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.
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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
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ABSTRACT: A range of crystalline and nano-sized carbonate- and silicate-substituted hydroxyapatite has been successfully produced by using continuous hydrothermal flow synthesis technology. Ion-substituted calcium phosphates are better candidates for bone replacement applications (due to improved bioactivity) as compared to phase-pure hydroxyapatite. Urea was used as a carbonate source for synthesising phase pure carbonated hydroxyapatite (CO(3)-HA) with ≈5 wt% substituted carbonate content (sample 7.5CO(3)-HA) and it was found that a further increase in urea concentration in solution resulted in biphasic mixtures of carbonate-substituted hydroxyapatite and calcium carbonate. Transmission electron microscopy images revealed that the particle size of hydroxyapatite decreased with increasing urea concentration. Energy-dispersive X-ray spectroscopy result revealed a calcium deficient apatite with Ca:P molar ratio of 1.45 (±0.04) in sample 7.5CO(3)-HA. For silicate-substituted hydroxyapatite (SiO(4)-HA) silicon acetate was used as a silicate ion source. It was observed that a substitution threshold of ∼1.1 wt% exists for synthesis of SiO(4)-HA in the continuous hydrothermal flow synthesis system, which could be due to the decreasing yields with progressive increase in silicon acetate concentration. All the as-precipitated powders (without any additional heat treatments) were analysed using techniques including Transmission electron microscopy, X-ray powder diffraction, Differential scanning calorimetry, Thermogravimetric analysis, Raman spectroscopy and Fourier transform infrared spectroscopy.Journal of Biomaterials Applications 09/2012; 28(3). DOI:10.1177/0885328212460289 · 2.76 Impact Factor
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ABSTRACT: High-throughput continuous hydrothermal flow synthesis has been used as a rapid and efficient synthetic route to produce a range of crystalline nanopowders in the Ce-Zn oxide binary system. High-resolution powder X-ray diffraction data were obtained for both as-prepared and heat-treated (850 degrees C for 10 h in air) samples using the new robotic beamline I11, located at Diamond Light Source. The influence of the sample composition on the crystal structure and on the optical and physical properties was studied. All the nanomaterials were characterized using Raman spectroscopy, UV-visible spectrophotometry, Brunauer-Emmett-Teller surface area and elemental analysis (via energy-dispersive X-ray spectroscopy). Initially, for 'as-prepared' Ce(1-x)Zn(x)O(y), a phase-pure cerium oxide (fluorite) structure was obtained for nominal values of x=0.1 and 0.2. Biphasic mixtures were obtained for nominal values of x in the range of 0.3-0.9 (inclusive). High-resolution transmission electron microscopy images revealed that the phase-pure nano-CeO(2) (x=0) consisted of ca 3.7 nm well-defined nanoparticles. The nanomaterials produced herein generally had high surface areas (greater than 150 m(2) g(-1)) and possessed combinations of particle properties (e.g. bandgap, crystallinity, size, etc.) that were unobtainable or difficult to achieve by other more conventional synthetic methods.Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 09/2010; 368(1927):4331-49. DOI:10.1098/rsta.2010.0135 · 2.86 Impact Factor