Core–shell micron-scale composites of titanium oxide and carbide formed through controlled thermal-plasma oxidation

Photocatalytic effects of titanium dioxide nanoparticles on aquatic organisms-Current knowledge and suggestions for future research

Nanoparticles are entering natural systems through product usage, industrial waste and post-consumer material degradation. As the production of nanoparticles is expected to increase in the next decade, so too are predicted environmental loads. Engineered metal-oxide nanomaterials, such as titanium dioxide, are known for their photocatalytic capabilities. When these nanoparticles are exposed to ultraviolet radiation in the environment, however, they can produce radicals that are harmful to aquatic organisms. There have been a number of studies that have reported the toxicity of titanium dioxide nanoparticles in the absence of light. An increasing number of studies are assessing the interactive effects of nanoparticles and ultraviolet light. However, most of these studies neglect environmentally-relevant experimental conditions. For example, researchers are using nanoparticle concentrations and light intensities that are too high for natural systems, and are ignoring water constituents that can alter the light field. The purpose of this review is to summarize the current knowledge of the photocatalytic effects of TiO₂ nanoparticles on aquatic organisms, discuss the limitations of these studies, and outline environmentally-relevant factors that need to be considered in future experiments.

Synthesis of functional TiO2-based nanoparticles in radio frequency induction thermal plasma

A method of synthesizing functional nanostructured powders by using reactive thermal plasma processing has been developed. Nanosized TiO2 powders have been synthesized by the plasma oxidation of solid and liquid precursors. Quench gases, either injected from the shoulder of the reactor or injected counter to the plasma plume from the bottom of the reactor, are used to affect the quench rate and hence the particle size of the resultant powders. The experimental results are well supported by numerical analysis of the effects of the quench gas on flow pattern and temperature field of the thermal plasma as well as trajectory and temperature histories of the particles. The plasma-synthesized TiO2 nanoparticles showed phase preferences different from those synthesized by conventional wet processes. Nanosized particles of high crystallinity and nonequilibrium chemical composition were formed in one step by reactive thermal plasma processing. The plasma-synthesized nanoparticles were spherical and hardly agglomerated. Applications of highly functional nanoparticles are thought to require nanoparticles structured in the forms of (1) dispersoids, (2) fillers, and (3) patterns. For these purposes, plasma-synthesized nanocrystallites seem to be suitable.

Electrochemical properties of core-shell TiC–TiO2nanoparticle films immobilized at ITO electrode surfaces

Titanium carbide (TiC) nanoparticles are readily deposited onto tin-doped indium oxide (ITO) electrodes in the form of thin porous films. The nanoparticle deposits are electrically highly conducting and electrochemically active. In aqueous media (at pH 7) and at applied potentials positive of 0.3 V vs. SCE partial anodic surface oxidation and formation (at least in part) of novel core-shell TiC-TiO2 nanoparticles is observed. Significant thermal oxidation of TiC nanoparticles by heating in air occurs at a temperature of 250 degrees C and leads first to core-shell TiC-TiO2 nanoparticles, next at ca. 350 degrees C to TiO2 (anatase), and finally at temperatures higher than 750 degrees C to TiO2 (rutile). Electrochemically and thermally partially oxidized TiC nanoparticles still remain very active and for some redox systems electrocatalytically active. Scanning and transmission electron microscopy (SEM and TEM), temperature dependent XRD, quartz crystal microbalance, and voltammetric measurements are reported. The electrocatalytic properties of the core-shell TiC-TiO2 nanoparticulate films are surveyed for the oxidation of hydroquinone, ascorbic acid, and dopamine in aqueous buffer media. In TiC-TiO2 core-shell nanoparticle films TiO2 surface reactivity can be combined with TiC conductivity.