Low-temperature catalysts of mesoporous Co 3 O 4 and Au/Co 3 O 4 with high catalytic activities for the trace ethylene oxidation at 0°C are reported in this paper. The catalysts were prepared by using the nanocasting method, and the mesostructure was replicated from three-dimensional (3D) cubic KIT-6 silicas. High resolution transmission electron microscopy (HRTEM) studies revealed that {110} facets were the exposed active surfaces in the mesoporous Co 3 O 4 , whereas the Co 3 O 4 nanosheets prepared by the precipitation method exhibited the most exposed {112} facets. We found that the mesoporous Co 3 O 4 was significantly more active for ethylene oxidation than the Co 3 O 4 nanosheets. The results indicated that the crystal facet {110} of Co 3 O 4 played an essential role in determining its catalytic oxidation performance. The synthesized Au/Co 3 O 4 materials, in which the gold nanoparticles were assembled into the pore walls of the Co 3 O 4 mesoporous support, exhibited stable, highly dispersed, and exposed gold sites. Gold nanoparticles present on Co 3 O 4 readily produced surface-active oxygen species and promoted ethylene oxidation to achieve a 76% conversion at 0°C, which is the highest conversion reported yet.

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Contamination of water and soils with arsenic, especially inorganic arsenic, has been one of the most important topics in the fields of environmental science and technology. The interactions between iron and arsenic play a very significant role in the environmental behavior and effect of arsenic species. However, the mechanism of As(III) oxidation in the presence of iron has remained unclear because of the complicated speciation of iron and arsenic. Photooxidation of As(III) on nascent colloidal ferric hydroxide (CFH) in aqueous solutions at pH 6 was studied to reveal the transformation mechanism of arsenic species. Experiments were done by irradiation using light-emitting diodes with a central wavelength of 394 nm. Results show that photooxidation of As(III) and photoreduction of Fe(III) occurred simultaneously under oxic or anoxic conditions. Photooxidation of As(III) in the presence of nascent CFH occurred through electron transfer from As(III) to Fe(III) induced by absorption of radiation into a ligand-to-metal charge-transfer (LMCT) band. The estimated quantum yield of photooxidation of As(III) at 394 nm was (1.023 ± 0.065) × 10(-2). Sunlight-induced photooxidation of As(III) also occurred, implying that photolysis of the CFH-As(III) surface complex could be an important process in environments wherein nascent CFH exists.

a b s t r a c tIn this study, bimetallic Ni/Fe nanoparticles were prepared and the ability of this material to degrade DDT in aqueous solution was investigated at room temperature. Besides comparing the degradation rates of DDT using monometallic zero-valent iron and bimetallic Ni/Fe, batch investigations with bimetallic Ni/Fe nanoparticles were conducted to explore the influence of pH value on the degradation rate of DDT in aqueous solution. Results indicate that weakly acidic (4 ≤ pH < 7) or alkaline reaction (7 < pH ≤ 10) conditions afford faster degradation rates, whereas higher or lower pH inhibits the DDT degradation. In addition, the DDT degradation exhibits an interesting pathway and mechanism at higher pH value (pH > 10) in reaction solution. In strong alkaline solution, the DDT degradation becomes slow but is not quenched. The electron transfer for DDT degradation is enhanced by creating numerous galvanic cells under the Ni catalysis, and promotes the dehydrochlorination reaction. The hydrodechlorination reaction in alkaline condition is also unbroken. This phenomenon is quite different from those reported in other studies previously.

A series of ordered mesoporous carbon (OMC)-supported Au catalysts were successfully prepared by nano-replication, followed by colloidal gold deposition method. Structural analysis showed that the mesopore sizes of the catalysts can be tuned controllably in the range of 3.2-7.6 nm by adjusting the dosage of boric acid used to prepare the carbon supports. TEM observations revealed that the Au nanoparticles were dispersed uniformly in the mesopore channels of the carbon supports. These Au/OMC catalysts were tested for the aerobic oxidation of glucose to produce gluconic acid at 40°C and pH 9. As demonstrated by the structural analysis and reaction results, the activities of these catalysts were closely related to their mesopore sizes. The catalyst with a mesopore size of 5.4 nm exhibited a superior catalytic activity with a TOF of 4.308 mol glucose mol Au −1 s −1 to the catalysts reported previously by other researchers. This high activity was mainly ascribed to its unique structure, consisting of 5.4 nm mesopore channels incorporated with 3.3 nm Au nanoparticles, which facilitates contact between glucose molecules and Au nanoparticles. Besides, the abundant active oxygen species existing on this catalyst surface also promote glucose oxidation.