Current Physical Chemistry - Volume 5, Issue 2, 2015

We report a theoretical investigation of the field emission from aligned carbon nanotubes (CNTs) grown by the direct current and hot filaments catalytic chemical vapour deposition method referred to the DC HF CCVD process that have previously been studied by other techniques. SEM/TEM images and GISAXS patterns were analyzed to extract structural and morphological parameters required to interpret the field emission. These parameters were needed to simulate the standard Fowler-Nordheim plots which were in agreement with those previously reported in the literature. Analysis of these plots allows one to determine the field enhancement factor β which results with a high content of ammonia (3%) in the gas mixture are remarkable. On the other hand, the surface emission is found to be lower with a high content of ammonia. We saw an improvement in the field emission properties with a high content of ammonia in the gas mixture and low surface emission during our analysis. These CNTs have excellent emission characteristics such as a low threshold field for emission and a high current density, a small effective surface emission and high field enhancement factor. By processing these characteristics, the CNTs produced here are good candidates to be used in CNT field emitter devices application.

Investigations of low-temperature-transformation pathways that exist during tungsten carbide formation revealed the novel formation of ‘inverted’ core-shell nanoparticles comprising a tungsten carbide (WC) core and a tungsten shell assisted by an ‘asymmetric heating’ of a compacted tungsten/carbon monolith. X-ray Diffraction (XRD) characterization of the product revealed that tungsten was present in both elemental and carbide forms. The core-shell morphology of the tungsten carbide particles was deciphered from High Resolution Transmission Electron Microscopy (HRTEM) measurements and results from the thermal decomposition of the initially formed metastable W2C nanoparticles. Simultaneously, a portion of the initially formed metastable W2C nanoparticles in the vicinity of excess carbon became stabilized producing carbonensheathed W2C nanoparticles. These findings open new avenues to access unique core-shell morphologies of refractory carbides and for the ambient stabilization of metastable nanoparticles by means of asymmetric heating of monoliths of selected binary or higher compositions. Furthermore, the obtained core-shell nanoparticles provide a platform to produce other experimentally challenging structures.

The behavior of interfacial liquids adsorbed alone or co-adsorbed as miscible or immiscible pairs or triples strongly differs from that for bulk liquids because of several effects, and the main of them is the confined space effect. In the confined space of pores the mobility of molecules decreases, the activity of solvents is reduced, and the freezing temperature decreases. This can lead to the separation of bulk-miscible liquids into weakly miscible or immiscible structures in pores. The pore size distributions and the chemistry of pore walls affect the interfacial behavior of adsorbates because these factors can enhance differentiation of co-adsorbed liquids. These effects were analyzed upon co-adsorption of water and a set of organic solvents, acids, and polymers onto a variety of adsorbents including chars, activated carbons, fumed oxides, silica gels, and porous polymers using low-temperature 1H NMR spectroscopy, differential scanning calorimetry, thermally stimulated depolarization current, thermogravimetry, adsorption, infrared and Raman spectroscopies, SEM, TEM, and quantum chemical methods.

Hydrotalcite-like compounds (HTlc) are the only layered materials with positively charged layers and exchangeable interlayer anions. Their tunable layered charge density and chemical composition make HTlc versatile materials suitable for a wide range of applications such as fillers of polymeric nanocomposites, pharmaceutics, adsorbents and catalysts. In this short review we report an overview on some methods used to prepare luminescent HTlc nanoparticles and films. First we focused on the most common intercalation process based on the insertion of anionic dyes species in the interlayer region of HTlc, then two more recent approaches, aimed to modify only the HTlc layers, are presented. Specifically, we review the silylation with organic dyes, a method which exploits the OH groups of HTlc, and the insertion of lanthanide cations in place of Al(III) into the HTlc layer. The possibility to obtain luminescent HTlc in form of nanoparticles and films by using different approaches highlights the potential use of these nanostructured materials in important applications ranging from diagnostic biomedical tools to photonics, sensing and opto-electronic devices.