Comparison of ultrasonic degradation rates constants of methylene blue at 22.8 kHz, 127 kHz, and 490 kHz

Techniques such as solvent extraction, incineration, chemical dehalogenation, and biodegradation have been investigated for the degradation of hazardous organic compounds. We found ultrasound to be an attractive technology for the degradation of hazardous organic compounds in water. However, the effects of ultrasonic frequency on degradation rate constants were not investigated quantitatively. In this study, the degradation process of a model for hazardous organic compound methylene blue was investigated using ultrasonic irradiation. The study focused on the effects of ultrasonic frequency and ultrasonic power on the degradation rate constant. The apparent degradation rate constants were estimated based on time dependence of methylene blue concentration assuming pseudo-first-order kinetics for the decomposition. A linear relationship between the apparent degradation rate constant and ultrasonic power was identified. In addition, the apparent degradation rate constants at frequencies of 127 and 490 kHz were much larger than those at 22.8 kHz. A relationship between the apparent degradation rate constant and the sonochemical efficiency value (SE value) was also found. Based on these results, a simple model for estimating the apparent degradation rate constant of methylene blue based on the ultrasonic power and the SE value is proposed in this study.     

Secondary metabolites from polar fractions of Piper umbellatum

Seven known secondary metabolites were isolated from the methanol extract of the branches of Piper umbellatum. The identification of these compounds was mainly achieved by 2D NMR spectroscopic techniques and FAB-MS. Among them, the known cepharadiones A and B can be considered aschemotaxonomic markers of the genus Piper.     

Complex diversity in Ligularia kanaitzensis

Two samples of Ligularia kanaitzensis collected in the Shizhongshan Mountain region of Yunnan Province, as well as one sample collected in Sichuan Province, were analyzed with regard to root constituents and neutral DNA sequences. The two Shizhongshan samples were found to be different from each other and from other samples analyzed previously, indicating that the intra-specific diversity in the species was highly complex.     

Synthesis and polymerization of new styryl and methacryloyl monomers containing acidic saccharide moieties

New styryl‐type water‐insoluble and methacryloyl‐type water‐soluble monomers, N‐(p‐vinylbenzyl)‐1,2‐O‐isopropylidene‐6‐D ‐glucofuranuronamide and N‐(2‐methacryloylamino)ethyl‐1,2‐O‐isopropylidene‐6‐D ‐glucofuranuronamide, were synthesized from the most common acidic saccharide, D ‐glucuronic acid. Their radical homopolymerizations and copolymerizations with styrene and acrylamide were tried under various conditions. The isopropylidene groups in the resulting polymers were removed in a mixture of trifluoroacetic acid and water (2/1 v/v) to give the corresponding polymers with many pendant D ‐glucopyranuronyl groups with reactive reducing groups. The pendant reducing ends may be useful as potential binding sites under a hydrophilic atmosphere. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3893–3901, 2001     

Physicochemical and electrochemical hydriding–dehydriding characteristics of amorphous MgNi x (x=1.0, 1.5, 2.0) alloys prepared by mechanical alloying

 Physicochemical and electrochemical hydriding-dehydriding characteristics of amorphous MgNi _x (x=1.0, 1.5, 2.0) alloys prepared by mechanical alloying have been investigated. It was found that the increase of Ni content in the alloys resulted in greatly enhanced kinetics for both absorption and desorption of hydrogen, while the saturation capacity showed the reverse tendency. Charge–discharge tests showed that the increase in Ni content lead to a significant enhancement in cycle performance of MgNi _x alloy electrodes. X-ray photoelectron spectroscopic and X-ray excited Auger electron spectroscopic investigations indicated the existence of a significantly thicker Ni-enriched layer for the MgNi_1.5 and MgNi_2.0 alloys than for the MgNi alloy. These results reveal that excess of Ni in MgNi _x alloys may improve the cycle performance of alloy electrodes by suppressing the segregation of Mg during electrochemical cycling, and the Ni in the topmost surface layer is mainly responsible for the improvement in the kinetics of hydrogen absorption. Received: 28 August 1999 / Accepted: 23 November 1999     

On generalized Dedekind sums attached to Dirichlet characters

Generalized reciprocity formulas and Dedekind-Petersson-Knopp-type formulas are given to generalized Dedekind sums attached to Dirichlet characters, defined on a certain congruence subgroup of SL₂($\text{Z}$). In addition, these formulas are respectively construed as transformational and eigen properties of those sums redefined on a certain set of cusps.     

A new simple preparation of platinum-nickel alloy nanoparticles and their characterization as an electrocatalyst for methanol oxidation

Pt-Ni alloy nanoparticles were produced by casting 2 or 10 mM H₂PtCl₆ solutions on a Ni column. The apparent particle size for the resultant Pt-Ni alloys increased with the concentration of the H₂PtCl₆ solution, while the content of Pt in the alloy decreased. The potential sweeps of 5 cycles in an H₂SO₄ aqueous solution for Pt-Ni (2 mM)/Ni and Pt-Ni (10 mM)/Ni electrodes led to electrochemical behavior similar to a polycrystalline Pt electrode, suggesting the formation of a few thin Pt layers on each Pt-Ni alloy surface. In electrochemical measurements, both Pt-Ni/Ni electrodes showed more negative onset potential of methanol oxidation and slower degradation of oxidation current of methanol than the polycrystalline Pt electrode. X-ray photoelectron spectroscopy of both Pt-Ni/Ni electrodes showed the shift of Pt4f peaks to a higher binding energy, suggesting that the increase in the d vacancy in the balance band 5d orbital of Pt contributed to the improved electrocatalytic activity and durability of the Pt-Ni/Ni electrodes.     

Polyimides derived from bismethylolimides. I. Polyamide–imides from bismethylolimides and dinitriles

New polyamide–imides were synthesized from bismethylolimides and dinitriles. The bismethylolimides, N,N′-bismethylolpyromellitdiimide and N,N′-bismethylolbenzophenonete-tracarboxylic diimide, were prepared by the hydroxymethylation of the corresponding diimides with formaldehyde. The polymerization reaction was carried out in either concentrated sulfuric acid or poly(phosphoric acid), and the former was found to be superior to the latter. The polyamide–imides had inherent viscosities in the 0.08–0.41 dl/g range. Most of these polymers were soluble in m-cresol and dichloroacetic acid. The thermal stability of the polymers was examined by thermogravimetric analysis, and they were found to start to decompose at 275–350°C in air.