Optimised phase compositions and improved microwave dielectric properties based on calcium tin silicates

The Ca_(1+2y)Sn_(1-x)Si_(1+y)O_(5-2x+4y) low-permittivity microwave dielectric ceramics were prepared through solid-state reaction at 1350–1450 °C for 5 h. The relations between microwave dielectric properties and phase compositions for non-stoichiometric Ca_(1+2y)Sn_(1-x)Si_(1+y)O_(5-2x+4y) ceramics have been investigated. A single CaSnSiO₅ phase with abnormally positive temperature coefficient of resonant frequency (τ_f = + 62.5 ppm/°C) was synthesised at 1450 °C. This composition was an effective τ_f compensator of CaSiO₃ and Ca₃SnSi₂O₉ phases with typically negative τ_f value. The CaSiO₃ second phase was related to the Sn deficiency in the CaSn_(1-x)SiO_(5-2x) (0 < x < 1.0) composition, whereas the Ca₃SnSi₂O₉ second phase was obtained by controlling the Ca:Sn:Si ratios on the basis of the Ca_(1+2y)SnSi_(1+y)O_(5+4y) (0 < y < 1.0) composition. A promising low-permittivity millimetre-wave ceramic with most excellent microwave dielectric properties (ε_r = 10.2, Q×f = 81,000 GHz and τ_f = −4.8 ppm/°C) was produced from the Ca_(1+2y)SnSi_(1+y)O_(5+4y) (y = 0.4) ceramic.     

四元相图在复分解法制硝酸钾中的应用

在硝酸铵和氯化钾复分解反应制硝酸钾和氯化铵多温相图中，由于氯化铵的结晶区随温度变化而变化不大，导致欲获得较纯的氯化铵与硝酸钾十分困难。本实验通过加入大量与本盐互体系无关的酸、碱、盐，或有机物质，使上述反应的共饱和曲线发生较大漂移，使氯化铵的结晶区随温度化而变化明显增大，结晶曲线增长，从而在相同条件下，能顺利地分离出较纯的氯化铵与硝酸钾粗品。硝酸钾粗品经过重结晶一次可达到或超过GB／T1918—1998标准的优级品。     

Factors influencing magnetic polymer microspheres prepared by dispersion polymerization

Magnetic iron oxide (Fe₃O₄) was prepared by a coprecipitation method. Core–shell composite magnetic polymer microspheres with carboxyl groups were synthesized by the dispersion polymerization of styrene and acrylic acid in the presence of magnetic oxide, and dibenzoyl peroxide was used as an initiator. The synthesized magnetic polymer microspheres were characterized with X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and so forth. The results indicated that the product was single‐phase Fe₃O₄, and its average size was about 10 nm. The configuration of the microspheres, which contained carboxyl groups, was spherical, and the average size was about 2 μm. The results of vibrating sample magnetometry tests showed that the magnetic powders produced by different surfactants had different saturation magnetizations. When poly(ethylene glycol) with a weight‐average molecular weight of 4000 was used as a surfactant, the saturation magnetization of the samples reached 69.2 emu/g. The factors that affected the shape, magnetism, size, and distribution of the microspheres were also studied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A high Cr (VI) absorption efficiency and easy recovery adsorbent: Electrospun polyethersulfone/polydopamine nanofibers

Cr (VI) is a highly toxic pollutant to humans, to achieve high adsorption capacity, easy recovery, and good reusability, polyethersulfone/polydopamine (PES/PDA) ultrafine fibers were prepared successfully. A series of preparing effect factors were investigated systematically and the optimum one is 8.5 pH value at room temperature and 2 g/L dopamine concentration. And then they were used as an adsorbent for the removal of Cr (VI) ions from wastewater. The effect factors pH, the adsorbent dosage, and time were discussed on Cr (VI) adsorption process and the Cr (VI) adsorption behavior was investigated. It is found that the maximum Cr (VI) adsorption capacity is 115.2 ± 4.8 mg/g at pH = 3 using 0.06 g PES/PDA with 80 mins. The Cr (VI) adsorption process followed the pseudo-second-order model (r² ≥ 0.99) and adsorption isotherms were fitted to the Langmuir model (R² ≥ 0.999). Furthermore, the Cr (VI) adsorption mechanism was supposed according to the X-ray photoelectron spectroscopic results. Finally, PES/PDA ultrafine fibers were considered to be a promising adsorbent with good stability (decomposing temperature, 356°C), high adsorption efficiency (112.1 ± 2.5 mg/g), and good reusability (three times) on the coexistence of anions and the actual industry wastewater environment.     

Structural characterization of CdS nanoparticles grown in polystyrene matrix by thermolytic synthesis

Cadmium sulfide nanoparticles embedded in a polystyrene matrix (CdS/PS) were successfully prepared by in situ thermolysis of a cadmium thiolate precursor dispersed in the polymer. The heat-induced formation of cadmium sulfide was studied by thermogravimetric analysis and differential thermal analysis, while the chemistry of the reaction forming the CdS/PS compound was investigated by nuclear magnetic resonance and X-ray photoelectron spectroscopy. The structural characterization was performed by X-ray diffraction and transmission electron microscopy. The CdS nanocrystals are single crystals of cubic phase (zincblende structure) of spherical shape. The average diameter of the nanocrystals embedded in the polystyrene matrix achieved by our synthesis process is as small as 2.5 ± 0.5 nm. Room temperature UV–VIS absorption spectra exhibit a shoulder at 412 nm that is consistent with the presence of CdS nanocrystals of ∅ ≈ 2 nm. The role of the polymer on the nanoparticle growth was also discussed.     

Strong organic acid-assistant synthesis of holey graphitic carbon nitride for efficient visible light photocatalytic H2 generation

A facile and cost-effective method was developed for the synthesis of holey N-deficient graphitic carbon nitride nanosheets (FCN) using trifluoroacetic-acid-treated urea as a precursor. The role of trifluoroacetic acid on the composition, structure and photocatalytic performance of the prepared catalysts was carefully investigated. The obtained samples displayed laminated porous morphology with nitrogen defects, larger specific surface areas, extended range of spectral response and enhanced electron mobility of charge carriers. Consequently, the optimized catalyst FCN-400 exhibited superb photocatalytic performance and excellent cycling stability for hydrogen evolution. The hydrogen evolution rate over FCN-400 reached 309.3 μmol/h under visible light irradiation, which is 11.3-fold of that of urea-derived graphitic carbon nitride (27.3 μmol/h).     

Keggin type inorganic–organic hybrid material containing Mn(II) monosubstituted phosphotungstate and S-(+)-sec-butyl amine: Synthesis and characterization

A new inorganic–organic POM-based hybrid material comprising Keggin type mono manganese substituted phosphotungstate and enantiopure S-(+)-sec-butyl amine was synthesized in an aqueous media by simple ligand substitution method. The synthesized hybrid material was systematically characterized in solid as well as solution by various physicochemical techniques such as elemental analysis, TGA, UV–vis, FT-IR, ESR and multinuclear solution NMR (³¹P, ¹H, ¹³C). The presence of chirality in the synthesized material was confirmed by CD spectroscopy and polarimeter. The above study reveals the attachment of S-(+)-sec-butyl amine to Keggin type mono manganese substituted phosphotungstate through N → Mn bond. It also indicates the retainment of Keggin unit and presence of chirality in the synthesized material. An attempt was made to use the synthesized material as a heterogeneous catalyst for carrying out aerobic asymmetric oxidation of styrene using molecular oxygen. The catalyst shows the potential of being used as a stable recyclable catalytic material after simple regeneration without significant loss in conversion.     

Tunnel spoil classification and applicability of lime addition in weak formations for muck reuse

Tunnel construction planning requires careful consideration of the spoil management part, as this involves environmental, economic and legal requirements. In this paper a methodological approach that considers the interaction between technical and geological factors in determining the features of the resulting muck is proposed. This gives indications about the required treatments as well as laboratory and field characterisation tests to be performed to assess muck recovery alternatives. While this reuse is an opportunity for excavations in good quality homogeneous grounds (e.g. granitic mass), it is critical for complex formation. This approach has been validated, at present, for three different geo-materials resulting from a tunnel excavation carried out with a large diameter Earth Pressure Balance Shield (EPB) through a complex geological succession. Physical parameters and technological features of the three materials have been assessed, according to their valorisation potential, for defining re-utilisation patterns. The methodology proved to be effective and the laboratory tests carried out on the three materials allowed the suitability and treatment effectiveness for each muck recovery strategy to be defined.     

A three-dimensional lead borate with a fluorite net constructed from different cluster building units

Presented here is a new three-dimensional lead borate, namely, PbB₂O₄ (denoted as SCU-8). This compound has a fluorite net constructed from two different cyclic building units: 4-connected Pb₃O₆ cluster and 8-connected B₁₂O₂₄ cluster. It is a wide-gap semiconductor with the band gap of 4.0 eV. The band structure and density of states of the compound were also calculated based on density functional theory.