Zoilo Gonzalez

Influence of ultrasound on the instantaneous synthesis of tridimensional α-Ni(OH)2 nanostructures and derived NiO nanoparticles

Nickel hydroxides present an extraordinary importance in the development of electrochemical devices. In contrast to the use of ammonia as a direct precipitating agent, we present herein the instantaneous precipitation of α-Ni(OH)2 nanopowders by the addition of a nickel salt to an ammonia solution. The synthesis is based on the oversaturation of the solution in the absence of any additive or other metallic cations, where ammonia plays a role as a complexing agent for intermediate nickel compounds. The influence of ultrasound on both the microstructure and the crystalline structure is discussed and the differences are referred to a new parameter (S parameter) which quantifies the amount of power in watts per cm2 that a mol of [Ni(NH3)6]2+ experiences. The description of the nucleation and growth processes of the different powders studied led to the understanding of the effect of ultrasound on the crystallography of α-Ni(OH)2. The porosity of the samples is also evaluated and its percentage and type are also correlated to the synthesis conditions. The transformation of α-Ni(OH)2 to NiO is also considered and their optical properties are evaluated as an initial indicator of their promising use as electrochemical devices.

Nickel Oxide/Nickel Foam Composite as Supercapacitor Electrode via Electrophoretic Deposition

Nickel oxide/Ni foam composite was studied as an electrode for electrochemical capacitors. The material has been processed by a simple, green and cost-effective electrophoretic deposition (EPD) method directly from the post-reaction medium in an one-pot synthesis and its later heat treatment.NiO films were obtained after calcination (325 and 450ᵒC) of β-Ni(OH)2 deposits. β-Ni(OH)2 nanoplatelets were produced by chemical precipitation of Ni precursors and the aid of ultrasound, free of modifiers. The stabilization of the hydroxide powder in suspension in different mixtures of Ethanol:Water (4:1, 9:1 and 19:1) and the optimization of the EPD parameters allowed coating the commercial Ni foams via colloidal processing.Electrochemical properties of the electrodes were evaluated by cyclic voltammetry (CV) showing significant differences in terms of specific capacitance of 192 and 79 F/g for the electrodes calcined at 325 and 450ᵒC, respectively.

Dispersion and Stabilization of TiN and TiC Nanoparticles in Organic Suspensions

In this work the stability of TiN and TiC nanopowders in isopropyl alcohol as well as the fabrication of dense and well adhered thin coatings based on TiN and TiC by electrophoretic deposition (EPD) have been evaluated in terms of zeta potential and mass deposited when hydrazineis added. The surface of TiN and TiC nanoparticles has been modified to improve the dispersion in isopropyl alcohol adding a cationic polymer (polyethylenimine) as dispersant with two different molecular weights. The influence of acidic/basic character of the solvent also has been evaluated in order to reach the most efficient EPD process. It was found that the adsorption of polyethylenimine with higher molecular weight can preserve the homogeneity of TiC coatings. The surface of TiN nanoparticles can be tuned in order to achieve a similar polyethylenimine adsorption which also improves the deposition in basic media.

Rapidly growing vegetables as new sources for lignocellulose nanofibre isolation: Physicochemical, thermal and rheological characterisation

Rapidly growing vegetables could be an abundant and cheap sources of lignocellulose biomass for lignocellulose nanofibre (LCNF) production. The aim of this work is to study the feasibility of using Chamaecytisus proliferus and Leucaena leucocephala for LCNF isolation by mechanical, enzymatic and TEMPO-mediated oxidation pre-treatments. Characterisation of the nanofibres shows that there are significant differences in the production of LCNF depending on the raw material and pre-treatment used. XRD and FTIR analysis show that homogenisation has a strong negative effect on the crystallinity index; however, the higher lignin content of tagasaste (10%) protects the fibre, causing a smaller decrease in crystallinity. The thermal stability of LCNF is also affected by the high lignin content in the case of tagasaste, which exhibited maximum degradation temperatures of 340-315°C, that were higher than those for leucaena (330-310°C). A strong shear thinning behaviour was observed in most of the LCNF, which revealed a great degree of interconnectivity in the gel like-network.