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Adsorptions of dimethyl phthalate (DMP) on carbon nanotubes (CNTs) in aqueous phase at various pH and temperatures were studied. The increase in pH results in the increase in adsorption coefficient. The adsorption is governed by the π-π electron interaction which is affected by the changes in pH of the medium. The outer diameter of the CNTs greatly influences the adsorption behavior of CNT for DMP. Under the same working temperature, the adsorption capacity of CNTs for DMP is inversely related to the average outer diameter of the CNT: single-walled SWCNT (1.4 nm)>multi-walled MWCNT10 (9.4 nm)>MWCNT30 (27.8 nm)>MWCNT40 (42.7 nm). The larger surface area of CNTs provides many active sites for adsorption of DMP molecules. The Freundlich model can describe well the adsorption isotherms of DMP on CNTs. The thermodynamic parameters of standard free energy, standard enthalpy (ΔH), and standard entropy changes are determined, showing that the adsorption of DMP on CNTs is an endothermic and spontaneous reaction. The ΔHvalue of 27.8 nm-sized MWCNT (22.69 kJ/mol) is higher than 1.4 nm-sized SWCNT (6.05 kJ/mol), inferring that the adsorption process becomes more endothermic with the increase in the outer diameter of CNTs. [ABSTRACT FROM PUBLISHER]

In the present work a novel strategy for improving and/or tuning the selectivity of gas chromatographic (GC) separation by combining three different stationary phases (SPs) without premixing was introduced. A fused silica fiber coated with polydimethylsiloxane (SE30) and another coated with cyanopropylphenylmethylpolysiloxane (OV1701) were serially inserted into an 8-m polyethylene glycol 20 M (PEG20M) capillary column to form a GC annular column with ternary SP, abbreviating as SE30-OV1701-CF/PEG20M-CC. The separation capability of this ternary SP annular column was compared with a SE30-coated fiber-in-PEG20M-coated capillary annular column and a PEG20M-coated open tubular column by a test mixture of 19 organic compounds. Among these three columns, SE30-OV1701-CF/PEG20M-CC produced the best separation when the SE30-coated fiber and OV1701-coated fiber was 3 and 5 m, respectively. Selectivity can be easily tuned by changing the length of the SP-coated fibers in the ternary SP annular column. The proposed ternary SP annular column shows additional tunability, thus making it a promising tool for separation of organic solvents that are often used in the manufacturing process of pharmaceutical formulations and lacquer thinners. [ABSTRACT FROM AUTHOR]

Currently there are very few researches on studying the vertical changes of metabolic and thermodynamic properties of microbial communities in freshwater lake sediment. In this work, a multi-channel microcalorimetric system was applied to investigate both the metabolism and thermodynamic properties of 0-35 cm sediment cores from Lake Honghu (Jingzhou, Hubei Province, China). It is suggested that the catastrophic flood in 1998 had changed the structure of the 20-25 cm sediment layer. In this layer, both the physicochemical properties of sediment and the thermodynamic activities of microorganisms exhibit distinct differences from other layers. It displays the highest TOC, TN and C/N values. The power-time curves of microcalorimetric measurement on the sediment samples were plotted to illustrate their microbial activities. The 20-25 cm sediment layer showed the lowest microbial activities with a maximum heat flow rate of 56.97 μW, a growth rate constant of 0.06 h-1 and the time to reach the peak was 98 h. A positive correlation (r= 0.972, P< 0.001) was found between the cell specific metabolic enthalpy change rate (ΔH0) and the TOC of the sediment samples. ΔH0 could indicate the utilization efficiency of carbon source which is not affected by the biomass but relies on the intrinsic properties of sediment. Our work shows that the higher the TOC in sediment; the lower the efficiency in assimilating carbon into biomass by the microbes. [ABSTRACT FROM AUTHOR]

The aim of this research is to investigate the electro-oxidation of methane on roughened Pd electrode (RP) in acidic media. The results showed that RP electrode has large surface-to-volume ratio, good reversibility, and facile electron transfer kinetics. Electro-oxidation of methane on RP electrode was studied by cyclic voltammetry and differential pulse voltammetry. Higher electro-catalytic activity and shorter response time for methane oxidation were found on the RP electrode in acidic media at ambient temperatures than those found on the smooth Pd electrode. Differential pulse voltammetry was employed to study the response of RP electrode to various concentrations of methane. The increase in peak current was monitored and related to the methane concentration. The mechanisms for electro-oxidation of methane on RP electrode were also discussed. [ABSTRACT FROM AUTHOR]

A galactose biosensor was first fabricated using a galactose oxidaseimmobilized eggshell membrane and an oxygen electrode. The detection scheme was based on the depletion of dissolved oxygen content upon exposure to galactose solution, and the decrease in oxygen level was monitored and related to the galactose concentration. The effects of pH, buffer compositions, phosphate buffer concentration, and temperature on the biosensor were investigated. The linear range is 0.1 to 8.5 mM with relative standard deviation (RSD) is 3.74% and the response time is 100 s. Some possible interferents such as L-ascorbic acid, ethanol, sucrose, glucose, maltose, and fructose did not give significant interference and retained 83.6% of initial enzyme activity after 3 months when stored in a pH 7.0 phosphate buffer solution at 4°C. The proposed biosensor was applied to the determination of galactose added to plasma samples with the recoveries of galactose is 94%-110%. [ABSTRACT FROM AUTHOR]

A novel, simple, and small synchronous fluorescence and absorbance device in conjunction with a homemade passive gas sampler for the determination of formaldehyde in ambient air is described. A purple-blue light LED is used as light source, and two perpendicular photoresistors are applied to measure absorbance and fluorescence, respectively. An absorbing reagent, which consisted of a 2,4-pentanedione, ammonium acetate, and acetic acid solution, is enclosed in the sampler and used to collect and react with airborne formaldehyde. The reaction product, yellow 3,5-diacetyl-1, 4-dihydrolutidine, is then detected by the synchronous fluorescence and absorbance detectors. The light intensity is inversely proportional to the resistance of the photoresistor. The proposed device has been successfully applied to the determination of formaldehyde at various sites. [ABSTRACT FROM AUTHOR]