The surface properties and photocatalytic activities of ZnO ultrafine particles

We prepared ZnO ultrafine particles (UFPs) by thermal decomposition of the precursor zinc carbonate hydroxide. The surface properties of the as-prepared particles were studied using TEM, XRD, BET, SPS, EPR, IR, and XPS. The surface contains active species such as oxygen deficiencies and hydroxyl that improve photocatalytic activities. The concentrations of active species decreased as the calcination temperature increased along with the surface areas and photovoltage. The ZnO UFP have a significant EPR signal resulting from O²⁻ deficiencies on the surface, which can capture and trap electrons. During photocatalytic degradation of phenol, the photocatalytic activities of the particles decreased as their size increased, which means that these activities depend mainly on surface properties.     

Environmental Isotopes as a Useful Tool for Studies at Mixed Uranium Mill Tailings Sites

Abstract

Groundwaters in the area of a mixed landfill (domestic waste above uranium mill tailings) in Dresden (Saxony, Germany) were investigated for their isotope signatures to distinguish between different groundwater types. To determine between the two contamination sources (waste and uranium mill tailings) a multi parameter interpretation was done using both, the main hydrochemical parameters the radionuclides ²³⁴U, ²³⁸U, ²²⁶Ra and ²²²Rn as well as the environmental isotopes of the elements hydrogen, oxygen, sulphur and carbon.

The seepage water from the landfill shows higher δ³⁴S, δ¹⁸O and tritium values as the inflow. The tritium values give an idea about water movement in the dump and mean residence time of the groundwater. The water in the dump shows varying δ¹³C values which indicate different processes occurring in the dump.     

Anomalous adsorption of Cs on Pt(1 1 1)

The adsorption of Cs on Pt(1 1 1) surfaces and its reactivity toward oxygen and iodine for coverages θ_Cs?0.15 is reported. These surfaces show unusual “anomalous” behavior compared to higher coverage surfaces. Similar behavior of K on Pt(1 1 1) was previously suggested to involve incorporation of K into the Pt lattice. Despite the larger size of Cs, similar behavior is reported here. Anomalous adsorption is found for coverages lower than 0.15 ML, at which point there is a change in the slope of the work function. Thermal Desorption Spectroscopy (TDS) shows a high-temperature Cs peak at 1135 K, which involves desorption of Cs⁺ from the surface.The anomalous Cs surfaces and their coadsorption with oxygen and iodine are characterized by Auger Electron Spectroscopy (AES), TDS and Low Electron Energy Diffraction (LEED). Iodine adsorption to saturation on Pt(1 1 1)(anom)-Cs give rise to a sharp LEED pattern and a distinctive work function increase. Adsorbed iodine interacts strongly with the Cs and weakens the Cs-Pt bond, leading to desorption of Cs_xI_y clusters at 560 K. Anomalous Cs increases the oxygen coverage over the coverage of 0.25 ML found on clean Pt. However, the Cs-Pt bond is not significantly affected by coadsorbed oxygen, and when oxygen is desorbed the anomalous cesium remains on the surface.     

LCAO study of the Cu(1 1 0)-p(2 × 1)O surface

We have performed semi-empirical LCAO calculations of the electronic structure of the Cu(1 1 0)-p(2 × 1)O surface. This has been done accounting for the Cu-Cu interactions by means of a recently proposed set of parameters, which give very good results for the bulk as well as for the surfaces of lowest Miller indices. Furthermore, the O-O interactions, which have been neglected in the preceding similar studies, have been taken into account. The resulting surface bands are in very good agreement with the overall set of the available experimental data. Several issues concerning the physical properties of this surface are addressed in the present paper: the changes induced on the clean surface bands by the adsorption and the reconstruction; the arrangement of the Cu and O atoms in the added rows; the position of the p_y antibonding band of the oxygen. In particular, we have found that the latter has an energy of −0.2 eV at the point. This result confirms an experimental indication in the same direction previously reported by Courths et al. [R. Courths, S. Hüfner, P. Kemkes, G. Wiesen, Surf. Sci. 376 (1997) 43].     

Ultrasound mediated destruction of multifunctional microbubbles for image guided delivery of oxygen and drugs

We synthesized multifunctional activatible microbubbles (MAMs) for ultrasound mediated delivery of oxygen and drugs with both ultrasound and fluorescence imaging guidance. Oxygen enriched perfluorocarbon (PFC) compound was encapsulated in liposome microbubbles (MBs) by a modified emulsification process. DiI dye was loaded as a model drug. The ultrasound targeted microbubble destruction (UTMD) process was guided by both ultrasonography and fluorescence imaging modalities. The process was validated in both a dialysis membrane tube model and a porcine carotid artery model. Our experiment results show that the UTMD process effectively facilitates the controlled delivery of oxygen and drug at the disease site and that the MAM agent enables ultrasound and fluorescence imaging guidance of the UTMD process. The proposed MAM agent can be potentially used for UTMD-mediated combination therapy in hypoxic ovarian cancer.     

Surface effects on the photoluminescence of Si quantum dots

Si quantum dots (SiQDs) with sizes ranging from 5 to 20 nm were fabricated by vapor condensation. They showed red photoluminescence (PL) in vacuum with the peak located at around 750 nm. After the specimen was exposed to air, the PL intensity became higher, and continued to increase during the PL test with a cycling of vacuum-air-vacuum. In pure oxygen, the PL intensity exhibited an irreversible decrease, while in nitrogen a smaller amount of reversible increase of PL intensity was observed. Furthermore, the PL intensity exhibited a remarkable enhancement if the SiQDs were treated with water. With HF treatment, the PL peak position showed a blue-shift to 680 nm, and was recovered after subsequent exposure to air. Si–O–H complexes were suggested to be responsible for this red luminescence. The irreversible decrease of PL intensity due to oxygen adsorption was speculated to be caused by the modification of chemical bonds on the surface. In the case of nitrogen adsorption, the PL change was attributed to the surface charging during adsorption.     

Low and room temperature measurements and calculations of O2-broadening coefficients in the ν3 band of CS2

O₂-broadening coefficients have been measured for 16 lines in the P and R branches of the fundamental ν₃ band of ¹²C³²S₂ at room and low temperatures (298.0, 273.2, 248.2, 223.2, and 198.2 K), using a tunable diode laser spectrometer and a low temperature cell. These lines from P(62) and R(64) are located in the spectral range 1519-1547 cm⁻¹. The collisional half-widths are obtained by fitting each observed profile with the Voigt and Rautian lineshape models. The broadening coefficients have also been calculated at all experimental temperatures using a semiclassical calculation performed by considering in addition to the electrostatic quadrupole-quadrupole interaction, a simple anisotropic contribution. Finally, from all the results, the parameter n of the temperature dependence of the broadening coefficients has been determined both experimentally and theoretically.     

XPS study on the correlation between chemical state and oxygen-sensing properties of an iron oxide thin film

We have studied the correlation between the chemical state and the oxygen-sensing properties of an iron oxide thin film using a setup that allows simultaneous sensor resistance measurements and X-ray photoelectron spectroscopy (XPS) data acquisition. The gas exposures were performed at the highest operating pressure of the XPS spectrometer at a controlled sample temperature which allows direct comparison between the sensor response and the chemical state of the surface. The iron oxide film was modified by a sequence of argon ion sputtering steps and the induced changes in the chemical state, resistance, and sensitivity to oxygen were investigated. The sputtering was found to reduce the iron from the Fe³⁺ to the Fe²⁺ state and to decrease the sensor resistance. The measured sensitivity to oxygen first increased by a factor of two but then collapsed to its original level. The mechanism for oxygen sensing was found to be filling of the oxygen vacancies in the lattice. The effect of the sputtering on the resistance and sensitivity could be explained first with an increase in the density of oxygen vacancies and then, as the iron became more reduced, with an increase in the p-type conductivity.     

Cobalt and nitrogen codoped porous carbon as superior bifunctional electrocatalyst for oxygen reduction and hydrogen evolution reaction in alkaline medium

Metal (cobalt)/nitrogen codoped carbon was first fabricated by pyrolysis of coordinated “noncarbonizable” polymer as bifunctional catalyst for ORR and HER, which showed better electrocatalytic performances than most bifunctional doped carbon catalysts in alkaline electrolyte.     

测定血浆中微量硒的三元包合物荧光分析法

采用氧瓶燃烧法对血样进行破坏,利用β－环糊精和十二烷基硫酸钠形成包合物的性质,将4,5－苯并苯硒二唑包合,建立了三元包合物荧光分析法,不经萃取,直接测定血浆中的硒。方法的日内精密度为5．4％－9．3％（n＝7）;日间精密度为3．5％－14．5％（n＝7）;线性范围为10－500μg／;回收率为91．0％－97．8％。对新疆汉族、维吾尔族和沈阳汉族58人的血样进行测定,结果表明：新疆汉族与沈阳汉族间血硒值无显著性差异（F＝1．36,P＞0．05）;新疆汉族与维吾尔族间血硒值有非常显著性差异（F＝1．01,P＜0．01）;男女之间血硒值有非常显著性差异（P＜0．01）。