Light absorption across the bandgap in semiconductors is exploited in many important applications such as photovoltaics, light emitting diodes and photocatalytic conversion. Metals differ from semiconductors in that there is no energy gap separating occupied and unoccupied levels; however, it is still possible to excite electrons between bands. This is evidenced by materials with metallic properties that are also strongly coloured. An important question is whether such coloured metals could be used in light harvesting or similar applications. The high conductivity of a metal would preclude sufficient electric field being available to separate photocarriers; however, the high carrier mobility in a metal might also facilitate kinetic charge separation. Here we clearly demonstrate for the first time the use of a red metallic oxide, Sr(1-x)NbO(3) as an effective photocatalyst. The material has been used under visible light to photocatalyse the oxidation of methylene blue and both the oxidation and reduction of water assisted by appropriate sacrificial elements.

No abstract

Ordered mesoporous rutile and anatase TiO2 samples are prepared using mesoporous silica SBA‐15 as template and freshly synthesized titanium nitrate and titanium chloride solutions as precursors. The rutile material formed from the nitrate solution is monocrystalline and contains minimal amounts of Si with a Si:Ti ratio of 0.031(4), whereas the anatase material formed from the chloride solution comprises nanocrystals and contains a higher content of Si with a Si:Ti ratio of 0.18(3). It is found that control of temperature and selection of Ti‐containing precursor play important roles in determining the crystal phase and crystallinity. A possible formation mechanism of porous crystalline TiO2 is suggested. Characterization of these porous materials is performed by XRD, HRTEM, and nitrogen adsorption/desorption. SBA‐15‐templated mesoporous rutile TiO2 exhibits a higher Li ion insertion capability than KIT‐6‐templated TiO2 due to its larger surface area. Likewise mesoporous anatase TiO2:SiO2 composite has a better photoactivity than bulk TiO2 or TiO2‐loaded SBA‐15 for bleaching methylene blue.

The prevention of implant-associated infections has been increasing clinically in orthopedic surgery. Hydroxyapatite with antibacterial properties was synthesized using a microwave-assisted combustion method. High crystallinity at low temperature can be achieved using this method. The synthesized hydroxyapatite exhibited a superior clear zone for both Gram-positive and Gram-negative bacteria. Electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS) were used for the radical investigation. The application of intelligent ink testing and an antioxidant assay using DPPH reduction were also used to confirm the existence of radicals. These techniques provided data confirming that radicals are responsible for the antibacterial properties. The synthesized antibacterial hydroxyapatite would be a good candidate for the prevention any infection with medical implants and injection materials causing failure in bone repair.

No abstract

Visible-light-activated yellow amorphousTiO2(yam-TiO2) was synthesised by a simple and organic-free precipitation method. TiN, an alternative precursor forTiO2preparation, was dissolved in hydrogen peroxide under acidic condition(pH∼1)adjusted by nitric acid. The yellow precipitate was obtained after adjusting pH of the resultant red brown solution to 2 withNH4OH. The BET surface area of this sample was 261 m2/g. The visible light photoactivity was evaluated on the basis of the photobleaching of methylene blue (MB) in an aqueous solution by using a 250 W metal halide bulb equipped with UV cutoff filter (λ>420 nm) under aerobic conditions. Yam-TiO2exhibits an interesting property of being both surface adsorbent and photoactive under visible light. It was assigned to theη2-peroxide, an active intermediate form of the addition ofH2O2into crystallinedTiO2photocatalyst. It can be concluded that an active intermediate form of titanium peroxo species in photocatalytic process can be synthesised and used as a visible-light-driven photocatalyst.

Hydrated titanium dioxide, h-TiO 2 , was prepared by hydrolysis of TiCl 4 with concentrated NH 3 solution. Due to its considerably high surface area h-TiO 2 can adsorb a large amount of methylene blue on its surface, about nine times as much of Degussa P25. It can photocatalyze the decomposition of methylene blue, albeit slightly inferior to Degussa P25 if adsorption is excluded. In the presence of dilute H 2 O 2 and with UV light, h-TiO 2 can bleach methylene blue as well as Degussa P25. However, under similar conditions, but without UV light, h-TiO 2 can bleach methylene blue much better than Degussa P25.

No abstract