Ammonium-tungstate-promoted growth of boron nitride nanotubes.

Ammonium tungstate ((NH4)10W12O41 · xH2O) is a kind of oxygen-containing ammonium salt. The following study proves that it can be successfully used as a metal oxide alternative to produce boron oxide (B2O2) by oxidizing boron (B) in a traditional boron oxide chemical vapor deposition (BOCVD) process. This special oxidant promotes the simplistic fabrication of boron nitride nanotubes (BNNTs) in a conventional horizontal tube furnace, an outcome which may have resulted from its strong oxidizability. The experimental results demonstrate that the mole ratio of B and (NH4)10W12O41 · xH2O is a key parameter in determining the formation, quality and quantity of BNNTs when stainless steel is employed as a catalyst. We also found that Mg(NO3)2 and MgO nanoparticles (NPs) can be used as catalysts to grow BNNTs with the same precursor. The BNNTs obtained from the Mg(NO3)2 catalyst were straighter than those obtained from the MgO NP catalyst. This could have been due to the different physical forms of the catalysts that were used.

Growth of boron nitride nanotubes from magnesium diboride catalysts.

The difficulty in synthesizing boron nitride nanotubes (BNNTs) in a conventional horizontal tube furnace by chemical vapor deposition (CVD) may be ascribed to the failure to identify suitable catalysts and nucleation particles. This report demonstrates that magnesium diboride (MgB2) can effectively catalyze the growth of BNNTs in such a tube furnace from various boron sources, including boron oxide (B2O3), boric acid (H3BO3), and a mixture of boron (B) and calcium oxide (CaO). This catalyst is more efficient than the possible magnesium oxide (MgO) or magnesium nitride (Mg3N2) catalysts. MgB2 efficiently catalyzes the formation of BNNTs by maintaining a liquid state and showing a dissolving capacity for B2O3 at the growth temperature, thus satisfying the criteria for the vapor-liquid-solid (VLS) mechanisms of one-dimensional nanomaterials. First-principles simulations demonstrate that B2O3 can be dissolved into the MgB2 nanoparticle. We believe that the strong catalytic behavior of MgB2 can be attributed to its robust nucleation for BNNTs and dissolubility for B2O3.

Monitoring of phthalates in foodstuffs using gas purge microsyringe extraction coupled with GC-MS.

Phthalate esters (PAEs) are commonly used as nonreactive plasticisers in vinyl plastics to increase the flexibility of plastic polymers. Numerous studies have indicated that the PAEs as a class of endocrine-disrupting chemicals. In addition, the studies have also shown that a major source of human exposure to phthalates is the diet. To date, the largest problem in PAEs analysis is the high blank value because PAEs are widely used in various applications and products. To overcome this shortcoming, gas purge microsyringe extraction (GP-MSE) was applied, which established a new and low-blank-value analytical method for PAE analysis to analyse PAEs in foodstuffs. In this study, GP-MSE was used as a clean-up method, and the overall recoveries ranged from 85.7 to 102.6%, and the RSD was less than 10%. More importantly, this method can overcome the problem of the high blank value in PAE analysis. This method was applied for measuring PAEs in 78 foodstuffs. The results showed that a wide variety of PAE concentrations were found in the different groups, and the content of PAEs (varies from 658 to 1610 ng g(-1) fresh weight) is greatest in seafood. The concentrations were in the following order: DEHP>DBP>DEP≈DMP>BBP≈DNOP. Finally, the daily intake of PAEs was estimated for adults based on the levels of PAEs in foodstuffs. The total EDIdiet values of 3.2 and 12.9 µg kg(-1) bw d(-1) were calculated for DEHP based on the mean and highest concentrations in foodstuffs, respectively.