ABSTRACT
This paper describes a supercritical hydrothermal synthesis method as a green solvent process, along with products based on this method that can be used as green materials that contribute to solving environmental problems. The first part of this paper summarizes the basics of this method, including the mechanism of the reactions, specific features of the supercritical state for nanoparticle synthesis, the continuous flow-type reactor and applications; this provides a better understanding of the suitability of this method to synthesize green materials. The second part of the paper describes the method used to synthesize Cr-doped CeO(2) nanoparticles, which show an extremely high oxygen storage capacity, suggesting their high potential as an environmental catalyst. Transmission electron microscopy and scanning electron microscope images showed octahedral Cr-doped CeO(2) nanoparticles with sizes of 15-30 nm and cubic Cr-doped CeO(2) nanoparticles with sizes of 5-8 nm. Octahedral Cr-doped CeO(2) nanoparticles exposing (111) facets and cubic Cr-doped CeO(2) nanoparticles exposing (100) facets were determined by high-resolution transmission electron microscopy and selected area electron diffraction. The X-ray diffraction peaks shifted to a high angle because the radius of the Cr ion is smaller than that of the Ce ion.
ABSTRACT
Multilayer thin films composed of poly(allylamine hydrochloride) (PAH) and carboxymethyl cellulose (CMC) have been prepared on the surface of a gold (Au) disk electrode by a layer-by-layer deposition of PAH and CMC and ferricyanide ions ([Fe(CN)(6)](3-)) were confined in the film. [Fe(CN)(6)](3-) ions can be successfully confined in the films from weakly acidic or neutral [Fe(CN)(6)](3-) solutions, while, in basic solution, [Fe(CN)(6)](3-) ion was not confined. The [Fe(CN)(6)](3-) ion-confined Au electrode showed clear redox peaks in the cyclic voltammogram around 0.35V versus Ag/AgCl. The amounts of [Fe(CN)(6)](3-) ions confined in the films depended on the thickness of the films or the number of layers in the LbL films. The [Fe(CN)(6)](3-) ion-confined Au electrode was used for electrocatalytic determination of ascorbic acid in the concentration range of 1-50mM.
ABSTRACT
Polyelectrolyte multilayer thin films were prepared by an alternate deposition of poly(allylamine hydrochloride) (PAH) and anionic polysaccharides {carboxymethylcellulose (CMC) and alginic acid (AGA)} on the surface of a gold (Au) disk electrode, and the binding of ferricyanide [Fe(CN)(6)](3)(-) and hexaammine ruthenium ions [Ru(NH(3))(6)](3+) to the films was evaluated. Poly(acrylic acid) (PAA) was also employed as a reference polyanion bearing carboxylate side chains. A quartz-crystal microbalance study showed that PAH-CMC and PAH-AGA multilayer films grow exponentially as the number of depositions increases. The thicknesses of five bilayers of (PAH-CMC)(5) and (PAH-AGA)(5) films were estimated to be 150 +/- 20 and 90 +/- 15 nm, respectively, in the dry state. The PAH/polysaccharide multilayer film-coated Au electrodes exhibited a redox response to the [Fe(CN)(6)](3)(-) ion dissolved in solution, irrespective of the sign of the surface charge of the film, suggesting the high permeability of the films to the [Fe(CN)(6)](3)(-) ion. In contrast, the PAH-PAA film-coated Au electrodes exhibited a redox response only when the outermost surface of the film was covered with a positively charged PAH layer. However, the permeation of the [Ru(NH(3))(6)](3+) cation was severely suppressed for all of the multilayer films. It was possible to confine the [Fe(CN)(6)](3)(-) ion in the films by immersing the film-coated electrodes in a 1 mM [Fe(CN)(6)](3)(-) solution for 15 min. Thus, the [Fe(CN)(6)](3)(-)-confined electrodes exhibited a cyclic voltammetric response in the [Fe(CN)(6)](3)(-) ion-free buffer solution. The loading of the [Fe(CN)(6)](3)(-) ion in the films was higher when the surface charge of the film was positive and increased with increasing film thickness. It was also found that the [Fe(CN)(6)](3)(-) ion confined in the films serves as an electrocatalyst that oxidizes ascorbic acid in solution.
