Electrospun crosslinked poly(acrylic acid) fiber constructs: towards a synthetic model of the cortical layer of nerve

In an attempt to mimic properties of the polyanionic nanofibrous cortical layer (ectoplasm) of nerve, tube‐shaped poly(acrylic acid) (PAA) nanofiber constructs were prepared via electrospinning. The influence of processing parameters on the morphology of the electrospun PAA nanofibers was systematically investigated. Smooth and uniform PAA nanofibers with average fiber diameter of 820 nm were produced at a concentration of 4 wt% with a flow rate of 0.8 mL h^?1 when a high voltage of 15 kV was applied. Water‐stable PAA nanofibers were obtained by thermally crosslinking PAA with ethylene glycol. The resulting tubes were neutralized to the sodium polyacrylate form and were shown to undergo reversible and abrupt length changes upon titration with CaCl₂ followed by titration with sodium citrate. The sharpness of the length transition was found to be highly dependent upon the bathing NaCl concentration and the operation temperature. It is suggested that electrospun PAA may be a promising candidate as a key element of an abiotic macromolecular mimic of selected properties of axons. © 2014 Society of Chemical Industry     

Synthesis, characterization, and magnetic properties of monodisperse CeO2 nanospheres prepared by PVP-assisted hydrothermal method

ABSTRACT: Ferromagnetism was observed at room-temperature in monodisperse CeO2 nanospheres synthesized by hydrothermal treatment of Ce(NO3)3.6H2O using polyvinylpyrrolidone (PVP) as a surfactant. The structure and morphology of the products were characterized by; X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), and field-emission scanning electron microscopy (FE-SEM). The optical properties of the nanospheres were determined using ultraviolet and visible spectroscopy (UV-Vis) and photoluminescence (PL). The valence states of Ce ions were also determined using X-ray absorption near edge spectroscopy (XANES). The XRD results indicated that the synthesized samples had a cubic structure with a crystallite size in the range of ~ 9-19 nm. FE-SEM micrographs showed that the samples had a spherical morphology with a particle size in the range of ~ 100-250 nm. The samples also showed a strong UV absorption and room temperature photoluminescence. The emission might be due to charge transfer transitions from the 4f band to the valence band of the oxide. The magnetic properties of the samples were studied by Vibrating Sample Magnetometer (VSM). The samples exhibited room temperature ferromagnetism (RT-FM) with a small magnetization of ~ 0.0026-0.016 emu/g at 10 kOe. Our results indicate that oxygen vacancies could be involved in the ferromagnetic exchange and the possible mechanism of formation was discussed based on the experimental results.     

Relationship between Surface Roughness,Internal Crystal Perfection,and Crystal Growth Rate

Potential mechanisms affecting growth rate dispersion (GRD) are investigated. Previous studies have identified surface roughness and internal lattice perfection as key mechanisms which are both evaluated with respect to GRD. Crystal growth of potassium dihydrogen phosphate was studied in two solvent mixtures, water and water‐ethanol. The surface roughness was analyzed by atomic force microscopy and the internal crystal perfection by X‐ray diffraction using a synchrotron source. The crystals grown at higher supersaturation have more pronounced and more frequent surface irregularities, supporting previous findings on a feedback mechanism between surface roughness and growth rate. No significant relationship was found between internal crystal perfection and growth rate, however, this is likely due to the size of the crystals analyzed herein and not the absence of any such mechanism in small crystals.     

Porous Host–Guest MOF-Semiconductor Hybrid with Multisites Heterojunctions and Modulable Electronic Band for Selective Photocatalytic CO2 Conversion and H2 Evolution

Optimizing catalysts for competitive photocatalytic reactions demand individually tailored band structure as well as intertwined interactions of light absorption, reaction activity, mass, and charge transport.  Here, a nanoparticulate host–guest structure is rationally designed that can exclusively fulfil and ideally control the aforestated uncompromising requisites for catalytic reactions. The all-inclusive model catalyst consists of porous Co₃O₄ host and Zn_xCd_1-xS guest with controllable physicochemical properties enabled by self-assembled hybrid structure and continuously amenable band gap. The effective porous topology nanoassembly, both at the exterior and the interior pores of a porous metal–organic framework (MOF), maximizes spatially immobilized semiconductor nanoparticles toward high utilization of particulate heterojunctions for vital charge and reactant transfer. In conjunction, the zinc constituent band engineering is found to regulate the light/molecules absorption, band structure, and specific reaction intermediates energy to attain high photocatalytic CO₂ reduction selectivity. The optimal catalyst exhibits a H₂-generation rate up to 6720 µmol g⁻¹ h⁻¹ and a CO production rate of 19.3 µmol g⁻¹ h⁻¹. These findings provide insight into the design of discrete host–guest MOF-semiconductor hybrid system with readily modulated band structures and well-constructed heterojunctions for selective solar-to-chemical conversion.     

Prevalence of coronary heart disease and major cardiovascular risk factors in Thailand

BACKGROUND: Coronary heart disease (CHD) is expected to become one of the major health problems in developing countries such as Thailand where prevalence data are scarce. This study reports the prevalence of CHD, as indicated by electrocardiogram (ECG) Minnesota coding, and its risk factors in Thailand. METHODS: In 1991 we conducted a cross-sectional ECG survey in a multistage random sample of the Thai population, aged > or =30. All major cardiovascular risk factors were measured. Standard supine 12-lead ECG data were collected; amplitudes and intervals were measured manually and entered into a computer. Abnormal tracings were verified by five cardiologists, and agreement among at least three of them was accepted as final. RESULTS: The total sample included 3822 men and 4967 women aged > or =30 years. The age-standardized prevalence rate of CHD was 9.9/1000 (men 9.2/1000, women 10.7/ 1000). The age-standardized level of major cardiovascular risk factors among men and women respectively were: total cholesterol 4.8 mmol/l (187.3 mg/dl), 5.1 mmol/l (197.7 mg/dl); hypercholesterolaemia (> or =6.2 mmol/l) 12.2%, 16.9%; systolic blood pressure (mmHg) 117.8, 117.7; diastolic blood pressure (mmHg) 76.9, 75.8; body mass index (kg/m2) 21.7, 22.8; fasting blood sugar 4.8 mmol/l (87.9 mg/dl), 5.0 mmol/l (90.3 mg/dl); hypertension (> or =160/95 +/- on antihypertensive drugs) 6.3%, 8.1%; smoking 65.1%, 8.5%; diabetes mellitus (> or =7.8 mmol/l) 2.4%, 3.7%; obesity (>25 kg/m2) 15.2%, 27.2%. CONCLUSIONS: Most of the age-adjusted mean values and proportion of major cardiovascular disease risk factors as well as the prevalence of total CHD in the Thai population were much lower than the median of those values found in developing countries.     

Copper incorporation in Mn2+-doped Sn2S3 nanocrystals and the resultant structural,optical, and electrochemical characteristics

Sn₂S₃ nanocrystals (NCs) with both Mn²⁺ doping and Cu²⁺ incorporation were synthesized using a chemical bath deposition method. The Cu²⁺ ions formed an anorthic Mn²⁺-doped Cu₂SnS₃ structure with E_g =?1.44?eV, which altered the material's optical and photo/electrochemical properties. After coating the bare Nb₂O₅ electrode with Mn²⁺-doped Sn₂S₃ or Mn²⁺-doped Cu₂SnS₃ NCs, the photoluminescence spectrum was blue-shifted to 411.13?nm from 411.69?nm. Compared to the sample without Cu²⁺, the Cu²⁺-incorporated sample showed a slightly stronger emission at the same position, possibly due to disorder in the crystalline structure based on variations at the interface of Mn²⁺-doped Cu₂SnS₃ NCs. Electrochemical analysis showed a lower charge transfer resistance in the Mn²⁺-doped Cu₂SnS₃, which is related to its larger electroactive surface area. The larger electroactive surface area is attributed to the Faradaic redox processes at the electrode surface, which suppresses the carrier recombination. The coexistence of Cu²⁺ and Mn²⁺ ions shortened the electron transport pathway at the interface and improved the carrier diffusion coefficient and diffusion length, leading to a higher specific capacitance that implies higher energy storage performance. Finally, the I-V characteristics of the Mn²⁺-doped Cu₂SnS₃-coated Nb₂O₅ electrode under various light illumination conditions indicated its better efficiency in photoresponse, electron generation, and charge collection, owing to a superior charge transport mechanism. Detailed results were obtained about the charge dynamics in the as-prepared photo/electrochemical devices with Cu²⁺ incorporation in the Mn²⁺-doped SnS₃ electrode.