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.
"However, this nitrogen was found to have been accumulated at the film surface, since its peak disappeared along with that of adsorbed carbon upon in-situ erosion . Z. Zhang et al.  observed a peak at 395.9 eV, upon doping of a nano-TiO 2 powder with nitrogen through nitriding in NH 3 /Ar atmosphere at temperatures in the range of 400e1100 C, that was attributed to atomic b-N substituting oxygen in the TiO 2 sublattice and a peak at 395.5 eV that was considered as more perplexing and believed to be due to nitride in a non-ideal co- ordination. "
[Show abstract][Hide abstract] ABSTRACT: Electrochemical capacitors (EC) in the form of packed films can be integrated in various
electronic devices as power source. A fabrication process of EC electrodes, which is
compatible with micro-fabrication, should be addressed for practical applications. Here, we
show that titanium nitride films with controlled porosity can be deposited on flat silicon
substrates by reactive DC-sputtering for use as high performance micro-supercapacitor
electrodes. A superior volumetric capacitance as high as 146.4 F cm-3, with an outstanding
cycling stability over 20,000 cycles, was measured in mild neutral electrolyte of potassium
sulfate. The specific capacitance of the films as well as their capacitance retentions were found
to depend on thickness, porosity and surface chemistry of electrodes. The one step process used
to fabricate these TiN electrodes and the wide use of this material in the field of semiconductor
technology make it promising for miniaturized energy storage systems.
Journal of Power Sources 09/2015; 300. DOI:10.1016/j.jpowsour.2015.09.012 · 6.22 Impact Factor
"In contrast to other technologies, hydrothermal synthesis; • Does not tend to use noxious chemicals – with water soluble precursors and water as a solvent • Uses relatively simple chemistry – generally following hydrolysis and dehydration stages • Allows straightforward downstream processing -the process is dispersion based • Uses relatively cheap chemical precursors – acetates, nitrates and phosphates • Can produce stoichiometric compounds like YAG  or BaTiO3 . • Can produce non-stoichiometric materials where precise alloying  or doping  can be achieved. "
[Show abstract][Hide abstract] 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
"Continuous Hydrothermal Flow Synthesis of nanoparticles (using a flow of supercritical water) is a route that allows rapid, single step synthesis of ceramic nanoparticles for diverse applications          . The authors previously demonstrated in an initial communication that the rapid crystallizing continuous environment in a CHFS system, resulted in one-step rapid formation of hydroxyapatite . "
[Show abstract][Hide abstract] 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.
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