Hydrothermal Synthesis and Crystal Structures of Cd(II)-Based 1D Coordination Polymer and Mn(II) Coordination Complex with Mixed N- and O-donor Ligands: [Cd2(4-4′-bpy)2(pa)4]n·0.25(H2O) and [Mn(4-4′-bpy)2(pa)(H2O)3]ClO4·2(H2O)

Two new complexes, [Cd₂(4-4′-bpy)₂(pa)₄] _n ·0.25H₂O (1) (pa = phenylacetate), and [Mn(4-4′-bpy)₂(pa)(H₂O)₃]ClO₄·2H₂O, (2), have been obtained from hydrothermal reaction of Cd(NO₃)₂·4H₂O and Mn(ClO₄)₂·6H₂O with a mixture of the ligands, 2-phenylmalonic acid (2-phmalH₂) and 4-4′-bipyridine (4-4′-bpy). The pa is formed in situ by decarboxylation of phenylmalonic acid. These complexes have been characterized by elemental analysis, FT-IR spectroscopy, thermogravimetric analysis and single-crystal X-Ray diffraction. The Cd(II) center is seven-coordinate and linked via pa ligands to form a binuclear complex in the asymmetric unit of 1. A ladder-like 1D chain of binuclear units is formed by Cd(II)–N coordination bond through 4-4′-bpy ligands. Complex 2 consists of a mononuclear manganese center based on a distorted octahedral geometry and exhibits a supramolecular structure containing hydrogen bonds and extensive π···π and C–H···π interactions.     

Boron-Doped Strontium-Stabilized Bismuth Cobalt Oxide Thermoelectric Nanocrystalline Ceramic Powders Synthesized via Electrospinning

Boron-doped strontium-stabilized bismuth cobalt oxide thermoelectric nanocrystalline ceramic powders were produced by using a polymeric precursor technique. The powders were characterized by using x-ray diffraction (XRD), scanning electron microscopy (SEM), and physical properties measurement system (PPMS) techniques. The XRD results showed that these patterns have a two-phase mixture. The phases are face-centered cubic (fcc) and body-centered cubic (bcc). Values of the crystallite size, dislocation density, and microstrain were calculated by using the Scherrer equation. The lattice parameters were calculated for fcc and bcc phases. The SEM results showed that needle-like grains are formed in boron-undoped composite materials, but the needle-like grains changed to the plate-like grains with the addition of boron. The distribution of the nanofiber diameters was calculated and the average diameter of the boron-doped sample is smaller than the boron-undoped one. PPMS values showed that the electrical resistivity values decreased, but the thermal conductivity values, the Seebeck coefficients, and figure of merit (ZT) increased with increasing temperature for the two samples.     

Three-Dimensional Modeling and Simulation of Heat and Mass Transfer Processes in Porous Media: An Application for Maize Stored in a Flat Bin

If the relative humidity and temperature of the air inside a granular mass of stored grain exceeds a certain threshold value, microorganism activity is likely to increase. Lower relative humidity and temperature, when uniformly distributed inside the grain mass, prevent moisture migration and an increase in microorganism activity. To cool down or maintain the temperature of the grain mass below a threshold value, forced ventilation with an appropriate airflow can be used to remove excess moisture or heat generated by grain or microorganism respiration. The objective of this work was to solve the equations that describe the conservation of heat, mass, and momentum in order to predict heat and mass transfer processes in the environment inside a grain mass of maize, stored in a flat bin. Three-dimensional computational fluid dynamics was used to solve the equations. The analysis of heat and mass transfer was performed considering the geometry of a two-ton-capacity bin prototype using a hexahedral mesh for the finite volume analysis. The numerical grid was defined to discretize the physical flow domain of interest to calculate velocity, temperature, and moisture distribution in the bulk of stored grain. The predicted results were compared with experimental data, and the agreement between them was very good.     

Preparation and characterization of acrylic polymer nanocomposite films obtained from aqueous dispersions

A functionalized fumed silica was dispersed in water using a nonionic surfactant, yielding a stable nanodispersion. This was blended with an aqueous acrylic polymer dispersion to produce hybrid nanocomposite films. The silica particles were shown to be well dispersed in the polymer matrix, with little agglomeration. Further evidence of good compatibility between the silica and acrylic polymer was given by the improved thermal stability of the nanocomposite compared with the pristine polymer. The nanocomposite films exhibited significantly lower dirt pick‐up behavior, which seems to be associated to the nanoroughness of the composite film surface observed in AFM analysis. This decreases the contact area between film and micrometric dirt particles. Surface tension and hardness do not seem to be significantly different in the composite and noncomposite materials. This approach may provide a strategy to obtain hybrid coatings with self‐cleaning properties, taking advantage of the relatively low cost, and large availability of fumed silica. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of incorporation of graphene oxide and graphene nanoplatelets on mechanical and gas permeability properties of poly(lactic acid) films

Nanocomposite thin films of poly(lactic acid) (PLA) were produced incorporating small amounts (0.2 to 1 wt%) of graphene oxide (GO) and graphene nanoplatelets (GNP). The films were prepared by solvent‐casting. Mechanical properties were evaluated for plasticized (by residual solvent) and unplasticized films. Plasticized nanocomposite films presented yield strength and Young's modulus about 100% higher than those of pristine PLA. For unplasticized films improvements in tensile strength and Young's modulus were about 15 and 85%, respectively. For both film types, a maximum in mechanical performance was identified for about 0.4 wt% loadings of the two filler materials tested. Permeabilities towards oxygen and nitrogen decreased, respectively, three‐ and fourfold in films loaded with both GO or GNP. The glass transition temperature showed maximum increases, in relation to unloaded PLA films, of 5 °C for 0.4 wt% GO and 7 °C for 0.4 wt% GNP, coinciding with the observed maxima in mechanical properties. Copyright © 2012 Society of Chemical Industry     

One-Step Synthesis of W/O and O/W Emulsifiers in the Presence of Surface Active Agents

The main goal of this study was to describe the method of the synthesis of the dodecyl-, tetradecyl-, hexadecyl- and octadecyl-propylene glycol emulsifiers in the presence of selected anionic and nonionic surfactants. Acyl propylene glycol emulsifiers were produced by esterification of propane–1,2-diol (propylene glycol, PG) with C_12:0–C_18:0 fatty acids in the presence of anionic sodium dodecyl sulfate (SDS) and nonionic-poly(ethylene glycol) monolaurate (PEGML). The presence of SDS and PEGML in the reaction system caused microemulsion formation. Depending on the structure and amount of the surfactant in the system reactions proceeded at different rates and with different efficiency levels. The esterification of propylene glycol carried out under applied conditions causes products with the desired contents of propylene glycol monoesters (MAPG) to be obtained in a one-step reaction. Knowledge of the reaction kinetics creates the possibility to program the composition and properties of the synthesized emulsifiers. The interaction of nonionic, lipophilic MAPG with anionic, hydrophilic SDS or nonionic, hydrophilic PEGML influences the hydrophile–lipophile balance (HLB) values of the products which may be used to stabilize water-in-oil (W/O) and oil-in-water (O/W) emulsions. Use of the synthesized compounds allows stable emulsions to be prepared which include the following vegetable fats in the oil phase: mango oil, palm oil, shorea butter and hydrogenated soybean oil.     

Modification of Waste Poly(Ethylene Terephthalate) (PET) by Using Poly(L-Lactic Acid) (PLA) and Hydrolytic Stability

The purpose of this study is the preparation of hydrolytically degradable copolymers of waste poly(ethylene terephthalate) (PET). To achieve this, we modified PET by using biodegradable poly(lactic acid) (PLA). Modification reactions were carried out in o-nitrophenol as solvent at 140 and 170°C for 8, 16, and 24 h in the presence of dibutil tin oxide (DBTO) as catalyst. The amount of the total polymers (PLA and PET) in the reaction mixture was 30% by weight, and the weight ratios of PLA/PET were 10/90, 50/50, and 90/10. These modified products were characterized by Fourier transform infrared spectrometer (FTIR), differential scanning calorimeter (DSC) as well as by hydrolytic degradation determinations. Hydrolytic degradations of the products were determined gravimetrically. Disc-shaped samples were placed in tubes containing phosphate buffer solution of pH 7.2 and kept in a water bath at 60°C for 28 days. The weight loss of the products after hydrolytic degradation ranged from 1.25% to 48.75% after 28 days.     

环境经济学教学实践浅谈

环境经济学家认为,资源短缺和环境污染的根本原因在于其背后的经济驱动力,如何应用经济杠杆来解决环境问题是环境科学专业本科生要掌握的最基本理论与技能之一。文章针对环境经济学课程自身的特点以及学生学科背景的特点,主要从教学方法的改进,如优化案例教学、引入叙述性教学等,探讨了教学改革的思路和成效。     

Free‐radical copolymerization of [(4‐isopropyl phenyl) oxycarbonyl] methyl methacrylate with acrylonitrile and methyl methacrylate

The present investigation has been achieved in accordance with the Diels–Alder reaction (1,4 cycloaddition) to produce a new halogenated bicyclic adduct. ortho‐Bromoallylbenzoate is a new dienophile that was prepared in a pure form, and its structure was confirmed. The Diels–Alder syntheses of hexachlorocyclopentadiene and the new dienophile were studied to determine the optimum condensation reaction conditions under a temperature range of 90–160°C, reaction times of 1–8 h, and molar diene/dienophile ratios from 1:1 to 5:1 as a consequence. The optimum conditions reached were a temperature of 140°C, an initial diene/dienophile molar ratio of 3:1, and a duration time of 6 h. The maximum stoichometric yield under these optimum conditions (82.5%) was obtained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2331–2338, 2003     

Synthesis, structure and thermal properties of a novel 3D aluminophosphate UiO-26

The synthesis of a novel 3D aluminophosphate is described. The thermal properties of the material were investigated, and the existence of three high-temperature variants was revealed. The crystal structures of the as-synthesized material (UiO-26-as) and the material existing around 250°C (UiO-26-250) were solved from powder X-ray diffraction data. UiO-26-as with the composition [Al₄O(PO₄)₄(H₂O)]²⁻[NH₃(CH₂)₃NH₃]²⁺ crystallizes in the monoclinic space group P2₁/c (no. 14) with a=19.1912(5), b=9.3470(2), c=9.6375(2) Å and β=92.709(2)°. It exhibits a 3D open framework consisting of connections by PO₄ tetrahedra with AlO₄ tetrahedra, AlO₅ trigonal bipyramids and AlO₅(H₂O) octahedra forming two types of layers stacked along [1 0 0] and connected by Al–O–P bondings. The structure possesses a 1D 10-ring channel system running along [0 0 1], in which doubly protonated 1,3-diaminopropane molecules are located. UiO-26-250 with the composition [Al₄O(PO₄)₄]²⁻[NH₃(CH₂)₃NH₃]²⁺ crystallizes in the monoclinic space group P2₁/c with a=19.2491(4), b=9.27497(20), c=9.70189(20) Å and β=93.7929(17)°. The transformation to UiO-26-250 involves removal of the water molecule which originally is coordinated to aluminum. The rest of the structure remains virtually unchanged. The crystal structures of the two other variants existing around 400 (UiO-26-400) and 600°C (UiO-26-600) remain unknown.