水热合成Bi2WO6/ZnO异质结型光催化剂及其光催化性能

在不同温度下(120～220℃),利用水热法制备了含1wt%、2wt%、4wt%和8wt%Bi2WO6的异质结型Bi2WO6/ZnO复合光催化剂,采用X射线粉末衍射(XRD)、扫描电镜(SEM)、傅里叶变换红外光谱(FT-IR)、紫外可见漫反射(UV-Vis)吸收光谱及光致发光光谱(PL)等系列手段对所制备的光催化剂进行了表征,并以紫外光(365nm)为光源,酸性橙II为降解对象,进行光催化活性测试,考察了不同Bi2WO6复合量及不同水热温度对ZnO光催化剂反应活性的影响.研究表明,异质结型Bi2WO6/ZnO复合光催化剂的光催化活性明显优于纯ZnO和Bi2WO6.当复合4wt%Bi2WO6水热处理温度为150℃时,所制备的复合光催化剂的光催化活性最佳,为纯ZnO的2.6倍.活性提高的主要原因是形成的Bi2WO6/ZnO异质结能显著降低光生电子和空穴对的复合几率,并改善了异质结型Bi2WO6/ZnO复合光催化剂的表面性能.     

High-accuracy measurements of the normal specular reflectance

The French Laser Megajoule (LMJ) is designed and constructed by the French Commissariat à l'Energie Atomique (CEA). Its amplifying section needs highly reflective multilayer mirrors for the flash lamps. To monitor and improve the coating process, the reflectors have to be characterized to high accuracy. The described spectrophotometer is designed to measure normal specular reflectance with high repeatability by using a small spot size of 100 mum. Results are compared with ellipsometric measurements. The instrument can also perform spatial characterization to detect coating nonuniformity.     

Carbonaceous characteristics of atmospheric particulate matter in Hong Kong

To determine the characteristic of carbonaceous species in atmospheric particles in Hong Kong, PM₁₀ and PM_2.5 samples were collected using high volume (hi-vol.) air samplers from November 2000 to February 2001. The organic carbon (OC) and elemental carbon (EC) were analyzed by the selective thermal manganese dioxide oxidation (TMO) method. The ratios of PM_2.5/PM₁₀ mass ratios were 0.61, 0.78 and 0.53 for particulate matter collected at PolyU station (PolyU, near a major traffic corridor), Kwun Tong station (KT, mixed residential/commercial/industrial) and the Hok Tsui background station (HT), respectively. These results indicate that the PM_2.5 concentrations constitute the majority of the PM₁₀ concentrations, especially in urban and industrial areas of Hong Kong. The average concentrations at the three sites ranged from 73.11 to 83.52 μg/m³ for PM₁₀ and from 42.37 to 57.38 μg/m³ for PM_2.5. The highest daily mass concentrations of PM₁₀ and PM_2.5 were 125.89 μg/m³ and 116.89 μg/m³ at KT, respectively. The correlation between PM₁₀ and PM_2.5 was high at KT and HT (r>0.9, P<0.01). This means that the sources of PM₁₀ and PM_2.5 may be the same at both sites. The highest mean concentration of OC (12.02 μg/m³) and EC (6.86 μg/m³) in PM₁₀ was found at the PolyU among the three sites. For PM_2.5, the highest mean concentration of OC (10.16 μg/m³) was at KT while the highest mean concentration of EC (7.95 μg/m³) was at PolyU. However, the background concentrations at HT were higher than another background area, Kosan, Korea. Transportation of pollutants from the Asian continent may be responsible for the elevations of EC+OC at the remote site. More than 74% of the EC and more than 79% of the OC were found in the PM_2.5 fraction at the three sampling locations. At PolyU station, PM_2.5 consisted of 18.18% OC and 11.16% EC while 17.70% OC and 8.81% EC were found in KT station. Thus OC and EC are major constituents of aerosols in Hong Kong. OC/EC ratios for PM₁₀ and PM_2.5 were less than 2 at PolyU and KT stations while the ratio exceeded 3 at HT background station. This indicates that OC measured in the urban area may be emitted directly as a primary aerosol.     

Density Fluctuations during the Early Stages of Polymer Crystallization: An Overview

The present work provides a critical review of polymer crystallization studies using SALS; experimental methods, analysis techniques, observations and their relations with respect to other techniques are discussed. Furthermore, the fact that nucleation might be accompanied by large scale density fluctuations has been investigated for the flow‐induced crystallization of iPB. SALS was applied to measure density and orientation fluctuations, whereas complementary results were obtained from optical microscopy. The observations from both crystallization and melting experiments seem to indicate that the detected density fluctuations result from the presence of weakly anisotropic structures, rather than being an indication of densification before the onset of crystallization.

     

A Survey of Nitrate and Nitrite Concentrations in Conventional and Organic‐Labeled Raw Vegetables at Retail

A national survey of the nitrate () and nitrite ( ) concentrations in raw and highly consumed vegetables available at retail in the United States was conducted. A total of 194 samples of fresh broccoli, cabbage, celery, lettuce, and spinach categorized as conventional or organic by label were collected from 5 major cities in different geographic regions of the United States and analyzed to determine and concentrations. There were no differences in the mean values of conventional compared with organic vegetables taken from the 5 metropolitan areas. However, significant differences in mean pairwise comparisons between some conventional and organic vegetables for content were observed. The mean concentration of both conventional and organic vegetables ranged between 0.1 and 1.2 mg/kg of fresh weight (FW) with the exception of conventional spinach that contained 8.0 mg/kg FW. Mean contents of conventional broccoli, cabbage, celery, lettuce, and spinach were 394, 418, 1496, 851, and 2797 mg/kg FW, respectively, while their organic‐labeled counterparts averaged 204, 552, 912, 844, and 1318 mg/kg FW. In most cases, organic vegetables were numerically lower in content than their conventional counterparts. Based on survey results, the finding that low levels were observed in some organic vegetables in different cities may warrant further study to determine if true differences exist, due to production practices, seasonal differences, and the magnitudes of those differences. Furthermore, the geographic differences in content of vegetables may flaw estimates of daily and exposure.     

Variation in the content of glucosinolates,hydroxycinnamic acids,carotenoids, total antioxidant capacity and low‐molecular‐weight carbohydrates in Brassica vegetables

Bioactive compounds were investigated in genotypes (cauliflower 10, white cabbage 10, curly kale 1) and plant parts of the three crops. The content of most of the major glucosinolates glucobrassicin, sinigrin and glucoiberin differed significantly between cultivars. Samples harvested in 2000 had higher amounts of several glucosinolates than samples from 1999. Within cauliflower the buds of the floret had 1.5 to 2.5‐fold higher concentration of glucobrassicin and 4‐methoxyglucobrassicin than the stalk. In white cabbage several glucosinolates had their highest content in the outer leaves (up to 2‐fold higher). Upper leaves of curly kale contained 5‐fold more of total glucosinolates than lower leaves. Chlorogenic acid was the dominating hydroxycinnamate in curly kale, which also contained at least ten times more of carotenoids (mainly lutein) than white cabbage. Total antioxidant capacity (TAC) assayed with the FRAP method was 0.76 (0.06) µmol/g fw (mean (SD)) in water‐soluble and 0.32 (0.04) in water‐insoluble extracts of cauliflower which was 62–68% higher than in white cabbage. Curly kale contained 6.4 and 6.1 µmol/g fw TAC in water‐soluble and water‐insoluble extracts. TAC did not differ between plant parts. Progoitrin and 4‐hydroxyglucobrassicin were correlated to water‐soluble TAC in white cabbage, probably reflecting a variation in other compounds. Cauliflower contained less glucose, fructose and sorbitol but more sucrose than white cabbage. Curly kale had lower contents of glucose (～2 times), fructose (～4–5 times) and sucrose (20 and 36 times, respectively) than cauliflower and white cabbage, while inositol was only found in curly kale. Storage of white cabbage reduced the amount of sorbitol and sucrose. The study shows that cultivar, plant part and storage affect the content of bioactive compounds in Brassica vegetables. The variation between years, as in cauliflower, is due to environmental factors. Since the cultivar ranking order was rather stable for several components the data could provide a basis for the selection of cultivars optimised for valuable health components for fresh market consumption. Copyright © 2005 Society of Chemical Industry     

Condensation/Hydrogenation of Biomass-Derived Oxygenates in Water/Oil Emulsions Stabilized by Nanohybrid Catalysts

The synthesis of fuel-range molecules by condensation of biomass-derived furfural and acetone has been studied in a biphasic emulsion system. Nanohybrids composed of basic oxide nanoparticles fused to carbon nanotubes have been used to simultaneously stabilize water/oil emulsions and catalyze the condensation reaction. Under the same conditions, higher conversions and higher fractions of fuel-range condensation products (C₈?CC₁₃) have been obtained in the emulsion compared to those obtained in the single phase. Furthermore, when using metallized nanohybrids these emulsions have been used to hydrogenate the oil-soluble condensation products. Both model compounds and synthetic bio-oil mixtures have been used to demonstrate that catalytic emulsion systems could be effective for upgrading complex mixtures, such as pyrolysis oil.     

Accelerating earthquake simulations on general‐purpose graphics processors

Parallelization strategies are presented for Virtual Quake, a numerical simulation code for earthquakes based on topologically realistic systems of interacting earthquake faults. One of the demands placed upon the simulation is the accurate reproduction of the observed earthquake statistics over three to four decades. This requires the use of a high‐resolution fault model in computations, which demands computational power that is well beyond the scope of off‐the‐shelf multi‐core CPU computers. However, the recent advances in general‐purpose graphic processing units have the potential to address this problem at moderate cost increments. A functional decomposition of Virtual Quake is performed, and opportunities for parallelization are discussed in this work. Computationally intensive modules are identified, and these are implemented on graphics processing units, significantly speeding up earthquake simulations. In the current best case scenario, a computer with six graphics processing units can simulate 500 years of fault activity in California at 1.5 km × 1.5 km element resolution in less than 1 hour, whereas a single CPU requires more than 2 days to perform the same simulation. Copyright © 2015 John Wiley & Sons, Ltd.