Metal Oxide

Oxygen vacancies at the SnO2(110) and (101) surface and subsurface sites have been studied in the framework of density functional theory by using both all-electron Gaussian and pseudopotential plane-wave methods. The all-electron calculations have been performed using the B3LYP exchange-correlation functional with accurate estimations of energy gaps and density of states. We show that bulk oxygen vacancies are responsible for the appearance of a fully occupied flat energy level lying at about 1 eV above the top valence band, and an empty level resonant with the conduction band. Surface oxygen vacancies strongly modify the surface band structures with the appearance of intragap states covering most of the forbidden energy window, or only a small part of it, depending on the vacancy depth from the surface. Oxygen vacancies can account for electron affinity variations with respect to the stoichiometric surfaces as well. A significant support to the present results is found by comparing them to the available experimental data.

The highly ordered mesoporous silica media, SBA-15, was synthesized and incorporated with iron, aluminum, and zinc oxides using an incipient wetness impregnation technique. Adsorption capacities and kinetics of metal-impregnated SBA-15 were compared with activated alumina which is widely used for arsenic removal. Media impregnated with 10% of aluminum by weight (designated to Al 10SBA-15) had 1.9-2.7 times greater arsenate adsorption capacities in a wide range of initial arsenate concentrations and a 15 times greater initial sorption rate at ph 7.2 than activated alumina. By employing one- and two-site models, surface complexation modeling was conducted to investigate the relationship between the aluminum oxidation states in different media and adsorption behaviors shown by adsorption isotherms and kinetics since the oxidation phase of aluminum incorporated onto the surface of SBA-15 was Al-O, which has a lower oxidation state than activated alumina (Al2O 3). Surface complexation modeling results for arsenate adsorption edges conducted with different pH indicated that the monodentate complex (SAsO42-) was dominant in Al10SBA-15, while bidentate complexes (XHAsO4 and XAsO4-) were dominant in activated alumina at pH 7.2, respectively. In kinetic studies at pH 7.2 ± 0.02, Al10SBA-15 had only a fast-rate step of initial adsorption, while activated alumina had fast- and slow-rate steps of arsenate adsorption. Therefore, it can be inferred that the monodentate arsenate complex, predominant in Al10SBA-15, leads to faster adsorption rates than bidentate arsenate complexes favored with activated alumina. An arsenate adsorption behavior and arsenate surface complexation were thought to be well explained by aluminum oxidation states and surface structural properties of media.

http://www.ncbi.nlm.nih.gov/pubmed/14620839 
http://pubs.acs.org/doi/abs/10.1021/es0343712

Pure CuFe 2 O 4 nanoparticles were synthesized using sol-gel method technique. Effect of Zr/Cu substitution (Cu 1−x Zr x , where x = 0.25, 0.50, 0.75, and 1.00) on the structural, morphological, and magnetic properties was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), infrared Fourier transform infrared (FTIR), and vibrating sample magnetometer (VSM). The photocatalytic behavior of pure CuFe 2 O 4 as well Zr-substituted samples was investigated for degradation of phenol in aqueous solution in the presence of ultraviolet irradiation. The XRD results of pure CuFe 2 O 4 confirmed the formation of single tetragonal structure phase, while introducing zirconium in the structural composition resulted in a decrease in the crystallinity and gradual disappearance of the cuprospinel phase accompanied with appearance of single metal oxides species (Fe 2 O 3 , ZrO 2 , Cu 4 O 3). Based on the scanning (SEM-EDX), the samples consist of agglomerated particles with varying sizes and shapes related to their compositions. The magnetic hysteresis loops of all samples exhibited room temperature ferromagnetism with variable shapes, saturation magnetization, and coercivity values. All samples showed a significant photocatalytic activity when irradiated with ultraviolet light. The highest photocatalytic efficiency (92%) for phenol degradation was achieved through the 25% Zr-substituted sample under irradiation time of 150 min.

Abstract: Environmental pollution and industrialization on a global scale have drawn attention to the vital need for developing new hygienically friendly purification technologies. Existing wastewater treatment technologies demand high capital investment and operation & maintenance cost, and large area. Cost-effective treatment of pollutants requires the transformation of hazardous substances into benign forms and the subsequent development of effective risk management strategies from harmful effects of pollutants that are highly ...

Metal oxide gas sensors are predominant solid-state gas detecting devices for domestic, commercial and industrial applications, which have many advantages such as low cost, easy production, and compact size. However, the performance of such sensors is significantly influenced by the morphology and structure of sensing materials, resulting in a great obstacle for gas sensors based on bulk materials or dense films to achieve highly-sensitive properties. Lots of metal oxide nanostructures have been developed to improve the gas sensing properties such as sensitivity, selectivity, response speed, and so on. Here, we provide a brief overview of metal oxide nanostructures and their gas sensing properties from the aspects of particle size, morphology and doping. When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called "small size effect", yet small size o...

The effect of Nano fuel additives on the performance and emission characteristics of CI engine fueled with a blend of Pongamia pinnata biodiesel and diesel. The ball milling process is used to prepare the Nano rhodium oxide (Rh2O3) particles. The Nano rhodium oxide (Rh2O3) particle size is characterized by using scanning electron microscope (SEM). The Nano rhodium oxide size obtained in the range of 100 NM. The Nano Rhodium oxide is circulated in the biodiesel with the help of magnetic stirrer with the surface concentration. Various proportions of Pongamia biodiesel blends (10%, 20% and 30%) were used for showing the performance and emission test at different load situations. A single cylinder, air cooled, direct injection diesel engine is used for the test. The addition of rhodium oxide Nano particles, with the biodiesel at different dosing levels of the additive showed an improvement in the efficiency of the engine. During combustion the additive release the energy in the fuel, reduce the energy consumption and improves the thermal efficiency. Metal additives quite effective in controlling NOx formation. With the help of fuel base metal additives is reduced HC emission and PM emission. The addition of Nano rhodium oxide additives in fuel it reduces NOx emission up to 17% at B20 when compare with B10 and B30. Also reduces the unburnt hydrocarbon (UBHC) up to 25% at B20.

In this review, we summarize the recent research progress on the preparation and catalytic performance of meso-and macroporous metal oxide or mixed metal oxide (including manganese oxides, cobalt oxides, iron oxides, chromium oxides, and perovskite-type oxides) catalysts and their supported transition metal and noble metal catalysts for the oxidative removal of typical volatile organic compounds (VOCs), which were prepared using the hard-templating and polyvinyl alcohol-protected reduction methods, respectively. Most of these porous catalysts performed well for the addressed reactions, which was associated with their surface areas, adsorbed oxygen species concentrations, lowtemperature reducibility, interactions between noble metal or metal oxide and support as well as porous structures. In addition, the perspectives for developing high-performance catalytic materials and novel VOCs removal technologies are also proposed.

Metal oxide gas sensors are predominant solid-state gas detecting devices for domestic, commercial and industrial applications, which have many advantages such as low cost, easy production, and compact size. However, the performance of such sensors is significantly influenced by the morphology and structure of sensing materials, resulting in a great obstacle for gas sensors based on bulk materials or dense films to achieve highly-sensitive properties. Lots of metal oxide nanostructures have been developed to improve the gas sensing properties such as sensitivity, selectivity, response speed, and so on. Here, we provide a brief overview of metal oxide nanostructures and their gas sensing properties from the aspects of particle size, morphology and doping. When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called "small size effect", yet small size o...