Photocatalytic activities of N-doped nano-titanias and titanium nitride
ABSTRACT TiO2 doped with various loadings of nitrogen was prepared by nitridation of a nano-TiO2 powder in an ammonia/argon atmosphere at a range of temperatures from 400 to 1100 °C. The nano-TiO2 starting powder was produced in a continuous hydrothermal flow synthesis (CHFS) process involving reaction between a flow of supercritical water and an aqueous solution of a titanium salt. The structures of the resulting nanocatalysts were investigated using powder X-ray diffraction (XRD) and Raman spectroscopy. Products ranging from N-doped anatase TiO2 to phase-pure titanium nitride (TiN) were obtained depending on post-synthesis heat-treatment temperature. The results suggest that TiN started forming when the TiO2 was heat-treated at 800 °C, and that pure phase TiN was obtained at 1000 °C after 5 h nitridation. The amounts and nature of the Ti, O and N at the surface were determined by X-ray photoelectron spectroscopy (XPS). A shift of the band-gap to lower energy and increasing absorption in the visible light region, were observed by increasing the heat-treatment temperature from 400 to 700 °C.
- Acta Biomaterialia. 01/2011; 7(2):791-799.
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ABSTRACT: A rapid and continuous hydrothermal route for the synthesis of nano-sized hydroxyapatite rods co-precipitated with calcium-doped zirconia nanoparticles using a superheated water flow at 450°C and 24.1 MPa as a crystallizing medium is described. Hydroxyapatite and calcium-doped zirconia phases in the powder mixtures could be clearly identified based on particle size and morphology under transmission electron microscopy. Retention of a nanostructure after sintering is crucial to load-bearing applications of hydroxyapatite-based ceramics. Therefore, rapid consolidation of the co-precipitates was investigated using a spark plasma sintering furnace under a range of processing conditions. Samples nominally containing 5 and 10 wt% calcium-doped zirconia and hydroxyapatite made with Ca:P solution molar ratio 2.5 showed excellent thermal stability (investigated using in situ variable temperature X-ray diffraction) and were sintered via spark plasma sintering to >96% sintered densities at 1000°C resulting in hydroxyapatite and calcium-doped zirconia as the only two phases. Mechanical tests of spark plasma sintering sintered samples (containing 10 wt% calcium-doped zirconia) revealed a three-pt flexural strength of 107.7 MPa and Weibull modulus of 9.9. The complementary nature of the spark plasma sintering technique and continuous hydrothermal flow synthesis (which results in retention of a nanostructure even after sintering at elevated temperatures) was hence showcased.Journal of Biomaterials Applications 04/2012; 27(1):79-90. · 2.64 Impact Factor
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ABSTRACT: The S HYMAN (Sustainable Hydrothermal Manufacturing of Nanomaterials) project address scale up, formulation, weight loading, cost and sustainability of nanomaterials hydrothermal synthesis processes. Final outcome will be a 100 tons per annum continuous plant built at Solvay's site in Warrington, UK. The University of Valladolid High Pressure Processes Group leads the Process Dynamics and Modeling Work Package, whose objective is the generation of an integrated kinetics model that can predict particle size and particle size distribution of a range of different nanomaterials (including TiO2, Fe2O3, hydroxyapatite, Ag, Co3O4, ZrO2, ZnS and CuO) with the continuous system at production scales of 1, 10 and 100 tons per annum. CFD simulations based and validated on bench and pilot scale reactors data had been used to determine the limits of the existing design in terms of flow dynamics and to assess confidence on scaling up to the final plant, two orders of magnitude away. Variables explored include pipe diameter, flow rate, flows ratio and internal to external pipe diameters. The combined thermodynamics/kinetics/fluids model is used to predict the mixing dynamics, fluid variables profiles (temperature, pressure, velocity, age of the fluid...) inside the reactors, Residence Time Distributions at the outlet, an estimation of the shape of the Particle Size Distribution and average particle size at the outlet. The Peng-Robinson equation of state with translated volume and transport properties models integrated in a CFD code are used.III Iberoamerican Conference on Supercritical Fluids; 04/2013