polypropylene/clay nanocomposites
Published: 05 September 2018 by MDPI AG in 1st International Online Conference on Nanomaterials session Spectroscopy & Microscopy

The morphology and properties of polypropylene (PP) /organoclay nanocomposites prepared by melt processing were investigated with a special interest on the different effects of the use of different grafted PP as compatibilizers, i.e. maleic anhydride or silane-grafted species, PP-g-MA or PP-g-Si. When either PP-g-MA or PP-g-Si was added, better improvement of properties was achieved. The addition of PP-g-Si was found to increase the crystallization temperature upon the clay addition in comparison to PP-g-MA. Moreover, the PP-g-MA proved to be more efficient than PP-g-Si. The degree of reinforcement was found to be dependent on the interaction forces between the polymer matrix/clay, which resulted in intercalated/partial exfoliated structures for PP-g-Si while increasing clay content induced a change from exfoliated to intercalated using PP-g-MA, as revealed by transmission electron microscopy observations and X-ray diffraction analysis.

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