W-Ni-Fe nanostructure materials synthesized by high energy ball milling

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Study of a supersonic thermal plasma expansion process for synthesis of nanostructured TiO2

The paper reports the application of supersonic thermal plasma expansion technique for controlled chemical synthesis of non-agglomerated, mono-dispersed nanoparticles of TiO₂ and also deposition of a nanocrystalline porous coating in a single-step, continuous process. The phase transformation of the nanoparticles was investigated as a function of feed rates of the basic reactants. The possibility of the particle charging and its consequences are also discussed. The grain structure of the coating was found to retain the characteristics of the seed nanoparticles. Optical Emission Spectroscopy performed at the injection section of the reactor identified the presence of TiO and TiCl molecules, which are suspected to be intermediates in this chemical route.     

Preparation, characterization and photocatalytic performance of Nd-doped titania nanoparticles with mesostructure

Nd³⁺-doped titania nanoparticles with mesostructures were synthesized via hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as directing and pore-forming agent. The obtained materials were characterized by XRD, nitrogen adsorption-desorption, TEM and DRS. The existence of neodymium ion affect significantly the phase transition of the amorphous to anatase, and the band-gap energy was reduced because of the defect energy level induced by the 4f atomic orbital of Nd³⁺ with the optimal content of 1.5 at.% Nd. Density functional theory calculations can explain the band-gap narrowing. The maximum photocatalytic activity corresponds to the 0.5 at.% Nd³⁺-doped anatase nanopowders with mesostructures, which is higher than that of undoped samples.     

Effect of nitrate ion on formation of TiO2 nanoplate structure in hydrothermal solution

Nanoplate structure of TiO₂ was synthesized by surfactant-assisted hydrothermal method. The existence of nitrate ion with a high concentration prohibited the rolling of the nanosheets and played the key role on the formation of nanoplates of titanate. After calcinations, the titanate was transformed into TiO₂ nanoplates (anatase) of micrometer-size with 20-30 nm in thickness.     

Characterization of TiO2 photocatalysts used in trichloroethene oxidation

Kinetic studies show deactivation of TiO₂ catalysts during aqueous-phase and gas-phase photooxidation of trichloroethene (TCE). Temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) were used to examine adsorbed species on TiO₂ photocatalyst surfaces after reaction, and TPD was used to determine how reactants and products adsorb on the TiO₂ surface. Used and deactivated catalysts were analyzed after participating in either aqueous-phase or gas-phase photooxidation of TCE. The XPS spectra showed little difference between the surface composition of fresh TiO₂ and that of a deactivated catalyst from the aqueous-phase photoreactor. Chlorine was observed only on catalysts used in the gas-phase photocatalytic decomposition of TCE. Differences due to photoreaction were observed in TPD spectra of water, carbon monoxide, and carbon dioxide. Both the total amount desorbed and the temperature of desorption of carbon monoxide and carbon dioxide were quite different for used and deactivated catalysts from the two photoreactions. Apparently strongly bound species, such as carbonates, accumulated on the surface and formed carbon monoxide upon high-temperature decomposition. Small amounts of chlorinated compounds desorbed from the used and deactivated catalysts following gas-phase photoreaction. Dichloroacetyl chloride (DCAC), a reaction intermediate, can adsorb strongly on TiO₂ and readily displaces TCE. Thermally decomposed DCAC reduces the number of available adsorption sites for DCAC and TCE. An interesting low-temperature oxygen desorption peak was observed from catalysts treated with H₂O₂, which improves catalytic activity. This feature indicates that H₂O₂ is stable on TiO₂ at room temperature and decomposes at 420 K.