The annealing effects on structure and magnetism for Co-doped ZnO films under air, Ar, and Ar/ H 2 atmospheres at 250°C have been systematically investigated. Room-temperature ferromagnetism has been observed for the as-deposited and annealed films. However, the saturation magnetization ͑M s ͒ varied drastically for different annealing processes with M s ϳ 0.5, 0.2, 0.9, and 1.5 B / Co for the as-deposited, air-annealed, Ar-annealed, and Ar/ H 2-annealed films, respectively. The x-ray absorption spectra indicate all these samples show good diluted magnetic semiconductor structures. By comparison of the x-ray near edge spectra with the simulation on Zn K edge, an additional preedge peak appears due likely to the formation of oxygen vacancies. The results show that enhancement ͑suppression͒ of ferromagnetism is strongly correlated with the increase ͑decrease͒ of oxygen vacancies in ZnO. The upper limit of the oxygen vacancy density of the Ar/ H 2-annealed film can be estimated by simulation to be about 1 ϫ 10 21 cm −3 .

Small-size (o5 nm) gold nanostructures supported on reducible metal oxides have been widely investigated because of the unique catalytic properties they exhibit in diverse redox reactions. However, arguments about the nature of the gold active site have continued for two decades, due to the lack of comparable catalyst systems with specific gold species, as well as the scarcity of direct experimental evidence for the reaction mechanism under realistic working conditions. Here we report the determination of the contribution of single atoms, clusters and particles to the oxidation of carbon monoxide at room temperature, by the aid of in situ X-ray absorption fine structure analysis and in situ diffuse reflectance infrared Fourier transform spectroscopy. We find that the metallic gold component in clusters or particles plays a much more critical role as the active site than the cationic single-atom gold species for the room-temperature carbon monoxide oxidation reaction.

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Removal and recovery of high levels of arsenic (As) in copper smelting wastewater present a great environmental challenge. A novel approach was investigated for the first time using TiO 2 for As adsorptive removal from wastewater and subsequent spent adsorbent regeneration and As recovery using NaOH. EXAFS results demonstrate that As(III), as the only As species present in the raw water, does not form an aqueous complex with other metal ions. An average of 3890 ( 142 mg/L As(III) at pH 1.4 in the wastewater was reduced to 59 ( 79 µg/L in the effluent with final pH at 7 in the 21 successive treatment cycles using regenerated TiO 2 . Coexisting heavy metals including Cd, Cu, and Pb with concentrations at 369 mg/L, 24 mg/ L, and 5 mg/L, respectively, were reduced to less than 0.02 mg/ L. As(III) adsorption followed pseudosecond-order rate kinetics, and the adsorption behavior was described with the charge distribution multisite surface complexation model. Approximately 60% As(III) in the waste solution after the TiO 2 regeneration process was recovered by thermo vaporization and subsequent precipitation of sodium arsenite, as suggested by the EDX and XPS analysis. This "zero" sludge process sheds new light on successful As remediation technology for acidic metallurgical industry wastewater.