Size-activity threshold of titanium dioxide-supported Cu cluster in CO oxidation.

Development of non-noble metal cluster catalysts, aiming at concurrently high activity and stability, for emission control systems has been challenging because of sintering and overcoating of clusters on the support. In this work, we reported the role of well-dispersed copper nanoclusters supported on TiO2 in CO oxidation under industrially relevant operating conditions. The catalyst containing 0.15 wt% Cu on TiO2 (0.15 CT) exhibited a high dispersion (59.1%), a large specific surface area (381 m2/gCu), a small particle size (1.77 nm), and abundant active sites (75.8% Cu2O). The CO oxidation activity measured by the turnover frequency (TOF) was found to be enhanced from 0.60 × 10-3 to 3.22 × 10-3 molCO·molCu-1·s-1 as the copper loading decreased from 5 to 0.15 wt%. A CO conversion of approximately 60% was still observed in the supported cluster catalyst with a Cu loading of 5 wt% at 240 °C. No deactivation was observed for catalysts with low copper loading (0.15 and 0.30 CT) after 8 h of time-on-stream, which compares favorably with less stable Au cluster-based catalysts reported in the literature. In contrast, catalysts with high copper loading (0.75 and 5 CT) showed deactivation over time, which was ascribed to the increase in copper particle size due to metal cluster agglomeration. This study elucidated the size-activity threshold of TiO2-supported Cu cluster catalysts. It also demonstrated the potential of the supported Cu cluster catalyst at a typical temperature range of diesel engines at light-load. The supported Cu cluster catalyst could be a promising alternative to noble metal cluster catalysts for emission control systems.

Complete degradation of ciprofloxacin over g-C3N4-iron oxide composite via heterogeneous dark Fenton reaction.

Graphitic carbon nitride (g-C3N4) supported iron oxide (CN@IO) composite was first fabricated via synthesizing g-C3N4 in-situ onto iron oxide. The fabricated CN@IO composite was characterized by several techniques including XRD, XPS, TEM and nitrogen adsorption-desorption analysis. This composite was then used as a catalyst for the dark Fenton oxidative degradation of ciprofloxacin (CIP). Results demonstrated that the incorporation of g-C3N4 profoundly changed the structure and chemical properties of iron oxide, endowing CN@IO composites with high-efficient catalytic activity in dark Fenton system. In the synthesis process of CN@IO composites, iron oxide nanoparticles were successfully intercalated into the layers of g-C3N4, enlarging the surface area and thus providing more active sites for the reactions. Meanwhile, the existence of g-C3N4 can accelerate the Fe3+/Fe2+ redox cycle during the Fenton reaction, which further facilitated CIP degradation. In addition, the effects of reaction parameters, including pH, catalyst dosage, initial concentration of CIP and H2O2, on CIP degradation were investigated. Without any assistance of light irradiation, complete degradation and 48.5% mineralization of CIP were achieved under the best conditions of pH 3.0, 1 g/L CN@IO-2, 20 mg/L CIP and 0.0056 M H2O2. The trapping of iron oxide between g-C3N4 layers helped to stabilize iron oxide so the metal leaching problem that usually occurred in acidic media (pH = 3) can be effectively overcome. This work provides a new thought to develop environmental-friendly and high-efficient catalysts for the degradation of refractory pollutants in dark Fenton system, which is much easier to scale up for industrial application comparing with the photo-Fenton reaction.

Adsorption behavior and mechanisms of ciprofloxacin from aqueous solution by ordered mesoporous carbon and bamboo-based carbon.

The performances of ordered mesoporous carbon CMK-3 (OMC), bamboo-based carbon (BC), and these two kinds of adsorbents modified by thermal treatment in the ammonia atmosphere at high temperatures were evaluated for the removal fluoroquinolone antibiotic (ciprofloxacin) from aqueous solution. The adsorption behavior of ciprofloxacin (CIP) onto OMC and BC including adsorption isotherms and kinetics were investigated. The effect of various factors (pH, ionic strength and temperature) on the adsorption process was also investigated. The results demonstrated that the modified OMC and BC can further enhance the adsorption capacity due to introduce of alkaline nitrogen functionalities on the carbon surface. And their maximum adsorption capacity reached as high as 233.37mgg(-1) and 362.94mgg(-1) under the same experimental conditions, respectively. This is primarily ascribed to the positive effect of the surface basicity. The highest sorption was observed at the lowest solubility, which indicated that hydrophobic interaction was the dominant sorption mechanism for CIP uptake onto the four adsorbents. The adsorption data of antibiotics was analyzed by Langmuir and Freundlich model, and the better correlation was achieved by the Langmuir isotherm. The kinetic data showed that the adsorption of CIP onto OMC and BC follow closely the pseudo-second order model. The removal efficiency and adsorption capacity increased with increasing temperature. The results of thermodynamic study indicated that the adsorption process was a spontaneous and endothermic.

"Giant" enhancement of the upper critical field and fluctuations above the bulk Tc in superconducting ultrathin lead nanowire arrays.

We have produced ultrathin lead (Pb) nanowires in the 6 nm pores of SBA-15 mesoporous silica substrates by chemical vapor deposition. The nanowires form regular and dense arrays. We demonstrate that bulk Pb (a type-I superconductor below Tc = 7.2 K with a critical field of 800 Oe) can be tailored by nanostructuring to become a type-II superconductor with an upper critical field (Hc2) exceeding 15 T and signs of Cooper pairing 3-4 K above the bulk Tc. The material undergoes a crossover from a one-dimensional fluctuating superconducting state at high temperatures to three-dimensional long-range-ordered superconductivity in the low-temperature regime. We show with our data in an impressive way that superconductivity in elemental metals can be greatly enhanced by nanostructuring.

Thermal decomposition of carbon precursors in decorated AFI zeolite crystals.

Mass spectrometry and thermogravimetric analysis are used to explore the thermal decomposition of carbon precursors (primarily the tripropylammonium cations) occluded within AlPO(4)-5 (AFI) crystals prepared in various media (in the presence or absence of F(-) ions, Si(4+) substations of P(5+)), with the aim to fabricate high-density 0.4-nm single-walled carbon nanotubes (SWNTs). It has been found that the tripropylammonium precursors exist in the as-synthesized crystals in three different forms: tripropylammonium fluoride, hydroxide, and tripropylammonium cation compensating for the negative charge of the framework. The latter is bonded to the framework by strong chemical interaction and its decomposition takes place by a series of beta-elimination reactions to give propylene and ammonia, with the stepwise formation of dipropylammonium and n-propylammonium cations. The 0.4-nm SWNTs filling density was found to be higher than that resulting from the carbon precursor of tripropylammonium fluoride and hydroxide, because of the strong adsorption force of the channel walls to pyrolysate, as evidenced by the clear and strong radial breathing modes in Raman spectra.

Ordered mesoporous carbon as an efficient and reversible adsorbent for the adsorption of fullerenes.

An ordered mesoporous carbon, CMK-3, was synthesized using a mesoporous siliceous material, SBA-15, as the template. CMK-3 was characterized and used for the adsorption of fullerenes C60 and C70. It was found that the adsorption capacity of CMK-3 is 4 times higher than that of activated carbon. The adsorption equilibrium isotherms of C60 and C70 on CMK-3 were studied for both single and binary systems. The reversibility of fullerene adsorption on CMK-3 was also explored. The results showed that CMK-3 is an effective and reversible adsorbent for the separation of fullerenes by adsorption.