Properties of lead zirconate-alumina ‘nanocomposites’

Microstructures, Vickers hardness and dielectric properties of PbZrO₃ ceramics with co-additions of 0.5-5 vol% Al₂O₃ nanoparticles have been investigated. The additive inhibited grain growth, with average grain size decreasing from ∼13 μm for PbZrO₃ to ∼1 μm for the nanocomposites. The mode of fracture also changed, from predominantly inter-granular in PbZrO₃ to a mixed-mode of intra- and inter-granular fracture in the composite samples. Vickers hardness values increased from 2.9 GPa for PbZrO₃ to 4.1 GPa for the sample with 1 vol% Al₂O₃, but there was a more gradual increase for higher Al₂O₃ contents. Plots of relative permittivity versus temperature indicated subtle differences which were attributed to a chemical reaction between the additive and matrix during sintering. X-ray powder diffraction showed that lead aluminium oxides were the principal products of this reaction.     

Improvement in dielectric and mechanical performance of CaCu<Subscript>3.1</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12.1</Subscript> by addition of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

The properties of CaCu_3.1Ti₄O_12.1 [CC3.1TO] ceramics with the addition of Al₂O₃ nanoparticles, prepared via a solid-state reaction technique, were investigated. The nanoparticle additive was found to inhibit grain growth with the average grain size decreasing from approximately 7.5 μm for CC3.1TO to approximately 2.0 μm for the unmodified samples, while the Knoop hardness value was found to improve with a maximum value of 9.8 GPa for the 1 vol.% Al₂O₃ sample. A very high dielectric constant > 60,000 with a low loss tangent (approximately 0.09) was observed for the 0.5 vol.% Al₂O₃ sample at 1 kHz and at room temperature. These data suggest that nanocomposites have a great potential for dielectric applications.     

Antioxidant activity of protein hydrolysates derived from threadfin bream surimi byproducts

Antioxidant activities of protein hydrolysates from threadfin bream surimi wastes, including frame, bone and skin (FBS) and refiner discharge (RD), were investigated. FBS and RD were rich in Lys, Glu, Gly, Pro, Asp, Leu, His, Tyr and Phe. FBS was hydrolysed to a greater extent than RD regardless of proteinases tested (Virgibacillus sp. SK33 proteinase, Alcalase, pepsin and trypsin). Pepsin-hydrolysed FBS, at a 5% degree of hydrolysis (DH), showed the highest antioxidant activity based on 2,2′-azinobis (3-ethyl-benzothiazoline-6-sulphonate) (ABTS) radical (0.455 ± 0.054 mg Trolox equivalents/mg leucine equivalents), ferric reducing antioxidant power (FRAP) (0.221 ± 0.005 mM Trolox equivalents) and inhibition of β-carotene bleaching assays. FBS hydrolysates showed higher antioxidant activity based on chemical assays than their RD counterparts. However, FBS and RD hydrolysates protected HepG2 cells against tert-butyl hydroperoxide-induced oxidative damage to a similar extent. Therefore, FBS and RD hydrolysates have a potential as antioxidative neutraceutical ingredients.     

Isolation and identification of antioxidative peptides from hydrolysate of threadfin bream surimi processing byproduct

The objective of this study was to determine the antioxidant activity and possible mode of action of partially purified peptides derived from threadfin bream surimi byproduct. The frame, bone and skin (FBS) byproduct, which was obtained from a deboning process, was hydrolyzed by Virgibacillus sp. SK33 proteinase and fractionated using anion exchange and size exclusion chromatography. Three fractions, i.e., B1, B2 and B3, were obtained, and the amino acid sequences of the peptides in all 3 fractions were determined using LC-MS/MS. Fractions B2 and B3 contained higher amounts of Trp, Met, Cys and Tyr residues than fraction B1. Fraction B3 exhibited high ABTS radical scavenging activity and ferric reducing antioxidant power (FRAP), while metal chelation and hydroxyl radical scavenging ability were principle modes of action of peptides in fraction B2 and B3. In addition, fraction B1 and a synthetic peptide selected from the pooled de novo peptides of fraction B3, FLGSFLYEYSR, had a cellular radical scavenging effect when HepG2 cells were treated with H₂O₂.     

Photocatalytic H2 production from water splitting under visible light irradiation using Eosin Y-sensitized mesoporous-assembled Pt/TiO2 nanocrystal photocatalyst

Sensitized photocatalytic production of hydrogen from water splitting is investigated under visible light irradiation over mesoporous-assembled titanium dioxide (TiO₂) nanocrystal photocatalysts, without and with Pt loading. The photocatalysts are synthesized by a sol–gel process with the aid of a structure-directing surfactant and are characterized by N₂ adsorption–desorption analysis, X-ray diffraction, UV–vis spectroscopy, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray analysis. The dependence of hydrogen production on the type of TiO₂ photocatalyst (synthesized mesoporous-assembled and commercial non-mesoporous-assembled TiO₂ without and with Pt loading), the calcination temperature of the synthesized photocatalyst, the sensitizer (Eosin Y) concentration, the electron donor (diethanolamine) concentration, the photocatalyst dosage and the initial solution pH is systematically studied. The results show that in the presence of the Eosin Y sensitizer, the Pt-loaded mesoporous-assembled TiO₂ synthesized by a single-step sol–gel process and calcined at 500 °C exhibits the highest photocatalytic activity for hydrogen production from a 30 vol.% diethanolamine aqueous solution with dissolved 2 mM Eosin Y. Moreover, the optimum photocatalyst dosage and initial solution pH for the maximum photocatalytic activity for hydrogen production are 3.33 g dm⁻³ and 11.5, respectively.