Search

To improve fuel use and energy-conversion efficiency and reduce the emission of pollutants, oxygenation is now deemed an effective chemical treatment of water in supercritical and ultra-supercritical power plants. Supercritical water with dissolved oxygen significantly enhances the oxidation rate of steels in the main steam pipeline and super-heater header. However, at the atomic scale, the mechanism of metal oxidation in supercritical water containing dissolved oxygen is unknown and has not been investigated by simulation. In this work, the oxidation of iron in supercritical water containing dissolved oxygen is studied by ab initio molecular dynamics and first principles calculations. The results indicate that dissolved oxygen in supercritical water dramatically accelerates the oxidation of iron. With the help of oxygen, the decomposition of water occurs on the iron surface, thereby producing more iron oxides and iron hydroxides. Additionally, hydrogen peroxide (H2O2) forms as an intermediate product, instantaneously decomposing to form iron hydroxides, and this is another reason for the enhancement in the oxidation of steel by supercritical water containing dissolved oxygen. Based on the results from ab initio molecular dynamics, we develop herein typical models of water molecules and oxygen molecules reacting directly on the iron surface and then carry out first-principles calculations. The results show that water decomposes on the iron surface only with the assistance of adjacent oxygen molecules and in the absence of surrounding water molecules. This investigation deepens our understanding of the oxidation mechanism of metal in supercritical water containing dissolved oxygen. The ideas and methods implemented in this work can also be used to study other materials exposed to supercritical water involving oxygen. [ABSTRACT FROM AUTHOR]

To improve fuel use and energy-conversion efficiency and reduce the emission of pollutants, oxygenation is now deemed an effective chemical treatment of water in supercritical and ultra-supercritical power plants. Supercritical water with dissolved oxygen significantly enhances the oxidation rate of steels in the main steam pipeline and super-heater header. However, at the atomic scale, the mechanism of metal oxidation in supercritical water containing dissolved oxygen is unknown and has not been investigated by simulation. In this work, the oxidation of iron in supercritical water containing dissolved oxygen is studied by ab initio molecular dynamics and first principles calculations. The results indicate that dissolved oxygen in supercritical water dramatically accelerates the oxidation of iron. With the help of oxygen, the decomposition of water occurs on the iron surface, thereby producing more iron oxides and iron hydroxides. Additionally, hydrogen peroxide (H2O2) forms as an intermediate product, instantaneously decomposing to form iron hydroxides, and this is another reason for the enhancement in the oxidation of steel by supercritical water containing dissolved oxygen. Based on the results from ab initio molecular dynamics, we develop herein typical models of water molecules and oxygen molecules reacting directly on the iron surface and then carry out first-principles calculations. The results show that water decomposes on the iron surface only with the assistance of adjacent oxygen molecules and in the absence of surrounding water molecules. This investigation deepens our understanding of the oxidation mechanism of metal in supercritical water containing dissolved oxygen. The ideas and methods implemented in this work can also be used to study other materials exposed to supercritical water involving oxygen. [ABSTRACT FROM AUTHOR]

Shewanella baltica and Acinetobacter are among the predominant spoilage bacteria in refrigerated shrimp (Litopenaeus vannamei). S. baltica are incapable of producing acyl-homoserine lactone (AHL) quorum sensing signals, but can respond to environmental AHLs. In this paper, Acinetobacter was found to produce three AHLs, i.e. N-butanoyl-l-homoserine lactone (C4-HSL), N-(3-oxohexanoyl)-l-homoserine lactone (O-C6-HSL) and N-(3-oxooctanoyl)-l-homoserine lactone (O-C8-HSL), according to thin-layer chromatography using the bioreporter Agrobacterium tumefaciens A136. The agar diffusion and β-galactosidase assays revealed that S. baltica could eavesdrop on these three AHLs from Acinetobacter. Eavesdropping on Acinetobacter AHLs especially C4-HSL was found to boost the growth of S. baltica particularly under nutrient limiting conditions (up to 40-fold increase) in the co-culture experiments. The azocasein assay revealed that S. baltica produced fourfold more extracellular proteases in response to Acinetobacter AHLs. As demonstrated by the biofilm crystal violet staining assay and confocal laser scanning microscopy, eavesdropping also decreased the biofilm-forming capacity of Acinetobacter. By inoculation of S. baltica and Acinetobacter onto surface-sterilized shrimp, eavesdropping was found to endow a growth advantage to S. baltica in vivo, resulting in a 0.5 day shortened shelf life of shrimp according to total volatile basic nitrogen levels and sensory analysis. Overall, the AHL-dependent eavesdropping increased the spoilage potential of S. baltica, providing a fresh perspective on the spoilage process of refrigerated L. vannamei, and this may inspire the development of novel preservation techniques in the future to further reduce post-harvest loss of shrimp. [ABSTRACT FROM AUTHOR]

The spoilage potential of Shewanella putrefaciens and S. baltica isolated from spoiled refrigerated Litopenaeus vannamei was evaluated by in vitro assays for trimethylamine oxide reduction, extracellular hydrolytic enzymes and biofilm formation, and in vivo inoculation into surface-sterilised shrimp followed by microbial, biochemical and sensory analyses during storage for 5 days at 4 °C. S. baltica displayed higher spoilage potential than S. putrefaciens both in vitro and in vivo. Shrimp co-inoculated with them had one-day shorter shelf life than those mono-inoculated, based on the results of bacterial density, volatile base nitrogen, trimethylamine, volatile organic compounds and sensory analysis, which strongly suggests cooperation of Shewanella species in shrimp spoilage. Exogenous cyclo-(L-Pro-L-Leu) boosted bacterial growth, extracellular protease and collagenase activities, and biofilm formation of S. putrefaciens and S. baltica at least before they entered the stationary phase, indicating that cyclo-(L-Pro-L-Leu)-dependent quorum sensing, a recently suggested communication mechanism between them, contributes to the cooperation. [ABSTRACT FROM AUTHOR]

Lactobionic acid (LBA) is a novel antibacterial agent that has attracted much interest in recent years. However, the study on the antibacterial effect of LBA on spoilage bacteria is rare. This study aims to investigate the antibacterial activity and mechanism of LBA on Shewanella baltica and Shewanella putrefaciens , which are the common spoilage microorganisms in chilled seafood. The results demonstrated that LBA was an effective bacteriostat against S. baltica and S. putrefaciens , with the minimum inhibitor concentration (MIC) of 8 mg/mL. Both the two Shewanella species could be completely killed by LBA at 2 MIC. LBA damaged the cell membrane integrity and increased outer membrane permeability, causing the increase in protein leakage and conductivity, which was supported by the bacterial morphology observed with scanning electron microscopy. Besides, LBA could interact with the bacterial genome DNA, resulting in the dysfunction of cell function. Moreover, LBA exhibited an effectively inhibitory effect on slowing down microbial growth, melanosis and lipid oxidation rate in refrigerated shrimp. These results suggest that LBA would be a promising antibacterial compound used in seafood. • Lactobionic acid shows antibacterial activity against S. baltica and S. putrefaciens. • Lactobionic acid can damage cell membrane integrity and cause protein leakage. • Lactobionic acid can retard genome DNA migrate and quench the fluorescence intensity. • Lactobionic acid exhibits a preservative effect on Pacific white shrimp. [ABSTRACT FROM AUTHOR]

Thermal oxidative crosslinking results in the generation of oxygen bridges among polymer chains and helps regulate the membrane microstructure. Simultaneously, any strategy to increase the crosslinking sites of polyimide (PI) can improve the crosslinking efficiency and allow precise control of the pore structure of membranes. Phenolphthalein-based PIs are potentially suitable precursors for thermal oxidative crosslinking of membranes, since thermal treatment will result in the degradation of lactone ring leading to the generation of a pair of phenyl crosslinking sites. In this work, three phenolphthalein-based diamines with different structures were designed and synthesized. The three diamines were subsequently reacted with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) to prepare phenolphthalein-based PIs. The original membranes were post-treated by thermal oxidation crosslinking at 400 °C and 425 °C, respectively; the lactone ring underwent decomposition, and the imide ring opened at the same time, resulting in the generation of multiple crosslinking sites and correspondingly improving the crosslinking efficiency. The effect of the side groups (−CH 3 , –CF 3 or unsubstituted) of phenolphthalein-based diamine and thermal treatment temperatures on the gas separation performance of phenolphthalein-based PI membranes were investigated. Wide-angle X-ray diffractometry (WAXD) and wide-angle X-ray scattering (WAXS) analysis demonstrated that the π-π stacking distance were improved. BTDA-FPP-425 had a CO 2 /CH 4 selectivity of 37.68. This thermal degradation along with thermal oxidative crosslinking strategy provides a promising approach for fabrication of CO 2 /CH 4 separation membrane. [Display omitted] • Phenolphthalein-based polyimide is a suitable precursor for thermal crosslinking. • BTDA-based polyimide has low cost and good mechanical properties. • The lactone ring and the imide ring open, generating multiple crosslinking sites. • Thermal degradation and oxidative crosslinking improved the π-π stacking values. • A strategy for making CO 2 /CH 4 separation membrane with anti-plastic was achieved. [ABSTRACT FROM AUTHOR]

Carboxylated PIM-1 fibers were prepared by one-step hydrolysis of PIM-1 fibers using sodium hydroxide solution. The chemical structure and morphology of the hydrolyzed PIM-1 fibers were characterized. The adsorption behaviors of the hydrolyzed PIM-1 fibers towards different organic dyes and heavy metal ions in an aqueous solution were investigated. The results showed that the hydrolyzed PIM-1 fibers could effectively adsorb methylene blue (MB), safranin O (SO), and methylene violet (MV), but barely adsorb methyl orange (MO), indicating a selective adsorption property. Isotherm studies revealed that the Freundlich model was more suitable for describing the adsorption behavior of the hydrolyzed PIM-1 fibers than the Langmuir model. The adsorption mechanism was investigated by UV–vis absorbance spectra and solution pH effect. It was concluded that the adsorption process was based on the host–guest interactions between the hydrolyzed PIM-1 fibers and the dyes. In addition, the hydrolyzed PIM-1 fibers exhibited an improved adsorption capacity for heavy metal ions (41.2 mg/g for Pb 2+ , 16.9 mg/g for Cu 2+ , respectively) than the pristine PIM-1 fibers. Based on our results, the hydrolyzed PIM-1 fibers, as an easily prepared adsorbent material, show potential application for the selective removal of various organic dyes and heavy metal ions in wastewater treatment. [ABSTRACT FROM AUTHOR]

The influences of current density and saccharin concentration on nanocrystalline nickel coatings synthesized by direct current electrodeposition were analyzed. Results show that in the current density range from 0.5 A/dm 2 to 1.5 A/dm 2 , nanocrystalline nickel coatings with broad microhardness HV distribution from 4150 MPa to 6030 MPa can be synthesized by adjusting saccharin concentration. The preferred orientation in the deposits exists at 0.5 A/dm 2 , (111), (200) double orientation texture changes to a (200) orientation texture as saccharin concentration and (200) intensity increase. The internal stresses of the samples prepared at 0.5 A/dm 2 decrease to nearly 0 MPa as saccharin concentration increases to 1.2 g/L. The results of DSC curves show that the grains start to grow until 600 °C and keep the thermal stability near to bulk nickel when grain sizes are in the range from 28 nm to 98 nm. However, when the grain size is 10 nm, the grains grow abnormally at 317 °C, and their thermal stability decrease sharply. [ABSTRACT FROM AUTHOR]

This article reports synthesis and structure property studies of block copolyimides synthesized using diamino room temperature ionic liquids (RTIL) as diamine monomers. Specifically, polyimide oligomers of different lengths were synthesized using 2,2- bis (3,4-carboxylphenyl) hexafluoropropane dianhydride (6FDA) and diamino RTIL (1,3-di(3-aminopropyl) imidazolium bis[(trifluoromethyl) sulfonyl] imide). These oligomers were copolymerized with 6FDA and m-phenylenediamine (MDA) using in situ polymerization to form (6FDA-RTIL)-(6FDA-MDA) block copolyimides. The impact of the length and relative concentration of 6FDA-RTIL oligomer in the copolymer on the resulting thermal, physical, and gas transport properties was monitored. As the concentration of the 6FDA-RTIL segments increased, the backbone of the block copolyimides became more flexible resulting in a decrease in the glass transition temperature (Tg) and an increase in the density. The permeabilities of the RTIL containing copolyimides were consistently lower than those of the base polyimide, 6FDA-MDA, with some increase in selectivities. Interestingly, the permeabilities of films produced with the low molecular weight oligomers were very different than those produced with same composition of the high molecular weight oligomers. This may be indicative of very different morphologies within these copolyimides. [ABSTRACT FROM AUTHOR]

This study investigated the segregation behavior of alloying additives X (X = Si, Al, V, Ti, Mo, W, Nb, Y) on the Fe(1 1 1)/Cr 2 O 3 (0 0 0 1) interface as well as the effects of these additives on the interfacial adhesive strength by using the first-principles method. The results indicated that W, Mo, and Nb atoms were easily segregated at the Fe(1 1 1)/Cr 2 O 3 (0 0 0 1) interface, however, the introduction of them would weaken the adhesive strength of the interface through weak-electron effects. Moreover, Y, Al, Si, Ti, and V were difficult to segregate at the Fe(1 1 1)/Cr 2 O 3 (0 0 0 1) interface. Comparison of separation energies and interfacial structural properties suggested that introduction of Si and Al improved the adhesive strength of the Fe(1 1 1)/Cr 2 O 3 (0 0 0 1) interface through strong interactions between Si/Al and O. Thus, Si and Al improved the adhesion of surface oxide scales and enhanced oxidation resistance. [ABSTRACT FROM AUTHOR]

At present, people's environmental awareness gradually enhances, and the environmental requirements on production and living continuously improve. Urban sewage discharge management and sewage treatment intensity are increasing in whole country, and urban water environment has certain improvement. But in rural areas, due to relatively weak environmental awareness of residents, not high economic development degree and not perfect infrastructure construction, the issue has not been handled properly. It seriously restricts further development of rural economy, and contradiction between water pollution worsening and farmers eager to raise the level of living environment increasingly aggravating has become key problem restricting China's new rural construction. According to status quo of rural water pollution in China, causes and hazards of rural water pollution are analyzed in detail, and several treatment suggestions are put forward. [ABSTRACT FROM AUTHOR]

The aim of the present work was to evaluate initial secondary austenite phase microstructural changes (δ → γ′) in 2205 duplex stainless steel with N content of 0.36 wt% during hot tensile test. The results showed there is no secondary austenite microstructural change in zero deformation degree. The secondary austenite (γ2) phase transformation occurred only in the cooling process and under hot deformation condition. Initial secondary austenite (γ′) occurred within the ferrite matrix at the temperature range of 950-1150 °C. The precipitation of initial γ′ increased with the increase in aging time and deformation degree. With increasing time, a progressive transformation of initial γ′ to γ2 occurred. The orientation relationship between the initial γ′ phase and the δ matrix was different at varying high temperatures. A significant change in the hot deformation condition has been observed as a consequence of secondary austenite reformation. These results indicated the importance of control over the shape and volume fraction of secondary austenite phases on high nitrogen duplex stainless steels to improve hot ductility. [ABSTRACT FROM AUTHOR]