Mixed oxide

About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.

Obtaining CeO2–ZrO2 mixed oxides by coprecipitation: role of preparation conditions

Abstract: The preparation of CeO 2 –ZrO 2 mixed oxides preparation was studied by evaluating the influence of several conditions Coprecipitation was taken as the standard method and the effects brought about by the cerium salt precursor ((NH 4 ) 2 Ce(NO 3 ) 6 or Ce(NO 3 ) 3 ), the introduction of drying and aging steps as well as pH controlling upon precipitation were analyzed The samples were characterized by X-ray diffraction, Raman spectroscopy, temperature-programmed reduction, infrared spectroscopy, oxygen storage capacity and surface area The use of Ce(NO 3 ) 3 leads to the formation of c -CeO 2 and t -ZrO 2 mixed oxide whereas a solid solution is achieved by using (NH 4 ) 2 Ce(NO 3 ) 6 It was observed that the cerium precursor is the most significant parameter of preparation procedure since it defines the crystalline phases and consequently the reducibility behavior of the CeO 2 –ZrO 2 system

Ultrasmall Metal Oxide Particles: Preparation, Photophysical Characterization, and Photocatalytic Properties

Abstract: This paper gives an overview of the author's activities in the research of extremely small metal oxide particles in recent years. In particular, the synthesis of transparent colloidal solutions of extremely small zinc oxide, titanium dioxide, hematite, and titanium/iron mixed oxide particles (2 nm < d 20 nm) in water, ethanol, and 2-propanol is described. Quantum (Q)-size effects are observed during particle growth and at me final stages of synthesis. A simple molecular orbital (MO) picture is presented for the qualitative interpretation of these effects, while quantitative calculations have been carried out using a quantum mechanical model developed by Brus. The photophysical properties of the particles have also been investigated extensively. Fluorescence spectra of the ZnO sols suggest that adsorbed electron relays are necessary to shuttle electrons from the conduction band to lower-lying traps. Excess negative charge on the particles, resulting from either deprotonated surface hydroxyl groups or from photogenerated or externally injected charge carriers, causes a blue-shift in the electronic absorption spectrum, which is explained by electrostatic and MO models. The zero point of charge (pHzpc) of the aqueous colloidal suspensions has been determined by several independent methods. While zinc oxide, titanium dioxide, and titanium/iron mixed oxide particles exhibit considerable photocatalytic activity (as illustrated for the reduction of molecular oxygen and the oxidation of various halogenated carboxyl acids), hematite particles are only found to oxidize S(IV) under bandgap illumination to a reasonable extent (ϕ < 0.3). A mechanism involving surface-bound molecules and free radical intermediates is presented to explain these differences in reactivity.