The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

http://depa.fquim.unam.mx/amyd//archivero/FidelmarLechugaSanabria_4940.pdf

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

The miniemulsion process allows the formation of complex structured polymeric nanoparticles and the encapsulation of a solid or liquid, an inorganic or organic, or a hydrophobic or hydrophilic material into a polymer shell. Many different materials, ranging from organic and inorganic pigments, magnetite, or other solid nanoparticles, to hydrophobic and hydrophilic liquids, such as fragrances, drugs, or photoinitators, can be encapsulated. Functionalization of the nanoparticles can also be easily obtained. Compared to polymerization processes in organic solvents, polymerization to obtain polymeric nanoparticles can be performed in environmentally friendly solvents, usually water.

Miniemulsion Polymerization and the Structure of Polymer and Hybrid Nanoparticles

A series of N-doped anatase TiO2 samples have been prepared using a solvothermal method in an organic amine/ethanol–water reaction system. The effects of different starting N : Ti atomic ratios on the catalysts structure, surface property and catalytic activity have been investigated. The photocatalytic activity and stability of the N-doped TiO2 samples were evaluated through using the decomposition of Methylene blue (MB) and Methyl orange (MO) as model reaction under visible light irradiation. Characterization results show that the nitrogen dopant has a significant effect on the crystallite size and optical absorption of TiO2. It was found that the N-doped TiO2 catalysts have enhanced absorption in the visible light region, and exhibit higher activity for photocatalytic degradation of model dyes (e.g. MB and MO). The catalyst with the highest performance was the one prepared using N : Ti molar ratio of 1.0. Electron paramagnetic resonance (EPR) measurement suggests the materials contain Ti 3+ ions, with both the degree of N doping and oxygen vacancies make contributions to the visible light absorption of TON. The presence of superoxide radicals (O u � ) and hydroxyl radicals (OH) on the surface of TON were found to be responsible for MB and MO solution decoloration under visible light. Based on the results of the present study, a visible light induced photocatalytic mechanism has been proposed for N-doped anatase TiO2.

Preparation of highly visible-light active N-doped TiO2 photocatalyst

X-ray photoelectron spectroscopy (XPS) was employed to study the surface composition and electronic structure of Au/TiO2 catalysts in comparison with TiO2 (anatase) and to reveal time-dependent X-ray irradiation damage of the samples. The occurrence of Au nano-sized particles on a TiO2 support was found to result in a slight shift of Ti 2p core-level spectrum and in changes of the valence band and X-ray induced Auger spectra, compared to TiO2-only. It was shown that for different means of energy referencing the charge-corrected Au 4f7/2 binding energy in Au/TiO2 catalysts was 0.15–0.45 eV lower than that in pure bulk Au. Exposure to X-rays of Au/TiO2 catalysts and pure TiO2 caused a reduction of Ti 4+ oxidation state and desorption of oxygen from the surface. As a result, the surface chemical composition and electronic structure of the samples changed with time. The X-ray irradiation affected charge transfer processes in Au/TiO2 so that the pattern of X-ray induced damage in the Au-based catalyst turned out to be quite different from that in TiO2, with some characteristics displaying the very opposite features. Decreasing of the Au 4f7/2 binding energy and concurrent increasing of the fraction of Ti3+ species observed in the beginning of X-ray irradiation of Au/TiO2 may be taken as direct evidence for charge transfer from oxygen vacancies created by irradiation to Au particles.

/pdf/xps-characterization-of-au-tio2-catalysts-binding-energy-4jg04hvpzt.pdf

XPS characterization of Au/TiO2 catalysts: Binding energy assessment and irradiation effects

Multi-walled carbon nanotubes (MWNT) and nanocrystalline titania composite catalysts were prepared by a modified sol–gel method. Thermogravimetric analysis, N 2 adsorption–desorption isotherm measurements, powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy and UV–vis spectra were carried out to characterize the composite catalysts with different MWNT contents. The results suggest that the presence of MWNT embedding in the composite catalysts matrix prevents TiO 2 particle agglomeration. Additionally, a correlation exists between the MWNT content and the changes in the UV–vis absorption properties. The photocatalytic degradation of phenol was chosen as a model reaction to evaluate the photocatalytic activities of the composite catalysts. An optimum of the synergetic effect was found for a weight ratio MWNT/TiO 2 equal to 20%. The effects induced by MWNT on the composite catalysts may be explained in terms of a strong interphase interaction between MWNT and TiO 2 in the composite catalysts.

Photocatalytic degradation of phenol on MWNT and titania composite catalysts prepared by a modified sol–gel method

Titanium dioxide nanoparticles were prepared via a photoassisted sol−gel method in which ultraviolet light irradiation was used in the preparation process of TiO2 colloid. After characterization by X-ray diffraction, X-ray absorption near-edge structure (XANES) at the Ti K-edge, laser Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, it was found that the amorphous titania nanoparticles prepared by a photoassisted sol−gel method can be transformed into crystalline anatase phase at lower calcination temperature compared to those prepared by a conventional sol−gel method. In addition, the particle size distribution of anatase powder samples is also affected by UV illumination on the colloid. It is suggested that UV illumination can induce the formation of oxygen vacancies on the colloid and this results in the accelerated phase transition from amorphous to anatase titania.

Tiandou Hu

Papers

Synthesis and Characterization of Titania Prepared by Using a Photoassisted Sol−Gel Method