共查询到20条相似文献,搜索用时 15 毫秒
1.
Van Royen P Schacht E Ruys L Van Vaeck L 《Rapid communications in mass spectrometry : RCM》2006,20(3):346-352
The viability of static secondary ion mass spectrometry (S-SIMS) for selected applications of nanoscale analysis has been investigated, focusing on nanofibres produced by electrospinning (ES) as a test case. The samples consist of non-woven nanowebs of which the individual fibres have diameters in the range of 100 nm. Use of solutions with functionalised polymers or polar additives potentially allows the surface composition to be tailored as a function of the application. So far nanowebs are primarily characterised by morphological examination. This paper describes the first detailed characterisation of molecular composition at the surface of nanofibres electrospun from poly(epsilon-caprolactone) (PCL) solutions in acetone containing 0-15 mol% (relative to PCL) of cetyltrimethylammonium bromide (CTAB). Application of S-SIMS to nanowebs has allowed mass spectra to be recorded containing the major diagnostic ions of both components. Their relative intensities point to surface enrichment and depletion of the polar CTAB additive relative to the PCL matrix for samples electrospun from solution containing low and high CTAB concentrations, respectively. 相似文献
2.
S. Calvo J. Escribano M. G. Prolongo R. M. Masegosa C. Salom 《Journal of Thermal Analysis and Calorimetry》2011,103(1):195-203
The effect of a low profile additive, poly(ε-caprolactone) (PCL), on the thermal and mechanical properties of unsaturated
polyester resins (UP) was investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA),
and tensile tests. The morphology of the systems has been studied by scanning electronic microscopy (SEM). Two PCL molecular
mass were selected (PCL2: M
n = 2000 g mol−1 and PCL50: M
n = 50000 g mol−1) to analyze the influence of the molecular mass and the content of PCL on the UP resins and to establish the relation between
thermomechanical behavior and morphology. DSC and DMTA glass transition temperatures (T
g) of the UP cured samples containing PCL indicate that PCL2 is miscible with UP whereas for UP + PCL50 system, T
g values are very close to the ones corresponding to neat UP. Besides in UP + PCL2 systems, one phase morphology is observed
in which PCL2 would act as solvent of the reacting mixture along curing process; however, UP + PCL50 systems present phase-separated
morphology. The presence of PCL2 and PCL50 in UP resin leads to a decrease of the tensile strength and the Young′s modulus
as much notorious as the PCL concentration increases. For UP + PCL2 system the elongation at fracture increases in relation
to neat UP, increasing as well with the PCL content. 相似文献
3.
Chockalingam Karunakaran Premkumar Anilkumar Paramasivan Gomathisankar 《Monatshefte für Chemie / Chemical Monthly》2010,7(3):529-537
Abstract
Ag-doped TiO2 (anatase) samples (mass fraction w Ag = 0.01 and w Ag = 0.02) of 15.9 and 14.5 nm mean particle size and 11.46 and 10.14 m2 g−1 BET surface area were prepared by photodeposition. Doping results in surface plasmon resonance of the metallic silver nanoclusters at around 500 nm, but the absorption edge remains unaltered at 365 nm. Ag-doping remarkably enhances the photooxidation of iodide ion under UV light; iodine formation with Ag/TiO2 with w Ag = 0.01 is 16 times greater than with bare TiO2. The reaction conforms to Langmuir–Hinshelwood kinetics with regard to both I− and O2. Increase of pH slows down iodine formation and sacrificial electron donors arrest the reaction. Pre-sonication of the catalyst slurry hinders the photocatalysis. Generation of iodine is much greater in acetonitrile than in water. Under the experimental conditions, Ag/TiO2 with w Ag = 0.01 is more efficient than Ag/TiO2 with w Ag = 0.02, and the enhanced photocatalysis is likely to be because of suppression of electron–hole pair recombination. Kinetic analysis reveals that increasing the Ag mass fraction from 0.01 to 0.02 enhances the surface pseudo-first-order rate constant but inhibits the adsorption of iodide ion and the oxygen molecule on the illuminated oxide surface. 相似文献4.
Abstract
The effect of sodium benzoate (SB) and sodium 4-(phenylamino)benzenesulfonate (SPABS) on the corrosion behavior of low carbon steel has been investigated using gravimetric method in the temperature range of 30–80 °C, velocity range of 1.44–2.02 m s−1 and concentration range of 6.94 × 10−4 to 4.16 × 10−3 mol dm−3 SB and 3.69 × 10−4 to 2.06 × 10−3 mol dm−3 SPABS. Optimization of temperature, fluid velocity, and inhibitors concentration has been made. The obtained results indicate that the inhibition efficiency (w IE %) at 1.56 m s−1 is not in excess of 81.5% at 4.16 × 10−3 mol dm−3 SB and 84.4% at 2.06 × 10−3 mol dm−3 SPABS. The inhibitive performance of these compounds showed an improvement with increasing concentration up to critical values of SB and SPABS; beyond these concentrations no further effectiveness is observed. These inhibitors retard the anodic dissolution of low carbon steel by protective layer bonding on the metal surface. The adsorption of SB and SPABS on the low carbon steel surface was found to obey the Freundlich isotherm model. The FT-IR spectroscopy was used to analyze the surface adsorbed film. 相似文献5.
A. K. Lyashchenko I. M. Karataeva 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(2):320-328
The relation between concentration changes in the activity of water (a
w) and static permittivities (ɛ) of concentrated solutions of salts was studied over a wide concentration range. The dependence
of a
w on 1/ɛ was shown to be linear at 298 K for more than 15 examples. The concentration boundary of the first structural zone
of solutions where this dependence was observed was established. The appearance of deviations was related to concentrations
at which complex ion-water groups were present in solutions and the transition from a water-electrolyte to an electrolyte-water
solvent occurred. 相似文献
6.
Electrospinning is a recently rediscovered method to produce non-woven nanowebs of which the individual polymer fibres have diameters of 50-500 nm. Applications require specific functionalities to be present at the surface. The use of additives in the electrospun solution provides an elegant alternative to functionalised polymers. This study has focused on the use of the static secondary ion mass spectrometry (S-SIMS) to characterise the surface composition of nanofibres electrospun from acetone solutions containing 15% (w/w) of poly(?-caprolactone) (PCL, molecular weight 40,000) and 0-15 mol% (relative to PCL) cetyltrimethylammonium bromide (CTAB). Specifically, the calibration of the relative signal intensities of structural ions from PCL and CTAB as a function of the local concentrations requires adequate reference samples to be prepared. In general, this step becomes a major bottleneck in nanoscale analysis. A relatively simple method using a combination of spincoating and hand barcoating of solutions has been developed. Its applicability and limitations for monitoring the surface enrichment of CTAB in PCL nanowebs are discussed. 相似文献
7.
The electrode characteristics and selectivities of PVC-based thiocyanate selective polymeric membrane electrode (PME) incorporating
the newly synthesized zinc complex of 6,7:14,15-Bzo2-10,11-(4-methylbenzene)-[15]-6,8,12,14-tetraene-9,12-N2-1,5-O2 (I
1
) and zinc complex of 6,7:14,15-Bzo2-10,11-(4-methylbenzene)-[15]-6,14-diene-9,12-dimethylacrylate-9,12-N2-1,5-O2 (I
2
) are reported here. The best response was observed with the membrane having a composition of I2:PVC:o-NPOE:HTAB in the ratio of 6:33:59:2 (w/w; milligram). This electrode exhibited Nernstian slope for thiocyanate ions over working concentration range of 4.4 × 10−7 to 1.0 × 10−2 mol L−1 with detection limit of 2.2 × 10−7 mol L−1. The performance of this electrode was compared with coated graphite electrode (CGE), which showed better response characteristics
w.r.t Nernstian slope 59.0 ± 0.2 mV decade−1 activity, wide concentration range of 8.9 × 10−8 to 1.0 × 10−2 mol L−1 and detection limit of 6.7 × 10−8 mol L−1. The response time for CGE and PME was found to be 8 and 10 s, respectively. The proposed electrode (CGE) was successfully
applied to direct determination of thiocyanate in biological and environmental samples and also as indicator electrode in
potentiometric titration of SCN− ion. 相似文献
8.
Divanery Rodriguez-Gomez Linda Lehmann Nadja Schultz-Jensen Anne Belinda Bjerre Timothy John Hobley 《Applied biochemistry and biotechnology》2012,166(8):2051-2063
Plasma-assisted pretreated wheat straw was investigated for cellulase and xylanase production by Trichoderma reesei fermentation. Fermentations were conducted with media containing washed and unwashed plasma-assisted pretreated wheat straw
as carbon source which was sterilized by autoclavation. To account for any effects of autoclavation, a comparison was made
with unsterilized media containing antibiotics. It was found that unsterilized washed plasma-assisted pretreated wheat straw
(which contained antibiotics) was best suited for the production of xylanases (110 IU ml−1) and cellulases (0.5 filter paper units (FPU) ml−1). Addition of Avicel boosted enzyme titers with the highest cellulase titers (1.5 FPU ml−1) found with addition of 50 % w/w Avicel and with the highest xylanase production (350 IU ml−1) reached in the presence of 10 % w/w Avicel. Comparison with enzyme titers from other nonrefined feedstocks suggests that plasma pretreated wheat straw is a promising
and suitable substrate for cellulase and hemicellulase production. 相似文献
9.
Abstract The effect of sodium benzoate (SB) and sodium 4-(phenylamino)benzenesulfonate (SPABS) on the corrosion behavior of low carbon
steel has been investigated using gravimetric method in the temperature range of 30–80 °C, velocity range of 1.44–2.02 m s−1 and concentration range of 6.94 × 10−4 to 4.16 × 10−3 mol dm−3 SB and 3.69 × 10−4 to 2.06 × 10−3 mol dm−3 SPABS. Optimization of temperature, fluid velocity, and inhibitors concentration has been made. The obtained results indicate
that the inhibition efficiency (w
IE %) at 1.56 m s−1 is not in excess of 81.5% at 4.16 × 10−3 mol dm−3 SB and 84.4% at 2.06 × 10−3 mol dm−3 SPABS. The inhibitive performance of these compounds showed an improvement with increasing concentration up to critical values
of SB and SPABS; beyond these concentrations no further effectiveness is observed. These inhibitors retard the anodic dissolution
of low carbon steel by protective layer bonding on the metal surface. The adsorption of SB and SPABS on the low carbon steel
surface was found to obey the Freundlich isotherm model. The FT-IR spectroscopy was used to analyze the surface adsorbed film.
Graphical abstract Low carbon steel corrosion in presence of sodium benzoate and sodium 4-(phenylamino)benzenesulfonate has been investigated.
The adsorption mechanism obeyed Freundlich isotherm model. FT-IR was used to analyze the adsorbed film
相似文献
10.
Xia WJ Luo ZB Dong HP Yu L Cui QF Bi YQ 《Applied biochemistry and biotechnology》2012,166(5):1148-1166
A bacterial strain was isolated and cultured from the oil excavation areas in tropical zone in northern China. The biochemical
characteristics and partial sequenced 16S rRNA gene of isolate, WJ-1, was identical to those of cultured representatives of
the species Pseudomonas aeruginosa. This bacterium was able to produce a type of biosurfactant. Compositional analysis revealed that the extracted biosurfactant
was composed of high percentage lipid (∼74%, w/w) and carbohydrate (∼20%, w/w) in addition to a minor fraction of protein (∼6%, w/w). The best production of 50.2 g/l was obtained when the cells were grown on minimal salt medium containing 6.0% (w/v) glucose and 0.75% (w/v) sodium nitrate supplemented with 0.1% (v/v) element solution at 37 °C and 180 rpm after 96 h. The optimum biosurfactant production pH value was found to be 6.0–8.0.
The biosurfactant of WJ-1, with the critical micelle concentration of 0.014 g/L, could reduce surface tension to 24.5 mN/m
and emulsified kerosene up to EI24 ≈95. The results obtained from time course study indicated that the surface tension reduction and emulsification potential
was increased in the same way to cell growth. However, maximum biosurfactant production occurred and established in the stationary
growth phase (after 90 h). Thin layer chromatography, Fourier transform infrared spectrum, and mass spectrum analysis indicate
the extracted biosurfactant was affiliated with rhamnolipid. The core holder flooding experiments demonstrated that the oil
recovery efficiency of strain and its biosurfactant was 23.02% residual oil. 相似文献
11.
Roger Ibbett Jim Taylor K. Christian Schuster Mike Cox 《Cellulose (London, England)》2008,15(3):393-406
The uptake of solutions of sodium hydroxide by lyocell fibre results in a phenomenon in textiles described as swelling–shrinkage.
The response of woven fabrics in a tensile stress–relaxation experiment shows two time-dependent processes, corresponding
to different mechanisms of pressure development. Rapid diffusion has been assigned to osmotic swelling through the interconnected
pore structure of the fibre (D = 6–15 × 10−12 m2/s), which is influenced by the extent of ionization of hydroxyl groups at the pore surfaces. A ratio for the cellulose and
water dissociation constants (Kcell/Kw) of 70 provides best agreement with experimental data. A second slower diffusion process (D = 2–10 × 10−14 m2/s) is assigned to transport through the cellulose polymer structure, associated with the Na-cellulose transition. This can
be modeled assuming an ion-exchange equilibrium, where the cellulose gel converts reversibly between compact hydrogen and
expanded sodium forms, with K = 1.04 × 1014, in favour of the hydrogen form. The model successfully predicts the concentration dependence of the transition and the movement
to higher concentration with external constraint. The slow diffusion process only becomes apparent at high alkali concentrations,
as the pores in the fibre collapse due to the expansion of the gel. Continued gel-diffusion is only possible through the polymer
phase, which then dominates over fast pore-diffusion. 相似文献
12.
Rodrigues TH Rocha MV de Macedo GR Gonçalves LR 《Applied biochemistry and biotechnology》2011,164(6):929-943
In this work, the potential of microwave-assisted alkali pretreatment in order to improve the rupture of the recalcitrant
structures of the cashew able bagasse (CAB), lignocellulosic by-product in Brazil with no commercial value, is obtained from
cashew apple process to juice production, was studied. First, biomass composition of CAB was determined, and the percentage
of glucan and lignin was 20.54 ± 0.70% and 33.80 ± 1.30%, respectively. CAB content in terms of cellulose, hemicelluloses,
and lignin, 19.21 ± 0.35%, 12.05 ± 0.37%, and 38.11 ± 0.08%, respectively, was also determined. Results showed that, after
enzymatic hydrolysis, alkali concentration exerted influence on glucose formation, after pretreatment with 0.2 and 1.0 mo L−1 of NaOH (372 ± 12 and 355 ± 37 mg gglucan−1) when 2% (w/v) of cashew apple bagasse pretreated by microwave-assisted alkali pretreatment (CAB-M) was used. On the other hand, pretreatment
time (15–30 min) and microwave power (600–900 W) exerted no significant effect on hydrolysis. On enzymatic hydrolysis step,
improvement on solid percentage (16% w/v) and enzyme load (30 FPU gCAB-M−1) increased glucose concentration to 15 g L−1. The fermentation of the hydrolyzate by Saccharomyces cerevesiae resulted in ethanol concentration and productivity of 5.6 g L−1 and 1.41 g L−1 h−1, respectively. 相似文献
13.
G. F. Dvorko 《Kinetics and Catalysis》2011,52(6):775-784
The rate constant of the first-order rate equation w = k[RX] that is derived from the variation of the reaction product concentration or determined by the verdazyl method characterizes
the lifetime of the transition state or that of the solvent-separated ion pair rather than the heterolysis rate. The diffusion
rate constant is equal to the dissociation rate constant of the contact ion pair and to the reverse of the lifetime of the
solvent-separated ion pair: k
D ≈ k = 1/τ ≈ 1010 s−1. 相似文献
14.
C. Lucas I. Eiroa M. R. Nunes P. A. Russo M. M. L. Ribeiro Carrott M. I. da Silva Pereira M. E. Melo Jorge 《Journal of Solid State Electrochemistry》2009,13(6):943-950
The electrochemical properties of Ca1 − x
Ce
x
MnO3 perovskite-type oxide electrode have been investigated by cyclic voltammetry in Na2SO4 aqueous solutions with pH 14. The structural and morphological characterizations have also been investigated and the information
used to interpret the electrochemical behavior. An estimation of the electrode’s capacitance and roughness factor has been
obtained by means of cyclic voltammetry. The specific capacitance and consequently the roughness factor values are affected
by the presence of Ce ions in the oxide. These findings are in agreement with the increase of the oxide-specific surface area
by the introduction of Ce ion. The open-circuit potential and the voltammetric patterns are dependent on the presence of Ce
ion in the electrodes and support that the surface electrochemistry of the perovskite oxide electrodes is governed by the
Mn4+–Mn3+ redox couple. 相似文献
15.
Statistical Optimization of Recycled-Paper Enzymatic Hydrolysis for Simultaneous Saccharification and Fermentation Via Central Composite Design 总被引:1,自引:0,他引:1
Qing Liu Ke-ke Cheng Jian-an Zhang Jin-ping Li Ge-hua Wang 《Applied biochemistry and biotechnology》2010,160(2):604-612
A central composite design of the response surface methodology (RSM) was employed to study the effects of temperature, enzyme
concentration, and stirring rate on recycled-paper enzymatic hydrolysis. Among the three variables, temperature and enzyme
concentration significantly affected the conversion efficiency of substrate, whereas stirring rate was not effective. A quadratic
polynomial equation was obtained for enzymatic hydrolysis by multiple regression analysis using RSM. The results of validation
experiments were coincident with the predicted model. The optimum conditions for enzymatic hydrolysis were temperature, enzyme
concentration, and stirring rate of 43.1 °C, 20 FPU g−1 substrate, and 145 rpm, respectively. In the subsequent simultaneous saccharification and fermentation (SSF) experiment under
the optimum conditions, the highest 28.7 g ethanol l−1 was reached in the fed-batch SSF when 5% (w/v) substrate concentration was used initially, and another 5% added after 12 h fermentation. This ethanol output corresponded
to 77.7% of the theoretical yield based on the glucose content in the raw material. 相似文献
16.
N. M. Antovic I. Antovic N. Svrkota 《Journal of Radioanalytical and Nuclear Chemistry》2010,284(3):605-614
232Th activities in the South Adriatic Sea-water, surface sediment, mud with detritus, seagrass (Posidonia oceanica) samples, and the mullet (Mugilidae) species Mugil cephalus, as well as soil and sand from the Montenegrin Coast, were measured using the six-crystal spectrometer PRIPYAT-2M, which
has relatively high detection efficiency and a good sensitivity, and allows a short acquisition time, and measuring samples
of any shape, without preliminary preparation and calibration measurements for different sample geometries. An average 232Th activity concentration in surface soil layer is found to be 40.33 Bq kg−1, while in sand—4.7 Bq kg−1. The absorbed dose rate in air due to 232Th gamma radiation from surface soil layer ranged from 11.76 to 63.39 nGy h−1, with a mean of 24.06 nGy h−1. Corresponding average annual effective dose rate has been found to be 0.03 mSv y−1. The absorbed dose rates due to the thorium gamma radiation in air at 1 m above sand surface on the Montenegrin beaches have
been found to be from 0.41 to 9.08 nGy h−1, while annual effective dose rates ranged from 0.0005 to 0.011 mSv y−1. 232Th activity concentration in seawater ranged from 0.06 to 0.22 Bq L−1, as in the mullet (Mugil cephalus) whole individuals from 0.63 to 1.67 Bq kg−1. Annual intake of 232Th by human consumers of this fish species has been estimated to provide an effective dose of about 0.003 mSv y−1. 相似文献
17.
I. González-Mariño I. Rodríguez J. B. Quintana R. Cela 《Analytical and bioanalytical chemistry》2010,398(5):2289-2297
An expeditious method for the determination of triclosan (TCS) and methyl triclosan (MTCS) in sludge and sediment samples
is presented. Extraction and cleanup steps were integrated in the same process using matrix solid-phase dispersion as sample
preparation technique. Effects of different variables on the efficiency and the selectivity of the sample preparation process
are discussed. Under final working conditions, samples (0.5 g) were dispersed with diatomaceous earth (1 g) and transferred
to a polypropylene syringe containing 2 g of silica impregnated with sulphuric acid (15%, w:w). Analytes were recovered with 10 mL of dichloromethane. After solvent exchange to ethyl acetate, TCS was converted into
the tert-butyldimethylsilyl derivative, and the extract was analysed by gas chromatography-mass spectrometry, without any additional
cleanup. Obtained recoveries, for sludge and sediment samples spiked at different concentration levels, ranged from 86% to
113%, with associated standard deviations between 2 and 13%. Limits of quantification of the global method were 6 and 7 ng g−1 for MTCS and TCS, respectively. Both compounds were detected in all the processed sludge samples with maximum concentrations
of 191 ng g−1 (MTCS) and 2,640 ng g−1 (TCS). The parent bactericide was also found in some sediment samples at concentrations up to 200 ng g−1. 相似文献
18.
We investigate effects of Fe dopant concentration on the structure, as well as low temperature Raman scattering and electrical
transport properties in SrTi1−x
Fe
x
O3 (x = 0.00, 0.10, 0.20, 0.30, 0.40) nanoparticles prepared by sol-gel method. The results show an average particle size of powder
is about 30 nm, and the lattice parameters decrease as increasing the Fe content. In the Raman spectra, a broad structure
in the region 200–500 cm−1 is almost absent and the peaks in the region 600–800 cm−1 show different weights with respect to SrTiO3, relating to structural changes with increasing dopant concentration in conjunction with increasing grain boundary contribution
to the impedance. The abrupt change in Raman peak position as function of temperature suggests a phase transition in our samples
in the range of 110–150 K. These results indicate that the Fe ion has replaced the site of Ti in unit cell. These results
also demonstrate the feasibility of synthesizing the compound with low annealing temperature. 相似文献
19.
Li S Zuo Z Niu D Singh S Permaul K Prior BA Shi G Wang Z 《Applied biochemistry and biotechnology》2011,164(5):581-592
A putative α-amylase gene, designated as RoAmy, was cloned from Rhizopus oryzae. The deduced amino acid sequence showed the highest (42.8%) similarity to the α-amylase from Trichoderma viride. The RoAmy gene was successfully expressed in Pichia pastoris GS115 under the induction of methanol. The molecular weight of the purified RoAmy determined by sodium dodecyl sulfate polyacrylamide
gel electrophoresis was approximately 48 kDa. The optimal pH and temperature were 4–6 and 60 °C, respectively. The enzyme
was stable at pH ranges of 4.5–6.5 and temperatures below 50 °C. Purified RoAmy had a K
m and V
max of 0.27 mg/ml and 0.068 mg/min, respectively, with a specific activity of 1,123 U/mg on soluble starch. Amylase activity
was strongly inhibited by 5 mM Cu2+ and 5 mM Fe2+, whereas 5 mM Ca2+ showed no significant effect. The RoAmy hydrolytic activity was the highest on wheat starch but showed only 55% activity
on amylopectin relative to soluble corn starch, while the pullulanase activity was negligible. The main end products of the
polysaccharides tested were glucose and maltose. Maltose reached a concentration of 74% (w/w) with potato starch as the substrate. The enzyme had an extremely high affinity (K
m = 0.22 mM) to maltotriose. A high ratio of glucose/maltose of 1:4 was obtained when maltotriose was used at an initial concentration
of 40 mM. 相似文献
20.
Isothermal titration calorimetry has been used to determine the stoichiometry, formation constants and thermodynamic parameters
(ΔG
o, ΔH, ΔS) for the formation of the citrate complexes with the Mn2+, Co2+, Ni2+ and Zn2+ ions. The measurements were run in Cacodylate, Pipes and Mes buffer solutions with a pH of 6, at 298.15 K. A constant ionic
strength of 100 mM was maintained with NaClO4. The influence of a metal ion on its interaction energy with the citrate ions and the stability of the resulting complexes
have been discussed. 相似文献