Effects of MoOx modification on photocatalytic activity of hydroxyapatite and Ti-doped hydroxyapatite

Titanium-doped hydroxyapatite (Ti-HAp, (Ca_10-2x, Ti_x, □_x) (PO₄)₆(OH)₂, □: defect in Ca site) and hydroxyapatite (HAp, Ca₁₀(PO₄)₆(OH)₂) powders were modified with an ethanol solution of molybdenyl acetylacetonate (MoO₂(C₅H₈O₂)₂) using chemisorption calcination cycle (CCC) technique, which provides metal oxide clusters. Their photocatalytic activity under UV illumination was evaluated by the decomposition of gaseous 2-propanol. The photocatalytic activity of the Mo-modified Ti-HAp samples increased concomitantly with increasing Mo concentration up to 0.72% against P. The highest photocatalytic activity of Mo-modified Ti-HAp was about 13 times higher than that of Ti-HAp. The signal appearance of Mo(V) in electron spin resonance spectra and the decrease of photoluminescence intensity suggest electron transfer from the Ti-hybridized band to the MoO_x cluster, which suppresses recombination of the photoinduced electron and hole pairs. The photocatalytic activity of Mo-modified HAp samples was attributed to HOMO–LUMO excitation of MoO_x cluster.     

Cover Image,Volume 138, Issue 42

Methacrylate-containing polyesters exploited for digital light processing (DLP) are generally prepared through ring-opening polymerization followed by photoactivation via methacrylation, which commonly requires the additional chemical and reaction workup. Herein, such a drawback is overcome by introducing a facile method of sequential addition of ester monomer and glycidyl methacrylate into the reaction. Two different hydroxyl beginning monomers, that is, ethylene glycol and glycerol, were utilized. The chemical structures and molecular weights of the resultant copolymers were analyzed using ¹H-NMR and ATR-FTIR spectroscopy and size exclusion chromatography, respectively. The effects of the copolymer structures on the properties of both resins formulated with and without hydroxyapatite, for example, rheological behavior and printability, and DLP-printed specimens, for example, mechanical property and cytotoxicity, were assessed. By controlling the beginning monomer to monomer feeding ratio from 1:6 to 1:14, the M_n values of the resultant copolymers fell in the range of 1.7 to 2.5 kDa. The DLP-printed specimens possessed compressive moduli in the range of 10.20 ± 0.16 MPa and 18.65 ± 0.75 MPa. The cytotoxicity result suggested that the DLP-printed specimens were noncytotoxic to porcine chondrocytes. Altogether, these methacrylate-containing polyesters simply synthesized via a concise one-pot reaction revealed great potential for DLP printing resins in biomedical applications.     

Effects of trace amount of nanometric SiC additives with wire or particle shapes on the mechanical and thermal properties of alumina matrix composites

SiC nanowires (SiCNWs) are suitable candidates used as additives to improve the thermal conductivity of alumina, since they exhibit superior properties such as high chemical and thermal stability. In this study, alumina matrix composites reinforced with very small amount of β-SiC/SiO₂ core–shell nanowires were fabricated by hot-pressing. They were first characterized and compared with alumina matrix specimens containing SiC nanopowder. It was found out that with 0.2 wt% SiC additives, the grain sizes of the alumina specimens were reduced by 20 % of that of the monolithic one, regardless of the shape of the SiC additives. Vickers hardness of specimen containing both SiCNWs and SiC nanopowders slightly increased, while fracture toughness decreased more than that of the monolithic alumina. Thermal conductivity of the specimens increased with increased amount of SiCNWs and was better than those of the specimens containing SiC nanopowders. The alumina composite containing 0.2 wt% SiCNWs had higher thermal conductivity than that of the monolithic alumina by as much as 45 %. From these results, it is clear that only small amount of nanosized SiC as an additive material, particularly SiCNWs, has a significant effect on the properties of alumina matrix composites.